M20: More power.....ADVISE & DEBATE

Post Wed May 16, 2007 3:30 pm

Thanks Ed,that looks like a well thought out spec.What,ll she do,mister?....220bhp is my bet...perhaps a bit more with the head work you have planned.Is it for your daily driver?

Post Wed May 16, 2007 3:57 pm

I am not sure how much bhp it will kick out.
The e34 is my daily driver, I am not going to use the e30 all the time, I dont think it will go over the speed humps on the way to work

my cab used to hit them and that was 35mm drop this is going to be 80mm drop.

Post Thu May 17, 2007 2:54 am

Thats some drop,Ed,will it leave any suspension at all?My 2.7 is in daily use,main reason for a mild state of tune. Its ability to overtake in 5th still brings a smile.

Post Thu May 17, 2007 9:51 am

Thats some drop,Ed,will it leave any suspension at all?

The car is semi striped out so its sitting to high on the 35mm springs.

anyway back on topic

Post Mon May 21, 2007 10:48 pm

just been scanning through these 2.8 threads as i am interested in building one with the spare (2.5) engine i have at work. pulled the head off it and there is absolutely no wear despite having done over 200k.

one thread has mentioned the piston skirts not clearing the con rods which is the same for the 2.7 but i thought that this was only an issue with early pistons.

also am i right in thinking that the compression ratio will remain the same as the m20 its based on?

oh and if anyone happens to have an m52 crank and/or some 2.0 rods hanging around id like to hear from you

Post Tue May 22, 2007 4:52 am

Compression ratio is affected by the length of your stroke,Matt..there is more to compress..the early pistons give something in the area of 11.1,if I remember correctly.Eta pistons have a scallop in the sides to clear the rod/crank at BDC,Ed325 should know if they are needed with the M52 crank,he seeems to be gathering the bits together for his build.That steering rack is still sat on my garage floor,BTW.!!

Post Tue May 22, 2007 7:43 am

You should read these through, gives you overall idea about the conversion:
http://wp1016621.wp027.webpack.hosteuro ... f00080.htm
http://www.bmwe30.net/cgi-bin/datacgi/d ... Section=03

Basically, to achieve 240hp you need these:
-ITB:s, alpha N mod to motronic or Megasquirt
-Wild camshaft (~290deg)
-2.7 or 2.8 crankshaft, pistons with +10:1 compression ratio
-Good exhaust + exhaust manifold

You just can't get 40% more power from BMW's 12v engine easily. M30 which has 3.5l volume gives only ~220hp and Hartge / Alpina got only ~260hp out of it vs. ~210hp out of M20..

~200hp is quite easy to get, just change pistons, con-rods and crankshaft, build good exhaust system and get your motronic tuned up in dyno and that's it

It's also noteworthy that the whole nature of the engine changes with 2.7 crankshaft. More torque before the 4krpm powerpeak so the car gets much faster though top hp-number doesn't get much bigger.
Old saying about M20's "Everything forward from 200hp costs alot but 200hp is quite cheaply achieved."

Post Tue May 22, 2007 3:47 pm

one thread has mentioned the piston skirts not clearing the con rods which is the same for the 2.7 but i thought that this was only an issue with early pistons.

It depends with make of pistons you have.
You may have to take 11mm off the skirt but only if building a 2.7
zaust is getting some 324 cranks.

Post Tue May 22, 2007 5:30 pm

ed325i wrote:
one thread has mentioned the piston skirts not clearing the con rods which is the same for the 2.7 but i thought that this was only an issue with early pistons.
It depends with make of pistons you have.
You may have to take 11mm off the skirt but only if building a 2.7
zaust is getting some 324 cranks.

the engine im using is a late spec low comp unit but i am doing the 2.8

got the block on the engine stand and turned it over today and although you can clearly see the honing marks there is some scoring to no.5 bore.not sure if its going to need a rebore but if it does then piston choice becomes an issue.

went to my local bmw specialist today to ask about a crank and they said they must have thrown 30 bottom ends away with nikasil issues

theyre gonna call me if they get another in to do.

Post Tue May 22, 2007 5:36 pm

You would better getting a 320/323 block and getting it bored out to fit the 325 pistons it will be cheaper then Ã‚£100 each pistons.
You will not need to mod the pistons to fit with the 2.8
30 bottom ends

I think the 2.7 is going to be a thing of the past.

Post Tue May 22, 2007 5:50 pm

ed325i wrote:You would better getting a 320/323 block and getting it bored out to fit the 325 pistons it will be cheaper then Ã‚£100 each pistons.
You will not need to mod the pistons to fit with the 2.8
30 bottom ends
I think the 2.7 is going to be a thing of the past.

i like your thinking re the 320 block, i have a 320 breaker on my drive with a good engine which i offered someone for silly (cheap) money complete. ill have to see if he gets back to me cause that would be the rods and block sorted and im sure i can offload the 731 head to some old hat 2.7 builder :lol:

think this thread needs re titling or else we might have to start a new one which goes into detail about which parts can be used to get what approx power.i intend to build mine using standard parts to start with (pistons, cam, exhaust etc) and then add to it when i know how it performs. it sounds like you might be splashing the cash a bit more so it would be good for a comparison.

Post Tue May 22, 2007 7:46 pm

ill have to see if he gets back to me cause that would be the rods and block

You dont need the 320 rods you use the 325 ones.

NO you do use the 320 ones

I was thinking about something alse. [/b]

Post Tue May 22, 2007 9:47 pm

i was just going by this from andyboy

Andyboy wrote:325i or Eta block. 325i pistons. 320i/323i/Eta 130mm rods. 2.8 crank. Works perfectly!

For a crank just ring up someone like FAB, Quarry Motors, GCD etc and ask for a shagged 2.8 short engine. They're not falling off trees yet but someone will have one.

plus the fact that if you use a crank with a longer throw it will put the pistons well above the block face.

i will have both so i can mock them up when i find a crank and see whats what.

Post Tue May 22, 2007 9:58 pm

0.5mm off a head is LOADS! why ed?

Post Tue May 22, 2007 11:58 pm

I have the parts needed for a 2.7. Pm for details

Post Wed May 23, 2007 7:58 am

Simon13 wrote:0.5mm off a head is LOADS! why ed?

To give the same squish band as the stock M20B25K engines.

Post Wed May 23, 2007 1:13 pm

IMO if you have 11mm taken off the skirt of a 325 piston to provide clearance at BDC,you will get loads of piston slap.Perhaps this is not an issue with a track day warrior,but for a road car copy the eta scollop.This seems to be yet another area where the 2.8 starts to make more sense.

Post Wed May 23, 2007 2:46 pm

The later 325 pistons had a shorter skirt, 11mm shorter so you shoulnt get piston slap.

Post Wed May 23, 2007 6:07 pm

^ indeed, listed as weight improved on ETK

Bottom line, longer skirts give more contact friction, and add weight, neither are desirable in a performance orientated conversion , again we coompromise in some areas to gain the power, the cost is reduced longevity, but given the average M20 lifespan, not a real issue in my mind.

Slap is easily avoided, dont use worn pistons in worn bores :lol: