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ft_sjo · 10-26-2012, 02:19 PM

8:1 and 12.5:1 means nothing by itself. This is just the static compression ratio and engines, are by far, not very static. This conversation is way off track of actually relevant.

What matters are cylinder pressures. Yes, static CR affects this, but nowhere near as much as the dynamic CR does. The main reason I believe that these tuners are able to simply throw a turbocharger onto such a high SCR engine is because they are controlling the DCR adequately to keep it in one piece. There is no magic in forced induction, sure direct injection helps to some degree, but rarely gives you more than a ratio or so headroom on SCR compared to an equivalent engine.

The bottom line is when the cylinder pressures get too high you get detonation. A high static CR engine is going to have a pretty crappy VE curve to keep it in one piece. No offence to the tuners out there testing at the moment, but most of the bolt-on brigade are producing some very interesting torque curves - some are barely noticeable as forced induction! Some resemble centrifugal superchargers!

The best one in my opinion is the AVO conversion. I'm surprised that it's actually capable of producing such good torque at low engine speeds without det/egt/reliability issues on pump fuel is something to be commended on. I don't know if it's luck or engineering, but I am curious to see some actual data (particularly around final spark angle and the resulting EGT's, both at the exhaust port exit and cat inlet).

Producing a nice wide flat torque band gives you awesome, predictable driveability..

10-26-2012, 02:19 PM	#24
ft_sjo Banned Join Date: Oct 2012 Drives: GT86 Location: The Motherland Posts: 1,398 Thanks: 140 Thanked 473 Times in 271 Posts Mentioned: 22 Post(s) Tagged: 0 Thread(s)	8:1 and 12.5:1 means nothing by itself. This is just the static compression ratio and engines, are by far, not very static. This conversation is way off track of actually relevant. What matters are cylinder pressures. Yes, static CR affects this, but nowhere near as much as the dynamic CR does. The main reason I believe that these tuners are able to simply throw a turbocharger onto such a high SCR engine is because they are controlling the DCR adequately to keep it in one piece. There is no magic in forced induction, sure direct injection helps to some degree, but rarely gives you more than a ratio or so headroom on SCR compared to an equivalent engine. The bottom line is when the cylinder pressures get too high you get detonation. A high static CR engine is going to have a pretty crappy VE curve to keep it in one piece. No offence to the tuners out there testing at the moment, but most of the bolt-on brigade are producing some very interesting torque curves - some are barely noticeable as forced induction! Some resemble centrifugal superchargers! The best one in my opinion is the AVO conversion. I'm surprised that it's actually capable of producing such good torque at low engine speeds without det/egt/reliability issues on pump fuel is something to be commended on. I don't know if it's luck or engineering, but I am curious to see some actual data (particularly around final spark angle and the resulting EGT's, both at the exhaust port exit and cat inlet). Producing a nice wide flat torque band gives you awesome, predictable driveability.. Last edited by ft_sjo; 10-26-2012 at 03:48 PM.