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Discussion Starter #1
Ok I searched, went over 20 pages and couldn't find a clear answer.

Why? do people bother with after market TB's (on the mr2) like the 70mm Ford and such, they go from 2.5" piping to IC to 70mm TB, it doens't make sense; why not keep the same diameter on the TB as the IC pipes?
 

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I have the same question Cris K was recommending the ford or accufab 70mm throttle bodies for the sidefeed intake manifold I'm having him make up for me. I actually think I might want the 65mm for throttle response and the fact that you pointed out.

But 70mm is only a quarter inch off of the 2.5 anyway...
 

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Discussion Starter #3
OK after I posted I though about it for a sec, this would be my guess.
Is it because the TB is next to the intake Plenum making it easier to disperse the air evenly through the runners?
 

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keep in mind that the throttle plate and shaft is a HUGE restriction in a throttle body.

2.5" pipe has a cross sectional flow area of 31.67cm square...

A 70mm throttle body has a cross sectional flow area of 38.48cm square..

However, the throttle shaft is on average about 0.5cm thick across the diameter of the throttle (0.5cm x 7cm) giving a reduction of 3.5cm square.. bringing the flow area down to 35cm square... a mere 3.33cm square increase over that of the intake pipes.. sounds like as close to a perfect match as you can get to me!

This is interesting, Ive never sat down and worked out the figures for mine

I run 3" pipes and 2 x 55mm throttles...
pipes are 45.36cm square
Each throttle is 23.75... x 2 = 47.5cm square. Man.. how perfect am I. Unintentional perfect match at that :D
Well not exactly.. because of those shafts. 0.4cm or so x 5.5cm x 2 throttles = a reduction of 4.4.. bringing the throttles down to 43cm square, 2cm square below the pipework

Oh well, neither are showing any sign of being anything close to their limit anyway :) These twin throttles have the equivelant flow area of a 78mm (or so) throttle.

-Tristan
 

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Discussion Starter #5
flupstar do you have PICS of your set up? I was thinking on doing something similar by using a Twin throttle body off a Ford Truck 460 engine; what do you think?
 

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Discussion Starter #6
flupstar you said " bringing the flow area down to 35cm square... a mere 3.33cm square increase over that of the intake pipes.. sounds like as close to a perfect match as you can get to me!" but 3.33cm = 1.311 inches, is that close?
 

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jose rosario said:
flupstar you said " bringing the flow area down to 35cm square... a mere 3.33cm square increase over that of the intake pipes.. sounds like as close to a perfect match as you can get to me!" but 3.33cm = 1.311 inches, is that close?
which is 3.811 inches compared to the 2.5 inch intake pipe, I'm confused......
 

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jose rosario said:
flupstar you said " bringing the flow area down to 35cm square... a mere 3.33cm square increase over that of the intake pipes.. sounds like as close to a perfect match as you can get to me!" but 3.33cm = 1.311 inches, is that close?
3.33cm SQUARE.. we're talking about flow area, not distance measurement

3.33cm square = 0.65in square.

In very plain terms, a 70mm throttle has roughly 10% more flow area than a 2.5" pipe which is about what you want to ensure the throttle is no restriction

-Tristan
 

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jose rosario said:
flupstar do you have PICS of your set up? I was thinking on doing something similar by using a Twin throttle body off a Ford Truck 460 engine; what do you think?

of course

http://members.westnet.com.au/wtfauto/teamwtf/burninatemr2/burninatebuildup.html

Pics of engine bay and boot (where the throttles are) can be found there

Also see this thread, specifically about the manifold:

http://www.mr2oc.com/showthread.php?t=74132

Pics of the manifold before assembly are further down.


Have you got pics of the dual throttle ford thing? I havnt seen it so I cant give an opinion. You can read about why/how I went dual throttle in the above thread

-Tristan
 

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Discussion Starter #10
flupstar said:
3.33cm SQUARE.. we're talking about flow area, not distance measurement

3.33cm square = 0.65in square.

In very plain terms, a 70mm throttle has roughly 10% more flow area than a 2.5" pipe which is about what you want to ensure the throttle is no restriction

-Tristan
Got it, thanks! for the replies and the links.
 

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flupstar said:
3.33cm SQUARE.. we're talking about flow area, not distance measurement

3.33cm square = 0.65in square.

In very plain terms, a 70mm throttle has roughly 10% more flow area than a 2.5" pipe which is about what you want to ensure the throttle is no restriction

-Tristan

Ok I understand as well. Would there be an issue with throttle response time with the increased flow?
 

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mr2bats said:
Ok I understand as well. Would there be an issue with throttle response time with the increased flow?
With a throttle which is too big, throttle response actually increases... because your foot doesnt have to move the pedal as far before the engine is able to breathe at full noise (eg the motor can breathe fully with the throttle only being half open). Many people dont realise that half the trouble with throttle response is how long it takes you to actually push the pedal down with your foot! :)

With my current setup, I achieve full boost and full power with the throttles only 1/2 open.

The reason overly large throttles are not good is they dont offer as much throttle -control-.. the bigger you go, the more the throttle is like an on/off switch. It took me a few weeks to become accustomed to mine... now I love it and stockers just feel flat and lifeless in comparison.

-Tristan
 

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Discussion Starter #13
flupstar said:
With a throttle which is too big, throttle response actually increases... because your foot doesnt have to move the pedal as far before the engine is able to breathe at full noise (eg the motor can breathe fully with the throttle only being half open). Many people dont realise that half the trouble with throttle response is how long it takes you to actually push the pedal down with your foot! :)

With my current setup, I achieve full boost and full power with the throttles only 1/2 open.

The reason overly large throttles are not good is they dont offer as much throttle -control-.. the bigger you go, the more the throttle is like an on/off switch. It took me a few weeks to become accustomed to mine... now I love it and stockers just feel flat and lifeless in comparison.

-Tristan
Man! if your fault :smile: I'm building a side feed manifold and I'm going with a 70mm or a 75mm, what do you think? :evillaugh which TB do you recomend?
 

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Sounds good to me... I always thought the holley throttles looked nice. But Im not very experienced with many aftermarket throttles so you should ask around.

In essence though, all they are is a pipe with a plate.. in other words, a throttle is a throttle. The difference between one and another is usually very small

-Tristan
 
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