m20b25

[danbear]

hello all. what is the difference between the older and newer versions of the m20b25's? And how can i tell which one i have? sorry if thats a silly question, i'm a newbie to all of this

[Speedtouch]

Older pre-1988 ones are high compression, and are generally more responsive with better torque, power and fuel economy. Later facelift (mid 1988-on) low compression ones were catalytic converter prepared, and had different pistons to lower the compression ratio.

The high compression has a 25 6E engine code while low comp has 25 6K code. This can be seen on a machined flat to the right of the inlet side engine mount, just above the block:sump interface.

[danbear]

Thanks for the help. i'll check to see which one i have later. What is the better one to have?

[Speedtouch]

Common consensus of opinion on here reckon the earlier high comp to be better, and having tried examples of both I'm inclined to agree.

However, some later engines such as bss325i's on here produce the book horsepower figure of 171bhp, so they're not all bad, and can, of course, be perked up with a chip for instance

[Nay]

As above really.

The cooling systems are different. Earlier one has a coolant tank on the right (RHD drivers side) and the facelift has a different shaped one on the left... for simple knowledge.

I've heard, but am not sure, that the earlier engine has an older version of the Motronic ECU electrical wizardy.

Newer engines are nicer to drive, but the older ones have that brutality about them. (when both are running well!)

[Speedtouch]

That's true, most of the earlier ones ran Motronic 1.1, while Motronic 1.3 was introduced in 1988. Some high compression engines found their way into the mid-first year of the facelift cars, so you get the best of both worlds, i.e. high comp engine with later Motronic 1.3 management which had more resolution (available bitmap settings) than the Motronic 1.1.

[Nay]

I remembered something correctly... the brain is still there!

Ah, so can the motronic 1.3 be retrofitted to the high comp engines easily? (when I say easily I mean pull off the old and on with the new, remap/chip/leave alone)

I'm planning to go to MS anyway for a S/C setup... does MS just replace all motronic stuff?

[Speedtouch]

Early pre-facelift Motronic 325i had both crank and gearbox sensors, so no, you can't just swap the later ECU in alas. You can however convert using all the later type sensors/loom.

Yes, MS replaces all the Motronic stuff - check out Flappysocks' guide http://wiki.diyefi.co.uk/

[Nay]

Cheers Maurice. Thats what I was asking. Unplug everything and then plug all the later stuff in, then maybe alter the ECU settings via a remap or chip etc to accomodate for the slightly different engine.

I'll have a read up on the guide. Is installing (and learning about) MS any easyish task?

[Speedtouch]

It depends on your level of experience with vehicle electrics and understanding of engines - it's obviously beneficial to have some experience of the basics prior to considering changing to MS.

However, MS has an Autotune mode where having installed it, you drive around with a laptop and let it tune itself, so you don't need to be an absolute expert on engine management programming to get it up and running quite well.

Then, you can take your time to learn about the settings to tweak it.

[Nay]

Didn't know that. I knew you can tune/tweek with a laptop, but what, an autotune? So you can drive around, it'll do some fancy programming magic and tweek itself to a nice driveable level, then ontop of that gives you the ability to tweek as you drive? Nice.

I generally know about engines now (especially the M20!). I've learnt a lot, but upon my engine build I intend to learn a lot more.

The plan is rebuild a S/C ready engine (no expense spared!) and get the car rebuilt and running well as N/A. Then fit MS and get that sorted. Then S/C. MS I've heard is pretty much a requirement for F/I. Is that an acceptable way to go?

Get engine built and running. Rebuild all the suspension, brakes and go components, upgrading as I go. I'm going to give Mr. Ant from A-Tech a bell sometime to talk about rebuilding an engine in prep for his S/C kit. But I would like it to the point where its basically just install the S/C and then go, rather than a complete rehaul over the engine.

Is that a good idea?

[Speedtouch]

It sounds like a plan to me but the only engine I've ever built is a 1275cc MG Midget A-series, still going strong after 40,000 miles There's quite few S/C engine builders on here, STiBen is currently doing an M30B35 with S/C & MS so you've got company at least.

I gather you need a wideband exhaust gas sensor fitted in the downpipe(s) to enable the autotune facility to work, as it operates in closed-loop mode, i.e. using the feedback from the sensor to recalculate the correct parameters for exhaust CO, HC, etc.

An alternative could be to use a Miller WAR chip, which should enable you to use the Motronic setup. http://www.millerperformancecars.com/war-chip.html
http://www.millerperformancecars.com/fi ... Manual.pdf

[Nay]

Thanks again mate. Really helpful!

I've heard of the war chip, but dont know how good it actually is at the end of the day. Need to see some strong feedback.

Also, whilst replacing everything, replacing all the ECU will add a bit of security in its longlastivity, as opposed to using the old equipment. I dont want to be tied to the restrictions of the stock equipment either... but I need a good reseach. I might also be going for ITB's with a custom pipe for the S/C so that would have to be incorporated for in the EFI managment surely?

[chrisE318is]

so why was the lower comp engine brought in if there was no obvious advantages?

[Nay]

Maybe to help the stability of the engine. Head gaskets and cylinder heads enjoy popping and cracking...

[daimlerman]

so why was the lower comp engine brought in if there was no obvious advantages?

Main reason was American legeslation regarding emmisions,the lower c/r helps.The later motronic allows for greater efficency and relibility,both early and late engines are rated at 171bhp.
As already said,early pistons and late managment give the best of both...

[e301988325i]

Some high compression engines found their way into the mid-first year of the facelift cars, so you get the best of both worlds, i.e. high comp engine with later Motronic 1.3 management which had more resolution (available bitmap settings) than the Motronic 1.1.

Happy days, just been outside 256E in a facelift!!! That explains a lot. How I got 32mpg on petrol, how it kept up with m50b25s (before LPG), why the zone wild chip didn't work particularly well at all.

9.5:1 and 8.8:1?? is that the right ratio for the engines?
Can anybody tell me what the effects would be of m52b28 crank and 130mm rods? Interference?
Also does anyone do a chip specifically for the high compression engine on 1.3??

[gooner1]

A definitive guide on changing the early motronic engine management, to the later
type would be very handy. Yes i know it can be done Theo,s way, just get stuck in till it all
works, but for us less mechanically/elrctrically minded numpties, a step by faltering step
would be priceless. Apologys if i ,ve slightly spammed myself.

[ross_jsy]

nay, why don't you just s/c the standard engine.

doesnt it give like 300bhp on a standard engine? thats gonna be more than enough imo for a daily e30. mines lively enough atm

or s/c the std engine, buy a second engine, build that up to spec, dump it in the car, bolt s/c to it with a different pulley and run more boost?

[Nay]

nay, why don't you just s/c the standard engine.

doesnt it give like 300bhp on a standard engine? thats gonna be more than enough imo for a daily e30. mines lively enough atm

or s/c the std engine, buy a second engine, build that up to spec, dump it in the car, bolt s/c to it with a different pulley and run more boost?

Its possible to get about 300bhp, but I dont think its quite there.

I've been tempted to buy a second engine to rebuild, using the stock one for the time being, but theres not really much point.

Its again, not a daily. A car that is for occasional fun, track days in the UK and as much beef down a 1/4 mile as possible.

I think I'll be aiming to get an E36 (hopefully 328i Sport) or maybe even a Golf early next year for my daily... My 320i is on the verge of death. Too much to fix for a rusty 320i auto.

Anyway, the S/C is the last bit on the list. Costs a fortune and the better preped the engine is, the more returns you'll see. I could spend supercharger money (£3k) and pretty much completely rebuild the engine block for that money. So I'll do that, and run it as N/A whilst working on it, until engine, cooling and suspension (with all minor bits) are finished, then upgrade to MS (or do it from the start...) and have a car thats ready for a charger, as a solid wod of three bags is a lot of money and needs to be purchased as one big thing. Engine can be done section by section, piece by piece.

Anyway, hopefully my Dad will be able to get that kit car out of the garage sometime this side of the year and I'll be able to get my shittter in there to start work.

[ross_jsy]

give me a shout so we can tear this engine out!!

although im investing in an engine crane, so if you wanna use that we can.

im lookin at mine now, she looks sorry for herself! but on the plus side, i have found an s14 of one of the guys i work with

[Nay]

Ye? An s14 in Jersey. Grab it mate.

There is an engine winch built into the roof at the garage, but is yours is better to use?? I'll also be investing into my own engine stand when it goes in. (Which i really hope is sometime this year, but start of next will be ok...)

And I got my BTB3 today!

p.s. Danbear, sorry for spamming your post

[daimlerman]

Can anybody tell me what the effects would be of m52b28 crank and 130mm rods? Interference?
Also does anyone do a chip specifically for the high compression engine on 1.3??

Several zoners have built M20 2.8's now,most recent build thread is Stonesies,in the engine swaps section.
Regarding chips,Ant at A-Tec or speedtouch.