When is 75 really greater then 70 mm throttle body

caseypayne69

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Its a simple question really. I understand on a stock car, or 1996 model Mustang GT that a 75 mm throttle body is really to much airflow. Or so I've heard. So if your almost stock they say stay with 70 mm. My question is when is 75 good, or was it better in the first place and that 70 is better = crap? I'm compared plenum and throttle bodies and looks like accufabs plenum/75 tb beats everyone elses in dyno results. So I'm thinking of purshasing it. Thats why my question about 70 vs 75
 

ALITL8

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enquiring minds want to know ???

ive halfshafted, ported and polish an extra throttle body for our 97. i can feel a some difference and it made it sound a little better too. the P&P is basically just removing/decreasing the ridge on the intake side of the tb (you cant miss it) then by halfshfting it (simple, remove half the flapper shaft) you end up with approx. 69mm. thats pretty close to 70mm and its free! ive also heard if you can find someone to P&P the stock plenum, correctly, you'll get better flow from that than most aftermarket :dunno: YET!!

if youre not planning on doing a lot to the car or on a budget, i'd go this route. my next trip to the track will tell if the TB made any real difference in performance ;) im still looking for someone that i trust enough to P&P the plenum.
 

ALITL8

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all you need is a dremel and some bits ;)
 

Dalamar

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I have the 75mm
The 75mm is "supposed" to do well once you add forced induction.
I'm adding turbo's as soon as I find where I hid my 6000 bucks.

How much of a gain are you talking about on the dnyo results you mentioned.?
 

caseypayne69

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Not sure really, surely some here on this site knows of some tech background on this, or maybe actual dyno sheet comparision on 70 vs 75 on an almost stock GT. What does the Cobra's have? Maybe I should vary my options based on what a 320 hp Cobra has since my car should be very close to that if not a tick more after my mods, im saving for.
 

Dalamar

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Good info Alitl8

That goes to show how NA the 75mm is too big.

the cobra has more air volume to the 4V heads, so size comparison wouldn't do much for ya.


You're talking less than 10 HP.
Is it worth the cost?


edit: these test numbers are also on a car with long tubes and an X.
The car also has PI heads.
apples to apples?

save it for a blower man.
 

ALITL8

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Dalamar said:
Good info Alitl8

That goes to show how NA the 75mm is too big.

You're talking less than 10 HP.
Is it worth the cost?

thats why i chose to go the FREE route with mine. a fellow club member was getting ready to go over seas (military) and needed to clear out his garage. i got a tb and intake plenum off his 03 for FREE. like i said earlier, i can feel some difference just from the p&p'ed tb. i may be doing the plenum myself too... you dont really have to bore it out, just smoothing out some rough edges and removing the hump at the EGR will help eliminate unwanted turbulance and increase flow :thumb: i should get between 5 and 10 rwhp from it and its basically FREE!!!

FREE hp is the best hp!! casey, if you can find a used stock throttle body and want to pay the shipping both ways i'll halfshaft it and p&p it for you for 30 bucks ;D PM me if youre interested!
 

EThorpe

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Nice read there ALTIL8,

The deal is with larger throttle body's is you need to up your compression or put some wilder cams in with some longer duration on N/A stuff, When you have smaller motors they need a little resistance just like they need back pressure or the low-end dumps off and Idling becomes an issue for the street.
 

caseypayne69

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From the looks of those I see no harm in a NA sporting the 75. Guess i'll be going with that, again.
 

ALITL8

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Dalamar said:
That goes to show how NA the 75mm is too big.

edit: these test numbers are also on a car with long tubes and an X.
The car also has PI heads.
apples to apples?

everything i've heard says on NA to go 70mm, especially on the NPI cars. what have you done to your car so far and what do you plan to do?
 

Adam

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I ran the Accufab 75mm TB/Plenum. I ran [email protected] with it on. Car weighed 3270 and air was 1000'. I took the stuff off and ran [email protected] BUT, the car weighed 3348lbs, and the air was 1800'. So between the weight difference and the DA(density altitude) difference, I picked up VERY LITTLE with the 75 TB/Plenum and this is on a headswapped car (10.5-1CR), longtubes, cams,thats getting shifted at 6500rpms etc etc. So on a stock 2V or close to stock 2V? I'll let you guys make that call. :) The dragstrip is the best comparison for me. The stock stuff seems pretty adequate for a long time. Unfortunately the TB/Plenums are a flashy mod thats easy to do and relatively inexpensive so thats why everyone has them.


Adam
 

DropTopPony

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With the TB and Plenum you pick up like 6-7HP on NA cars. The difference between the 70/75 is like 1 hp so if your planning on going with more mods in the future get the 75mm. I had a BBK75mm and C&L plenum on my basically stock NPI with no bad effects and when i went PI it worked fine, then with The P&P heads /cams helped more. Now i'm adding the blower so it will again benefit.
All the TB/Plenums are about the same so find the best deal. If you look on ebay and on the corral in the 4 sale area you can find great deals on used ones. Accufab is way expensive for the 1HP it gains over C&L etc.....
 

Dalamar

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I agree with Droptop, if you adding a blower it's good, otherwise, 1 HP woot!
 

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