Gday all,

Got an EF XR6, and doing the head on it in a couple of weeks. Im dropping a wade 977b cam in it, and using the thinner AU head gasket. I dont have enough cash to get the engine ported, its already the tickford head so its mildly ported from what i beleive (even if it is minimal). I want to up the compression ratio a bit if i can.

My question is what is an achievable compression with the head only being shaved, and how much should i shave off to achieve this? I dont care if i have to use premium i run it on 98 always anyway, so if it needed a minimum of 95RON im not fussed.

Cheers

just get it machined flat and us the AU gasket. that's pleny enough, If you take to much off combined with the gasket you'll end up with timing chain rattle.

Take 20 thou off. It will need a min of 95 ron, but if you run it on 98 anyway then thats even better.

The information I have is that the AU steel shim head gasket is .025" vs .055" for the E-Series. The thinner head gasket is worth about .5:1 of compression - ie, a true 8.8:1 will become 9.3:1 just from the AU head gasket. Every .010" shaved will increase compression by about .15:1. So, 8.8:1 with an AU gasket and a .020" skim will give you about 9.6:1.

I took .020" off my XR6 and used an AU gasket. With the stock computer and a one step hotter cam, it ran fine on 95/96 octane.

remembering an EF will start 9.3:1

I am working off what Jim Mock told me a few years ago:

"Your stock compression that we find when measured correctly in our facilities is 8.7 to 8.9 for your model.
That means with the .025" Gasket and say a .015" surface of the head the new compression ratio will be 9.4 to 9.6."

You'll learn one day not to believe much of what comes from JMM

JMM might have been talking about the earlier motors... ED have 8.8:1, EF/EL 9.3:1, AU 9.6:1

Yeah, that may be right. In which case, I'm running about 10.0:1 compression

My old EF had more then that. AU gasket and 45thou off the head. 98octane feul only and had timing chain rattle.

If you run a bigger cam you will generally get away with more static compression before having to run 95/98 respectively.

Not attempting to hijack, but to gain more info on the same topic?
Does anyone know what the compression ratio of the EF Tickford is, standard? Can I get the same gains from using the AU head gasket? The cam I want needs 10:1

Cheers

Standard EF XR6 is supposed to be 9.35:1

I used an EB tickford head on my EF, had it shaved 25thou and used a Permaseal MLS headgasket (same thickness as MLS AU gasket). Not sure if the head had previously been skimmed or not, so had my cylinder head machinist CC the chambers and worked out compression to be 10:1

Mine is shaved a bit, and using an au mls gasket. Not sure of chamber volume but gets 235psi on the gauge with a very large cam.
Runs on BP ultimate only, with water/meth injection.

Hi roughredXR6,

Apologies to all for both thread mining and thread jacking .

I'm having a problem with my EF XR6 head on an AU bottom end - a reverse hybrid, I guess. I have had exhaust valve to piston contact, and it doesn't make sense.

I'm asking you because you have an extreme head shave (.060"?), a thinner head gasket and a longer duration cam, yet don't have valve to piston contact.

You do mention that your pistons have deep valve reliefs. The AU pistons have only shallow reliefs for the intake valves and none for the exhaust valves.

My EF Tickford head has been shaved twice (that I know of) - a total of .030"/.76mm - to get a compression ratio of 10.0:1. The chamber volume is 59.5cc. There is still .022"/.55mm to go before hitting the warning/reference pads.
- I used a BR522 head gasket with a compressed thickness of .055"/1.40mm, a lot thicker than the MLS's .026"/.65mm.
- The AU block has been skimmed .010"/.25mm for flatness.
- The top of the AU pistons is below the deck surface.
- I have a vernier cam gear, and have run the engine between 6 deg advanced an 4 deg retarded. I normally run it 2-3 degrees advanced to compensate for the retarding effect of the head shave.
- I have run two reground cams in this setup: a Franklin RH24B and an Auckland Cams 258 - both of which have less lift and duration than a Camtech 830.
- I'm running Crow 7739 valve springs.
- The EF and AU exhaust valves are both 41mm.
- Maximum I have revved it to is 6000 rpm.

So, I'm a bit baffled how I can get valve to piston contact. Maybe it's something specifically to do with the EF head on the AU block. Does anyone else have this combination?

All six pistons have lovely exhaust valve dents. Somehow, the valves didn't break or bend. One rocker arm broke at the lifter bore. Through all this, the engine continued to run quite normally. The only clue was a single noisy lifter during warm-up - presumably the one with the broken lifter bore. I dodged a bullet, I think.

The cylinder bores on the intake side have noticeable scoring - maybe related to the exhaust valve contact with the pistons. The bottom end was suffering from low oil pressure at idle when fully warmed up, and a couple of the coolant passages in the deck surface are corroded too close to the bores and have caused a head gasket leak previously. So, rather than replace the pistons, I'll probably get a another good used bottom end. If the valve clearance issue is because of the EF/AU combo, I will need to get the pistons flycut.

Any help you can give me would be appreciated.