Compression

[ingvey]

Vinnie is correct

I could not agree more usually you see street shops build engines with no understandiing of the difference a marine engine operates under. That ratio has no place.

 

[Taz]

Dreamer, Go w/ a retarded timing # like 30-33 BTDC, fatten up the carb. with bigger jets. And most important make sure they put in a good quality distributor like MSD. I had a 9.75:1 454 (ran 93 oct) in a jet boat built by one of those race car guys and they put a cheap Proform HEI distributor on the motor. The timing at full advance was ranging 4-5 degrees and pitted the pistons from predetination berore I figured it out. Learn how to read spark plugs. They can tell you if you have detination.

You should also try a different prop. to bring you WOT rpms down. 5300 rpm sound to high.

 

[vinny p.]

What alot of guys dont realize, is that retarding the timing too far generates more heat in the cylinder. Not a good thing in the marine environment. Retarded timing = high EGT temps. It causes a slower burn and later burn in the stroke cycle. It causes fuel to continue to burn while exhausting and if severe enough, detonation will occur..

Timing should be set correctly regardless of compression ratio. The correct fuel should be used to work with your compression. Then everything is happy.

 

[happy]

the hei distributor is definatly good to 6000 rpm.. w/no problems... if your timing is fluctuating... its because your set up is wrong.. or your distrib is malfunctioning.. the msd's i've seen have there problems too.. some of the roundabout track guys have two or three of em installed, so one one acts up.. they switch over to the next...

i see alot of 6al's (msd's) out on the water.. and i can tell you in salt water environment.. you may as well have a set of points that have been filed 18 too many times... they hick up... cough... spit ... and as far as i'm concerned as reliable as a set of points..

the hei's have some issues too.. but you'll get back home.. one moters better than none.. and one running is better than waiting on a tow..

after reading back thru the posts.. i'm a lil confused here.. is this gonna be some 1300 hp monster... or is it just lil lil baby... that your trying to detune, so you don't have to buy expensive gas..

if you want a stock engine... sell the one in the boat.. and buy a stock engine.. put 87 in it and be done...

theres some 470's out there that are tea sippers.. not to mention with a in line 4... tons of room to work on em...

 

[dreamer]

Well here is the deal, I was originally a little leary of the engine, thought it might be too much esp. for the drive. I was also worried that the motor was way too built and would be constant maintenance, as well as the constant ned to put 93 in it. I have gotten it home ran it on the water gone through it and it seems great. The boat has an MSD ignition coil and distrubutor, the chip is set for 6000 rpm's. The prop is a 21 mirage seems to work with the boat well, however I haven't been on a big enough body of water yet to really runn it for a long run.