Supercharger question, 3.0L vs 3.2L

[CA91NSX]

I had a question related to supercharging. For a normally aspirated engine, power should be roughly proportional to displacement, everything else being equal. A 3.2L engine would therefore be expected to produce about 7% more power than a 3.0L. In a forced induction engine, the power should be roughly proportional to the amount of fuel/air mixture which is forced into it. A supercharger is mechanically driven so the amount of fuel/air mixture is proportional to engine RPM. My question is, it seems like the identical supercharger installed on a 3.0L or 3.2L NSX engine would produce about the same power, not the 7% difference that you would expect from displacement. I realize that the 3.2L would more efficiently handle the increased intake charge, especially at high RPMs, but at lower RPMs it seems like the torque profile would be similar. There is no blow off valve on a supercharger so both engines should be getting the same charge, with the 3.0L seeing slightly higher intake pressure, maybe on the order of 7%.

I checked the FAQ to find a comparison between the 3.0L and 3.2L engines with the same supercharger, everything else being equal, but all I could find were some numbers on the Comptech supercharger:

Manufacturer Claims

Stock NSX : - 235 hp

With Comptech Header/Airbox/Exhaust: - 245-250 hp
With Comptech Header/Airbox/Exhaust/Cams/Heads : - 265-270 hp
With Comptech Header/Airbox/Exhaust/Supercharger: - 300-305 hp
With Comptech Header/Airbox/Exhaust/Supercharger/Cams/Heads: - 315-320 hp

3.2L NSX - (Horsepower at the rear wheel)

Stock: - 250 hp
With Comptech Header/Airbox/Exhaust/Supercharger: - 350-355 hp
With Comptech Header/Airbox/Exhaust/Supercharger/Cams/Heads: - 360-365 hp


These numbers indicate a 15% increase in horsepower for the 3.2L engine over the 3.0L with the same supercharger and everything else being equal. I am trying to find an answer to this dilemma.

 

[Marshall1]

You're on the right track, but there are alot of things at work here other than just displacement. You have different pressure losses through each respective engine -the 3.2 may be see more chamber pressure (power) because less pressure is lost through better heads, cams, intake, etc. A better exhaust side will give less reversion and charge contamination. If all things were exactly equal on the 3.0 vs 3.2 except for displacement, then yes, you would see slightly more pressure on the 3.0 and very similar power (supercharger only, as they are an "open loop" system). Engines, whether NA, turbo or supercharged, are just big air pumps.

This is not to say that the 3.2 is worlds better than the 3.0 as many FI users have gotten similar power from the 3.0. The numbers quoted from Comptech seem a little low for the 3.0 compared to what people are getting.

Superchargers can have blow off valves, FWIW.

 

[donwon]

Also it seems the number for CTSC 3.2 are a bit optimistic. Almost every tuner I spoke with said they USUALLY (not always) run in the 320 range. I have seen some that put out up to 360, some even higher with a standalone or other goodies. I think USUALLY around 320 is what is expected. I am sure I/H/E add to that in some cases as well.

As for everything else being equal, Its pretty hard to get "equal" data as each car has different things, and runs differently. Throw in temp and elevation and you have all kinds of variables. From the dynos I've read , it doesnt seem like the numbers you are comparing were extracted from a "controlled comparison" becasue I have seen both higher and lower numbers for both the 3.0 and 3.2 Too many variables.

 

[donwon]

Man,

I just jinxed myself. I got 330rwhp with a high boost kit I/H/E on the dyno today. Was hoping for more.

 

[NetViper]

Man,

I just jinxed myself. I got 330rwhp with a high boost kit I/H/E on the dyno today. Was hoping for more.

How does it feel though compared to your BBSC?

 

[socalx]

Don,

In my opinion 330 is not acceptable for your car.

i have a 97 with comptech Intake, Headers, exhaust and LOW BOOST and it make 360 rwhp on Autowaves dyno. (the dynoget conservative dyno). this is at sea level and my car has 15K miles on it. shane has told me that the high boost kit would generally add 20 rwhp to my numbers and i have seen dyno numbers at autowave for similar 97 and newer cars and they are in the 340-370 rwhp range with LOW boost I,H,E.

you problem could be as simple as a loose belt for the s/c (mine was loose once and it was costing my 10RWHP and i had no idea it was ever slipping) how did your a/f numbers look? Also what type of dyno was this measured on? What measurement (i know that their are different measure metheds-- some more conservative then others)?

 

[donwon]

Hey now,

Yeah my a/f is crazy rich. I am hitting 9 in some places. I know that eating up my power. I am going to dyno again at a different place today, see if they can get it leaned out.

Heres my dyno from last week.

here

They tried to adjust the FPR setting, but it didnt do anything. I have a more technical approach this time, thanks to some very knowledgable people offering advice. Hope it works out better this time.

 

[s-zero]

Hi guys,
I'm not positive but i think Shad at comptech said that the 3.2L runs the high boost smaller pulley already as compared to the 3.0L low boost kit. There is no high boost kit available for the 3.2L as far as i know.

 

[donwon]

Uhhh...

Theres a 3.8 and 3.6 pulley.

Standard boost kit comes with 3.8 on 3.2

 

[s-zero]

Sorry guys, when i talked to comptech i thought he said that the 3.0L had a standard pulley and a smaller high boost pulley and that the 3.2L came with the smaller pulley already and that you shouldnt spin the charger any faster. I must have gotten confused or something. Just trying to pass on some info, good luck boys.