How does a ignition system react to Overdrive

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Jul 14, 2019 | 10:16 AM

footjoy

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From: Shawnee, ks

How does a ignition system react to Overdrive

This is for the old school out there. I am curious to know how you set up a carburated engine with Hei for overdrive that does 2350rpm at 70 miles an hour.
Pontiac 400
I am set up at 34 degrees all in at 3100 rpm. and I get 11.5 miles to the gallon mechanical comes in a 25-2600 rpm.
Speedometer has been checked and double checked
I have used ported and full manifold vacuum
I have used 730 Quick fuel and 670 holley avenger.
2004r with 3.73 final 2.499:1

What happens to timing at partial throttle at 2350 rpm going down the highway?

I am not sure this makes sense. But give it a try.

Thanks
Greg

Jul 14, 2019 | 05:34 PM

footjoy

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From: Shawnee, ks

Quote:

Originally Posted by vorteciroc

Are you looking to reduce the ignition advance for better highway cruising/ fuel economy?

If you are... the vacuum advance is where this would be accomplished.

Let me know and I'll give you instructions.

Yes I would like to know

Thanks

Jul 14, 2019 | 06:43 PM

badass68

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Using vacuum advance will give you much more timing while cruising. 40+ which will help mileage. I have a 73 vette with a Vortec 350, 700r4, Holley 600, and hei that gets 25mpg at 80.

Jul 14, 2019 | 07:09 PM

footjoy

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From: Shawnee, ks

Quote:

Originally Posted by badass68

Using vacuum advance will give you much more timing while cruising. 40+ which will help mileage. I have a 73 vette with a Vortec 350, 700r4, Holley 600, and hei that gets 25mpg at 80.

How much vacuum advance are you using and are you using full manifold or ported?

what is your intial and mechanical timing?

Thanks

Jul 14, 2019 | 09:34 PM

badass68

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From: Houston

Around 10 degrees using manifold vacuum. 34 total without vacuum advance.

Jul 15, 2019 | 07:39 AM

MaroonMonsterLS1

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From: Iowa

vacuum advance distributor will help increase timing under light load (high vacuum) thus improving highway mileage.
what's the tire size. What's done to the engine? What fuel?
are you using the torque converter lockup function?

Jul 16, 2019 | 03:23 PM

footjoy

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From: Shawnee, ks

pontiac 400 bored .040
Crower cam 421 and 446 lift
8.75:1 compression
2004r transmission
3.73:1 rearend
28" tires

gets 10 mile mpg in town and 10 mpg cruising at 70

It cruises at 2350 and I dont think I am getting any advance while cruising.
Thanks