Motorcycle Throtte bodies for V8

Has anyone here fitted motorcycle throttle bodies to a 351w, what would be the best set up too use. Do they have weber ida/idf centre bore spacing?

Adrian
 
Lets take a closer look at this. The area of a single 75mm throttle body is 4415 sq mm. If this were broken down to a MC TB for each cylinder it would be 551 sq mm each. This would make the equivilent required 8 MC TB to be 26.45mm in diameter to have the same area as a 75 mm. Then take into account the MC will turn over 12000 RPM while the 351 will only turn 8000 RPM max. This should give about a 30% greater effect with MC TBs than with the 75mm. Are my numbers and assumptions wrong???? I think this should work just fine. Even if it isnt any better in performance it would be a killer look......
 
Lets take a closer look at this. The area of a single 75mm throttle body is 4415 sq mm. If this were broken down to a MC TB for each cylinder it would be 551 sq mm each. This would make the equivilent required 8 MC TB to be 26.45mm in diameter to have the same area as a 75 mm. Then take into account the MC will turn over 12000 RPM while the 351 will only turn 8000 RPM max. This should give about a 30% greater effect with MC TBs than with the 75mm. Are my numbers and assumptions wrong???? I think this should work just fine. Even if it isnt any better in performance it would be a killer look......

Yep, your numbers are wrong, get back to basics & look at it simply-- the common inlet valve dia on a FE is 2.000"+ which suggests a valve throat dia of around 1.850" ( 47mm ) dia. Now the 'ideal' inlet tract/runner will very gradually increase in area all the way from valve to the bellmouth on an IR setup. So as the TB is closer to the bellmouth this would suggest it should be up around 2.000" (50.8mm) dia. Going smaller kills ultimate power, but might be reqd for a street application to make it driveable, but 1.053" (26.45mm) would be a tad on the small side.
 
:thumbsup:just build it!! i will use 8 gsxr tb's as i have 8 of 'em, programmable ecu, etc already
 
Hi Wayne/ Jac Mac....Wayne you numbers are right, but what you need to see is that with your 75mm TB you will be feeding a plentium manifold, and as the valves open at individual times you have in efect 75mm off TB per cylinder. Jac Mac is right, when you are talking IR manifolds you need the TB to be that much bigger or you just can't get the cfm required, I have always used the theory of double the engine capacity to cfm (350 cu in = 700 cfm) remembering that is for a plentium type manifold, So I would think that your IR TBs would need to be capible of around 500/600 cfm. Jac Mac, am I correct in what I'm saying.
 
Not really, the higher flow numbers Ive seen for inlet ports on two valve heads is around 350cfm and they were pretty fancy stuff.

Going back to the single plenum TB for a moment there are two inlet valves virtually full open & another two below half lift at any given time in a V8, if you do a quick graph you will see what I mean-- thats why you need or can use the large single or in other cases dual TB.

Simple tests for your IR Motorcycle TB's, the cross section area should be slightly greater than the inlet port area @ manifold face, or if you have flow numbers for your heads send one TB to a Flow test shop & get them to flow it, if it doesnt match or preferably slightly exceed the flow rate of your cylinder heads inlet port then its going to restrict maximum power . Just make sure the flowbench facility is capable of testing at same rate as head info.
 
Jac Mac is right. And the only m/c throttle bodies that might approach the proper flow rate are going to be off of a BIG twin to get the approximate displacement/flow rate,i.e.,something like a racing Harley or KAW in the 1500-2000cc range, aftermarket stuff. Then there's all the calibration testing. You're spending a zillion on the car,why not get something that's a proven design for automotive application?
 
Jac Mac.....Of course you are right, I remeber the heads on my 383 chev flowed 295 cfm, I was just thinking off the cuff in that previous post as general explanation for Wayne. thanks for keeping us on the right path.
AJ....For guys in UK and in NZ things that don't seem that expensive in the US are Quite often a LARGE cost item and this tends to sporn the DIY ideas that you guys may see as not needed, and its alway good to see some of these things come out of neccesity, it makes one of the reasons this forum is so great. Leonmac
 
Bottom line here is that most guys on this forum are fitting IR Injection or Webers for 'The Look' that most associate with the GT40 and it could be said that outright power is a secondary consideration. Now the McLaren builders have no real choice, especially the big block cars, those big long/short injection trumpets are just about a 'must have', fortunately all that Hillborn stuff is still available for chevys from sprint cars /hydro boats etc, and it wont cost an arm/leg to make it work as a track car, or even as an open road car- wouldnt like to drive thru town on saturday night though.:)

BUT, for this old school guy I would have a couple of 4bbls on a 351w since there are a couple of manifolds now available which is where this thread started on IIRC for a MK2.
 
My original comment was just comparing the areas of a single TB vrs 8 smaller TBs. I still feel the 8 TBs would flow as much if not more than a single TB in a plenum type system but in a IR I agree that the single TB per port would be restrictive.

Wayne
 
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