Okay crew, I need your help. As I write this, my engine is sitting idle on a dyno until I can figure things out.
My 383 finally went to the dyno today. I'm using AFR 195's, Holley 750, custom marine cam (214/218) and stock Merc Thunderbolt V out of our '95 Baja Islander. Burning 87 octane with 9.5 comp ratio. Engine fired right up and after initial warm up/break in he pulled the lever. It seemed to run good up to 4700 then it started popping and missing. Dont' have the numbers in front of me since we aren't done but I think torque was 430 at 4500 and hp was 380 at 4700. Cam was ground to go to 5500.
Went online at the machine shop and found a thread on setting proper base timing with the Thun V thinking the timing was the issue. Ground out the purple/white wire with key off but this did not seem to keep the module from advancing the timing once it was brought off idle (still grounded). We un-grounded it during the next pull, still no good. Trying something else, machinist thought the stock knock sensor might be picking up some harmonics from the dyno so we pulled the plug. Made a difference. TQ went to 460 ft/lbs at 4600 (412 ft/lbs at 2900
) and hp went to 400 but everything went to hell above that.
AF ratio looks spot on so everything points to ignition. I printed out the Merc harness diagram from the net and thought everything was good to go. We wired the dyno ignition wire into the #5 slot in the harness. With 98% volumetric efficiency, my machinist thinks I can get another 40-50 hp out of it with an additional 800 rpm. Any thoughts?
Have already looked at an MSD pro billet marine distributor and 6AL with rev limiter. Problem is it won?t come in until Tue morning.
My 383 finally went to the dyno today. I'm using AFR 195's, Holley 750, custom marine cam (214/218) and stock Merc Thunderbolt V out of our '95 Baja Islander. Burning 87 octane with 9.5 comp ratio. Engine fired right up and after initial warm up/break in he pulled the lever. It seemed to run good up to 4700 then it started popping and missing. Dont' have the numbers in front of me since we aren't done but I think torque was 430 at 4500 and hp was 380 at 4700. Cam was ground to go to 5500.
Went online at the machine shop and found a thread on setting proper base timing with the Thun V thinking the timing was the issue. Ground out the purple/white wire with key off but this did not seem to keep the module from advancing the timing once it was brought off idle (still grounded). We un-grounded it during the next pull, still no good. Trying something else, machinist thought the stock knock sensor might be picking up some harmonics from the dyno so we pulled the plug. Made a difference. TQ went to 460 ft/lbs at 4600 (412 ft/lbs at 2900
) and hp went to 400 but everything went to hell above that. AF ratio looks spot on so everything points to ignition. I printed out the Merc harness diagram from the net and thought everything was good to go. We wired the dyno ignition wire into the #5 slot in the harness. With 98% volumetric efficiency, my machinist thinks I can get another 40-50 hp out of it with an additional 800 rpm. Any thoughts?
Have already looked at an MSD pro billet marine distributor and 6AL with rev limiter. Problem is it won?t come in until Tue morning.
