I have been working with HK Dyno www.HKMotorsportsDynoShop.com out in Van Nuys California for a few years now. They got a customer in with a TBI Camaro with a ZZ4 355hp 350 crate engine installed. Needless to say it didn’t run well with stock fuel system and chip when it arrived.
First upgraded the fuel pump as that’s mandatory on all decent performing TBI builds. We found some AC Delco 454 injectors brand new and so tried to use that instead of running the 350 injectors at 18psi since we had to change the 305 injectors anyway and well that didn’t work out. Don’t know what the issue with the 454 injectors was but ran terrible. So since we couldn’t return the 454 injectors the 305 injectors were put back in and I shipped them out the 18 psi spring. I had to run the duty cycle on those 305 injectors very high to support this engine and recommend the 350 injectors at 18psi route for a lower duty cycle. Also altered the Y pipe with the flowmaster Y250300 collector that I recommend for anyone merging 2 exhaust pipes into 1. Just great design. Car has a cat back exhaust but still wearing the stock 42mm 450cfm throttle body which definitely has an affect on those power numbers.
Below is our chassis dyno graph at the rear wheels pulled 248hp and 309lbs of torque. Factoring in 20% drivetrain loss for automatic = 310hp and 386lb of torque which is honestly better than expected with a 450cfm throttle body since GM rates that engine 355hp and 405lbs of torque with a 750cfm carburetor and long tube headers which is next to impossible to fit in a Camaro and not have them drag. I estimate with a bored 46mm 600cfm throttle body those numbers should climb about 20rwhp and torque which puts that potential at 335hp and the full 405lbs of torque as that engine really should only need that 600cfm of air flow and I am sure there is 20hp worth of restriction in that exhaust setup as its just VERY hard to have good exhaust in this body Camaro.
I have never really been a fan of the ZZ4 engine because the heads don’t flow as well as the GM vortec heads but with that nice roller cam that engine obviously did quite well. You can see that the air fuel ratio is still a bit lean out there on the top end and really needed those 350 injectors at the 18psi and that should help those numbers too. We may see an update to this project with the larger throttle body and 350 injectors and see if we can’t pull those GM rated numbers out of this engine. Also would like to note that the horsepower number peaked at a low 4900 rpms so that engine feels much stronger than say a LS1 car which has to rev a lot higher to get its horsepower numbers. On the street, very fun car.