In theory, wouldn't the knock sensors/ ECU pull the timing to keep things in order ? Within reason obviously.

 

or.....

 

yes, but knock is a EVENT, not a prevention. Meaning yes once it SEES knock it retards timing. But really .2 increase is nothing and equal to carbon buildup on higher mileage engines

Hopefully not a next time, but as Water D already said. I would also stud the heads for those with the same issue. Stock bolts s t r e a c h(why theyre torque to yield) and the head lifts under increased cylinder pressure and there goes gasket seal. Studs clamp much better. And for those in this issue too but going back with stock bolts, at least replace them even though jag says reuse 2x's ok. Japanese automakers give a bolt streach spec to measure the threads and replace if exceeded. I have never seen this from Jag so I think better to replace with new at least.

 

It's a bit complex calculation what's the compression ratio when head in my case is totally 0.7mm ( 0.0275" ) lower than stock. Need to know volume of cylinder displacement, volume of clearance, dome of piston, volume of head gasket and volume of chamber.

Discussion about head bolts: https://www.jaguarforums.com/forum/x...d-bolts-90344/

 

that'll do it. lol

 

if Im building a performance engine. Ill clean and smooth chambers and then cc them with a burret to measure chamber volume and piston dome. Then unshroud valve if needed and match cc of each chambers AFTER valve job, decking. Piston dome is easy for flat or dished unless a + dome then measure 1" down in hole. there are many formulas for figuring compression ratio once you have bore, stroke, piston chamber volume etc and compressed gasket volume which is given my manufacture of most head gaskets. make a chamber cylinder cover out of 1/4" plexiglass and chamfer a hole in the top corner to get air out. seal against head with vasaline thin coat and I like to use which hazel or colored rubbing alcohol to see fluid.

 

There was mention of ARP making custom head studs for the AJ-V8 HERE but he mentioned $1000 for a set, and 10 weeks lead time...ouch!

 

I spent about $400 something with them on the V6 Nissan. and talked to them gave dimensions needed and I dont think anything had to be custom. They just pulled pieces together and basically made a kit with what would work correctly

 

Although I like the idea of the ARP bolts although I haven't had any issues yet on my engine (4.2 mls head gaskets), and I have been running 24 psi, although for a short while, most was between 20 and 23 psi. Don't know when it becomes a danger with the stretch bolts and 4.2 mls gaskets though (outside of detonations). The main reason I haven't used them is that you can't take off the heads anymore without lifting the engine.

With the 4.2 MLS gaskets (instead of the 4.0 Composite) you increase the compression about 3 points, not that much.

 

I think it is hard to directly blame boost or even cylinders pressure increase due to added HP for that kind of failure. Isn't it almost certainly detonation?

 

There are a lot of stock 4.0 cars with headgasket failures (the composite ones, so pre 2001), and I don't know the causes for these, but would suggest indeed detonations as a main cause in combination with the weaker gaskets.

Am not sure if you will always be able to see traces of detonations, at least on my engine I was able to see them on my spark plugs when I was running the extreme high boost.

 

It's important to remember that head surface grinding increases the compression a bit . In my case, since it has been made twice, 2*0.1mm, so the ratio can be something like 9.3-9.5 at the moment. Not so low for quite high boosted engine. E85 would be good choice.

Anyway the engine runs very smoothly now. Thanks for full seat/valve job, new springs and careful valve measuring.

 

Can you run E85 in a nikasil engine? or is yours a steel replacement engine ?

 

What did you use for valve springs?

 

me too Sami -- I blew mine again, my own fault - 260KMH
But I was 4,000km from home, had to buy a car trailer and 4 wheel drive to get it home.
My problem was detonation, I need to fit a after market Piggy Back ECU

 

That's quite far away from home. I had just 85km on trailer. Did you blow your engine ( block or pistons ) or just head gaskets?

 

I pulled two plugs - 2 front right cyls again - plug electrodes smashed.
- I see compression ratio is being discussed.
it will always be swept volume over unswept volume.
the 0.2mm decking represents 0.295cc of unswept volume
I am going to look for a 4.2 litre block - I will speak with the "Big A" soon
Do you know of anyone who has had success using a piggy back ECU, you mentioned Viper on email somewhere, Local Jag dealer recommended Autronic s4 -
I would like to speak with someone who has fitted one

 

I will PM to you.

 

Since it is a fuel sytem with a return circuit on a regulator, how about a rising rate fuel pressure regulator?

 

We have changed to such a regulator type.