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HP versus Torque

2K views 13 replies 7 participants last post by  Hippie 
#1 ·
Can someone give some advise here. I've completed a configuration of a motor rebuild. 360 Magnum motor. Moving to a 4.00" lift crank and various other modifications, new heads, pistons and alike and the numbers I've come up with deliver a rebuild of this 360 to:

402 ci.
4.00 in. stroke
375 hp @ 4500 rpm
503 fpt @ 2500 rpm

My concern is the torque. Is the unrealistic to expect? What kind of motor stress issues should I be concerned with.

Should I be cocerned at all?

Magnum PI
 
#3 ·
Based purely on what I have seen from others builds, the torque figure seems a little optimistic.

Compare those numbers to these dyno numbers that I pulled off the web for the MP 402 crate motor:

RPM - Torque numbers
3100 - 421.7
3500 - 412.5
4000 - 430.5
4500 - 451.9
5000 - 430.5
5500 - 400.0
6000 - 361.9

For Horsepower
3100 - 251.9
3500 - 274.8
4000 - 327.9
4500 - 387.2
5000 - 409.8
5500 - 419.4
6000 - 413.4

ASSuming you can manage 375 hp at 4500, that would put the torque at 4500 at 437 lb-ft. My unscientific guess is that it would be more likely for torque to peak somewhere in the 440-450 lb-ft range.

YMMV
 
#5 ·
brainsboy said:
Well you didnt give alot of information but that seems like alot of torque for such a low rpm. Maybe some other people can comment but if your only making 375hp at 4500, I would bet your would be closer to 400tq.
"Only" making 375 HP at 4500?! Below 5,252 RPM TQ is ALWAYS higher than HP, they are equal @ 5252 and above 5252 HP is ALWAYS higher. To make 375 HP at 4500 he would still have to be making 437 LbFt. With the right combination it is entirely possible to make 500+ LbFt @ 2500 and 437 at 4500 on a Dyno especially with a 4 inch stroke. And you can't just look at peak numbers you have to look at the total curve, I bet from an idle to 3500/4000 the TQ curve is more of a slight "bow" than a curve. Look at the Buick, Olds, Pontiac and Cadillac motors of the late 60's. Rated around 375 to 390 HP at about 4500 RPM and a Peak TQ of 500+ down around 3000 - 3500. Granted those were "net" numbers but those were bone stock land yacht motors built to haul Grandma and Grandpa to Florida for the Winter. I would be willing to bet by 5,000 it is all done and both HP and TQ have fallen off sharply but from an idle to 4500 YeeHaw! Need any stumps cleared? :thumbup:
 
#6 · (Edited)
Hippi, I think your way off, I'm not trying to get in a pissing match, but even if he was making 437hp @ 4500, I still would have to say I doubt he will be at 500tq at only 2500. None the less the question wasn't "what if", I would have to agree with slowturbo's numbers, they look alot more realistic, given the information he has given us.

As far as what you said about under 5252 torque is higher then Hp this is true, at 2500rpm hes probably only making about 250hp.
 
#7 ·
I'd have to agree that the torque figure is a bit optomistic. According to The General, the 1970 4bbl 454 Chevrolet had gross figures of 380 horsepower at 4500 and about 490 foot-pounds at 2500. While this is very close to the figures quoted, it's also a much bigger engine.

But, really, who cares? Unless you're planning on putting the engine in a tractor, you'll never be running for more than an instant...during launch...at WOT and 2500 rpm anyway.
 
#8 ·
brainsboy said:
Hippi, I think your way off, I'm not trying to get in a pissing match, but even if he was making 437hp @ 4500, I still would have to say I doubt he will be at 500tq at only 2500. None the less the question wasn't "what if", I would have to agree with slowturbo's numbers, they look alot more realistic, given the information he has given us.

As far as what you said about under 5252 torque is higher then Hp this is true, at 2500rpm hes probably only making about 250hp.

I'm not saying one way or the other what his motor IS making only that it is entirely possible to make that kind of torque at 2500 RPM. From the information he's given us I wouldn't even venture a wild guess as to what he's actually making because other than cubes and stroke he hasn't told us squat so in his case the way I see it is that the question is VERY much "What if?" "What if" he's making 500 FtLbs of TQ at 2500 should he be concerned? YES! Concerned for the rest of his drivetrain! ;)

SlowTurbo's combo makes it's peak HP at a higher RPM indicating it's torque peak is also higher in the RPM range and his numbers are pretty representative of many combo's. Good running motor with a strong mid range, not too shabby at all. There is nothing wrong with what you guy's are saying in general except saying that it's "not possible" to make 500 FtLbs at 2500 and 375 HP at 4500 to which I say "HOOEY", it is very possible and people do it all the time but the "HP Worshippers" ignore those builds because of the low peak HP numbers. Just because most people don't build their motors that way doesn't mean it can't be done. There are a lot of people out here that build exactly that type of motor for heavy street cars, trucks, etc. but most people are too hung up on peak HP so that's what you hear about. We're not all drag racers, there are other performance uses for V-8 engines that don't need or even want high RPM engines. With today's camshafts and cylinder heads a 400 CI motor with a 4 inch stroke can most certainly make 500 Ft Lbs of torque at 2500 RPM and 375 HP at 4500 and would probably never see 4800. Is that what's he's building? Who knows? But that's what I have planned for mine, a HUGE torque curve from an idle to 4,000 with peak HP @ about 4800 RPM. I've put a lot of thought and research into my combo and have talked with several people that have built similar combos. Don't say it's not likely because it has already been done but it ain't cheap.

I've seen dyno sheets for a 406 CI small block street motor where the TQ was almost a flat line over 500 FtLbs from 2,500 through 4,000 and then dropped like a stone after 4500. I saw charts for two 383 Chevy engines that had nearly identical HP @ 5000 RPM, one had a torque curve from 2500 to 4,000 that looked like the Himalayan mountain range but the other was down compared to it by over 200 FtLbs of TQ at 2500! Where as the one was all done by 4800 the other was just getting going. Same bore and stroke but otherwise two very different engines with very different power bands and very different intended usage. It's all in the combo and the application. ;)

BillyShope said:
But, really, who cares? Unless you're planning on putting the engine in a tractor, you'll never be running for more than an instant...during launch...at WOT and 2500 rpm anyway.
I care, my old '67 GTO spent 90% of it's time cruising at 2500 RPM and when I mashed the throttle to pass somebody on the highway at just about any speed or RPM I rarely kicked it into passing gear and I never had to wait for the RPM to come up to start accelerating because it had the torque to start pulling immediately and to pull HARD. Same for my 383 Chevelle. On the street 500 FtLbs of torque at 2500 RPM would make a car a WHOLE lot of fun. :thumbup:
 
#9 ·
I have no problems with what you're saying and doing, Hippie. I tend to forget that people build specialty engines for street touring. I always assume competition usage, which is why I made the comment about launch conditions.

Even engineering managers get confused about the proper application of torque and horsepower. Don't know your age, so you might not be aware of this, but, back in the early sixties, Chrysler brought out a long branch ram intake manifold for their V8's. For your application, it would have been ideal. But, in a drag race with a conventional in-line dual quad setup, it didn't fare well. Many of us thought the managers screwed up big time, but, if they were aiming at the market characterized by people like yourself, their decisions were wise. Perhaps the solution would have been to continue to offer the earlier dual quad manifold for those more interested in competitive dragracing. Would have been interesting to know the sales volume for the two variations.
 
#10 · (Edited)
BillyShope said:
I have no problems with what you're saying and doing, Hippie. I tend to forget that people build specialty engines for street touring. I always assume competition usage, which is why I made the comment about launch conditions.

Even engineering managers get confused about the proper application of torque and horsepower. Don't know your age, so you might not be aware of this, but, back in the early sixties, Chrysler brought out a long branch ram intake manifold for their V8's. For your application, it would have been ideal. But, in a drag race with a conventional in-line dual quad setup, it didn't fare well. Many of us thought the managers screwed up big time, but, if they were aiming at the market characterized by people like yourself, their decisions were wise. Perhaps the solution would have been to continue to offer the earlier dual quad manifold for those more interested in competitive dragracing. Would have been interesting to know the sales volume for the two variations.
I guessed that Billy ;) I hope it didn't sound like I was taking offense at your post, I wasn't. Although I was still building AMT 3-in-1 kits and bicycles in the early 60's I do have some knowledge of the Chrysler cross ram wedge motors. From what I remember reading the set up made killer low and mid range torque but killed upper RPM. My auto tech instructor when I was a kid had been a Chrysler dealership mechanic back then and got to work on one of those purchased by a local racer. He told us they had some cool weather start up issues because of the cold fuel mixture and those LONG runners causing the fuel to deposit on the runner floor before it made it to the cylinder heads if I remember correctly.

"Street touring"? Yeah that describes what I'll be doing VERY well. :thumbup: A factory GM TPI set up with it's long smaller diameter runners would be a great setup for my motor and I am building it with the hope of one day swapping my beloved QuadraJet for a well tuned TPI but that's quite a way down the road. In the meantime the Q-Jet and dual plane will have to do the job.

PS: Being a Quality Engineer I have dealt with many a "confused" Engineering Manager! ;) :D
 
#11 ·
Hippie said:
I guessed that Billy ;)

early 60's I do have some knowledge of the Chrysler cross ram wedge motors. From what I remember reading the set up made killer low and mid range torque but killed upper RPM. My auto tech instructor when I was a kid had been a Chrysler dealership mechanic back then and got to work on one of those purchased by a local racer. He told us they had some cool weather start up issues because of the cold fuel mixture and those LONG runners causing the fuel to deposit on the runner floor before it made it to the cylinder heads if I remember correctly.
;) :D
Long Ram Chrysler = My very good friend built one 6 yrs ago for the wow-effect, 440 cubes with the oldest 383-413 long runner cross ram with a 625 Edelbrock out by each fender, 292/509 purple shaft, long tube headers with the 4 into 2 into 1 collector adaptors, 727 trans..... in a 70 Dodge pickup.
Damnest thing we ever saw.... It went past 5500 rpm like it went past 4000 and never quit pulling. We got scared of it above 6000. Not a clue why, but it was a super bad combination. Nothin we found could touch it. Wish I had a picture handy in digital.
 
#12 ·
xntrik said:
Long Ram Chrysler = My very good friend built one 6 yrs ago for the wow-effect, 440 cubes with the oldest 383-413 long runner cross ram with a 625 Edelbrock out by each fender, 292/509 purple shaft, long tube headers with the 4 into 2 into 1 collector adaptors, 727 trans..... in a 70 Dodge pickup.
Damnest thing we ever saw.... It went past 5500 rpm like it went past 4000 and never quit pulling. We got scared of it above 6000. Not a clue why, but it was a super bad combination. Nothin we found could touch it. Wish I had a picture handy in digital.
Maybe the cam was a better match for it than what they had back in the early 60's. Those were wicked looking set ups, that's for sure. :cool:
 
#13 ·
Hippie said:
Maybe the cam was a better match for it than what they had back in the early 60's. Those were wicked looking set ups, that's for sure. :cool:
We were talking yesterday about doing that same engine again...

The original got sabotaged/vandalized and destroyed... BBs down the carburetor........ That plays hell with the piston quench...
 
#14 ·
Hippie said:
A factory GM TPI set up with it's long smaller diameter runners would be a great setup for my motor and I am building it with the hope of one day swapping my beloved QuadraJet for a well tuned TPI but that's quite a way down the road. In the meantime the Q-Jet and dual plane will have to do the job.
Well the road got a lot shorter, I bought a TPI system off an '85 IROC, back to "school" to see if this old dog can learn some new tricks.
 
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