Need to lower compression....

Skimmed pistons?
or
Decompression plate?

(havent got the funds for low comp forgd)

 

Why do you need to lower the c/r mate?

 

you planing to got zvh, or full zetec ?

 

Had the head skimmed on an engine rebuild and i think its had a fair bit taken off. So now its all put back together its pinging a hell of a lot. Been through every possibility of it being running and fueling issues and even still on tesco 99 its still pinging.
Had it diagnosed the other day and they reckon its more than likely the compression ratio on the std pistons after the heads been skimmed.

 

+1
Also whats your current spec?

 

Air Filter
full s/s exhaust
chipped ECU
-31 actuator
airtec front mount.
group A coil + motorsport leads.
running 15psi.

 

1.6 CVH yeah?
Why do you want to lower it mate?

 

yeah 1.6 cvh yeah.

Well ive been told that pinging engines can be a sign of a higher compression ratio. I think the head thats on my engine now has been skimmed twice. So im guessing that could be accounting for the compression issue?

 

but yeah, does anyone know the pro's and cons of either.
skimmed pistons or a decompression plate?

 

If your pinging (Detonating), then your lean, timing is too advanced, or your running to much boost!
A setup will sort that out, or if you want to do something now to save an engine then retard the timing to 8degrees BTDC (if it's not already), run V-Power 99RON, and turn the boost down a couple of psi!

Why do you think it's Det'ing?

As far as skimming pistons, or decomp plate i'd do neither!
Skimming stock RS pistons will just reduce what BHP they can take and a decomp plate will alter the shape and size of the 'squish' area and as a result your burn pattern which if your really unlucky could actually increase the chances of Det!

 

Well this issue occured on the rollers whilst being set up.
and it just got worse and worse to the point where the timing was retarded right back and the boost knocked off. Yet its still det'ing at around 6psi.

At first I thought it was a fueling issue, but after renewing the whole fuel system the problem is still there.

 

who was doing the set up?

 

Woah!!!
Must be a fuelling problem surely?! Did you renew with all new parts or second hand?
Unless your compression really is that high?? Have you done a comp test? Freshly built RS should be about 175psi (12bar) across all 4, plugs out, WOT, warm engine, 10sec crank.
If it comes back at like 200psi+ then at least your know?!

 

well thats what i thought,
brand new pistons, freshly honed bores, band new rings. all points towards a nice bit of compression. However, if the head has been skimmed twice, you could be talking 1-2mm difference.

getting a comp test done in the week, so see what happens.

 

Mmm would really need to know the measurements i.e how much exactly has been taken off the head....pity you hadn't measured the c/r when building it if it's had that much taken off the head. The reason i say this is because you can run pretty big bhp on standard c/r and higher c/r's too, mine was running 245bhp with no detting issues on standard c/r pistons with a head that had been skimmed a couple of times (1.5 bar boost) so if the engine's fine i'm sure someone who knows what they're doing could set it up ok. If you need to lower the c/r slightly you could always take a bit out of the head (the bowls) instead of skimming pistons, would need to be done accuratly though etc but i wouldn't be too sure that's your problem, especialy if it's still detting running such low boost......

 

The car was set up at northampton motorsport.
The car made 160bhp on its old engine no bother. Until the big ends became worn which is why its had a rebuild. Also nothing has been changed on this new engine except for a better coil and some leads.

Also a c/r test is about the only thing i havent done. lol

I mean onto the list of things that im now going to try is a new metering unit off a 200bhp engine (as mine has never seen larger ammounts of power), get the injectors tested and go for a compression test as well. Going for the process of illimination! lol

at least this way everything will be sweet. touch wood.

 

dont be thinking that you can do a compression test and find out what cr your engine is because you cant. you would need to take the head off and measure it. and there also aint a squish area on the cvh, but saying that you still dont want a decomp plate.

 

Thats right you wont find your C/R but you will at least know what your compression is compared to what it should be (175psi).
I thought the squish area was the space left above when the piston is at TDC and so it applies to every engine, is that not right?

 

wouldn't it be easier to buy another std head rather than skimming pistons?

 

Were the chambers in the head de-razored after the skim? if not then this could be the cause.

 

De-razored? whats that when its at home lol. not heard that before

 

decomp plates ive heard are a nasty cheap way of lowering compression and not safe at all as its basically a cheaply made double head gasket.

 

Yeah thats what i thought.

Like low comp pistons are ŁŁŁ's and these decomp plates are Ł30! sounds to good to be true, wondered if anyone had ever had an success with them.

Got a comp test lined up this week to see what comp the chambers are making see if its a bit high or not.
New metering unit and getting my injectors tested as well incase its a fueling issue instead.

Im just a tad confused, the car used to run sweet before the engine rebuild, now its just gone to shit lol

 

sounds like maybe the metering head has died m8,like u said a new one might sort it.everyone knows mfi is unreliable,thats why i wanna go efi with mine and ive took it off the road

 

Yeah im gonna see what happens. Would love to go efi but i really odnt have the money, and im not after huge ammount of power. Id be happy with around 160bhp which it was, i just want it to work again. lol

 

lol yea ur runnin the same specish as mine,but mine needed to come of the road,an thats were its staying now until its done.thousands of ŁŁŁŁss later though.like urs alot m8,nice wheels,i love white wheels

 

thanks man. it doesnt look to great in the flesh, the old red paint is starting to look a bit tired.
but at the moment its "power not paint!" as a friend put.

Well its been off the road now for a few weeks while i did the sump gasket twice! as is the case with the cvh. Then went to start it again and it wouldnt idle. Somehow whilst doing the sump gasket my brake servo had split!! (gotta love these old cars) then with the whole det thing getting worse and worse I'm starting to lose hope.
Came so close to getting rid of it last week after the tools went flying across the yard for the 1000th time! 3 years ive had it, and i just want it to work :'( lol
But i keep saying to myself, what would i get to replace it, and the fact ive just spent ŁŁŁŁ's on the engine rebuild, new suspension etc... it just seems silly to give up.

 

too fcukin rite dont give up man,uve had it 3years and spent loads on it,bet wen it works u love it.ive driven mine 3 times at about 10 mins a time and then it got put away,but i love it,love when it comes on boost an how quick it feels.ive only just started on my project really but i know its gonna cost me bout 20k but wouldnt wanna spend it on anuva car,thats fo sure,dont give up m8.

 

What I think:

1.
Skimming the head twice hardly makes over 1mm difference to original.

2.
If the head has been overly skimmed, the easiest remedy is another head.

3.
Even standard carb CVHs with the 9.5:1 CR run over a bar of boost easily with a large front mount IC.

4.
Decomp plate would be my last choice for this.

5.
The original pistons have 7mm of material on their crown. Taking 1mm from the center is perfectly ok. (Don't reduce the distance from the crown to the first piston ring, so only a bowl in the center)

6.
During the setup, surely the AFR was recorded?

7.
Check your plugs. Is it a problem with only one cylinder?

8.
Running a large front mount IC and 15 psi of boost, I would personally like to have a compression higher than standard. If the engine can't handle it, you have a problem somewhere.

9.
Do the compression test.

10.
Have you checked that the ESC-II ecu is doing it's job at adjusting timing with the MAP reading.

11.
You do have the MAP hose connected, do you?

12.
You can measure the head total thickness even when it's on the engine. Compare that to standard or guideline value from manual.

 

lol I think he means having the sharp edges from where it was skimmed removed, they can get hot and glow (like a glow plug) and cause pre-ignition.

 

what about your timing have you backed it off to see if it stops,

 

Oh right lol, yeah that was done.

 

Well my metering unit came today, and tbh.. im not happy. Its is a right state, there is no idle screw and its a series 1 metering unit.
is there any difference between the series 1 and 2 metering units, other than the position of the fuel lines?

 

S2 has an aluminum bottom section that has separate locations for the boost control valve return air hose and the crankcase breather hose.
S1 version has a plastic bottom section, more travel for the air flap, and only one location for breather hose. The boost control hose is T-ed together earlier.

 

ah m8,savage,sounds like it wont work.check in the rs turbo for sale parts there was a guy selling 3 rs turbo metering heads cheap,an they looked mint

 

Just had a good look at this metering unit and the bottom half is broken where the bolts attach so it wont fix to the car, and where the idle screw is missing it has been filled with silicone?!!!?

 

 

Oh BTW it's the idle mixture screw, and was probably siliconed after the mixture was set last, if you are going to use it somehow it's not a big deal just dig out the silicone and replace with a screw to stop the air leak, or even a rubber bung!

 

Im not going to use it because of the state that its in. I dont even know how i would get it to stay in the engine bay.
Pretty pissed off tbh when i was told "came off of a 200bhp engine" "is in full working order"

 

Yeah dissapointing mate! Did you pay much? Ebay I guess?