Help me understand why one needs to upgrade to a 70-75mm TB?

5spd GT · Oct 31, 2006

Accufab states on their website that for 280 cubic inches (the 4.6L is 281.xx CI) at 6,000 rpm, they flow 486cfm at 6,000 rpm.

The 75mm TB they sell flows 924cfm. Nearly double the amount the engine could even use. This is even at 100% volumetric efficiency...in which 99% of the engines never achieve.

So why not just save money and keep the stocker?

Any thoughts on that...?

CobraRed_96_GT · Oct 31, 2006

because independant dyno tests show 6-8hp and 4-6tq for accufab and -1 or so for other brands. Plus it's about 490cfm stock and when you have less back pressure from a nice full exhaust maybe a pi intake man. and a real cold air set up your now over 510cfm and thats what 70mm is really good for anything aorund 550cfm and 75 not much more the 924cfm is BS from what iv seen, ill link the study if i find it.

Kilgore Trout · Oct 31, 2006

The accufab looks nice. If you want some bling, go for it.

5spd GT · Oct 31, 2006

Cobrared - The engine doesn't breathe at 480cfm. That is at 100% VE. The stock PI or non-PI headed cars aren't even close to that.

The independent test are the only real valid reason that someone might have I believe. So where is a test of a bone stock car on the same day getting just a bigger TB?

I do realize they look nice

George Klass himself credits the 75mm TB (non-race version) to 924 cfm. I wouldn't doubt it. Their 70mm TB wasn't much lower than that. I think in the high 700's...I can't recall.

bdcardinal · Oct 31, 2006

i like mine. the spring on the throttle body is lighter, so the pedal is easier to push. it was never hard to push, just noticed it was lighter.

DropTopPony · Oct 31, 2006

i think people buy aftermarket TB's cause they want to mod but don't want to spend 4k on a blower so they get a TB and Plenum fully knowing the combo is only good for like 5hp....the stock tb is fine for a bolt on car unless your trying to squeeze every little hp out NA.
If i was doing a budget build then a new TB/Plenum would not be on the list unless i found some used ones cheap.

04GTMustang · Oct 31, 2006

bdcardinal said:
i like mine. the spring on the throttle body is lighter, so the pedal is easier to push. it was never hard to push, just noticed it was lighter.

yea the pedal is a whole lot more sensitive. It was weird when i first put mine on shifting gears i was reving the heck out of it between shifts lol. And teh bling factor was a nice little touch under the hood.

And one of the ls1 guys saw my car at a show and said he wouldnt mess with me cause ive got a throttle body and intake with exhaust work and my tuner. Lol I thought it was hilarious he actually thought my car was fast with that stuff and thought i would beat his ls1 (I wish).

Gearbanger 101 · Oct 31, 2006

Were it a strictly N/A car, I'd say the advantages are minimal, but with an engine running any sort of Forced Induction, bigger throttle bodies are proven to provide a huge benefit all the way through the curve.

....and a this is precisely the reason I bought mine.

BennyBlown2v · Oct 31, 2006

04GTMustang said:
yea the pedal is a whole lot more sensitive. It was weird when i first put mine on shifting gears i was reving the heck out of it between shifts lol. And teh bling factor was a nice little touch under the hood.

And one of the ls1 guys saw my car at a show and said he wouldnt mess with me cause ive got a throttle body and intake with exhaust work and my tuner. Lol I thought it was hilarious he actually thought my car was fast with that stuff and thought i would beat his ls1 (I wish).

He was probably just making fun of you in hopes that you would post something on an internet forum saying how an LS1 guy thought he would loose to a stock-ish mustnag Hehe j/k j/k

Pedal feel is certainly improved. I figure throttle body/plenum together was good for 10-15whp in my caes (FI).

jstreet0204 · Oct 31, 2006

5spd GT said:
Accufab states on their website that for 280 cubic inches (the 4.6L is 281.xx CI) at 6,000 rpm, they flow 486cfm at 6,000 rpm.

The 75mm TB they sell flows 924cfm. Nearly double the amount the engine could even use. This is even at 100% volumetric efficiency...in which 99% of the engines never achieve.

So why not just save money and keep the stocker?

Any thoughts on that...?

That is true on a N/A car, but a forced induction car will go beyond 100% VE, so that is when the gains are noticable.

jasonh_86 · Oct 31, 2006

Throttle response and extra air-flow

sgarlic · Nov 1, 2006

From wiki:

Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways, but most notably the size of the valve openings compared to the volume of the cylinder and streamlining the ports. Engines with higher volumetric efficiency will generally be able to run at higher RPM, and thus power, settings as they will lose less power to moving air in and out of the engine.

So... wiki is saying if you apply boost, the percentage of volumetric efficiency possible rises?

5spd GT · Nov 1, 2006

Of course, blowing some air in the engine will increase it. But by how much...will it still flow 924 cfm?

I do agree though, despite numbers, that on a blown combo...sure, why not.

04GTMustang · Nov 1, 2006

BennyBlown2v said:
He was probably just making fun of you in hopes that you would post something on an internet forum saying how an LS1 guy thought he would loose to a stock-ish mustnag Hehe j/k j/k

Pedal feel is certainly improved. I figure throttle body/plenum together was good for 10-15whp in my caes (FI).

thats what i was thinkin at first but he seemed to really not know a whole lot about mustangs either he honest to god thought that the 99+ came with 5.0s lol.

But im pretty confident my bling bling accufab throttle body scared him off so my suggestion is get one.

Gearbanger 101 · Nov 1, 2006

5spd GT said:
Of course, blowing some air in the engine will increase it. But by how much.

Most guys have seen 10-15rwhp on the dyno, with increases all the way accross the board. That was a good enough reason for me to buy one.

5spd GT · Nov 1, 2006

Gearbanger 101 said:
Most guys have seen 10-15rwhp on the dyno, with increases all the way accross the board. That was a good enough reason for me to buy one.

I would believe what you would have to say.

I meant, how much cfm does it increase, with let's say 8lbs of boost over a 281's capability at 100% VE.

Gearbanger 101 · Nov 1, 2006

5spd GT said:
I would believe what you would have to say.

I meant, how much cfm does it increase, with let's say 8lbs of boost over a 281's capability at 100% VE.

I don't happen to have my flow bench handy , so I'll have to take a guess and say a 75mm Throttle body might show a 5-15% over the stock unit, depending on what the owner has done to the rest of the engine. I mean....what really defines a 281's capability? There's always going to be a measurable amount of restriction at both ends of the spectrum, so all anybody's really got to go on to gauge the effects of a throttle body swap are real world results.

Also....you can't really go by the amount of boost the engine is seeing. The only way to really rate it is to measure the CFM output of actual supercharger itself is producing at fixed intervals of blower RPM and then measure it again after the throttle body. But then all of that heads out the window when you consider all of the variations and possible intake and exhaust combinations and configurations possible that would skew the results by the time you got to the tailpipe. Big throttle bodies and high flow intakes cause boost figures to rise, as does a restrictive exhaust. You could end up with a guy with a high flow intake and stock exhaust seeing 8psi with for example a 3.0" blower pulley. His buddy next to him might have a stock intake set up and high flow exhaust seeing the same amount of boost with a 3.2" pulley, but both are obviously not going to be moving the same amount of air through the engine.

I can understand and relate to your curiosity about the subject, but there are certain things you just have to accept without overanalyzing them. With all of the combinations available to increase, decrease and optimize airflow, the only absolute you can be sure of is that there are no absolutes. If there were, we’d all be driving around in the same 10-second daily drivers, that had all the same parts, that got 30+mpg, all while scoring rosy emissions levels. I personally stopped racking my brain about it a long time ago and was satisfied that knowing that running the proper combination of parts as a group was more important than running one or more high flow parts on their own regardless of their rating.

streetstang03 · Nov 1, 2006

dont waste your money on something as stupid as a TB. you're not even going to feel it SOTP. save up for something that will actually make a difference like cams, LTs, o/r mid pipe, gears, suspension, nitrous, blower, [size=+1]FULL PI SWAP ON YOUR 98!!!![/size] etc...

Seraphitia102 · Nov 1, 2006

when you guys are talking 5-15hp increase, blah blah... do you mean adding a throttle body in conjunction with an aftermarket plenum?

Seraphitia102 · Nov 1, 2006

Would adding the "bullitt" intake manifold make a larger difference as opposed to a 75mm throttle body attached to the stock plenum?

Help me understand why one needs to upgrade to a 70-75mm TB?

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