Same here I would love to see a 94/95 302-306 with the 94/95 induction stystem (this includes the EGR which 90-95% still have) gain from a 65mm/70mm/75mm.I would be more then happy to accept I was wrong and there is a gain with x amount of CFM through an induction that handles less CFM. Until then I see no reason to believe other wise. Great info lets keep the ball rollin.....
Throttle Body Size
- Thread starter final5-0
- Start date
here is my take on the situation.
i think you should go as big as you can without disrupting the engine's vacuum signal. i'm sure grady can recall the days of pulling out the vacuum gauge to tune the carb--on those flatheads of course
for instance---a '02 BMW 745 has what is called the N62TU engine. it is a V8 that has variable valve lift, variable cam timing and infinetly adjustable intake runners. it does have a throttle body, but the t/b stays open all the time and is there only as a fail-safe. it maintains idle and vacuum by varying the valve lift.
another BMW example is every M car made(cept the US spec E36 M3) uses individual throttle bodies per cylinder. the very first iteration M3 used a 2.3L 4 juicer that utilized 4 48mm throttle bodies---doing the math prolly equates to a much larger surface area than a 75mm t/b on an engine that is half the size of ours. it does not suffer any driveability and actually manages a decent amount of torque for an engine that revs to 7500.
basically i cannot see a drastic drop off in vacuum when you mash the pedal if you go to a 75mm t/b vs a 70mm. does that mean that the same would be true if you put a 90mm on? i don't know.
as for t/b's effecting wave pulses i can't see that happening as wave pulses are a result of everything after the t/b----ie cam timing, runner length, burn time, etc.... i think the habit we fall into is thinking that t/b sizes do the same thing as increasing or decreasing plenum sizes when in reality is they control vacuum and can act as a restriction at wot.
btw, POST #1000 bitches
i think you should go as big as you can without disrupting the engine's vacuum signal. i'm sure grady can recall the days of pulling out the vacuum gauge to tune the carb--on those flatheads of course
for instance---a '02 BMW 745 has what is called the N62TU engine. it is a V8 that has variable valve lift, variable cam timing and infinetly adjustable intake runners. it does have a throttle body, but the t/b stays open all the time and is there only as a fail-safe. it maintains idle and vacuum by varying the valve lift.
another BMW example is every M car made(cept the US spec E36 M3) uses individual throttle bodies per cylinder. the very first iteration M3 used a 2.3L 4 juicer that utilized 4 48mm throttle bodies---doing the math prolly equates to a much larger surface area than a 75mm t/b on an engine that is half the size of ours. it does not suffer any driveability and actually manages a decent amount of torque for an engine that revs to 7500.
basically i cannot see a drastic drop off in vacuum when you mash the pedal if you go to a 75mm t/b vs a 70mm. does that mean that the same would be true if you put a 90mm on? i don't know.
as for t/b's effecting wave pulses i can't see that happening as wave pulses are a result of everything after the t/b----ie cam timing, runner length, burn time, etc.... i think the habit we fall into is thinking that t/b sizes do the same thing as increasing or decreasing plenum sizes when in reality is they control vacuum and can act as a restriction at wot.
btw, POST #1000 bitches
BlackVert
15 Year Member
Ben's talk about vacuum reminded me of something my engine builder told me. He said that if the induction system was correctly matched, then the vacuum reading at WOT would be in a certain range. If the value is above that range, then the induction system does not flow enough. If it is below that range, then it is too free flowing. Most of the engines he builds are for racing and use carbs, but he said that approach was also valid for determining the adequacy of the induction system on EFI engines.
And of course, vacuum is the determining factor in intake velocity, so it all seems to fit.
So perhaps that could be a way to empirically determine once and for all if a given induction system (throttle body size being a part of that mix) is correct or not.
Or perhaps there are 2 different target ranges: a part throttle vacuum range for a 100% street car, and a WOT vacuum range for a race car.
If we can agree on what those ranges should be, maybe there won't be any more arguing about throttle body size.
And of course, vacuum is the determining factor in intake velocity, so it all seems to fit.
So perhaps that could be a way to empirically determine once and for all if a given induction system (throttle body size being a part of that mix) is correct or not.
Or perhaps there are 2 different target ranges: a part throttle vacuum range for a 100% street car, and a WOT vacuum range for a race car.
If we can agree on what those ranges should be, maybe there won't be any more arguing about throttle body size.
WhiteDevil
New Member
gcomfx.com
Founding Member
I asked Don a similar question with my new combo. He said I should not just run out and buy a bigger T/B, but try the 65mm I have and see how it does with the new 331/Trick Flow setup. He mentioned plenty of higher horsepower (FI) cars on TurboMustangs running the same size T/B. Then later if I can get my hands on a bigger one, give it a shot and see how it runs.
Once I start spraying the car again, I should be able to test this even further.
Once I start spraying the car again, I should be able to test this even further.
blksn955.o
Founding Member
Its not just bolt on and go, you need to tune the eec with the proper maftransfer with a tune or tuner. People use the Lmaf/03cobra maf on 5.0's for more power why not a smaller version of the same maf then.
1. A good bit cheaper if one has a tuner that has access to the eec already over a Pro-m/PMAS.
2. Factory maf with a good known transfer that will be really accurate and in the proper format for the eec (no converting a 10pt transfer).
3. Ford made a few
.You will need the "new" style pigtail (and it isnt cheap) at around 45-60$, and an air filter adaptor of somekind...ebay has them for the Lmaf/older mafs in CIA kits and such.
gcomfx.com
Founding Member
BlackVert
15 Year Member
my builder says that for a racing application, if the vacuum is over 1/2" at WOT, then the induction system does not flow freely enough. of course, that means there is a restriction somewhere in the induction system, not necessarily just the throttle body.
if the induction system flows too freely (ie - it is too big), it will go below 1/4" at WOT.
if the induction system flows too freely (ie - it is too big), it will go below 1/4" at WOT.
Guys, in the vast majority of cases, the throttle body is not the weak link or restrictor in these N/A engines. I do not understand why people make such a big deal about getting the 'biggest and baddest.'
At 6,000 rpm a 347 can flow 600cfm. That is with NO restriction. Any 347 or similar has a ton of restriction. That cfm rating does not include a heads, cam package on it. The cam only is open for little amounts of time. So the cfm rating is further cut.
Guys are routinely sticking on throttle bodies that flow two to two and half times greater than their engine sees at it's peak.
I have to ask...why?
If you've got a throttle body that delivers 100% of the peak air requirements of your engine when the throttle plate is fully open, you have control of the air throughout 100% of the throttle position range. If you go to an oversized TB that delivers 100% of the air that your engine can consume while the throttle plate is only 60% open, you have given up usable throttle-control range for no advantage.
Guys that are constantly defending the oversized throttle bodies are only talking about wide open performance (WOT). What about the 99% of the time that we cruise around at part throttle?
Throttle modulation becomes more difficult. The gas pedal modulation becomes touchier.
Again, look somewhere else for a restriction, not an oversized throttle body.
An Accufab (for example) 65mm throttle body flows more than enough for a 347 stroker with 664cfm continously, while the 347 would see 600cfm if it had no heads, cam, or intake on it, which of course is impossible.
Enthusiasts need to quit ignoring the facts.
Read an article from the top throttle body maker themself and let them tell the tale:
http://www.accufabracing.com/article 3.htm
At 6,000 rpm a 347 can flow 600cfm. That is with NO restriction. Any 347 or similar has a ton of restriction. That cfm rating does not include a heads, cam package on it. The cam only is open for little amounts of time. So the cfm rating is further cut.
Guys are routinely sticking on throttle bodies that flow two to two and half times greater than their engine sees at it's peak.
I have to ask...why?
If you've got a throttle body that delivers 100% of the peak air requirements of your engine when the throttle plate is fully open, you have control of the air throughout 100% of the throttle position range. If you go to an oversized TB that delivers 100% of the air that your engine can consume while the throttle plate is only 60% open, you have given up usable throttle-control range for no advantage.
Guys that are constantly defending the oversized throttle bodies are only talking about wide open performance (WOT). What about the 99% of the time that we cruise around at part throttle?
Throttle modulation becomes more difficult. The gas pedal modulation becomes touchier.
Again, look somewhere else for a restriction, not an oversized throttle body.
An Accufab (for example) 65mm throttle body flows more than enough for a 347 stroker with 664cfm continously, while the 347 would see 600cfm if it had no heads, cam, or intake on it, which of course is impossible.
Enthusiasts need to quit ignoring the facts.
Read an article from the top throttle body maker themself and let them tell the tale:
http://www.accufabracing.com/article 3.htm
BlackVert
15 Year Member
good article, but i feel a need to point out that is does say that an oversized throttle body is not nearly as detrimental to lower and mid range performance as is an oversized carb, because of the way the carb needs air flow to properly mix fuel into the stream, whereas efi controls that via the computer.
Car Nut
Founding Member
5sp GT: Nice article. That makes sense to me.
Of course, that leads to the issue of choosing the right filter, intake, MAF and inlet tubing. Probably the MAF is the more difficult, particularly with the typical swap to larger injectors.
Of course, that leads to the issue of choosing the right filter, intake, MAF and inlet tubing. Probably the MAF is the more difficult, particularly with the typical swap to larger injectors.
Guys, in the vast majority of cases, the throttle body is not the weak link or restrictor in these N/A engines. I do not understand why people make such a big deal about getting the 'biggest and baddest.'
At 6,000 rpm a 347 can flow 600cfm. That is with NO restriction. Any 347 or similar has a ton of restriction. That cfm rating does not include a heads, cam package on it. The cam only is open for little amounts of time. So the cfm rating is further cut.
Guys are routinely sticking on throttle bodies that flow two to two and half times greater than their engine sees at it's peak.
I have to ask...why?
If you've got a throttle body that delivers 100% of the peak air requirements of your engine when the throttle plate is fully open, you have control of the air throughout 100% of the throttle position range. If you go to an oversized TB that delivers 100% of the air that your engine can consume while the throttle plate is only 60% open, you have given up usable throttle-control range for no advantage.
Guys that are constantly defending the oversized throttle bodies are only talking about wide open performance (WOT). What about the 99% of the time that we cruise around at part throttle?
Throttle modulation becomes more difficult. The gas pedal modulation becomes touchier.
Again, look somewhere else for a restriction, not an oversized throttle body.
An Accufab (for example) 65mm throttle body flows more than enough for a 347 stroker with 664cfm continously, while the 347 would see 600cfm if it had no heads, cam, or intake on it, which of course is impossible.
Enthusiasts need to quit ignoring the facts.
Read an article from the top throttle body maker themself and let them tell the tale:
http://www.accufabracing.com/article 3.htm
:Word:
Black95GTS
Active Member
Guys, in the vast majority of cases, the throttle body is not the weak link or restrictor in these N/A engines. I do not understand why people make such a big deal about getting the 'biggest and baddest.'
At 6,000 rpm a 347 can flow 600cfm. That is with NO restriction. Any 347 or similar has a ton of restriction. That cfm rating does not include a heads, cam package on it. The cam only is open for little amounts of time. So the cfm rating is further cut.
Guys are routinely sticking on throttle bodies that flow two to two and half times greater than their engine sees at it's peak.
I have to ask...why?
If you've got a throttle body that delivers 100% of the peak air requirements of your engine when the throttle plate is fully open, you have control of the air throughout 100% of the throttle position range. If you go to an oversized TB that delivers 100% of the air that your engine can consume while the throttle plate is only 60% open, you have given up usable throttle-control range for no advantage.
Guys that are constantly defending the oversized throttle bodies are only talking about wide open performance (WOT). What about the 99% of the time that we cruise around at part throttle?
Throttle modulation becomes more difficult. The gas pedal modulation becomes touchier.
Again, look somewhere else for a restriction, not an oversized throttle body.
An Accufab (for example) 65mm throttle body flows more than enough for a 347 stroker with 664cfm continously, while the 347 would see 600cfm if it had no heads, cam, or intake on it, which of course is impossible.
Enthusiasts need to quit ignoring the facts.
Read an article from the top throttle body maker themself and let them tell the tale:
http://www.accufabracing.com/article 3.htm
I can't find the post on here, it was a similar article about TB size, and the poster contacted accufab for advice for their 347 stroker. The accufab technician recommended the 75mm throttle body.
I'm going to keep looking, maybe some other peeps are better at it then I am?
There is a ton more then TB diameter that determines the flow into an engine. Just because the TB can flow 10000 CFM, do you really think thats the same amount that makes it into the combustion process? I don't.
Adam
I know which thread you are talking about and you are correct the tech did recommend a 75mm for his stroker (don't remember if it was a 331 or 347). Which is against the arcle Klass wrote. And you answered your own argument/discussion why buy a larger TB if the motor can't get/use it. Your intake will fall in CFM before "smaller" TB's will.
Black95GTS here's the thread
http://forums.stangnet.com/showthread.php?t=673966
Also Black95GTS I think it was you who remebers the movie "Wolfman don't have nards" what is the name of that movie??
http://forums.stangnet.com/showthread.php?t=673966
Also Black95GTS I think it was you who remebers the movie "Wolfman don't have nards" what is the name of that movie??
Right, fuel/air atomization is a solid amount different with a carbed application over a throttle body.
Black95GTS - Not all tech's are perfect, and some are also marketing. I specifically recall George Klass himself saying that they sale "bigger throttle bodies" to those that think that is what they need, simply because they will buy them. He was speaking in general about unknowing import owners. The facts are facts. Accufab lays them out on paper. If you do not wish to follow, that is your choice.
I totally agree with you on there being more to it than just the diameter of a throttlebody to being the sole variable. That is my whole point exactly. Many go by diameter instead of cfm ratings. That is counter productive thinking.
wytstang is right on!
Black95GTS
Active Member
In terms of answering my own question, I guess the point I was trying to make is unless you can figure out the losses that occur throughout your intake track, and the needs of your combo, you're better off going with a bigger TB and hammering out the tune if it affects driveability and low end grunt.
I think this is a good thread cause we have avoided (and I'm guilty of it) starting to be a wise a** which frequently degrades a conversation.
So as always, performance comes with a price. If you want to bolt it on there and go, you might have to sacrifice some HP, but if you're willing to either work out your own tune or pay to have someone tune, you would consider the larger unit.
:OT: That's the Monster Squad. It's one of those B movies thats so bad its good.
Adam
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