High Compression Ratio ----> Detonation

[robokill]

aparadal I am running 81.5 standard pistons with a worked head and I changed my timing to 15 degree BTDC. works alot better

[oldeskewltoy]

NoHachi Wrote:Backcalculating static compression ratio's from dynamic compression ratio's is a no-no. Certainly with headwork, different cams, pistons etc.

I didn't say it was the best option, but not much to choose if the engine isn't coming apart.....

*IF* he is indeed close to 13 to 1, it'll be VERY difficult to make it perform to his liking.

Even the replacement of the TRD head gasket with an oem one will claw him back nearly half a point, that might just be enough... if it is just too high....

[apardal]

The range of CR that Wiseco states for their pistons has to do with head skimming (combustion chamber volume)! 10.2 for stock head with 39cc's. 11.8 for combustion chamber with 35cc's. I measured my combustion which is around 34-34.5cc's.

Robokill, I have detonation with 0º BTDC... imagine if I tune it to 10 or 15º BTDC... that is a BOOOMM for sure.

Compression ratio calculation is not a problem. I'm sure I run 12.05:1 given every single characteristic of my setup.

ECU is a problem which I hope I can get around. If not, a MSnS will be on its way.

Bigger cams will also be in my thoughts.

Thank you for your replies.

Best regards

[NoHachi]

Ivan141 Wrote:Pig-rich mixtures arent the best way to go, that could cause accelerated cilinder bore wear due to washing the oil off.

Lambda 0.8 really isn't a problem.. Forced induction engines run this all the time to prevent knock. As long as you only run this mixture under full load it will be ok.

[apardal]

Hi again! Today I installed new spark plugs. Normal NGK as the manual states. BCPR6EY11

Detonation reduced, but still there.

Next step, check cam timing.

Best regards

[jamiemirror]

Why not colder ones, grade 7 ?

[robokill]

apardal set the check wire on turn the ignition to 13 degree instead of 10. adjust the fuel mixture (richer) and then unplug the check wire.

See if it is running between 16 and 20 degree. This worked fine for my engine. If timing is to low it will mess up you need to set it to more than 10 because of your cams.

[Ivan141]

Robokill, I doubt more advance will do him much good... if the fuel is ignited too early, it will increase peak pressure in the cylinders and only make detonation worse.
I think it would be a very wise idea to get a wideband lambda sensor and start tuning that SAFC to keep the fuel mixture in the safe area to begin with.
Guessing isnt ideal, detonation might ruin the engine before you get it right.
When you get it running good most of the time, maybe start thinking about ensuring the engine stays at the proper operating temperatures.
75 deg C engine and 85 deg C oil seems to be a good target (taken from Guy Croft site)

[Lipinhu]

Quote:Even the replacement of the TRD head gasket with an oem one will claw him back nearly half a point, that might just be enough... if it is just too high....

Thats what I would do if it was my case!

I dont understand the obssession for such a high cr. It ISNT that critical when it comes to make power, i mean, not for your cams, or the . And the ignition timing you're going, i believe is making you lose lots of hp, usualy it works the other way arround. I would never consider nothing lower than the 10º btdc.

A standalone ecu (as you mentioned), will defenitly help a lot.

[apardal]

jamiemirror, I'm still going to try those 7 grade spark plugs soon.

robokill, advancing timing is going to wreck the engine. I've been reducing the timing since I started the engine with this CR, and I started it the first time with 13-14º.

Now I ended up with -5º so that it doesn't detonate. Of course I don't make much power with this timing. But the fact that it still does make power, makes me almost sure that the cam timing (mainly the exhaust cam timing) is completely off!

I have already all the tools I need to measure and tune cam timing so that it stays correctly dialed in. After that matter is solved, I'll have some news. Good news, I hope.

Ivan, I already have a wideband O2 sensor to measure the mixture, as I stated before.

Lipinhu, like you, I also don't think is good policy to run the engine with less than 10º of ignition timing. Nevertheless, I need it to run like this so that it doesn't detonate. I don't have the need of such a high compression ratio, but OEM pistons were ruined and I changed pistons with better ones, which elevate the CR. Knowing this, I installed a thicker head gasket of 0.8mm. 12:1 CR is good because I can reach higher levels of power with bigger cams.

And 12:1 isn't that much of a problem. It just needs more care with ignition , fuel and cam timing.

Best regards