b20 very high comp???


BuddyClubctr

BuddyClubctr

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Dec 7, 2009
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Hello guys a friend of me tuned a b20 with b16b head high comp pistons and all the rest!! when he went for mapping if he tries more than 9 degrees ignition timing the ignition is knocking all the time!! the tuner said that his got excessive compression and he need either racing fuel or a different gasket that will lower the compression could this be right?? he did a tests and everything works ok on the engine no knocks no nothing
 
what comp pistons, did you check ignition timing before mapping ?
 
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Does not suprise me. Despite what a lot of people think, you can have too much compression, even with big cams.
 
Interesting thread, wish I could help but I leave stuff like this to the experts!

Post a more detailed description of the engine for more help.
 
Yes the ignition have been checked and corrected before mapping! Details : aem ec b20 boTtom eagle con rods je pistons 84.5 mm probably 12.5 mm he is not sure abou the comp he received blackworks headgasket and b16 b head valves retainers springs camshafts replaced with buddyclub spec 4 work on the head done and I think the head has been shaved at the machine shop 1-2 times
 
Where abouts in the rev range is it knocking?
 
He either needs to:

A. Drop the compression ratio

B. Run higher octane fuel
 
Same here, get those pistons machined down to the appropriate compression ratio. You don't need to replace them.
 
I was thinking about a turbo gasket somewhere around 2mm or even 2.5mm so I won't need to do work on the pistons!! What you guys think?
 
Given the lack of actual measurements, if we assume it's currently at 13.0 with a .50mm gasket:

1mm = 12.2
1.5mm = 11.6
2mm = 11.0

I would aim for a 1.5mm gasket, but obviously it would depend on what the actual compression ratio currently is. You'd need to cc the piston and combustion chamber to find this out really.

If it's really bad it could be even further north of 13 in which case the 2mm+ gaskets may well be the best bet...
 
It is quick and easy, but if you're experiencing detonation that early i doubt it will completely solve the problem. You should have done more research from the start. Instead of jumping on the higher the better boat.
 
Just did a compression test!! My compression is 12.7:1 I don't think is that much that the engine can't work!! Any other ideas why is we put more than. 9 degrees ignition timing is knocking?
 
BuddyClubctr said:
Just did a compression test!! My compression is 12.7:1 I don't think is that much that the engine can't work!! Any other ideas why is we put more than. 9 degrees ignition timing is knocking?
Click to expand...

How did you do a compression test and come up with 12.7?
 
You fill a piston when is down to dead end and count the quantity of liquid you put in my case thin oil!! Then you make a piston come to top dead end make sure you close all valves fill it again and then divide the first measurement with the second
 
Whats the base timing set at? What injectors and are they ok?

Murray
 
Everything is ok 17 degrees ignition!! And we drop it to 9 degrees so the car can rev without knocking any higher ignition make it detonate !! Injectors are working excellent I took them for test!! They are 440 cc injectors rc precision! If I use 9 degrees ignition it works fine and revs up to 8.5 k smooth with lots of torque!! Just is not fast as it should be because the ignition is restricting it
 
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