bryvelle

i have to agree with colonel. he has shed some light on this. but it also has to do with factory tollerances. not to say anything bad about our ls1 and lt1's out there, but they have a pretty wide tollerance on measurments. the reason that those cars can rev so high is simply because they were built to rev that high with tighter tollerances than the normal engine. the ls1 was designed to make max hp at around the 5600-6000RPM range. so that is the cam that chevy designed for it. now back to the Beemer and the s2000, the car was designed with a high end camthat produces max hp around the 7k-8k rpm range. beacuse anyone that has driven one of those vehicles can vouch that the car has nothing to offer in the low rpm range. that is when the cam is defined as "ineffective" until it gets to the high rpm's. it all has to do with how the designers made the car. honda wanted a high revving sports car. Good for them. Chevy wanted a car that made max torque right off the bat and continued strong through the mid range plain and simple. i hope this helped

Cheatin' Chad

iTrader: (3)

How about add 8 more and see how it works.Wait,that's been done, and the engine continues to rev well. See any: F1 car or the Porsche V-10 race engine of which the Carrera GT's engine is based off of.

Actually the problem with rotating mass and stroke is that it is worse to have a shorter stroke in alot of cases. Such massive acceleration occuring over such a short distance is far worse than the more "gentle" accelerative forces experienced over a longer stroke.

Yes, the stroke of my motorcycle engine is much shorter than that of an LS1.The rods are signifigantly shorter as well. My Honda motorcycle engine has a less favorable rod/stroke ratio than an LS1. Causing them to experience a greater amount of stress (side loading,etc.) under some circumstances. A shorter rod tends to exaggerate the movement of the crankpin at TDC. This causes tremendous stresses when the connecting rod is experienceing it's highest loads.At TDC (and BDC for that matter) the connecting rod has to abruptly stop the piston which is travelling at well over 80 MPH and start it back up to 80+ MPH in less than a few inches.

Anyway, this is totally off point from the original posters question. I'm assuming he is wondering how they can make power at 9k and still idle without the massive lope your average American V-8 would have with a cam intended for that operationg ceiling.


It is my opinion that engines such as those in the Honda S2000 and those found in modern sportbikes have such a wide range of operation is because of serious R&D put into the package at the factory.They are designed and built for HIGH rpm street car operation from the first drawing and will not work worth a damn outside of their normal parameters.You will almost never see an engine of this nature used in a variety of different vehicles. An engine like the LS1 could be used for anything from a tow truck to a sports car.I say there is no magic bullet. Just plain old testing and tuning.

When I tried aftermarket cams in my motorcycle I picked up about 5HP in the top 2kRPM and lost over 15 HP in the lower half of my rev range. Worth it in some cases but to most that would be considered a total failure.

You will almost never see many large gains out (without sacrificing in other areas) of these engines without power adders because they are so well optimized from the factory.

bryvelle

Very Very True!! the reason that a stroker engine makes soooo much torque is because of the extended angle of the rod actually pushing the piston into the side of the the engine bock. which is why most people get a longer stroke crank shaft but a piston that sits lower on the rods, the pin is virtually in the oil ring valley, almost eliminating the piston to wall friction, but keeping the longer stroke hence higher HP and Gobs of torque

Cheatin' Chad

iTrader: (3)

Piston acceleration is what truly limits max RPM potential. Piston acceleration is what causes ring flutter not mean piston speed.

The cause of ring flutter is the quick change from acceleration to deceleration and vice versa. Grab a piece of paper or something thin and light and hold it on both sides,Now move it up and down. See how the material bows toward the bottom when pulled upward and bows upward when pulled down? Now do this more quickly until the gentle bow turns into a chaotic flapping.EVen though the ultimate speed has not changed dramatically flutter has occured. That is what happens to rings. The ultimate speed achieved really has little bearing it is the rate of transition that causes the flutter.

1blkZ

Thanks. That is exactly what im getting at. It seems most people think that I asked "why won't an LS1 rev as high as an S2000"? Thats not it at all, of course a V8 can rev as high as an S2000 with the right parts. My question has nothing to do with what type of parts I need to spin an LS1 that fast, or piston speeds, or any type of durablitily at all.

My questions is simply what is going on with some of these heads and cams that allow them to flow enough air to support 8K-9Krpms yet still pull a nice healthy vacume at idle, run all the accessories, and basically just be totally streetable. I have no desire to spin an Ls1 that high, this is just a theoretical question since ive never seen a V8 that would idle like stock AND pull to 8K. Sorry for the misunderstanding.

And FWIW, I did read a few posts that I feel understood my question and Ive already kind of pieced together my own answer.

1blkZ

Oh wait, the LT-5 would. hmm......... DOHC 4-valve, I think im onto something.

McRat

Well, it's been a few years since I've "pushed the envelope" on rpm. But there is more than just transitional acceleration going on. You can accelerate a piston all you want, and the rings will stay plastered against the trailing lands. As the rings get moving faster in the bore, the friction between the ring and the wall starts to become an issue. There is little gas pressure on the rings on the combustion downstroke. If the sidewall friction exceeds the combustion pressure, the rings will unseat from the forward land and allow gases to pass around the rings. This causes overheating on the skirt, excessive blowby, and loss of power. It can even break the rings.

I shattered a few sets of rings on drag bikes before I realized what I was doing. Even though the motor wanted more RPM, the rings didn't.

But essentially, it's a matter of symantics. Too many R's in a big engine will give you ring problems. Whether you measure it using calculus, or average piston speed, there is a limit.

lsx24

iTrader: (45)

I read in Autoweek a few years ago that the piston speed of the E46 M3 approaches the piston speed of BMW's formula-1 engine. (!) Since then some manufacturers have approached high piston speeds, all up near that value. I have a post somewhere where I calculated a bunch of piston speeds, I'll see if I can find it in that post. The point is that I agree that friction will create some limitations, which might be why ironically a lot of high revvers are at or near the same piston speed regardless of application.

lsx24

iTrader: (45)

82.5 ft/s = Honda S2000 (3.3" @ 9000 rpm)
79.5 ft/s = BMW E46 M3 (3.58" @ 8000 rpm)
77.7 ft/s = Stroked ls1/ls6 (4" @ 7000 rpm)
76.5 ft/s = CobraR 5.4L DOHC (4.17" @ 6600 rpm)
73.4 ft/s = Ferrari 360 Modena (3.11" @ 8500 rpm)
72.2 ft/s = Saleen S7 (4" @ 6500 rpm)
72.2 ft/s = Lamborghini Murcielago (3.42" @ 7600 rpm)
70.4 ft/s = stock ls6/ls1 (3.62" @ 7000 rpm)
69.9 ft/s = Lamborghini Diablo 6.0 (3.31" @ 7600 rpm)
67.3 ft/s = Honda F4i SportBike (1.67" @ 14,500 rpm)
65.8 ft/s = Ferrari Enzo (2.96" @ 8000 rpm)
65.3 ft/s = stock ls6/ls1 (3.62" @ 6500 rpm)
65.0 ft/s = Porsche [996 based] Ruf RGT (3" @ 7800 rpm)

z98

Well its not like they put a truck cam in the newest cars or anything.

Oh wait.

Good info Carvinta.

Gen3Benz

iTrader: (4)

forget 9000 rpm.
what about 19050? that is what the bmw f1 motor spins at
titanium rods, pistons with practically no skirts, and no valve spring just nitrogen gas pushing against the valves.

v10 with a 3 liter displacement.
those are some small pistons.

DANSLS1GTO

That f1 motor also is a 2 liter v10, versus a 5.7 liter v8 - made with the best exotic metals they can find regardless of cost. There is considerably less rotating mass. And they don't want to sit and idle well, they have a computer that pushes the rpm up depending on the situation to keep them from stalling.
Oh, and they run like 500 kilometers for the entire life and are scrapped in most cases.
Dan

Gen3Benz

iTrader: (4)

2 liter? must be a typo they are 3 liter
no they dont idle well and get 1.2 mpg but they kick ***
and take a week to build, cost is 1.2-1.4 million per engine

Cheatin' Chad

iTrader: (3)

3L and they run around 10k during a pit stop. The McLaren Mercedes engines were being scrapped after every race last year. Williams and Ferrari could use an engine for two races with a rebuild in between.

Excal

a stock supra is not really a high revver, a stock s2000 is because it needs to be.

Obviously rotaries don't have many moving parts, so their RPM potential is tremendous too.

Rotating mass, and dohc design. Also cam profile, that's why heads and cam ls1/6 rev to 7000 or whatever.

there's many 4 cyls with ohv cam designs, that don't reach that like the 240sxs of the world. They too have a truck like cam "profile".

Iv_z28

Hm... very interesting comparison.
Basically it tells me that the talk about piston velocity is highly overrated - surely $$$$ short-life ferrari enzo race engine would at least match that of a lowly modena and be closer to the limit otherwise.

ChevyWeatherman

iTrader: (2)

I remember seeing that a Winston Cup engine sees the same piston speeds as an F1 engine, I don't know the numbers though..pretty interesting thread..

Gen3Benz

iTrader: (4)

i wouldnt doubt that. 358 cubes at 8900-9000 rpm....for 3 hours straight.

DriveATransAm

i read a few replies, most said that the lighter weight has a lot to do, which it does. i read somewhere that the forces of the 1800 cc honda bike engine exerts more force at 5K rpms (i think thats the redline) than my 600cc does at 15,000. its not that v8s dont make power that high, its that theres no way to safely (cheaply) spin all that mass that fast. thats 8 pistons that have to accelerate, come to a stop, and then reverse direction. 8 vs 2 or 4 is a big difference, not to mention the distance that it has to travel in the same amount of time. like a small engine thats piston might move a couple inches vs a large engine that has to travel 4 times that or more. of course im sure things like surface area makes a difference and the friction it makes at 5K vs 10K.

i think a good way to think of it is comparing a huge engine, say one with a 10' stroke vs one with a 2" stroke. it kinda makes it easier to think how a huge engine can idle so low (500 rpms) vs a small engine to idle at like 1300. look at the time it would take for that large engine to travel that 20 feet vs the small piston to move 4" (if that makes sense)

im sure most of this is all common sense though so ill stop babling now.

lsx24

iTrader: (45)

Well yea a lot of the theory is known through all spans of racing (Nascar, F1, GT, etc), and it seems to be a combination teeter-totter effect. You can't have too high a piston speed, regardless of weight. And you can't have move a large weight to a point, regardless of piston speed. With this set of rules you can build quite a few different configuration with all the same logic (i.e., itty bitty pistons in f1 v-10s and large slugs in Nascar small blocks). The combination or sweet spot is where they usually end up.