Nordicflame

iTrader: (4)

Just curious, I had just recently read in one of the post (don’t know which one) that with less timing at idle it caused you to open the throttle blades a bit more. This apparently would move more air through the motor reducing reversion.
Did I understand this right?
This would be a great help and safety measure for my wideband O2 sensor if correct. I have total control of my timing at idle, cruise WOT, acceleration, etc. with my laptop and could easily run less than the 20 that I run now.

Would cam timing play any substantial part in this?

Also, it seems my motor idled much smoother and quieter after I installed a M3 ProCharger. My imagination?
Thanks,
Dave

Falcon

Yes, less advance at idle helps reduce the chance of reversion. Not sure if it helps because of more air flow, less intake manifold vacuum, or both. It also raises the egt's at idle from the lower triple digits to the upper triple digits, depending on the previous settings and advance settings used.

Cam timing is potentially a bigger factor, but maybe some others here on the board can give more insight to this.

Nordicflame

iTrader: (4)

Thanks Falcon,
Also, when speaking of cam timing I'm refering to installing advanced or retarded.
Dave

Nordicflame

iTrader: (4)

My thinking on cam degreeing is that if you retard the cam say 4 degrees to make more power up top this will actually leave the exhaust valve open 4 degrees longer after the piston reaches TDC. This would allow a longer duration of pull/reversion on the exhaust.
So my thoughts lead me to believe that a cam slightly advanced would cause less reversion than one retarded.

Falcon

Maybe! Any others have some thoughts?

Kanookstr

Heard the same thing Dave. I'm running my 731 4° advanced not only to help there, but I don't plan on running the engine at 6000 to reach the peak HP. so doing this will lower that peak as well. this will also help my mid range cruising and economy.

Raylar

NordicHeat
Reversion is caused by exhaust trying to move to the place of lowest pressure, if the intake and exhaust are both open at the same time as they are in most big marine motors the exhaust pressure is suppossed to exit the exhaust system, but in some boats the exhaust backpressure at idle is higher than at mid-throttle and speeds, hence it tries to go out the intake tract a little more. No moderate change in timing is going to really affect reversion, only cam timing or exhaust pressure will really have an affect. Advancing the cam from true TDC zero will close the exhaust earlier and limit some reversion. Remember most cams have about 2 degrees of advance ground in, but most are off out of the box about + or - 2 to4 degrees, so the only way to accuretly advance your cam about 4 degrees is to degree the cam in the motor. Sorry to add to the confusion! Raylar

RLW

Kanookstr,
Out of curiosity, what size motor are you running that 731 in?
Russ

Kanookstr

502 MPI, with 50lbs injectors, 2 bar MAP, AFR 335/121 Alum. heads, Gil exhaust, AZSM ECU recal, and a Procharger with a max of 5-6 PSI boost. Should be close to 730HP +-. I originally was going with the 741, but that would of put me above 800, and I didn't want that much.