silent running

I'll keep it simple: my build is an EJ20 CDB, ported/polished STi3/4 heads, ARP head studs, Wiseco forged pistons coming out +0.25mm over the deck. Do I go with Cosworth 1.1mm head gaskets or Cometic 1.3mm? Either would give me the 0.7mm minimum clearance I need, but obviously the 1.1mm will give me higher compression. Any expertise welcome on this, plus this will be all mapped up eventually, so if I can run a decent bit of compression to improve fuel economy / off boost response, all the better.

steviecrump

comitec 1.3 mm
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frayz

iTrader: (7)

What compression ratio do you want to run?

silent running

Well there seems to be no fixed idea of what the CR even is as standard - some say 8.0:1, some say 8.5:1, some say in between. I'd prefer 8.5:1 really as it's a fast road car/commuter/family wagon most of the time and petrol isn't cheap, it'll be mapped for it and I use V-Power anyway. I'm thinking I already must have increased the chamber volume a little anyway with the mild port and polish I did in there. I wonder what the additional 0.2mm of head clearance equates to in terms of CR change?

YOu can see I'm leaning towards going with the thinner gaskets unless I hear horror stories not to! My secondary target is that I want to see what an EJ20 can ultimately make with a TD05-16G, everything will be in place and a decent CR will help efficiency, surely?

dazdavies

iTrader: (22)

My 2.0L with wiseco's ended up being 8.35:1
That was on version 5 engine and standard thickness gaskets.
Not sure if that's actually any use to you.

silent running

What thickness are the standard gaskets? I know the v1-4 get a slightly taller piston. How did you work out your CR and what sort of boost and power did it make in the end? I really want to know if say an 8.5:1 CR will work well up to 350bhp, up to 400bhp (possible 20G conversion in the future)? At what power level do we say, right, get that CR down to 8.0:1 to work best?

Legacy_Turbo_EJ22G

What CR you can run is all dependant on what fuel and turbo you are running.

8:1 CR was something they used before, when the technology both in engines and turbo`s were low, which gave massive backpressure, leading to low CR to help the engine survive

For a comparison, a built engine over here ran 9.4:1 compression, and boosted 2bar, made 700bhp on straight 98 pump fuel, all because of a properly built turbo with low backpressure.

Putting a ineffective 3082R on your car makes you need a low CR, a effective 3071R will allow you to run higher CR, and make more power both on and off boost! Just for an example.

stoneface

iTrader: (6)

Std thickness is 1.3 for v1-4 and 0.6 for v5>phase2.

dazdavies

iTrader: (22)

I think the standard Gaskets are 0.6mm on the V5 not 100% on that though.
CR was given by wiseco themselves. Everything was standard fit so no additional valve sizes and no skimming was done.

Power wise the engine was awesome and seemed to breath really well and was incredibly smooth. It made 358bhp at 1.5bar on a VF28. There were loads of other mods as everything was inplace for a bigger turbo (740's, headers, 3inch exhaust, parallel braided lines SX FPR, FMIC and a power FC)

This was on SC's rollers.

I would go with the thinest gaskets that give your pistons the required clearance. you should aim for any where between 8.3 and 8.5:1 this will give you a very responsive engine that will cope with anything upto 500bhp quite nicely.

iirc the gaskets for V1-4 were 1.3 mm

silent running

Sounds like the 1.3mm are right, as standard, for v1-4 which is what I have. I'm more and more inclined to go with the Cossie 1.1mm. If yours is running 0.6mm clearance (assuming pistons on the v5+ come up flush with the deck) then that's no different to me running 1.1-0.3mm(being generous)= 0.7mm clearance.

I used to have a turbocharged Clio 16v running something like 7.5:1 CR (down from 11:1 when normally aspirated) and that was absolutely gutless off boost. I don't want to go back to that and want more flexibility in the midrange, so sounds like 1.1mm is the way forward.

dazdavies

iTrader: (22)

I'd stick with the standard gasket size mate. Mine was the standard size for my engine and as I said it was a lovely engine.

silent running

Well I've plugged in the numbers going on the only info that I can find that says the phase 1 chamber volume is 44cc. So putting in bore/stroke/chamber vol/gasket bore/gasket thickness/deck clearance/piston dome I get:

Cosworth 0.78mm = 8.289:1 CR
Cosworth 1.1mm = 8.072:1 CR
Cometic 1.3mm = 7.937:1 CR

Seems that the CRs are on the low side for the gasket thickness, until you factor in that the overbore to 92.5mm has added around 5.5 cc to each cylinder as well. So anyway, the 1.3mm thick is ruled out. I'd like the thinnest 0.78mm, but don't think it gives enough piston to head clearance, Wiseco recommend at least 0.030"/0.76mm, so they are probably more suitable for the v5+ engines. It appears that the 1.1mm are the only choice then?

dazdavies

iTrader: (22)

It's not something I'd like to guestimate

ticky

I used this to help me work out my cr:

Engine Compression Ratio (CR) Calculator


I ended up using thicker h.gaskets, even though I should have used the thinner type but then my inlet manifold bolting holes would not line up using the thinner gaskets.
Phase 2 short engine with phase 1.5 heads.

I thought phase 1.5 were 46.5cc?

Ticky

bandit1216red

why dont u assemble 1 side with no head gasket but use grease on the gasket faces with a piston at tdc and tip engine on its side and measure it with a burette and thin oil thro the plug hole till oil reaches bottom of threads
then do the maths for the swept volume
that way yall know exactly what comp ratio u have with no gasket and then work out what thickness u want to get the comp ratio u want
also alow for rod stretch , piston crown expansion in ya final figures for piston to head (squish) clearances

silent running

Well I've just done it sort of the other way - taped over the plug hole from the combustion chamber side, then used a 1-5cc syringe to see how much it will take to fill up the chamber. And the answer is 52cc...

Your idea is a good one though, but won't oil (or any liquid) simply 'leakdown' past the ring gaps, even if only a little? The piston crown to squish area is the main clearance I'm worrying about because it will be fairly tight. Now I'm thinking of going back to the 1.3mm just to be on the safe side which will give me roughly 1mm of 'squish clearance' around the circumference of the crown at TDC.

Anyone got a definitive target squish clearance that I can work to?

silent running

Ticky, where did you get your CC figure from? I only found one thread on SN about it...

bandit1216red

lol if u did what i thought u have all you have done is measured the combustion chamber volume with the head on the bench ya could have put a spark plug in for a more accurate reading and used a piece of perspex greased with 2 small holes in on the gasket face
be aware that the piston MIGHT protrude into this volume so it MIGHT be SMALLER than you have measured
ok if ya do as ive suggested in the above thread you can use grease to seal above the piston ring so the oil stays put
bear in mind this is a turbo engine not normally aspirated so dont go 2 high on ya comp ratio and leave plenty of piston to head clearance

bandit1216red

also id dry build it without a head gasket
1/ do the comp vol measurement on 1 cylinder
2/ put blue tack on piston crown on other cylinder and turn engine over strip it and measure thickness of blue tack it will squash where things are close
ie head to piston and or valve to piston
then add ya gasket thickness whatever u decide to use to increase the clearances
if ya cant get what u want its machine shop time
feel free 2 ask me either in here or pm or ring my mobile

merlin24

iTrader: (1)

Safe Quench between 0.035~0.040" or 0.889 ~1.016 mm.
(Compressed Gasket thickness minus(if above deck) Piston Deck height.)
Aim for a CR of approx 8.3:1 for good driveability.
Nick - does the Wiseco spec list say what the piston dish volume is.

Mick

ticky

22b & Nasioc.
I remember finding a chart with various model heads on Nasioc & the head volume cc's.


22B Bulletin Board: Head chamber volume

silent running

Mick, the piston spec is (metric) bore 92.5/compression height 33.32/dish 17.8cc/deck clearance 0.30mm. The roughly 1mm clearance you mention seems a good idea so looks like it's back to the standard 1.3mm Cometics and see what CR can be had from that. I can't think of any way to sensibly increase the CR though - bore x stroke is fixed, as are piston specs. The only thing that I could alter would be block deck height which would simply cause more problems, although I suppose a head skim might do the trick? That way I could keep the 1mm clearance I need for the piston using the 1.3mm gasket, but reduce the chamber volume...

silent running

Wally update: Someone correct me if I'm wrong, but I think I entered the deck clearance as a positive value into the ready reckoner when it should have been negative. Keeping the 1.3mm gasket in the equation and going with 0.25mm over-deck clearance and a chamber volume of 46.5cc (to be confirmed!), I get a finished CR of 8.059:1. At least it's in the 8's with no further adjustments necessary. Interestingly, if I can take 4cc's out of the chamber, maybe with a skim, I can get the CR up to 8.478:1 and still keep all the clearances good...

OK, back in from ccing (more accurately this time) and they do come out at 46.5cc. leading to a CR of 8.076:1 on 1.3mm gaskets. A 0.25mm/0.010" head skim would roughly take an extra 1.5cc out of each chamber yielding a good CR of 8.228:1

Might do that anyway just to get a nice clean face on the heads.

Legacy_Turbo_EJ22G

Your CR seems just about right. Atleast with my calculations, which I have to presume is right.

However, my V4 heads CC`ed at 48cc. Not that I`m necessarily right though.

silent running

Well I will do them all again just to be sure, once I get my valve seats cut and the heads built again.

silent running

Update for any future SNers searching on this subject...

The seats have been recut at the engine builder's then the chambers CC'd properly and they come out at 48.2cc / 47.8cc on one head and 46.8cc / 46.4cc on the other. These are way too far apart from each other. Head heights are good at 127.58mm / 127.56mm (new spec is 127.5mm). As the chambers are a little bigger than I'd wanted, the head heights are plenty tall enough, and I need to take at least 2cc out of them to get my CR up; I've now asked for the max skim of 0.012"/0.3mm to be taken off and for them to be both matched to a finished height of 127.2mm. I might as well go as far as I safely can - to 12 thou - staying within spec.

I worried about leaving some meat on there if the heads ever warped and needed a skim again, but if they'd already had 10 thou taken off them as planned, the 2 thou still left to take off would not be enough to flatten them anyway.

I'll have them cc'd again once the skim's done, then armed with this info, I'll take the heads back and work the combustion chambers however I need to to equalize them as close as I can.

bandit1216red

carry on as you are now ya know where ya going
only thing i would say is make all the chamber vols equal
also check ya valve timimg once engines built up
if ya after every ounce of performance it might be woth getting vernier cam wheels to get the cam timing spot on

silent running

When I get the heads back I'll be equalising up the chambers. I hadn't thought of timing issues so far but assumed I wouldn't have any as the piston to head clearances should be the same as standard. What sort of problems might I expect? I can get hold of a set of adjustable pulleys if I have to, but I'd rather go standard if I can.