325 turbo confusion!?

[jondrift]

hey, after talking to many different people i am slowly getting more and more confused about my 1988 325 turbo project.

I am yet to find out if i have a low or high comp engine, but i definately have a problem!

I need someone to tell me in really dump and simple sentences the following:

1. If my engine is a high comp engine will it run with a turbo as standard?

2. If i have a high comp engine will i need to change the thickness of my head gasket or is this only necessary on low comp?

3. Same as above for a low comp?

4. Is there anything else i need to change internally to make it run?

thanks

[mattG]

If you have a high comp. engine you can still turbo charge but you can't run to much boost, may be 4-6psi max @ a guess.

Mine is a standard/factory low comp. (later m20 engine) running 8psi std injectors goes very well no problems.

I have now fitted a +0.3mm gasket meant for skimmed heads 40 quid from ecp will fitt new injectors 42lbs and go for 10 -12psi

The lower the compression the higher boost you can run, but then you're into lag and bigger turbos hth

[mattG]

Non-strech head bolts essential

[jondrift]

ok that makes sense. is the 1988 325 se a low or a high comp?

[Kos]

lower comp, however i have said this before, it will only take limited boost. dont read into it that it would be like a ford turbo low comp etc, there is a hell of a difference in a low com engine designed for a turbo application.

of exapmle a standatd cossied engine which is low comp will take 15 psi day in day out, but the bmw one will die at a sniff of that sort of boost.

8psi max, and thats with carfull mapping. any more you will kill it very quickly

[jondrift]

is there anything that can be done to allow for running over 10psi on this engine?

[mattG]

ok that makes sense. is the 1988 325 se a low or a high comp?

Not sure I think low comp. came out in 88, some one might be able to tell from the vin number.

[isTURBO]

Hi

Im not much of a mechanic but from my limited knowledge here goes :

1. Ideally you would want a low compression ratio for the turbo conversion. I think a high comp engine will "run" with a turbo but you would only be capable of low boosts. If you turned up the boost you loose gaskets. So low comp should equal a higher boost.

2.One way of lowering the compression is to change the gasket thickness. Ant advised me to go for an oversized std gasket from the agents on my 323i turbo conversion as it would be a cheaper alternative than the decomp.

You could use the decomp gasket which is the thicker metal one and its more reliable.

I believe the other way to lower the comp ratio involves changing the pistons etc.

3. I reckon if you have a low comp engine a turbo should be more compatible than the high comp engine.

4. Depending on the boost you want to run and the power you want the motor to produce you could go for the forge pistons like wiseco, change the con rods, crank etc. By strengthening these parts you would be able to boost higher and even put on a bigger turbo for more power.


Hope that helps you somewhat. As I said at the beginnig, Im a newbie at this myself so if I were you I would contact Ant who would definately be able to help you and also give Blingsta a call cos hes got a turbo cabrio and is also very knowlegeable on the subject. Ive also seen Kos answer some turbo threads exceptionally well, might want to give him a call too.

Cheers

[Kos]

is there anything that can be done to allow for running over 10psi on this engine?

yep, bespoke low comp pistons and matched rings, non stretch head bolts and a decent head gasket, but them you bottom end may give way, sop a good idea is to stregthen it with ARP rod bolts and sronger and bigger end caps.

the 324 deisel crank is forged steel and good enough to hold 15psi of boost, the standar on in all petrol M20's is cast and breaks. then there are your rods...........

using that engine you have, use non stretch head bolts and a good head gasket ( OE bmw one ) and stay to 8psi. sorry

while we are talking about head gaskets, i dont think you should think a oversized head gasket will act as a decomp plate, its not. the difference is minimal.

[mattG]

is there anything that can be done to allow for running over 10psi on this engine?

You can fit a decomp. plate availible in different thickness' 1mm upwards which bond to the head with a sealant then you use a normal gasket,
or get mechined pistons etc.

[jondrift]

thanks mate, yea i have been in contact with ant, as he did the megasquirts for me, but he's a busy man and i have far to many questions! lol i also have a slight memory problem i think he said something about the serial number with a K in it is low comp, but as my car is at a garage i cant tell for sure!

Is there an easy way to tell for definate that i have a low comp?

[Kos]

a decent multi layered steel head gasket will set you back £200-£300, then fittting a £150, that will let you run a bit more boost, are they are generaly thicker than you usual head gasket, seems a lot but if you think about it this way.....

replace head gasket with OE thiker one run a more boost than you should blow you engine, remove head, skim re fit etc it will set you back the same if not more so an investment now and it will pay for its self in the long run

[jondrift]

yea i guess so!

thanks for your help guys

just need to find out for definate if im low or high comp!

[blingsta]

to my knowledge, if you have the later lower comp engine, then you should use the oversized H/G together with non stretch head bolts which will help lower the compression ever so slightly more, im pretty sure from what info gathered that from this stage on the standard internals are good for upto 350bhp and a safe 10psi of boost with good mapping.. its all about money though! the more reliability and power you want, the more money its gonna cost! Upgrading pistons would be first on my list if my car wasnt my daily driver,. the list for modifying for a turbo conversion is endless !

[blingsta]

yea i guess so!

thanks for your help guys

just need to find out for definate if im low or high comp!

the radiator will tell you if its later or early engine.... does yours have the metal part at the top? or the little bleed screw at the bottom of the rad? or even the water expansion tank.. is it a capsule shape or the bigger square one?

[Kos]

engine numbers is the only way of telling really, rad's and coolant pipes etc can be interchanges as can engines erel

if its from a plastic bumpered car then chances are its the lower comp engine

[blingsta]

true Kos.. but just on the off chance mate.. trying to narrow it down a bit for him

[jondrift]

as i said before the car is not near me at the mo, but i will get the guys to check it out this morning. does anybody know the exact serial number im looking for, for a low comp engine?

ant has already told me but i didnt have anything to right it down on at the time so i can only part remember it!

[blingsta]

i think the K will be the relevant part mate

[jondrift]

yea i thought so!

[Morat]

I think calling the facelift M20b25 "low compression" causes a bit of confusion. It's more like "Lower compression" because its still an N/A engine, just has a little wiggle room for a low pressure turbo conversion. As KOS says in detail, if you're going for anything more than a few PSI you'll need to mod the internals.

[Colonel Sanders]

john volk is runnin 16 psi reliably on a stock facelift with just non stretch head bolts, think its around 350whp. all about the tuning..

[bigbhpwannabe]

last time i asked in here i was told that the standard crank was good for 1.5 bar boost, will be able to post up results of my explosion test on a standard low comp 325 engine lol

[Morat]

Sounds fun I'd be interested in the figures too!

[hairydave]

On a post facelift I would say 1bar is about the limit, that assumes new head gasket (standard) and new non-stretch bolts.

[Kos]

john volk, never heard of them , here's a question how reliable is the car and what do you call reliable ??

i very mush doubt its completly standard with just non stretch head bolts, has it been re built befor the turbo aplication .

if it lasts 2 years 10,000 mile before its tired and needs a new engine , i wouldnt really entertain that and call it reliable .

thay can be mapped to run more boost, but motronic wont cut it, a good stand alone DTA system and mapped to perfection and you may achive those figures, but its will not ba a daily driver and be able to drive it hard like say a factory audi turbo, but you will need to use good non stretch head bolts abd a decent head gasket but dont expect it to last long.

its not the best comparison to compare a factroy audi with lots of money spent on development to a bmw turbo set up costing a few thousand ( well minse going to owe me more than a few thousand ) but i want to build my car to be reliable when driving it hard every day, not have to worry about over heating, head lifting or something breaking.

from what i read here some of the turbo boys are scared to even put the cars down the 1/4 mile strip at the pod incase it goes bang.

why even go down the turbo route if you wont invest the money to do it right and be reliable ??

[Colonel Sanders]

look at this mate, he owns 666 fab
http://www.e30zone.net/modules.php?name ... t=jon+volk

[Kos]

looking at in now !

[Colonel Sanders]

dunno how reliable it is persay, but if you dont hammer it round all the time im sure it could last a while. personally i would spend the money on a proper job. as i have. im up to over 5 grand on turbo an brake/suspension upgrades at the mo.. im skint....

[Kos]

hes got a good spec there, to run it all but as you said, how longs it lasted and how's it driven.

the most i've seen for a standardish m20 was 250-260 bhp , non stretch head bolts, ne OE h/gasket and machined pistons and a different set of rings. it lasted 2 years but every time it was driven it was hammered LoL

[Colonel Sanders]

haha, i aint gonna hammer mine all the time but i will be puttin it up the pod! thats for sure! just bought a hooge ally intercooler to cope as i was gonna use the volvo one but seein as im goin big on everythin else might aswell go big on the cooler... its 3 1/4 inch thick!! aint got a clue what times il do though???

[jondrift]

im pretty sure its the lower compression one now. ive gone for a thicker steel head gasket and non stretch bolts. Will get it rolling road set up somwhere around 12 psi and then ask ant for advice on what psi to go to if i can run any more!
all i have to do now is keep pestering the garage as its been in there for over a month for a job that could have taken me two days if id had the time!

[jondrift]

oh and its got megasquirt from ant, not just the standard ecu. I cant really afford to do anything more to the internals, so ill kepp my fingers crossed than it lasts a year or two, as i dont thrash it all the time (honest)

[ShepsEvo3]

I've been looking into Turboing my touring, it has the lower compression engine but once build, it would have to survive track days and the like. Alot of it is to do with the mapping, although, as Kos and others have said, the engine will only take sooo much before something breaks.

The new Audi S3 has a compression ratio of over 9:1 and runs a bar of boost as standard! I also know of several other "old" cars running high compression (over 10:1 with lots of boost) and make stunning power....but some of them have been built to take it. People seem to be getting braver these days!

[ShakeyC]

I read on many topics you need low compression and you need anti stretch bolts and other bits but why will it not take to more than a few psi of boost? I am surpised thought bmw engine stronger than this?