302 Heads

[1967DartGT]

Hello all,

I've been reading posts on this website for quite some time and finally joined today. I'm sure I'll have alot of questions to come, but for now I have a couple of questions regarding 302 heads.

First, I've seen flow numbers for 302 heads as cast and fully ported, but I was wondering how much flow increase I might expect with a simple multi-angle valve job and back cut valves? I'll probably stay with stock sized valves to keep port velocity up since the heads will be used on the 273 that came with the car.

Second, if I want to gasket match the ports, should I match to a 273/318 gasket or should I match to a 360 gasket?

I anticipate a mild build with between 9:1 and 10:1 compression and using one of these 3 cams from Comp Cams:
XE256H
XE262H
XE268H

Thanks,

Kevin

 

[BJR Racing]

The valve job can increase the flow up to 35 cfm's but average is more like 10-15 cfm's. As for the port size it will depend on which intake manifold you'll be useing, I'd match it to the port in the intake.

 

[rumblefish360]

On cams. These cams;
XE256H
XE262H
XE268H

These all have an operating area. A bracket RPM band where they'll operate best in. Depending on what type of performance you wwant out of the engine/car.
You'll also have some lee - way on the gear you can run with it as well and still have good performance.

The problem you present us with doesn't have enuff info, so I'll give you my take on the cams on a "In General" level on how they work and what they should be used with.

The 256; An upgrade over the stock cam. It will provided a little more umph and probably mileage over the single pattern 318 cam @ 252. (or so) Everything on the engine cam remain stock with no ill effect. Headers would be a plus, not needed.

The 262; I believe you'll find this a excellent cam for an upgrade over stock and will work very nicely with headers, a small 4bbl. and dual plane intake. I'd look at the Edel. Performer or the older LD4B and a max of a 600 cfm carb.
You will retain good mileage with this cam. A very streetable grind.

The 268; This would be the first step into a street HI performance cam and could use a bump in compresion. A little extra stall in the converter would be a great help as well as a higher gear set.

IMO, a rear ratio of 3.21/3.23 at a min with stock height tires and converter.
But step up a bit in the gears and converter and you'll find this a capable cam for power. Mileage should still be OK, if you can keep your foot out of the new found fun.

Compresion for the cams should be lowish. 10 -1 is rather high for any of them. Do able with the 268.

 

[1967DartGT]

Thanks guys for the replies.

Sorry I was a little vague about my combo when I posted my question but I'm early in the planning stages now and don't have many particulars yet. I was originally planning on a milder version of the 322 based 318 build that BJR Racing outlined in one of his posts, probably using the XE268H cam at ~10:1 compression and using 3.55 gears. However gas prices now have me leaning towards rebuilding the 273, and based on Rumblefish360's comments, using the XE262H cam at ~9:1 compression (not sure which gears yet for sure).

BJR, do you have any exhaust flow numbers for your ported 302 heads besides the peak flow of 180 that you mention in you post? Sounds like they will outflow all stock LA heads and even magnum heads, making for a great stock looking combo in my dart.

Thanks again,

Kevin

 

[2 Darts]

Rumblefish360 hit the cam issue right on. You may want to consider your rear gear and tire size as this affects the engine revs per mile. Where do you want to be? On the Demon with 235/60-15s, a 2.76:1 ratio gives 2133 revs per mile. Change the rear gear to 3.23:1 and 2496 engine revs per mile. Because tire size affects the rolling diameter, a larger tire reduces rev per mile, a smaller tire increases rev per mile. If you want it expressed differently, my tires with a 2.76:1 require 2133 rpm @ 60 mph, with 3.23, 2596.
More to the subject, look at where you want the power to come in with your existing axle and select a cam that comes closest to that point that the cylinder head flow can support.

 

[1967DartGT]

Thanks for your input 72 Demon. The tires I'll be running will be 245/60R14 (25.6" diiameter) and the rear is currently an 8.25" with open 2.76:1 gears. I was considering swapping gears when I upgrade to a Sure Grip, so never really put much thought into matching the cam to the gears because I guess I was thinking about matching the gears to the engine combo later on. Right now I plan on getting the heads done first, then depending on how well they flow will plan the rest of the combination from there. Again, I'm still early in the planning stages so advice like this is great.
Cheers,
Kevin