421 HO motor rebuild
 

Looking for some guidance on building a 1966 Catalina 421 HO motor. 376 hp currently.
I am boring to .60 and thinking of putting in a stroker kit with all new stuff. Question is what do you guys suggest is a good kit, I looked at Eagle and a few others? Also what cam would work the best for mostly street but gain more hp? The cam that was in the motor is part number 524886.
I want to drive the car but still get a little more performance. Still want to be able to use pump gas. The heads are HO which are 093’s.
Thank you
Peter

Stroking the motor with those stock heads and a street cam to better feed the added CID will only pick you up like 30 hp , but you will have a lot more torque and the full peak hp will come in at a much lower rpm then stock.

Also if your not going to run headers then once again with stock heads I can see you gaining more then 30 some hp like I posted.

This is because a 421 motor already has the stock heads tapped out by 4800 rpm at best!

I can also guarantee you that the stock 376 hp rating of that motor was exaggerated!

Pontiac engine builder Jim Taylor a number of years ago built a stock stroke 421 with a 66 tripower sized carbs, ported heads flowing 218 cfm up from the stock mid 180s a long with a 11 to 1 compression and a big cam to tame that cylinder pressure down some and produced 475 hp thru what I recall to be headers.

One first thing you need to do is think about a ball park range as to how much hp you want the build to make!

If you want to drive it on pump gas you will need to lower the CR.My 421 HO was built a 9.5 and I run the 068 cam.If your going to the 4.25 stroke kit you will need to get a accurate CC on your heads after a valve job to know how much dish you are going to need.Your wallet will dictate what kind of cam you want to run.I chose to stay with a hft,all my other engines use hyd roller cams.Your 461 can use 230-236 or a touch more with no issue and drive well in traffic if done on a 112-113.Tom

421 HO rebuild
 

Thanks guys I appreciate the input from both of you. I’m calling Bulter Performance tomorrow to check on what kits are available I hear they’re pretty good when it comes to Pontiac. I should of mentioned before that I have the original tri-power set up for this motor too.
Currently I am running it on my 400 motor that was rebuilt last year. Runs great on this motor.
Thanks again
Peter

Wasn't it Butler that did a stock 421 build several years ago, and it came in above 400hp.?

If it was mine and I had the original Armasteel 4" stroke crank I would run that over a stroker.
Do you need to go .060?
I would take the money I was going to invest in the stroker kit and invest it in dished pistons, h beam rods and have the heads ported, larger valves and screw in studs. With a 230ish @ .050 cam you will have plenty of power.
Stroker kit with stock 093 and tripower IMHO would be wasting money.

Really hard to get iron heads ported these days in a timely matter.VERY hard.Tom

My thought exactly. Don't go any larger than necessary. If you are getting custom dished pistons any bore size is available so you're not even stuck with standard .030", .040", or .060" pistons. If it hasn't been apart before and will clean up in .010" then do that. If you are using the 93 heads with custom pistons you just need to tell them you need the piston made with the early eyebrow locations.

421 HO rebuild
 

Guys I have to bore .060 even though I really didn’t want to. Motor was already bored .040 and pistons were stuck badly. As it is one cylinder has to be sleeved but the rest will clean up at .060. The original crank would clean up but couldn’t decide the best way to go. So thinking rotating assembly to save this motor.
Thanks for all your advise.

This is just my opinion as I really like the 4" stroke Pontiacs.
If you have to go .060 use a 428 style .030 piston with dish of your choice, your 4" stroke crank, a set of forged rods and a set of 72CC D Port Aluminum Heads. The heads will cost you about the same amount of money as the rotating assembly and would be better for pump gas and power.

You have a pretty rare engine block there and going to +.060 shouldn't be an issue IF and it's a big IF the machine shop doing the work is good, reputable, and knows something about Pontiac engines. Boring for a sleeve, it is essential that they DO NOT bore through the bottom and expect friction to hold the sleeve in place. They must bore only deep enough to leave a shelf for the new sleeve to sit on. Also, If the sleeve to be installed is cylinder, 4,6 or 3,5, their will be significant distortion on the cylinders on either side of the new sleeve. This will require a torque plate as a must to get round and straight cylinders at .060 over especially. IMO, if they don't have a Pontiac torque plate, they need to get one or the block needs to go someplace else. If your goal is around 400 HP and just under 500 Ft. Lbs torque, I see no reason to buy a stroker kit for this build. I would do as others have recommended and and use 428 pistons with dish to reduce compression, and even stock rods and crankshaft. Once again, if the shop is good, they can install new hardware and recondition the OE rods. I have no issue using stock rods for a rebuild like this. Best of luck with it. My 66 421 HO 2+2 ran 13.60's @ 104 with 093 heads, stock rods and crank, and a tiny Ultradyne flat tappet hydraulic cam. 276/284. Nothing fancy.

Good info mgarblik!!

A friend purchase a 67 numbers matching GTO. Had coolant in the oil so we tore into it. Previous owner actually spent the money to sleeve all eight cylinders, but unfortunately the machine shop didn't leave the step and took the sleeves to the bottom of the bore. Five out of the eight cylinders leaked when the block was pressure tested. The friend now has a numbers matching boat anchor.

My 421 at .070 over has been making lots of passes at the strip for 14 yrs.

If it where me, Seeing as you need to get a cylinder sleeved and you will be up at .060” over I would not stroke the motor unless I hard blocked it also.