Author Topic: Bigger TB for M42 ? (Read 8159 times)

daqqer · « **on:** December 29, 2008, 04:11:39 AM »

Currently porting and doing pulse chamber for my intake.

My setup is such that the AF ratio is quite always too rich. Means more air is needed.

All the channel from airbox and in intake is quite good, but im concerned about the little tiny TB valves. This seemes to be the bottleneck in the system atm.

Is there some TB that can be swapped 1:1 on there that has bigger valves ? Or if not, what could be the solution for me there. Any info appreciated.

I searched the forum also, did not find anything that could help me yet.

swiss318is · « **Reply #1 on:** December 29, 2008, 06:22:18 AM »

no bigger direct bolt on TB available! next step... ITB or a DIY TB

daqqer · « **Reply #2 on:** December 29, 2008, 06:38:42 AM »

Quote from: swiss318is;63642

no bigger direct bolt on TB available! next step... ITB or a DIY TB

Ok, what would be rather similar but a tad bigger TB i could use tho ?
Is it vital to have 2 different size valves in there ?
Or is it just made for smoother ride...
As assembly i would weld an extension on the intake i guess.

swiss318is · « **Reply #3 on:** December 29, 2008, 08:11:15 AM »

i have to be honest! due to our soooooooo restricted law... i cant change anything on de TB or intake on my car, so i dont have any idea.. the only thing i know is that theres no direct bolt one..
but if you can weld etc..go to a junkyard and search a bigger TB?! and make it happen...
and yes.. the two valves are for smoother ride...

KenC · « **Reply #4 on:** December 29, 2008, 01:58:36 PM »

Didn't Dinan make a larger TB?

roundel318 · « **Reply #5 on:** December 29, 2008, 02:01:38 PM »

They used to, I spoke with Dinan about 6 months ago regarding a chip and he mentioned the TB was DISCO.
I think the McHenry article refers to TB enlargement, a DIY affair.....

gearheadE30 · « **Reply #6 on:** December 29, 2008, 02:36:49 PM »

Just have a machine shop bore one out for you. You will also need a larger throttle plate.

papercutout · « **Reply #7 on:** December 29, 2008, 03:05:13 PM »

I've got a distinct feeling they do larger TB's for M42's over here in the UK, I'll ask on e30zone.

They do, but they're expensive. Everyone on E30zone reckons its a lot easier (and a heck of a lot cheaper!) to get a standard on machined out, but here's the link anyway:
http://www.evo-s.co.uk/shop/index.php?cPath=6_2279_2290_2291

daqqer · « **Reply #8 on:** December 29, 2008, 04:47:26 PM »

Ok, ill look into that then. Maybe i can find someone to do it for me here. If i get it done ill post smth here.

tjts1 · « **Reply #9 on:** December 29, 2008, 08:03:53 PM »

I'm not sure the throttle body is the biggest restriction in the intake system. I would start with the opening airbox muffler (2" round) then the AFM (2" square).

I don't think a bigger throttle body is going to do you any good until you fix these restrictions.

daqqer · « **Reply #10 on:** December 30, 2008, 12:07:58 AM »

Thats all done already.

Btw does anyone have a M42 TB closeby and could you measure both the valves there ? (Preferrably in metric system

)

tjts1 · « **Reply #11 on:** December 30, 2008, 12:45:16 AM »

35mm and 54mm according to this.
http://www.motortraders.net.au/groups/group.asp?group=1&menu=89
Way, way down the page. Lots of other good info if you're interested.

One thing I did to my TB was to knife edge the throttle plates and trim the excess screw length on both plates. Then I tightened up the throttle linkage and adjusted the plates so both were parallel at WOT. Might not be as radical as what you had in mind, but its a start.
Good luck

EDIT: Here it is
http://www.m42club.com/forums/showthread.php?t=5675

daqqer · « **Reply #12 on:** December 30, 2008, 01:20:44 AM »

Quote from: tjts1;63685

35mm and 54mm according to this.

WOT area if we take those 2 surfaces:

M42B18 = 100 %
M30B30 = -3,63 %
M20B25 = -9,56 %

Ok, i think ill do the little enchancements you mentioned and be happy with it atm. Noone wants to bore it anyway here.

Still its haunting me that one big valve might actually be alot better.

PS both very good links you posted, thanks.

swiss318is · « **Reply #13 on:** December 31, 2008, 09:37:56 AM »

hm... if i would let do a machine shop... the increasing of the diameters of the two valves.. does the increasment has to be similar? on both perhaps 5% more or so? or only the big one?

DutchM42 · « **Reply #14 on:** December 31, 2008, 11:16:54 AM »

I bought the Alpina527 throttlebody on e36coupe.com. It has got a bigger diameter, bigger valve, less restriction and fully polished inside.

I can�t say I noticed any improvement though.