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Old 10-20-2008, 07:16 PM
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Oldsmobile Distributor Curve for Marine Use?

OK-
This is a little off topic but perhaps someone can help me.
I have a 20' Jet boat with a 1976 455 Olds V-8 and HEI.
Max revs are 5500 and the distributor has no vacuum advance.

Can anyone recommend the optimum advance curve for such a beast?
Would it be similar to an automotive application?

Specs are:
455- Stock w/8.5:1 Compression.
Moderate 'Jet Boat' flat tappet, hydraulic Comp Cam (I can get specs if required).
Single 4bbl (Edelbrock 650) on an Edelbrock Performer dual plane manifold.
Berkeley 12-JE jet with Place Diverter.

Any advice would be greatly appreciated.
Thank you!
Elm

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Old 10-20-2008, 09:03 PM
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Boat motors don;t need a vacuum advance.
A good advance curve would be 12 to 18deg at idle. Advancing smoothly from off idle to a max limit at around 3000-3200rpm maxing out around 32-34 deg.
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Old 10-21-2008, 01:18 AM
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Play with total timing to see what gets you best speed. The jet will let you rev up quick and limit "loading" on the engine, so you can get pretty aggressive if you're not getting detonation. You probably are also running a 165 degree stat which keeps things a little safer.

Depending on the heads, Olds like to see 34-38 degrees total. Have it all in by 3000 or so. If you have a marine distributor (you do have a marine distributor, don't you? ) it won't have vacuum which is good. Some squirters run vac advance because they think it helps holeshot, but you really don't need it.

Initial timing is pointless as long as you're not getting part throttle detonation or starter kickback.
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Old 10-21-2008, 07:48 AM
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Marine Distributor?

Marine distributor? With all due respect, other than some waterproof connectors and no vacuum advance, there is really nothing different about a marine vs automotive distributor other than the outrageous price difference.

My friend bought a DUI 'Marine' HEI- We took it apart to see what gives.
Other than a plate lock replacing the vacuum canister, there was NO difference vs an automotive HEI.
A scam IMO. Now Marine fuel pumps, carburetors and alternators, that's a different story..

Thanks for the advance tip!
I didn't think about just winding it up and setting the timing for top speed/RPM.
Should be simple enough- Then I can just tweak springs and maybe advance weights to dial in the rate of advance.

Thanks again!
Elm
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Old 10-21-2008, 08:49 AM
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Quote:
Originally Posted by ezobens
Marine distributor? With all due respect, other than some waterproof connectors and no vacuum advance, there is really nothing different about a marine vs automotive distributor other than the outrageous price difference.
I highly disagree. Marine distributors have to have spark arrestors just like alternators and starters. There is a 40,000 volt spark in there, you might want to isolate it from the fumes.

Plus, if you ever boat where the law is a concern, not having a USCG approved distributor can mean impounding your boat.

I also disagree with the price. You can buy brand new marine distributors from Summit, Jegs, and many other sources for much LESS than automotive dizzys because they don't have vacuum. The main difference is the spark arrestor which costs them 35 cents.

Pertronix billet marine dizzy for $222
Same Pertronix billet dizzy with vac advance/without spark arrestor for automotive use; $229

Those are chevy examples, but there are a few million olds engines in marine junkyards that you should be able to find one for $25. During the fall and winter when marinas are trying to generate income, you'll see a few hundred of them on Ebay for next to nothing. If your Olds is in an open engine room, the chances of it igniting fumes is slim, but I've seen it happen. I've worked/lived summers at a Marina since I was born. I've seen my share of exploded boats and almost always it was a non-marine component that caused it.

Its really more important than you think... but you're right... there is no difference in the guts of the dizzy except for no vacuum advance. The spark arrestor and USCG approval number are the main things. Since they cost the same or less than automotive dizzys, it not only saves money, but it makes you safer and legaler. (that's not even a word )

But on the topic of advance, I think you're on the right track. Try not to burn your hand on the headers like I did

Last edited by curtis73; 10-21-2008 at 08:59 AM.
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