Ok here's my situation. I was running 14. 8 at 93mph. I added a smog pump elimenator, under drive pulleys, 22lb injectors, a Hypertech thermomaster, adj fuel pressure regulator, 58 mm tb and my best time was a 15.3 at 91. I have a new exhaust leak and my main cat smokes. do you think these 2 things could effect my times by almost a second? if your wondering why I only run a 14.8 it's because I live in Utah and we don't have any air. thanks for any input :cheers:


[Modified by 88421VETTE, 6:21 PM 9/12/2002]

 

Sounds like you may be running too rich with too big of a throttle body for almost no mods.

Sell teh TB, put on a set of 1.6 rockers and new valve springs and you will run MUCH better.

 

Just guessing, but the 58mm TB is hindering you BIGTIME, you are probably running too rich, Your cat might be clogged if it's original, get a better exhaust and fix your leaks, return your CAT clogged mainly..
That CAN cost u a lot right there.

 

Good point.

I was thinking the too rich part was from the bigger injectors and throttle body and boosted fuel pressure ( maybe ), I totally forgot to mention the cat converter will hate you for running too rich, as will the O2 sensor.

 

As stated before the new throttle body is WAY too big! Your setup does not even need a 52mm yet...stick with stock and you will get as much if not more power than a 52mm and much better throttle response. Best of luck! :chevy

 

Swap out the 58mm TB and the Hypertech chip for the stockers and then hit the track again. :yesnod:

 

Like said above. Throttle body is killing you! ditch it!....and give it to me :p:

 

You dont need a bigger TB than stock until you dig into the motor and give it more cubes. And a Hypertech chip is worthless.

Ditch both of them.

 

I think the throttle body needs an explanation. You won't make less power with it, you just won't make any more. As long as your engine is normally aspirated it relys on the amount of air that it can suck in.

Let's just play with some numbers, probably not accurate.

A 58 usually is rated at 1000 cfm. Assume the 48 will support 600 cfm. If your engine at top RPM only demands 600 cfm, adding the 58 will not flow more. It will only flow what the engine sucks in, no more. Now the problem you run into is throttle resolution. If the 48 flows 600 at WOT, the 58 may flow that same 600 at 3/4 throttle. This essentially makes the top quarter of the pedal dead. A lot of people think a 58 helps and they claim they feel it. In fact the useful 3/4 of the pedal will respond with more power than they previously did, but the useful pedal travel is smaller. So 1/2 throttle might feel faster, but it's the equivelent of 3/4 throttle previously. In short it's harder to give it a little air.

So what I'm say is this, don't ditch the 58 if you don't want to. It isn't hurting anything, it's just making your throttle less accurate. As such my guess would be like the others have mentioned, the issue is in the fuel.

 

Check your cat to see if it clogged and adjust your fuel pressure to try and eliminate the overly rich condition that you mention. Scan your O2 sensor while you have your car floored and try and get your 02 voltage between .850 and .900 for max power. Contrary to popular belief, a fuel injected TPI car is not effected by a throttle body that is larger then needed. At full throttle the air limiting pieces of a TPI car are the intake manifold and runners. When you floor the throttle with either the 48 MM stock throttle body or the 58 MM aftermarket throttle body the plenium drops to a near zero vacuum level, the amount of air entering through the throttle body will be virtually the same with either throttle body. Since the TPI system is a dry flow system you do not need air velocity through the throttle body to get good performance. What you need is air velocity in the runners and intake manifold, and you will have very similar air velocities through the runners and intake manifold with either throttle body. The fuel is injected at the entrance to the cylinder heads which is not being to be effected by the throttle body. If you have a very high flowing TPI system some performance can be gained if the throttle body is increased to 58 MM but you will not loss performance on a stock TPI with a large 58 MM throttle body you just won't gain any performance. You may not believe what I have just written, but if you do some research you will find out that John Lingenfelter book on modifying small block chevy's will also support this position. Keep your 58 MM throttle body and look for some other problems.

 

I have to disagree to a point about the 58mm TB not hurting performance on a rather stock L98. The fuel/spark matrices tables have TPS vs MAF/MAP look-ups when at tip-in, off idle and part throttle while in closed loop. The 58mm TB allows a substantial additional flow at throttle tip-in and part-throttle compared with the OEM 48mm unit. This equates to a lower TPS signal, for a given MAF signal level. It also allow a larger inlet charge of air, per a given tip-in enrichment constant, this can make the A/F screwy. This also produces a lower than expected TPS signal compared to the O2’s Voltage/cross-over counts. In open loop this can cause stumbles/hesitation on tip-in, and when in closed loop is causing a lot of extra ECM/PCM state changes, which requires more dynamic control over the spark/fuel control. This increased adaptive spark/fuel control, is just more teeter-totter of under & over shoots of optimal control the ECM/PCM has to perform!

Although at open loop WOT, the ECM/PCM is ignoring a lot of sensors, and relying on look-up tables. So as long as the injector pulse width/flow constant, injector size, fuel PSI is correct per a given rpm, all is well and the A/F is good. It’s all about how much of an error margin of operation you want the ECM/PCM to deal with. The more error, the sloppier the dynamic response gets. Just my 2-cents!
:crazy:NanoBrain:crazy: