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Old 02-02-2013, 09:46 AM   #1
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75mm throttle body too big for 5.0

Will a 75 mm TB hurt a stock shortblock combo ?

I'm using the following parts now and anticipate a turbo kit in the next year.
stock 5.0 shortblock
F cam
TFS 170 heads
Saleen/Vortech intake w/Systemax lower
Accufab 75mm TB
Anderson n/a power pipe
BBK shorty headers
Haven't decided on a MAF yet, but will be at least 80mm.

I see a lot of posts saying a 75mm TB will kill throttle response on a setup like mine. Anticipate a turbo down the road, but I still want it to run good until then.
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Old 02-02-2013, 10:23 AM   #2
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I daily my F cam/TFS/ported explorer/Accufab 75mm combo with a T70 for what it's worth...
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Old 02-02-2013, 10:39 AM   #3
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Re: 75mm throttle body too big for 5.0

frank, you planning on using the powerpipe once you add the turbo? Reason i ask is i need a new throttle body pipe for my install
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Old 02-02-2013, 10:46 AM   #4
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Quote:
Originally Posted by Madspeed View Post
frank, you planning on using the powerpipe once you add the turbo? Reason i ask is i need a new throttle body pipe for my install
No, it'll be sold or put away for another project. I don't think you could use it with a turbo kit anyway.
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Old 02-02-2013, 11:31 AM   #5
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Originally Posted by frankstang View Post
I see a lot of posts saying a 75mm TB will kill throttle response on a setup like mine.
That's a load of baloney. My set-up is a lot milder than yours and a 75mm TB definitely didn't kill the throttle response. Very much the opposite.
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Old 02-02-2013, 12:30 PM   #6
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I have a buddy who used to have a 306, Eddy Performer heads, Eddy Performer intake, longtubes, and Accufab 75mm TB and didn't have any throttle response issues that I knew of.
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Old 02-02-2013, 02:54 PM   #7
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Quote:
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I see a lot of posts saying a 75mm TB will kill throttle response on a setup like mine. Anticipate a turbo down the road, but I still want it to run good until then.
Old wives tale. Ask David Claflin/Super Irish about that.
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Old 02-02-2013, 04:37 PM   #8
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im planning on running a 75mm throttlebody i already have it actually but im currently running my stock 60mm throttlebody and my 76mm c&l maf, ima throw my throttlebody on though today but it wont hurt my car will it?

stock ported e7s
302 stock short block
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hopefully the 75mm throttlebody lol
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these are my mods currently
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Old 02-02-2013, 04:45 PM   #9
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Re: 75mm throttle body too big for 5.0

doubt it will hurt it, but dont expect it to give you any gains
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Old 02-02-2013, 04:52 PM   #10
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doubt it will hurt it, but dont expect it to give you any gains
still using the stock throttlebody with the c&l 76mm maf im seeing a better throttle response it seems to take off alot quicker
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Old 02-02-2013, 08:00 PM   #11
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They run a 90 mm on the new 5.0.
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Old 02-02-2013, 08:48 PM   #12
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I used an 85mm, the throttle response was annoying by how much it hurt my neck. I would use a 60mm and save on chiropratic visits
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Old 02-03-2013, 12:34 AM   #13
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You will give up about 1 hp down low and will gain a few up top. There really isn't a significant difference. Efficiency wise you want the largest opening at the filter and for everything to taper up to the tb. Just don't expect any gains na. Once the turbo is on the tb might be a factor, but even then not a significant one. The tapering of parts builds velocity in theory...
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Old 02-03-2013, 11:22 AM   #14
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Cool way to describe velocity.
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Old 02-03-2013, 11:26 AM   #15
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I'm using the 75mm race TB with the 4" PP and 90mm LMAF on mine. FTI prepped TW170 heads & FTI cam.
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Old 02-03-2013, 12:14 PM   #16
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my latest build is ported e7's, fti cam and fti ported stock intake. i am using an accufab 75mm tb and powerpipe combo. i wouldn't put anything smaller on.
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Old 02-04-2013, 07:13 PM   #17
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Quote:
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They run a 90 mm on the new 5.0.
And its also a brand new dohc motor.

Its very hard to tell what a 75mm does for throttle response, an aftermarket t/b usually has a stiffer spring so it may seem like it has better response, because you can squeal the tires easier.

Keep in mind throttle bodies support hp they don't make it

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Old 02-06-2013, 10:21 AM   #18
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Its very hard to tell what a 75mm does for throttle response, an aftermarket t/b usually has a stiffer spring so it may seem like it has better response, because you can squeal the tires easier.
A stiffer spring? Hadn't heard that one before. The throttle lever where the cable attaches to is longer on the larger throttle bodies. Pics with a caliper have been posted a few years ago I believe. People will say the larger throttle body kills low RPM torque, or the throttle is too twitchy when in fact the engine is wanting to accelerate faster, which isn't a bad thing. If it pulls harder in the mid range the low range might "feel" softer when in reality it isn't. You can't put one part on without changing timing and fuel too in order to optimize the new combination.
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Old 02-06-2013, 10:46 AM   #19
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Re: 75mm throttle body too big for 5.0

i dont think a throttle body change would neccesitate a timing and fuel adjustment, but im not a tuner. I have never adjusted anything to compensate for a swap of something that small.
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Old 02-06-2013, 11:51 AM   #20
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because you can squeal the tires easier.
I run a accufab 90 and get some mad squeal out of my tires........ chicks dig it and the neighborhood kids always want me to give'm a squeal coming down the street..........only reason i run a big one, for the SQUEAL!!!!!!!!!!!!!!
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Old 02-06-2013, 09:52 PM   #21
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I run a accufab 90 and get some mad squeal out of my tires........ chicks dig it and the neighborhood kids always want me to give'm a squeal coming down the street..........only reason i run a big one, for the SQUEAL!!!!!!!!!!!!!!
LOL!!!!!!!!!!!!!
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Old 02-07-2013, 08:50 AM   #22
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i dont think a throttle body change would neccesitate a timing and fuel adjustment, but im not a tuner. I have never adjusted anything to compensate for a swap of something that small.
That's because I swapped a 75MM spring onto your 90MM throttle body when you weren't looking.
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Old 02-07-2013, 08:56 AM   #23
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Re: 75mm throttle body too big for 5.0

does that make me stiffer? :what:
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Old 02-07-2013, 09:45 AM   #24
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The reason a carburetor gets too large and hurts response is the carburetor requires a certain flow velocity across the booster venturi to pull fuel out of the bowl. It stops metering fuel properly when air velocity is too low, so the mixture gets lean at WOT with too large a carb.

In an EFI system, the velocity critical area is from the plenum to the cylinder. With enough plenum volume the size of the inlet mostly just affects vacuum in the plenum. It doesn't change velocity in the runners or fuel mixture.

The result of this is we can grossly oversize a throttle body with no effect on mixture or airspeed in the runners. This doesn't mean the extra size helps, it just means it does not hurt. If we did that with a carburetor or with throttle body injection (pre-plenum injection) it would kill the same engine's mixture and power. Fuel would settle out in the plenum from the lazy air in a throttle body injection, or not be drawn with a carburetor.

It's a case of too big an inlet won't hurt if the plenum and runners are right, so we can take the vacuum to zero at the throttle body with EFI and a proper intake system. I still have a 70 mm on a 363 SC engine. The air pressure is ~15 at the TB inlet, and around 14+ in the plenum. With a bigger TB I could take that pressure drop to nearly zero, but I'm not sure that is first on my list for changes. If I was pulling air through it under vacuum, it would be a whole lot different story!! 90mm might be too small.

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Old 02-07-2013, 01:23 PM   #25
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I run a accufab 90 and get some mad squeal out of my tires........ chicks dig it and the neighborhood kids always want me to give'm a squeal coming down the street..........only reason i run a big one, for the SQUEAL!!!!!!!!!!!!!!
well, hell yeah dude, but you only have a 2 or 4 seater. I can stack up chicks like cord wood in my lightning
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Old 02-07-2013, 01:27 PM   #26
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just saying, when i swapped in a bbk 75mm over my 65mm stocker it has a stiffer gas pedal its harder to ease into the throttle from a stop. So unless I gained a ####load of low end torque...im pretty sure its the return spring or throttle lever ratio that changed
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Old 02-08-2013, 07:56 AM   #27
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The springs aren't any different, unless either the one on your old throttle body was junk, or your throttle cable routing changed. The lever is a little longer on the aftermarket throttle bodies, dependent upon what size it is, those that I have measured were the stock, 70, 75 and 90MM.
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