head gasket and de-compression plate questions

[basil]

i own a 325i turbo (87 engine hi-comp) and am going to change the head gasket as its on the way out. I was de-bating weather to put a de-comp plate on, has anyone done this? if so is it worth it how much and where can i get one?. Im also wondering what headgasket is best and where to get it from and how much? im not planning on putting the boost past 7psi.
thanks for your help

[e30_Turbo]

i own a 325i turbo (87 engine hi-comp) and am going to change the head gasket as its on the way out. I was de-bating weather to put a de-comp plate on, has anyone done this? if so is it worth it how much and where can i get one?. Im also wondering what headgasket is best and where to get it from and how much? im not planning on putting the boost past 7psi.
thanks for your help

The de-comp plate has been tried and is used on a A-Tech conversion, M20B25 turbo, seems to work with no issues and A-Tech can supply them No idea on price, give Ant a call

But if you're limits are set at 7psi then a stock compression & head gasket will be fine, they're supposed to be good for about a bar aslong as they're held down tight enough.

Have you fitted uprated head bolts?

And have we seen pics of your car yet?

HTH, Mark.

[basil]

no my engine is totally stock thats why i dont want to go any hire than because i want re-liability etc. which head bolts do you recomend? as im going to do the head gasket i want to do it properly i posted pics last summer if you search in the photo gallery for turbo cab you will find it

[BimmerBoi]

soz to jump the post but what sort of bhp do you get on standard compression at at 7si, regards

[e30_Turbo]

soz to jump the post but what sort of bhp do you get on standard compression at at 7si, regards

Alex was seeing 270bhp & 240ftlbs @ 7 psi on his M20B25 twin turbo.

[Turbo-Brown]

Make everything as free flowing as you can and that should be attainable for all

Especially exhaust back pressure, no little turbos guys! Either one big one or a couple of littler ones.

Next restriction to concentrate on is the IC, but the Volvo ones that fit easily have quite large flow areas by the looks of it.

Last up is the inlet manifold and throttle body which are probably the largest restriction on the inlet side of things.

Mark, you couldn't connect a pressure gauge up to the output of your turbo, and reference it against the manifold pressure you see could you? Be interesting to see what the pressure drop accross the IC, plumbing and throttle's like.

If you could take a reference from by the head somehow (probably not practical thinking about it) we could factor in for the manifold too.

Will do the same for mine and we can compare numbers

[e30_Turbo]

Make everything as free flowing as you can and that should be attainable for all

Especially exhaust back pressure, no little turbos guys! Either one big one or a couple of littler ones.

Next restriction to concentrate on is the IC, but the Volvo ones that fit easily have quite large flow areas by the looks of it.

Last up is the inlet manifold and throttle body which are probably the largest restriction on the inlet side of things.

Mark, you couldn't connect a pressure gauge up to the output of your turbo, and reference it against the manifold pressure you see could you? Be interesting to see what the pressure drop accross the IC, plumbing and throttle's like.

If you could take a reference from by the head somehow (probably not practical thinking about it) we could factor in for the manifold too.

Will do the same for mine and we can compare numbers

So I'll need to have a reading from just after the turbo outlet and just after the intercooler?

Hmm, what could I use to record that info.....maybe some pressure sensor's rammed into the silicone after each, got to swap that out anyway as it's pretty old now.

I've been thinking of chaging my IC now anyway as it's really not big enough, IIRC it was originally on a GTI-R but has the end tanks remade to suit. It flows bottom left to top right so I think I need bigger one which is just east to west.

Ants been supplying som ereally nice IC's, guess I'll running my A-Tech tab up a little more

[Turbo-Brown]

Be interesting to see what sort of restriction the throttle represents too.

I've got a take off just after one of the turbos, and takeoffs right next to the head too so if I do the same exercise we should get the same plumbing, intercooler and throttle losses as if you can measure the manifold pressure......I think

[e30_Turbo]

Be interesting to see what sort of restriction the throttle represents too.

I've got a take off just after one of the turbos, and takeoffs right next to the head too so if I do the same exercise we should get the same plumbing, intercooler and throttle losses as if you can measure the manifold pressure......I think

I see where you are coming from

I'm swapping the wastegate feed from the compressor housing to the inlet manifold so both ECU & WG see the same boost level, that will leave me with a spare output on the turbo.

If I can get a gauge ( boost gauge I was thinking ) rigged up to the compressor I'll have pre-intercooler and post intercooler pressure readings, only thing is I can datalog the MAP sensor readings but not the extra boost gauge...... hmmmmm Maybe I just need a passenger for a hour or so!

[Gunni]

The only reason for stronger bolts is NOT the boost levels,
it´s when you get detonation and or pinging, to not allow the head to stretch the bolts to destroy the headgasket,

[Turbo-Brown]

Anyone know what the peak cylinder pressures are likely to be with a good bout of knock going on?

Interested to know what the force on the bolts is if we assumed that each cyl has 4 fixings and an area of 5.19sq"

And then what we could expect the deflection of the head to be if it were just covering one cylinder (worst case scenario)

SO...step right up with your best peak cyl pressures guys

[benjy]

A std figure of 192 bar creeps into mind, but divant quote me like!!

[Turbo-Brown]

Hmmmm, based on nothing at all, that sounds quite high to me. That's 2822.4psi whereas I've got around 1500psi stuck in my mind.

Be interested to find out for sure, ballpark that is. Sure there are a thousand and one factors affecting it

[Gunni]

To reply,
Cylender pressure sensors range from 50-250bar.
So it´s in the range
This is similar pressure as in a brake system

[Turbo-Brown]

Fair enough, that is high