New Build 340/420 Questions

Just because I have issues, can you tell me the rpm you are shifting?

I'm going to say that 32-34 at 2800-3000 is in pretty early. I'm guessing that your torque curve is starting to flatten out right there and probably peaks at 3800ish. Maybe a bit higher.

You need less timing at peak torque. So you'll fight tip in rattle and probably end up retarding the timing to stop it.

Then you add in the VA at cruise and it gets worse.


IMO you need to slow the curve down to get the timing at peak torque down to 24-26. and by peak rpm you can be in the low 30's for total.

Also, you should drive the car with a vacuum gauge. Watch what you have for vacuum at various loads and throttle position. You can then work out the VA timing.

Depending on your gearing, engine coolant temperature, spark plug heat range and such you may have to delay and/or reduce the amount of VA the vacuum can adds.

It's a process and it takes some time but it's well worth it IMO.
My shift rpms should be around 5800 to start. My current converter is a 9.5 that was setup at 3800 when it was a 340, so I am guessing it will raise a few hundred now being a 420.
I will choke down the VA for now and I do have a vacuum gauge in the car.
Thanks!