2 cars same problem

[Tuffregal83]

This has been going on last year and now took the car out o Sunday
I'll start with my regal BBC 468 new plugs wires, has a 6AL box with distributor
And rebuilt the carb and timing is fine.
And running 110 octane
While driving and trying to shift at 5200rpm
It starts to break up like a miss fire
But in park I can take it to 5500 with no problem
Car #2 is my buddy's
65 Lemans with a 65 gto tri power set up
New plugs, wires,cap, rotor with pertronix set up. Timing is good. Stock build
He runs 110 and 93 mixed octane
While driving and trying to shift it won't go pass 4200rpm stats to break up like a miss fire. But in park I can take it to 4500 with no problem.

Is there something I'm over looking

 

[ck80]

Double check your distributor rotor. I've had trouble like that where a regal and a c10 pickup developed the same problem similar to that at the same time.

For some unknown reason the tab wasn't making good contact under driving conditions, and I could see where it would arc and leave residue

I gently bent it outwards so it made better contact, cleaned it up, and problems cleared up on both.

Mine did it much lower rpm though it was when shifting like yours.

Just a small chance it could be related to low quality modern manufacturing like my issues, especially since you mention having had new parts...

I could Rev to the moon in park, but driving conditions, near shift points, pffffft. Engine would be skipping and lose speed/power.

 

[Tuffregal83]

I'll be checking that out this weekend for sure

 

[olds307 and 403]

My breaking up issue only occurred at the track, of course above 4000 rpm. The coil was the basic Accel higher resistance coil for points, too weak. The Proper Mallory coil for the Breakerless distributor fixed it. Get a replacement coil and try it on both cars if everything else checks out.

 

[maxi426]

Could be a lot of things, but start with fresh plugs

 

[lilbowtie]

Have had that problem w/ plugs and also when I had the polarity hooked up wrong in the box.

 

[Steve 82 Elly]

My breaking up issue only occurred at the track, of course above 4000 rpm. The coil was the basic Accel higher resistance coil for points, too weak. The Proper Mallory coil for the Breakerless distributor fixed it. Get a replacement coil and try it on both cars if everything else checks out.

I've had this issue at the track as well. It usually only happened the first pass, especially if I had been driving the car on the street a bit. In my case it was the plugs, I changed to 1 level hotter plug and the problem went away. Good luck!

 

[bracketchev1221]

What is the engine compression? 110 octane is a lot if you don't have the cylinder temperature and timing to burn it.

 

[Tuffregal83]

My 468 has 13:1 and I run timing at 32 to 34 if I remember correctly

 

[Steve 82 Elly]

My 468 has 13:1 and I run timing at 32 to 34 if I remember correctly

Yeah, mine was 12.5:1 406 ci sbc with the same timing and 110 octane. Does it happen everytime you hit 5200 rpm?