problem with decomp plate

[Andyboy]

[RowdyBurns]

Hmmm, the comment about Cosworth YB's says it all really.

Does it say that I helped build, and mapped the fastest BMW engined E30 at a the PBMW brunters thrash a few years ago???

Mate, I helped build an engine for an Audi Quattro that won the 1/4 mile at GTi International. Yes, I washed the block in a parts washer and took all the bits to and from the machine shop. Doesn't give me the right to come here full of 'know it all' attitude.
As in most things, those who shout the loudest know the least and I'm surprised a chap of your undoubted expertise hasn't made himself a big name by now.

As for decomp plates - please show me a standard production turbo car that has one.......

Maybe i should have said "I MAPPED and helped build.....

I was just trying to show relation to your E30 world as it had been suggested i had a cosworth YB habit.

[RowdyBurns]

[Andyboy]

Who are Hartge???

Oh come on!!!

Anyway, to your assertion that my comments about decomp plates being a bit iffy are 'probably crap'.

Hmmmm. Decomp plates to me are like wheelspacers. Sure, Ant has made it work (and I'd expect nothing less) but an M20 cylinder head has a lot of meat in the chambers to be removed - particularly the 325i head. So rather than using a bit of machined tin, why not dust off that burette and starting with a standard chamber volume (you know, cyl vol plus chamber vol divided by chamber vol - not forgetting to add the volume of a compressed - i.e used - head gasket to the equation) open up those chambers? The standard CR is just 8.8:1 so when you've added a fatter HG you're not going to have to remove that much to drop the CR below 8:1.

Obviously this will cost a lot of an engine builders expensive time (and therefore your money) but ultimately it's a far nicer solution. Decomp plates are used on YB motors because the four valves don't exactly offer much scope for head doctoring. YB heads are a lot shorter and don't have anything like the potential for bending. And in this guy's case, the decomp plate just didn't work. Maybe he's still using standard head bolts which will not only stretch under boost but because of this fat plate between head and block won't engage fully in the block threads.

[RowdyBurns]

I have never seen a decomp plate used on a YB in my life??

You are right about re shaping the chambers though. Much more do able on a two valve head.

[e30_Turbo]

[Maybe he's still using standard head bolts which will not only stretch under boost but because of this fat plate between head and block won't engage fully in the block threads.

He's using 12.9 grade non stretch bolts, like Dimmy, Erel, myself, Ant, Fowler etc Hass's are also 160mm long which means he uses as all of the thread there is and some of the unthreaded space too, we discussed this at length ( no pun intended ) before he purchased them.

It's not the bolts, having spoken to Hass the other night he's thinking it may be a cracked head afterall.

All this talk of head work, anyone got a rough cost for removing enough meat properly from a 885 casting to lower the CR to 8:1?

[RowdyBurns]

What is the bore, stroke and CR of a stock engine with an 885 head casting?

[Andyboy]

No idea, but it wouldn't be cheap! I reckon removing the raised bit that corresponds with the 325i piston crown would do it. You'd just need to do one gradually and keep rechecking the volume and then do the other five to match.
You'd need to increase chamber volume by around 10cc to get the CR down to 7.4:1. You'd need to compare the volumes of compressed standard and thicker head gaskets to see how much you can gain there.

Another alternative to be looked at during the engine build would be offset small end bushes to bring the piston down 1mm in the bore.

[Andyboy]

What is the bore, stroke and CR of a stock engine with an 885 head casting?

84mm bore, 75mm stroke, 8.8:1 compression. The total chamber volume including piston dish and standard gasket is @53.5cc's.

[RowdyBurns]

If you had a spare head we could put a bandsaw through it to check material thickness, get another chamber 3d scanned, put it into solidworks for me to change, and then re-shape on a CNC mill.

[e30_Turbo]

I have a spare head!!!

Rowdy, Shall I drop it by your workshop? Round the side be ok?

Do you need cam and rockers in it? ( IIRC it's just teh cam in there, rockers and shafts are just laying in the casting, it's been skimmed to death which is why it's not being used anymore )

Mark.

[Demlotcrew]

My customers??? As you have implied that you have customers I take it that you build engines for a living?

I build engine/work on cars as a side job. Im not a garage or am i trying to be. (Thanks Andy, but im not getting into a pissing contest with 'Big D-')

Yes of course static CR effects dynamic CR

So whats the problem? Hass (the thread originator) has said nothing about the spec of his engine, so am i to assume? NO because assumptions end in tears.

Correct me if im wrong but the whole point in having a decompression plate (the clue is in the name) is to lower the compression as its easier and in most cases cheaper than sticking in different pistons, decomp plates also have other advantages such as being easier to calculate the thickness needed to get you to the compression ratio you are aiming for. (as everyone has different ideas on what a fast car is) But it ends there. Show me an engine making reliably 40-50% more power with a decomp plate and a stock head gasket over an engine with a multi layered oversized metal gasket or an engine with a decomp plate and sleeved bores. Oh thats right you cant.

but a head gasket change effects static CR unlike cam timing as you mention above which does not effect static CR only dynamic. Can you see my point?

Yes i see your point, but its only valid on cranking pressure. And as you quite rightly pointed out "static CR effects dynamic CR" (i think you meant affects ) but im sure that if i had originally said static you would have chimed in with "What a load of crap!" anyway.
It seems that your input to this thread has been pure willy waving and nothing more. You have given no solutions to the problem, and as soon as you do then maybe ill take you seriously.

I believe my comments are highly related to the original thread and its replies. Are you going to ban me for questioning some of the dubious replies given as advice?

Show me one dubious reply. And if you cant BAN

[e30_Turbo]

@ Andyboy

Do you mean the small crest in the combustion chamber? If so I did have a go at removing them but figured there was no way I could get all six the same, so I wimped out and fitted the thicker HG instead, whoops, won't be doing that again.

[Demlotcrew]

If you had a spare head we could put a bandsaw through it to check material thickness, get another chamber 3d scanned, put it into solidworks for me to change, and then re-shape on a CNC mill.

Yeah and that will be easy to replicate time after time after time on each cylinder chamber and head.

It will also be cheaper than six new low comp pistons, im sure you will get quite a few takers on your offer from the Zone

[Andyboy]

@ Andyboy

Do you mean the small crest in the combustion chamber? If so I did have a go at removing them but figured there was no way I could get all six the same, so I wimped out and fitted the thicker HG instead, whoops, won't be doing that again.

Yep, that's the one, griding it away to the chamber looks more like a 320i head. There is loads of meat in these heads as i cut one in half with a bandsaw for a laugh. I don't think it would be too much of a problem with a decent die grinder. It doesn't have to be a work of art and you could use some 240 grit and do the final bits by hand to equalise them.

[e30_Turbo]

Hmm, food for thought IIRC Ant's mentioned the same thing before but each time I had the head off and the tools ready I talked myself out of it. When I get the water channels welded up I'll have a go then, before the skim it for the last time. I work with a engine builder ( Dunnel ) who have a lovely setup with all the toys and they sort the machine work out for me, they know what's what and I've spent some time with them while blueprinting a zetec, which I have to say was so unbelievably complex it blew my mind, so maybe they'll be up for a challenge, they've laughed at the M20 head everytime I've taken it there but they're happy as long as it's for something special and they have a soft spot for nutters like me.

Would you happen to have a pic of the head in half? If not then I'll drop the spare one I have to Rowdy and see what's what. I like the CNC idea very much, having used CNC lathes & milling machines etc before I much prefer that sort of manual labour

Mark.

[RowdyBurns]

Show me an engine making reliably 40-50% more power with a decomp plate and a stock head gasket . Oh thats right you cant.

Oh but I can!



If you can make out the numbers it reads 298.5 bhp up from an original reading of 194 bhp.

If my maths is right i'm pretty sure thats an increase of nearly 54%

This was the first run we ever did and later on after a bit of tuning and some higher octane fuel it made nearly 330 bhp. Thats an increase of 70%

It ran for a few thousand very hard driven miles like this before it was destroyed in an accident.

This car was running a aluminium decomp plate and a stock headgasket! Amazing hey?

Bet you will ban me now i have proved you wrong

[Andyboy]

By Jove he's right. Turbo M50 eh?

[RowdyBurns]

[Maybe he's still using standard head bolts which will not only stretch under boost but because of this fat plate between head and block won't engage fully in the block threads.

He's using 12.9 grade non stretch bolts, like Dimmy, Erel, myself, Ant, Fowler etc Hass's are also 160mm long which means he uses as all of the thread there is and some of the unthreaded space too, we discussed this at length ( no pun intended ) before he purchased them.

It's not the bolts, having spoken to Hass the other night he's thinking it may be a cracked head afterall.

All this talk of head work, anyone got a rough cost for removing enough meat properly from a 885 casting to lower the CR to 8:1?

Mark,
Are you running a standard thickness HG? If you are you will need to remove 6cc from each chamber to achieve 8:1 static CR. Have you got any pictures of a combustion chamber from an 885 casting?

[RowdyBurns]

Yes i see your point, but its only valid on cranking pressure.

Static CR is not a measure of cranking pressures or cylinder pressure at any other point.

It is a ratio of two physical volumes. How much you fill those volumes is what most people refer to as your dynamic CR.

A thicker HG changes both of those physical volumes hence static CR.

[Demlotcrew]

Andy thats the print out of that Blue M3 which rolled at the photo shoot.

Here is the spec;

STD 2.3ltr s14 engine with 2mm decomp plate (now 8.7:1) from ferriday engineering i believe as they have the S14 plates on file ready to produce.
Garrett T3 turbo with 0.63 exhaust housing and T04 compressor side. I think its called a T04b but i'm not sure as i built it myself.
Megasquirt fully mappable engine management with Ford EDIS4, crank sensor and coil pack. (mapped by Doug )
Home made manifold and 3" stainless steel exhaust.
Ford cosworth fuel pressure regulator.
525cc/min Delphi injectors.
Pace RS500 size intercooler core with homemade end tanks.
2 1/2" boost pipes throughout.

A pic of the engine bay.



Thats probably the best example you will ever find. The S14 is a very strong engine and descends from FI anyway so has that reliability built in.

See how it makes power really low in the RPM range, im almost 100% sure its because of the cams being retarded so much with the decomp plate. There is no mention of adjustable sprockets to take up the extra head height (2mm)

Hass i believe that you need to use a thin smear of high temperature non-setting sealant around the water & oil galleries between the 2 metal surfaces only.

Andrew

[fowler]

he was told about the sealant when he got the decomp plate !!!!!!!

@demlot
Baby turbo on that s14

[Demlotcrew]

@fowler
It doesnt need to be anything bigger on a proper engine

[fowler]

Its still missing 2 cylinders !!!! LOL

[e30_Turbo]

Mark,
Are you running a standard thickness HG? If you are you will need to remove 6cc from each chamber to achieve 8:1 static CR. Have you got any pictures of a combustion chamber from an 885 casting?

I'm about to run a cometic MLS slightly thicker than stock steel head gasket along with ARP head studs and some modded pistons. The spare head I have is free to you if you want it. I'll try find a pic or two of the old head I have. Found one.....see where it blew out on 6 that time.
(DET killed it, IAT's were 45+'c )
Mark.

[e30_Turbo]

Or this one:

[fowler]

oooH shiney wheres cliffy !!!!

[Andyboy]

S14 Turbo

You wouldn't break that in a hurry...........

Fozzy is that head new or beadblasted and skimmed? Looks too nice to use!

[e30_Turbo]

IIRC that's a fresh head, new casting and just had valve seats sorted.

It's amazing how quick they lose that fresh look

[Ant]

My spare head perchance Mark ?

[e30_Turbo]

My spare head perchance Mark ?

No not that one, the other spare one.....

[Chris-W]

Another nice one

[maxfield]

Its still missing 2 cylinders !!!! LOL

It has the extra valves to make up for it

[Jhonno]

It ran for a few thousand very hard driven miles like this before it was destroyed in an accident.

to be fair tho a few thousand miles is nothing.. these engines are reliable for 250k looked after..

[hass]

he was told about the sealant when he got the decomp plate !!!!!!!

@demlot
Baby turbo on that s14

yea i did put the non setting sealent (curl t) i think
erel (blingsta) gave it to me