HG blown on supercharged MPI
Turbo Mini Forums

Chaps,

I finally got my engine run in and took it down to Emerald for its full mapping session yesterday. Everyhing went well and the car produced god power with bags of torque and it was driving really well.

Anyways half way home i noticed that there was a slight occasional pinking when at full throttle and mid to high revs.

I had just been giving it a bit of wellie and decided to slow down again when i noticed that the coolant temp was shooting up so i quickly pulled over and shut down the engine.

To cut a long story short i was getting water in to cylinder 4 so i take it that the HG has blown. (Big thanks to RAC organising a flat bed in pretty quick time and getting me home)

What could cause the HG to fail the problems/issues i had were as follows:

1) At the mapping session Dave said that the charger was producing 17-18psi !! can this be correct i thought they only produced 10psi when there on the standard pulleys?

2) The coolant temp remained correct on the mid point of the gauge untill the trouble started but the exhaust gas must have been pretty blimin hot as it had fully melted the rear most polyflex exhaust hanger (admittadly this was pushed against the tail pipe)

3) Plugs seem fine with a light brownish coating

4) Whilst on the rollers the car made approx 140bhp but wouldnt make anymore as the fuel began to lean off when held at consistent high revs 5-6k. Dave said that the fuel pressure was dropping off slightly and it was likely that the standard mpi fuel pump wasnt up to the job.

So guys let me know what you think?

Cheers

Have you had the head off yet? Is it 9 stud or 11 stud?

Do you not run a boost guage?

Pull the head and have a look, sounds like too much boost to me, if Dave Walker says it was making 17-18psi then it will have been making 17-18psi.

What charger are you using?

In the 13's at last!.. Just

what is the engine spec Ie compression ratio bore size piston type ect ??

A super one!

How have you reduced the compression ratio?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

one thing you can be sure of is that Dave Walker know's his onions. You really need to pull the head off and take a look. What is your CR

Team www.sheepspeed.com Racing

18 psi without an intercooler = bang.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

OK I've just read some of your earlier threads to get an idea of your spec.

You have a CR of approx. 8:1. This would not normally cause a problem with 18 psi boost.

However, you are using 18 psi boost from a supercharger without an intercooler. As a result your intake temperatures must be very high. This will cause detonation that you describe.

The supercharger is operating around 50% adiabatic efficiency at this pressure ratio. That means that half of the power to drive it is just causing heat!

A turbo would normally operate at about 70% efficiency and then an intercooler would then remove most of the heat produced from the compression.

My suggestion would be to slow the supercharger down to get around 10 psi boost.

Did you do the airflow and blower speed calcs as suggested in an earlier thread?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Cheers for the quick replies

Yes agreed Dave is blimin marvelous on the rollers and i was amazed at how quick he was able to make my engine run very well and he is a throughly nice bloke.

My engine was rebored to 1293 and then assembled by Morspeed. I wanted to do away with the decompression plate so i had them fit Omega FIS 18cc pistons. Im not 100% sure but i think that they may also have taken some out of the head.

The charger is an eaton m45 and the kit is based around the vmax one but i have changed the manifold and induction pipe for the charger to improve flow etc.

The refitted the head whilst they had the engine so im not sure what gasket they used although i did spec a BK450. Ive been trying to get a spec sheet/reciept of them for months but suprisingly it never turns up!!

What would the compression be if they didnt take anything out of the head would it be low enough from the piston dish alone? I will have to measure the CC in the head once i get it off over the next week but i told them that i would be running 10-12 psi of boost not 18psi !

Is it possible to get bigger pulleys for the M45 chargers so that i can slow it down?

Also is it normal for the exhausts to get this hot?

Cheers

Edited by Andy500 on 9th Sep, 2008.

When I was looking for a bigger pulley for the M45, I drew a blank.

I concluded that the only option was to have a smaller crank pulley specially made.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I thought that the M45 with a standard pulley and a a noramal crank pulley would put out 10ish PSI at 6.5k. I know that min is not far off that>

Well i just found out why my boost was so high...... Stu Gurr said i need to run a recirc from the supercharger port (where my map sensor takes off) to the vacuum side of the charger which would reduce the boost to the required level of 10-11psi.

Not a big problem so hopefully i should get it all sorted pretty quick. I just hope any detonation hasnt damaged the pistons!!

I was running at 17.6 psi !

Are you running a de comp plate?

AlexF

"Cars are a lifetime of pain"

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Am running the standard mpi crank pulley and the standard bmw charger pulley. Not totally sure but i think the charger pulley is 69.8 mm or 2.75", will measure it when i get home.

this is how it should read dave

On 10th Sep, 2008 ministef1 said:

On 9th Sep, 2008 Andy500 said:
My engine was rebored to 1293 and then assembled by Morspeed. I wanted to do away with the decompression plate so i had them fit Omega FIS 18cc pistons. Im not 100% sure but i think that they may also have taken some out of the head.

On 10th Sep, 2008 AlexF2003 said:
Are you running a de comp plate?

and coming from a forum mod.....tut tut

Edited by Sprocket on 10th Sep, 2008.

What has that got to do with anything? It was a question being asked?

I'm more interested in the 'boost control' method adopted... This must be dropping an already low efficiency down even more...

Alright chaps,

I measured the charger pulley last night and its 65mm diameter which i believe is the standard eaton/bmw/mercedes/chrysler/mini/ whoever owns the engine rights on them damn things. Started the strip down and will get the head off this evening. Will post pics once ive found any damage.

So how do i drop the boost? Is the recirc acceptable? as its whats Stu Gurr runs on all his engines. I think its pointless droping the compression further to deal with the boost as the chargers are massivley inefficient or do i try and get a pulley manufactured which is 40% larger to drop the boost? But this may cause issues with things fouling.

It all depends on how big the crank pulley is and the ratio of blower speed to engine speed.

How big is the crank pulley?

My guess is that it's 115mm, in which case you are running the blower too fast for 10 psi boost.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Why dont you buy one of the aftermarket changable pullies and get a larger pulley section machined to bolt onto that???

Measure the crank pulley.

I recall the 'super coupe' M90s were a 80mm diameter pulley, so that is a good start. I also recall the Mercedes M45 pulleys were larger than the Mini M45 pulleys.

If you tell me what pulley dia you need, I'll have a chat with my colleagues at the S/C division and see if i can get you a source for a comparable part.

Edited by TurboDave16V on 11th Sep, 2008.