[blakethechop]

hi i have a pontiac firebird 455 with 4x heads 113cfm i want to port heads and have read jim hands book has any body ported 4x heads and would you do chamber as in jims book or would this lower cr i want to keep heads and would appreciate info should i use higher cr pistons smaller head gasket mill heads ?any help would be great. i live in australia so locating different heads is a impossibillity and dont want to spend 3 grand on new heads shipped from usa
thanks blake

[hcompton]

Originally Posted by blakethechop

hi i have a pontiac firebird 455 with 4x heads 113cfm i want to port heads and have read jim hands book has any body ported 4x heads and would you do chamber as in jims book or would this lower cr i want to keep heads and would appreciate info should i use higher cr pistons smaller head gasket mill heads ?any help would be great. i live in australia so locating different heads is a impossibillity and dont want to spend 3 grand on new heads shipped from usa
thanks blake

Yes you can use a thinner head gasket to make up for a little less compression. But when you cut the chamber only do what is needed to allow for flow around the valves. You will loose very little compression just by tpuching up the chambers.

Do your self a favor and get a set of edelbrock heads before you put more money into the heads you have. Most of the after market heads will out flow ported heads stock heads.

[LATECH]

113 CFM??? Do you mean 133 CC chambers?
What is your project goal? street car? strip?
I have to agree with Hcompton, having spent some change on head work.

[WDCreech]

Blake, Have those heads milled. For every .005" that they are milled, you will reduce the combustion chamber by about 1cc. I wouldn't go more than .060" and you'll need to have the intake side of the head milled an equal amount so that you won't have trouble putting any intake manifold on that engine.

Bill

[blakethechop]

thanks for replies the car is for street and i would like to port heads myself could anyone give me what they would do with the 4x heads what pistons what gaskets how much to mill of heads would they reshape combustion chamber changing heads is not an option i am going to put an xe 268 comp cam and a edelbrock rpm intake 750 carb .would love some ideas

[cobalt327]

Originally Posted by blakethechop

thanks for replies the car is for street and i would like to port heads myself could anyone give me what they would do with the 4x heads what pistons what gaskets how much to mill of heads would they reshape combustion chamber changing heads is not an option i am going to put an xe 268 comp cam and a edelbrock rpm intake 750 carb .would love some ideas

If the heads are from a 455, the chambers are too big. If it was me, I'd find a set of smaller chamber heads like the well known 6X-4 or 4X heads from a 400. I used a set of these on a 455 in a '81 Camaro and was very satisfied w/the results.

I didn't go w/the 1.77" exhaust, either. Stock valve sizes. Much is made of using the bigger exhaust valve, and that's fine if the budget allows. But my way of looking at it is, every penny you spend on a set of iron production heads is a penny better spent on a set of aftermarket heads. Not saying you cannot get good results from iron heads- but keep the expensive mods out of the picture.

The best results are sometimes the cheapest: owner bowl work and porting, careful attention to quench, as well as other areas of the valve train.

Cleaning up the bowls by removing the lip just below the last angle of the valve seat (see image below) will help as much as anything. The valve guides have to be right before doing the valve job. The guides, valve job (three angle, but do not be tempted to change the intake seat from 30 to 45 degrees), and milling the heads to help compression are the only things I would recommend outsourcing. Everything else you can do yourself.



Choose a head gasket to raise after you've measured the piston deck height (as well as the actual combustion chamber volume) during the mock-up phase of the build.

Rods are bound to come up any time a performance Pontiac build is mentioned. If you have the budget, buy a set of forged rods for peace of mind if nothing else. But an iron head 455 is not going to make power past about 5200 unless you've done a lot of porting and have the cam to match. FWIW the stock cast iron rods are what I used- with ARP bolts and resizing- and they worked just fine. And according to Hand, he also thinks the cast iron rods are OK at that level.

From a recent post:

...(my 455/Camaro) was the tamest, easiest to drive anywhere, everyday, regular gas, 3.31 rear gear, 650 DP, all steel, full interior, 12 second vehicle you'd ever want to see.

I mean, how many cars w/those specs can stage in Drive, mat the gas from an idle and let the tranny shift out on its own (no governor work) and still run 12's on street tires? With a 10-bolt 3.08 run the same way (in Drive) it went 13 seconds flat in the quarter. Oh, and it had a 4777 Holley on a Performer intake (not the RPM, it hadn't come out yet). It was a ball.

The engine shifted out at about 4400 rpm by itself. For the best ET I shifted it at 5000 rpm.

Some Pontiac info:
• Info/sites
• Pontiac engine info

[hcompton]

I would not worry about the rods more to worry about what year engine you have. Some have good rods some have bad ones. Either way you will want to find out. I am no expert but i dont think the 4x heads came on the 455. I think they were 16 but some of the trans ams may have come with 4 x low compression heads. At some point pontiac just started slapping cars together with left over parts.

A little research my be in order to find out which engine you actually have.

If you really want your heads to make power i think butler will port them for you. Probably make a lot more power than a home port job. He may also have a better set of heads ported and ready to go if your looking to buy.

Butler Performance - Specializing in Pontiac Engines Heads and Performance Parts.

I built a nasty 455 HO for my gp. The heads i had stock were some of the best heads after they were ported and these had some nice work done. But they were always a problem since the big ponchos love lots of timing and compression. Cast heads were always a tuning issue. They knocked when it was hot out and ran low et when it was cold. Alum edelbrocks fixed all my problems with one big swipe of the credit card.

Fyi when i was done i realised i could have gotten a turn key 800hp from butler for the money my poncho cost to build from scratch. More ifit was a chevy motor for the same dollars. You live and you learn i guess.

I just helped someone that was doing port work on a chevy head the thread is still current and has lots of great info from alot of ppl on the forum. You may want to check it out. " first time head porting" i think is the tag line. Too hard to paste a link with my ipad it reloads when you move between safari windows.

Here is some good info on the heads out there for pontiac. You will notice the 4x heads are not in the top 5 heads to have for a 455. They work and will make some power just not top of the mark.

The Ultimate Pontiac Head

hope this helps sorry for the disjointed post i had to do a few searches to complete so i kind lost focus.

[cobalt327]

4X was used on 400 and 455 Pontiac engines. Fortunately, Pontiac engines are not overly sensitive to lower than "normal" compression ratio.

Pontiac production rods are mostly either just OK (cast iron, need ARP bolts) or real pos (forged production rods used in 1959-'62). There were decent factory Pontiac $uper Duty rods, but why even think about them when there's cheap aftermarket forged rods everywhere.

I'll reserve comment on "slapping cars together with left over parts", except to say GM might have lost their balls, but Pontiac didn't. Pontiac stuck to their guns longer than anyone else- they had a 455 Firebird as late as '76 IIRC. Yeah, it had low compression, but the raw material was there at least.

[V8&4spd]

Get a different set of heads. By the time you dump money into new pistons and all the machine work you would be further ahead with a different set of heads.

[WDCreech]

Originally Posted by V8&4spd

Get a different set of heads. By the time you dump money into new pistons and all the machine work you would be further ahead with a different set of heads.

You don't read very well, do you? He had posted that changing heads was NOT an option!

[V8&4spd]

Originally Posted by WDCreech

You don't read very well, do you? He had posted that changing heads was NOT an option!

Oh well, changing the pistons, paying for machine work to mill the heads and special head gaskets is a option. There is more than one way to skin a cat.

[V8&4spd]

Stock a 455 with those 4X heads is only rated at 250hp. How much does the book say you will make with the recomended changes?

[blakethechop]

i hope to get 450 hp with head ported and milled new comp cam new edelbrock rpm intake 800cfm carb roller rockers.i have read that pontiac under rated the horsepower on the 455 during the fuel crisis is that true

[hcompton]

Originally Posted by blakethechop

i hope to get 450 hp with head ported and milled new comp cam new edelbrock rpm intake 800cfm carb roller rockers.i have read that pontiac under rated the horsepower on the 455 during the fuel crisis is that true

No they lowered the compression to save on fuel. It also made the engines turds. Happened to all gm and fords mopar.

I actually think the stock rating for the passenger car was over rated. But the sd and ho had some real good combos that slipped out of the factory. They only under rated for two reasons one to be lower than the corvette which gm still insist on the corvette being its fastest car. The second reason was insurance and a 290 hp motor was much better on insurance than a 325 hp motor.

450 should be a good goal. I think it will make it. But going to be tuff to hit with 8:1 compression.

[cobalt327]

Originally Posted by blakethechop

i hope to get 450 hp with head ported and milled new comp cam new edelbrock rpm intake 800cfm carb roller rockers.i have read that pontiac under rated the horsepower on the 455 during the fuel crisis is that true

The compression changes were made due to emissions standards being tightened. This meant no (or reduced) amounts of lead in the gasoline, which lowered the octane ratings, which led to lower compression. It had nada to do w/mileage.

Again- you need to CC the heads (both of them) first to try to determine if they've been milled before you got them. After that, mill the heads so the chambers are equal to one another (both heads match). When you're done, the compression ratio you will have depends on what heads you started out with and how much was milled. I don't cut them more than 0.050", personally.

If the heads have screw in studs, you may be in luck as far as the chamber size. Pressed studs are going to be the too-large 455 chambers. But screw in studs began to be used in more heads after mid '73, so that's not always going to help as an identifier. Pressed studs are a no-no, regardless.

Or just read up on them, instead of listening to me or anyone else: 4X Cylinder Heads - How to Pick the Right 4X Heads for your Pontiac - High Performance Pontiac Magazine

The factory ratings are not anything you need to concern yourself with IMO. Some were too high, some too low, some about right. But so what? What matters to YOU is how your engine is assembled, and it is not going to be the same as any factory engine anyway.