-
So the motor in my boat is a Harman Marine 405hp,454. As far as I know it's all original (1981) except intake and carb. Tag on the block says run 94 research octane, initial timing at 10 degrees. The heads are open chamber rectangle that I think are 118cc. I havn't had the heads off but by sticking a wire in a spark plug hole with the piston at the top the pistons seem to be flat top. I found an old spec sheet on the motor that says 8.75:1 compression and the flat top pistons seem to comfirm this.
My questions are: is my timing OK at 10 degrees initial and 35 total? And with that timing should I be OK with 91 octane pump gas?
Thanks
Gary
-
You'll be fine on pump-gas. You can likely even run 87 on it if you want to. I'm running a 454 at 400HP with large oval port heads flat tops, and 123cc chambers. That runs me just a hair under 8.5:1 .You don't really need to get over 90 IMHO untill you get a bit over 9:1 and liklely could get close to 10:1 on 93 octane. I usually run premium to go with my Nitrous usage, as a backup for detonation protection.
10 degrees initial timing is fine, 35 to 36 is good total, right where it belongs. I'm currently running 8 initial breaking in my rebuild and she does run strong! Will goose her to 10 to 12 or so in a few weeks. See what she'll take without problems.
Incedentally, here's a link to data qued to your casting numbers if you care to look at the back of the block above the bellhousinbg and under your valve-covers:
http://www.mortec.com/bbc.htm
-
Just for reference, I run 10.8:1 and 36 deg timing on 91 octane and have zero problems with detonation. There are a few things in my favor though, aluminum heads, ceramic coatings, and 120-130 deg max coolant temp... and a knock sensor, just in case!
-brian
-
So the motor in my boat is a Harman Marine 405hp,454. As far as I know it's all original (1981) except intake and carb. Tag on the block says run 94 research octane, initial timing at 10 degrees. The heads are open chamber rectangle that I think are 118cc. I havn't had the heads off but by sticking a wire in a spark plug hole with the piston at the top the pistons seem to be flat top. I found an old spec sheet on the motor that says 8.75:1 compression and the flat top pistons seem to comfirm this.
My questions are: is my timing OK at 10 degrees initial and 35 total? And with that timing should I be OK with 91 octane pump gas?
Thanks
Gary
Ok to make it simple, with that compression you don't have anything to worry about with 92 skunk piss!. As far as timing goes there are several factors that determines optimal timing but the easy way is to experiment with what you have and see what performs best!.. I would recomend putting 24 in the distributor and have it all in by 2500-3000 and 36 total to start off with and go from there!... But that's what I would do!...
-
Thanks to all for the replies. I currently have 25 degrees in the distributor so with 10 initial I'm looking at 35 total. I may try dropping back to 89 octane and see how it runs. I was starting to get worried about detonation eating up my pistons but I'm feeling a little better about that now.
Thanks again
Gary
