joelevelis@comcast.net

The engine was built from a 318 long block from Marshall engines. It was assembled with:
1- Mopar cam and lifters PN 4452759 .221/.228 duration and .430/.450 lift.
2- Edelbrock Performer maifold Pn 3776
3- Edelbrock 600 CFM carb.

.
The Factory spec base Ignition timing timing is supposed to be 5 degrees BTDC.
With the 5 degrees cranked in the engine idles poorly, and manifold vacuum is only 8-9 in./hg and idle mixture screws require four turns out.
As the timing is advanced the performance improves, for example
At 14 degrees idle smooths out and vacuum is 12 in./hg
At 28 degrees vacuum is 19 in./hg.

The cam is indexed correctly.
Compression check was 125- 135 across all cyl
swapped carbs /no joy
swapped distirbutors /no joy

Is Any one out there running this combination, if so what are you seeing for vacuum/ what base ign degrees are you using?

The distributor is mechanical advance only and it works correctly.
my thoughts are to modify dist. to only 20 degrees advance so i have 14 degrees at idle and full advance to 32-34 degrees .

The engine is in a boat clearances are minimal so any thing to do with timing tape would require expensive engine removal.

Any thoughts or comments would be appreciated

Joe

RacerHog

I think your on the rite track..... My thoughts....
Set your base timing at 18 @ Idle
Have all the advance in by 2200 RPM's....

OR

Try setting the the 34-38* of timing @ 2200 RPM and see were the base idle is when the engine comes back to idle.....

I feel with that cam you should be able to get at least 18hg of vacuum. so thats a little puzzling to me. But a little less is ok. You can live with that...

If the above dose not work, You might try a re-curvered dist.

Just my 2 cents

Boats are fun......

440roadrunner

"In a boat" you need to be mindful of marine approved components for explosion hazard, no small thing

You can recurve your factory dist by brazing/ welding up the advance slots and filing them back out. If this seems to be similar to a Mopar automotive dist, "somewhere" on the internet are figures for approximate slot lengths vs distributor degrees:

Dimensions for Mopar distributor slots, in DISTRIBUTOR degrees

Modifying advance slots
degrees / slot size
6.............. .340
7................355
8................375
9................390
10...............405
11.5 ...........420
12...............435
13...............445
14...............460
15...............475
16...............490
17...............505
18...............520

Now the above is DISTRIBUTOR degrees which are HALF "crank" degrees so if you want 16* advance at the crank, you want EIGHT in the dist, or about a .375" slot length

If you are unable to mark or tape the balancer, your only alternative is to find a GOOD "delay" or "dial back" timing light. I would use a piston stop to make darn sure the timing mark is correct