Author Topic: Bored out Throttle Body (Read 4737 times)

max123 · « **on:** January 13, 2009, 12:48:59 AM »

Total Beginner, so please forgive me if this has been covered. I've been reading the E30 Restoration Manual and one of the steps suggested for starting an upgrade to the M42 is to 1) get a chip (done) 2) bore out the throttle body as the engine is somewhat restricted.

I couldn't find a thread on this, so if it exists please redirect me - but if not - what have others done. What is the most that it can be safely bored out, or better still - what is the best size? Once bored out, what is involved in resizing the butterfly valve? Also - is this a worthwhile modification - what kind of power could I expect, and does it kill driveability (jerkiness, poor fuel economy). My goal is always to retain the essential characteristics of the engine but to liberate the potential.

Cheers,

Max

tjts1 · « **Reply #1 on:** January 13, 2009, 04:31:28 PM »

You can find some good info in these threads.
http://www.m42club.com/forums/showthread.php?t=5675

http://www.m42club.com/forums/showthread.php?t=7566

good luck
Justin

max123 · « **Reply #2 on:** January 13, 2009, 04:52:17 PM »

Thanks for the links Justin - you knife edged the two throttle plates - but did you ever consider boring out the throttle body itself? The British m42 guys seem convinced that this is the bottleneck in the whole system - everyone else seems unconvinced from what I've read. Also, if I bored out the throttle body would the basic mechanism for the butterfly valve still work (with resized plates of course) - also, could I use a thinner gauge aluminium for the plates or is that just getting tedious?

Anyway - I'm buying a used throttle body off craigslist today to play around with - I'll look into the cost of getting it machined.

Cheers,

Appletree IS supercharged · « **Reply #3 on:** January 16, 2009, 06:07:28 AM »

Hi i bought a Big bore throttle body from the e30zone shop ( evolve) cant say i felt a major difference but i was only running standard ecu at the time without a chip so maybe if i had chipped it id have got a better result.

Cheers Matt:)

balobas · « **Reply #4 on:** January 17, 2009, 10:19:53 AM »

Quote from: Appletree IS supercharged;64789

Hi i bought a Big bore throttle body from the e30zone shop ( evolve) cant say i felt a major difference but i was only running standard ecu at the time without a chip so maybe if i had chipped it id have got a better result.

Cheers Matt:)

Do the idle get nervous or is it still firm/stabil?

How important is it to bore out right, how and both holes due to the flow when you go diy on this operation?

I can understand that it would be a proper done job at a workshop who`s done it before an have som skills/experiense with machined jobs..

soo,, how important are there to get the right form when you diy..? I mean,, who`s got an flow-machine at home:o

About you guy who got the lower lock in the hole knife-edged,, what does that operation lead to? got some feedsback?

max123 · « **Reply #5 on:** January 21, 2009, 02:20:39 PM »

I got the spare throttle body and took it to a machinist to see what was possible. Just looking at it, the larger main butterfly valve doesn't have a lot that can be taken off as you end up running into a vacuum line. Also, because of the way the throttle body is made, the only true side to set up a jig for machining is on the manifold side, but that means you would be honing from the wrong side and this makes things difficult because the bore must be dead centre or the butterfly valve won't work.

In any event, it isn't quite as simple as just plunking it on a honing machine and taking off a few mm's. If anyone has any experience on this (or pictures) it would be much appreciated.