Smitty1955 wrote:SocialSecurity wrote:dont drop your C/R down too much if your gonna use a good ECU, cause a good tuner can tune out most pinging
snip ...
sorry..but that was the story 15 years ago....
when we had petrol with a decent octane rating
and if you couldn't find it...you went to the airport...
oh...for avgas..
these days.....
even the Optimaxes and Synergy fuels
can't handle too much in the way of a DECENT compression ratio
even V8 supercar engines have this problem too...
I have tried...and I have tried and tried...
to get modern engines (with ECUs Motecs etc etc) to run
WITHOUT holing pistons or pinging or detonation
on anything more than a max of about 10.5:1
some turbo engines... i couldn't get to run
on more than about 8psi..without the 'rattles'....
not very conducive to making hp!
It seems modern 'alloy' engines are more affected by poor octane ratings of our fuels....
the older cast iron engines (think Falcon and Holden 6) will take more ignition advance and more compression
than anything with alloy in it....(which is most modern engines)
and don't even think about the 'cheap' fuels from Singapore
a standard BA falcon or Vy Holden 6 will sometimes rattle
and our petrol companies and regulators (that is, the government)
couldn't give a shit...
and I know..i have tried and given up...
cheers
Yeah, what with that? Fact: the higher the octane rating, the cleaner the fuel burns. Bikes aside, I consider myself an environmentalist. But governments and and EPA are kidding themselves if they think our modern fuels are good. We use poluting inefficient fuels while the Epa books you $1000 coz your exhaust is a bit loud for other road users.
On the compression ratio, a general, but very effective rule is that for staic compressions of 10:1 you can safely use as low as 100 octane, 9.5:1 /95octane, 11:1 110 octane etc...
The older iron headed engines resist knoking best. This is coz the iron conducts or draws heat awy much more efficiently. But then our clevo is extremly tempirmental and we've emptied the sump out the pipes as a big flame a couple of times now. It is impossible to hear knocking in water when the engine is solid mounted.
On the other hand, there are exceptions. Our 392 will run on a 50/50 mix of Lrp and premium all day. It has a comp of 11:1 The explanation here is that the combustion chambers are huge, dead smoothe and flow at an insane rate. These where cast in 1954 (again, how far have we really come) and have to be seen apart to be appreciated. With a bare head on the bench with no valves in it, you can literally see into the inlet port, across the combustion chamber, and straight out the exhaust port. We are also running pistons with no fly cuts. This all means that heat gets out quicker, and there are no corners or points in the cylinder to get particularly hot and promote detination.
But there is an almost fool proof answer. I'll have to check the ratios, and heat ranges of the plugs required, but you can buy toluline (the base of most additives) straight from Shell. There are three down sides.
1. the stuff will seperate from the fuel if let sitting over night.
2. It can turn to jelly when left in small quantities, ie. carby bowls.
3. fumes are not good.
We solved the first two easily though. We run a small efi pump in each tank drawing from the bottom at one end and returning straight back in at the top at the other end. We run these for about 5min each morning to stir it all up before the engine fires. These are switched off one stirred coz driving stirs it up enough. We also run a tap just below the fuel rail wich is switched off at the end of the day and let the engine epty the bowls. You should have a return line to the tank to make this safe though. We have never had an engine fail using this stuff yet, and it's cheap(ish).
It's a bit of messing around but well worthwhile if you get it right.
Otherwise, you will need to back compression of to as little as 7:1 if you're gonna run real boost. This also means you can get a bigger air fuel charge in as well.
Athough some electronics do have anti knock systems, they only save your engine from self destructing. While they are operating, retarding ignition etc.., they are robbing you of power, big time. Surely the goal is to make reliablbe and predictable power?
Do you home work and do what YOU feel is right and logical. If it doesn't make sense, keep thinking and talking untill you come to an answer that you know is atleat safe for pride and joy.
.
