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Originally Posted by XJR-99
(Post 954521)
It's combination of compression ratio, boost, ignition timing and used fuel.
Detonation is the enemy. |
2 Attachment(s)
Originally Posted by andrew lowe
(Post 954528)
In theory, wouldn't the knock sensors/ ECU pull the timing to keep things in order ? Within reason obviously.
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Originally Posted by andrew lowe
(Post 954528)
In theory, wouldn't the knock sensors/ ECU pull the timing to keep things in order ? Within reason obviously.
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. |
Originally Posted by Brutal
(Post 954560)
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. Discussion about head bolts: https://www.jaguarforums.com/forum/x...d-bolts-90344/ |
Originally Posted by XJR-99
(Post 954552)
or..... :)
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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.
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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!
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Originally Posted by Cambo351
(Post 956159)
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!
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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?
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Originally Posted by sparkenzap
(Post 956392)
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?
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. |
Originally Posted by XJR-99
(Post 956457)
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. |
Originally Posted by XJR-99
(Post 956457)
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. |
2 Attachment(s)
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 |
Originally Posted by dc4prez
(Post 956982)
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 |
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 |
Originally Posted by dc4prez
(Post 957154)
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 |
Since it is a fuel sytem with a return circuit on a regulator, how about a rising rate fuel pressure regulator?
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Originally Posted by plums
(Post 957440)
Since it is a fuel sytem with a return circuit on a regulator, how about a rising rate fuel pressure regulator?
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