b25 - what's all the fuss?!

[Cloggy Saint]

After 15 years of 2.0ness I finally put an M20b25 in my touring. I was fully prepared to be pushed back into my seat and for time to slow down when I hit the accelerator but it wasn't the white-knuckle ride I was expecting. It's more eager to pick up from low revs and it's definitely more spritely than the 2.0 but it sure aint the rocket I've been led to believe. Unless my engine is a pup but I don't think it is. Just saying!

[jimbom30cab]

Get an eta crank to stoke to 2.7. Add in a light flywheel, a BBTB and a cam with a proper chip and hey presto a little screamer to enjoy.

[macas]

I was the same till i drove it a couple of days and got the feel of when the power comes in,in which gear etc.

Dont get me wrong its not a rocket but you can definatly feel the big difference from the 2.0

[Brianmoooore]

E30 325 was fast in it's day, but things have moved on, and what was fast then is at the top end or ordinary now. It's not slow by any means, but there's plenty of boring repmobiles out there that can match or beat it in the acceleration department.
Don't bother with all that 2.7 or 2.8 crank nonsense. You'll still be twelve valves short, with fuel and sparks controlled by ZX80 technology.
M52B28s are cheap now, and with the normal mods. to get up to 210+ bhp, your touring would see off most that it meets in a day.

[Jesus325iTouring]

I think my best example was when myself in a 325i (high comp) and a mate in his 320i were having a sprightly drive, we both pulled out to over take a car at the same time (I was behind him), difference was, I wasn't paying attention and floored it, I know he did too, but I nearly crashed into the back f him such was the accelaration difference.
Low comp 325i such as my Touring doesn't have quite the same get up and go, but still a lot more than a 320.

[B7]

You can drive one B25 and it'll feel great and on the money. You can drive another and it'll feel like a knackered B20.

I remember one touring Si and I had and we had to check it was a 2.5. The thing was as sluggish as hell. Yet the original 2.5 in my convertible was a screamer compared. It can be a very different experience, driving two different cars.

[Mitchen]

You can drive one B25 and it'll feel great and on the money. You can drive another and it'll feel like a knackered B20.

I remember one touring Si and I had and we had to check it was a 2.5. The thing was as sluggish as hell. Yet the original 2.5 in my convertible was a screamer compared. It can be a very different experience, driving two different cars.

what's the reason for that Trev? Condition of engine?

[Cloggy Saint]

M52B28s are cheap now, and with the normal mods. to get up to 210+ bhp, your touring would see off most that it meets in a day.

I'm not overly concerned with power, or the lack of it. My b20 was a tired old lump with a noisy gearbox and a mysterious intermittant electrical fault that no one cauld diagnose. The b25 I now have is a sub 100k engine and much quieter and smoother than it's predecessor so I'm happy.

[Jesus325iTouring]

Put it this way Mitchen, I had a 325i on a rolling road recording just 133bhp

Yet I had anther 325i recording 163bhp

First engine was just tired TBH Second engine spent the first 15 years or so you living in a big lazy 5 series before I put it in my Touring.

[Mitchen]

Put it this way Mitchen, I had a 325i on a rolling road recording just 133bhp

Yet I had anther 325i recording 163bhp

First engine was just tired TBH Second engine spent the first 15 or so you living in a big lazy 5 series before I put it in my Touring.

Ah ok, so basically maintenance and servicing.. worn engine, well maintained engine.

Always pondered whether to upgrade the B2O

[Brianmoooore]

With regular oil changes, using decent oil, a the basic mechanical parts of a B25M20 will last just about for ever, without hardly any deterioration from new. Exhaust valve guides renewed and valves recut and cleaned up, and most should be within new spec.
150,000 mile old injectors, non working throttle switches, a distributor cap with worn poles and carbon button, plus numerous minor air leaks, can easily take 30 bhp or more off of it.

[magpie]

the best thing about an m20 b20 is that my 318is m42 p1ssed all over them

[Mitchen]

With regular oil changes, using decent oil, a the basic mechanical parts of a B25M20 will last just about for ever, without hardly any deterioration from new. Exhaust valve guides renewed and valves recut and cleaned up, and most should be within new spec.
150,000 mile old injectors, non working throttle switches, a distributor cap with worn poles and carbon button, plus numerous minor air leaks, can easily take 30 bhp or more off of it.

I presume it's the same case with a B20 right Brian?

[Brianmoooore]

Same with the B20, and any other E30 engine

[pony]

Put it this way Mitchen, I had a 325i on a rolling road recording just 133bhp

Yet I had anther 325i recording 163bhp

First engine was just tired TBH Second engine spent the first 15 years or so you living in a big lazy 5 series before I put it in my Touring.

Mine Sport after 12 owners / 172k mileage was dynoed at 167.8bhp !!!!

[Speedtouch]

A decent chip will bring it alive, particularly if it's a low compression later M20B25.

[pony]

What u need OP is S54 E30 and some big balls !

[Cloggy Saint]

A decent chip will bring it alive, particularly if it's a low compression later M20B25.

I bought a chip from you for this engine a while back!

[Speedtouch]

Ah, but did you fit it? A healthy M20B25 should feel pretty potent still, with good pickup from around 3,500rpm onwards.

[Brianmoooore]

No engine should be considered for a 'chip' until it is running as it left the factory.

Injectors are often the culprit for several lost horses, which isn't surprising when you consider that they open and close around 25 times a second when the engine is running.
100k miles equates to around 3500 hours of running, so it's reasonable to assume that after operating around twelve and a half million times, they might have lost their accuracy, and could benefit from a rebuild.

[Cloggy Saint]

This engine has had refurbished injectors, all gaskets renewed, temp' sensors etc etc. I'm not saying it's slooow, just not as quick as I expected. But as I said, it's a huge improvement overall. The car also got a new prop bearing and guibo, gearbox mounts, arb bushes, gear linkage etc so it feels pretty tight.

[pony]

I have not had my injectors refurbished

Is it worth getting distributor cap, rotor arm, HT leads, ignition coils replaced ? Will I get more power ?
How much power will injectors refurb give me ?

[Brianmoooore]

I have not had my injectors refurbished

Is it worth getting distributor cap, rotor arm, HT leads, ignition coils replaced ? Will I get more power ?

If there's anything wrong with the originals, then yes. Leads (if originals) and coil are likely to be fine.

How much power will injectors refurb give me ?

Every bit that their poor flow rate and spray pattern is losing you.

[325ftmfw]

yeh.. theyre not fast at all lol. Wouldnt waste money trying to get measly NA horses from it either

Turbo it and be done with it. only way its going to feel fast and put you in your seat

[Andyboy]

Don't bother with all that 2.7 or 2.8 crank nonsense. You'll still be twelve valves short, with fuel and sparks controlled by ZX80 technology.

Unless you dislike torque?

A 2.8 crank is a great upgrade. It gives you another 15-20 bhp and about the same lb.ft of torque. It has a higher compression and won't use any extra fuel.
You probably wouldn't take the engine out specifically do do it, but with so many now needing a rebuild it would be daft not to with the engine in bits. A set of 2.0 rods for 50 quid and a single vans 2.8 crank at around 150 quid - it's almost free power.
It's when you start buying expensive cams, exhausts and stuff that it starts to become a bit pointless - you then lose some of the superb low end torque and flexibility of a stroked M20 and in effect build a very expensive version of what an M52 can do as standard.

[sweep]

M20 325i cult classic bmw engine the end..... if you want fast go and buy a golf tdi.

[magpie]

i have an m52 crank and a full set of 320i con rods for sale if anyone's interested also have a 320i cylinder head .....

[Andyboy]

M52's are nice, but a good M20 is still a great engine. It looks at home under the bonnet, a good old fashioned engine for a good old fashioned car.

[pony]

Back in the 1980s M20B25 325i was a big hitter slaying giants such as 635CSi, Capri 2.8i, GTi etc

[HairyScreech]

It is only 35-50hp we are talking here, its not a 150hp jump like an S50 vs b25.

You might find the engine needs a lot of love as Brian has said, a B25 touring should be quick (like hot hatch or 2l saloon quick) but is no way fast like an m3 or similar.

Factor in another 20-25hp by going 2.8 and then it makes more sense.

I didn't find my 320 to be that slow to be fair and the B20 in the e21 is enough for the lighter car to still be quick.

Oh and one huge factor - what diff have you got in it? a b20 with 4.1 feels about the same as a b25 with 3.64 up to about 50.
Combine a 4.1 with a b25 for surprising acceleration followed by diff munching in 6 months time.

[dave525]

Don't bother with all that 2.7 or 2.8 crank nonsense. You'll still be twelve valves short, with fuel and sparks controlled by ZX80 technology.

Unless you dislike torque?

A 2.8 crank is a great upgrade. It gives you another 15-20 bhp and about the same lb.ft of torque. It has a higher compression and won't use any extra fuel.
You probably wouldn't take the engine out specifically do do it, but with so many now needing a rebuild it would be daft not to with the engine in bits. A set of 2.0 rods for 50 quid and a single vans 2.8 crank at around 150 quid - it's almost free power.
It's when you start buying expensive cams, exhausts and stuff that it starts to become a bit pointless - you then lose some of the superb low end torque and flexibility of a stroked M20 and in effect build a very expensive version of what an M52 can do as standard.

+1. Ive done it and my 320 auto cab is a different car.Before you had to be 3500 rpm plus before it would go,then it went ok. now it just pulls hard,especially in top. The torque is the key.

[HairyScreech]

That's because of the size of the ports on the b25 885 head, the airflow is sluggish until higher revs as there is not enough flow volume, making the cylinders 300cc larger by lengthening the stroke helps move this further down the range.

On the B25 the cylinder filling is poor until about 3000rpm like a car with a cam that is too big.

The low compression of the late engines makes this effect worse.

[pony]

So basically high compression engines Sports are lighter and quicker than low compression engine Sports ?

[Andyboy]

So basically high compression engines Sports are lighter and quicker than low compression engine Sports ?

Certainly are - but later ones have the lower 3.91 diff innit.

[pony]

I have a rebuilt BMW LSD 40% lock 3.91 rebuilt by Gareth with New Genuine BMW Z3 M Coupe diff cover / gasket / washers / bolts

40% lock for more sideways action
3.91 so can embarrass newer BMWs