ok im not looking for combinations here. ill worry about that later. im curious to know why so many LT1 owners and builders want the highest horsepower number possible while the torque numbers are not great. im used to old big cube engines where the torque is much more than the horsepower. so seeing the typical LT4 conversion put down 380hp/360tq at the wheels is not bad, but for my car thats a 110hp increase but only 60 ft lbs more. i would think thats since its torque that moves you and its what allows you to light up the tires easily, then thats what you would want to build for.

so why not build an engine that has torque numbers right there with the hp numbers or with more torque than hp. stock LT1s have more torque than hp. yet most people that have 400rwhp or more have torque numbers just at or below the 400 mark. i want my torque numbers right at or more than my hp numbers. so why dont more people pay attention to their torque numbers? thanks. Trey

 

you have to remember that horsepower is a function of torque over time. So generally, the more horsepower you have, the more torque you have thoughout the powerband

edit: I meant more average torque over time

 

So generally, the more horsepower you have, the more torque you have thoughout the powerband.

Horsepower is a function of torque over time (rpm). Even though horsepower may increase, the actual measured torque may not, and wouldn't have to, because of one function, (variable) rpm, being the driving (determinent) force in the power increases, providing the actual torque doesn't nosedive. This is how short stroke high winding imports can generate high power readings without high measured torque readings.

So why don't more people pay attention to their torque numbers?

Good question. Maybe they don't realize the importance of torque.

 

so how does one compensate for this in a stock cube motor?

 

I think you will sacrafice top end for good torque on a stock ci. motor. Because you would have to have a cam with a "low" powerband, which would not spin very high.
-You can't have your cake and eat it too, so to speak.

 

Alot of little things.

-More compression, that always helps everywhere in the TQ curve.

-Better head flow, and more anti-reversion. Those two things will always allow you to gain more TQ in the motor.

-A longer runner intake, longer runners make better TQ down low.

-reduction in friction losses, this is going to happen in a built motor like a 355 more than a "stock" bottom end.

Bret

 

Or you run shorter gears to take advantage of the extended top end torque. The net twisting force at the wheels thanks to the shorter gears can end up being the same as with a stump pulling TQ monster with no top end.

 

Actually, he would run shorter gears to take advantage of the extended top end horsepower NOT torque. The purpose of the gears would be to transfer this horsepower into useable torque.

This is how high reving 'crotch rockets' can make mincemeat outta mega torque harleys. Their lack of stump pulling torque is more than offset with their high revability (and horsepower) being converted into useable torque when combined with steeper gearing. Even if I was dumb enuf to rev my long stroked harley to 7 grand, I couldn't compete with my kid's 900RR.

 

ok. i would like to see an example, more tq than horespower,
not much maybe 10-15+ on the tq side on a stock displacement Lt1 making at least 370 rwhp and keeping LT1 intake

 

if you've got an automatic, put in a torque converter that has a high STR. My stock iron head LT1 with bolt-ons put out 255rwhp and 320rwtq with a vacuume leak. Now with a few more bolt ons and the leak fixed, I'd bet the that number would be 270hp/330tq.

 

It is torque that accelerates a vehicle. If acceleration is what you want, build the engine to produce the most average torque in the rpm band you will use. This is the oft-quoted "area under the torque curve". Peak numbers give you bragging rights, but it's average torque that makes you go.

One of the reasons modified engines have a higher hp than torque "number" is because the peak torque is probably occuring in the high 4000s or low 5000s, rather than high 3000s, and peak hp is @ 6000 or higher. Remember that hp is a derived (or calculated) number from torque and rpm. HP= torque x rpm / 5252. At 5252 rpm, torque and hp numbers are the same. At any point above that the hp number will be larger than the torque number. At 15756 rpm, easily within the hp peak range of an F1 engine, the hp number is 3 times the torque number.

Example: A 383 producing a (rearwheel) peak of 420 lb-ft @ 4800 and 433 hp @ 6000 is still producing 379 lb-ft, or 90% of peak torque @ 6000.

If this engine produced the same 420 lb-ft peak torque at 3800 rpm and the torque fell off at about the same rate, it should have about 355 hp @ 6000 (and only 310 lb-ft @ 6000). If you think the 420/433 engine will accelerate the car faster than the 420/355 engine, you are correct.

The trick, of course is to get the torque to peak in the high 4000s and not fall off a cliff ater that. Head/manifold flow and optimized cam timing can do this.

A really driveable production engine will have 90% or more of it's peak torque from converter stall to shift point. The Vortec 4200 I-6 is just about that. Over 245 ft-lb from 1900-5600 with 275 peak.
The LS6 has about 80% of peak torque from 2000 or so to 6500 or so. It drives like that also.

 

great information guys.

i knew average torque and horsepower is what matters. i was very pleased with the torque curve on my basically stock LT1. thats if you consider a 160 thermo and a KN filter mods. i was hoping and thinking that reproducing this only higher with more power overall would be the best for a car driven on the street mainly. i also dont wont to change my 3.42 gears out back. which means i need a lot of torque that comes on from the beginning and stays there.

360ft lbs is nothing to laugh at, but i was thinking more would be better even if the hp level didnt change much from 380 or even if it didnt change at all. i just wasnt sure.

i guess the old saying still holds true among most people even car people. horsepower sells cars, but torque wins races.

so now the question is, is anybody out there running a modded LT1 that has torque ratings right there with the horsepower ratings or more torque than hp? im talking heads and cam. a stroker should have gobbs of torque.

thanks. Trey

 

TQ is what accelerates the car. HP is calculated from TQ and RPM.

Transferring horsepower into useable tourque? Not sure what that means since HP is already based on TQ.

TA Dreaming: strokers that have gobs of low end TQ are great for the street. Their driveability and throttle response tend to be good since you have power available down low in the RPMs, and this setup usually has a smaller cam that doesn't surge as much or require as much tuning. However to do well at the track you want to make your TQ higher up in the RPMs since you only see 1000-4000 rpm once (in first gear) for 1 or 2 seconds. Therefore I wouldn't say that strokers *should* have gobs of low end TQ when to win races, they would want to extend their TQ as high in the RPMs as possible.

 

very true, but i meant gobs of torque period not just low end. your right if you only have low end power your going to be shifting low in the rpm band, much like stock L98 motors.

i plan to build a motor one day that has very good power though out. more so down low simply becuase it is a street car and i dont rag on my car anyway. as it is now i shift at or below 3k rpm just driving around.

the post in LT1 tech about the 452 rwhp motor got me thinking. id like to actually think about and study what im going to be doing versus just following what everyone else did. not saying that i wont follow in their steps if its the way to go but id like to think about what im putting together.

thats the reason i posted this. i see everyone talking about how much rwhp they have and whats the peak cfm their heads flow. not trying to start a war here, but i believe theres a better way and better characteristics to look at. so i asked about torque versus hp simply cause thats better for me than getting in over my head and asking about flow numbers and characteristics. ill get to that later.

if anyone has anything else to add that might be of use to me or this topic speak up. id like to hear what you have to say. aside from that thanks for all the input everyone.

Trey

oh yea, ill post this in a seperate topic but has anyone tried porting factory ex manifolds? i know doing this with old motors mainly smog motors yeilded pretty good results. what about my manifolds. im sure they flow pretty well as is but can more be gotten out of them?

 

But it is not flywheel torque, it is torque at the rear wheels (or force at the contact patch) - which is a function of flywheel torque * gear multiplication.


Since gear multiplication doesn't have to be fixed you can't say that potential acceleration, etc. varies only with torque. It is like what was pointed out above - you can use gearing to increase your acceleration also.

You can actually make less torque, but if you can produce it at a much faster rate you can take advantage of that through gearing and actually accelerate quicker.





I would submit that this should read "average hp of the RPM range". Yes, HP is a function of torque and RPM (as torque can also be a function of hp and rpm) - but this is only valid for a single "rpm point". When a range is specified you can not use the terms interchangeably.

You could achieve the same average torque with a "curve" that sloped from 450 down to 400 over an rpm range of 1000rpm as with one that sloped from 400 to 450 (up) over the rpm range. If area is the only metric then both of those should be equal. They are not. The second one will allow for the potential for more acceleration since your high torque values will all be delivered at a higher rpm - thus a higher rate. If we use area under the hp curve as the metric then the second instance will be the one that is (correctly) evaluated as superior.


When you want the greatest potential to accelerate average hp is what matters - you can always adjust your gearing to accomidate for it.

On a street car the greatest potential acceleration isn't neccecarily your goal though (stated or unstated). It still isn't neccecarily required to "start building for torque", etc. - you can just as easily specify that you want to build for the greatest horsepower in the range of issue. If you specify a single rpm point the issue between the terms is irrelevant - they are directly related. When you specify a range max torque (avg.) and max hp (avg.) may be different (as pointed out above) - and so will give you slightly different results. The question then comes down to how you define your operating range.

And alot of that is academic - unless you have tons of time, engine dyno, etc. you can't very well try out multiple camshafts, intake manifolds, etc. to try and "optimize" over a range.


Or you could say screw it and just slap some nitrous on there until you are happy


Chris