How come the turbo makes more torque than s/c'er

[flosho]

How come Toolman's car makes soo much more torque than most of the supercharged SHOs? I remember reading the reason somewhere but can't find it after searching.

Also is it true that a turbo running at.. 15psi will make the same amount of power as a s/cer running at 15psi? Sorry if that is common sense just makin sure.

 

[AutoSHO]

The turbo makes more torque because unlike a centrifugal supercharger, it develops full boost early in the powerband, and holds it until close to redline. A centrifugal supercharger builds boost linearly to redline (i.e. 3 psi at 4000, 6 psi at 5000, 9 psi at 6000, 12 psi at 7000, etc...).

A turbo running at 15 psi will make more HP than a supercharger running at 15 psi given that they both have the same adiabatic efficiency (heat) and that they are both being run at the same RPMs. The turbo does not cause much parasitic drag to the engine in order to produce power, whereas a supercharger takes power to spin.

 

[flosho]

Thank you!

 

[SHOguy 92]

AT full boost lets say 15PSI a turbo should make more hp, but probably not tons more. Turbo's run off the exhaust while a sc is another accesory that needs to be spun therefore it isn't as efficent.

 

[Toolman]

Here you go :

The first two are Pat McGrath's righteous 91 Vortech'd car.

The third is my last dyno with the SHO.

Pat can fill us in on the specifics, but I believe he was @ 12psi on the first one, and @ 15psi on the 2nd, with race gas. All this on a stock compression 3.0, right Pat?

Mine was @ about 13psi on pump gas on a lowered CR 3.2. Keep in mind my added displacement will complement my TQ numbers, and Pat's higher compression will help his HP numbers accordingly.

Here is how I read the charts.

1) Peaks - 385hp @ 7000rpm - 308ft lbs @ 6000rpm
Torque curve - over 275ft lbs from 4700-7200rpm
@3500rpm - 160hp, 230ft lbs
@4000rpm - 180hp, 240ft lbs
@4500rpm - 225hp, 265ft lbs
@5000rpm - 275hp, 287ft lbs
@5500rpm - 310hp, 300ft lbs
@6000rpm - 350hp, 308ft lbs
@6500rpm - 370hp, 295ft lbs
@7000rpm - 385hp, 285ft lbs

2) Peaks - 445hp @ 7450rpm - 325ft lbs @ 6250rpm
Torque curve - over 275ft lbs from 4700-7400rpm
@3500rpm - 155hp, 225ft lbs
@4000rpm - 180hp, 240ft lbs
@4500rpm - 215hp, 265ft lbs
@5000rpm - 260hp, 285ft lbs
@5500rpm - 310hp, 305ft lbs
@6000rpm - 360hp, 320ft lbs
@6500rpm - 400hp, 325ft lbs
@7000rpm - 435hp, 320ft lbs 445hp @ 7450rpm

3) Peaks - 430hp @ 5900rpm - 412ft lbs @ 4850rpm
Torque curve - over 350ft lbs from 4150-6300rpm - over 310ft lbs from 3900-6800rpm
@3500rpm - 155hp, 230ft lbs
@4000rpm - 240hp, 320ft lbs
@4500rpm - 340hp, 400ft lbs 412ft lb peak @ 3850rpm
@5000rpm - 380hp, 405ft lbs
@5500rpm - 400hp, 380ft lbs 430hp peak @ 5900rpm
@6000rpm - 420hp, 370ft lbs
@6500rpm - 405hp, 325ft lbs
@6800rpm - 405hp, 310ft lbs

 

[Toolman]

So while at the lower RPM's we are very close in power, HP and TQ wise. Very quickly though, literally as soon as the turbo starts making boost, my numbers start climbing VERY quickly. See below:

Net gain from 3500-4500rpm: SC - 60hp, 35ft lbs; Turbo - 185hp, 170ft lbs

Looks like the turbo is running and hiding, but pay attention. My boost has now leveled out, whereas the SC is just starting it's vicious climb.

Net gain from 4500-5500rpm: SC - 95hp, 40ft lbs; Turbo - 60hp, -20ft lbs!

Now I am close to flowing as much as I can comfortably can with the stock heads and cams. More boost is not going to do much good, except raise my intake temps and increase the chance of detonation. I hit my peak before 6000rpm, and things start going downhill after my 30hp gain. I am getting choked off. Again, the SC is just beginning to REALLY come alive.

Net gain from 5500-6500rpm: SC - 125hp, 20ft lbs; Turbo - 5hp, -55ft lbs!

This is why I feel my torque advantage is not really doing me much good against the big dog SC guys like Pat and Tony and Mike. While making LOTS more torque down low, in the meat of the power range they are making as much and many times more HP. The only time my torque will really help me is if we did a 4th gear run starting @ 3500 rpm or so. Then I would probably run and hide. That and maybe if we strang out 5th gear, since you would spend more time at lower rpms, but those speeds would be ludicrous.

Wildly different curves, but very close results (as far as straight line roll-on accleration goes). On a road course, my gear selection would not be as critical, since I am making a lot of power down low, and an advantage may present itself, but in straight line acceleration, where you can stay in the SC's sweet spot, I really don't have an edge. Now, slap some cams in some massaged heads, along with tuning and upping the boost, then things might start looking a little different

 

[SinisterSHO]

Net gain from 3500-4500rpm:SC - 60hp, 35ft lbs; Turbo - 185hp, 170ft lbs

Net gain from 4500-5500rpm: SC - 95hp, 40ft lbs; Turbo - 60hp, -20 ft lbs!

Net gain from 5500-6500rpm: SC - 125hp, 20ft lbs; Turbo - 5hp, -55ft lbs!

On those second two from 4500-5500, and 5500-6500 are they listed as a loss in the torque?

 

[Toolman]

On those second two from 4500-5500, and 5500-6500 are they listed as a loss in the torque?

Yes, my torque peaks below 5000rpm. I still gain from 4500-5000rpm, but I am at 380ft lbs @ 5500rpm, 20ft lbs less than @ 4500rpm. So while I am losing tq, the SC'd SHO's are still building. So while the SC'd SHO actually has a flatter curve, I am still making more torque from 3500rpm all the way to 6500rpm. It is just that I peak 1400rpm sooner and 87ft lbs higher. So even though I am losing torque as the revs climb, I am not making less torque until after 6500rpm. I shift sooner and rev the engine lower than the SC'd guys, but it is okay since I have plenty of torque to spare at the lower rpms.

 

[PanamaPat]

The turbo makes more torque because unlike a centrifugal supercharger, it develops full boost early in the powerband, and holds it until close to redline. A centrifugal supercharger builds boost linearly to redline (i.e. 3 psi at 4000, 6 psi at 5000, 9 psi at 6000, 12 psi at 7000, etc...).

A turbo running at 15 psi will make more HP than a supercharger running at 15 psi given that they both have the same adiabatic efficiency (heat) and that they are both being run at the same RPMs. The turbo does not cause much parasitic drag to the engine in order to produce power, whereas a supercharger takes power to spin.

Bingo, the boost down at low RPM's makes a big difference. Plus a supercharger can consume around 30 HP in parasitic losses. Also, I think a Turbo will out pull a centrifugal supercharger because the average HP over the RPM range is greater on a Turbo than on a centrifugal supercharger. Peak HP does not make for a faster car - average useful HP I think is the key.

 

[PanamaPat]

Pat can fill us in on the specifics, but I believe he was @ 12psi on the first one, and @ 15psi on the 2nd, with race gas. All this on a stock compression 3.0, right Pat?

Mostly right. The first curve was also with 36# injectors, whereas the second is with 47# injectors and a gatorback belt tightened up real good. Stock compression.

 

[Toolman]

Off topic, but who built your coilovers Pat? I WANT!!

 

[Oz]

Interesting comparison.

I read Pats torque curve according to the HP scale by mistake, and was thinking "What the ****?"

Lol.

 

[PanamaPat]

Off topic, but who built your coilovers Pat? I WANT!!

My set came from Gary Morrell who put together a limited set of these beauties thru SHOnut, and they are all gone at this point. The real value is in the upper mounts (strut plates and spherical bearings), which are custom machined from billet aluminum. I'd contact him directly by email if you want more details.