I recent purchased and installed a GM Performance ZZ4 350 in my 68 Camaro.  It was a turnkey package from a GMPP dealer.  It has a GMPP dual plane aluminum intake and a Holley 750 which were installed by the dealer.  The car has a close ratio 4sp followed by a 10 bolt posi and 373 gears.  The timing and carb seem to be setup correctly, the car runs smooth and there are not any unusual noises.  When you get it on the road, it has little to no pull.  How bad is it - it won't even break the tires loose.  I attached a vacuum gauge to the manifold and in the garage the vac is great.  Under hard acceleration, the vac. goes to zero and stays there until you let off the gas.  Under regular acc. it has some pull, but not anything like it should for a 355hp/400ft.lb engine.  I have also been through the carb and made sure the HEI dist has a constant 12V.  What am I missing?  

A buddy of mine installed the same crate engine in a costomers 1970 camaro and had to change a lot of parts like the intake,cam+lifters,heads to get it to have some good power. The 355hp. crate engine has no were near what they say it has.  

Something's up, because under acceleration you should still have some vacuum.

Before really tinkering with anything, I'd see about taking it to a shop with a chassis dyno and getting the car run, see how much power it has at the rear wheels. Look at the power bands and start diagnosing what could be wrong from there.  

I fully agree that the horsepower ratings are out to lunch. You should still have decent acceleration though. Holley 750 carb is too big for an engine that is 350cid. and making peak power at 5300rpm. Makes for very lazy low to mid rpm mixture velocities. Good reason for having low or no vaccum when the throttle is stabbed. If you can, borrow a 600cfm carb from someone and give it a try. Always carb as small as possible, without running lean in the top end. Also, what is your base ign. timing set at?  JW.  

Yep, gotta agree with that, the carb is probably too big for that displacement and the ZZ4 cam. A 600-650 cfm carb will probably do wonders. I'd also find hte specs on your intake, and tlak ot osmeone like Edelbrock or Holley, the intake could be too big for the motor also.  

i just go a 1991 camaro rs  it has the 5.0 v8 but it has the power to go to point a to point b just like that  

A buddy of mine has the same as the 1 one you have, he put a comp. cams solid roller I think it was 294 duration extrem energy. he runs 7.5 to 7.6 in the 1/8 he has a 750 on that also. they are right I'd check to see why you are loosing vaccum first.  

Wìth God behind you and His arms around you... you can face whatever is ahead of you... may God's loving arms carry you always near His heart. Gud Day!
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charles
Used Cars