aTX427

In my experience, it has been fairly constant as I added displacement, race heads, etc., however, when I went from 6L to 7L, my boost dropped because the engine was more efficient. The same will occur with different cams, more efficient exaust and heads. If that Camaro has a super efficent component build, there is no reason, it could not be making 800hp at 8#, but I doubt that is the case if it is just a bolt on system.

PowerLabs

No, your boost dropped because your engine was, well, bigger If your supercharger is pullied to flow 12litres of air per engine revolution, and you have a 6L engine, you'll see 1ATM of boost: 14.7PSI (simplified). If you increase displacement to 7L your boost will drop to 12.6PSI even if nothing else is changed.

Incidentally larger engines are typically less efficient because you have more air space to fill from the same heads; unless head flow is increased, volumetric efficiency decreases. Power still goes up of course, but increasing displacement by 20% would net a power increase of, say 16%, all other things remaining the same.

Spying Beast

I always feel so dumb after reading your posts....

I guess that they're right about Hawaii being in the bottom 10% in education...

I still got that money though!

aTX427

I have done the math and I am certain that my 7L is more efficient than my 6L was; however, you are correct, everything else constant increasing displacement will lower boost because of the additional volume.

To the OP, an engine with a higher VE will make more power per pound of boost than the same engine with a lower VE. PM me if you want a copy of my power to boost calculator, but my engine made roughly 25whp per pound of boost. I would air on the low side (20whp) and hopefully make more with your final results.

PowerLabs

You must have changed heads then: If you kept the same heads you had on the C6, that is highly unlikely...
You can easily visualize why by creating a simple thought experiment: Imagine you had the ability to put those heads on any size engine. Would it make more power if the engine was 8L? 10L? How about 70L: Would it make 10 times more power? Clearly we can only flow so much air thrugh any given head port size so unless the head port and the valve lift area becomes larger as the engine grows, the head will choke the engine and VE will go down (even though power DOES rise; it just doesn't rise in direct proportion to the size increase).

Another very good possibility is that since you have a larger engine, your boost has gone down; with less boost, the supercharger has to work much less to compress air, so parasitic drag from the blower is down (supercharger drive power is an exponential function of boost; even a small blower like mine is dragging over 100HP from the crank to make 15PSI at redline!). In that situation engine efficiency might be lower, but the overall system efficiency is still higher because the supercharger is operating more efficiently.

Sorry I like to rant some times but this is one of those topics that really interests me since my job is in fuel economy research

aTX427

Correct - my heads were upgraded as well. I am running fully ported ET LS7 heads, a DP ported LS7 intake and a custom ground blower cam on my 427 vs. the stock heads, stock cam and stock intake wthat was originally on my LS2.

speedydog5

Wow i wish i understood all the unbelieveable info you guys are giving i just wanted to know the basics like what will i gain by goin down to a 4.0 pulley from a 4.5 i wich i,m totally confused now (sorry ) i just want to get to maybe 7 psi wich i,m told i should be safe with that on a stock motor hoping to get to like 530sh rwhp on a mustang dyno

PowerLabs

Ahhhh... It all makes sense now
Killer setup btw. Your car makes some insane power.

aTX427

Silverboost

You most likely will make a good bit more than 7 pounds of boost with a 4.0 pulley. With my p1sc I make 8 lbs with a 4.25 pulley, kooks, corsa sport and dallas performance air intake. If i were going to guess I would say you would be closer to 9lbs plus. I dont know what you have for injectors or fuel pump but you will need more fuel. My stock pump was only good for 500rwhp

mr. e

My findings from my car

Baseline 377
Post SC 715
PSI 13

715 - 377 = 26 lbs per PSI

speedydog5

that sounds what i might need 4.25 then dont want to over do it , i have 60lb inj and a kb boost a pump what kind of rwhp and tq are you at

NJLS708

If you are making 500 to the wheels and the Cobra is making 560 as you state I think you will walk him as is. If you are going from a dig and you get a good launch he won't catch you. Thats my belief.

AirBusPilot

7% x 377 = 26 hp/lb boost

I guess Gale Banks does know something about forced induction after.

FIREC6

Techco...for what its worth showed dyno charts of 170 with the standard 6.0 kit. the math comes out to 28.3 per lb. That is with a reverse flow (like the ZR1) intercooled twin screw 3.O ltr s/c. The dyno this weekend will tell the story.


Lee

Jonathan Roberts

Just want to point out that the 2007-18 Shelby is just svt Shelby , Not Shelby cobra. The cobra program ended in 2004 ish and came out with the 2007 shebly gt500 . Signature product Carroll Shelby supervised production by SVT through Ford. Cobra is by itself. Predecessor SVT Cobra the successor GT500 or Shelby.