Most Powerful N/A 2.5 possible??

[Geoff]

As the title suggests, what is the most power you can achieve from a n/a M20 2.5? You can obviously use Mega Squirt and all manor of tuning tricks but the bore and stroke need to remain the same.

I know one guy on here has 260, but is that not a 2.7??

[player6]

no its a 2.8

[Simon13]

full race spec M20 2.5's made nearly 230bhp back in the day

imo u won't get more than 190-195 out of one. And to get it like that u will spend alot of money

[e30_Turbo]

e21jasons m20 was around 250bhp with Carbs etc

Scots is a mutant 2.8 which doesn't count

My 2.5's running 280/300+ but then again I have cheated haven't I!!

[Blitz]

240bhp

[Blitz]

the 24 valve has 192bhp

[e30_Turbo]

As the title suggests, what is the most power you can achieve from a n/a M20 2.5?

The thread is reffering to 12v M20's

[M5pilot]

If your using a stock 8.8:1 late setup then you might just touch the 200bhp mark.

Nadz325i was dynoed at over 190BHP even with a massive airleak on the inlet manifold.

He had:

Stock 8.8:1 CR
BTB 2 Manifold
MAF Conversion with ITG Filter
Schrick 284/272 Camshaft

The car was very quick and had a very good torque spread. 3rd gear was really impressive and didnt last long! Made a brilliant noise aswell.

Dale's 325i had:
Schrick 284/272 Cam
Dbilas Throttle Bodie
Alpina Stainless Manifold
MBE Stand Alone management

197bhp.

It's not impossible!

If you used an early block and ported the head aswell you'd get 200bhp-205bhp IMHO.

[Blitz]

As the title suggests, what is the most power you can achieve from a n/a M20 2.5?

The thread is reffering to 12v M20's

Is there any other difference except power.

[Andreas]

full race spec M20 2.5's made nearly 230bhp back in the day

imo u won't get more than 190-195 out of one. And to get it like that u will spend alot of money

In South Africa we had the 325is which had a 2.7 M20 engine with 210 hp as standard. Surely a heavily worked 2.5 could easily surpass that figure.

The standard M20 325 engine has 170 hp. Now consider that raising the compression by 1 point gives 5% power increase. So, if we change the compression from 9.5 to 12.0, we've gained about 20 hp.

Add a nice chip, performance air filter and replace the restrictive airflow meter with a hotwire mass air flow meter, we should get another 20 hp.

Put in a hot camshaft, add 15 hp.

Replace the cast iron exhaust manifold with branches / headers and do the rest of the exhaust and we should get another 15 hp (especially considering the above mods)

So. lets add up
170 + 20 + 20 + 15 + 15 = 240 hp

In the above we haven't even included individual throttle bodies, bigger valves, revving the engine over 7000rpm, or installing a dry sump oil system which has been known to free up 20 hp in racing Hondas. You could still install lightweight Titanium conrods, Aluminium flywheel and a carbon fiber propshaft to speed things up.

Although it does not seem likely that an old 2 valve per cylinder engine could come close to achieving 100 hp per liter, I think you can agree that none of the above power estimates are over the top. The engine would need to run racing fuel with that compression, but it is still naturally aspirated.

[Simon13]

i assumed a tuned road car for my 190bhp!

remember the M20 as us plebs recieved it was in economy mode. The head is anything but a performance one.

Andreas i don't think your estimates are entirely plausible for the engine in question.

We all forget how hard and notorious the M20 is to tune. Even going down the tried routes doesn't always yeild the power we expected on paper, or what it should of made in theory.

I'll be interested to know how your alpina engine goes once u have finished it, and if it makes significantly more power than the 210bhp stock figure

[Kos]

how deep are you pockets!!!

i recon 200 is failry simple, use TB or carbs mental cam higher cr and you can hit 250 plus

[Stevin]

I think it's really possible 2 get oddles of power out ur 2.5lt ... I mean if money wasn't an option. I would real high CR, running on Methanol, with ITB's and Heavily worked head.... yada yada.


Nobody said it had 2 be streetable.

[e30_Turbo]

As the title suggests, what is the most power you can achieve from a n/a M20 2.5?

The thread is reffering to 12v M20's

Is there any other difference except power.

the 2.5 started life with the M20 12 valve engine. Around 1991 the marvellous M50 24 valve 2.0 and 2.5 litre engines replaced the M20, these need less maintenance and have more power. In mid-93 the M50TU was introduced with VANOS variable valve timing for better mid range power.

Good old John G Burns

[Andreas]

Simon13, I have to admit that you are right, the M20 engine is difficult to tune, but I suppose that is true for many engines.

Now that I think back, my first few mods to the engine went quite well and did achieve something, however as I added more and more stuff I got smaller and smaller returns.

When I replaced my B3 cam with an aftermarket 292 deg camshaft, my power gain was a big fat zero, I did get a nice 'lumpy' idle though.

I think selecting the correct complementing parts is the secret behind big horsepower, everything has to be perfect.

In my previous post I was getting carried away (dreaming) and the normal man in the street like you and I could most probably never build a 240 hp M20 2.5 but I believe that if BMW M Division put their heart into it, they could do it.

[Stevin]

Or if u ever got a hold of the Racing Dynamics 24v head, that would give u 250hp on a stock 2.5lt bottom end... but thats real wishful thinking.

Image a 2.9lt stroker, with RD 24v head, ITB's... damn u looking at way over 300hp.

Cause i mean if u get 250hp out of the RD head... just think of the other gains :p

Ok snap outta it :p

[Blitz]

The thread is reffering to 12v M20's

Is there any other difference except power.

the 2.5 started life with the M20 12 valve engine. Around 1991 the marvellous M50 24 valve 2.0 and 2.5 litre engines replaced the M20, these need less maintenance and have more power. In mid-93 the M50TU was introduced with VANOS variable valve timing for better mid range power.

Good old John G Burns

So are 24 V engines a popular swap in E30's

[M5pilot]

The m20 isnt THAT HARD TO TUNE!

How many people have actually tried to get big HP out of a 2.5? Most people just do 2.7's and get it all wrong and barely make 200bhp.

The Schrick 284/272 cam works very well in the m20 engines. The BTB Manifold works extremely well. Throwing away the AFM works wonders if the mapping is good.

190-200bhp is a very realistic figure to aim for from a 2.5.

As for getting 250+ from a 2.5, question has to be asked how driveable would it be, what would the emissions be like etc etc.

A very well built dogshit idling 2.7 will make 230 brake.

If you want these high power fugures just do as Ian Haynes wisely did - fit a bigger better engine.

[zaust]

how deep are you pockets!!!

i recon 200 is failry simple, use TB or carbs mental cam higher cr and you can hit 250 plus

[Jhonno]

obtainable power.. whatever you can get out of a 2.7 minus 10 or so bhp.. altho you can use more revs due to shorter stroke so might even be able to match it with a bigger cam etc..

best bet to start with is a higher compression early lump

main restriction is your wallet, not hard to tune, but expensive to get big power

[Kos]

i really wish i had the cash to build a 2.5 at the mo, maybe if i get rid of the IS at some stage and finish the M3 i might go for it, i'v had 5 325i sports , each one with different mods, but if i put them all together i'd be laughing!!

dips 323i e21 puts out 180bhp with triple carbs, thats just shy of 40 hp gain over factory figures, now if he were to dump in a 2.5 engine and head (early tech1 type with the higher CR) , port it and go for bigger valves and a screaming cam up the CR a touch he will make near to 240

the other option woul be go for a TB's and good managment system, this would give you better drivability and better tourque curve, but personally i'd say fuck that , TB cost a fair bit more than the carbs and the management is pretty expensive as well as the mapping, you'd be looking at 2k plus there, i'd spend that towards a bomproof bottom end, light weight alloy fly wheel and have a screamer and a hooligan car to twat about with which will spit out flames and chew up the tarmac!!

[Jhonno]

i really wish i had the cash to build a 2.5 at the mo, maybe if i get rid of the IS at some stage and finish the M3 i might go for it, i'v had 5 325i sports , each one with different mods, but if i put them all together i'd be laughing!!

dips 323i e21 puts out 180bhp with triple carbs, thats just shy of 40 hp gain over factory figures, now if he were to dump in a 2.5 engine and head (early tech1 type with the higher CR) , port it and go for bigger valves and a screaming cam up the CR a touch he will make near to 240

the other option woul be go for a TB's and good managment system, this would give you better drivability and better tourque curve, but personally i'd say fuck that , TB cost a fair bit more than the carbs and the management is pretty expensive as well as the mapping, you'd be looking at 2k plus there, i'd spend that towards a bomproof bottom end, light weight alloy fly wheel and have a screamer and a hooligan car to twat about with which will spit out flames and chew up the tarmac!!

[Simon13]

bla bla bla!

we have discussed this many times!

and i shall say it again, whats the point in throwing all that money on a 2.5 when u can go 2.7 along the way and get a shit load more torque.

like they say it's cubic capacity!

Anyone remember Dales old 325i sport? 6 branch,cam,diblas throttle bodies all the bits. did it make 200bhp? did it f**k it barely made 190.
He threw the money!

Find a good high comp engine?! they are all shagged. I'm glad this is a thread is made up with our made up wallets.

Sal u talk a good M20 along with the Bexley dyno behind u, so bloody build a 200bhp 2.5! Johnno u do it aswell! Go on piss the money up the wall! ho ho ho

I've put my money where my mouth is and went 2.7 with the pina.
There are not any tuning products out there now, that were not really available back in the E30 heyday. If hartge/racing dynamics couldn't do it back then, i doubt any of us chumps will now.

Where are we getting the fuel to run a 2.5 with a 304 race cam which won't idle at the traffic lights outside ace cafe?

All my opinion of course with a bit of my version of common sense thrown in!

[Turbo-Brown]

Think there are some interesting comparisons to be drawn here between the M20 2.5 and Pug's XU 1.9 litre engine as found in the 205 GTi.

Supposedly, and it's quite well documented, Peugeot did very well to make about 68bhp/litre out of the 2v/cyl engine, but had to resort to what's practically a race cam to get that much power. Seemingly the fast road and race cams available for the XU engine are in some cases milder than the standard factory cam.

Now people claim all sorts of silly power figures for the XU engine, but it seems that a practical limit is 160bhp (from what I understand) which gives us 84bhp/litre.

The M20B25 on the other hand has a couple of advantages over the XU in that it has electronic ignition instead of a clockwork dizzy, and it is of course an inline 6 which waste less in terms of vibration than I4 engines and appear to produce more torque per unit capacity too, presumably as a result of overlapping power pulses etc.

By coincidence the M20 also makes about 68bhp/litre in standard trim, although possibly some part of this is down to the electronic ignition.

If we were to work along the same lines as our XU engine and gain a pretty healthy 84bhp/litre, we'd still only end up with 210bhp from the M20.

84bhp/litre is a pretty decent figure for a N/A 2v engine by all accounts, it just doesn't add up to all that much when you don't have all that many litres.

Not really drawing any conclusions there, just giving a grid of reference.

[M5pilot]

Dale's car made 197bhp and that was on a different dyno. His engine started off making 136bhp!

Bexley dyno is pretty accurate and fuck the dyno figures, Nadz's 325i was rapid. It was a fair bit

Your also missing the point. People can tune the hell out of a 2.5 with bolt on mods and engine management and then they have all of the required ingredients to make a very well tuned 2.7.

[whiterhino]

im sure ive got an old max power mag where griffin motorsport had a 200bhp m20? ill dig it up just to make sure.Also I dont think alpinas even made the 210bhp they quoted.

[Turbo-Brown]

Of course the other thing is that RR figures aren't particularly accurate as we all know.

Think the yanks have got it right by quoting power at the wheels.

Supposedly Dastek (think it was them) now make the most accurate system in terms of calculating for coast down losses etc, and even the guy who designs and markets their system admits they're not ever gonna be 100% accurate!

Of course the other thing is that people didn't seem to think that much of exaggerating their power figures a bit back in the day

For my money, if I was gonna build an N/A M20, I'd track down the forged crank from the diesel (assuming they fit that is) to make a 2.7 so that the thing can rev to the heavens (with the right reciprocating components), but then why bother when 7psi gets you more power than you're likely to see N/A and gives a fair chunk of torque too!?

[Dan318-is]

theres a simple yet effective way of unleashing hell from an m20 2.5

a racing dynamics 24 halve head, simon knows

[Turbo-Brown]

Again though, why bother when there's a cheaper way in the M50 (or whatever it's called)

Unless you're racing in a class that dictates you keep the original block, why spend a fortune creating an engine that's likely not gonna be as friendly to drive as a standard M50 or something?

Not that I wanna discourage anyone from tuning an N/A M20, afterall I've got TBs laying in wait!

[Andreas]

. . . , but then why bother when 7psi gets you more power than you're likely to see N/A and gives a fair chunk of torque too!?

Because nothing gives me more pleasure than beating a turbo BM with my n.a. Alpina B3 (292 cam, 733i air flow meter, exhaust, laptop programmable piggy-back, alu flywheel, 4.44 custom diff).

I will never forget racing a guy in his E30 325 Turbo with 10psi boost. His turbo was slightly faster than my car (at 1500m altitude, at sea level I would have been faster) but coming out of a corner I had good throttle response and he had to overcome turbo lag. By the time he was in boost I had already pulled him 2 car lengths.

I do about 25 laps whereas the turbo guy does maybe 5 laps before he has to come in because everything is getting too hot.

So Geoff, I hope you build yourself a good solid n.a. motor, trust me people will be impressed.


Alpina B3 2.7 Racecar under construction.

[M5pilot]

Have to admit the M50 vanos unit is brilliant. I've got it in my 525i Touring at the moment and even with it pulling the heavy touring the top end power is really good.

Engine sounds much much nicer than an M20.

Even in Auto form the 525iT gives me much better MPG than any M20 325i I've owned.

The only problem with the M50 conversion is getting a decent 6 branch manifold to fit!

If i remember correctly Nadz'z 325i made around 160+bhp at the wheels. It was defo a bit quicker than the H26 Hartge's Ive been in.

[Geoff]

Some good responses guys. Its just a question that always bounces around in my mind.

The spec that I would like to build would be

M20 early head, but with Hartge H27 spec (valves, porting and polishing)
284/284 Cam
Ported/Polished Inlet manifold
BTB2 Manifold
Mega Squirt (raised rev limit to 7200)
Striaght through pipes Hartge rear box
BMC Carbon airbox


I think with that spec 225bhp is definately on the cards. And hopefully money permitting someday in the future i'll be able to bosh one together.

What do you guys think? Do-able?

[Turbo-Brown]

Something else that interests me is that lots of people with 205s see TBs as being a necessary part of the tuning process to get the best out of all the other work they've done, like their hairy cams etc.

Practically no one here seems to see the benefit and you hardly ever see them on people's dream spec lists.

[Rosc0PColtrane]

This has bee a reall interesting thread to read. Especially as my pipe dream is to take my 320i cab off the road next autumn and look to replace the engine.

Am undecided which route to go. Obviously I'm going to see a big power gain whichever route I go down as I'm replaceing a 2ltr lump. However, as this will be my daily driver, it needs to be completely reliable but able to put a bigger smile on my face. I also have to consider which is the most cost effective route along with ease to build/obtain parts.

So should it be a 2.7? A standard 2.5? A newer 2.5 vanos? 2.5 turbo?

[Stevin]

2.5 lt M50

Most reliable, cause it's stock and will make some decent power 2... plus u can do the cams branches... etc leaving it still reliable, with a little more go. IMO