Low Torque @ High RPM VS High Torque @ Low RPM

[ZDan]

Would be good to see a dyno plot. If the 330 peak is down low enough, he could conceivably pull timing down there and not really hurt performance. But if its in the meat of the powerband, could be a bad move.

[ZDan]

Originally Posted by rice_classic

Take the same car, remove 30 ft/lbs so it's 300/300 and now, according to the rules, it can weigh 3000lbs and should be noticeably quicker because the engine still does the same amount of "work" but now the car weighs 150lbs less.

It can do the same *maximum* rate of work at peak power rpm, but it depends on where the 330 peak is whether you could get away with lopping that 30 lb-ft off the top and not have it hurt performance. Depending on the gear ratios, the engine will have to perform over a ~2500-3000rpm range. If the 330 lb-ft torque peak is in that range, then knocking it down will have a negative effect on performance, which would be partially offset by the weight reduction.

[chrisl]

Originally Posted by Whitigir

There is no argument here. Flat Torque Curve is the perfect one every-body want. Unless you can not have it, then it is depend. Torque is all relative to RPM and gear ratio.....when it is down to that, that is where people differ from each other, and that is why you need a test drive

I'd rather have a flat power curve (which means torque that decays as 1/rpm). That's not very common though...

[Whitigir]

Originally Posted by rice_classic

Second question..

How would you go about getting a turbo engine to reduce torque and increase more HP up top? Change in turbo size, tuning, boost pressure?

To inter change Torque and HP, you have to do it from the sheet metal. It involves a lot of stuff

Compression, displacement, AFR, Cams profiles, Engine RPM.......gear boxes...

take S2000 for example, 2.0, AP1 = 9k RPM engine redline vs 2.4 , AP2 = 8,300 RPM redline, and AP2 have the same HP, just with more Torque

[Whitigir]

Originally Posted by chrisl

I'd rather have a flat power curve (which means torque that decays as 1/rpm). That's not very common though...

Not so much on Petrol engines alone

So far, Flat torque curve can be obtained easier by using Electric motors. Either Full Electric Vehicle, or Hybrid.

[pheoxs]

Having a flat power curve (with torque decaying) isn't fun. As soon as the turbo spools up it feels like it sort of falls flat on its face. Something like this with the Jettas. Typically its a result of a small turbo being pushed beyond its efficiency range and not flowing enough at higher rpms.

[Whitigir]

Originally Posted by pheoxs

Having a flat power curve (with torque decaying) isn't fun. As soon as the turbo spools up it feels like it sort of falls flat on its face. Something like this with the Jettas. Typically its a result of a small turbo being pushed beyond its efficiency range and not flowing enough at higher rpms.

Well....that is BECAUSE TURBO. But basically every manufacturer want to achieve that flat.

[chrisl]

Originally Posted by pheoxs

Having a flat power curve (with torque decaying) isn't fun. As soon as the turbo spools up it feels like it sort of falls flat on its face. Something like this with the Jettas. Typically its a result of a small turbo being pushed beyond its efficiency range and not flowing enough at higher rpms.

A flat power curve will be the fastest though (for a given peak power), since it lets you stay in the powerband more of the time.

[ZDan]

Originally Posted by chrisl

A flat power curve will be the fastest though (for a given peak power), since it lets you stay in the powerband more of the time.

Flat power curve at 300hp will be faster than 300 PEAK hp, yes. But if the power curve is flat over a broad range, it's because torque is falling off rapidly which means you're not breathing well at higher rpm. Open up high-end breathing and you could have a powerband that starts at 300hp and ends up at 330hp, which would of course be faster.

[ZDan]

Originally Posted by rice_classic

Take the same car, remove 30 ft/lbs so it's 300/300 and now, according to the rules, it can weigh 3000lbs and should be noticeably quicker because the engine still does the same amount of "work" but now the car weighs 150lbs less.

If your buddy's power curve looks like this one:

Scaled up to ~330 lb-ft/300hp, I'd say yeah, lop off the top of the torque curve below ~4500rpm by pulling timing or something. Wouldn't hurt track performance much if at all, and he could lose that ballast!

[pheoxs]

Originally Posted by chrisl

A flat power curve will be the fastest though (for a given peak power), since it lets you stay in the powerband more of the time.

This is true for events that limit you to X hp and I full agree. But for street driving, I'd much rather keep torque and gain peak hp.

I'd rather a slightly larger turbo that can pull right to redline than a small turbo that spoolers quicker but starts to struggle beyond 5k

[rice_classic]

I had a conversation with him last night. His TQ peaks at 4.1k and then drops like a typical STI dyno graph. The big clue is that he's boosting up to 21-22 PSI earlier and as the revs climb the boost falls to 16-17 PSI. That would explain it. He could run boost at 17 or 18PSI max and run it all the way through the rev range, as well as playing with timing. Either he removes the weight with this exercise or he stays at his current minimum weight and finds a way to reduce the the TQ spike, broaden the band and bump up the HP by 15WHP and boogy down the straight a little better.

[serialk11r]

Originally Posted by Whitigir

Not so much on Petrol engines alone

So far, Flat torque curve can be obtained easier by using Electric motors. Either Full Electric Vehicle, or Hybrid.

Not so much flat torque curve, power electronics can deliver any amount of power you want to the motor, up to the peak output of the battery if the hardware can handle the current. The mechanical limits of the motor (including thermal), transmission, or tire grip are why you'd limit the torque for most of the rev range. In the case of mild hybrids with smaller motors you'll see that the torque of the electric motor drops off, as the battery/motor controller is delivering about the same power, but rpm is increasing.

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[serialk11r]

Originally Posted by rice_classic

I had a conversation with him last night. His TQ peaks at 4.1k and then drops like a typical STI dyno graph. The big clue is that he's boosting up to 21-22 PSI earlier and as the revs climb the boost falls to 16-17 PSI. That would explain it. He could run boost at 17 or 18PSI max and run it all the way through the rev range, as well as playing with timing. Either he removes the weight with this exercise or he stays at his current minimum weight and finds a way to reduce the the TQ spike, broaden the band and bump up the HP by 15WHP and boogy down the straight a little better.

If possible, the best solution would be a much bigger turbine housing (free flowing) since the early torque peak suggests the turbine is going to be a significant restriction at higher exhaust flow rates. In fact clipping turbines to bypass some exhaust isn't a bad strategy (though the better approach would be a wider diameter turbine with reduced height aka don't increase the inlet area more than you're increasing the outlet area).

With the turbine efficiency at high rpm sorted out better you can cut the boost a little bit and run more efficiently.
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