Can I run a 75mm TB on a stock plenum?

[astronut1885]

Hey guys. I bought a 75mm BBK TB for my blower setup, and it came in today. Will this thing fit with a factory plenum, or will it cause a problem? I figure rather than having it sit on the shelf, if I can run it, why the heck not... Fill me in.

PS- I didn't buy a plenum because my blower comes integrated into a FRPP intake with it's own plenum molded in.

 

[streethorse]

I can tell you that a 70mm TB will work on the stock plenum. Never tried a 75mm
but it should.

 

[astronut1885]

I get one or two more "yes it will" and you can guess what I'll be up to for a little while

 

[SVT32VDOHC]

It will fit, but you are installing a 75MM throttle body in front of a stock intake hole which is like 55 or 60mm if I remember correctly. The air will be rushing up to that point, then cut off. For a stock plenum to be efficient with that throttle body, I would hone out the inlet of the plenum.

 

[sch382]

I'm pretty sure it will mount up, but like stated before it will not be as efficient unless you bore out the stock plenum to match it. It will have a bottleneck effect.

 

[astronut1885]

Ah. Well, I don't feel the need to get into all that, so on the shelf it goes with the rest of the parts...

 

[astronut1885]

BBK's tech department just sent me a reply to this question that says it can be done without a problem...I mean, the air isn't "rushing" into the throttle body, it's actually being sucked in, so it can't bottleneck in there. Realistically, giving the plenum a bigger area to pull air from (bigger TB) shouldn't hurt anything.

 

[Jbauer]

no- it won't hurt anything....it just won't help anything either

 

[Roos85]

The stock plenum can't handle more than 60mm. Its kinda pointles

 

[CobraRed_96_GT]

The stock plenum can't handle more than 60mm. Its kinda pointles

stock is 65mm, so i'd hope it could

 

[astronut1885]

Sounds like it's not worth the effort at all. Especially since the car is running fine. It's sitting on the shelf now, right next to the blower. I gotta check the plenum opening on that, I hope it's 75mm.

 

[5spd GT]

It will bolt-up, no problems.

 

[SVT32VDOHC]

Boy, do I fell dumb, I thought I was in the 5.0L Tech forum!!!!!! HAHA...I jump so much at work, I didn't even realize I was in the 4.6L Tech!!!

 

[Winters98GT]

I still dont get the craze with bigger tb's.

 

[astronut1885]

Try breathing through a straw, and then through a piece of PVC pipe. You'll get the idea. I'm not trying to be a smartass though. I am adding a supercharger soon, and it's going to want more air in the motor. By increasing my TB and inlet size, I'm giving it as much as I can. You really don't see the benefits until you get to that point with a car. Most guys who are n/a or bolt on aren't getting crap from their TB, it's more of a "I got a bigger on than you" thing.

 

[5spd GT]

I still dont get the craze with bigger tb's.

I agree.

 

[Winters98GT]

Try breathing through a straw, and then through a piece of PVC pipe. You'll get the idea.

thanks for the analogy. Ive pretty much figured out how a throttle body works by now.....

 

[astronut1885]

Then how can you not understand the concept? I'm not saying they're worth getting for a stock or bolt-on car, and the only reason I wanted to know if I could use it without hampering the car was because I have all ready, so why not. It is, however, going to compliment my setup when I add my roots blower with 6 (eventually 9 with meth) pounds of boost, and a 90mm Lightning MAF with my Roush inlet tubing. I just wanted to know if I could bolt it on the car for giggles without harming my current level of performance.

 

[Pearl02]

no- it won't hurt anything....it just won't help anything either

Put it on. It may give some better throttle response. You've already bought it so use it. Pearl02.

 

[CobraRed_96_GT]

Then how can you not understand the concept?

That's because you're analogy is laughable. straw to pvc is assuming the draw at the plenum (lets say even intake manifold) is trying to suck through but it cant cuz of the TB restriction. This just isn't so.
Factor in the limits of 165cfm intake ports, limits of stock intake manifold (and stock plenum if you're only talking TB improvement).
A comparable analogy would be sucking through a 2' straw, then lopping off the last 6 inches and changing it to the PVC. Well you're still suck through the staw - the big part at the end doesn't do much of anything.

Unless you have ported heads, a good intake manifold like a Bullit or P-51, good sized plenum (apart of those two intakes) then the TB size would matter, or if the case is you're blowing in air like in FI.