46 replies to this topic

[hydra]

Pardon the elitist subject title, its just that I've read (over and over) pretty most of the major books on engine design (Heywood, Taylor, Ricardo, Maleev, Heisler) as well as a lot of the popular engine building/modding literature out there (Vizard & co) and I was looking for answers not found hitherto...

I am currently working on squeezing as much power out of a Mercedes M117 (SOHC 2V 5.6L) V8 as I can. I've modelled the engine in as much detail and accuracy as I can using Engine Analyzer Pro, and I have found that my biggest bottleneck is (surprise, surprise) the cylinder heads. Mach Index at redline (6000rpm) is in the region of 0.62, and average intake velocity is 354ft/s or 108m/s which are both a little too high for outright performance. Before I go any further, here are some relevant specs on the engine.

5547cc
Intake valve diameter 46.2mm
intake port volume 140cc
intake port length 100mm
which means that average port diameter = 42.25mm
port is round all over, with no major obstructions save for injector bosses (yes they're in the head not in the manifold), and the valve guide boss (pretty well streamlined as is) So the port is geometrically rather simple, and well-designed and cast unlike a stock small-block port...
intake port entry = 41.5mm
vena contracta = 40-41mm (didn't have a micrometer handy)
flow coefficients are assumed to vary from ~0.67 at low L/Ds to 0.55 at L/D = 0.25
this is the only tidbit of information that I have assumed, due to lack of a flow bench or any relevant data. My guesstimate was based on an extensive study of other (typically aftermarket small-block) head data
valve inclination 22 degrees
valve/port angle 90-22 = 68 degrees
valve seat angle 45 degrees
valve seat width 2.0mm
valve stem thickness 8.5mm
no port bias/offset to speak of
valve L/D 0.25-0.26
L/R ratio 3.25


First off, due to valve/head geometry, intake valve diameter cannot be increased much if at all, so let us assume that we're stuck with the stock valves. What we can do though is maximize valve lift and flow coefficient to reduce mach index to something more reasonable. (Taylor cites average flow coefficient, the one used in the Mach Index formula, to be 1.6L/D)
Ideally, I would like max valve lift to be in the region of 0.600" using a custom cam and roller rocker setup to keep valve spring requirements reasonable. This gives us a L/D of 0.33. Here are a few thoughts/ideas:

I would like to get intake port velocity down to 310-320ft/s or so to maximize volumetric efficiency. This shouldn't harm my bottom end too much, but what I am concerned about is just how much I can "open up" my port before actually HURTING port discharge coefficient. Doesn't the ratio of vena contracta/valve diameter have to be less than 0.9 or so? Just how high can I go here?

Another idea that I am currently entertaining is to actually raise the intake port by 2cm to benefit high-lift flow. This should reduce the port angle to around 45 degrees. Is it really worthwhile though?

Peak intake flow depression occurs around the top 20% of the lift curve, and is on the order of 2.5-2.7psi (assuming 270 degree cams, L/D = 0.33, and free flowing intake/exhaust) so I would think that for a given area under the flow curve, high-lift flow is more important than low lift flow... With that said, this IS a pretty radical modification...

That's all I will say for now. Please help me design a mathematically ideal (or close to ideal) intake port using our combined experience and common sense. I don't have access to a flow-bench, but I am CONFIDENT that we can approach an ideal port design due to its geometric simplicity. Remember, this isn't "tricky" like a small-block port is. Of course it goes without saying that a custom straight shot IR-type manifold will be fabricated for the job... With that said, how do I go about posting pics up here?

[Bill Sherwood]

Another idea that I am currently entertaining is to actually raise the intake port by 2cm to benefit high-lift flow. This should reduce the port angle to around 45 degrees. Is it really worthwhile though?

Yes, very much so.
Try to get your inlet speed down to just under 300 if you can.

[bobqzzi]

A better place to enquire may be here:

http://www.speedtalk...ewforum.php?f=1

[hydra]

Bill,
I would like to be able to get intake port velocity down to 300ft/sec or so, but I am limited by intake valve diameter and port geometry restrictions... Again, how big can I go on the vena contracta/valve diameter ratio? The port entrance/vena contracta ratio?

Bobqzzi.
Great site, thanks for the link... However, I am confident that there are people in here who will have some of the answers I'm looking for

[J. Edlund]

If larger valves can't be fitted the ports can be made larger by increasing the valve inner seat diameter in relation to the valve or reducing the valve stem diameter. This may of course be impossible due to other reasons.

Using "slanted squish" can also improve flow somewhat but requires matching machined pistons and heads (combustion chambers).

Manifold to port area ratios have been mentioned by for example Blair. He found that most engines work well with a ratio according to:

Cim = 0.94801 + 0.00084783*bmep
Cem = 0.85824 + 0.040262*bmep

[hydra]

Larger valves indeed cannot be fitted. Do you mean that I will have to use a seat angle greater than 45 degrees? Wouldn't that mean that I would have to replace the intake valves and seats?
Narrowing the valve stems is an option, but from what I understand it compromises reliability, while returning a minimal performance advantage - unless you were referring to replacing the valves outright.

EA Pro is giving me max BMEPs of 203psi with an all-out engine combo, taking into consideration knock ******, this works out to 14MPa, which I am assuming is the unit that needs to be plugged into your formula, this gives a Cim of 0.96 (diameter ratio of 0.98) and a Cem of 1.422 which doesn't really make sense. I will assume that you forgot a zero in the slope of the second function, which would mean that Cem = 0.9146 (diameter ratio of 0.9564) which also seems a little high.
Can you please confirm that I am using the formulas correctly?
I am also assuming that Cim is the ratio of initial port diameter to minimum port diameter andthat Cem is the ratio of minimum port diameter to intake valve (head?) diameter

[McGuire]

If I follow you correctly, you intend to enlarge the port area (and perhaps raise/straighten the port) while otherwise maintaining the proportions and minimum port cross-section (relative to enlargement). Seems like the absolutely correct empirical approach to me. Of course increasing the relative minimum c/s or straightening the port will tend to kill the velocities, which is exactly what you want...as far as you know. :

I would not get too hung up on simulated flow numbers...except for the physical dimensions, every bit of your data is coming at you via several layers of abstraction. Calculated flow velocities depend on a lot of assumptions. Even real flow bench numbers do not provide direct linkage to airflow in a running engine, or what you can expect in results on the dyno...IC engine airflow is of course an extremely complex issue, finite amplitude waves in wild, crazyass flux. If you have simulated it to significant predictive accuracy there are several OEM's and R&D companies who would like to talk to you, all carrying big fat checks.

The first thing I would advise is getting your arms around and understanding just what you are starting with...lots of photos and measurements, and latex casts of the port. Then you can make some educated guesses about what you need to do, but without a flow bench and a dyno that's all they are. It's not that diffcult to obtain real positive gains (especially with your approach, which is spot-on) but unless you are one lucky, clean-living SOB it will be nowhere near optimal -- you will have no way to know what you left on the table. But the majority of your gains will generally come from "bowl porting"...the first inch or inch-and-a-half behind the intake valve. The short-side radius behind the intake valve is especially critical, and one of the keys to flow velocity, but without a flow bench or a known experience base on the specific head it's often hard to know which way to go. Wish I could see an example of the head in question.

Of course you also need an accurate idea of how much material thickness is available for opening things up or moving them around. Depending upon jacket access, you may have to saw up a couple of core heads to find that out. Seems wasteful, but it's no fun getting halfway through a good head, finding daylight and then having to scrap all your exquisite workmanship. Been there, done that.

Ya know, there is really no reason you can't have a flow bench if you want one. When I couldn't afford to buy my first bench way back years ago, I built one. It's no big deal, everyone did back then. I probably didn't have $250 in it to start and it originally only pulled 10", but it worked perfectly and I used it for years, upgrading and updating as I went. The only difference between an SF and homemade is the price and the fancy cabinet, really. As for accuracy, we have to remember what we are doing here. Do we need a 32 oz. ball peen hammer, or a 31.91 oz. ball peen hammer? There have been plenty of how-to magzine stories through the years, and I have to believe there are now plans and descriptions all over the Internet (though I haven't checked). Like most of us here you are probably more interested in the journey than the destination, so why not?

[hydra]

McGuire,
Yes, I would like to take an empirical approach to designing an optimal (or close to optimal) port.
Based on angles and diameter ratios, I am confident that the combined experience and countless flow-bench hours of the people in the know will be reflected in these empirical ratios, but more on that later...

Yes, my intention is to "kill", or more appropriately reduce mean intake port velocity to something more conducive to making high-rpm power. However since I am limited by my intake valve diameter, this becomes a case of reducing velocity from a figure that is way too high, to a figure that is just a little too high. No risk of killing low-rpm torque here. Average port velocity by itself is quite easy to calculate, and is mean piston speed/(average port diameter/bore)^2 , and experience has shown that the figure in question should be 270ft/s if one is looking for peak power, or 320ft/s if one is looking for a nice, fat power/torque curve. Everything good so far?

I've already got a nice silicone port mold right here on my desk, and I've taken some photos of it (which I would like to upload here for all to see given a chance), all that's left is for me to take some accurate measurements of how its cross section varies, and for that I need to borrow a vernier caliper from somebody

Regarding the empirical approach, wouldn't you agree that it relies on the past experience and accumulated data of several people who are smarter and more knowledgeable than I? Therefore , when faced with a geometrically simple port such as this (as opposed to a small block port, which has all sorts of tricks and nuances to making it work) couldn't we get something 80-90% close to optimum just by using my approach? I agree 100% that a flowbench would be a very useful tool, even a DIY one, and I have repeatedly come across several designs for a cheap DIY flowbench. Its just that I wouldn't want to go through with all that bother if I can get to within (at least) 70% of the optimum, which I really believe can be done. Hell, if I've got the time and the patience, I might cook up a small CFD model of the port and see what happens, but before I do so, I'd like a good base to start with...

Core heads should be like $50-100 a piece, which isn't too bad I guess, but why can't I just weld up the areas which have hit daylight? I did that on a (cast iron) exhaust port once with no apparent problems... And if I am to raise the port like I intend to, then there will be a lot of daylight/welding/epoxying etc anyway
I'd love to post the pics up here so I can show you guys just what I am talking about...

[bobqzzi]

What is the bore dimension?

[Bill Sherwood]

Also consider simply using less revs, and making the engine work well at those lower revs.
That'll get the airspeed down.

[soubriquet]

Hydra. Check out the first sticky thread "solution for posting your images". All you have to do is to upload to imageshack and copy and paste the link from "thumbnails for forums" into your post. It is so simple, that even geologists can manage it.;)

[hydra]

Bobqzzi,
Bore is 96.5mm ,and stroke is 94.8mm, but valvetrain geometry is such that the intake valve seat is close to hitting the edge of the combustion chamber at the 6-o'clock position, and the spark plug boss at the 1-o-clock position. Oh, and there's only 2mm of metal between the valve seats :

Bill,
I want to make the engine work "well" at the highest rpm I can, for obvious reasons. The stock engine makes peak power at 5000rpm, and I can't seem to get it to make more power beyond 5750rpm, at which the average port velocity is 307ft/s and the mach index "Z" is 0.465.
This is assuming an average port diameter of 42.5mm and a port coefficient that is 0.7 at L/D = 0.1, 0.56 at 0.25, and 0.63 at 0.33, which is healthy, but still within the bounds of reason. The end result is 481bhp at 5750 rpm and 455lbft at 5000-5250, with a redline of 6500

Sobriquet,
That thing has been in front of me so long that I have ceased to notice it.... How very silly of me
I will put up the pics in a bit, thanks!

[hydra]

This is the combustion chamber, notice where the valve is shrouded


This is a close up of the intake port/bowl/chamber


Another shot of the intake port/bowl/chamber


Intake port from above


Detail of intake port and (mechanical) injector boss, this is where I would like to raise the port


Now for the port mold

[Bill Sherwood]

Can you perhaps send me a copy of the engine file so I can fiddle with it a bit?
billzilla_at_billzilla_dot_org

[hydra]

done

[J. Edlund]

Originally posted by hydra
Larger valves indeed cannot be fitted. Do you mean that I will have to use a seat angle greater than 45 degrees? Wouldn't that mean that I would have to replace the intake valves and seats?
Narrowing the valve stems is an option, but from what I understand it compromises reliability, while returning a minimal performance advantage - unless you were referring to replacing the valves outright.

EA Pro is giving me max BMEPs of 203psi with an all-out engine combo, taking into consideration knock ******, this works out to 14MPa, which I am assuming is the unit that needs to be plugged into your formula, this gives a Cim of 0.96 (diameter ratio of 0.98) and a Cem of 1.422 which doesn't really make sense. I will assume that you forgot a zero in the slope of the second function, which would mean that Cem = 0.9146 (diameter ratio of 0.9564) which also seems a little high.
Can you please confirm that I am using the formulas correctly?
I am also assuming that Cim is the ratio of initial port diameter to minimum port diameter andthat Cem is the ratio of minimum port diameter to intake valve (head?) diameter

Should perhaps have mentioned that the bmep should be inserted in bar units. It's also bmep at max power that should be used. Cim is the ratio of the intake and Cem is the ratio for the exhaust ports.

Defined as (for exhaust and intake ports respectivly)

Cm = Am/nv+Ap = Am/Apt

where

Am is the port area at the manifold, exhaust or inlet
nv is the number of valves
Ap is the exposed port area, exhaust or inlet
Apt is total exposed port area

Apt is defined as

Apt = nv*Pi/4(dip^2-dst^2)

where

dip is the diameter of the port, usually measured slightly under the inner seat diameter but sometimes the inner seat diameter value can be used as an replacement if it's the smallest diameter.
dst is the valve stem diameter

203 psi is about 14 bars (or 1.4 MPa). That means about Cim = 0.96 and Cem = 1.42, but these values are a little high since it's max bmep and not bmep at max power.

Some examples mentioned by Blair was

engine - Cem/Cim
G50 Matchless - 1.260/0.670
Ducati 955 - 1.210/0.930
Nissan IRL - 1.448/0.925
2.0L I4 4v F2 - 1.26/0.84
3.5L V12 4v F1 - 1.60/0.90
3.0L V10 4v F1 - 1.40/0.90
8.2L V8 2V OPB - 1.55/1.05

It was also noted that the small Cim at the G50 Matchless was probably due to a limited number of carb. sizes availible.

As the port area is the minimum area of the port in the head minus the area of the valve stem a smaller valve stem can increase the port area somewhat. Sometimes the valve is given a neck but a different valve with a smaller diameter stem is probably recommended for reliability reasons.
With a larger inner seat diameter, a larger port can be achieved with the same 45 degree angle if the height of the seat is reduced. This may however make valve cooling suffer as well as sealing. In any case I would assume that the gains here are small, so it's probably not that cost effective to experiment with.

If the valves are close to the combustion chamber or cylinder wall larger valves shouldn't be fitted as they may not improve the flow since they are partly "shielded" by the wall. This is one of the things "slanted squish" can improve.

[jluetjen]

I'm no "expert", but I'll share my observations based on some "back of the envelope" calculations that I've developed.

1) The model output numbers you described are basically assuming absolute top shelf BMEP output, comparable to fully developed 4 valve head Super Touring numbers.

2) They way that I've modeled it, you're really talking about the airflow numbers at the peak torque engine speed, after which the torque tails off while the rev's still increase. Once the torque drops faster then the rev's increase, you've reached the peak HP engine speed. The stock 5.6 liter M117 engine is pulling a pretty good intake gas speed of 81 meters/second (~263 ft/second) at it's peak torque speed of 4750 RPM, and about 99 m/s (321 ft/second) at it's peak HP engine speed. Getting up to your modeled 5750 RPM for peak HP just doesn't seem possible.

When Sauber was racing that engine, I wonder if there was a reason why the ended up using a turbo?

Just food for thought...

[bobqzzi]

Since you seem willing to weld, and are perhaps are going to overbore the engine a bit...I think you can get in larger valves. There is plenty between the seats to enlarge them (look at some pics of typical "smallblock" heads- the seats often interlock. You can weld the plug boss up and retap for a 10 or 12mm plug.

[Fat Boy]

I saw somewhere a graph that showed HP in a fully developed race engine was almost a direct function of valve area. I can't remember where it was, but if anyone has something like this, it would be interesting to see again.

I'm not an engine expert, so take this with the necessary amount of salt.

A place to find a good amount of power is in the oiling system. Specifically, reducing the losses due to windage and excessive oil pressure. None of this helps you get any more air or fuel into the system, but it has a big influence on the amount of negative work done. If you minimize the negative work in the system, then you've maximized the positive work that actually gets out the back of the crank. It's especially important at higher RPM.

The side benefit to this is that when you spend a big chunk of time on the oiling system, you end up with a more reliable engine.

[McGuire]

I hate to be the bearer of unhappy tidings, but I don't think 481 bhp is in the cards here. If that kind of power is required, I would be looking into the 4V heads or a blower or turbo.

What is the application?

[hydra]

jluetjen,
1) I disagree, state of the art NA engines approach BMEPs of 240-250psi, and there are an increasing number of production engines (which have to meet all sorts of emissions, mileage, and noise constraints) with BMEPs of 200+psi

2) The numbers I provided were correct at 6000rpm, you're probably forgetting the effects of the smaller diameter (40mm) intake manifold

I realize that the stock M117 is quite undervalved, and there's not much we can do about that except maximise port efficiency and increase valve lift.

Bobqzzi,
The engine block is Alusil (hypereutectic 390 Aluminum), and I don't think there's anybody over here with the expertise to bore one of those. Besides, I would have to get custom pistons, which are a whole lot of money for relatively little benefit. Furthermore, the old AMG 6.0 blocks (100mm bore) were known to crack due to wall thickness issues

Your ideas for making the valves bigger are right on, but look how close the valve seat is to the edge of the combustion chamber, there's a smidgen under 1mm between them. What do you think?


Fat Boy,
I'm all for the reduction of negative work, and I will do everything I can to do so. But the oil pan already comes with a pretty well designed windage tray (after all, this is an M-Benz product) and the most I can do I guess is add a crank scraper and maybe fiddle around with the oil pump a little. I have yet to disassemble the short block btw...

McGuire,
480+ bhp does sound pretty crazy for a 339ci V8 with 1.82" valves. But you've got to remember that this is an "optimized" setup, and not a collection of somewhat mismatched off the shelf parts. That and I'm assuming 0.650" lift with heads that flow 255cfm @ 28" at that lift. I'm well aware of GIGO, and I've done everything I can do provide reasonable inputs. Performance Trends say that the program is accurate to +/- 5% at worst, and I'd like to believe them

The engine is for a purely street application, it is going in my Euro 1977 450SLC, and I'd like to create something like an old-school SL55, a hot-rod Benz if you will... This is what I'd like it to look like when its done, give or take a few details:

[hydra]

[zac510]

Sorry to get off topic but I'm interested in the induction you intend to use. Doesn't the 450SL come with K-jetronic ?
Are you converting that to pulsed fuel injection with individual throttles? Or something else innovative?

[McGuire]

Originally posted by hydra


McGuire,
480+ bhp does sound pretty crazy for a 339ci V8 with 1.82" valves. But you've got to remember that this is an "optimized" setup, and not a collection of somewhat mismatched off the shelf parts. That and I'm assuming 0.650" lift with heads that flow 255cfm @ 28" at that lift. I'm well aware of GIGO, and I've done everything I can do provide reasonable inputs. Performance Trends say that the program is accurate to +/- 5% at worst, and I'd like to believe them

The engine is for a purely street application, it is going in my Euro 1977 450SLC, and I'd like to create something like an old-school SL55, a hot-rod Benz if you will... This is what I'd like it to look like when its done, give or take a few details:

I think the software is leading us into the trap of chasing numbers instead of trying to build the best engine for the application. First, we are not going to get 255 cfm and we really don't want it anyway. We have no idea how this valvetrain will appreciate .650 lift, and relocated ports and similar schemes seldom pay off in street engines. When we take a few steps back and look at the big picture, we are taking exactly the wrong approach for a successful street engine. Here max flow numbers and max hp@rpm are not the goals at all.

If you are asking me how to do this: I would assemble a solid bottom end with good rods and quality forged pistons, perform a mild cleanup on the cylinder heads and install a blower. That will get us the 450 bhp far easier and cheaper than trying to build a full-race engine with no development base to speak of, and with far superior reliability and driveability. This is also the very same approach used in the current AMG V8.

[clSD139]

The newest exclusive AMG V8 on germancarfans.com doesn't have a charger, it's done with the intake. In this application the valves would still be a bottleneck if I understand all this right. The "kompressor" of non AMG V-engines is sometimes installed on 4cyl. instead of a turbo but on the big engines it's only done for efficiency.

[bobqzzi]

Originally posted by McGuire




If you are asking me how to do this: I would assemble a solid bottom end with good rods and quality forged pistons, perform a mild cleanup on the cylinder heads and install a blower. That will get us the 450 bhp far easier and cheaper than trying to build a full-race engine with no development base to speak of, and with far superior reliability and driveability. This is also the very same approach used in the current AMG V8.

Ah, I agree with McGuire here. I was assuming this was a race engine. Any type of cam that gives .650" lift is going to be unstreetable, and probably require valve spring replacement fairly frequently.

A well matched centifugal supercharger and programmable fuel injection on an otherwise stock engine would exceed your goal and could do so at stock RPM levels.


I am quite familiar with reynolds 390 bores as I used to race a Cosworth Vega. If it does turn out you need pistons, a nikasil coating will work with the 390. Boring the block is not a problem, but finish honing requres a special sunnen "stone". I had to buy some, and , as I recall, they were fairly inexpensive and fit standard sunnen holders. Porsche 944s also used this bore material, so imagine there must be some expertise over your way.

[shaun979]

Are there any companies in the US that Nikasil coat large bores and hone them to tight tolerances. What are their rough costs? I know LSM sells Nikasil liners and also installs them, but beyond that.. say if you wanted to coat a linerless block.. can this be done?

Apologies Hydra, for the short OT.

[12.9:1]

US Chrome

.

[McGuire]

Originally posted by clSD139
The newest exclusive AMG V8 on germancarfans.com doesn't have a blower, it's done with the intake. In this application the valves would still be a bottleneck if I understand all this right. The "kompressor" of non AMG V-engines is sometimes installed on 4cyl. instead of a turbo but on the big engines it's only done for efficiency.

To me the most impressive thing about the supercharged 5.5 liter AMG V8 is not the 469 -500 bhp (depending on model rating) but the 400+ lb ft of torque across the entire operating range, from 2000 rpm up. Part of why I consider the E55 perhaps the best all-around sedan in the world. Some of the chassis electronics are a little wacky tho...

How they did it is with a Lysholm twin-screw compressor and water intercooler...as I recall max boost is a reasonable 11 PSI. And they got around the one major drawback of the Lysholm -- high operating losses at low boost levels -- by incoroporating an A/C-like magnetic clutch on the blower drive. Adapting this setup would be a great foundation for a project like this... though I suspect f you looked up the components at the M-B dealer it might induce a heart attack, and even at salvage prices the stuff would probably be very dear. Still cheaper than launching a full-on race engine development program for the M117 however.

But you could do a parallel sort of setup building around an Eaton Roots-type blower for bargain prices. Not as efficient but just as effective, really. And for dead simple and easy you can't beat a centrifugal blow-though setup. Eyeball-engineer a belt drive, sort out a fuel system and there you are.

[hydra]

Originally posted by zac510
Sorry to get off topic but I'm interested in the induction you intend to use. Doesn't the 450SL come with K-jetronic ?
Are you converting that to pulsed fuel injection with individual throttles? Or something else innovative?

Zac510,
I intend to go with a MegaSquirt II-type setup and I'll probably be using ITBs as well... If for whatever reason that proves to be a problem, I'll just make do with dual 75mm TBs instead ;)

[hydra]

Originally posted by McGuire


I think the software is leading us into the trap of chasing numbers instead of trying to build the best engine for the application. First, we are not going to get 255 cfm and we really don't want it anyway. We have no idea how this valvetrain will appreciate .650 lift, and relocated ports and similar schemes seldom pay off in street engines. When we take a few steps back and look at the big picture, we are taking exactly the wrong approach for a successful street engine. Here max flow numbers and max hp@rpm are not the goals at all.

If you are asking me how to do this: I would assemble a solid bottom end with good rods and quality forged pistons, perform a mild cleanup on the cylinder heads and install a blower. That will get us the 450 bhp far easier and cheaper than trying to build a full-race engine with no development base to speak of, and with far superior reliability and driveability. This is also the very same approach used in the current AMG V8.

McGuire,
You're absolutely right, the point is to make as much power as possible and not win paper dyno contests, but with all due respect, what makes you so sure that 255cfm is unattainable? That's about the same specific flow (per unit valve area) as a good aftermarket SBC head, and I've got (or will have) a straighter shot into the cylinder, and won't have to contend with a head bolt or pushrod hole along the way. And just to push my point home, take a look at this graph of valve flow potential vs. L/D ratio
http://highperforman...flow05_zoom.jpg
at a L/D of 0.36, I'm assuming I can get to within 90% of the state of the art which I like to think is within reason. As for the valvetrain, I will be using Comp Cams ovate springs with ~90lbs on the seat and 290lbs over the nose, which is by no means excessive for a roller cam or for a well engineered M-B V8
The M117 bottom-end is pretty beastly as is, with 6 bolts per main cap, forged everything, etc... And since I'm only raising the redline by 500rpm, I see no reason to go with aftermarket anything. The problem with FI is that an Eaton M112 (the biggest supercharger that can be had for cheap) is only good for 3-4psi on this engine. Do the math and see for yourself... A brand new aftermarket SC is out of the que$$tion. Turbos as nice, but there's no space to package them. This is secondary though, when you consider that 10-11psi will net you 650lb-ft of torque (and 600+bhp), and I'd have to re-engineer the entire drivetrain to make it live. I'm not all that keen on spending $2-3k on a tranny buildup ALONE. You're probably going to laugh at me and call me insane, but I don't see myself spending much more than $1k on the engine buildup. Also this will NOT be a race engine McGuire, with the cam specs I have assumed (more on that later) I should be pulling 19" of vacuum at idle. Pretty mild, don't you think? As for reliability, the only changes that will affect MOVING parts (so things like headers and intake manifolds don't enter the equation) are cams, valve springs, rockers, and retainers. I can keep the stock valvetrain in exchange for ~50bhp or so, and I'd still end up with a powerful RELIABLE engine...

[hydra]

Originally posted by bobqzzi


Ah, I agree with McGuire here. I was assuming this was a race engine. Any type of cam that gives .650" lift is going to be unstreetable, and probably require valve spring replacement fairly frequently.

A well matched centifugal supercharger and programmable fuel injection on an otherwise stock engine would exceed your goal and could do so at stock RPM levels.


I am quite familiar with reynolds 390 bores as I used to race a Cosworth Vega. If it does turn out you need pistons, a nikasil coating will work with the 390. Boring the block is not a problem, but finish honing requres a special sunnen "stone". I had to buy some, and , as I recall, they were fairly inexpensive and fit standard sunnen holders. Porsche 944s also used this bore material, so imagine there must be some expertise over your way.

Bobqzzi,
Here are is the cam lobe I intend to use for both intake and exhaust
265 degree seat duration
214 degree duration @ 0.050"
141 degree duration @ 0.200"
0.353" lobe lift
1.85 rocker ratio

Its an "inverted flank" roller, but should have no problems with the spring loads I mentioned above at 6500rpm. Remember, this is an OHC engine using beehive springs..

Again, going the FI route sounds like a great idea on paper, but I am faced with three problems:
a) Supercharged procurement is a problem since I am overseas and shipping is expen$$Ive, and an Eaton M112 (biggest OEM supercharger that can be found apart from the SL55 unit) is just not big enough for the engine
b) TORQUE! Torque is what breaks parts, and I don't want to have to upgrade EVERYTHING south of the flexplate. On the other hand, I don't think a 40% torque increase is going to give me major headaches assuming I drive sensibly (assuming I stick with an NA buildup)
c) And I just thought of this one while I was writing this - HOOD CLEARANCE
I want to leave the car stock looking, turbos wouldn't fit, and an Centrifugal SC would cost more than I'm willing to pay. Did I mention that I got this engine, which also happens to be in GREAT shape for FREE?

Seriously though, there's also the challenge of going down a path nobody's been on, and the buzz from designing/engineering something new... Surely you guys understand

[clSD139]

Suppose, I have a Jetta GLX but I want for some reason an I6 and RWD.



What would you advise me? To start welding or to buy a synchro rear-axle?

[hydra]

Simple...
Sell the Jetta and buy an E21 or E30 BMW 3-series ;)

[Greg Locock]

Buy a Ford Falcon, 185 kW of BMW beating taxicab. (Hey where's Pat?)

[bobqzzi]

Originally posted by shaun979
Are there any companies in the US that Nikasil coat large bores and hone them to tight tolerances. What are their rough costs? I know LSM sells Nikasil liners and also installs them, but beyond that.. say if you wanted to coat a linerless block.. can this be done?

Apologies Hydra, for the short OT.

What kind of block? If it is cast iron, and larger than a small 4 cylinder, the answer is no. If it is aluminum, then US Chrome and Perfect Bore should be good bets

[Powersteer]

That Benz looks hardtop. I thought all SLs came in open top.

[clSD139]

Originally posted by hydra


I've already got a nice silicone port mold right here on my desk

Molds...

[Halfwitt]

Originally posted by hydra

Detail of intake port and (mechanical) injector boss, this is where I would like to raise the port


[/B]

Well, if you're really serious, and you can move your injector somewhere else, I'd weld the injector hole up, build the bottom of the port up with weld, possibly seom extra material on the face and get to work straightening the port out. That right-angled (well,almost right-angled) kink in the port will do you no favours and tidying it up will do more for flow than increasing valve sizes or lift will.

I don't know anything about this engine, i.e. if these kind of mods are possible, but if you are serious about getting the most power out of your engine, then sorting this port out is a good start.

[Powersteer]

Raising the intake port and shapening its entry create problems with manifold design. With the current straight 90 degree port, you can create an intake manifold that is 100% straight while getting the needed length for your targeted RPM. You might cut down on overall bends if the ports are not raised. I'm not too sure whether you intend to change the port entry angle and this post assumes you do.

If you don't might having intake stacks sticking out of that beautiful cars bonnet(hood) then its all your show.

P.S; Oh! its an SLC

[Joe Bosworth]

Hydra

I can't help but notice that you are thinking of running a valve lift of 0.65 inch with a 1.82 inch dia. valve with 45 degree seats all for a lift/diameter ratio of .36.

I also notice that you seem to be choosing this lift based on a chart that shows flow potential for Pontiac heads measured on a flow bench.

It is interesting that the flow area at the circumference of a valve with 45 degree seats equala the area of the port under the valve at very near a L/D ratio of .25.

In other words, while the circumferencial area increases at higher lifts, the gas has to actually slow from port velocity at the valve seat if the area is utilised, which I suspect it is not.

I have kept track of port gas flow and lift/diameter data for an awful lot of very successful race and good hot road engines for a very long time and have never seen one with an L/D ratio more than about 10% greater than .25.

I suspect that this is so because of two factors:
1. Lift uses internal HP and extra lift costs extra HP which needs to be created to make flywheel HP
2. Not reducing port gas velocity until the combustion chamber is reached helps port tune.
3. Keeping velocity to past the edge of the valve improves cylinder filling and flame front advance.

I have always found that the best engines are those that match all of the various design features. Going overboard on one factor reduces dramatically the sum of the lot.

I know new things are being developed every day and sometimes it is difficult to keep up but if someone knows of a good engine running a L/D of greater than about .28 or so I would love to hear the details.

Unless someone comes up with some real life good experience I recommend that you re-think the valve lift that you are considering.

Regards

[hydra]

Joe,
A very experienced and successful Pro-Stock engine builder once said that intake L/D should be in the region of 0.41 for an ALL-OUT 2V race engine, and ~0.37 for a 4V race engine. (with max Exhaust L/D = 0.52 if anybody's interested) It makes sense to me, because Pro-Stock engines run ~1" of valve lift with ~2.5" intake valves, and F1 engines run 16mm of valve lift with 40mm intake valves, so I'm sure there's some very valid logic behind it.

Production engines rarely run more than 0.25 L/D. In fact, a lot of modern 4V engines run a L/D ratio below 0.25, and while I'm sure there's a reason for it, it doesn't mean that its the best thing for power and BMEP...

As an aside, I would think that the optimal valve seat angle would be closer to 50 or 55 degrees at such a high L/D...

[Bill Sherwood]

FWIW had a fiddle with some of the variable in the file Hydra sent me and I got it to nearly 500hp, though at the expense of a bit of mid-range torque.

[hydra]

Joe (and everybody else) Check this link out...

http://www.eng-tips....d.cfm?qid=92513

[McGuire]

Originally posted by hydra


I'm assuming I can get to within 90% of the state of the art which I like to think is within reason.

Then you must not think much of professional engine developers. If what you say is true and it is that easy, they are a bunch of crooks. Personally, I think you are going to have serious trouble getting your eight intake ports within 90% of each other. No offense.

In many ways this whole engine is a collection of unlikely specifications, a combination that can be constructed on a PC but not in reality. But let's put that aside and let's talk about the "state of the art" for a moment.

We know that when we try to pull ye big numbers through a single small valve, the port will become hyper-critical -- like a musical instrument. It will be in tune in one very narrow range, and hopelessly out of tune everywhere else. We know similar things about larger L/D ratios. And the state of the art also contains the knowledge that large, straight ports do not work well in street engines. We also know that relocated, fabricated and welded ports are always more trouble than they are worth in this application. The payoff is not there. And we especially know that it is ALWAYS a mistake to develop a street engine for max horsepower @rpm at the expense of power and torque everywhere else.

We KNOW these things. They have been established time after time in hard-won, real-world experience; they are chapter one in any decent DIY how-to book about performance engine development. But we are going to ignore all these facts which constitute "the state of the art." We have are going to skip down the golden path laid out for us by some PC software, without a flow bench or a dyno or even a pair of calipers. Good luck.

[Joe Bosworth]

Hydra

Thanks for your feedback and reference provided.

However:

Let me 100% endorse the advice that McGuire has provided immediately above. His advice is absolutely correct and is irrifutable. Read, re-read, absorb and take to heart.

And then, of course do what you feel best is for you. It is your money and time.

However:

Engine development is a matter of evolution, not revolution. The best practices known today have been acheived through long term trial and error. Little bits of improvement come at a time, often more by happenstance and hunch than by design. Interestingly, when new things are deliberately tried in the way of new break through, only 1 in 20 or 30 or 40 or more prove useful.

You need to keep in mind that you are in effectively new territory with your planned programme. Staying inside known parameters means that you will probably be relatively happy at the end. Stray into new parameters and you can expect to redo much at the cost of time and money.

One of your more interesting references clearly refers to Pro Stock engine technology. The Pro Stock guys are taking a 2350 pound, 500 cu inch cars down the track in sub 7 seconds. This takes some 1500 real HP. They are willing to put up with an engine that has a life measured in minutes, certyainly less than an hour. Also low rev, part throttle performance is meaningless as they are at near wheel spin all the way to the end of he track. They are making over 180 HP per liter, probably more than twice any expectation that you have. They are also turning revs 60% more than any of your expectations. Any similarity between they and your technology targets are minimal.

Some may well be using lifts as you describe but the flow theories thay are working with are beyond roadable. They are using ultra lifts in part to get the valve un-shrouded by the edges of the combustion chamber. They are also depending in a major way on inlet ram and exhaust tune to achieve things impossible to utilise in a roadable car.

The figures that I gave you for lift ratios are all proven both on the dyno, road and track. By comparison, they will get you into the low nines in the quarter mile and yet still allow you to drive home. The engines will also last for 100's of road hours or possibly 15 hours on the track.

Having said that, re-read McGuire yet again. And of course build as you wish.

Good luck and tell us how it all faired when you get done.

Regards

[alpa]

Hi Hydra,

I'm reading the thread only now. It's a little bit difficult to follow all the discussed directions .
I don't know US engines, but have seen some old (not so old in fact) Porsche engines, yours seem to be close to the Porsche 5L V8 2V.
I think it's really interesting to raise the angle of the intake port (look at modern Honda head ports which are very close to ideal). The way we are planning to do on a flat6 (air cooled) is to insert an alu tube inside the head. Of course the alu material must be careful choosen to have the same temperature expansion as the head. And this isn't cheap.

If you don't raise the angle I believe raising the lift above 0.25 will bring more air. Even if theoretically the valve flow don't raise much above a 0.25 lift, this isn't true for 'badly' designed ports because valves don't flow across the whole seat surface, the air follows the direction given by the intake port runner and don't flow towards the wall. This is also the case on A-Series engines (BMC Mini).

However I believe your main problem is that the head isn't a crossflow one. You can not take as much advantage of an overlap as on a cross-flow head. These heads seem to flow less efficiently during the exhaust cycle. Also the pressure level in the chamber is highly not homogenous at the end of the compression cycle (squish areas, plug location), which is the source of knocks and a not optimal ignition timing. And of course the side plug location does not help you.
That's why I don't think you'll be able to get much more power from the production setup.
And I DO believe that even a low FI will greatly help you to scavenge the cylinder and to improve the VE. It will fill in better on low lifts and will create an intake pressure level which will overtake the resident chamber pressure and thus allow less backflow and EGR at the intake valve opening.

It's a great car ! Even if I don't appreciate much Mercedes.