Offshoreonly.com - 454 420 question...jetting and timing...

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Quote:

Originally Posted by Full Force (Post 3682901)

what props??

23 mirage but plates where mounted high. That boat would blow out and would have to start over on take off.

Quote:

Originally Posted by billy boats (Post 3683114)

I have a lot of experiance with 420's
Just a few things you need to think about
Stock comp ratio is 8.8 with the stock 990 head which is 119cc
Most Merlin heads come 124cc or more
At 124cc comp ratio is now 8.4, that is assuming you used the same thickness head gasket
Next is the intake runner of the Merlin heads WAY toooo big for a 420
Single plane intake manifold will make less power under 5500 rpm than the stock dual plane high rise, more important the torque is MUCH better with the dual plane.
Last is the Jetting of the HP500 carb. It is really 830cfm but merc changes the jetting to stagger left and right in both the primary and secondary's call Holley and jet the stock jetting for that carb and leave it
Timing with that low compression 36

From what I remember the Merlin heads I have were just a tad bigger then stock 420 heads, I know there were a couple different runner sizes, been 5 years so I cannot recall, I used the heads and intakes I got because I got them free with a huge pile of parts I bought, I would have to think the intakes may be more an issue then the heads? I thought about putting in 36 degrees this weekend and see how it runs..??

Quote:

Originally Posted by legend (Post 3683139)

Known Lester for many moons. Good man. Cuts the five hairs that I have left on my head. He loved that boat. You would have a lot of fun with boost!

Yea, he's a good guy, I have redone the whole boat besides paint, thats coming soon.... saw him last summer at his shop and showed him pics of the boat flying... he just laughed and said he never ran it like that....poor boat..

Force, did you ever get a chance to bump your timing to see if that helps any? I am considering the same thing for my 489.

Quote:

Originally Posted by Budman II (Post 3702969)

Force, did you ever get a chance to bump your timing to see if that helps any? I am considering the same thing for my 489.

I did, I am gonna do it again this weekend to check stuff out, so far it went fastest at 34 total...