blowby>>>There is a chance you have a piece of debris stuck to a valve seat.>>> Which reminds me, pull the cover and make sure a keeper-half hasn't somehow worked its way out of the retainer. And do it soon before the other half decides to let go if that's the problem. Though it still wouldn't explain how that plug got so mangled unless something was also rattling around in there. Jack E/NJ
The engine is 12.5 cr. I don't know the duration of the cam as I didn't build the engine.. I do know that it's a nitrous cam. The engine had a 350 shot of nitrous in a fogger system that we removed.. Posted using the Full Custom H.A.M.B. App!
He has no intention of running this on pump gas. How hard is it to actually read the entire thread before replying to it? Posted using the Full Custom H.A.M.B. App!
Some of the newer cars sold in the U.S. have 12.5 compression ratios. They run on 91 octane gas. Somehow this is is made possible with direct injection and computerized ignition.
The computer can retard the timing if the octane isn't high enough to prevent detonation, from what I've heard about new cars.
Geeze oh Pete man ! Read the damn thread. If you want to know why it was ran on 91 read the thread If you want to know why "he" ran it on 91 read the thread If you want to know who "he" is read the thread. I know I shouldn't expect much , but damn ! Read the thread Starting with the first post
I've heard of pre-ignition and detonation, I used to know the difference even, but not pre-detonation?
... I wish I could get 98 octane without my friendly neighborhood state trooper giving me a big ticket...
Pre detonation= detonation... Detonation is the spontaneous combustion of the unburned fuel/air mixture caused by excessive cylinder temps/ octane problems. Pre-ignition is the firing of the fuel/air mixture prior to the normal ignition.
I apologize to you and the others I may have offended I went back again and read it again, sorry, I see the shop put the wrong octane:banghead: Posted using the Full Custom H.A.M.B. App!
Sorry Vicky, I over looked that the shop screwed up:banghead: Posted using the Full Custom H.A.M.B. App!
True but knock sensors, computerized ignition timing and variable valve timing have been around for many years. I think direct injection has allowed more accurate timing. The new cars running 12+ : 1 compression on 91 octane have direct injection. This means more power and better fuel economy (and higher car prices).
Got a call from the tuner today and he performed another leakdown test and it's at 25% now instead of the 45%. I know that's still bad but the tuner said at that rate he expects to regain all of the compression. Once again this is from the tuner.. just getting opinions from you guys. Is this common? Could heat in theory expand the ring back if it was in fact a pinched ring? Or if it was a chunk that came out of a valve seat ? Posted using the Full Custom H.A.M.B. App!
All of these things, direct injection included have been around for a long time- but they've been figuring out how to get them all to work together.
The performance shop where the car is at now is going to tear it down this week to see what exactly is wrong.. Posted using the Full Custom H.A.M.B. App!
Be sure that you aren't chasing windmills given the chassis dyno numbers and other positive observations that you noted. Do all the external checks like checking all the plugs, broken springs, bent pushrods, etc...then repeat a leakdown on the warm motor
depends on many things, squish, combustion chamber shape , piston shape, cam...... its suck it and see if your doing something one off or unusual (meaning Im sure SBC answers could be found easily for nearly any combo). I dont think the OP knows any of the details so its up to the dyno guy to do some sorting/suggesting as to what it needs.
That's correct since we didn't build the engine. According to what the dyno guy found we could get away with 100 octane. Race gas is 110 octane and also leaded. Posted using the Full Custom H.A.M.B. App!
To my understanding at least part of the reason the new DI engines can incorporate higher compression ratios (and turbocharging) is that when the fuel is injected into the combustion chamber the latent heat of evaporation sucks the temperature down, reducing the propensity to detonate. (The high pressure fuel absorbs chamber heat when it atomizes in the chamber. Port injected engines or carbureted engines atomize the fuel outside the chamber so they don't get this benefit). Think of what happens when you operate a die grinder or cutoff wheel....It gets cold in your hand. Can't control the combustion without the knock sensors or electronics though.
Been too busy lately to take the project any further. I have made some time to pull the engine this weekend and haul it to the machine shop. Plans are to change to a hydraulic roller setup instead of solid, go to a single carb for hood clearance issues, complete freshen up, and lower the comp ratio for pump gas. I will keep everyone posted as the tear down and build come along. Posted using the Full Custom H.A.M.B. App!
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