Q: Engine Rebuild (Revisited)
I’m looking for feedback/suggestions on rebuilding my 326 HO. I am restoring the car to as close to original as I can, but would like to get a few more horse power. I will be keeping the stock (points) ignition, headers are not an option, stock carter AFB 4bbl, stock intake. Given this, are there any suggestions on bore,cams, heads(port/polish), lifters ect… or should I stick with stock rebuild? would like part #’s and specs to give to machine shop. Is the extra $200 they want to balance it necessary? The shop says they will use a cadillac rear seal, will this work with no leaks? open to any ideas/critisizm.
A: As I’m sure most expert motor builders will tell you, the key to making good horsepower is to make the engine breath. Having said this and knowing your limitations on the stock exhaust and intake, there are still a couple of this you can do to give the car a little more zip…
1) Camshaft. This will be the least expensive purchase you’ll make. Mainly because your going to replace it anyway. I would look for a good grind that make most of it’s power at the lower rpms… say, idle to 4000. Since your motor will stat to choke down at the higher RPM due to your restrictions, a cam designed for higher RPMS will most likely reduce your engines performance. Also, consider matching the grind with the head characteristic (see #2)
2) Heads: here is where the power comes from. A mild pocket porting job on the intake bowls will help reduce the restrictions and help to obtain more flow or at least as much as the exhaust manifolds can handle.
Have the heads plained to obtain a 9.5 to 10:1 compression ratio (you may already be here since they are the original heads). This is kind of on the high side for cast heads and today’s pump gas but you will be OK with premium fuel as long as you don’t advance the timing too far (see 3).
Install hardened exhaust valve seats to reliably run unleaded gas.
3) Pistons: 0.030 over bore with flat tops. You’ll need to calculate the total volume of the cylinder and head chamber to obtain the proper compression ratio. Too much compression means you’ll have to use an av-gas or racing fuel blend to prevent detonation.
4) Block: decking the block is another way to increase the compression but may not be advisable with your current heads. I would figure out what the current compression ratio is and discuss this with a local motor builder (preferably one who builds racing motors) and then decide which way to go (decking the block vs plaining the heads).
5) Balancing: This is very gray area when considering your limitations. Balancing the components will help the motor to run smoother but at the lower RPMS the benefit are small. I would ask the mechanists to weight match the pistons and rods (use the heaviest piston on the lightest rod and vice-a-versa to get the best “overall” balance and let it go at that.
6) Cadillac Main Seal: I’ve never done it but it sounds like a great idea. There was a god article in the December 98 High Performance Pontiac magazine about this topic and I will try it on my next rebuild.
7) Engine Tuning: Once the motor is together, try experimenting with different jetting. You may be able to increase the jet size by a couple of notches because of the larger camshaft and better breathing heads.
8) Other stuff: There is literally no limit to what you can do to squeak out a few more horses: Hotter coil, performance points, low resistance spark plug wires, K&N air filter, high flow mufflers and exhaust, etc. Pick up a Summit or Jegs catalog and let your fingers do the walking.
If you want max HP and still have the stock look, consider having the intake and exhaust manifolds extrude honed. This is a process where they forcibly push an abrasive compound through the ports to open them up and remove restrictions. Kind of radicle but some of the limited late model racers use it to improve the flow on mandatary stock components.
Well enough from me. How about some additional tips (or rebuttals) from the rest of you guys???
A: Regarding tips for more horsepower, if youve got some money:
We went with a set of those aftermarket edelbrock heads for several reasons:
from what I understand, a well ported set of stock pontiac heads will flow about 240 cfm, while the edelbrocks flowed close to 300 right out of the box. Ported, they flowed way over 300 cfm.
Many pontiac heads flow well only to a certain level of lift, after which a larger lift cam does not help flow. The edelbrocks continued to see increases after .600 inches of lift, allowing a large roller cam.
With those things said, we had some problems all you considering this upgrade might want to hear:
Our eldelbrock torkers ports did not match with the heads, and so the manifold had to be milled. (Strange since both were new and the heads were not shaved, and the parts were made by the same company.) Although the intake would have bolted on, we would have lost some power.
since the edlebrock has the round port configuration on the exhaust, youll have to locate some factory style Ram Air IV manifolds or try to find some hedders (which is very hard) We had to settle for some hedders that were incompatible with air conditioning and power steering. We also had to cut a hole in the fender well to get one of the primaries that went outside of the frame to fit, as well as a little banging on the primaries.
if you want to run more agressive than stock ratio rockers, the heads have to be modified for valvetrain clearance.
Although all this might sound daunting, the heads were well worth it, as we made 570 dynoed hp @ 5800 rpm, with lots of good old low end pontiac torque. (576 under 5000 rpm)
Finally, DO NOT run copper head gaskets with these heads, as they may leak. Our motor had to be torn down because it had water in the oil the first time we ran it on the dyno.
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Content last modified: January 16, 2014 at 7:07 am