915 heads vs 302 heads

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kempkan

kempkan

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Somehow is just snagged a set of of 915 heads for $36. Now they have been sitting in this guys garage for 5 years collecting dust. Hardly any rust on the outside and none on the mating surfaces. My question is how much performance will I gain putting the 915 heads on and taking the 302s off. The 915 heads I just got are only the 1.88/1.60. Intake runner differences? Any jump in compression ratio? Or is it just a bigger intake valve?
 
915s have a little bigger valves and the chambers are a little bigger as well usually 68-72cc. You will loose compression. i have ported 915s to get them to flow 250 @ .550 and planed them down to 58 cc to put on low compression 340s to help flow #s and bump the compression up a point.
 
The chambers on the 915's are larger meaning all else being equal you'll lose some compression. The ports themselves are also bigger and flow more, but a larger port can hurt low RPM throttle response. Larger intake valves will make a cam seem "larger" which could be good or bad depending on your current setup.

Assuming you are running a 318 now, the 302 heads will support 275-325 HP depending what's been done to them. If you are actually making over 300 HP now, the bigger heads would be a worthwhile swap, otherwise you probably won't gain much.
 
What is the chamber size on the 302s? Or what I should ask is how much needs cut from the 915s? What about pushrod length and bolting on the intake with cutting the 915s.
 
Generally the chamber size on the 302 is about 62ccs. It's advertised at 60 but they always run a little bigger. The chamber size for the 915s are generally in the 72cc area. You're going to regret the swap unless you change to a piston that fills the 915 chamber some, or you mill the living hell out of the 915s.
 
I thought I did good getting the 915s. I figured the 302s would be less productive coming out of a mid 80s vehicle with all the emission crap on it. The car is strictly for the track and want it to be productive as possible. I eventually want to do a 318 stroker would I be better off using the 302 heads or the 915s? What direction do I go now?
 
Well, your options are either to get bigger valves put in the 302 heads and retain them for the compression advantage, or, change to the 915 heads and make up the compression difference in a piston change or milling the snot out of the 915s. Either way, if your engine is making much over 300 HP, you will benefit from 2.02s and 1.60s in either head, so you're gonna spend a chunk in the heads anyway. If you retain the 302s, you will only need to spend the chunk in the heads for larger valves and not in the short block to raise compression. But all that is just my humble opinion.
 
..........If u look in the mopar books, a 302 head is a 25 hp bolt on over the 915,.......swirl port always wins out........kim........
 
Or as you can ditch them both and spend your money on a set of RHS heads. These will help you now and in the future, RHS heads are cast iron.
 
kempkan said:
Can the runners on the 302s be taken out just as big as the 915s?
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I wouldn't try it. You'll be getting into water pretty quick especially on the exhaust side. If you are going to the 390 stroker I'd personally rather have the 915's. I had 915's on my 75 Dart 4 speed 318 +0.040 and swapped to worked over 302's with a slightly larger cam and can't tell much difference. It seemed to wind up tighter with the 915's actually....
 
With the amount of money you're going to be throwing at either of these heads (porting, bigger valves, etc...) you'll have spent enough to buy a set of RHS, that will still out do the 915 and 302 heads. Just pointing that out.
 
StrokerScamp said:
Well, your options are either to get bigger valves put in the 302 heads and retain them for the compression advantage, or, change to the 915 heads and make up the compression difference in a piston change or milling the snot out of the 915s. Either way, if your engine is making much over 300 HP, you will benefit from 2.02s and 1.60s in either head, so you're gonna spend a chunk in the heads anyway. If you retain the 302s, you will only need to spend the chunk in the heads for larger valves and not in the short block to raise compression. But all that is just my humble opinion.
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well said, x 2
 
oldkimmer said:
..........If u look in the mopar books, a 302 head is a 25 hp bolt on over the 915,.......swirl port always wins out........kim........
Click to expand...

Depends, not on a 7,000 rpm 340-360.

Those 302 head ports are too small for 6,000 plus. Now on the 273, maybe 318 motors, OK. Those 302's can be a great set of heads but the tiny ports do choke / limit the flow

For his little motor, I would say larger valves and a little milling on the 302 heads he be happier with unless hes got a 4.56 gear
 
Well that's what im running. I have a 28 in tall tire with 4.56s right now. I thought it was too deep myself but I was happy on friday when I went through at 5800. I know the 318s can scream higher than that if needed and its at the point where im starting to run out of cam so its perfect. So the 915s are a better rpm head if I had the head shaved or a decked block? Im going to look into the rhs for valve and runner size. I was trying to do it the cheapest way with the best performance. I know cheap and performance don't go together usually.
 
Well those heads aren't cheap

But don't they come closed chamber and around 62cc's, you could mill them .030--.040 and find a .030 thick head gasket. The larger ports should be good for a few hundred more rpm with the same cam. A large port single plane intake might help also, the victor is super-don't be afraid of losing power down low, not with those gears

http://www.ebay.com/itm/Edelbrock-V...Parts_Accessories&vxp=mtr&hash=item35bb56cb35

Even if those heads can be milled more then .040 not sure I would. It kill the re sale value and if you ever change the pistons you might regret it then
 
What valve size are the 915's?

All sb LA heads are swirl port, that is....if any are.lol

FWIW the 302's i have off of a stock motor come out to 64cc, just as the book says... 'probably the only 318-360 head to actually be as advertised'.
The 318 intake ports are all the same shape between 302 and 675 castings are around 124cc's int port volume.
The 915's intake port volume is 'from what ive measured' 155cc for 2.02 int valve & 160cc for 1.88 int valve.
Ive also measured 69-72cc. One set i got as cast had one of the middle chambers that was 64cc's while rest were 69cc's.
I would use use the 915 heads, milling them .045 off the deck and .040 off the intake side.
When it comes down to it...the j's flow more air, about 30 + cfm more 210-228cfm... thats a fact. the 318 porting heads stock numbers r identical to 302's-17-175cfm
 
...............U already have the 302s on there, don't waste ur money on the 915s unless ur gonna build a better short bock..........kim.....
 
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