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De-Comp Plate 

 

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 Post subject: De-Comp Plate
Posted: Sat Apr 05, 2008 11:21 am 
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How much are de-comp plates worth for E series 4.0l's

is there any companies that sell them ?
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Posted: Sat Apr 05, 2008 12:12 pm 
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about $60, permaseal make a nice fitting one.. available in .5 .8 and 1.5mm from memory

 

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Posted: Sat Apr 05, 2008 5:53 pm 
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2nd question. Which is the best solution to de-comp an engine? Opened up combustion chambers? Low comp pistons? Or de-comp plates?

What are the pro's and cons of each?
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Posted: Sat Apr 05, 2008 8:09 pm 
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Ride: AU III XR8 Pursuit 250 ute

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ACL Race Series copper headgaskets are reuseable and avaliable in 0.8 and 1.6mm. Although ACL don't do a decomp plate specially listed.

 

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Posted: Sun Apr 06, 2008 12:11 am 
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The BEST way is to fit lower comp pistons..
But up to 270 rwkw the std comprssion [A.U ll ] can do fine... Plenty have just fitted TWO A.U gaskets...
But it can cause detonation even though it lowers compression... The better quench capabilities with tight deck is much better...
Having said that with these some what small bore engines, get away with it...

 

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Posted: Sun Apr 06, 2008 12:17 am 
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Ride: AU111 XR6 VCT Supercharged

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Thats what I've got (ACL copper 1.6). Don't bother getting unless you plan to o-ring also, as they don't seal very well. I've had lots of trouble with mine, and think it may be blown again as of last week...if so I'd like to investigate opening up combustion chambers to reduce compression a little. Pro - improve flow and reduce compression. Con - I think dished pistons or similar is the best way to do it (but expensive). De-comp plates upset 'squish' apparently, so aren't ideal.

 

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Posted: Sun Apr 06, 2008 12:22 am 
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Ride: AU111 XR6 VCT Supercharged

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'But it can cause detonation even though it lowers compression... The better quench capabilities with tight deck is much better...'

EBXR, how come a decomp plate causes detonation even though compression is reduced? I've heard something along these lines but not understood...

 

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Posted: Mon Apr 07, 2008 11:04 pm 
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NOT so much on these engines...Due to long stroke and rather small bore...
But on V8s where the bore is around 4.00 or larger the fire in chamber hangs around and detonates next incoming charge... With tighter piston to head there is much better chance of swirl in chamber and scavenging out any charge left, with tight clearance there's no room for fuel to burn...

The old M351 and M400 Cleveland engines where well known to be bad detonation engines.. There comprssion was low.. Under 8.5 ?? Yet they still detonated.. The piston was near 10mm down bore.. As a fix to this some smart people fitted pistons with lower pin height.. The strange part is comp was much higher but this engine didn't detonate as bad and economy power was much better..

To use copper gaskets you need to have good s/steel O rings and I fitted thin silicon type O rings around water and oil passages.. Used sealant on both surfaces head gasket [both sides] and block...The O rings prevented sealant blocking coolant and oil galleries...
Not a job to do by yourself!! My turbo V8 is runing copper gaskets.. But now days you can buy MLS or Cometic head gaskets.. The latter AU are MLS...Multy layer steel...

 

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331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
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Posted: Wed Apr 09, 2008 11:24 pm 
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Ride: AU111 XR6 VCT Supercharged

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Thanks for detonation info EBXR.

My car in its previos ownership blew the standard AU gasket, and then a cometic gasket in my ownership. My mechanic at the time fitted the current 1.6 copper gasket as it was a performance item, before I knew what I do about them now! Its not o ringed, so has never sealed quite right (initially starting issues, used chemiweld to improve that, but never perfect). Its lasted the longest of all the gaskets so far though.

Last week the car became low on power, lost throttle response, lost engine breaking compression and the exhaust note has more overun burble. I'm pretty sure this sounds like another blown gasket. Booked in to get it diagnosed tommorow. I'm not looking forward to the cost again, but thinking this time of headwork to reduce compression, and going back to AU gasket will be the go. I think this will be the cheapest way to do it properly? Also considering water/air intercooling to cool charge air and reduce detonation that way.

Any other suggestions/comments re: de-comp methods? I'm keen to get it right this time.

 

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Posted: Wed Apr 09, 2008 11:41 pm 
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Id be looking at other reasons as to why you are blowing head gaskets....

each time have you had the head inspected ? your head might not be 100% flat or something along those lines.

lots of people seem to run boost on an AU motor no worries.....
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Posted: Thu Apr 10, 2008 12:48 am 
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as MMD said, its not the headgasket design that is causing you grief here by the sounds of it...

id say you have some ign timing or fuelling issues to sort.. give us some info on your setup

for example right, heres what ive got and how its performing...

two AU std mls gaskets, one gasket sits either side of a 1.5mm decomp plate, ive been upto 17psi of boost, and running 19-21 degrees of ign timing advance, using ultimate 98 and made around about the 350-370rwkw range... not one gasket issue yet.

 

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Posted: Thu Apr 10, 2008 12:53 am 
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holy crap, 17psi and 20 degrees advance? must be making some good power!

i cant even stik 20 degrees in on 12psi

 

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Posted: Thu Apr 10, 2008 1:47 am 
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Depends on compression.. Mine is 18* at 16 Lb at its peak torque then advances up to 25*,Twisted Wedge heads 7.8 compression...
On a std block your better off with good Fel pro gaskets and new head bolts or better studs....Blown gaskets is a sign of detonation and bad tune...

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

Last edited by EBXR8380 on Thu Apr 10, 2008 11:58 pm, edited 1 time in total.

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Posted: Thu Apr 10, 2008 10:47 am 
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fritzz wrote:
holy crap, 17psi and 20 degrees advance? must be making some good power!

i cant even stik 20 degrees in on 12psi

lol, you know, i was just waiting for this to get a response from you, as i remember a timing discussion a while back..

anyway, just to confirm, i just had another look in my cal file, this is exactly what im running

1bar 22deg 6000rpm 19deg 5000rpm (15psi)
1.25bar 18deg 6000rpm 16deg 5000rpm (18psi)

my limiter is 5800 so you can get an idea of my max timing, like i thought, about 20deg at 5800 at 17psi

 

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Posted: Thu Apr 10, 2008 8:36 pm 
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yes i remember that discussion, back then i think u were running sum thing like 16psi and 14 degrees?.

ive got 18 degrees in at 12psi. on my 16 psi road tune ive got around 14 degrees.

i dont realy have an issue with it any more, i think those are about right for my engine, as the comp is still around 9:1 and cam with little ova lap.

i did have a bad problem with advance when it had stock head on it, would take anymore than 8 degrees at 12psi.

 

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