I have a 69 Cutlass conv with a 455 installed as well as a HEI distributor. From what I have read I should use the 43S plugs. Is that correct or is there a better plug to use? Also from what I've read the gap should be significantly larger with HEI than original. What should they be gapped at?
thanks,
Steve

 

What year 455 and what heads? C's for example use a much different plug than J's.

With HEI start at about .045. That way you get benefit of the hotter and fatter HEI spark without risking a wide gap misfire. Even the factory realised they'd screwed up with gapping original HEI at .080. A service bulletin was soon issued dropping it to .060, and even that's a little wide IMO.

 

It is a Fa block with G heads. I have been told that that is good. Is there a way to know what year the block is out of and what year the heads are from? If the PO pulled the motor and trans out of a donor at the same time I would assume that it's from a 79. That is what the # on the TH400 shows.
thanks,
Steve

 

The last 455 Olds motor was built in 1976. G heads were never factory installed on an FA block. Your motor has been apart and pieced back together. There is no telling what cam, pistons, valve sizes, or anything else are in that motor. The block will have a VIN derivative stamp that will tell you the exact year of the block.

 

Fa is a 71-76 block and G heads are 1971. This is a decent combination and can use 43 plugs. Can't be a 79 block as 76 was last year for 455.

There's a machined pad at left front of engine block that has the VIN of the car the engine was originally installed in stamped into it. 3xxxxxxx. 3=Oldsmobile, 2nd number is year produced (8=1968, 9=1969, 0=1970 and so on for 1, 2, 3, 4, 5, 6), last six numbers are original car's VIN. By 1979 TH400s were generally only in GM trucks and maybe some fullsize wagons.

 

Glenn, I'm not aware of any 1971 applications of the FA casting. Of course, it isn't worth disagreeing about it, the OP simply needs to read the block VIN derivative to find the year of the block.

 

So I have a 33M326551, So I am looking at a 73 with 71 heads? God only knows what has been done. So far he put a 455, TH400, 3.23 posi rear, aluminum intake and Edelbrock carb, Erson chrome valve covers, and a significant rumble through the dual exhaust. The mpg is considerably less than desired to say the least. Unfortunately I have no way of contacting the owner who did the mods many years ago. I'd have to open it up to find out whats in it. I couldn't find any info on the Erson covers and assume there a performance products company, any info is appreciated. Am I correct on the block year and heads?

thanks,
Steve

 

Yup, exactly.

 

So just the AC Delco 43, no "S"? I've seen Rapidfire plugs out there as well.

Steve

 

I sometimes tend to drop the S on AC plug numbers...

R43S will be fine though .045 may be stretching it on gap with those- side electrode may not open up enough without breaking or losing alignment with center electrode. You may have to stick with .035-.038 gaps with those.

My mistake on Fa block Joe- and I knew better.

 

Gas mileage and 455 are mutually exclusive! and an Edelbrock AFB doesn't help any. Unless the intake is for a square-bore carb, I'd look into a properly set-up Quadrajet.

You might also look into a 200-4R transmission built to take mildly built 455 torque. It has good gear ratio spread and you get the advantage of overdrive 4th gear.