mustangmark

2 & 3 are swapped along with 4 & 7 on my custom ground cam for my bbc gen6 502. Is this common. Is there real benefits to swapping the firing order on 4 of 8 cylinders? I set tdc with a piston stop...so I'm 99.9% sure tdc is dead on. When I back the timing off at all the motor will start to run a little rough. There is really no margin to retard the timing which is currently set at 11 degrees initial and 31 degrees total. The motor has a b&m 250 blower on it and I would feel more comfortable with the timing backed down to 28 degrees total. Also, when the motor is cold...it pops out the carb (Nickerson stage 5 dominator) but when it warms up it is fine. Any opinions?

ThisIsLivin

Basically you have the LS timing order, they found that the engines have less harmonics with this firing order. When you back down the timing, how much and at what rpm range is it rough? It's not unusual for a real cold motor to backfire through the carb. When the engines cold the fuel tends to fall out and causes a lean mixture that causes the backfire, although it is more uncommon with a blower as the blower helps to agitate the fuel mixture. How much timing are you backing out to get the rough condition? What's your static compression, how much boost are you running and what octane fuel are you running?

mustangmark

Great info! Thank you!
The static compression is just under 9 to 1 and it should produce 4-5 lbs of boost (haven't dumped it in the water yet with the new motor....waiting in an oil cooler). I can only assume as to the amount of timing I'm backing out of it right now because I haven't checked with a light what it is at when it runs rough but if I barely turn the distributor it runs rough. I would have to say 3-5 degrees?...which would put my inital down at 7 to 9 degrees. I could recurve the distributor again if needed. I'm just a little leary about haveing the timing up at 31 degrees total. I honestly don't know if it's to much, not enough or just right? Also fuel is 91 octane from last year. Haven't filled the tank up yet. Thank you for your help ThisIsLivin. Mark

ezstriper

you might try running the dist timing locked...I run mine and some others I've set up that way....with the low compression starting not been a issue..really cleans up the idle and low end. the firing order change has been done to help take some load off the crank...drag race tech...Rob

mustangmark

I might give locking the timing out a shot.....any ideas on where total should be set on a 516 with a 250 blower and single dominator? Thanks Mark

ezstriper

I would start at 28 see how it goes from there