75 replies to this topic

[Canuck]

At the risk of ending up in another HP/TQ discussion...

We're engaged in an engine build where the focus is weight reduction of anything that moves. We're introducing lots Ti components where we can, lighter pistons, rods - you get the idea. In discussion with one vendor he warned me that weight was torque, which sounds like absolute crap - torque is a function of cylinder pressure and stroke is it not?

While I understand that eliminating all the mass from a crankshaft might leave an engine without the necessary momentum to let the clutch out at idle and roll away, the actual torque produced at any given engine speed is the same is it not?

[Greg Locock]

I love thread convergence.

By definition in a racing car you are accelerating. So, unless you have a CVT you have to accelerate the guts of the engine, and the transmission and to a less significant extent the driveline and wheels. The effect depends on the square of the gear ratio.

Accelerating the rotational inertia takes power or torque. So if you reduce the rotating inertia of the engine you will accelerate faster. You won't see this on a waterbrake at steady speed.

So, to some extent I agree with your vendor.

For him to justify his claims he needs to tell you what the reduction in inertia is.

Incidentally if you are trying to work it out yourself you may find it hard to deal with the pistons etc, I find it easier to work out the change in total kinetic energy for the whole thing and then work back to an effective inertia at the flywheel.

[Paul Ranson]

IMO yes.

Next!

The practical issue of course is that if your ultralight engine won't run below 4000rpm, and your clutch is a bit sharp, then you're going to stall it a lot, or be slipping the clutch with 9000rpm on the engine.

Paul

[Canuck]

Originally posted by Greg Locock

Accelerating the rotational inertia takes power or torque. So if you reduce the rotating inertia of the engine you will accelerate faster. You won't see this on a waterbrake at steady speed.

Precisely my point - if the goal is to accelerate quicker then within reason, less mass is a good thing no? Oddly enough it was our piston vendor that mentioned it when I asked about various piston designs and their weights. By far the majority of the mass is contained in the crank/rod assy (34lbs, less if we use Al rods) so I wouldn't think reducing overall piston weight would be an issue in the grand scheme of mass.

I know of a supplier that makes 'Torque Master' cranks for touring bikes - much heavier than stock. Great if a guy is pulling a sidecar along, not much fun in a lighter application.

I don't want to make this bike overly sensitive to throttle input, just get allow it to spin up faster.

[Canuck]

While I'm at it - is there an engine modelling package that's somwhere between GT-Power/Adams type stuff and the $100 software one finds at the local speed shop? While I'd like to have GT-Power at my fingertips I doubt I can effectively 'fill in the blanks' and I know I don't have that kind of budget. On the other end of things none of the speedshop software has the features or flexibility I'd like.

[J. Edlund]

Originally posted by Canuck
At the risk of ending up in another HP/TQ discussion...

We're engaged in an engine build where the focus is weight reduction of anything that moves. We're introducing lots Ti components where we can, lighter pistons, rods - you get the idea. In discussion with one vendor he warned me that weight was torque, which sounds like absolute crap - torque is a function of cylinder pressure and stroke is it not?

While I understand that eliminating all the mass from a crankshaft might leave an engine without the necessary momentum to let the clutch out at idle and roll away, the actual torque produced at any given engine speed is the same is it not?

Torque depends on cylinder pressure and displacement, not stroke.

Mass (weight is dependand on acceleration) has nothing to do with torque. The interia will however affect the torque output/input needed to change the angular velocity of for example an axle.

[McGuire]

Originally posted by Canuck
While I understand that eliminating all the mass from a crankshaft might leave an engine without the necessary momentum to let the clutch out at idle and roll away, the actual torque produced at any given engine speed is the same is it not?

Depends what we mean by "same," as torque is not constant at the output flange. In an inline four it can vary over 300% four times per operating cycle...or, why engines have flywheels. Obviously the crankshaft is not going to stop and change direction twice per rotation but it is sure going to try, subject to rotating inertia. Also, there is a 100% torque reversal running up and down the driveline at 2x crank speed so you will want to put in the good parts.

[McGuire]

Originally posted by Canuck
While I'm at it - is there an engine modelling package that's somwhere between GT-Power/Adams type stuff and the $100 software one finds at the local speed shop? While I'd like to have GT-Power at my fingertips I doubt I can effectively 'fill in the blanks' and I know I don't have that kind of budget. On the other end of things none of the speedshop software has the features or flexibility I'd like.

I don't think there are any that are worth any amount of your own money, unless you have a very specific purpose or area for study in mind. As I see it, if you don't know what you are doing you have no use for them, and if you know what you are doing you have no need.

At this stage of the game, for general purposes engine simulation software is a sort of Mr. Tea machine. The Mr. Tea machine was invented by Father Guido Sarducci. You put a tea bag in a cup and place it at the bottom of the unit. Then you pour hot water into the top of the unit. Voila, instant tea.

[Fat Boy]

Some a deez saints. They got the 3 miracles, but 2 a dem are card tricks. Sorry, a Father Sarducci relapse.

Canuck, my guess is that the vendor you are dealing with is confusing torque for kinetic energy. Yes, when you put a big flywheel on a car it is easier to pull away from a stop light. That is not a torque production issue. It is an energy storage issue. Flywheels store rotational kinetic energy and which you can use to pull away from a stop light.

2 scenarios.

0 rotational inertia. Leaving from a stop. All of the energy that is used to get the car rolling will have to come directly from the explosions going on in the cylinders. A portion of each cylinder firing will be used to slip the clutch and drive the car. If you let the clutch out just a little too fast, it will stall the engine.


Massive rotational inertia. Leaving from a stop. All of the energy that is used to get the car rolling will come from the flywheel. The actual explosions in the cylinders will have little effect on the torque at the input shaft and you can pull away from a stop without slipping the clutch at all.

Once the vehicle is rolling, it's a different story, the lack of rotational inertia will allow car #1 to use all of the power of the engine to push the car forward (linear kinetic energy) and the massive rotational inertia car #2 will barely accelerate at all because nearly all of the power of the engine is converted to rotational kinetic energy with little 'left over' to accelerate the car.

Make sense?

1 more thing. In going very light with the rotating assembly, make sure you get the balancing correct. You can really beat the hell out of stuff when you try to get clever. That _will_ reduce the torque of the engine (as well as it's life).

[Canuck]

Ah yes - I'm by no means Mr. Smartie-Pants. I often don't have a clear picture of exactly what the results will be when I stray outside my experience - but that's the point of going there right? For example, I know that moving IVC farther along will reduce my cranking pressure, taking load of the starter but it will also sacrifice some low-end torque in exchange for more power higher in the RPM band. I know that changing my rocker-arm ratio from 1.625 to 1.725 will increase lift at the valve, but I don't know how it might affect the overall performance of the engine. These aren't things they bother teaching at school.

I had a copy of Engine Analyzer Pro once upon a time. While I could never get the simulation curve to duplicate the shape of rear wheel dyno curves, changes made to the bike in the real world were reasonably reflected when the same changes were entered. It gave me some idea of how various changes might affect the motorcycle in the real world, and in doing so furthered my understanding of how things work together.

Back to the question at hand - these aren't challenges to what's being said, just trying to get my head around things.

If torque isn't directly connected to stroke length, why do long-stroke engines (in my experience) always produce more peak torque than an engine of the same displacement with a shorter stroke?

I suppose I should know better here - I'll try to be more clear. Regardless of flywheel mass, the torque produced is the same (momentum is different of course) - or have I missed the boat yet again?

[jb_128]

Originally posted by Canuck


By far the majority of the mass is contained in the crank/rod assy (34lbs, less if we use Al rods) so I wouldn't think reducing overall piston weight would be an issue in the grand scheme of mass.

Remember that the mass that is far away from the centre of rotation will have a quadratic influence on the rotational inertia. Saving weight in the piston will be much more effective than saving weight at the cranc.

Rotational inertia: I=int r^2 dm

EDIT: Come to think of it, this probably isn't true since the pistons are not really rotating. While they are further away from the centre of rotation than the mass of the crankshaft, they are not being accelerated harder on average than the mass of the crankshaft. So I think you were right Canuck about the 'grand scheme of mass'.

[Greg Locock]

I think the other advantages of lighter pistons and conrods (reduced sidewall loads, reduce big end loads) are so great that it is not surprising that people put a lot of effort into the pistons.

So far as simulations go, when spending your own money and time, just remember that "all models are wrong, some of them are useful".

[McGuire]

Originally posted by Canuck
If torque isn't directly connected to stroke length, why do long-stroke engines (in my experience) always produce more peak torque than an engine of the same displacement with a shorter stroke?

In my experience they don't. Here is one good use for engine sim software: construct two engines of identical displacement, valve area, etc, but with different bore/stroke ratios. You will find little to no difference in their output. You will find some tendency for the long stroke version to produce its peak torque at a lower rpm, but that's about it. And out on the extremes of bore/stroke ratio the long stroke engine will make less output due to greater friction hp -- the pistons must travel further per crank rotation.

Here is the real lowdown: Big bore/short stroke will make more torque and power than small bore/long stroke across the entire operating range, because it has more valve area per unit of cylinder displacement. Long stroke/small bore is limited in valve area, thus limited in rpm due to its limited breathing capacity. So it's not that long stroke engines produce greater torque or at lower rpm. More like low rpm is all they can do, so they are typically optimized for max output at the speeds they can run.

A month or two back David Frieberger of Hot Rod did a pretty decent piece on this subject complete with engine builds and dyno tests. There is a thread here discussing it you can access via the search function...

[Canuck]

I'll try it (the simulations) - always good to learn new stuff.

It's been a long time since I worked on anything automotive, but I recall that our motorcycle bore/stroke ratios are radically different than automotive stuff. V-Twin engines are bore--limited by the cylinder-stud arrangement - only so much room between the studs. One can gain extra bore size with an aftermarket cylinder and boring the engine cases within the realm of what the studs will allow. The particular engine I'm working with is hampered by a lack of available cylinders due to their odd-ball cylinder-stud pattern and unusually short cylinder/tall deck arrangement. In stock configuration we run a 3-7/8 bore with a 4-1/4" stroke and the stock liner thickness is .125" . Those who know don't seem to be willing to part with an acceptable minimum liner thickness so for the time being we'll leave well enough alone and just clean them up with a .010" piston. The stroke is being taken to 4-5/8" yielding a displacement of 109" - give or take. By Harley standards we have a large intake valve 1.94", and a fairly standard exhaust (1.615"). In real-world application we know we can survive engine speeds of 6500rpm though as you've noted above mechanical losses and wear-and-tear become exaggerated and the trade-off is too great for a reliable street engine. The rev limiter will be set for 6000rpm with a peak hp RPM of 5700. Stock rod-length is 7.440" and we'll end up with either 7.470 if we stay with a Carillo-style rod or 7.5" if the aluminium rods are deemed suitable for long-term street use. While it does happen that modified stock heads have an intake port that is too small, we generally see stuff that is 'hogged-out' and slows the flow down, sacrificing some torque. Typically the biggest restriction to air-flow is at the carb, but there's lots of options available to address that. God knows if you live anywhere in North America you're aware that exhaust flow is not an issue - good pipe design is, but flow is not.

I'll build those two engine configurations and we'll see what they say - thanks for the input.

[Canuck]

Well....egg on my face. I'll be damned - don't really know what to say.

In building two identical engines, changing only the b/s to maintain the same displacement (within .05 CU^3), the short-stroke engine produced the same average torque, same peak torque, same average hp and near identical peak hp. Gob-smacked to be honest.

Okay - I need some clarification. When I was doing some research on AlBeMet (hey - it's not banned for road use right?;) ) and McClaren's use the impression I got was that they'd used the Be compound to decrease their rod (and perhaps piston, I'm unclear on that) weight. This allowed them to maintain the same displacement with a smaller bore and longer stroke and ultimate rpm. This was supposed to give them more midrange performance. I need to find that article again.

[desmo]

I don't think AlBeMet was ever considered for rods. The only engine parts I'm aware of that were done in AlBeMet were pistons and liners.

The Influence of Stroke-to-Bore Ratio and Combustion Chamber Design on Formula One Engines Performance- SAE Paper 980126 has some good basic info on bore/stroke ratios and their implications from an F1 perspective.

[Canuck]

I couldn't find the article I was thinking of, but both Perfect Bore and Brush Wellman were trying to develop AlBeMet gudgeon pins with rods next on the list. I assume the FIA regulations put an end to that development.

Edit - The paper discussing the pins and rods is available from the literature section at Brush Wellman . Article is MAAB-13, a Race-Tech reprint regarding AlBeMet in F1.

[Engineguy]

Originally posted by Canuck ... This allowed them to maintain the same displacement with a smaller bore and longer stroke and ultimate rpm. This was supposed to give them more midrange performance. I need to find that article again.

F1 is at B/S ratios and revs that give them combustion chamber problems you won't see. Backing off their B/S ratio may have given them a better total power band simply by getting them out of a problem area (i.e. allowed them to get the compression ratio they want without resorting to a poor chamber configuration).

Horsepower AND torque are almost totally dependent on valve curtain area and engine displacement. A long stroke only makes more torque when it creates more displacement. When a longer stroke is used at the expense of bore size (to maintain a fixed displacement), low RPM torque stays about the same (give or take a little) and high RPM torque suffers.

With McGuire's example you didn't change valve size, and power didn't change. If you allow valve size to follow the bore size you'll find power will follow it pretty closely. In the following example I incresed bore diameter AND valve diameter 10% and reduced the stroke as needed to maintain the original displacement. Horsepower increased over 9% and max torque increased 3%. Only at very low RPM did the smaller B/S have a small (2%) torque advantage.

[McGuire]

Originally posted by Canuck
Well....egg on my face. I'll be damned - don't really know what to say.

Hold the eggs, it's not your fault. The world of vehicle performance is full of myths. The old yarn about long strokes making torque is just one example. There are plenty more and they die very hard, while more are generated every day.

[McGuire]

Originally posted by Canuck


The particular engine I'm working with is hampered by a lack of available cylinders due to their odd-ball cylinder-stud pattern and unusually short cylinder/tall deck arrangement. In stock configuration we run a 3-7/8 bore with a 4-1/4" stroke and the stock liner thickness is .125" . Those who know don't seem to be willing to part with an acceptable minimum liner thickness so for the time being we'll leave well enough alone and just clean them up with a .010" piston. The stroke is being taken to 4-5/8" yielding a displacement of 109" - give or take.

So it's a Harley-style V twin for the road? Exotic materials and ultra-light reciprocating components might be the last place I would spend my time and money in this application.

[Canuck]

Originally posted by McGuire


So it's a Harley-style V twin for the road? Exotic materials and ultra-light reciprocating components might be the last place I would spend my time and money in this application.

Lucky for me you're not my client then 'eh.;)

[Canuck]

Okay, so using Engine Analyzer Pro from Performance Trends, I built two engines - 4.125"B/3.750"S and 3.875"B/4.25"S, the latter being the actual stock dimensions. In the original test, the HP and TQ changed only marginally between the two, leaving the stock intake valve size for both.

When I re-ran the tests with a larger intake valve for the short stroke engine, power did increase dramatically, however when that same valve size was used in the long stroke engine, the power curves were again nearly identical. Either the stock engine has an undersized intake valve or my simulations are out to lunch.

Friction losses are higher with the longer stroke however.

So then assuming bore size isn't creating breathing issues, a longer stroke is the second choice for increasing displacement - right?

Charts and data from simulation

[Engineguy]

If you maximized the valve sizes in the big bore/short stroke engine, those valves will not physically fit in the small bore/long stroke engine of the same displacement (even those your software may blindly ignore that and spit out results). You've got to be careful to not model impossible combinations of parts.

[Canuck]

Is there a calculation I can use to figure the 'best' intake valve size for a given bore then?

[Engineguy]

Originally posted by Canuck
Is there a calculation I can use to figure the 'best' intake valve size for a given bore then?

For a two valve head:

Intake dia. / Exhaust dia.

.51 x Bore / .40 x Bore
("practical" maximum)

to

.53 x Bore / .39 x Bore
(requires perfection in spacing & machining)

======================

For a four valve head:

Intake dia. / Exhaust dia.

.38 x Bore / .33 x Bore
("practical" maximum)

to

.40 x Bore / .32 x Bore
(requires perfection in spacing & machining)


Stick with the "practical" maximums unless you've already spent years developing everything else.

[Canuck]

Thanks. I learn something new every day. Now if I can just keep my foot out of my mouth I'll be all right.

In that spirit, McGuire - where would you be spending your money?

[McGuire]

I would need to know more about the application.

[McGuire]

BTW, I had a minor hand in the PP100....I think almost everyone in town did at one time or another. There were several versions making the rounds and to be honest I have no idea what the final engine was. I recall hearing the whole deal ended up at Roush, production management and all.

[Canuck]

AFAIK Roush was responsible for the head design, Thunderheart out of TN had a hand in it - have heard several folks like yourself say they were involved at one time or another. Performance Assembly Solutions did the final assembly. United Engine supplied pistons, Jim's USA supplied all sorts of bits, Eagle supplied the Carillo-style rods and somewhere I have name of the folks that did all the castings.

At the end of the day the PP100 is a very poor execution of a good idea. Like this exhaust valve seat -
Notice how the seat protrudes nicely into the combustion chamber? This is one of the better ones.

The geometry of the engine cases (block) is such that there is plenty of room for a large cylinder bore - easily enough to have a 4.125 and perhaps a 4.25 bore - but they installed the cylinder studs and oil drain back passages too close to the existing bore so we're very limited to how large we can go without serious surgery.

Despite being a blatant copy of every other v-twin in it's basic form, Indian management determined that the oil pump and oil filter locations must be opposite the existing H-D locations so they've put the oil filter directly behind the rear header pipe - fantastic for maintenance.

The crankshaft is the killer though. Again, a direct copy of existing V-Twin design, 5-piece bolt-together (sprocket shaft, pinion shaft, crank pin, 2 flywheels) - simple, tried and true. But not Indian's - we're finding in excess of .018"TIR runout on the pinion shaft with mileage as low as 4500 miles. Theories abound as to the cause - the cast-in insert for the pinion race comes loose and spins, pulling the shaft out of true, the tape between the crank pin and the flywheel is wrong, the flywheel hardness is not to spec, too soft and sliding out of true... I don't have the experience or education to determine the cause of failure (and they do ultimately fail, snapping the pinion shaft right off) so we use a crank from S&S to do the job. So far no failures on the new cranks.

I won't even bother talking about porous cases, the cast-in race that spins, valves that are out of true, guides that are too tight and seats that don't seat.

[Canuck]

Originally posted by McGuire
I would need to know more about the application.

Hot-street application without requiring weekly maintenance. The bike is heavy but we've taken weight out of the drivetrain in the wheels and tires, drive pulley and trans pulley.

If it's simply a question of $ vs. return, you need to keep in mind the market we're in - I build $100,000 motorcycles for these guys. At the end of the day the $ isn't reflected in it's technical or performance prowess but rather it's fit and finish and real-world useability. I have a chassis in my shop now that retails for almost $30,000 - frame, forks and swingarm. It won't handle 10 times better than a $3000 chassis, it's just far sexier.

[McGuire]

Originally posted by Canuck

Hot-street application without requiring weekly maintenance. The bike is heavy but we've taken weight out of the drivetrain in the wheels and tires, drive pulley and trans pulley.
[/IMG]

The OHV twin holds few if any secrets. Some people know what they are doing and some don't, that's all. I would look over the 109" S&S, use that combination as a baseline guide and adapt from there as necessary. You have to get up pretty early in the morning to beat George's boys.

[McGuire]

Originally posted by Canuck
Performance Assembly Solutions did the final assembly.

PAS = Roush.

[McGuire]

Originally posted by Canuck
At the end of the day the PP100 is a very poor execution of a good idea.

Don't even get me started. I got my $$$ so I have no professional grievance but jeezus, what a clusterf**K.

I think I heard about the soft flywheels and the incorrect taper on the crankpin joins. That is just classic. Congratulations to the lowest bidder. I can hear how that meeting went: "Hey boss, should we bid this flywheel job?"

"Sure... what's a flywheel? Can they send us a sample?"

[McGuire]

Originally posted by Canuck
somewhere I have name of the folks that did all the castings.

I'm thinking that would be a long-distance call.

Alll this said, I don't believe the Powerplus is an inherently bad engine. As you say, the execution got totally screwed up... and you can see how that can easily happen given the resources and lead time. Besides: it's a V-twin, how screwed up can it be? If a shovelhead can be made into something decent, anything can.

[Canuck]

I don't know much about Roush, but I wouldn't be bragging about PAS if I were them. Early recalls on the PP100 included missing pin clips and a host of other assembly-related stuff.

The folks at S&S are indeed on the money. The biggest difference between what they offer off the shelf and what we're building is cost. They have to build an engine that's price-competitive on the market where-as I have the freedom to pursue those smaller gains at greater expense. At the end of the day I don't expect to extract a ton more power than anyone else, we're just trying to make it a little more lively.

S&S doesn't always have the answer though - ol' Bobby Wood makes some mean camshafts. In real-world testing the cam swap between equivalent S&S/Wood cams made a tremendous difference. 'Course, Bob's cams are little harder on the valvetrain with their almost-square lobe design.

What was your input on the PP100?

[Canuck]

I was thinking of Uniboring in Howell, but they did the machining of the castings, not the castings themselves.

[McGuire]

PAS is billed as a joint venture of Roush Industries and Uniboring. Builds a lot of the crate engines in the GM performance catalog and for the other OEMs as well. Seems to have a pretty decent reputation with that stuff.

I can't pass any judgement on this deal as I have no idea what kind of cost basis PAS had to work with or who was calling the shots. For all I know they were only operating a line for them.

[McGuire]

Originally posted by Canuck
What was your input on the PP100?

None, I am pretty sure.

But my area is dyno work with specialized instrumentation, stuff like that. Program auditing, blah blah blah.

[McGuire]

Originally posted by Canuck



The folks at S&S are indeed on the money. The biggest difference between what they offer off the shelf and what we're building is cost. They have to build an engine that's price-competitive on the market where-as I have the freedom to pursue those smaller gains at greater expense. At the end of the day I don't expect to extract a ton more power than anyone else, we're just trying to make it a little more lively.

S&S doesn't always have the answer though - ol' Bobby Wood makes some mean camshafts. In real-world testing the cam swap between equivalent S&S/Wood cams made a tremendous difference. 'Course, Bob's cams are little harder on the valvetrain with their almost-square lobe design.

Exactly right. The other thing is S&S builds to a very wide market so they build somewhat conservative combinations with some margin in them. When they ship an engine they have no idea where it will end up or who will be running it in what.

[McGuire]

If I had some extra budget to work with, I might be looking into coatings and finishes. I have to think there would be special benefits on air-cooled engines with various marginal properties.

[Canuck]

I'd talked to Perfect Bore some time ago about working with the PP (not my PP mind you). They felt they had some power to bring to the table but we never went much further. JE is building our pistons for us and they'll apply a fairly standard MTE (MTB?) coating to the skirts. A local outfit can apply a similar coating to the cam and lifters, crankcase and heads but no one there really seems to know much about it beyond sales-flyer knowledge. I've not found anyone that can answer many questions about the benefits of various coatings - I don't even know what's available out there.

And what of the whole cryogenics thing?

[desmo]

I think we've avoided the cryo-treatment controversy thus far here...

[McGuire]

Originally posted by Canuck
The folks at S&S are indeed on the money. The biggest difference between what they offer off the shelf and what we're building is cost. They have to build an engine that's price-competitive on the market where-as I have the freedom to pursue those smaller gains at greater expense. At the end of the day I don't expect to extract a ton more power than anyone else, we're just trying to make it a little more lively.

So for example, you have the freedom and budget to put together things like specialized cam & induction combinations with specific customers in mind. Sounds good.

[McGuire]

Originally posted by desmo
I think we've avoided the cryo-treatment controversy thus far here...

Then someone throw down and let's get started. I don't even know what I think about it so I will just take the opposite side. That's what we're here for...to answer the tough questions.

[J. Edlund]

Cryotreatment is mostly used on steel in addition to the heat treatment where it on certain steels can improve the transition between phases and also reduce the stress within the material. Advantages are very dependant on the material, not only the type but it also must be defect free or the result can even be worse.

Mahle has a piston coating called grafal (graphite) and of course the well known nikasil for liners. Nikasil is a metal matrix composite and there are other similar coatings.
Top Fuel engines use a mix of hard anodization and a PTFE coating on the pistons, just like graphite PTFE it's a solid lubricant.
Much of the developement of coatings are however focused on diamond like coatings and ceramics such as aluminum oxide, titanium nitride and so on.

[Canuck]

And what then of dimpling piston tops, combustion chambers and intake ports?

I'd love to use Mahle pistons - don't think anyone else has a better understanding of pistons for air-cooled engines. Sadly they aren't making anything for us at this point.

Originally posted by McGuireSo for example, you have the freedom and budget to put together things like specialized cam & induction combinations with specific customers in mind. Sounds good.

Exactly. If we have a guy pulling a sidecar, we can tailor the engine to his needs instead of building him the same combination we put in a rigid frame/aluminium bodied street-racer.

This new-found knowledge that stroke has little relation to torque answers lots of questions about why the ultra-rare S&S produced 92" Indian engine with a 3-7/8" square design produces so much more torque than the previous 88" 4-1/4" stroke model.

[Greg Locock]

Hmm, if we are doing this for bragging rights, why not fit custom variable length trumpets?

What a hoot! (Hahaha)

[Canuck]

I'm glad someone brought that up I've been wondering (and yet somehow afraid to further expose my ignorance - go figure) if it's feasible. Considering these are typically carb and not EFI, to make a variable tract effective do you need to change the carb position relative to the valve or can you utilize a variable-length tract on the outside of the carb?

[desmo]

I think the difficulty would be managable... the control input can be a direct function of rpm albeit it probably will need to cycle up and down two or three times depending on the rpm range and the mechanical implementation looks pretty prosaic on the one's I've fiddled with. I found it exceedingly strange that they were disallowed in F1 when the V-8s come in, seems a really trivial expense on an F1 car. I assume it'd be easiest to use a fixed carb and just vary the trumpet lengths. And yes, I'd think it'd work just as well on a carburated engine as an injected one. Why wouldn't it?

[Canuck]

I must be losing my touch - I should know better. I think from now on I'll write my post in a text editor then let it sit for a day or two - probably make less of a fool of myself. I understand wave timing just fine - messed with the Buell's ugly breadbox for days trying to make something just as functional but a little more pleasing to look at.

This god-forsaken foot-in-mouth will be my downfall.