421 engine build for pump gas
 

Hi All,

I have a 1966 WG code 421 block with 1968 #62 heads, 67 Ram Air exhaust manifolds, and a 1966 TriPower. I am looking for recommendations on how I can build this engine to run on unleaded premium pump gas but still retain good performance.

Some additional details:
- I would like to continue using the 66 tripower setup and RA Exhaust manifolds
- The car will be street driven, not raced
- The existing cam is a Crane Cams p/n 283941.
- Want the finished engine to look basically stock, but am open to using parts from different years as it will be used in a non-numbers matching car
- am open to changing heads and camshaft if these will help

Any advice or suggestions are welcome!

Brad

I put a set of 96 heads on my 63 HO 421 block.Tom

Is the block assembled and will stay with whatever pistons are in it now ?

If so what pistons are in it, or what is the deck height and can you post a picture of the top of a piston ?

https://forums.maxperformanceinc.com...d.php?t=771741

My 1964 421 HO mildly modified street engine build thread is linked above.

I used dished pistons so I could retain the original high-compression 421 heads. I wanted the engine to look original with the correct 9770716 head castings.

Are you driving this yet, Bart? If so, how does she run?

It’s fast.

Surprisingly powerful, just a stock 421 HO with compression dropped to 8.82:1. Has just log exhaust manifolds and a 2-1/2” mandrel bent H-pipe exhaust with Dynomax Super Turbo mufflers. No head porting or port matching whatsoever.

Really moves out even with 2.56 gears.

I’m really tempted to buy a Dragy now to get some 1/4 mile data, hoping for high-13s.

Years ago I built a 421 bored out to 428 with #62 heads with slightly opened chambers and a mild port job. It used a 1968 intake manifold and the original 1967 GTO carb, headers, HS roller rockers and an UltraDyne cam (sorry don't remember grind but it was not too radical). The car had T400, 3.89 to 1 gears and weighed 3725 lbs with me and a 1/4 tank of gas. It used pump gas and ran consistent very low 12 second quarter miles. Hope this gives you some ideas.

I run several 428's. I run one that has the factory replacement TRW pistons with a 13cc dish, 670 heads, 1965 tripower, 3:90 gears, 1967 ram air manifolds and a 4 speed. The cam in that engine is a Melling 744. It idles with a slight loap, has very good low end torque and never overheats. I'm really running nothing fancy on this engine. It has stock rockers and the stock 1966 421 points distributor with a good set of points. In my heavy '66 Tempest convertible, it has no trouble burning the tires. I have never run it down a track and do not think I ever will. I would estimate my compression to be just under 10:1. I have only ran 91 octane in the engine and it does not ping.

It would really depend on what pistons are in your engine. If they are flat top, I would run 6x4 heads or something similar. If you have a 13cc dish like a factory 428 piston, I would use the 62 heads. They should have around a 75CC chamber if they haven't been milled.

Here is a thread on a 428 with a tri-power. A 428 is basically a 421 that is .030 over. Anyway, might be worth a look: https://forums.maxperformanceinc.com...&highlight=428

Although it’s nice to see these track times posted up here the OP is not interested in such gang.

He wants simple everyday drivability and years of longevity.

My example ran for years with no problems and you could drive any place. With a milder cam and higher gears it would be a great street combo.

Hi Steve,

Thanks for responding to my post. I was hoping to retain the existing pistons and short block assembly. I'll have to pull the heads next and get some pictures of the pistons to post. I believe the deck height should be stock, but just to be sure, how does one measure this?

Brad

Hi tempest1964,

Thanks for this link. Very interesting build and surprisingly good dyno performance results!

Apparently the key to this build was the SD "Stump puller" cam. I've been told there have been a lot of advances in camshaft tech over the last few years, so I wonder if there are any newer cam grinds for Pontiacs out there?

Brad

Hi Steve25,

Thanks for providing this guidance to the thread. I 100% agree with your assessment of my goals with this engine build. Of course, having more power that's reliable is always a plus. :)

From what I've been reading it appears that I could retain the use of my existing 62 heads if I change to a dished piston to drop the compression ratio to around 9:1. The next major decision would be the cam shaft. I've been told that camshaft design has advanced quite a lot over the last decade or so, which makes me wonder if there are any newer cam designs for Pontiacs out there. Would builders like Butler be a good source for this info?

Another concern I have is overheating. I am considering changing to a 69 or later timing chain cover to use the later design 11 bolt water pump which appears to do a much better job with cooling. The problem with this is that since I want to run my 66 tripower I need a timing chain cover that has the dimple cast in to clear the thermostat housing. Apparently the repro parts don't have this. Also, there are pully offset considerations to worry about when making this change. Wonder if it's worth the effort. Are there things I can do with my existing 66 setup to improve cooling performance?

Brad

HI Goatracer1,

Thanks for responding to my post. Although I won't be racing my car it's good to know that you can get lots of power from a stock appearing engine that can run on pump gas. My engine is similar to yours (same block and heads), but were you running dished pistons to lower the compression ratio?

Brad

Hi John,

Thanks for responding to my post. Your engine sounds a lot like what I'm looking for. To lower the compression ratio, is it advantageous to keep the 62 heads and change pistons because the 62 heads flow/perform better than low compression heads? Or, are there low compression heads that would perform just as well as the 62 heads?

Brad

The dimple in the timing cover is no longer required with the new water neck available from KRE. Even so, Pontiac continued to produce 11-bolt timing covers WITH the dimple cast into it til around 1973 or so. You should be able to find a nice used one. It's worth it to make the swap to the 11-bolt cover for better cooling performance. You'll just have to run the early-'69 water pump for the sake of the pulleys.

Contact KRE. I bought both a few months ago.

I use stock replacement forged pistons. I got the drop in compression from the chamber work on the cylinder heads. The #62 heads already had bigger chambers than the 421 heads. The engine had just under 9.6 to 1 compression. Years later I used those very same heads on my wife's 1962 389 to temporarily be able to run the car on 89 octane while I built a new engine. The engine would not run even on 93 octane with the 389's original heads.

Hi 65 Lamnas,

This is great info on the timing chain cover! So, If I did upgrade to a 11 bolt timing chain cover and used an early 69 water pump, would I be able to retain my existing crank pulley and 65 style power steering and alternator mounting bracket?

Brad

Hi Goatracer1,

I'm really glad to hear that enlarging the chambers on the #62 cylinder heads is a viable way to drop compression ratio. This might be the easiest way to get my engine to run on pump gas. Can you provide some more details about the cylinder head work you had done?

Brad

If you did all that, I'm not sure how you would verify your ignition timing. The 68-later cars used a different timing tab than the 67-earlier cars. The damper (balancer) was changed in '68 and was a different diameter. I'm not saying it could or couldn't be done, just have not done that type of a swap myself, and that would be the only headache. Your pulleys and brackets (belt-alignment) would not be an issue with the early-'69 11 bolt pump.

So it sounds like the easiest solution is to upgrade to a 68 and later damper and crank pulley if you’re going to use the 69 and later timing chain cover. Are the 68 and later dampers + crank pulley easy to find?

Are there any issues running the 68 damper with a 66 engine?

Brad