Forum » General Tuning Discussion » Compression increase, base timing and detonation

Compression increase, base timing and detonation

General Tuning Discussion

Forum Posts



Tech Articles

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads

Page 1


Assuming a 1 point increase in compression, would 1-2 degrees of base timing retard (at the distributor in this case) be sufficient to prevent detonation on a worst case scenario? Or it isn't that simple?

That is with the same camshafts and cam timing (so no changes to dynamic CR) and no access to higher grade fuel. The engine didn't suffer from detonation previously, but consider it was already at the octane/CR limit.

It would run in this scenario during break-in and until I get all the parts to get it tuned on ethanol/flex fuel setup as it's the only high octane fuel available. The engine in question is a Honda B16A, and unfortunately only E27 87 octane is easily available around here.

I wouldn't think a 1 point compression increase would change the tendency of an engine to detonate (or knock from too much timing). However removing 2-3 degrees of timing while breaking in an engine is a totally reasonable thing to do.

Thank you for the response, David. I see, so it wouldn't be an issue running it at 11:1 with base timing retarded 2-3 degrees.

The engine ran fine on the stock 10.2:1 compression, but with the fuel being only 87 octane I'm under the impression it's in the verge of being prone to knock, knowing people always run it on 91 at other parts of the world.

My theory (correct me if I'm wrong) is that the increased ethanol content compared to other places (10-17% more), keeps the combustion chamber temperatures lower, helping prevent preignition, even if the octane rating is kept the same compared to pure or even E10 gas, for example.

Reducing the timing will likely reduce the power slightly. But it won't hurt anything. If you reduce it by 10 degrees, then you get into the range where you could see increased exhaust temps, and or head cooling issues. Proper ignition timing tends to allow the engine to run cooler (which will also reduce the tendency to knock). Extra ethanol tends to raise the octane rating, so not sure how you can have extra ethanol and low octane.

Does the ECU have knock control? If so, it may automatically tolerate the lower octane fuel if it detects knock.

I see, so in this case with a slight compression increase the timing retard required to prevent knock wouldn't affect anything considerably. Regarding the ethanol, I was trying to compare the ethanol content on both 87 octane ratings and if it made a difference to preventing knock due to its cooling properties. Even with 17% more ethanol the octane rating is still 87 compared to an E10 87 octane blend. The gas used in the E27 blend surely has a lower octane rating than the one used in the E10 mix, so it needs more ethanol to achieve the same rating.

Yes, the ECU has a working knock control system but it's known to have issues with interference at engine speeds over 4000rpm.