Engine is Happy at a Certain RPM Range

[Murd]

The speed hut tach can be configured for different numbers of cylinders. Any chance yours is set up for something other than a V8?
You are disconnecting vacuum line from distributor when setting timing correct?

[91 Tiger]

First post for me! I am very interested in how the idle situation on the 427 played out. I have a 393 stroker with similar issues. Does not like to idle below 1250rpm. Happy at this RPM but would like to have idle around 800rpm. Mine will also lurch with my Tremec Magnum trans in 1st gear. I have CompCams 35-426-8, RPM Air Gap, QF 750 SS mech secondary, I think my timing is 14* initial 36* total by 3000rpm. My MSD vacuum is not adjustable. I've been told I may need more that 21* initial timing and use 14* busing in the MSD so that I am all in at 35*. I am pulling 15" of Hg at 1250rpm idle. Vacuum shakes a little. I would get the M/E PCV if that would solve the problem.

[GWL]

This thread was started by ThickCobra in 2018, who's last post on the forum was on April 19, 2021, just a few days ago. So, send him a PM with your questions or you may be able to exchange phone # via the PM.

George

[RRussellTx]

First post for me! I am very interested in how the idle situation on the 427 played out. I have a 393 stroker with similar issues. Does not like to idle below 1250rpm. Happy at this RPM but would like to have idle around 800rpm. Mine will also lurch with my Tremec Magnum trans in 1st gear. I have CompCams 35-426-8, RPM Air Gap, QF 750 SS mech secondary, I think my timing is 14* initial 36* total by 3000rpm. My MSD vacuum is not adjustable. I've been told I may need more that 21* initial timing and use 14* busing in the MSD so that I am all in at 35*. I am pulling 15" of Hg at 1250rpm idle. Vacuum shakes a little. I would get the M/E PCV if that would solve the problem.

I have/had a similar issue and I believe mine is due to the Manifold and Cam. I replaced my AirGap with a lower RPM intake and it got much better and saved some room under the hood. Cam still makes it a little rough but it is much better. I have the Edelbrock #2281 cam with a Basic Operating RPM Range of 1,500-6,500

From the Summit Product page for your Manifold and Cam:
The AirGap has a Basic Operating RPM Range: 1,500-6,500
The CompCam has a Basic Operating RPM Range: 2,200-6,200

Kleiner mentions it in post #3 of this thread and he is generally on the money.

[Jeff Kleiner]

Jay (Thick Cobra) and I have discussed this at length all the way back to when I the car with me for paint and again last fall when I drove it while visiting him. The cam isn't especially aggressive for the cubic inches. He's made attempts at tuning around it both with fuel and ignition but I still believe that the root of the issue is the Performer Air Gap intake. At lower RPMs I think the mixture velocity in the very large runners isn't enough to keep the fuel well atomized. That intake isn't designed to really start breathing until >1,500...but once you get it wound up it'll let it scream like a banshee to 6,000+

Jeff