Good post, MT, and I agree that you have to be smart about tuning these engines. The discussion in the article about combustion chamber design and timing greatly interested me. I am switching from stock GM heads to AFR 265's on my little old 489, and I am wondering how much that will affect the timing curve for the engine. Not sure if the AFR chambers are a true "fast burn" design, but they have to be more efficient than the 50-year old technology that the GM heads were sporting.

My plans for this engine are to end up in the 575 - 580 HP range with a conservative tune to help promote longevity. I like turtles too - don't want to be the hare blowing up out on the water.

Food for thought. Stock Supercharged Cobra Mustangs fuel down to 11.1-11.2 at power enrichment. Turbo Buick guys, are fueling into the 10's on afr. A buddy of mine with a boosted up Grand National, actually made more power on the chassis dyno at the richer AFR. Leaning it down lost some power.

I personally think on a boosted marine engine, tuning to upper 11's, at full kill, is gonna cause an early death. I personally pulled some fuel from my setup this year, thinking I was giving up power in the 10's on afr. By leaning it out some, the boat actually slowed down. Maybe on the dyno it works for making max hp, but maybe for me, the added fuel helped cool things down. IDK.

Say it MILD THUNDER....say, i like turtles with small blower pulleys!!!!!!!

265's are too small for a 489,,i would step up to the 295's...you will hit a wall @ 5k with the lower cfm number..

Glad

Off topic but...., that is 100% incorrect, and bad advice.

enlighten me!!!! EDIT.. did not want to hand out the popcorn on this one..

afr,s website sais the 265 is for 396 to 468 cu in,i know we are talking about 21 cu in difference but if it was my decision id go with the 290s,just my opinion.

"enlighten me!!!! been their done this would not rev over 5 k,,maybe good for a cruiser..switched to 295's and picked up 1200 rpm.. "



Here we go!

I'm going by what was recommended to me by a highly regarded marine valvetrain designer who ground the cam I am running. Have read several articles that says that these heads can support 700 HP - not saying a 489 would ever make that, but just what I have read. I never plan to spin this rig above 5500 RPM, so I guess that is a factor. Sounds like your results varied.

Oh $hit. How does every thread get into a pi$$ing match! Just wanted to share an article that I found informative.

Im going back to playing with my Turtles.