HP Estimate

[91 Droptop]

I bought a 91 Z-28 converible about 12 years ago, it came with a Paxton Novi GSS 3300, I stuck the car in storage after a week and just pulled it out 2 months ago. I am in the midst of finishing up the body, I have the motor on a stand ready to be rebuilt. I am keeping the 305 but am going with Aluminum Heads(190/64CC), 1.6 roller rockers (aluminum) and a custom ground cam, I also have a Holley Stealth-Ram (all vortech) I just rebuild the Paxton and added a new upgraded impeller, I am thinking the motor is going to do 350-370HP, how much will the Paxton add? thanks for any help you guys can provide

[Michael]

Hi there, and welcome to SCH. Sounds like you've got a very nice project in the works.

It's difficult to estimate the horsepower increase you'll see from the GSS as there are a lot of unanswered questions/variables that you yourself probably won't know until the engine is all put together and running right. The biggest question mark has to do with airflow - how much CFM will the engine you're building take in at max RPM? That will be a major determining factor as to how much boost you'll see from the GSS, and ultimately how much power increase you'll get. Of course, how much air the engine will ingest is governed by the intake, the heads (and any porting that may be done), intake valve size, and the cam. And while you could probably calculate - to a fairly accurate degree - what CFM your engine will take in, you won't know for sure until the engine is put together and running.

All Paxton SN superchargers (excluding the VR-4) flow about 750-800 CFM at approximately 40,000 rpm. Over-spinning an SN beyond 40,000 RPM in search of more CFM or boost is not a good idea since you'll be moving away from the impeller/scroll housing design parameters; all you'll be producing is more heat and more wear on the blower's internal ball-drive/components. A stock, healthy 305/350 TPI engine draws about 700-750 CFM, so an SN running at it's intended 40,000 RPM (with the upgraded impeller) will produce about 6psi - 6.5psi of boost; about 5psi - 5.5psi with the standard impeller. That's good for about 350-375hp at the crank.

However, in your case, with the increased intake capabilities of the engine you're building, you'll more than likely not see over 5psi of boost even with the upgraded impeller (assuming you're spinning the supercharger at 40,000 RPM). I can't stress enough that this is just an estimate... exactly how much boost you'll see is tricky to determine without actually bolting everything together and taking a reading. As such, estimating how much power you'll get is just as difficult.

Assuming that this engine you're building produces 350bhp without the supercharger, I would conservatively estimate that you would probably see about 400-425bhp with the GSS. But again, given the number of unknowns/variables here, this is a very loose estimate.

[91 Droptop]

Thank you, I figured about an additional 75 HP; I will know better once I get the motor and trans back in. I plan to take her to be dyno tuned after all is done.

Well no mater what, people will always wonder whats under the hood, especially with the whine of a super charger.

[Michael]

Getting a proper dyno-tune will be critical to ensure the car is running right.

Unfortunately, Paxton SN superchargers are known for their quiet operation (compared to ProCharger and Vortech) due to being ball-drive (internally) instead of gear-drive, so people may not hear it as much. But they do make a nice sound when you get on it. Of course, by then anyone next to you is seeing tail lights long before hearing any hint of the supercharger whine... LOL!!

Good like with the build-up and install; keep us posted on your progress.