4AGZE head skimming

[ohms]

Hi all,

I am about to replace the headgasket on my GZE and whilst the head is off I am planning a freshen up with new cams etc. My question concerns skimming the largeport head and raising the comp ratio. How much can be skimmed off the head and would it be possible to raise the comp ratio upto about 9.0:1 purely through skimming. Any ideas how much to skim to achieve such a gain in compression if possible?

Also, what cams for the 4agze, HKS seem highly regarded but are bloody expensive!

[nick.parker]

Don't know about the head skimming but as for the cams...
Wade Cams make an "872A" (aka Wade 267) for $440inc gst new. These will give a good mid and top end improvement, but low end will be quite stuffed compared to stock cams which may or may not be quite disapointing to you. Also you WILL need adjustable cam gears otherwise your car will have terrible drivability, as on two cars I have found that the exh cam needed to be advanced about 10 degs (cam degs) compared to stock to get a reasonable idle and low end. I don't know how well a stock computer would handle these, my car and my mates both have after market EFI.

I have tried a 240 deg (stock) inlet cam with a Wade 267 on the exhaust and it is a good compromise. Kelford Camtech in New Zealand make a 248 inlet and a 260 exhaust to go with it for street use and 8ish mm lift each - I imagine this would keep a near stock low end and still have improved mid/top due to extra lift.

People have said 264's loose too much, I have heard 256's are pretty good..opinions vary.

Cheers, Nick.

[Sam_Q]

I will not work it out right now but I think to go from 8.5 to 9:1 would require losing about 0.3mm about what you lose by changing to a cheap trd 0.8m gasket. How does that sound?

[ohms]

Pretty good, cheers chaps! So to get from 8.0:1 to say 9.5:1 how much to be skimmed and how thin of a headgasket?

Also, has anybody tried or had experience with Crower cams?

[ohms]

So if we said 0.3mm per 0.5 increase in comp ratio that would be about right? What is the thickness of the standard GZE headgasket?

[motard_mike]

try Iven Tighe in QLD, look him up on google and give him a call. he will regrind your stock cams to what ever spec you like. or if you are smart you can take his advice and let him do what he thinks is right. i got him to do a few bike cams and they have all been fantastic and a great price, he charges $10 to express post them to your door. top bloke top cams and tops service. doesnt sound as cool as "hks cams" though.

[Hen]

Speak to Terry O'Bierne at Road and Track in Ipswich, QLD. I've found him to be very knowledgable and helpful when dealing with my 4A questions.

Hen

[Sam_Q]

even if it is 0.5mm per 0.5:1 you cant use that again because the realtionship isnt linear. What that means in english is if you shave 0.3mm off to go from 8.0 to 8.5:1 then shaving another 0.55mm off will raise it more than 0.5:1 next time you do it.

I will dig up the formular to work it out for you, sound good?

[Ben Wilson]

Copied from www.mr2oc.com

This is on stock un-modified heads and stroke.

Stroke is 3.03" (77mm)

Standard TVIS 4age N/A
9.4:1 old skim 0.020 = 9.9:1
9.4:1 old skim 0.035 = 10.3:1

10.3 High comp small port 4agelu N/A

10.3:1 old skim 0.007 = 10.5:1
10.3:1 old skim 0.023 = 11.0:1
10.3:1 old skim 0.037 = 11.5:1
10.3:1 old skim 0.050 = 12.0:1

SilverTop 4agelu 20v 1992-1994

10.5:1 old skim 0.016=11.0:1
10.5:1 old skim 0.030=11.5:1
10.5:1 old skim 0.043=12.0:1

BlackTop 4agelu 20v 1995-1999

11.0:1 old skim 0.014= 11.5:1
11.0:1 old skim 0.028= 12.0:1
11.0:1 old skim 0.040= 12.5:1

Large Port ZE

8.0:1 old skim 0.029 = 8.5:1
8.0:1 old skim 0.049 = 8.9:1

high comp small port ZE

8.9:1 old skim 0.005 = 9.0:1
8.9:1 old skim 0.014 = 9.2:1
8.9:1 old skim 0.018 = 9.3:1
8.9:1 old skim 0.023 = 9.4:1

[nick.parker]

Thanks for the great info Ben.
Someone please +rep Ben for me I am never allowed to!!!

[Ben Wilson]

LOL - I kinda wish I'd found that info before I went nuts with a mill this afternoon

FWIW, this is what a largeport head looks like after it's had 1.2mm (0.047") taken off...



I was hoping for around 11:1, but couldn't be bothered doing the maths. This should be around 11.5:1 which might be a bit high for pump fuel and a standard ECU. I'm now thinking about Somender Singh style grooves to hopefully stop it pinging....

[Ben Wilson]

Groovy...

[YLD-16L]

Interesting read on Singh there Ben.

Let us know how you go with those grooves.

[ohms]

Top info Ben, thanks a lot m8!

[Sam_Q]

ben: thats interesting do you have a before/after pic?

ohms: just curious why do you want to go up with the compression?