w8less

but why not have the max airflow you can have going into the motor? if anything is going to restrict airflow it will be the intake and heads......correct?

Hamutoff

I believe that too large of a TB for an application... will hurt low end because the airflow will be sluggish thru it compared to the "breathing capacity" of the engine

have a cigeratte smoker blow thru a straw at a friends face
have a cigeratte smoker blow thru a 3" dia pvc tube at a friends face

if you had Lance Armstrong blow thru the straw his ability would not be realized -- he can produce much more flow - he is a 347 or the like he might want to use the 3" pipe....however he would still produce good pressure BUT limited flow w/ straw

lets say that the smokers velocity of air thru the straw was exactly the same as L.A. thru the 3" pipe,
so then straw might fit stock 5.0 but 3' pipe might fit 347....


The 347 would idle just fine with the 3" but be choked with the straw (but still idle just fine)
the stock would idle just fine with the straw but idle poorly with the 3"

w8less

sounds like it would need to be tuned for the increased airflow correct?

Hamutoff

no. lets imagine extremes for the moment. this always allows me to visualize things. if you had a 3foot MAF and 3foot TB on a reg engine, you could imagine that all finesse would be lost.... its about resoluton here....

the angle of the tb blade would stay the same at the same foot to pedal movements but that same angle would allow much more air into the engine. you would loose fine control

same thing with fuel injectors, too bit and you cant control them at low engine speeds you dont have the fine tiny ajustments at very low output....

Joel5.0

.... I guess a few of the setups I've worked, including a 100% stock SD '86 with an AOD on which I installed a 80mm TB, were exceptions to the "rule" then. Keep in mind that EFI deals with dry air flow, as opposed to a carburetor setup, where the restriction is a must.

93 LX FiveO

i put a 65mm tb and 75mm maf on my car with a bbk cai

all were put on separately, at different times.

the tb was last to be installed, and it made a noticable difference throughout all rpm's

Hamutoff

yup I would imagine that would be a perfect mod for even a stock car, if you kept stock maf and 80 mm tb I would guess not work as good

Hamutoff

well that still fits the formula as Ive stated: less restrictive, more restrictive, less restrictive; like so: >-<
which you've followed in your 'stock 86' as stated.
you did not state, however, how they were exceptions; are you saying that you had better off-idle response and fuel economy?
I do not propose a "rule" in any case, just general practice, concept, understanding

93 LX FiveO

first pass with the tb swap (with maf+cai) car dropped 3 tenths in 1/4 mile

Hamutoff

http://www.amazon.com/gp/reader/0760...51983-9707811#

Steve Turners book, page 26

...installing too large an oversized throttle body can hurt performance, particularluy torque
...this is mostly true regarding (page 27) naturally aspirated 5.0's.... torque loss
...tb shouldnt be larger than your maf... you want to create a funnel for the air...

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