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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: fiddler on September 25, 2019, 08:49:37 pm

Title: retard timing to use regular gas?
Post by: fiddler on September 25, 2019, 08:49:37 pm

I have a 1974 chevy C10 stepside with a 350.  It has an edelbrock carb and intake manifold and ACCEL high voltage ignition.  I have set the timing to 6 degrees before tdc in an effort to use regular gas as the regular here in California seems to be too low in octane for this engine.  I still get a lot of pre ignition with regular gas.  What are the risks of retarding the timing to use a lower octane fuel??  Thanks for your help,

Title: Re: retard timing to use regular gas?
Post by: 75gmck25 on September 26, 2019, 05:15:46 am

Are you sure your timing pointer is correct?  Factory timing was probably about 4 degrees BTDC, and in most cases you can run about 12 degrees BTDC on regular without any pinging issues with a stock 350.   

Bruce

Title: Re: retard timing to use regular gas?
Post by: Irish_Alley on September 26, 2019, 08:24:24 am

im with bruce. i would verify TDC is actually TDC on the timing marks before doing anything else. a low compression engine should be able to run regular gas with at least 12° timing with no issues and thats before the vacuum advance kicks in.

Title: Re: retard timing to use regular gas?
Post by: roundhouse on September 26, 2019, 09:36:32 pm

I always just set the timing with a vacuum gauge or by ear

Just drive it up a hill and floor it
If it pings , retard it 2 degrees
At a time till it stops pinging and don’t worry about what the pointer or light says

Using a timing light on  My bronco says it’s at 28 degrees idling
 But it runs great so what the light says is irrelevant

Title: Re: retard timing to use regular gas?
Post by: JohnnyPopper on September 26, 2019, 11:03:57 pm

I'm with roundhouse, timing lights are so unreliable I just gave up and time with a Tachometer and my ear.

Find your average highway RPM range and twist that girl till she bucks and back off till she purrs.

Jus sayin... ;)

Title: Re: retard timing to use regular gas?
Post by: FlatBlack77 on September 27, 2019, 08:39:12 am

I'm at 12btdc with only minor mods and I run 87 all day every day. That advance in timing was like turning a horsepower knob. Night and day difference

The timing cover and pointers might be bent or not even original to that motor or balancer

Title: Re: retard timing to use regular gas?
Post by: roundhouse on September 27, 2019, 02:46:55 pm

Quote from: JohnnyPopper on September 26, 2019, 11:03:57 pm

I'm with roundhouse, timing lights are so unreliable I just gave up and time with a Tachometer and my ear.

Find your average highway RPM range and twist that girl till she bucks and back off till she purrs.

Jus sayin... ;)

For the vacuum gauge I hook a gauge to the manifold and advance the timing till you reach max vacuum and back off about 2 inches

http://automotivemileposts.com/garage/v2n8.html

Title: Re: retard timing to use regular gas?
Post by: fiddler on September 29, 2019, 01:51:51 am

So I will run a sanity check on my timing light on another vehicle.  Thanks for the replies all.  Information I needed before I did something drastically wrong....

Title: Re: retard timing to use regular gas?
Post by: FlatBlack77 on September 29, 2019, 04:05:58 pm

Just to make sure
You are unhooking the vacuum line from the vacuum advance and plugging it before checking the timing right?

Title: Re: retard timing to use regular gas?
Post by: fiddler on October 03, 2019, 05:01:24 pm

Yes on the vacuum line.  Thanks for asking.  The digital advance knob on the timing light is easily jostled.  I may have inadvertently moved it.  I ordered a light without any fancy advance stuff.  I just want a strobe when I hit the spark at number 1!

Title: Re: retard timing to use regular gas?
Post by: VileZambonie on October 03, 2019, 06:07:33 pm

Your base timing setting is just a starting point and will provide you with no performance improvement if you are setting it there and leaving it. An advance timing light is the way to go.

Title: Re: retard timing to use regular gas?
Post by: JohnnyPopper on October 03, 2019, 07:50:10 pm

Thanks RoundHouse!

That link is solid gold, BOOKMARKED!

Title: Re: retard timing to use regular gas?
Post by: VileZambonie on October 05, 2019, 08:09:57 am

I do not agree with that method but beware if you are following those directions in that link. For sbc or bbc the instructions for advance or retard are reversed.

Title: Re: retard timing to use regular gas?
Post by: JohnnyPopper on October 06, 2019, 09:42:15 pm

Thx for the heads up VZ  :D