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I fully understand what you are saying. The point you're making is that as long as the timing is correct to burn the most fuel efficiently and still allow the cylinder pressures to peak at the point of highest torque transfer, it'll make more power. This is in complete disreguard to octane rating, as octane rating have no bearing on the speed of a fuel's burn.
This is correct and is what I'm trying to get across, as the first post you replied to didn't bring fuel octane into the picture as you only stated about boost and timing and only later brought octane into the picture. So to answere yes, the previous post have been under Ideal conditions where the timing, boost pressure and A/F mixture are Ideal. Octane does play a huge role as the fuel needs to have enough resistance to initial light off under high cylinder pressure to prevent detonation. Although this may seem to heavily effect timing it doesn't, fuels can have an identical octane index but burn at total different rates and speeds. Heres some info from someone who has more knowledge in chemistry and the makeups of automotive fuels
------A lot of people also confuse octane with flame-front propagation speed which is yet another independent factor. Take the old-days measurement of octane-ratings with iso-octane (2,2,4-trimethylpentane) with a octane-100 rating and n-heptane with a 0-octane rating. They both have the exact same flame-front speed, yet one of them has a fairly high anti-knock index. The other, n-heptane, has such low knock-resistance that you can just tap the beaker and the stuff would explode!-----
this here is just further food for thought on detonation caused by timming vs. detonation related to high cylinder pressures, and goes to show one fuel can have high resistance to preignition from high cylinder pressure but still needs similiar ignition lead due to similar flame travel speeds.
On paper this is fine. The problem comes in from the heat and compression in the motor. Eventually it's going to knock because 91 octane just can't take that heat and compression no matter how much timing you take out. This is the point where it's not going to make more power with more boost because it's simply overcome the ability of the fuel to resist the heat and compression.
This is true and as I have pointed out previously these high cylinder pressures require less timing for many reasons and I didn't bring octane ratings into the equation because I was refering to the statements made saying lowering boost and increasing timming will make more power not statements about octane and cylinder pressure. You are correct that eventually timming will not be the final factor in finding the boost thresshold, it will be the octane of the fuel used. If this had been said in the first place I would have agreed but it wasn't and therefore was not the topic/point of my previous post.
I'm curious to know what sort of turbo Therin runs that is still efficient with sane intake air temps at 27psi. In my opinion, there is no way his motor can't be knocking.
The turbo is fairly large T04B with 66mm compresor wheel I believe, but may be out of its efficiency range on the pressure side but probably not by much. The car does have a nice FMIC and the temps here have been around 20-40degrees which is helping....a data logger to see intake temps and total timming values at WOT would be very nice. We have though slowly rasied the boost pressure and kept the things rich because of the pump gas,the motor is not detonating or at least showing zero signs. Crazy as it may sound I know three guys with 4G63s and Hahn super20's running over 25lbs on 91 octane, one of them was on a stock bottom end. I'm actually going to tune one right now.
This is a good discussion. Do you just troll the 'net looking for opportunity to educate the vast, ignorant, unwashed masses, or were you directed here from elsewhere? Just curious.
One of Therien10's freinds lol
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