stoker motor/ hp loss

[dave571]

I thought some of you may find this interesting.

I was playing with my desktop dyno simulation. I still don't know if I put any weight in it, but I found this very interesting.

First I put the specs for my 400 in and got around 400hp

Then I made some changes to the simulation, to make it a 451. Roughly the same accesories. It made about 450 horsepower, with a fairly big improvement in low end torque(about 70 lbs initialy with the same peak torque). All around the same rpm band.

Then I made one change. I made the stroke 4.15 inches. There was an improvement in torque(475 to 525) but a DROP of about 15 to 20 horse power at 5200.

Yes a drop in horse power.

There was a similar thread on this subject before, where real examples of slower et's were achieved with race stroker motors. I think the thread was one of Andy F's.

I was surprised at the least. Just thought I'd pass it on.

[JVMopar]

The longer stroke increases the piston speed. Hence creating more frictional hp losses. So I can believe that it lost some HP because there is quite a big difference in the piston speeds.

The average piston speed of a 451 (3.75" stroke) is 36.9 miles per hour @ 5200 rpm.

The average piston speed of a 4.15" stroke engine is 40.87 mph @5200 rpm.

[FearThe4Doors]

wow.. i never thought of that. What about all the strokers, namely SB ones, that have increased performance? Just because of the more torque?

[JVMopar]

The bore does effect the friction some but not nearly as much as the stroke increase. The calculation is really easy to find the average piston speed.

((stroke x rpm)/6) x (60/5280) = average piston speed in MPH

The reason strokers usually increase HP is because of the cubic inch increase. If all you do is increase stroke you are going to reach a point in which friction overcomes the gain.

So how do you regain the HP?? increase the bore. By doing this you increase the force applied on the piston and again increase HP. It's really kinda interesting

[Slingshot383]

You also could play with increasing rod length, and since your building a bigger airpump, you need a cam change to give it a bigger breath.

[Kevin Garceau]

I believe the cam is whats holding it back. Lots more cubes..... needs more air in also. Maybe carb chance, intake, and cam. Its not apples to apples comparison because so many factors involved.

[b-1ken]

You didn't say what heads you had. If the engine gets too big for the heads, then you won't gain power.

[dave571]

Modifications to valve size and air flow file, make virtually no difference to the output (on the simultaion of both motors)

Perhaps cam would, but I havent tried it yet.

[violent valiant]

Try changing the installed centerline on you similator program 1 degree at a time. I was using one of those programs when I was planning out my 408 s/b.going from 110 degree centerline to a 106 madequite a bit of differnce!!!
I think the more the motor gets over square The less efficient it gets.It is probally caused,like the other guys said,by the fact of more stroke robs more power from the engine

[rumblefish360]

This is what makes these things so much fun.

[dave571]

I guess what I was trying to get at with this thread, is that bigger isn't always better.

People have put a lot of thought into why some engines make more power than others, when there is no obvious reason.
I guess things like piston velocity, are considered when engines are being designed.

There must be a reason why Mopar b/rb never had a stroke longer than 3.75", while other brands did.

B engines are said to be low on torque(3.380 stroke), yet my 400 powered 5500 lb van can keep up with a my dads, 66 charger with a 70 440 magnum. Why?

I'm not really asking why, I'm just saying there's more to it, than bigger is better.

I still plan on putting together a 451 though So don't think I'm bashing stroker engines.

[jelsr]

The old addage "No replacement for displacement" (except for cubic money) will usually hold true, but there are limits. My father explained it like this, "There's a difference between scratching your fanny and tearing it all to pieces".
Seriously though, while 4000 fpm is the figure usually cited as a safe practical limit for piston speed (with good ones) there are engines running over 5000 fpm without turning into a cloud of aluminum and cast iron dust. Extremely lightweight high tech (read that as expensive) parts are required. One of the premier Nascar engine builders was quoted "The complete piston, pin, and rod assy we now use is lighter than than just the piston from a 60's Nascar Hemi". The NHRA Pro Stockers use 500 inchers at over 9000 RPM and generate over 1200 HP with relatively long stroke engines and the IHRA "Mountain Motors" are even worse although the numbers are not that much better considering the 100+ CID advantage.

[violent valiant]

Well all I know is I'm building a 408 stroker small block with aluminum heads.I figure when I'm done I'll have the horsepower and torque of a good Big Block with less weight of a standard small block. Look out mudtwangs and chebbies!!!

[b-1ken]

Those numbers are from a COMPUTER PROGAM. I wouldn't necessarily consider them to be gospel.

[dave571]

Of course it's a simulation.

I found the thread I was thinking of (with the real examples of bigger not better) and bumped it to the top.

"Hemi vs. Hemi......Kinda long......"

Just trying to get some thinking going here.

Not

What the hell do I know anyway? I'm the moron who put a bigblock in a van.

[rumblefish360]

LOL, but your right to bring it up. Computer program or not, you have seen something, and asked about it.
The computer programs are fine to a point. Desk Top Dyno is a cheap and fun thing to mess with.
b-1ken, your on target, no gospel there, just a little something to play with and help people understand what certain changes will do.
Bigger can be better, but only if you know what to do with it.
When the engine becomes huge, the racer is looking at the torque advantage over the HP.
Huge torque all the way down the 1/4 with killer HP to boot.
He doesn't have to spin the engine to 7000.
He'll spin it to 5000 and get there (5000) faster than he would to 7000. Since such is the case, he'll be changing gears faster.
All in theroy.

[darren509]

Loosing a little HP and gaining a heap of torque dosent sound like a bad thing to me, I was under the impression that torque was what moved us down the trac. Im planning on a 408 myself and dont mind the 15-20 loss so long as my motor can hold the torque through the top of the power band.

[rumblefish360]

Better do some heavy planning then.
Longer stroke engines produce more torque, but it falls off faster than a shorter stroke engine.
Your impresion is right, but HP is what gets us moving after the intial off the line grunt is up.

[sanborn]

The horsepower achieved by an engine is determined by the carburator, intake manifold, cylinder heads, camshaft and exhaust system. If you have a specific combination on, say a good, race 360 short block, and take that combination off and install on a good, race 408 short block, your horsepower will be essentially the same on both engines. Horsepower is determined by the breathing ability of an engine.

If you want to go to a 408 engine AND maintain the same HP/Cubic Inch relationship; then you must improve EACH component of the induction system by the same % of the cubic inch increase. Did I lose anybody with that explanation?????? Sure, you can add a larger carb, larger cam, larger exhaust and get part of the increase needed; but, if the heads are maxed out (flow wise) then you won't get an increase in the same %. What I'm telling you is not theory, it's real!

You will get an increase in torque(as Rumblefish said) and torque wins races. But the torque peak is much lower with a larger engine AND falls off much quicker than with a smaller engine.

Parasitic friction losses are real! Let me give a "real life" example. A friend is an oval track racer(Mopar of course). They race in the Nascar late model series. One of the silliest rules is they must use a 350CFM Holley two barrel carb. These things make great restrictor plates. This guy has his own dyno. He prepared three short blocks; a 408, a 360 and a 340. He used the same W2 heads(specified), the same carb(specified), the same exhaust(specified) and the same camshaft on all three short blocks. The 340 made 321HP, the 360 made 314HP and the 408 made 308HP. The only possible reason we can think of is friction loss! ?This one case where torque doesn't win races! The 408 torque peak was at 3800RPM; and they never get the RPM this low during the course of a race. The 360 combination had a torque peak at 4100 but they never get the RPMs below 4500. Guess what? This is one case where bigger isn't better! The 340 wins hands down!!! This is a real life example; different from your situation, but I use it to prove a point.

Hope this helps

[rumblefish360]

The professor has spoken! LOL

Thanks Sanborn. Theres allway an exception to the rule. I was think on one line and you came up with the other.
Circle tracks, road course's and dirt tracks all have a need for a specific combo to have the car perform best.

[djswwg]

The single biggest reason the 340 won the horsepower battle over the 360 and 408 stroker motors in Sanborn's story is almost surely because the rod ratios got worse as the cubes increased. A stock 340 has a beauty rod ratio of 1.84 if memory serves me correctly. I'll bet the 360 and 408's didn't get longer rods to go with the increased stroke. However, correct me if I'm wrong!.......................djs