M42 on M3 throttle bodies

[chips]

I havent really been on the forum for a while, but heres what I've been up to - 318is M42 with E36 M3 Evo throttle bodies





Obviously the M3 throttle bodies are for six cylinders, but they are in three pairs. The left end pair has the tps mounted on it and the right end pair has the throttle cable linkage, plus each of these pairs has a mounting for the fuel and vacuum rails.

I've binned the centre pair and shortened the fuel and vacuum rails by cutting out a chunk in the middle. That way the mounts are still in the correct place to match the bodies, and the fuel rail still has the flow and return in the correct place to be used with the M3 fuel pipes. I still need to get someone to weld them back together in the middle and to add connections to the vacuum rail for brake servo and idle control valve. The original M42 injector control rail can still be used I also had to modifly the tps bracket to clear the head.

There are a few problems though;

First and main problem is that the holes on the throttle bodies for bolting them to the head dont all match up with the ones on the head. There are 3 holes on each pair, one in the bottom centre and one at each side at the top. The bottom one is almost perfect, but as you can see in the picture below, the top holes don't match. Still not sure what to do about this. I don't want to use an adapter or spacer, I'll explain why below.



The other problem is the port shape. The cutout in the port for the injector jet on the M42 begins in the lower inlet manifold, and continues into the head. On the throttle bodies, this cutout begins and ends in the throttle body itself. I dont want to use a spacer because I will be moving the injector in the throttle body even further from the inlet port. Not sure how to tackle this yet either. Another person who has done this mod modified the port shape on both the head and the throttle bodies.



Let me know if you have any ideas

[kdw215b]

I suppose you could cut the ends off ans ali weld it back together. I would use an adapter.

[jaistanley]

To fix the problem on the head I'd be tempted to hammer a slighty oversized ally dowel into the cutout, have it tigged in place and die grind the port back to shape, then match the throttle body to head so there is no step.

You could also have the tb's welded together and material added to allow you to re-drill them to match the studs already on the head.

That is a large throttle for the 1.8. Might mean mapping is a bit of a pain in the prosterior. Are you going to increase the cam overlap and capacity of the engine too?

Fine work you are doing there though.. They should look very 'factory' when you are finished!

[Jhonno]

Part throttle will be nasty.. Full throttle high rpm might be ok with cams and decent mapping though

[appletree]

IIRC Tim_s ground off some metal from each pair of bodies and then used a plate with a bolt throught the middle of it (imagine a T ) to hold both sides down. dont think he was ever realy happy with it though....

[chips]

I'm modifying the throttle bodies at the moment, plus a couple of other custom modifications. Once they are done I'll strip the whole engine down for rebuild.

It'll be stroked to 2 litres using an M44 crank and S50 pistons, so per cylinder it will only be about 50cc lower than the S50 that the bodies came from. I'll also be lightening the valvetrain and using some better cams.

I'm under the impression that with the throttle bodies I can run some pretty wild cams and see a decent power hike.

The engine is also for my track/fast road car project, so I'm not overly concerned about how it behaves at low revs, as long as its reasonably manageable.

[e21Jason]

Hi Chris

Good work you are doing there, I just seem to be creating a pile of parts, I take it you have checked out m42club.com for threads on valve train upgrades etc. Also do you know a e36 subframe fits the e30 but moves the engine back, every little helps esp if you are doing a 5-stud swap.

Also I have found a good engine machine shop out at rosewell I will see how they get on with my s14 parts. I am still on the look out for a local cage fitter, plus I havea name for an alloy wwelder, he done all of the manifolds on steve forsters UK fasted Subaru.

Also I have Euro 1 EFI ecu and mill spec harness ideal for an m42

Jason

[chips]

Hi Chris

Good work you are doing there, I just seem to be creating a pile of parts, I take it you have checked out m42club.com for threads on valve train upgrades etc. Also do you know a e36 subframe fits the e30 but moves the engine back, every little helps esp if you are doing a 5-stud swap.

Also I have found a good engine machine shop out at rosewell I will see how they get on with my s14 parts. I am still on the look out for a local cage fitter, plus I havea name for an alloy wwelder, he done all of the manifolds on steve forsters UK fasted Subaru.

Also I have Euro 1 EFI ecu and mill spec harness ideal for an m42

Jason

I've been on M42club.com a lot which has helped me to come up with the spec I want. There is a lot of information on stroking and head work.

If I were to use an E36 subframe, would the engine be moved back enough to require use of a shorter propshaft? I'm not going to do a 5 stud conversion anyway. This car won't need it.

I have 2 standard looms here which I will butcher to use with Megasquirt. If not Megasquirt then something else, but not a standard or chipped ECU. I don't think it will be able to handle it.

Let me know how you get on with the machine shop and welder though. Both of those will be required within the next few months And I will need a cage fitter too, but not for aaaaaages

[GrindCulture]

Pretty interesting build, been following it on M42club, hope you get some good results with it all!