318is M42 to m20b20 swap....

[newportimports]

Ok so first you are saying why the hell do I want to swap out a M42 318is motor to a slower heavier M20b20 engine?
Well i have to to comply with racing technical regs.
I have bought a really nice straight 318is so want to use it as a base for the race car, the car does not run and is missing the inlet manifold and airbox so cant tell if the engine is any good or not.
I have a blueprinted m20b20 engine complete with NO ancillaries.

My questions are:

Will the 318is M42 engine 5spd gearbox mate up to the m20b20 engine without modification as i would like to use the original box and diff as they are low mileage?

Will a m20 with ac flywheel mate up?

What ancillaries will be interconnectable if any?

Are the engine mounts in the same place on the cars frame?

Any other general help / info in the techincal dept for the above swap would be greatly received........

[Duke137]

Ok so first you are saying why the hell do I want to swap out a M42 318is motor to a slower heavier M20b20 engine?
Well i have to to comply with racing technical regs.
I have bought a really nice straight 318is so want to use it as a base for the race car, the car does not run and is missing the inlet manifold and airbox so cant tell if the engine is any good or not.
I have a blueprinted m20b20 engine complete with NO ancillaries.

My questions are:

PBMW ? Get some pics up!

Will the 318is M42 engine 5spd gearbox mate up to the m20b20 engine without modification as i would like to use the original box and diff as they are low mileage?

I believe the gearbox fits (bell housing pattern) but the M20 boxes sit at 10 degrees difference to the 4 pots stuff as far as I know? You can get a M20 manual box for pretty cheap, I have 2 in my shed one from a 109k car. The M42 box will be of interest to a M52/M50 swap person as the M42 gearbox alows the use of diffs from cars that are easier to source. If you use the M42 box, you will have to mod the gearbox cross member and mounts potentially

Will a m20 with ac flywheel mate up?

Yes, as long as you use the M20 starter and clutch too. Many people take this opportunity to get the flywheel lightened to below 6kg but I am not sure how this affects your regulations....?

What ancillaries will be interconnectable if any?

Not many I don't think as the 6 cylinder and 4 cylinder M42 are pretty different, alternator may be ok with the correct bracket?

Are the engine mounts in the same place on the cars frame?

Yes they are, but the mounting arms and rubbers will be different. In all honesty you could probably pick up most of the bits you need by buying a complete M20b20 for spares for under £100 as they are not a sought after engine

Any other general help / info in the techincal dept for the above swap would be greatly received........

Best thing you can do is take some time to read through the forums as most people have asked the same questions before and more than one occasion. However, picking a 318is is a good move IMO because you already have the 51mm front struts, rear disc conversion etc and the 4.10 diff that came on the 318is is the same that was on the majority of the 320i's, well the later ones at least.

No doubt though you will have to replace your shocks and springs for quality track use, and moving up to 6 pot will mean the current shocks and springs won't be the best option anyway!

Above all, what is your budget and what are you trying to achieve long term

Oh and welcome to the zone

[newportimports]

Thanks duke 137!
I did read all the wiki stuff but none of it said about the box angle being different.
Yeah it is for a pbmw car, i currently have one but fancy building one up from scratch, you know where you are then not to mention that you learn so much more about the cars when you do it this way.
Might make sense to just drop my m20b20 engine and box from my old car with all ancils and connect up to the prop in the 318is, or will i need the prop from the m20b20 engine and box to be the right length for the diff?
That way i can keep the m42 box and source a cheap m52 engine at a later date putting it in the old 320 shell?????

[Brian28]

If it's for PBMW you need to be careful about posting on an open forum that you have a blueprinted engine (assuming that blueprinting included machining components to balance it) .

You will need to weld in brackets to the ns bulkhead to take the expansion tank, and drill a hole/weld a bracket to the os bulkhead for the coil. The airbox mounts on the ns bulkhead are different so you can bodge up something to take the airbox or weld in a set of M20 airbox brackets. You would be sticking in new rubber engine mounts for the M0 anyway, these mount on the 318is subframe/crossmember with no issues, same subframe. Will need the 320 box regardless (regs), if the diff is original it is Ok same as 320 (4.1 open diff).

A couple of swaps to do on the underside, remove the rear ARB, remove the front ARb and fit the (thinner) 320 one.

[newportimports]

not ported / polished and balanced. just rebuilt to manufactures tolerances. A cheat will never truly win!

[newportimports]

Thought the Gertrag box was the same for the 320 as the 318is, but changing it anyway so doesnt matter. As the diff is the same I assume I will use the one out of the 320 engine / box config.
Thanks for the notes on this, have you built a PBMW car out of a 318is shell then?

[Brian28]

Built quite a few PBMWs in the past from different base cars, probably ten or so over the years. Ran a 318is in TTRS/P8R that is now converted to an M20 325. Although all of the shells are basically the same, there are a few odd brackets etc in the engine bay that are different and a pain if you're not anticipating them. When you get the 320 box see if you can get the shift linkages/selector arms whatever they are called at the back of the box as well as there are a few different length versions. Also check the sticky post ref wiring at the top of the engine swaps forum section, if you sort the brown earth wire out all of the engine loom wiring is a simple swap on one multiplug. Good luck wth the build.

[newportimports]

cheers Brian! I have a complete 320 PBMW (ex dengate) car, so will be pulling all the bits from that into the 318is as the shell is really good and I am having a new cage so made sense to put it in a new shell.