91 Z28, SLP cat-back, Edelbrock base, SLP intake runners, plenum match ported to runners. Would running a holley 58mm throttle body be to much. Well I know its to much but do you think I may lose power and would be better off running the stock TB? A friend of mine gave my the TB so its no like I wasted any money on it, and it sure looks alot better then the stock one.

 

I dont have any facts to base my comments on, but here are my educated guesses. The same thing will probably happen to you as happens to the guys with Vortec 350s that cut the air foil off their throttle blade. Your throttle response may suffer, and you'll get to wide open throttle way sooner. You will actually lose some ability to modulate the throttle. Think of it this way. That big throttle body at 75% open can flow as much or more than the stock TB at 100% open. The engine will be sucking in as much air as it is going to suck when that big TB is not all the way open. It will make the engine more like a light switch on and off. You will notice no gain in power, you will only notice the same power coming earlier in the range of your throttle pedal. Make sense?

 

Thats about what I was thinking. Just for fun I'll run the car at the track(1/4 mile) with the stock TB and with the holley.

 

why not use a 52mm tb?

 

I got the 58mm TB free from a friend.

 

try it and see what happens. Id say its overkill, even for a stock 350. If you feel a difference then stick with it if not maybe you could trade it for a 52 or sell it on ebay or something.

 

Without tuning to compensate for that TB, its likely going to run slower at the track. There was an article in Car Craft with the same sort of swap and the car ran slower and it was a 350.

 

I do have an adjustable fuel pressure regulator. A little extra fuel pressure may help, but would probably need some PROM work to make a difference.

 

With the huge TB, youll see high MAPs at very low throttle openings and the engine will be more difficult to control. You also need to adjust the PE thresholds to come in much earlier with the large TB. Otherwise, youll be in closed loop at 90-100 kPa of MAP. This is especially important with a stick as itll see high load, low RPM operation.

Itll work, but the car wont be as easy to drive as youll pretty much be at WOT by the time the thing is a third of the way open.

 

The 58mm is to big for anything under 400 cubic inches with aftermrket heads and cam in my opinion. The stocker could probably support up to 425HP. Sell the 58mm here and buy the 52mm from Performance products here as well $200.

 

Sounds good, thanks

 

Ok, so I just got around to putting the t.b. on my car, along with a edelbrock base, slp runners, match ported plenum, tpis afpr, and the holley t.b. So now the car pulls hard all the way to like 5700 rpms (feels like it would keep going, but don't want to rev it more then that). But, I have a friend with a CRX that was dead even with my car when it had all the stock stuff on it. So I race him. By the time where at about 90mph He had 2 cars on me.
Now when I raced him I had not set the fuel pressure or the timing because my fuel pressure gauge and timing light where at work when I put the stuff on the car. So today I set the fuel pressure and timing. Fuel pressure was at about 38 psi with the vaccum hose off, set it at 45 psi. Timing was at 2* btdc, set it at 8* btdc. Took the car out and drove it, seems to run better, hard to tell though.

 

In theory you can't over throttle body a fuel injected motor. Like was said above you might have to tune the ecm for it. Also like was said above the throttle response will be quicker or touchier.

Did you port match the plenum to the 58mm throttle body? If you did not it might acually hurt flow.

 

I have a 3.1 V6 and the stock TB is 54mm. The 3400 GM came stock with a 58mm TB, and the newer 3500 comes with a 65mm. My new engine is a 3.4 with 3500 heads, ls6 springs, 1.7 roller tip rockers, cam and a 75mm Northstar TB.

^^ All these are V6 engines .

As long as you tune, the TB should work fine.

EDIT: I agree with 1989GTATransAm about the boring of the plenum to match the TB you are using. Any disruptions of air can cause issues.

 

Could you point me in the direction of the 52 mm TB for $200

 

Yes, the plenum is port matched to the runners and the throttle body.