Timing for my 408 stroker

[EMCD]

The stroker is in and plumbed. We ran it for 25 mins at 2500 rpm to break in the bearings. So far so good. What should we set the timing at for 5.5k altitude? I'm running my 670 Holley for now, but will likely upgrade to a 750 soon.

[Jim]

What heads?

32-37 init+mech generally works the best depending on the rest of the combination. That's only part of the equation though. For best performance, you need to limit the mechanical and run 15-20 initial. That will give you the sharpest response off idle. Stock distributors have way too much mechanical advance (like 25 degrees).

[EMCD]

Stock J heads, 2.02-1.60 with a mild Comp cam. You think the carb is too small?

[MEK-Dangerfield]

I guess we should ask if you are using a stock Mopar ignition and distributor?

I'm in the 14-16* BTDC range, but I did need to tweak the vacuum advance back some. The pod on the distributor for the vacuum advance is adjustable with a small Allen wrench. Counter clock-wise to reduce advance.


And yes, the 670 carb is way small.

[Cuda Cody]

My stroker is running best at 32 with a stock carb.

[Jim]

The 670 will be fine up to a point. Really need to know some specifics before recommending more carb. Intake, cam duration, exhaust, compression ratio?

Lots of bad advice floating around about ignition timing. Do your homework. Use the search function.

As I stated previously though, due to the excessive mechanical advance on the stock distributors, they really need to be re-curved. Setting initial timing at 14 might give you way too much total timing. The stock curve is set up for lower initial timing to give better idle emissions and easier cranking. There are several ways to limit mechanical, either by modifying the slots in the stock-type distributor, or using an aftermarket unit with an adjustable curve. Also, disconnect and plug the vacuum during your initial tuning. That's strictly for fuel economy and should be tuned in last.

[EMCD]

I'm running a crane fireball ignition with an HEI distributor. I have an eddy 750 carb but my last eddy was a POS, so I'm a bit eddy gunshy.

[Jim]

I'm not that familiar with HEI's, but I know they can be re-curved fairly easily. Lots of weight and spring kits for them.

The open chamber J-heads will probably like a little more timing than a closed chamber head. Shoot for 16-18 initial, and then another 18-20 mechanical. 34-37 degree total would be the max.   You want it all in below 3000 rpm.

I've run Avengers, Edelbrocks, Carter AVS's and Thermoquads... and several Six Packs to boot. At one time or another, all have given me headaches. I do like the throttle response of a thermoquad.

The 670 cfm should serve you just fine up to about 5000 rpm or so. Feeding 408 inches, your J-heads won't make much power beyond that anyway unless they've really been worked over. You haven't mentioned your intake. That might be your bottle neck.

[EMCD]

Sorry, the intake is a RPM airgap. The builder said the HP would be 400 at sea level.