89 replies to this topic

[DOHCPower]

Just curious if this has been covered at all on these forums, i tried searching, and found plenty of information about CFD in regards to body work, but nothing on the cylinder head side of things.

One of the things i was curious of, and have debated with a few people about, is the sharpening of the intake port dividers. Here is a picture of a Honda B16A head that i recently did. On the left is the untouched port, on the right, obviously, is the port at 95% completion.



Now, i thought this was helpful at 'slicing' the air in order to direct it better to each valve, but after doing a bit of reading, im not so sure this is case, as people keep pointing to a tear drop as the perfect aerodynamic shape. Any input on this subject is very much appreciated.

Here is some more eye candy to hopefully jump start the convo.

[Powersteer]

You can always make it round at the egde but really really thin.

[phantom II]

Glow plug.

Originally posted by Powersteer
You can always make it round at the egde but really really thin.

[Powersteer]

What?

[McGuire]

Originally posted by phantom II
Glow plug.

LOL if the intake port walls are getting that hot we have a larger problem.

[McGuire]

Originally posted by DOHCPower
One of the things i was curious of, and have debated with a few people about, is the sharpening of the intake port dividers.

I know there is some controvery about this issue among Honda tuners but since I don't work on the things myself I don't have an opinion. My hunch is it won't make a big difference one way or the other on the bench.

However, one thing immediately catches my eye. Judging from the location of the boss in the top of the port, the injector appears to be pointed right at the port divider. Fuel that runs headlong into the divider will be kicked out into the airflow, which is a good thing. Fuel that hits a surface tangentially will just stick and dribble...especially if the port is highly polished. Right now the fast guys are getting best results from a ball finish. They are skipping the sanding roll.

CFD is the growing trend in cylinder head development. However the learning curve is tough and the process is expensive. The software isn't cheap nor is all the required scanning. At the OEM level the cost is reasonable but it will take awhile before it makes sense at the street level.

[Ben Wilson]

The way I look at it is that an airfoil is more aerodynamic at different angles of attack. A sharp edge will probably be more aerodynamic as long as the air is coming straight at it. Weather the differences are worth worrying about is another matter...

I will acknowledge McGuire's point about fuel atomisation, if you take that into account then there are issues arising from different injector types/positions/rail pressure etc..

[Greg Locock]

Software:

You can build a world class CFD workstation for the cost of hardware alone.

OpenFOAM is a full featured free CFD program, of professional quality. I know of at least one reasonable sized company that is switching to it.

It only runs on Linux, I use Ubuntu. They play well together.

If Iwere you, figure >1G of RAM and the fastest processor you feel like affording - on 256 M and a P3-800 MHz one of the sample files took >2 days to analyse, at which point I pulled the plug.

[McGuire]

My worry is open source software = fiberglass car kit. If you are clever and work hard you could be driving down to the corner and back in a year or two.

Even with a turnkey package you will have to put one guy on it 24/7 and leave him alone for a year before you see anything. Not many shops can afford that. I'm not knocking it at all. It is the future. If I had an engine or cylinder head business I would be finding a way.

[DOHCPower]

I didnt think the CFD stuff would be that complicated to set up but i guess i was wrong. I am familiar with 3d modeling programs such as 3D Studio Max and Maya, but i was never super proficient with them. I really didnt want to model the entire port; that would be a bonus if i could, just try some different shapes and turns to see how airflow reacts when applied. Like the blunt port divider vs sharp port divider issue. Thanks for all the responses so far..

[Halfwitt]

CFD... you only need to model half of the port, half of the chamber etc, and have the top of your inlet poking into a big box. The success of the analysis comes from being able to predict what is happening at the walls, so lots of small elements to capture the detail in the boundary layer. It's not the sort of thing you are likely to get good results from by trial and error, and it's easy to get a dazzling, coloured picture displaying nonsense. You need to correlate them with a flow bench (not easy) to be sure that you're going in the right direction.

I bet there are some SAE papers or similar detailing methodology etc.

CFD is widely used for development of ports, combustion chambers, valves etc.

A big problem with port dividers which are too sharp, especially on fully-stressed engines is their tendency to crack. There are reasonable gains to be had from playing with the shape of the divider, and this can be done with plasticene on your flwo bench. Sharp isn't always better, and different shaped ports like different shaped dividers.

[Canuck]

Anyone familiar with the SolidWorks add-in Cosmos FlowWorks? I haven't had a chance to use it (yet) but I'm wondering if it's of much use. I'm not so concerned with whether or not the software could be better, but whether or not a non-engineering guy would be able to use it to advantage when looking at port and chamber stuff.

[McGuire]

Well there ya go... a headache for someone is really only an opportunity for someone else.

You guys with the computer savvy who know how to scarf up the necessary software and hardware, develop the expertise and produce results can step right into the void and make some serious $$$. Guys who are asking where they can get a foot in the door, well here it is. You can write your own ticket.

[shaun979]

Every high speed 4V racing head I've seen has sharp intake dividers, but then again they have their injectors much further upstream. If anyone has photos of blunt intake dividers on a race engine or similar type, can you attach them please?

[Halfwitt]

I've been lucky enough to have a quick look down the port of a couple of recent F1 engines in the last year: one was quite blunt, one was much sharper. I'd say that,being F1, both are proabably optimised for the particular engine concerned.

They wouldn't let us take pictures.

[J. Edlund]

Usually four valve racing engines has a sharp intake divider, with CNC porting, which is usually used, it's possible to make the edge very sharp. In some engines there isn't much of a divider used.

Stock fuel injectors are usually designed to spray fuel onto the (hot) intake valves, and they use a two spray injector for this. This gives a very good vaporisation of fuel.

Racing engines on the other hand tend to place the injector further back in the runner.

[shaun979]

Halfwit, how recent?

[hydra]

Don't race 4V engines usually have 2 separate intake ports? (i.e. no divider) I know at least the old Ilmor Indy engine was like that. What are the advantages of keeping the ports separate anyway? All I can see is added wall friction...

[McGuire]

Not necessarily. With a common plenum (like a Champ Car turbo V8) you can run individual runners from the manifold flange to each valve. Otherwise you will need a port divider somewhere in the head or intake manifold, or you will need double the number of throttle valves...which has certainly been done, though it is heavy and complicated. Or you can run a wide open oval port with no divider -- that's certainly been done too.

[hydra]

McGuire,
But why bother with twin runners in the first place? Like I said, all I see to it is added wall-friction and slightly higher intake temps. Surely there must be some advantage to it, I just don't see it.


With that said, why aren't Toyota T-VIS type systems a lot more prevalent in the real world? If we could halve area and double intake runner velocity at low rpm, we could end up with much better swirl/tumble/whatever and better combustion, not to mention added torque. So we don't we see mfgrs doing this more often?

[Engineguy]

Originally posted by hydra But why bother with twin runners in the first place? Like I said, all I see to it is added wall-friction and slightly higher intake temps. Surely there must be some advantage to it, I just don't see it.

The divider supports the valve seat... if you cut it down too far the seat area of the chamber will flex and fatigue. Nevertheless, there are some new engines that push it pretty far and are pretty much a single oval port as far as they dare.

Originally posted by hydra With that said, why aren't Toyota T-VIS type systems a lot more prevalent in the real world? If we could halve area and double intake runner velocity at low rpm, we could end up with much better swirl/tumble/whatever and better combustion, not to mention added torque. So we don't we see mfgrs doing this more often?

They probably have nightmares about ending up like the ZR1 Corvette (GM/Lotus) LT5 World's Heaviest Aluminum Engine that had such a system (8 primary butterflies/8 secondary butterflies, 16 injectors).

The Ford 4.6L 32-valve V8s have(had?) a spacer between the head and manifold with butterflies that closed one of the two ports, even after they changed the head to not have the divider come all the way to it. Sean Highland, who wrote the book (literally) on these engines says removing the system only gains 5 or 6 HP (despite the shaft intruding through both ports, the one with a butterfly and the one without) but seriously hurts drivability, so he always recommends putting them back in unless it's a road racing app that never sees below 4000 RPM. So they can be effective, apparently. The Ford system opens at 3200 RPM, the LT5 was at 3000.

If I'm not mistaken I think some of the GM Northstar engines have(had) the system. They may be more prevalent than you think?

[hydra]

[QUOTE]Originally posted by Engineguy
The divider supports the valve seat... if you cut it down too far the seat area of the chamber will flex and fatigue. Nevertheless, there are some new engines that push it pretty far and are pretty much a single oval port as far as they dare. [/QUOTE]

Perhaps I wasn't as clear as I should have been, I meant why do some 4V engines, race and otherwise, have as many intake runners as valves? Where's the advantage in doing that if you're not going to use a system like the one described below?

They probably have nightmares about ending up like the ZR1 Corvette (GM/Lotus) LT5 World's Heaviest Aluminum Engine that had such a system (8 primary butterflies/8 secondary butterflies, 16 injectors).

The Ford 4.6L 32-valve V8s have(had?) a spacer between the head and manifold with butterflies that closed one of the two ports, even after they changed the head to not have the divider come all the way to it. Sean Highland, who wrote the book (literally) on these engines says removing the system only gains 5 or 6 HP (despite the shaft intruding through both ports, the one with a butterfly and the one without) but seriously hurts drivability, so he always recommends putting them back in unless it's a road racing app that never sees below 4000 RPM. So they can be effective, apparently. The Ford system opens at 3200 RPM, the LT5 was at 3000.

If I'm not mistaken I think some of the GM Northstar engines have(had) the system. They may be more prevalent than you think? [/QUOTE]

You've only mentioned 2-3 engines, why don't the Hondas and BMWs (and Peugeots and Kias, and and and...) of this world use a similar system if its advantages really are that great? A slide valve with an E-gas setup (max throttle opening allowed being a function of pedal input AND rpm) would be the cat's ass wouldn't it?

On a somewhat unrelated note why do we still have 4V DOHC engines producing 55-60bhp/L?
Why don't lower-spec engines like that revert to 2V? Before anybody goes on about wedge chambers having inferior combustion characteristics compared to a pentroof, the Z06 is/was a LEV (or was it a ULEV?)...

[desmo]

People like to buy DOHC 4v engines I think. Sounds high tech.

[hydra]

Sure, but not when its a bread and butter 75bhp 1.2L Opel Corsa-type car, and it just happens to be an additional $500 cheaper than its competitors (or comes with more goodies)

If 4V DOHC used to have marketing cache at one point, it probably doesn't anymore, now that even the most anodyne vehicles are so equipped.

[Canuck]

I'd like to get my hands on one the later Porsche 928 32-valve engines, or sort some way to convert BMW's V-12 to a 4-valve head. I put together a little article a while back that compared 2 BMW engines of similar bore and stroke where one was a 2V and the other 4. It was the first time I'd looked at the theory behind 4-valve stuff and by the time I'd done my homework I was sold on the idea.

I do find it ever so interesting that Yamaha's paper on the 5-valve claimed success while the rest of the world including F1 has stayed with 4 (or rather claimed 5 to be unworkable). Maybe that's a good project for the flow modeling.

[desmo]

Ferrari went with the 5v layout for a couple of years, late '80s I think, in F1. They even tested a desmodromic version!

[Engineguy]

Originally posted by hydra Perhaps I wasn't as clear as I should have been, I meant why do some 4V engines, race and otherwise, have as many intake runners as valves? Where's the advantage in doing that if you're not going to use a system like the one described below?

You've only mentioned 2-3 engines, why don't the Hondas and BMWs (and Peugeots and Kias, and and and...) of this world use a similar system if its advantages really are that great? A slide valve with an E-gas setup (max throttle opening allowed being a function of pedal input AND rpm) would be the cat's ass wouldn't it?

I've seen others, but my memory isn't good enough to state which engines they are. In any case, you can ask the same question about many engine features or add-ons. I.E. if turbochargers are so great, why don't all engines have them? If superchargers are so great, why don't all engines have them? If variable intake cam timiing is so great, why don't all engines have it? If variable intake AND exhaust cam timiing is so great, why don't all engines have it? If cylinder deactivation is so great, why don't all engines have it? If dry sump systems are so great, why don't all engines have them? Etc., etc. The answer is that the engine designer has a whole bag of choices to choose from, all coming with their various financial, complexity, and reliability implications. Not everyone wants and/or wants to pay for the things we think we are neat or powerful. A simple, minimal modern engine with its electronic fuel/ignition management is a pretty wonderful, powerful thing, with great drivability. Plenty good for the masses, so they're not interested in paying more for more.

Originally posted by hydra On a somewhat unrelated note why do we still have 4V DOHC engines producing 55-60bhp/L?
Why don't lower-spec engines like that revert to 2V? Before anybody goes on about wedge chambers having inferior combustion characteristics compared to a pentroof, the Z06 is/was a LEV (or was it a ULEV?)...

There are other reasons to go 4V besides its max power @ max RPM potential. Better torque curve, emissions, super low valve spring rates, small cheap valvetrain components (2 million little valves and springs are far cheaper than 1 million titanium valves and big critical quality springs), and yes, marketing necessity. The Z06 loafs in the emmisions cycle due to its displacement... and it doesn't scale down well. A 3.5L 4.125 bore x 4" stroke inline four would be a bulky, shaky, horrid proposition... and of course, the Z06 engine is not a typical 2V example. For an economical engine, something like the GM 5.3L is more appropriate, and in V8 configuaration IS a quite compelling package. Cut it in half though, and you have a 160HP four that is bulkier, and needs a double-speed balancing shaft that adds as much cost as going DOHC 4V... and you'll get crucified for selling a big "crude" 2V engine instead of a sophisticated 160HP 2L 4V.

[hydra]

I know what the touted advantages of 4V over 2V are, but if you're only targeting 60-65bhp/L on a low-end car (e.g. a 1.2L Opel Corsa or Fiat Punto or whatever) I don't see the advantages of going 4V DOHC. You can just as easily get your 65bhp/L without using titanium valves, killer valve springs, or anything higher than a 6500rpm redline. Furthermore, you'd (usually) end up with better low-end torque than you would with a 4V engine. Granted the concept doesn't scale up to larger cylinders where you've got 55mm valves and need 15mm of lift, but then again basic transportation calls for neither... Remember, most cars have a redline somewhere around 6500rpm, regardless of cylinder displacement (and piston speed)

[McGuire]

The T-VIS deal never made a huge amount of sense to me... when the valve timing and port volume are right it should be superfluous. If a 2V doesn't need two "breathing bands" or ranges I don't see why a 4V should. The beauty of 4V is the nice gentle valve action, at least at road car rpm. It should work fine at low flow rates.

Sort of a parallel deal... I used to scratch my head that split valve timing was never really catching on big... in other words the opening rates on the two intake valves are staggered, to set up some swirl and/or tumble in the cylinder. In modeling it works but in a real engine it doesn't seem to do much of anything at all. From what I have seen of recent wet flow work there is good reason to doubt any of that stuff really works as advertised. Until CDI is developed to the point where charge stratification can truly be exploited, it could be there isn't much there.

[McGuire]

Originally posted by Engineguy
They probably have nightmares about ending up like the ZR1 Corvette (GM/Lotus) LT5 World's Heaviest Aluminum Engine that had such a system (8 primary butterflies/8 secondary butterflies, 16 injectors).

That was mainly just a dumb gadget.

[McGuire]

Originally posted by Engineguy
For an economical engine, something like the GM 5.3L is more appropriate, and in V8 configuaration IS a quite compelling package.

Yes indeed... also, was talking to a buddy last week in Detroit (then saw him in LA this week and we had the same conversation LOL) who is very smart about this stuff and he is convinced that the 5.3 will be the engine that takes off and becomes the basis for Gen III/Gen IV hot rodding at the grass roots level. As he sees it there will be millions of them out there in the pipeline all selling dirt cheap in the salvage and crate markets. While the 6 and 7 liter versions can put up the big numbers, from his POV the 5.3 is just a real sweet engine that wakes up big with basic mods.

[hydra]

Originally posted by McGuire
The T-VIS deal never made a huge amount of sense to me... when the valve timing and port volume are right it should be superfluous. If a 2V doesn't need two "breathing bands" or ranges I don't see why a 4V should. The beauty of 4V is the nice gentle valve action, at least at road car rpm. It should work fine at low flow rates.
.

Why would it be superfluous? That's a little like saying VVT is superfluous no? Assuming intake runner diameters are set to give us 80-90m/s at peak power, wherever that may be, and valve timings are in-line with modern production-car practice, how can doubling intake runner velocity at the lower 1/2 of the rev range not help greatly? Assuming a ~7000rpm redline with a ~4000 torque peak, implimenting a system such as this should extend the torque "hump" by around 1000-1500rpm or so. More importantly, we would have excellent swirl at low-rpm/low load, where engines spend most of their time, eliminating problems with fuel puddling, insufficient vaporization, and high cylinder pressure COV. IMO its much better than VVT (although use of one doesn't preclude the other) so it boggles my mind why we don't see this more frequently...


On an unrelated note - again - can somebody please explain to me how its possible to have a dual-plenum intake manifold on a cruciform crank V8 like the LS1 without messing up intake tuning? Check this out:






Sure its a work of art, but at $3500USD+ , I'm not convinced :

[Hans Derbe]

Sort of a parallel deal... I used to scratch my head that split valve timing was never really catching on big... in other words the opening rates on the two intake valves are staggered, to set up some swirl and/or tumble in the cylinder. In modeling it works but in a real engine it doesn't seem to do much of anything at all. From what I have seen of recent wet flow work there is good reason to doubt any of that stuff really works as advertised. Until CDI is developed to the point where charge stratification can truly be exploited, it could be there isn't much there.

I know just one engine where this is used at the moment.....The actual BMW 3l I6 with valvetronic has phased intake valve events at low load together with a masked intake valve. This enhances swirl at part load without sacrificing VE at full load to much.

Hans

[phantom II]

Except that with a turn of a key, the valet only had 150hp to park your car.

Originally posted by McGuire


That was mainly just a dumb gadget.

[J. Edlund]

Originally posted by hydra
I know what the touted advantages of 4V over 2V are, but if you're only targeting 60-65bhp/L on a low-end car (e.g. a 1.2L Opel Corsa or Fiat Punto or whatever) I don't see the advantages of going 4V DOHC. You can just as easily get your 65bhp/L without using titanium valves, killer valve springs, or anything higher than a 6500rpm redline. Furthermore, you'd (usually) end up with better low-end torque than you would with a 4V engine. Granted the concept doesn't scale up to larger cylinders where you've got 55mm valves and need 15mm of lift, but then again basic transportation calls for neither... Remember, most cars have a redline somewhere around 6500rpm, regardless of cylinder displacement (and piston speed)

Even if the output is low the 4V head will still be offering lighter valves and softer springs which offers a smaller friction loss.

For a given output the 4 valve head will also offer the best torque curve, so tuned for a low output the 4 valve head actually gives a better low end.

In many cases though, the head is going to be used in several engine versions so you can't design for the lowest output and to make a separate two valve head for the low output engine is most likely going to be costly.

Then there's also the chance that you lose customers just because every one else offer a four valve head.

[hydra]

Originally posted by J. Edlund


Even if the output is low the 4V head will still be offering lighter valves and softer springs which offers a smaller friction loss.

For a given output the 4 valve head will also offer the best torque curve, so tuned for a low output the 4 valve head actually gives a better low end.

In many cases though, the head is going to be used in several engine versions so you can't design for the lowest output and to make a separate two valve head for the low output engine is most likely going to be costly.

Then there's also the chance that you lose customers just because every one else offer a four valve head.

The difference in FMEP between a 2V engine and an equivalent 4V engine is minimal, and is more than offset by the difference in weight, size and co$t between the two.

What makes you think the 4V engine will have a better torque curve? Sure if you fit it with VVT and all sorts of bells and whistles, but a basic 2V engine will be better low-down than a basic 4V engine, as magazine reviews have shown repeatedly

You can lose the added cam and valves, but you can make up for that with something more tangible, like higher quality materials or extra options. At the end of the day, I don't really think that the average motorist will care if an engine is 2V or 4V if the 2V engine matches, or betters its immediate competitors. Again remember, we're talking about the cheap and cheerful market segment not an S-class competitor...

[Canuck]

Originally posted by hydra

a basic 2V engine will be better low-down than a basic 4V engine, as magazine reviews have shown repeatedly

Doesn't the higher velocity from the smaller dia. runners and the greater combined flow area / curtain area of the 2 smaller valves give you greater low end torque?

[hydra]

greater curtain area = lower velocity = lower torque over the first 1/2 of the rev range

[hydra]

Another point I wanted to bring up,
Wouldn't a single intake valve flow slightly better than two geometrically similar valves at a similar L/D given the same curtain areas? My reasoning is as follows, with 2 intake valves the flow streams might have some interference, reducing overall flow. And with the smaller intake runners of the 4V version, there is added wall friction, admittedly a minor effect, the boundry layer is a bigger % of the overall diameter, and intake heating effects are greater. On the other hand with a single intake valve there is swirl which I would imagine would reduce flow coefficients somewhat...

[imaginesix]

Was just browsing the F1 tech regs and noticed that in 5.1.5 it is stated "Engines must have two inlet and two exhaust valves per cylinder".

I guess the OEs didn't want GM to join the fray and embarrass them with a pushrod 2V engine.

[Engineguy]

Originally posted by hydra
What makes you think the 4V engine will have a better torque curve?

There's way too much over-generalization going on here... ports can be shaped to fit your goals regardless of how many there are... however... because of superior, quicker low lift flow a 4V head intrinically fills well (which is what, in the end, makes torque) across the RPM spectrum with conservative cam timing. A 2V on the other hand is far more RPM targeted and needs tuning parlor tricks (i.e. overlap) to maximize filling at a particular RPM range sacraficing filling efficiency at other RPM ranges. Ironically, DOHC VvT (so that overlap could be varied) would be more valuable on a 2V engine... but who's gonna do that (DOHC Vvt) and not go ahead and make it 4V?

[McGuire]

Originally posted by hydra


The difference in FMEP between a 2V engine and an equivalent 4V engine is minimal, and is more than offset by the difference in weight, size and co$t between the two.

What makes you think the 4V engine will have a better torque curve? Sure if you fit it with VVT and all sorts of bells and whistles, but a basic 2V engine will be better low-down than a basic 4V engine, as magazine reviews have shown repeatedly

You can lose the added cam and valves, but you can make up for that with something more tangible, like higher quality materials or extra options. At the end of the day, I don't really think that the average motorist will care if an engine is 2V or 4V if the 2V engine matches, or betters its immediate competitors. Again remember, we're talking about the cheap and cheerful market segment not an S-class competitor...

The 4V will make more torque and power over a greater rpm range every time. End of story. So it really comes down to weight, cost and packaging... and all these considerations are relative with respect to the target market.

[McGuire]

Originally posted by hydra



can somebody please explain to me how its possible to have a dual-plenum intake manifold on a cruciform crank V8 like the LS1 without messing up intake tuning? Check this out:

I don't see two plenums there. I do see two airboxes upstream of the throttles where they will behave nothing like plenum chambers.

That said, V8's with two plenum chambers (either isolated or connected with a balance tube or volume) are not rare at all. Essentially that is what a dual-plane intake is. There the cylinders are split two outboard/two inboard bank-to-bank... but the manifold can also be configured to feed individual banks as in the classic "crossram" manifold... which is not "dual plane" in the traditional sense but works just fine anyway.

[J. Edlund]

Originally posted by hydra
The difference in FMEP between a 2V engine and an equivalent 4V engine is minimal, and is more than offset by the difference in weight, size and co$t between the two.

Why should the 4V head be more expensive or heavier than a 2V head?

In the past 4V heads have been seen as something expensive, the casting is probably a bit more complex and you need to machine the head in additional directions. But with modern casting and machining techniques I doubt there is much of a problem. At least if you use the same 4V head for engine versions with higher outputs.

The difference in FMEP between these two heads are most likely very small, but in these days when manufacturers even try to reduce the consumption taken by the water and fuel pump, a small reduction in the valve train isn't going to be ignored.

To this you also can add that some manufacturers haven't made a 2V engine for one or two decades.

Originally posted by hydra
What makes you think the 4V engine will have a better torque curve? Sure if you fit it with VVT and all sorts of bells and whistles, but a basic 2V engine will be better low-down than a basic 4V engine, as magazine reviews have shown repeatedly

Back in the eighties swedish car manufacurer Saab tested a 4V head against a 2V head. The 4V head was a "detuned" rally head, so both heads was designed for the same power output. Of these two heads it was shown that the 4V head gave a better torque curve.
Compared to the rally head the ports was made smaller and the timing was very mild.

Originally posted by hydra
You can lose the added cam and valves, but you can make up for that with something more tangible, like higher quality materials or extra options. At the end of the day, I don't really think that the average motorist will care if an engine is 2V or 4V if the 2V engine matches, or betters its immediate competitors. Again remember, we're talking about the cheap and cheerful market segment not an S-class competitor...

Haven't you seen those "16 valve" stickers on small japanese cars from the eighties?

Originally posted by Engineguy
Ironically, DOHC VvT (so that overlap could be varied) would be more valuable on a 2V engine... but who's gonna do that (DOHC Vvt) and not go ahead and make it 4V?

Doesn't GM have some engine with 2 valves per cylinder and variable valve timing? If I remember correctly they have a two valve push rod engine with variable valve timing, there are two cams in the block, one for the exhaust valves and one for the intake valves.

[imaginesix]

Originally posted by J. Edlund
Haven't you seen those "16 valve" stickers on small japanese cars from the eighties?

I also remember some early 80s Escorts vaunted their great new manual transmissions by clipping a chromed '4-speed' tag on the rear hatch. Of this, they were proud? Yikes.

[hydra]

This discussion has degenerated into one of 2V versus 4V, that was never my intention. Like I said, I understand full well the benefits of a 4V engine, but when you're only pushing 60-65bhp/L , you don't utilize any of those benefits and needlessly add cost, weight, and complexity. Surely we can all agree on that?

[phantom II]

I must get one of those stickers for my Vette.

One of the single cam pushrod V6s in GM's minivans has VVT mechanism.

Originally posted by J. Edlund



Haven't you seen those "16 valve" stickers on small japanese cars from the eighties?



Doesn't GM have some engine with 2 valves per cylinder and variable valve timing? If I remember correctly they have a two valve push rod engine with variable valve timing, there are two cams in the block, one for the exhaust valves and one for the intake valves.

[McGuire]

Originally posted by hydra
This discussion has degenerated into one of 2V versus 4V, that was never my intention. Like I said, I understand full well the benefits of a 4V engine, but when you're only pushing 60-65bhp/L , you don't utilize any of those benefits and needlessly add cost, weight, and complexity. Surely we can all agree on that?

No, I don't really agree. Even in the well-under-two-liter class, the 4V will make more power and torque over a wider range... and in this class you need it. Nobody will buy a busy, thrashy engine anymore. Even the bottom-feeder consumer expects a little refinement.

The market where 2V makes most sense these days is big V8. That could be around 65 hp/L... but probably not what you had in mind. This engine works because you can fit a lot of displacement in a small, light package with low friction and an absurdly small component count. It can even make sense in racing... word on the street is the LS7R/C6R Corvette ALMS engine weighs under 300 lbs. Not too shabby for 7 liters.

[McGuire]

Originally posted by phantom II


One of the single cam pushrod V6s in GM's minivans has VVT mechanism.

Also the 6.2 liter Vortec V8 (L92) used in the Escalade etc.

[hydra]

Originally posted by McGuire


No, I don't really agree. Even in the well-under-two-liter class, the 4V will make more power and torque over a wider range... and in this class you need it. Nobody will buy a busy, thrashy engine anymore. Even the bottom-feeder consumer expects a little refinement.

The market where 2V makes most sense these days is big V8. That could be around 65 hp/L... but probably not what you had in mind. This engine works because you can fit a lot of displacement in a small, light package with low friction and an absurdly small component count. It can even make sense in racing... word on the street is the LS7R/C6R Corvette ALMS engine weighs under 300 lbs. Not too shabby for 7 liters.

Why do you automatically assume that the resulting engine will be "busy and thrashy"? One can design a perfectly satisfactory 2V SOHC engine with a B/S of 1-1.05 and a Rod/Stroke of 1.55 and a cylinder size between 333-400cc making SIGNIFICANTLY more than 65bhp/L using good detail design and a redline no higher than 6500rpm, with a cam small enough to give idle vacuum of 22"...