TB too small? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 13 Old 12-13-2017, 11:03 AM Thread Starter
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TB too small?

for some reason it just randomly occurred to me that i have a 70mm TB on my car which feeds into a CL 75mm plenum. car is an '01 single turbo hellion car on 14#'s. once i upgrade the wg spring i will likely bump it to 16# (still have plastic lower intake). Should i upgrade the TB to a 75mm or maybe swap in the bbk 78mm tb/plenum all-in-one, or is this worth fooling with at all?


'01 Hellion'd single turbo 2v
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post #2 of 13 Old 12-17-2017, 12:00 AM
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I have made 891whp with my 70mm accufab. Upgraded to a twin 57mm and noticed no changed.

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post #3 of 13 Old 12-18-2017, 05:10 PM
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While we don't know dyno numbers, my friends car went [email protected] 3300# with a 75mm TB. I can't say that's holding it back at all either at this point.

While not exactly the same thing, I really don't think it's going to be hurting you all that much if at all.

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post #4 of 13 Old 12-19-2017, 09:30 AM
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Quote:
Originally Posted by slowmod'01 View Post
for some reason it just randomly occurred to me that i have a 70mm TB on my car which feeds into a CL 75mm plenum. car is an '01 single turbo hellion car on 14#'s. once i upgrade the wg spring i will likely bump it to 16# (still have plastic lower intake). Should i upgrade the TB to a 75mm or maybe swap in the bbk 78mm tb/plenum all-in-one, or is this worth fooling with at all?
You can measure pressure drop across, to determine if needed

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #5 of 13 Old 12-19-2017, 09:39 AM Thread Starter
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I came across a return stock 78mm bbk for almost half price. Went ahead and bought it since i can sell my old plenum and tb for close to that anyway. Its on the car now but had to order a different size tclamp as the original 3.5" was too small. I kind of figured it wouldnt make much difference since it is forced induction but wasnt sure. Thanks!

'01 Hellion'd single turbo 2v
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post #6 of 13 Old 12-19-2017, 11:49 AM
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fyi, the throttle body airflow will change with an increase in size

this can affect closed throttle operation, like idle and decel

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #7 of 13 Old 12-21-2017, 08:13 AM
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Unless flow is grossly turbulent, flow through a restriction with a given characteristic media is proportional to pressure delta across that restriction. This works with head ports, exhaust, oil pumps, and everything else including your throttle body.

If the throttle body is flowing enough for NA on that engine and you increase boost, the flow will go right up with boost. If you go from a N/A pressure drop of 14.7 psi between atmosphere and perfect vacuum to 20 psi boost with no port or throttle body or temperature changes the air flow increases (14.7+20)/14.7 = 2.36 times. You get 2.36 times the base power minus the pumping power required to run the compressor.

The bottom line to this is if a throttle body is good enough at NA for your base power without being a choke point, it is also good enough for the boost. The throttle body only needs to be larger if it is a choke point or restriction without boost in the same combo.

This is the same reason a high volume pump can't "pump the pan dry" unless the high volume pump adds a tremendous amount of additional oil pressure. Flow is always proportional to pressure differential across the restricted path.
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post #8 of 13 Old 01-01-2019, 03:50 PM
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YouTube search turbo Windsor throttle body. They switch out a 75mm for a 90 on the dyno with only minimal power increase
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post #9 of 13 Old 01-01-2019, 06:46 PM
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YouTube search turbo Windsor throttle body. They switch out a 75mm for a 90 on the dyno with only minimal power increase
and all they had to do, was measure for a pressure drop

to justify even trying a 90

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #10 of 13 Old 01-01-2019, 09:16 PM
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Friend ran 8.67 at 163mph with a 65mm TB in a 3200lb street car with a GTS 76mm. And the cold side piping was only 2 1/2" fwiw.

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post #11 of 13 Old 01-03-2019, 10:14 AM
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My car runs 8.50s @ 160+ with a 70 mm TB at 18-ish psi boost.


93 Notch 347 twin 66s TH400...8.54 @ 162 Radials

91 Notch 410W Novi 2000 5 speed...10.99 @ 136
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post #12 of 13 Old 01-04-2019, 06:59 PM
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My cold piping is 3" so I matched it with a 75mm. That's where my thinking is.
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post #13 of 13 Old 01-08-2019, 03:52 PM
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I had to hog it from a 70 to a 75..



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