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Old 11-26-2014, 07:17 AM   #1
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WTB- 83mm throttle body

Anyone happen to have a 83mm GT3 throttle body for sale ?
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Old 11-26-2014, 07:21 AM   #2
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don't know your application, but a cayenne tb may work and is cheap on ebay.
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Old 11-26-2014, 08:36 AM   #3
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Cayenne 78mm throttle body is my back up plan if I can't find a 83mm GT3.
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Old 11-26-2014, 03:41 PM   #4
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A dumb question.....how does this help a stock car ?
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Old 11-26-2014, 04:28 PM   #5
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Here is one

Porsche 997 GT 3 Throttle Body Part No 99760511601 E Gas 82 5mm | eBay
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Old 11-26-2014, 05:04 PM   #6
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A dumb question.....how does this help a stock car ?
It doesn't.
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Old 11-26-2014, 06:16 PM   #7
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if you are tuning for midrange torque you want an intake that gradually decreases in diameter. this serves to accelerate the incoming air charge and facilitate the filling of the cylinders on the intake stroke.

if you are tuning for max hp at max rpm then you want as little resistance as possible to the large volume of incoming air.

street cars are tuned to be useable at low and mid rpms, and on you boxster you will find an intake system that decreases in diameter as you move from airbox to throttle body to the plenum. the gt3 is a track car designed to live at high rpm. as such the intake system is as wide open as possible.

you can put a gt3 throttle body on your car, but it only means anything if you have removed all the other restrictions from your intake system. otherwise the air will restict at the airbox, then expand when it reaches the throttle body, then constrict again when it hits the plenum. that's a lot of useless work that your engine has to perform.

a larger throttle body will also change the performance characteristics of your throttle. think about the 1/2" tap on your sink. say it is attached to a 1/2" water pipe. open the valve halfway and you have half flow. open it fully and you have full flow. now put a 3/4" valve on the 1/2" pipe. open the valve halfway and you get 75% flow, open it two thirds and you get full flow. so, power comes on sooner with a larger throttle body.

the real question is - say you have a 3/4" pipe with a 1/2" valve - even fully open the valve isn't letting all the water through - did porsche leave any power on the table with the 986? jake says not in this case.

sorry for hijack.
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Old 11-26-2014, 06:32 PM   #8
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It's real easy to get "big throttle body syndrome" with these engines if they are stock or near stock.

What the OP is needing this throttle body for, is about as far removed from stock as possible.
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Old 11-26-2014, 06:58 PM   #9
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Thanks

I had seen this tried on BMW E36 cars and saw the actual Dyno information and the result was always in my mind just not there.

I always like straight answers and you guys give good ones.

Happy THanksgiving

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Old 11-26-2014, 08:59 PM   #10
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The "bigger is better" crowd is always the easiest to beat.
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Old 11-26-2014, 09:16 PM   #11
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Are you tell me the 74mm tb on my 3.2 is no bueno?
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Old 11-27-2014, 04:14 AM   #12
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The cat is partially out of the bag but I'm not saying anymore as I have been sworn to secrecy As stated above my motor is being " built " over the next few months and the end result will be a engine that can be docile as a daily driver or a beast if you put your foot in it.........nothing like anything currently out there to my knowledge. As far removed from stock as can be without being a dedicated race engine. Happy Thanksgiving !
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Old 11-27-2014, 05:05 AM   #13
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Thank you for the link I just snagged that one !
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Old 11-27-2014, 07:03 AM   #14
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jk - i'd say 74 mm on a 3.2 is fine. Porsche did it on the 987 3.2's and the 2004 special edition 3.2.

if you are feeling sporty, pull out the mechanical engineer in you: 3.2 litre engine displacement = 1.8 litres / rotation = 12,600 litres / minute at 7000 rpm = 210 litres / second = 0.21 cubic metres / second.

now you have three options for the size of path you want to push this air through:

inside diameter of throttle body:

986 = 67 mm = 0.0035 square metres
99x/987 = 75 mm = 0.0044 square metres (some say 74 mm, some say 76 mm; I used 75 mm)
GT3 = 83 mm = 0.0054 square metres

from here you can calculate the velocity of air in each case (unit analysis says simple division should work):

986 = 60 metres / second = 216 km / hour
99x/987 = 48 metres / second = 173 km / hour
GT3 = 39 metres / second = 140 km / hour

not sure what this tells me. I do know that it would take a heck of a lot less work to accelerate air to 140 kmph than 216 kmph. also more opportunity for ram air benefits with the slower airflow. but I presume there are other things at play; restrictions at the intake manifold itself, low rpm trade-offs, intake tuning effects, etc.
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Old 11-27-2014, 03:19 PM   #15
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My T1 touareg v8 measures 82.5mm that I used on my cayman s fyi
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Old 11-27-2014, 04:19 PM   #16
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Are you tell me the 74mm tb on my 3.2 is no bueno?
Did I say that? Nope. We're talking 82.5 (83) mm here.

I leave stock displacement engines stock.

Size doesn't matter- its all in the combo.

BTW- Stop PM'ing me asking if Rfurerst911sc is getting my 4.1L! He is not. The 4.1 is a hell of a lot easier to create than what he is getting; which is smaller than even a 4 liter. Nothing that it takes to create this engine is off the shelf.
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Old 11-27-2014, 07:52 PM   #17
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[QUOTE=BTW- Stop PM'ing me asking if Rfurerst911sc is getting my 4.1L! He is not. The 4.1 is a hell of a lot easier to create than what he is getting; which is smaller than even a 4 liter. Nothing that it takes to create this engine is off the shelf.[/QUOTE]

Wasn't me man....err em who is getting it?
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Old 11-27-2014, 08:02 PM   #18
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Old 11-28-2014, 01:10 PM   #19
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jk - i'd say 74 mm on a 3.2 is fine. Porsche did it on the 987 3.2's and the 2004 special edition 3.2.

if you are feeling sporty, pull out the mechanical engineer in you: 3.2 litre engine displacement = 1.8 litres / rotation = 12,600 litres / minute at 7000 rpm = 210 litres / second = 0.21 cubic metres / second.

now you have three options for the size of path you want to push this air through:

inside diameter of throttle body:

986 = 67 mm = 0.0035 square metres
99x/987 = 75 mm = 0.0044 square metres (some say 74 mm, some say 76 mm; I used 75 mm)
GT3 = 83 mm = 0.0054 square metres

from here you can calculate the velocity of air in each case (unit analysis says simple division should work):

986 = 60 metres / second = 216 km / hour
99x/987 = 48 metres / second = 173 km / hour
GT3 = 39 metres / second = 140 km / hour

not sure what this tells me. I do know that it would take a heck of a lot less work to accelerate air to 140 kmph than 216 kmph. also more opportunity for ram air benefits with the slower airflow. but I presume there are other things at play; restrictions at the intake manifold itself, low rpm trade-offs, intake tuning effects, etc.

TRK! My gosh numbers..! How did you arrive at your swept intake volume per rev. Just out curiosity?

Well if you are able to stay clear of destructive turbulence at the higher velocities you would have more authority over the air flow...but this is not likely. The flow would start to die. I would guess that the GT3 size is suited to higher volume higher rpm operation more so than the other sizes, but at what minimum displacement??
CFD might put you in the ball park for the intake tract(s) but you have this crazy variable air pump below which makes calculative/modelling processes for the whole system ....crazy difficult.

You would need flow testing to get the real answers and this would have to be done with engine performance characteristics and goals. For the hobbyist all we can do is: take notes on driving impressions; time throttle response; time acceleration; chassis dyno before and after changes...

But alas this starts to feel like work! So we put it on and just try it!
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Old 11-28-2014, 01:29 PM   #20
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meh, messed up on the vary first bit of maths. was aiming for 3.2/2 = 1.6. somehow I got 1.8. me dum dum.
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