Hey guys:

I have a pair of 1999 Merc 7.4ltr engines. They now have HP500 style intake and Holly 750 carb. Edelbrock alum heads, 502 roller cams, emi thunder exhaust and msd 6al boxes with pro billet dist.

Nothing fancy, just made to breathe better.

Lower is all stock.

What is a safe wot RPM?

Plug Gap? Now set at 35 thousands

Timing? 8 deg btdc at 750-800 idle rpm

Any thoughts would be appericated.

I'm not certain on your plug gap however it sounds like you could open it up a little since your running the MSD box (about .005 more than stock). Someone who runs those should chime in and let you know or otherwise go to MSD's site and do a search. In regards to your timing I assume you have different curves you can use or set? Regardless of what works with your application be sure and time it at full advance. when checking with your timing light continue to rev the engine until you timing is fully advanced. All engines vary what works best for timing however to be on the safe side I would set it at 34 deg with your set up. Perhaps up to 36 but no more. I would think your idle would be pretty rough at the moment and your only at about 32 degrees total advanced assuming you have the box set at a 24 deg curve. Be sure and check your total advance before you do any running on the water.

Read the owners manual on the MSD box if you have one. In most cases the shorter the curve the better. That's why you'll see many boaters who use the TB ignitions like to use the v-6 modules with a 16 degree curve. It helps get you to full advance quicker as well as cleans up the idle while allowing you to have a higher base timing. Just remember though regardless of your base timing make sure your total advance is as mentioned above. Do you use marina fuel or 92?

Should have mentioned, total timing is at 34 deg .

Being as compression is stock I run 89 mid grade fuel.

I think I'm where I need to be, safe for best overall performance.

Thanks for the help.

You should be able to open the gap to .040-.045.

Open up the gap! I was running .050 with my Jacobs setup, I tried setting them at a tight .040 it scrubbed about 1mph of top end plus the idle was not a smooth. If you have the fire power use it that is what it is for!