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I've been offered a 2.5 m20 including the gearbox and loom very cheap from a friend. Just wondering what is involved before I decide to go for it....I've read up a few 2.3 to 2.5 conversions and the wiring seems an issue, but are there any parts that require changing in order to fit on into a 316 with a 1.8 m10?
Any advice greatly appreciated

my advice, use the forums Search fields



there are at least 5 well documented M20 swaps on here, as is mine too.

Haha, as said I've already searched and all I found was 2.3 to 2.5 swaps?
Was yours a 1.8 m10 then? I was only after some quick advice from someone in the know as to whether it's worth the effort and roughly what's involved, what bits you need etc as certain things for e21s are extremely hard to find sometimes. I don't want to miss out on this engine if it's a fairly basic swap over and I havnt got to source a tonne of rare parts in order to fit it. Hope that makes sense.

Thanks

People more technically minded than me will know more/correct me if I'm wrong. But for starters i think you need the front subframe from an m20 engined e21.

Definatly needed are
6 cylinder subframe
323/320 6 cylinder rad
Exhaust to fit
Some sort of header tank 323/320 is best
Prop
E21 5spd gearbox is ideal but e30 will work you just wont have a speedo
Some cutting in the engine bay battery tray needs to come out, battery relocating somewhere else slam panel needs recess cutting for rad
Wiring is actually quite simple in total theres about 6 wires that need splicing in

Overall its quite easy to drop in and make it work just depends on how anal you want to be about it

fuel pump?

Fuel pump will need to be an electric one. Any injection model fuel pump will do the job. Or you can buy an in-tank fuel pump, DrGonzoPow recommended I use a e30 318is fuel pump. As far as I know that is the only one that will work, although I haven't tried any of the other e30 in-tank pumps. The is pump just drops right in, next you just need to lengthen the + wire for the fuel pump ( and get an inline fuse to put between it somewhere.) and ofcourse ground it somewhere.

I have had some problems with the fuel level sensor though, when my tank is empty the meter sits at 20 l, the warning light does come on though. I guess it has to do with the e30 having a 65l tank ( if memory serves right ) and the e21 a 55l tank. You could probably fix it by taking a fuel level sensor out of an early e30 with the smaller fuel tank. I myself cannot be arsed to sort it out.

I hope this is of some kind of help to you.

The m20b25 engine really is alot of fun to drive, I myself went from a 315 1.6 m10 to the m20b25 and it is just a blast to drive.

I've got 6pot subframe, m20 mounts, header tank, speedo cluster with rev counter and a rad if you need. Chuck us a pm

brennon wrote:I've got 6pot subframe, m20 mounts, header tank, speedo cluster with rev counter and a rad if you need. Chuck us a pm

that's pretty much all you need besides prop, box, engine and a fuel pump / maybe diff. I use the e30 318is in tank fuel pump its got more then enough flow and it also has a return.

you just have to juggle some spanners and the wiring isn't too bad either. but really you should use the search function this swap has been done tons of times.

Check my thread, I've documented it well and I'm a bit of a noob, or I certainly was before I did the swap.

You'll learn loads and it's great fun. Get searching for the 318is pump now, they're uncommon and carry a premium.

As a note, don't do what I did and forget to wire the reverse light switch into the gearbox, as once the box is in, you'll never the get the plug on.