So i am playing with a old 1987 mirage intruder payed 8000 and its been garged by a little old man most of its life and sadly maintained by him. Ive pulled a 180 degree thermostat out for starter's and have propped it from a 19 to a 23 and the deeper i look the more thing's start to show wtf was he doing. Ive gotten the old book's out and was going to start from scratch when i noticed the timing curve's from merc.. are they conservative.



If i have this right the motor's all in at 2500 and 3o degree's...its a tbolt 4 sytem...Any suggestion or input would be welcome...Ahh he also muffled the thing..quite large round caniter's ss about 7" in circumfrance would they restrict it a bit...the 19 only pushed to to 5000 and it very under propped..very sluggish throttle response and have changed the fuel water filter.

So i intend to try 34..36 degree's total timing this should not be to agressive for a big block or am i wrong

Stock is 32* total timing.
It depends on which ignition module you have as to where full advance occurs.
Most 454 mags had V8-24's and full advance is around 3700rpms
34* total is fine, but I doubt you'll gain anything over stock.

Have a 1986 Century 4500 454 magnum. 23' and 4300 lbs.Hull is very similar in design and runs a 17 pitch prop. Tried a 21 and it wouldn't pull over 3800. Early magnums used Alpha drives with high gear ratio, 1.32:1. Starting in 88 they came with Bravos and had 1.50:1 ratio. Yours is probably an Alpha and you are fighting high ratio. Those engines were also only rated to just over 4600 rpm for longevity. If it is pulling 5000 with the 19 and it has the higher ratio leg you are probably set up quite well. Those were only rated at 330 hp unless it is the hp version which was about 365hp. Cast cranks were reason for keeping revs and hp down. As far as throttle response, check compression, plugs, how much old fuel was in it etc.

Funny setup or different from what i am used to..I took a close look at the total timing and Griff is right 25 at 4000 add the intial 8 and 32 wins i am still going to try 34 maybe 36. As to the propping i tried a 21p alum good shape and it still just ran up to 5000 and quit....But the slip on the 21 was 25% next stop 23 good ss 4 blade and off with the muffler's.one would expect mid 60's with that much touqre i will find out. Yes it is a old mcm 454 330 hp

21 aluminum was probably near equivalent to the 19 ss due to flex. Like to hear how 4 blade 23 works. I am in process of converting to Bravo 1.50:1 leg with higher hp 454(400hp?) and was going to try a 23 or higher prop to start. Hope to get the old girl into mid 60s at 5K rpms. Was good for high 50s at 1500 ft before. She had stock manifolds with thru hulls below waterline but that is going.to be changed too.