302 heads on my 318

[1245heathen]

I recently picked up a pair of 302 casting head near me for pretty cheap.
Is it worth swapping them out on my car (original motor with a new 4 barrel and Weiand ac+) if I used a thinner head gasket, also why does ever set of head I find always have the rocker shaft and arms always pulled.
Thanks and merry Christmas.

 

[Sedanman]

I think they had rotators on the exhaust valves. I thought I seen someone mention a while back that they would add a point to compression over open chamber heads. I'm curious as well since I have a 68 318 and a set of these heads too.

 

[1245heathen]

I think they had rotators on the exhaust valves. I thought I seen someone mention a while back that they would add a point to compression over open chamber heads. I'm curious as well since I have a 68 318 and a set of these heads too.

Hot rod magazine has a few articles about budget builds and they always go with 302 head since magnum heads lower the compression quite a bit.

 

[Sedanman]

https://www.forabodiesonly.com/mopar/search/32697546/?q=302+heads&o=relevance

 

[YY1]

Most 302 heads are on pre-Magnum LA roller engines.

These are advertised 9.2:1 motors.

IIRC the 1968 318 is also a 9.2:1 engine but the rating may be more "true" on the later builds.

I've asked a few times on both boards what the actual measured differences might be but no one seems to know.

The best answer so far, from the A body side is that the pistons although having different part numbers have a "similar" installed height.

IIRC the "low" compression (8.x:1) 318s were 71-84-ish

 

[toolmanmike]

There was difference in 318 piston but the early teens and the late roller teens had closed chamber heads which helped the compression. Have the 302's checked for cracks between valves. They are prone to cracking. The combustion chambers are very efficient and they flow pretty good for a small port head and respond well to larger valves and some porting.

 

[YY1]

also, no one seems to know the differences and/or similarities of the 920 head (pre-1970) and the 302.

 

[1967coronet440]

@rumblefish360

 

[toolmanmike]

also, no one seems to know the differences and/or similarities of the 920 head (pre-1970) and the 302.

Not much. The chambers are very similar in size and shape. The port flow is similar as well. The 302'in stock form have induction hardened valve seats. The 920 and older heads do not.

 

[rumblefish360]

I recently picked up a pair of 302 casting head near me for pretty cheap.
Is it worth swapping them out on my car (original motor with a new 4 barrel and Weiand ac+) if I used a thinner head gasket, also why does ever set of head I find always have the rocker shaft and arms always pulled.
Thanks and merry Christmas.

Merry Christmas to you and yours!

My take on the 302 heads are kind of like which side of the quarter is shining better. If your heads pass inspection, the best way to prep the head for a noticeable gain over the other head is to at the very least have the shop race prep them in the valve area, with or without larger valves. If you move to larger valves, which would be good, they will take them without issue. The valve size depends on what your doing with them as I have had really nice results on street vehicles with stock valves and 360 (1.88) intake valves, and a bowl porting under it.

The difference between the 302 and the earlier heads are the ever so slight changes made through out the years ending with a better exhaust port. It is a minor advantage. Which also works better with a 1.60 valve and a bowl porting under it.

There isn’t much gain with bigger valves without a bowl porting under the valves. It’s yhere but IMO not worth the small gain and expense unless ported.

The rocker arm shaft pedestals are in a racers perspective in the right position. Look for B3 for his rocker arm geometry correction kit. His kit works great and even better when you start swapping cams and changing rockers around. The OE manufactures rocker position is fine enough for stock specs and good longevity but far from what is ultimately the best.

For a compression ratio, you’ll need to know all the specs of where the piston sits in the hole, cc valve relief amount, gasket thickness and diameter and cylinder head cc amount. Plug them into a program. FWIW, your not going to notice a 1/2 point of compression ether way unless it is up and regular gas does play nice.

 

[rumblefish360]

I think they had rotators on the exhaust valves. I thought I seen someone mention a while back that they would add a point to compression over open chamber heads. I'm curious as well since I have a 68 318 and a set of these heads too.

I think they did have rotors. I forget as well. I think they should. You can live without them if need be and most aftermarket places do not design there material with rotors in mind so you sometimes have to move away from them.

 

[rumblefish360]

Hot rod magazine has a few articles about budget builds and they always go with 302 head since magnum heads lower the compression quite a bit.

It’s all in the cylinders head cc amount and head gasket used. Keep the ratio close to 8.5-1 or lower for best use with regular 87 octane.

 

[rumblefish360]

There was difference in 318 piston but the early teens and the late roller teens had closed chamber heads which helped the compression. Have the 302's checked for cracks between valves. They are prone to cracking. The combustion chambers are very efficient and they flow pretty good for a small port head and respond well to larger valves and some porting.

Good reply my man!

Through out the years, piston heights change.

I’d like to add that no matter the cylinder head being considered, they should all be checked for cracks anywhere. Also note that the cracks between the valves may very well not hurt a running engine. Though I would not bother building them.

 

[rumblefish360]

also, no one seems to know the differences and/or similarities of the 920 head (pre-1970) and the 302.

There all pretty close in design. From a hot rodder point of view. A lot depends on the ultimate goal and willingness to spend money on the goal. Is it really super important to run that 318 head on the street as quick as possible? In what vehicle?

IIRC, on FABO, a fella did a comparison between a 302 & a 920 head. Again, IIRC, the result reported was the 302 would have an edge in performance due to the better exhaust port even though it was behind in the intake flow by a half a hairs amount. The cfm differences were very small.

While a 318 can be a decent performer in a light, oh, Duster or early Valiant for say, I don’t know how well anybody would like it in a B body 500lbs. or greater weight.

If 1245heathen is looking for a minor power upgrade, that’s fine. Even a mild cam would be nice. I just wouldn’t expect mid 14’s out of it and 20 mpg’s.

 

[rumblefish360]

@1245heathen, What is the goal of the engine and car? More pep? Better mileage? Both?
Is a cam change in the future?
Are headers in the future?
What trans and rear gears are in the car?

 

[rumblefish360]

FWIW, LMAO, I had a beat up Duster that I took a ‘79 - 318 and added a Edelbrock LD4B, 4bbl. 600 carb, headers into a Jegs 2-1/2 true dual exhaust and a small Crane Cam. (IIRC, but I don’t think so but....) it was a split cam @ 216/228-.454/.480-112. Stock 904 & 3.23 gears with a stock tire size that ran the car to its first outing of 15.14 spinning the tires a lot at Atco in Jersey. Not exactly a great outing but it was better than running the thing in the mid 17’s. It did get 18 mpg’s.

(It was a fun time wasting project.)

The heads were only equipped with the matching valve springs.
Let me go find the link. That will be better.

Here it is;
https://www.forabodiesonly.com/mopar/threads/rumblefishs-duster-project.10508/

 

[1245heathen]

@1245heathen, What is the goal of the engine and car? More pep? Better mileage? Both?
Is a cam change in the future?
Are headers in the future?
What trans and rear gears are in the car?

Thanks for all the great info guys.
Originally I was going to build up the 318 the car came with, hence buying those heads and they were cheap, old guy just had me sitting on the shelf.

Shortly after that I found a good deal on a big block so I started moving away from keeping the small block, the small block runs good so now I’m kinda in the middle like I might mod the small block just to get more oomph until I get the big block where I want it.

I was having trouble sourcing a bb727 and that was also keeping me from moving forward on it. I am kind of sixes either way, and will probably change my mind ten more times before I make a decision.

Mostly just questions and wanted to hear everyone’s take since you guys have a metric ton of knowledge.

 

[1245heathen]

Also not looking at mpg at all I got a vw diesel for that this car is strictly smiles per gallon

 

[toolmanmike]

I think they did have rotors. I forget as well. I think they should. You can live without them if need be and most aftermarket places do not design there material with rotors in mind so you sometimes have to move away from them.

Rotator on the truck heads from what I understand.