Can someone help me out? I have an 88 Fiero GT 5 spd with a TPI/ZZ4/24# injectors and an old worn out IROC 48 mm throttle body. I also have Sanderson headers, 2.5" dia exhaust, crossover, and one in/two out Flowmaster. The car was really strong and I just added a 52 mm BBK throttle body and the performance is terrible. The car runs like it has a restrictor plate and is worse than before. I am returning the BBK and getting my money back. I thought the quality was poor with a rough cast inlet area and it did not perform as advertised. No other changes were made. What happened?

I'm still stuck with the worn out 48 mm and need advice. At a minimum I need to have the 48 mm rebushed because it is so worn out you can move the shaft back and forth, resuting in a bad tip in stumble.

 

I Imagine the horrible performance you describe was a big loss of low end power?

With possible small gains of higher rpm power.


As mentioned many timeson the board, the RamJet 502 Uses a 48mm Throttle body, why would you need one thats bigger than whats on a big block?

 

Did you port the plenum before you added the throttle body?

If not I'd bet this is what caused your loss of power. The walls behind the throttle blades,(and even more when you added the bigger throttle body) will cause alot of turbulance.

You should be able to look through the butterflies when they're opened and not see any restriction . I think this is the reason why most people see little or no gain when they install a throttle body. But regardless, you definately shouldn't see a loss.

As far as the ramjet 502 goes, I've seen 2 barrels and TBI on 454's, but I don't think that means I'd put one on my 355, or for that matter, even a 305.

 

I just ordered a holley 52mm unit. It appears to be much higher quality than the BBK, although it's got issues of it's own (no throttle stop). I didn't get it in yet, but I'll give a full report when I do. TPIS and arizona speed & Marine both sell TBs with a much better reputation (albiet substantially inflated price tag).