What total timing is required for N/A engines?

[snailmont5oh]

I'm in the final stages of getting my most recent setup ready to run, and I would like some advice on where the total timing needs to be. I'll be running a COMP XE270HR, and GT40-P heads. I'd like to know the total timing, because I am also running a Crane electronic distributor, so I have a few choices for mechanical advance, vacuum advance, and base timing.

Any suggestions? Tuners?

Thanks for the help.

Later,
Mike.

[Killercanary]

Start at 32* and ensure that it doesn't detonate. With an aluminum head generally the total timing will be around 34-36* the GT40P irons may not allow this much.

[yeahloh95]

stat at 10 deg base and up it from there til it rattles

[Rodeheaver's]

is this a carb set up? how much additional timing can you add?

[yeahloh95]

YES he has a demon 625 carb i think

[Rodeheaver's]

if its an msd dizy, you can change the bushings inside to change how much total timing you are adding, then you can change the springs inside to change how soon the timing will come in, on a small block car i like to start with one heavysliver and one light silver spring and the blue bushing, i would set initial timing at 12 degrees and total will be 33degrees @ 3500rpms (+ or - 200rpms), then go up from there, the only way to really know what you change is doing is to have the car on a dyno, it is very hard to tell on the street if you are helping or hurting the power.. this should be a good safe starting point..

[Pure Stock]

It's a guess, until it's dynoed.

[snailmont5oh]

stat at 10 deg base and up it from there til it rattles

I'd like to know the total timing...

I'm talking about total timing, Troy. Besides, I've been told that the P head will give up power WAY before it starts to knock. Are you trying to make me slow or something?


is this a carb set up? how much additional timing can you add?

I can add 20º, 24º, or 29º


if its an msd dizy

...because I am also running a Crane electronic distributor...

I have selector switches that allow me to choose different mechanical and vaccum curves, and I adjust baseline timing the standard way.

I'm thinking that I'll be starting at 28 to 30º, and doing some third gear pulls through the RPM range to see what is quickest. Dynos are neat, but the road is freeeeee.

[blaze00]

its free unless you blow your motor. iv always done street tunes but i had electronics data logging my afr's, timing, and knock. id keep it conservative until you have the time\money to get it on the dyno.

[Rodeheaver's]

cool man, lmk it you need a hand..

[badf250]

We run 30 deg in our race motor but it locked down at 30 deg, with no advance, but it is a race only circle track motor with dart iron heads.

[snailmont5oh]

Thanks for all the help, guys.

[Mark Aubele]

Sorry I saw this so late, but way back when I ran GT40p's, we found the best numbers at 32 degrees (total) timing. FWIW, the heads didn't seem too sensitive to timing changes. If I remember correctly, from 26 to 34 degrees total peak power was very consistent, we ended up at 32 because it was stonger off idle with a little more timing. Was speed density, stock 86 shortblock, explorer heads and intake, stock cam and rockers, stock airbox and aftermarket exhaust (short tube headers). Made 258 at 5300 rpm and 300 lb/ft or torque flat. I can't remember the exact rpm, this was back in 01. Ran 12.7 at 107 on little 235 bfg dr's.

[snailmont5oh]

... but way back when I ran GT40p's, we found the best numbers at 32 degrees (total) timing. FWIW, the heads didn't seem too sensitive to timing changes. If I remember correctly, from 26 to 34 degrees total peak power was very consistent, we ended up at 32 because it was stonger off idle...

That's inline with what I've been hearing from other sources. A fella from MaximumMotorsports told me on another board told me to expect it to like between 28 and 32º, and not to bother going any higher than 32º because the heads would give up on power long before they detonated.

It seems to run pretty good with 30º total right now, but I think I have too much jet in the primary side of my Speed Demon. I have a tip-in stumble when accelerating from cruise, and it gives up a bunch anywhere over about half throttle.

Other than that, it's GREAT to be driving a Fairmont again!

Later,
Mike.

[snailmont5oh]

Well, the people at Demon tell me that the cam needs 14-16º initial timing, and that's why I'm having hesitation problems. That means that I'll be running in the 34-36º total range, because the Crane distributor won't let me add any less than 20º. Shit.

[LX2NV]

Well, the people at Demon tell me that the cam needs 14-16º initial timing, and that's why I'm having hesitation problems. That means that I'll be running in the 34-36º total range, because the Crane distributor won't let me add any less than 20º. Shit.

these are the same issues i'm running into. you have to get creative.

[Killercanary]

Mike, can you hook up some sort of retard device to pull some timing out up top if 34-36* is too much? How does the advance work in the setup you have now?

[snailmont5oh]

How does the advance work in the setup you have now?

I believe that the distributor uses counts from the optical sensor to determine RPM, and applies electronic doodadery to decide exactly when to send the "okay.....NOW" signal to the ignition amplifier.

I'm not exactly sure how a stand alone timing retard box works, but that would probably be the only solution. On the bright side, if I needed to use one of those, I would be just that one step closer to the twin turbo setup, would't I.

Also, I set the timing to 14º, figuring that I could give up a couple of top-end horsepower if I could get the driveability that I want, and it worked. The hesitation is gone. Using Mark's data, I can rationalize that I'm probably not giving up much, but gaining tons down low. I'll take it for now.

Thanks for the help, all.

Later,
Mike.