I am upgrading the 502 in my 66 roadster and am trying to decide what heads to put on. The car currently has -840 iron heads, rect. port, closed chamber, but with small valves (2.06/1.72). By my calcs if the stock JE pistons give 8.75:1 with open chamber (119cc) heads and 9.6:1 with 112cc chambers (per the 502/502 setup), they should result in about 10.1:1 with the closed chamber GM heads (108cc) they have now. I don't want to open up the short block, which is relatively fresh. I would like to have the higher compression, I think 8.75:1 will be soggy. But I also want bigger valves, 2.19/1.88 at least, and it would be great to switch to aluminum also.

I will be running a mid-size roller cam (234-242 duration at .050, .610/.632 lift), headers, single plane intake, 750 or 850 carb. I would like to make 575-600+hp and lots of torque, up to around 6000 rpm, on pump gas.

So, my options as I see them:

1. Used GM closed chamber aluminum heads from the 60s. Such as these, on ebay: http://cgi.ebay.com/ebaymotors/ws/eB...401973318&rd=1

Easy bolt-in but maybe old race parts are worn out. (too many valve jobs, unknown repair history).

2. New aftermarket aluminum heads, which I would then have to angle mill to get down to acceptable chamber volume. Starting with something like the Canfield 310's, such as these: http://cgi.ebay.com/ebaymotors/ws/eB...&category=6770

Presumably will flow great, but I assume I'll need custom pushrods and to mill the intake, and maybe other issues. Would guess I'll also end up with parts that are harder to sell when I switch combos.

3. Edelbrock Performer RPM oval ports? 110cc chamber and oval ports. Bolt-in solution, though I have rect. intake and kinda want rect. port heads.

4. Maybe have the -840 iron heads I have refit with 2.19/1.88 valves? Bolt in solution, not sure of the cost or feasibility of this option.

Thanks everyone for your advice!
Gerry

PS -- raised exhaust port is ok, I have not had the headers + JCL baffle setup welded yet.


[Modified by Hank, 9:33 AM 2/1/2003]

 

Hank:
Are you 100% sure that the heads you currently have are equipped with 2.06/1.72 valves? R-Port heads only came on the higher horsepower big block motors so they should have 2.19/1.88 valves.

If it were me, I would stick with a closed chambered head. I am most certain that you will not like the decrease in compression. I would find a closed chambered head from around 1968 or back. Those aluminum ones on eBay would be something that would be good for your setup.

I would be sure before doing anything that you do indeed have 2.06/1.72s because my gut is telling me that you have 2.19/1.88 valves.

 

The small valves surprised me too. But they're there -- I've measured them, and the GM documentation I've seen indicates small valves are stock. It's an odd thing to do -- big 325cc intake ports with small vavles. That's why I want to swap out!

Some 3919840 heads do show up for sale with larger 2.19 valves. I think that some applications had larger valves and / or over the years people have swapped in the bigger valves.

Gerry

 

I think you can get rect ports with the smaller chamber vol if you want --Canfields come with 113 and I think 110cc .. Edelbrock too has a CNC ed version that comes with the 110 cc. What kind of headers and exhaust setup do you have. I havee the canfields 310 with the 113 chambers but haven't got the exhaust figured out yet .. ?

 

I've also never seen 2.06's in a rectangular port head. Early ones did have 1.72 exhausts though. Maybe someone decided to put in hardened seats or something and decided to use smaller valves for some reason? Beats me...

1) I wouldn't use the early Gm aluminum heads. First is they weren't all that great compared to just about anything out there today. Second is they aren't very strong castings and if raced much usually have rocker stands broken and seats falling out after awhile. Steer clear.

2) Just about any aftermarket head would run better than what you have. Canfield, Brodix, Dart all make killer heads. Most can be ordered with chambers down near 100cc from the factory. And they usually will cut the intake face of the heads so that the intake manifold doesn't have to be whacked up. That way they always fit ANY intake instead of being a "one off" matched set. Pushrod length has lots of variables and may be an issue with head cutting or heads with taller ports/longer valves. But you can get anything you want in .050 increments easily.

3) Oval ports can run great on a 502. I have a friend with a homebuilt 502 similar to yours with heavily ported GM oval iron heads and a pretty serious hyd roller but still streetable. It made 625 hp or so on engine dyno and runs 10.30's in a Camaro with 3.73 gears and a 2500 converter on pump gas. But if you aren't going to spend the time to re-work the ovals, I think a reasonable sized 315-325cc rectangular port would work best too.

4) Headers usually DO become an issue with raised ex ports and a 2" or larger tube size. The right side is usually OK, but the left may require a tube or two to be repositioned. Not a big deal, but still a PITA. But the extra power is worth it if you ar ebuilding a hot rod toy anyway.

JIM

 

I have a set of Brodix-2 heads that have been fully ported (intake & exhaust ports & chambers) by Bernard Mondello that I'm selling. These heads have been flat milled to 112 cc and have 2.25/1.88 valves. They are being reconditioned by Mondello as we speak.

These heads are a true high velocity head -- I obtained my chassis dyno figures with these heads. They retain a relatively modest intake port volume.

$2400 for the pair. Not cheap, but you are getting a set of 100% refurbished heads w/ a *lot* of $$$ in porting.

Let me know if you're interested.

Take care,

Mark

 

Hank, I have a 502 in my 69 that I have apart. I bought a set of Brodix BB+2's angle machined to 100cc's. With the 502 pistons and zeo deck that would give me 10.4 to 1 static compression. The problem is when I got my engine apart my engine guy told me my crank was shot which is strange as the cylinder bores and the pistons look like new, so maybe it was a used crank, who knows. Anyway, I will now build it with a 4.25 in. stroke so I need to get a bigger head so if you are interested in the BB+2's I will sell them to you. They are rect. port with 312cc intake ports. They are bare and machined for 2.25 intakes and 1.88 exhausts. They are still new in the box. I bought them for $1925 and would sell them for $1750. The intake face has been corrected as well. Good luck with the project. Bill.