Guest WESTCORT Posted July 19, 2005 Share Posted July 19, 2005 Just after some info on compression like why high compression isnt good with turbo engines and why low comp is better. And why certain octane petrol is better for certain compression etc. thanks Quote Link to comment Share on other sites More sharing options...
lowlancer Posted July 19, 2005 Share Posted July 19, 2005 Higher octane gas detomates at higher compression, thus no pinging (pre detonation) Quote Link to comment Share on other sites More sharing options...
esky boi Posted July 20, 2005 Share Posted July 20, 2005 Its best to run low compression with a turbo, because otherwise on full boost there will be a shitload of pressure in the cylinder and it will detonate real bad... I think And yea, if you run too low an octane petrol in a high comp engine it will ignite under compression, rather than by the spark plug which causes pinking/detonating. With your 11hundy pistons the compression ratio will be about 10:1 ish aye?... should definitely run it on at least 96, preferably 98 Quote Link to comment Share on other sites More sharing options...
Guest WESTCORT Posted July 20, 2005 Share Posted July 20, 2005 yea i neva run 91 even though im hell poor. usually bp's 98 but 96 from gulls when im really short on cash. my comp ratio is 10:2:1 i believe, although thats according to spanner fodder but when i calculated it myself it was more like 10.9:1 so i duno Quote Link to comment Share on other sites More sharing options...
Jerm Posted July 20, 2005 Share Posted July 20, 2005 Yeah high comp just doesn't work with turbs. I always run 98... You need to run high octane with high comp, i probably wouldn't even run 96 in yours alex... Quote Link to comment Share on other sites More sharing options...
esky boi Posted July 20, 2005 Share Posted July 20, 2005 mm, anything over 10:1 and you should run 98. Mine is meant to be at about 10.5:1 so yea... looks like running it is gonna make me even poorer haha Quote Link to comment Share on other sites More sharing options...
Heretic Posted July 20, 2005 Share Posted July 20, 2005 Why run low compression in a turbo motor? To fit more fuel in, plain and simple. High compression motors can run turbo's, but you can't fit as much fuel in without having reliability issues. From memory, Ronnie Lim was running something like 7.5:1 compression with 40psi boost, or some crazy combination like that - you'll make a bit more power and be reliable, but you'll get really crap fuel economy. As for the octane, thats a safety thing - the higher the octane, the less likely detonation/pre-ignition will be. Thats not to say that 98 will make your 1.3 corolla run any better than 96, since its probably not got the intake system to make detonation/pre-ignition a problem, but with a turbo vehicle, this can make the difference between reliablilty and detonating itself to bits! Also, theres a common misuse of the word detonation - detonation is not so bad, as its not that destructive, but the one you want to avoid is pre-ignition, which is when the air/fuel mixture is compressed to a point where the mixture gets too hot and ignites itself without a spark. This is not necesarily bad, as this is how a diesel engine works (in principle, except the diesel is added to the already compressed air to ignite the mixture), but with a petrol motor, this usually happens when the piston is still in its compression stroke, so the piston is pushing against the expanding ignited fuel (very very bad!) http://www.streetrodstuff.com/Articles/ ... /index.php Quote Link to comment Share on other sites More sharing options...
Bistro Posted July 20, 2005 Share Posted July 20, 2005 ^^^ Awesome explination. Cheers Carlos. Quote Link to comment Share on other sites More sharing options...
Guest WESTCORT Posted July 20, 2005 Share Posted July 20, 2005 thats what i was after mate, cheers Quote Link to comment Share on other sites More sharing options...
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