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Old 11-21-2017, 02:58 PM   #1
GreatDaneShane
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Default ITB sizing?

How do you figure out what size to use? Looking at using some on a B30f after ditching the djet stuff and I found some 50mm ones from an e46 m3. I've seen people run triple 45 dcoe carbs on these, so would the extra 5mm per hole be too large?
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Old 11-21-2017, 03:16 PM   #2
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It would be fine if you can cobble a very progressive throttle linkage, since you would likely see zero runner vacuum long before those throttle bodies see even half throttle.
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Old 11-21-2017, 03:47 PM   #3
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Quote:
Originally Posted by GreatDaneShane View Post
How do you figure out what size to use? Looking at using some on a B30f after ditching the djet stuff and I found some 50mm ones from an e46 m3. I've seen people run triple 45 dcoe carbs on these, so would the extra 5mm per hole be too large?
A B30 is just a slightly longer B20.
Typical B20 DCOE sizing for high compression rally motors with cams with 280-312 degrees (at nominal lash)--and rally motors are made for BROAD powerband from say 3500 to 7000 is 45 DCOE with 36 or 38mm venturis..

Typical B21-B23-B230 sizing is 48 DCOE

50 is huge..do the math for the AREA of these numbers..50 is YUUUUUUuuuuuuuuge.

50 sounds huge for an E46 M3

People bullsh!t and BMW fan-bois are both bullsh!tters and ignorant sluts so have you actually measured the throttle plate?? or is are you taking some guys word for it?
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Old 11-22-2017, 03:34 PM   #4
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Quote:
Originally Posted by John V, outside agitator View Post
A B30 is just a slightly longer B20.
Typical B20 DCOE sizing for high compression rally motors with cams with 280-312 degrees (at nominal lash)--and rally motors are made for BROAD powerband from say 3500 to 7000 is 45 DCOE with 36 or 38mm venturis..

Typical B21-B23-B230 sizing is 48 DCOE

50 is huge..do the math for the AREA of these numbers..50 is YUUUUUUuuuuuuuuge.

50 sounds huge for an E46 M3

People bullsh!t and BMW fan-bois are both bullsh!tters and ignorant sluts so have you actually measured the throttle plate?? or is are you taking some guys word for it?
50mm seems to be accurate. Bmw ones were up high on the list because there's 6 of them already hooked together, and they're relatively inexpensive (250-500)

Gsxr 600 throttle bodies are 38mm, and seem to be pretty cheap. Just have to figure out how to stick 2 more onto the factory set.
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Old 11-22-2017, 04:11 PM   #5
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I'm in the process of adapting 3 sets of GSXR 1000 (42mm butterfly valve) itb's onto a V12, I'm planning on making a linkage like BMW uses on their ITBs for most engines; a single rod with a linkage to each itb. Planning on using the orignal fuel rail mounting ponts to mount this linkage rod.
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Old 11-24-2017, 02:21 AM   #6
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I did a set of 06' R1 itbs on a b230. 50mm or so. Too big, it was a cobbled together setup, we saw great gains in torque and WOT power, but low speed driveability and transient throttle was difficult and cranky. I am now just finishing off a second setup on the same motor, using Toyota 4age20v ITBs, which are around 43mm. That, plus a better injector location and progressive throttle linkages (I kept it as Toyota engineered it, they are smarter than me) should hopefully get me a nicer overall setup.
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Old 11-24-2017, 03:06 AM   #7
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Originally Posted by GreatDaneShane View Post
50mm seems to be accurate. Bmw ones were up high on the list because there's 6 of them already hooked together, and they're relatively inexpensive (250-500) .
Seems? So you got out some very-near calipers, nice cheezy $16 elctronic ones and it read
SEEMS to be 50mm?

Does seem right..

That way huger on a road car stock than a road race car modded..
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Old 11-24-2017, 03:38 PM   #8
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Quote:
Originally Posted by John V, outside agitator View Post
Seems? So you got out some very-near calipers, nice cheezy $16 elctronic ones and it read
SEEMS to be 50mm?

Does seem right..

That way huger on a road car stock than a road race car modded..
Yes I used my very-near calipers and measured them. It seems to read 50ish millimeters, therefore I have decided on my own volition that they seem much too large.

I think the gsxr 600 38mm units will suit my needs. The engine will have a cam and some head work, a header/exhaust, microsquirt, etc.
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Old 11-27-2017, 06:42 PM   #9
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Ovethinkers anonymous up in here... do what yo brudda done told you and stick some modern injektors in the existing d jet manifold and add Mike Rowe Squirting and lets go cruise the boulevard.

This is gonna be an airbagged, bangin', cruiser not a fekkin race car.

I decided on the personalized plate for you too:

VOLDIN
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Old 11-27-2017, 07:44 PM   #10
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Quote:
Originally Posted by GreatDaneShane View Post
Yes I used my very-near calipers and measured them. It seems to read 50ish millimeters, therefore I have decided on my own volition that they seem much too large.

I think the gsxr 600 38mm units will suit my needs. The engine will have a cam and some head work, a header/exhaust, microsquirt, etc.

38 SEEEEEEMS small to me..
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Old 11-28-2017, 12:15 AM   #11
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Quote:
Originally Posted by kyote View Post
Ovethinkers anonymous up in here... do what yo brudda done told you and stick some modern injektors in the existing d jet manifold and add Mike Rowe Squirting and lets go cruise the boulevard.

This is gonna be an airbagged, bangin', cruiser not a fekkin race car.

I decided on the personalized plate for you too:

VOLDIN
A boy can dream.
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