02GF74
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 posted on 10/5/06 at 07:51 AM |
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... back to DIY throttle bodies - sorry
is the recommended diameter the same as for side draught? e.g. for 2.0l that is about 38 mm (from memory).
so current idea is getting 4 bodies of a smallish car from scrappies and using the throttle disc part?
(more of an idea than actually doing anything)
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paulf
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| posted on 10/5/06 at 11:11 AM |
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Sizing isnt as important as with carbs, but if you go too large with them then the throttle action will be less progressive due to the body being able
to flow all the air that the engine is using when only partially open.
I have 35mm kawasaki bodys fitted to my crossflow , as the ports are only about 32 mm I could see no advantage in going any bigger.
Paul.
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Noodle
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| posted on 10/5/06 at 11:14 AM |
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You can use slightly smaller bodeis than the carb equivalents because there is no intrusion into them
A 40mm Weber may, in reality only have a choke size of say, 36mm after the restictions are taken into account for the choke.
I think that was another Dave Walker-ism from somewhere.
Calvinx is right about FI helping to smooth out ill-specced venturi sizes.
Cheers,
Neil
Your sort make me sick
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Schrodinger
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| posted on 10/5/06 at 12:01 PM |
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One problem with going too big is the throttle reponse at light throttle. At very low speeds / throttle opening, very small changes in pedal position
have can have a dramatic effect on the air flowing into the cylinders.
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WIMMERA
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| posted on 10/5/06 at 12:24 PM |
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As I understand it you can go a bit bigger due to fact the fuel is added just prior to the valve so high air velocity through the manifold to stop the
fuel dropping out of suspension and make the venturi work is not as important. But have heard other theories as well.
I made a set of 4 , 1 3/4" T/B's using SU butterfly's and spindles and 65mm square alloy machined to length for the bodies, found it
easier to run the spindles vertical with the actuating arms below the body, (away from fuel rail and injectors), each arm is connected by small
turnbuckles with rod ends to allow individual adjustment, no air bleeds were used, the TPS is mounted on the rearmost T/B (also underneath) the
spindles run directly in the alloy,(no bushes) if you decide to go ahead and want to use bushes I suggest you do these first prior to the bore, then
when you do the bore the inner ends of the bushes will automatically be machined to the correct radius, a square ended bush would create an air leak
around the butterfly. While they do need to be accurate it's not precision due to the fixing holes in the butterfly having a bit of clearance it
would be different if they had to revolve, I found the other bits (fuel rail, linkages etc ) a bit of a pain.
Wimmera
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stevebubs
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| posted on 10/5/06 at 03:49 PM |
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No venturi so you can actually go slightly smaller. Jenvey site gives some approx size - bhp mappings.
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WIMMERA
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| posted on 10/5/06 at 10:21 PM |
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As I said, lots of theories, but when I made these 5-6 years ago information was thin on the ground, these were made to replace 45mm Webers with 36mm
chokes so they are bigger with no ill effects, the engine idles slower and smoother than it did on the Webers with the same cam, and runs clean to the
red line, Max HP is about the same but driveability is better.
Wimmera
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02GF74
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| posted on 11/5/06 at 08:24 AM |
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re: WIMMERA
hey - this is what I want to hear!! The motivation is to avoid this:
http://cgi.ebay.co.uk/40mm-jenvey-throttle-bodies_W0QQitemZ8064070017QQcategoryZ72205QQrdZ1QQcmdZViewItem 
Do you have any photos?
how did you do the machining (CNC?)
Ta.
Now where can I buy 44.45 mm internal diameter ali tubing 
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NS Dev
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| posted on 11/5/06 at 11:27 AM |
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Ebay is most certainly NOT the place to buy throttle bodies etc, the chavs bid them up to high heaven on there.
This setup (Jenvey 45mm SF bodies)including an MBE 956e ECU, loom, air filter, injectors, tps, crank sensor, coil pack etc etc etc cost me £600:
 
XE throttle bodies
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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MikeRJ
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| posted on 11/5/06 at 05:44 PM |
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quote:
Originally posted by CaLviNx
quote:
Originally posted by NS Dev
Ebay is most certainly NOT the place to buy throttle bodies etc, the chavs bid them up to high heaven on there.
Thats funny please explain why I shouldnt buy on Ebay, as I procurred GSXR throttle bodies below then from ebay for £86.00 + postage,
They used to go for quite a bit less than that, and I've seen GSRX TB's go for up to £120. In any case I think Nat was primarily refering
to TB's like the Jenvey units that can be bolted straight onto DCOE manifold. These apeal to those that haven't got the
patience/skill/inclination to adapt bike ones so they invariably go for stupid money.
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WIMMERA
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| posted on 11/5/06 at 11:24 PM |
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No sorry can't do the photos. Done all the machining on my own lathe, bored the alloy 1 3/4" then cross drilled and reamed for the spindle
then a hole in each corner to sandwich it between the manifold and ram tube, nothing much to it really.
Good luck with it , good to see somebody having a go .
Wimmera
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