454 mag max RPMS

Timing sounds too low for that big block. Try adding about 5 degrees and see if any improvement.

I believe that you should have a 24 degree box, so with your 8 initial that should be 32 total, did you change the prop?

desperado said:

Timing sounds too low for that big block. Try adding about 5 degrees and see if any improvement.

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8 is pretty low. You should be able to run at 13* initial timing with no problems.

and here and another thread you say you are also using these heads : 14097088...91-up...rect...OPEN...Gen.V 454/502 HO, 118cc chamber

What cam manufacturer and part# (post specs to if you have them) are you using ? What was the part# to your old heads ? What did the final compression ratio come out to ? What carb ? Did you unhook the MSD and try stock TBIV (which will run your motor no problem) ?

Are you using same prop as before ?

I've never put Gen V heads on a IV block so I can't

The cam number is CRN-134242 226/ 236 286/296 112 lobe sep, I had 990 heads before that were stock with 5 inner valve springs. Final compression is 9.2 to 1, I havent tried pulling the MSD out of the loop, and I am still using the the same prop as last year.

Timing is off, but not too far off, check your plugs..

wildchild212 said:

8 is pretty low. You should be able to run at 13* initial timing with no problems.

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I set mine at 8 at direction of the shop manual and motor builder, he said if I run more timing I might have detonation and I won't hear it on a boat. I havent't messed with it, do you think I can run mor without a problem??

I have always used 34 total without a problem. Stock Merc motors claim to be 8.8 compression but with the deck heights these motors have, most are closer to 8.0. You would have to run really bad gas to detonate.