ali123

I guess a GM programmer made an error :P.

Stunt

Lol, yep just saw that too from the other post made.

So if tq is truly 650, then this thing will be a monster! Actual hp is probably closer to 700, maybe even 728 fully uncorked!

jvp

More so than you realize. These aren't the numbers GM will be discussing next week. Not only did they jump the gun, they got them wrong.

And the numbers we'll hear next week are the same type of, "At least..." numbers we heard when the C7 was released last January. Nothing more concrete will be made public because no testing, validation, and verification have been performed yet.

Anything other than that is pure speculation.

DoctorV8

Makes sense....there's no way the HP peak is below 5252 rpm.

Runge_Kutta

Good job!!

racerns

Not saying the numbers are correct, but just because the peak torque is greater than the peak hp does not mean the HP peak is below 5252 rpm. It just means the peak torque is at a lower rpm and has fallen off at the higher rpm. My old 396 LT4 stroker motor use to be like this with a higher peak torque number than HP but my peak HP was @ ~6000 rpm.

Racer X

Could it be an indicator of boost or electronic power control?

It is an indicator of a peak torque below 5252 and a curve that falls faster than would allow the HP to rise. In other words peak horsepower of 620 could be held flat from 5000-6500. That is what electronic control of all engine parameters allows you to do. This would allow you to have better acceleration performance than a 620 peak would suggest, as acceleration is determined by the area under the power curve, not the peak; in the operating range on a track. 620HP may be all the power they think can be safely covered by the current injector size. Perhaps it has an overboost state (like Porsche on certain models) that would allow say 670 HP for 12 seconds; but not sustained steady state power of more than 620 HP.

It may surprise some of you that GM powertrain engineers are quite clever, and capable of achieving any design criteria, that the best teams in the world could meet.

DoctorV8

Actually, it does. HP= tq X rpm/5252. You can't argue with math.

This is simply not possible with an n/a 396. If your peak HP was at 6000, then your torque is less than your HP. Unless you are measuring TQ in Newton Meters. ;-)


Now Racer X brings up a valid point with the possibility of electronic boost control, but again, on an n/a motor, the math doesn't lie.

jvp

Actually, yes you can Sanjay. Peak torque will be below 5252, but not peak HP. See the current LT1:

455HP @ 6000
460ft-lbs @ 4600

More torque than HP, and the HP peak is over 5252. The torque peak isn't.

ZZMike

All "The Math" states is that torque and HP must be equal at 5252, the formula is not a determination of peak numbers.

In the example below, peak TQ is higher than peak HP, but peak HP is still produced past 5252 RPM.

MudZ06

I love how the guy with the "insider" tips was wrong twice on the numbers.

arcticblast

I could live with that.

DoctorV8

jas, I trust you understand the equation as well as I do, so I'll leave it at that. Obviously it is the shape of the curve that matters most.

We know the LT1 takes full advantage of DI, VVT and high compression to generate a nice fat torque curve, but if you look at any stock C7 dyno curves, and you'll see that peak rwhp is the same or slightly higher than the peak tq in ft lbs. Whether GM chooses to adhere exactly to J1349 or not is really just splitting hairs. A difference of 5 hp or a few hundred RPM is just marketing BS.

Does the NPP exhaust add 5 ft lbs of torque to match the +5 HP in the marketing literature? Should it? Do we care?

We all know the concept: torque falls off faster than RPM rises above 5252 rpm in the LT1, and any other production pushrod motor. If it didn't, we'd have S2000/458 Italia shaped curves.

Now look at the HP vs torque peak of a C6 Z06, where the higher revving LS7 clearly makes more HP than torque both in the brochure and on the dyno. 505/470 at 6300 and 4800, respectively.

The 458 Italia would be a more extreme example, at 560/400 at 9000/6000rpm respectively. On the dyno, it makes 300+ft lbs of torque all the way to 9000 rpm.

In contrast, the base C7's numbers are basically a wash.

Now my point was, we know the LS9, with its TVS blower, makes 638/604 at 6500/3600 rpm. That's a delta of 34 hp with the peak substantially above 5200 rpm. As you recall, GM sandbagged in the initial promotional literature saying "a minimum" or "at least" 620 hp, and ended up adjusting things upwards.

Yes, there is all kinds of trickery the OEMs can throw into the equation to affect the curves, with boost curve/timing/AFR tailoring and variable cam timing, but I would be shocked if the actual numbers are 620/650, since I assume the general shape of the blown LT-whatever will be very similar to the LS9. 650 hp/620 tq sounds more plausible, but if in fact it is 620/650, I have no doubt that they are really limiting the airflow (presumably mostly via boost) on the top end, and we'll see tune only cars mirroring what we've seen in the highly detuned 2013 Shelby GT500.

jvp

The shape matters in driving, but that's not the point of this mini-discussion we're having here.

Look at the C4's LT4 engine as another example:
HP peak: 330 @ 5800RPMs
Tq peak: 340 @ 4500RPMs

Again: The HP peaks higher than 5252, but it's still a lower numeric value than the torque is.

Where the HP peaks with any engine is, of course, a function of how fast the torque falls off after its peak. The C4's LT1 had a HP peak of below 5252; it was 5000 to be exact. That's because the LT1 started gasping for breath pretty badly after it's torque peak of 4000RPMs.

Note they have the same torque peak values of 340ft-lbs. But the LT1's torque peaks way before the LT4's does. As I remember, the LT4's torque curve was truly a table-top flat one up to it's 6300RPM redline.

In summary: a higher torque than HP number doesn't mean anything as far as where the HP peaks. All that matters is how fast the torque falls off past its peak.

DoctorV8

Please refer to my splitting hairs argument on the C7 LT1, and subtract 20 years. ;-) You know that SAEJ1349 wasn't around back then, right? And there's no way Chevy Marketing was gonna have the LT4 outperform the upcoming LS1.....real world dyno data was becoming common by those days. The LS1 was rated at 345/350, and yes, again at a bit more than 5252 rpm, but.....you know my stance on hairs that have been split. Both motors were virtually interchangeable on a chassis dyno, with a slight torque edge going to the LT4, which I think is partially related to early drive by wire/torque management in the LS1. See graph below.




Exactly, but not as badly as an L98, and much more badly (is that a term?) than an LT5, if we are talking Clinton era torquitude.

Not even close. See the attached graph.....if it didn't peter out above 5000, it would have been a 450+ hp motor, and the DOHC LT5 would have been superfluous....even that mighty merc motor fell on its face, all 32 valves and all, above 5500 rpm until I took mine to LPE. ;-)

C'mon man! Both of those sentences are essentially saying the same thing. How fast the torque falls off past its peak is PRECISELY what determines where the HP peak occurs, thereby determining whether the tq or hp number is higher.

If your first sentence were true, there would be no difference between a 245 hp L98, a 300 HP LT1, and a 405 HP LT5. They all make basically the same torque in different RPM ranges.

http://roadstarclinic.com/content/view/104/118/

jvp

I'm well-versed with that graph, since that's my LT4. My friend Dave had a brand new (at the time) '98 C5 and we were interested in comparing the two on the same dyno.

You're saying the same thing I am, and yet coming to a different conclusion because of it. The MATH says nothing about a higher torque than HP number requiring that the HP peak below 5252. Absolutely nothing. At all.

Really. I promise it doesn't. Do all the math you want, you won't be able to prove it. The only thing it says is that they have to be equal at 5252.

DoctorV8

Then you'd surely remember that it certainly didn't have a table top flatness to 6300, right?



This would be true if you use boost, etc to create all kinds of cool spikes and squigglies, but you know as well as I do that na motors generally have smooth curves. They rise and fall at different rates, so they have to intersect.


Wow. I am really surprised at this.

If you agree hp and tq intersect at 5252, one has to be rising, and one has to be falling, or one has to be falling faster than the other......right?

If hp is rising (ie its peak is past 5252), then you have higher HP than tq. If we are talking diesels or L98s, HP peaks before 5252, and therefore it will be lower than the peak torque. If we are talking LT4/LS1/LT1, then the peak is close enough to 5252 to be a wash IMO.

Therefore, if tq is higher than hp, the motor peaked in HP before 5252rpm.

It's really just 7th grade pre-algebra, Jason.

If you decide that adjusting wastegates, bypass valves, or marketing literature makes your point valid, then I guess we'll just agree to disagree.

jedblanks

Not only do they have to be equal at 5252, but they have to INTERSECT at 5252, with one going down and one going up, and that is the ONLY point they can be equal.

HP = Torque x RPM ÷ 5252

zeshawn

I hope I don't sound rude but this doctor dude doesn't know **** about math, kindly explain this DoctorV8, regardless of what GM uses to get this weird *** power curve (assuming its even real for starters) I aknowledge the fact that its not a typical supercharged engine's graph unless they electronically restricted the power up top for some reason.

On the issue of not being able to have more torque below 5252 than HP AFTER 5252, hers a graph, stop arguing please.

racerns

Here is a dyno sheet from a stock LT4 where the peak tq value is greater than the peak hp value and the peak HP occurs well above 5252.


Even with an NA motor it depends on how fast the tq is dropping off after it peaks and when in the rpm band it starts to drop.