Members:

What is your reccomendation for the proper plug gap for moderately booster LT1 motors? (6-10 psig)

Thanks in advance for your replies

 

A lot of us gap to .035. Most use an ignition amp/msd, too.

 

Just an update. Again, thanks for the reply. I asked because I was replacing my plugs and had recently seen a posting by a knowledgeable member favoring a larger gap. I had originally installed at .035" (Autolite AP 104). The car had run well up to 6200 rpm after setting up the spark tables. I repullied for more midrange boost, dropped the fuel cutoffs to 5900 and sorted out the tables as this is a daily driver only car. When I began playing with a 2 BAR MAP sensor I found the motor laying down very seriously above 5000. Reminded me of the first days after the PD install when I found the AC plugs had lost their pucks (gap must have been out around .080") and the engine wouldn't pull beyond 4600 until I installed the AP 104 plugs. With this plug replacement, I hoped I'd find a puck or 2 missing but they were fine, good color and all still at .035" and the wires are fine. I still have the stock coil so I'll try that next. The engine will run cleanly to 5900 but only at part throttle. 6.5 psig had been fine before but now only ~3 psig is all it will take.

(BTW I found this "Go-Thru" sae and metric socket and ratchet set from Harborfreight (# 67974) to be very helpful with plug removal)

 

Sure your fuel system is providing enough fuel? Get a gauge on there and watch it in boost - maybe it is insufficient now.

We know about the cut off socket - that is what we used in the past, and yeah you need something like that for our cars.

 

Temporary change back to the original coil seems to be the fix. It pulled cleanly to 5900 at full throttle ... 5.5 psig (it's hot out there today!) I guess the MSD 8226 disease has caught up to me. Fuel was pressure is good ... 40 to 52 psig. I'm thinking of going to the Mallory Promaster E-Series MMA-30440 coil (if possible, needs wiring mods) otherwise the Accel ACC-140011 coil (plug & play)