'fast-revving' short stroke is BS

[Heavy Z]

For anyone out there who thinks that a 302/327 will wind up faster than a 350/383, read on. The short answer is that they don't. In fact, it's quite the reverse.

 

Let's take 2 engines identical in every regard (cam, heads, etc) except that one is a 327 and the other is a 383. The 383 will make around 70 more torque at 2500 and by 5000 it still makes 30 more torque. In two cars going down the road, at exactly the same rpm(lets say 2500), if both drivers step on it then that 383 will rev 'faster' because it has more torque and will accelerate to redline quicker than a 327, which makes less torque and thus takes more time to wind up to redline.

 

To say 'fast revving' is wrong about a short-stroke engine. What they do have is 'rev potential,' meaning they can safely rev beyond a stroker motor. If you want 'fast-revving,' then a stroker is the way to go. Just my .02 cents.

[dsommer]

OK that makes sense. Now reduce the friction ie roller engine and you would have an even quicker winding engine, just watch the rev limiter!!!

 

ds

[Guest Nic-Rebel450CA]

I thought you said you like your 327 cuz it revs faster?

 

BTW, you cant really make such a comparison like that. You have to take into account a number of other factors. Just because one engine has higher torque and/or HP at peak doesnt mean that it has the same power curve. If you wanted a more accurate comparison you would have to figure out what the average HP is, and that still wouldnt even be a perfectly accurate comparison. You also have to consider that no one is going to have a short-stroke engine geared the same way as a stroker, but, assuming the gearing was the same then yes, the stroker should be able to accellerate faster, assuming that it has a respectable power curve.

[Heavy Z]

Yes I like my 327(that i can hold it at at 5000+ and not sweat it), but I have a 383 in my truck that would run circles around it.

 

I ran two identical engines aside from stroke through DD2000 and came up with my figures. I wanted to keep it simple. If the race was from 5000 rpms to 6000 rpms, then maybe the 327 would have a chance(as rebel 450 pointed out), under street conditions however I stand by my conclusion that a 383 will wind up quicker.

[JMortensen]

I am really curious about this subject. What I wanna know is about rod ratios. If your rod ratio is 1.5, then you are subjecting the pistons to a lot of side load, and your pistons move faster, and they do not stay at TDC as long so aren't able to take advantage of the burn as much. Better rod ratio, say 1.8 means that the pistons move slower (higher redline), you have more leverage on the crank, and less side load on the pistons.

 

How big a difference does that make??? Apparently most don't think that a 383 is a bad idea despite a less desireable rod ratio. Is .2 or .3 difference in the ratio a deal breaker??? Does this only come into play at 5000 rpm and higher?

 

Still confused about rod ratios...

 

Jon

[Guest Nic-Rebel450CA]

If you are trying to say that you are going to swap out your 327 and put a 383 in your Z then I will put my 302 Z up against it...

 

Is there a "money where your mouth is" smiley somewhere?

 

BTW, I am not saying that you are wrong, you are quite correct. I'll just make sure that my car isnt setup with a 302 where a 383 should be.

[SleeperZ]

Thanks HeavyZ for exposing another engine myth. In order to "rev faster" under the same load, you need more torque, hence a stroker will "rev faster". The short stroke will have a higher redline potential, but that doesn't mean it will get there faster, in fact, it will get to the same rpm as the stroker slower.

[grumpyvette]

Just some things to keep in mind, the first one is that if the tires are not spending much of their time spining and the engine is connected to the drivetrain the engine's ability to rev,or build RPM's will be directly related to the amount of distance the car covers and the amount of time it takes to do so, if you're tires are 27 in. height, which is about the largest tire that I can imagine you sticking a modified wheel well. The tire rolls approximately 85 in. per revolution

now that's approximately 185 revolutions and a quarter-mile., if your geared correctly and have the correct cylinder heads,ETC, a 383 will spend most of its time between 5800- 6200 rpm, at 327, and will more than likely be in the 6200-6700 rpm range, but will be geared and this is important it will be geared so that the car covers the same distance but has more power strokes applied during that distance, yet those power strokes have less total torque per strokes but the average torque because of the higher number of power strokes will tend to be slightly higher. But the difference will not be as large and as the you might think, playing with my computer, it would appear you only have about 8% more power strokes in the same distance covered with a smaller engine, but the larger engine in this case at 383, should have approximately 15% more power per stroke, now playing around with different gearing will allow you to keep the difference slightly smaller but no matter how you gear the car, the extra displacement longer stroke and more power per stroke of the larger engine will tend to be more useful. In the slightly higher number of power strokes with less overall torque per stroke.

In short we keep coming back, to the fact, at the larger the engine , in relation to the weight of the car and more horsepower per pound we can apply the more likely we are to have the car that shows exciting performance.

Also keep in mind. The car with an engine like a 406, it as a useful rpm range of 3500 rpm to 6400 rpm is going to make from much nicer car to drive and a 302 and as a useful performance rpm of 4500 rpm 7500 rpm it will also have, far less of a tendency to break or burnout parts simply because stresses cumulative and the higher the RPMs involved the greater the stress. I have built lots of 383 engines and have over 100,000 mi. on them, most of the 302-327 size engines are used to build, have been upgraded to the 383 displacement simply because the owners got tired of watching taillights, those engines all made excellent power, but the power range was slightly narrower and less useful on the street, a something the owners eventually came around to realize. The only reason I don't build almost exclusively 406 displacement engines is that the 400 blocks of far harder to find in good condition, than the much more common 350 blocks which I build 383s from

and yes theres a hell of alot more factors involved and yes thats just a rough over view, and it disreguards many other things

[JMortensen]

So to sum up, I've read many many articles on rod ratio in the past few days, and I've searched this forum as well. It appears that despite the worse rod ratio of a stroker, the limits of rpms seems to be more connected to the oiling capacity than the rod ratio itself. That being said, more displacement gives more power, so the stroker seems to be the best way to go, and using the longest rod available for the stroker motor is a good idea.

 

Anyone think I need a rectal/cranium extraction for saying the above???

 

Jon

[Heavy Z]

Anyone think I need a rectal/cranium extraction for saying the above???

 

I'll support your argument even if you don't go through with the medical procedures.

 

That said, you could do one or the other, I'd recommend both. That way you can tell people you didn't leave anything untried.

[jt1]

The 383 will be quicker if gearing is the same. If gearing is optimized for each engine, then you've got a good race, and the 383 might well lose.

 

If the induction, heads, cam and exhaust are the same, the horse power will be close, but the 302 will make it at a lot higher rpm. Since the 383 has about 27% more displacement, assuming the same volumetric efficency, the 302 will have to turn 27% more rpm than the 383 to make equal horsepower. So if you turn the 383 to 6500, the 302 needs 8250 to move the same amount of air. Not many people want to see that on their tach. Assuming the same VE is a little risky, since a ton of things affect it, but you get the idea about the rpm.

 

The 302 has a big advantage in that it has much less rotating weight, lower bearing speed, better R/S ratio, less piston speed, and less internal friction. IIRC, rotational inertia has some 4th power functions, so a lighter rotating assembly means a lot more power goes to the wheels, not towards accelerating the internal mass of the engine.

 

The 383 wins most races because not many people will turn the 302 enough. But a really buzzin 302 can surprise you.

 

The real downfall of a high rpm 302 is if you plan on turning the bottom end 8500, you damn sure better have a 8500 rpm capable valvetrain, which gets expensive.

 

John

[David K]

For anyone out there who thinks that a 302/327 will wind up faster than a 350/383' date=' read on. The short answer is that they don't. In fact, it's quite the reverse.

 

Let's take 2 engines identical in every regard (cam, heads, etc) except that one is a 327 and the other is a 383. The 383 will make around 70 more torque at 2500 and by 5000 it still makes 30 more torque. In two cars going down the road, at exactly the same rpm(lets say 2500), if both drivers step on it then that 383 will rev 'faster' because it has more torque and will accelerate to redline quicker than a 327, which makes less torque and thus takes more time to wind up to redline.

 

To say 'fast revving' is wrong about a short-stroke engine. What they do have is 'rev potential,' meaning they can safely rev beyond a stroker motor. If you want 'fast-revving,' then a stroker is the way to go. Just my .02 cents. [/quote']

 

Whoa, the term "fast revving" means high revs. It doesnt mean anything about how fast the revs increase.

[SleeperZ]

Whoa' date=' the term "fast revving" means high revs. It doesnt mean anything about how fast the revs increase.[/quote']

 

Not sure if the dictionary has a standard definition. but given the context, YES, it means how fast the revs increase (acceleration, not total velocity).

[Guest Nic-Rebel450CA]

Anyone think I need a rectal/cranium extraction for saying the above???

 

Woah, my phrase made it all the way up to Washington already?

[Heavy Z]

Whoa, the term "fast revving" means high revs. It doesnt mean anything about how fast the revs increase.

 

Exactly my point, David. Some people misunderstand and think the motor actually revs faster. As Sleeper Z pointed out, this is a myth and so I figured I'd mention it out as we've had a few posts lately dealing with this topic.

 

Using terms like 'fast revving' when you really mean 'high revving' is bound to confuse a few along the way. Anyone who speaks english (but has limited engine knowledge) would be easily fooled by this play on words. My point is that if we recognize this play on words for what it is, then we'll be less likely to confuse people into thinking that a short-stroke engine is going to be "fast revving."

[David K]

Sometimes when i read a post, i take it wrong if smilies arent abused to show emotions

[SleeperZ]

Sometimes when i read a post, i take it wrong if smilies arent abused to show emotions

[johnc]

Another meaningless bench racing discussion. There's so much more to how quickly an engine gains rpm then just displacement. These four items have the greatest affect on the "zingability" of an engine:

 

Reciprocating weight

Moment of inertia

Internal friction

Pumping losses

 

Then, putting the engine into a car adds a huge number of other variables like:

 

Gearing

Driveline MOI

Driveline friction

Driveline alignment

Wheel weight and MOI

Tire traction

 

I guess if you use the "everything else being" equal logic crutch, then you could possibly construct a flimsy arguement about how displacement affects how quickly an engine can gain rpm. But why? What's the point?

[SpeedRacer]

I was going to stay out of this one but I can't because johnc is right. First let me say that for the street - torque rules! Why, because driving on the street means stop and go where you need torque, (unless maybe you are lucky enough to live in Nevada).

 

Seriously, you can't use the "everything else being" equal because, when you design a car with a small high revving engine, you design the powertrain differently than when you design a car with a high torque producing engine - so it isn't equal. Yes, if you simply replace the 327 with a 383 then chances are, the 383 will out rev the 327. But.... change the transmission gear ratios and rear axle ratios and you have a different story. Why, because they are used to MULTIPLY torque!!!!!

 

BTW, please don't tell the Formula 1 guys that short stroke engines are not high (or fast) revving!!! 3.0 litre V-10's that generate 900 HP @ 19,200 RPM. Hmmm - why do those guys use 7 speed automatic transmissions?

[SleeperZ]

Maybe it's just coincidence, but it seems most people considering an engine swap trying to choose which displacement to use don't design their drivetrain - they just drop it in and run it. Not saying it's right, but it seems like you can make most things equal, and run it down the strip to see what the differences are.

 

JohnC is right, there are too many differences to account for technically, but the fact you gain more power due to displacement than you lose due to redline loss has got to dominate the more equal all other factors are.