Strange Power drop on dyno

[Guy Croft]

If the power drops with more than 28 deg total advance something is seriously amiss. If the dyno shop is referring to 16v Hondas I'll just remark that 16v engines commonly need a lot less advance because they burn way better. So does the SOHC Fiat, but you have to have a lot more than that on an 8V TC. Instead of setting the ignition so low they should have explored why it would not perform better with more.

I don't know your ignition system (the settings on mapped units vary widely according to load and throttle posn and I can't read them off for you, you have to find enter them yourself) but a distributor system will need 34-36 deg at peak adv at anything from 3800 to 5500rpm.

Now that 'thing' seriously amiss' will be the fuelling - or the engine 'knocking' (detonating). And you can be sure that if it's only got 28 deg adv it's no way burning all the charge, so that unburned HC is going to cause havoc with the lubrication system. I read (given that photos can mislead you, I can't see the real thing) the valve and plug condition as very high ex temperature (white ex valves and plug) and over-rich or impaired burn (tons of carbon on inlets). 28 deg advance is 'retarded' ignition and that can certainly cause very high ex temps and the high in-cylinder temperature that results would make her knock. I strongly suspect that if the power dropped over 28 deg adv detonation was actually present.

My two-pennyworth at this juncture.

BTW - thanks for your open-mindedness in sharing this interesting thread with us all.

GC

[vandor]

Guy,

Thanks for your response. We did try more advance, up to 4 more degrees, but it produced less power. Not significantly, but 2-3 hp. I did not think running it with less advance would have such adverse effects.

The ignition is a waste-spark distributorless system, but I do not think that would matter much.

We will put it all back in a few weeks and then we'll head back to the dyno (rolling road). As always, we appreciate your input!

Do you have an opinion on the type of rings to use?
Thanks,

Csaba

[Guy Croft]

I don't have a preference for any particular type and I don't favour Total Seal.

Low outspring race rings are best, OE are OK, all depends what your pistons accept. The att may help some,

G

[Guy Croft]

DID YOU GET IT FIGURED CSABA?

G