tpabayflyer

Not yet......I will have the engine on a run stand tomorrow or Thursday....... I will pre-oil and get the compression tester on it when I can crank it.....

bobl

Every N/A BBC (with traditional heads) I've dyno'd runs best between 34-36 degrees total timing. Running less than 34 starts dropping power fast. Generally speaking, if you need less than 34 degrees of timing to stay out of detonation there's something wrong with the combination or fuel quality. I personally wouldn't run a 10:1 engine hard on less than 91 octane, even with aluminum heads.

Bob Lloyd
Full Throttle Marine

Black Baja

iTrader: (2)

Rod length and stroke have alot to do with what timing to run. The longer the piston dwells at top dead center the less timing you need... Your setup 32-36 degrees will be fine I doubt you would be able to notice 4 degrees of timing difference in a boat. Barely notice a 50 hp increase.

tpabayflyer

I did go with the longer 6.385 rods as I had a choice as I needed to get new pistons and rods...... Also the shorter piston made the weight a little less which can't hurt but I did not know about dwell time.... I will read up on that... Thanks.... I should have some compression numbers tomorrow....

Budman II

iTrader: (1)

In MildThunder's thread about detonation and preignition, I touched briefly on the issue of timing with the more efficient "fast burn" combustion chambers that are common on modern heads. I think someone chimed in (Haxby?) saying that a fast burn chamber should make good power with less timing advance than what is needed on the 40-year old chamber designs on the stock heads. Not sure what kind of chambers your heads have - might be worth consulting them to see if they say anything about timing advance.

Like MER said, the dyno is the best way to determine optimal timing, but even that could change when it is in the boat, under a different load in different conditions. Good luck, I'll be crossing the same bridge soon with my 489.

tpabayflyer

That was an excellent read about detonation and pre-ignition..... I saved it for my archives!
I have the pro-comp heads and the chambers look like just about any other BBC so nothing
Special there...... I will run the engine for a while on the stand and set the timing at 32-34 degrees for my ride home. Marine shop is in St. Pete and I am over in Tampa so I will go pretty easy on the way Back.....3000rpm at the most and I will vary that for a good break in..... I have a protected lagoon I can use for tuning and dialing in the jetting using the wide band once I get the boat back on the dock.......

Donzi1979

iTrader: (1)

tpabayflyer ,

I have the same boat with a HP500 (carbed) I run 34* total seems to work well (less compression and use 93 octane). I'm able to get 71 mph out of a stock 24p bravo and 73 mph with a labbed 26p both at 5200RPM bravo and my drive is an XZ. I think you expectations are realistic.

Michael

Unlimited jd

iTrader: (5)

Michael you should save some money and run 89 octane. No need in the hp500 for 93.
As far as the op I think 34 will be fine. 36 may make a slight bit more but 36, 10:1 and nothing special chambers may not be worth it.

Black Baja

iTrader: (2)

Hp500 only need 87 octane any more and it will make less power.

FIXX

iTrader: (2)

i would not sweat it at 35* of timing,,your going to be running in water which rund cooler,,you can shave 1 point of compression when using aluminum cylinder heads..in other words it will act like a 9:1 motor..cast iron heads build and hold more heat which will detonate faster..the only thing i forsee you having issues with is the procomp heads,,they dont like salt water or any water and dont seal too well..