Larger throttle body made car feel slower

philstad28

Registered User
Last week I bought a 75 mm tb to replace my stock unit. When I put it on I thought I would feel a big improvement over the stock one. After installation it feels kinda slower :( how would a larger tb make it feel slower? I have a MP plenum too so it should've helped a lot. I guess im just confused lol. Any suggestions would be greatly appreciated :).

Thanks, Phil
 
Is the inlet plenum blended out to the 75mm? Also, improper TB setup would effect the "feel" of the car afterward.
 
Its an MP plenum so its bigger than 75mm. The tps sensor read the proper volts and everything. Its just puzzling I was able to chirp 3rd before I swaped it and now I cant lol
 
Did you confirm full throttle opening?

Did you disconnect the battery to force the computer to relearn inputs?

Was the new tb the only change made?
 
Ill check on full throttle opening. The only change I made was the throttle body. I reset the computer yesterday to see if it helped so I guess im waiting for it to relearn itself. I don't think its running lean I still have a stock sc pulley on it and everything. I might throw the stock one back on and do a little comparison test to see if im crazy or not :rolleyes: lol
 
Mine would feel quicker with the smaller TB but the dragstrip told me otherwise. You might lose a little bottom end torque but it should run quicker at higher RPMs. Definitely make sure the throttle plate is opening up completely.
 
Ok it felt like it lost bottom end a decent amount and idk about top end I only ran the stock tb on the new blower setup for a few days before I put the larger tb on. I just know it cant chirp 3rd anymore :(
 
If you are still using the stock MAF the bigger TB isn't going to do much. You need a 76mm MAF and a 3" cold air pipe.

David
 
How much of an improvement would get from going from my 70 to a 75mm maf? Is it worth the extra money?

I don't know, but I can tell you this much...the stock MAF is a restriction and you aren't getting the full benefit of your 75mm TB, MP inlet plenum or the MPII supercharger. Try finding a 76mm C&L and the correct sample tube. I would also hold off on doing the additional 5% overdrive until after increasing the MAF size.

David
 
Well yesterday tom offered to sell me his 76mm maf with sampling tube so I guess I better jump on it then. I just didn't know if it was worth the money or not but its looking like it is. Do the larger mafs still fit with stock intake tubes?
 
You have to think about your intake as a system, not a bunch of pieces that do individual things. If you widen one part, all of the other parts now need to be just as wide, or the air will not flow smoothly from start to finish. At least you have the MP plenum on there, whereas the stock plenum is usually the narrowest part after everything before gets upgraded.
 
Yeah I know the 70 is kinda a bottleneck. I think im going to get the 76mm maf and a cai and see how it helps my car out. Im going to check my throttle opening all the way tomorrow when I put my new 5% pulley on
 
Hows about putting a vacuum gauge on the intake side of the plenum and watch the gauge as you go WOT. It might help with visualizing how much of a priority a larger maf would be. Are you able to monitor afr in any way on your car? Do you have a wideband hooked up? Im not sure how accurate a stock boost gauge is, but you could just disconnect the stock boost gauge vacuum line from the fuel pressure regulator T and hook it to one of the nipples on the mp plenum. Block off the open port that the boost gauge line was originally hooked up to of course.
 
I don't have a wideband yet even though I should probably start investing in things like that. My boost gauge is a little off I think. I bootleg fixed it :rolleyes: but im probably going to get some sort of aftermarket boost gauge. Any suggestions? lol
 
Does the SC's computer re-learn it's throttle and shifting, no matter where the TPS is at? Or does the TPS need to be set to the .99 to 1 volt range? If so, i'm wondering if the TPS is off, or whether some sort of damage happened to it in transfering it over to the new TB.
 
I checked the volts on the tps and it was at .97 which is where a stock one should be at I think. The tps was already on the tb when I bought it :). So was the other sensor I think its the iac or something like that lol I forget :rolleyes:
 
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