602 timing ?

[SRXSRULE]

What have you found to be the best ignition timing when using 105 octane? Sealed crate, just as it comes from GM, with the GM distributor. 500 CFM 2bbl carb. Thanks Eric

[rubbinsracin]

We like ours at 32* but we use 98 renegade

[dynoman14]

Eric,
Is your 500 a stock 4412, or a Dorton carb?
What jet, power valve, & power valve orifice ( 2 holes behind PV ) are you running? How many holes does your metering block have in the jet well column ( right above the jets is a tube with 2,3 4 or 5 holes in it ).

105 octane is a pretty generic number. To me the important numbers are the MON - Motor Octane and the burn curve of the fuel and if it has oxygen and if so how much %.

The 602's I have run on the chassis dyno like pretty laid back timing 24-28, a good medium burn fuel, a projected tip plug not too hot and pretty rich fuel curve as you hit peak torque and then getting a little leaner as you get up above 5500rpms. As you can see I run way less timing than most and make up for it in fuel burn in the combustion chamber. The later you can delay the spark the less your engine fights the piston coming up to TDC with combustion on top of it.

When I spend a day on determining the timing curve of a distributor on an engine type there is 15-20HP just in delaying initial lead timing and adding it back in closer to peak engine torque where the engine really wants it. Above that it is nice if you can induce a little retard to help the engine run up on the top end.

500 2bbl is pretty unique as you have to address a couple problems inherrent to the carb like top end pullover, midrange lean out, and low end fat conditions. Pretty much the carb was designed for pullling a heavy street car and the way the carb pulls fuel reflects that.

Running your carb on an engine dyno or chassis dyno can easily pull another 15-20HP out of it.

Rubbinracin, is about dead on for Ren98 as I have a coulple carb customers in TN and IN that run it.

As far as all the timing stuff, I have been running this way for 25 years or more, if you want to look at dyno sheets and how a couple engines ran utilizing this you can look at the engines that won the Engine Masters competition this year. This months issue of Engine Masters explains theory on small bore, big stroke, short rod to stroke ratio, fat fuel curve and all the other BS I get hammered on here about.

Looks like there are more dumb people like me out there after all.

[stock car driver]

What have you found to be the best ignition timing when using 105 octane? Sealed crate, just as it comes from GM, with the GM distributor. 500 CFM 2bbl carb. Thanks Eric

Eric, I wouldnt think you would be running 105? Tracy and I are mixing fuel for our 10.5 motors. When I did the mix vs 110 on the chassis dyno it smoothed out my power a lot and also gained some hp.

Also since you have a rochester 2 brl and exhaust manifolds Eric your timing will be different from mods or lates with the same motor most likely.

[Matt49]

All fuel curve issues aside (as I won't claim to be an expert there), keep that motor UNDER 32 degrees advance timing. Anybody I know that has had major problems with a 602 or 604 (i.e. burnt pistons, etc.) was past 32 on full advance timing.

[SRXSRULE]

Ok.....more info here.

I run a 602 crate in a 3,000lb street stock car. We have to run a 2 bbl rochester carb, cast iron exhaust manifolds with 2" od down pipes on them.

I am mixing 110 race gas with 91 pump gas. I looked at 3-4 online octane calculators and thats where I came up with 105. After checking 4-5 more sites tonight it looks like the real number might be more like 98 ocatne.

I have to run the distributor that came in it from GM. I and currently using the stock weights and total advance is at 32*. It has been tuned on a chassis Dyno and the fuel curve looks good.

Just wondering if there was anything to be gained with the timing as the last two trips to the dyno was for testing in other areas. Thanks Eric

[stockcar5]

vortec heads like 30-32 degrees typically. with that said the best thing to do is dyno it and find out what the motor likes.

[stock car driver]

You go pay for dyno time and dont try the timing at different settings? Ive heard some goofy stuff about Johns dyno service but thats a new one on me if your not optimizing your timing.

All my vortec head motors have always liked one setting up to 6000 rpm and a few more degrees of advance from there on. Thats what dyno dumb is always talking about in matching timing to the motor. I can gain 10hp by having advance that comes in at about 6000.

jj

[SRXSRULE]

With my claimer motors we always played with timing along with many other things on the dyno.

Last year we played with the timing on the crate but I was using different fuel.

This year I have been doing a bunch of testing with all the parts on the outside of the motor Have picked up 24 RWHP. Its hard for me to get to the dyno during the week so testing is kind of limited. I can only try so many things.

Next time on the dyno I will be trying different timing and fuel. Eric

[stock car driver]

Gotcha, I would bet that fuel is way too much, its more than Im running on 10.5 compression motor, BUT my heads arent vortecs so we cant really compare.

[dogface]

we are running a msd dist in a 602 should it be factory or locked

[Dirt Knife]

Vortec

Run vortec headed 2pc seal block with 4bbl on my S.S.
550 lift mec cam Q-Jet Jet proformance cast iron intake and exhaust

Run 38 deg If I run less the stock 2.25" exh manif glow

Plugs look nice

[Egoracing]

If you are running rich then adding timing will hide the rich condition. I have not seen many vortec heads that like much past 30-34 if everything else is right.

[sj valley dave]

Ego is right...with Vortecs heads get the timing down to 32* or so and go leaner on the jetting...

[SteeringGuy]

Dynoman14, Do you prep HEI for Dirt Track racing? Email me some contact info. I have a few questions. Thanks Larry