How does cid make power?
- Thread starter 273
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When compairing two motors with simular shaped curves and one is higher at every rpm point it is easier to pick the winner with some certainty. When the shapes are different (flat vs peaky) or peaks occur at different levels (higher and lower) and or at different different rpm points (requiring different gear ratios) it all gets complicated. There are trade off points somewhere along the spectrum of each variable. Often it can be hard to judge where the trade off points are. Ultimately it will be a stopwatch or checkerd flag that decides at a race track. And on the street it's decided by a fun meter attached to the seat of your pants. This might explain why so many street motors appear to not be optimized for the race track, whatever type of race track that might be. For what its worth, I've looked and not been able to find a standarard for calibration of a fun meter.
Rat Bastid
Dunamis Metron
Rat Bastid
Dunamis Metron
I have already said that you need torque AND RPM to make horsepower. In my example we are talking about what happens AFTER peak torque. As long as horsepower is going up, torque doesn’t matter.
Ever seen a dyno curve for a Comp Eliminator or Pro Stock engine? Or even a decent bracket engine?
As for the SS&DI article (best car magazine EVER…too bad Hot Rod bought it and killed it…I’ve never forgiven HR for that shitty deal) if you are UP 15 MPH you have way more HOSEPOWER. You just don’t have it hooked up. MPH is horsepower. ET is hook.
33IMP
Well-Known Member
Per another thread on this forum, if someone asked for a guess on power output, and didn't tell you the cubic inch, but told you everything else.... could you give a decent guess? I couldn't.
(I've got an engine with 11 to 1, ported aluminum heads, 750 holley dp, solid lifter 250° at .050 cam, edelbrock intake, 1 7/8 headers, pulls cleanly to 6500. How much horsepower do I have?)
What's the first question?
(I've got an engine with 11 to 1, ported aluminum heads, 750 holley dp, solid lifter 250° at .050 cam, edelbrock intake, 1 7/8 headers, pulls cleanly to 6500. How much horsepower do I have?)
What's the first question?
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Phreakish
Well-Known Member
Sure it does - stroke isn't the best way to get the CID, it's just the only way left once bore is at max. The engine will still make more power, just not as much more as with bore. An increase in bore size will pay off to a much greater extent since piston area increases with the square of the radius.
Also, the piston speed is higher with a stroker which would suggest the need for an over-capable head. Piston speed obviously has an effect on how fast the engine is trying to move the air through the port and past the valve. Trying to feed a bigger motor from the same tiny ports is always going to pull the peak rpms down. Most folks don't even want to play with offset rockers, so it's no surprise most strokers run out of huff over 5500.
Look at 410 sprint motors - they're running near a 4" stroke, but much larger bores (4.1+). They wind out past 8k and make over 800 hp as a result. The biggest difference between a 4.04x4 408 and that 4.13x3.8 410? The 410 heads flow 400+ cfm. Sure, the smaller bore won't make as much as the bigger, even with those massive heads - but the better heads would damn sure feed the 408 better than any over-the-counter head on the market today.
Sounds like the same issue as above. I suspect Pontiac gets as much love from the aftermarket head guys as MOPARs do.
Only applies when cheap-asses actually invest in good valve train ;) Most guys don't, then whine about underachieving results. Just look how many people shy away from doing any B3 type corrections to their heads - and all the guys who do tend to have better results.
Similar for custom-ground cams. Ramp rates should have some relationship to total lift AND geometry, otherwise losing valve control can happen super early. But that applies to all engines independent of CID. It's just that to get larger strokes to breathe better, it requires more of everything to run 'right'.
33IMP
Well-Known Member
Ten pages trying to convince a member that two plus two equals four......
Problem is that's wasn't question
I stated in the OP i'm not talking about how cid makes torque and torque makes hp
So people been telling me for ten pages a question they think I'm asking.
And it's my fault cause I couldn't come with a clear question cause it's kind of abstract, which I think I figured out and started a new thread.
What I'm trying to get at is the conventional wisdom here is if built same/similar the larger cid gonna always make more peak and under the curve hp and if this true I can't see what stopping the smaller cid spin up to catch up and make similar power since the top end is obviously capable of ir. Everyone says it obvious and been explained to me a million times and I must be really dumb cause I haven't seen it or get it.
33IMP
Well-Known Member
I'll try again.
I'll agree, displacement, ON ITS OWN, doesn't guarantee power. Look at the 1760 cu in four banger that makes 290 hp. But if you FEED the displacement increase, power increases. Rpm has limits as to what displacement it can overcome, and what gearing is required to overcome the bigger motor can become onerous.
If I have a 6500 rpm 632, that makes 900 hp n/a, with a 3.55 gear, how much rpm and gear ratio will your 273 need to have to beat me?
I'll agree, displacement, ON ITS OWN, doesn't guarantee power. Look at the 1760 cu in four banger that makes 290 hp. But if you FEED the displacement increase, power increases. Rpm has limits as to what displacement it can overcome, and what gearing is required to overcome the bigger motor can become onerous.
If I have a 6500 rpm 632, that makes 900 hp n/a, with a 3.55 gear, how much rpm and gear ratio will your 273 need to have to beat me?
If this was the general census they yes no debate needed but it's not.
33IMP
Well-Known Member
The four banger mentioned above was the world's fastest vehicle at one time. (Faster than the then current airspeed record. )
They didn't have the technology at that time to make an engine more powerful by other means, so they made it BIGGER. Displacement, then, was how you made more power.
Post ww1, after technology had made leaps and bounds, a much smaller engine became the land speed record holder..... for about ten minutes. Till a huge, inefficient, airplane engined car cruised past the record, with out having to have huge rpm.
And sometimes conventional wisdom is conventional, because it IS wisdom.
They didn't have the technology at that time to make an engine more powerful by other means, so they made it BIGGER. Displacement, then, was how you made more power.
Post ww1, after technology had made leaps and bounds, a much smaller engine became the land speed record holder..... for about ten minutes. Till a huge, inefficient, airplane engined car cruised past the record, with out having to have huge rpm.
And sometimes conventional wisdom is conventional, because it IS wisdom.
Displacement has lot of advantages and not against idea of started from a larger displacement makes sense especially in a street why car manufacturers generally go that way, I got 360 now thinking about 440 or maybe 400/440 stroker in the future.
But I also like the idea of turning 170, 273 7000+ rpm
After I eat a lot of tacos, the cubic inches of my *** can make lots of power.
Sometimes you follow the herd off a cliff.
I'd definitely build a stock stroke 383/400 over a 408.
33IMP
Well-Known Member
If conventional wisdom led you over a cliff........ it would not be conventional (they'd all be dead) OR wisdom.
Maybe it's conventional until we get to the cliff
I get what yours saying.
Rat Bastid
Dunamis Metron
Again, you ignore architecture.
I could build a 572 that would make the same power and drag that 632 like a little *****.
Rat Bastid
Dunamis Metron
HEY!! I gotta sleep tonight. I don’t need nightmares about your *** and tacos!!! Damn…I can’t stop thinking about it now. How will I sleep??
All I can see is you shitting your brains out like a dude in a truck stop stall in 1989 who got his *** kicked by the Easter bunny.
Oh great. Now I’ll be reliving that real life **** show.
Phreakish
Well-Known Member
15,000 ish rpm's and 8:1 to tie
Then spin the 632 to 15k, now who's winning again? This is why this argument is circular. The 'common wisdom' is correct - bigger wins every time, but you keep throwing imaginary crutches at the 'bigger' motor. Apples to apples, displacement wins. HP is just torque times rpm, and torque is just force at a distance. Increase the force (bore), the distance (throw) and you increase torque. Displacement ups both of those. Whether an engine can continue to make HP above the torque peak all depends on the heads and the valvetrain. Using 'similar' build arguments is meaningless with such a rhetorical question.
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