915 vs 516 heads

[SGTPaul]

Hi,

I’ve been told these heads have similar volume and performance but the 516 head has a smaller exhaust valve. Is this correct? If not what is the difference? If I have the 1.74” exhaust valve installed will this match the 915 head performance? Any help would be appreciated!

Thanks
Paul

 

[polkat]

I've read somewhere that if you install the bigger exhaust valve, open up the pocket below the seats a bit, and maybe radius the short side a bit, they will flow as well as the 915's. Don't know for sure if this is true, but people have done it. If you install the bigger valve, it's a good idea to install hardened seats.

 

[Cranky]

Installing the 1.74 valve helps a lot and so does doing the pockets but they will never be as good as the 915. You may get close to a stock 915, however the 915 is more like a 906 as far as ports go. The exhaust port is small and has a nasty bump in the floor that needs to be smoothed out but you have to be careful you don't break through. Also, about the hardened seats....I've heard way more problems with the seats coming out than sunk valves from not using them and never have done any of my cast iron heads. Mom's castings are from a good grade of cast iron (yes, there's many grades of cast iron) and are not soft like what GM used....and I'd rather deal with a valve that's trying to sink than a seat coming out.

 

[Propwash]

Yes that is correct........516 has a 1.6" Exhaust valve. Same 73.5 CC Chambers

 

[Meep-Meep]

Some 915's have the 1.6" exhaust valve so you need to pay attention when you find a set. 516's have a flat intake port floor and the 915's have a nice radius that I believe helps the mixture make a nice laminar flow transition as it makes the bend to the valve pocket.

 

[69 Runner]

Some say that if you're wanting to port a set of these heads, the 516's are better to port than a 915.

I cannot say that for sure

 

[Cranky]

Yes that is correct........516 has a 1.6" Exhaust valve. Same 73.5 CC Chambers

I've never measured a set of closed chambered heads that came out that low in stock form. The ones I have on a 440 checked out at 80. The books all say low 70's tho.

Some say that if you're wanting to port a set of these heads, the 516's are better to port than a 915.

I cannot say that for sure

Never did any 915's but have done 516's, 906 and 452's.....the 516's had me worried that I was going to cut through.

 

[racedodge]

i put a set of 2.14/1.81 valves in a set of 516's without any port work whatsoever. got my 71 charger into a 12.17 at 108. they can make power even if you dont massage them.

 

[Cranky]

Pretty impressive.....think they would go that fast with 2.08 and 1.74's? What size cam? Large valves and moderate lift/duration.....might could work well? I have a Hemi grind cam in my engine and maybe before I die, I'll get a chance to put it in something and see what it does lol

 

[racedodge]

Pretty impressive.....think they would go that fast with 2.08 and 1.74's? What size cam? Large valves and moderate lift/duration.....might could work well? I have a Hemi grind cam in my engine and maybe before I die, I'll get a chance to put it in something and see what it does lol

i had a 292/.509 cam, dual quad tunnel ram with two 600 edelbrock's up top. TRW forged 11 to 1 pistons, headers and 4.56 spool.

 

[72 Charger SE]

Installing the 1.74 valve helps a lot and so does doing the pockets but they will never be as good as the 915. You may get close to a stock 915, however the 915 is more like a 906 as far as ports go. The exhaust port is small and has a nasty bump in the floor that needs to be smoothed out but you have to be careful you don't break through. Also, about the hardened seats....I've heard way more problems with the seats coming out than sunk valves from not using them and never have done any of my cast iron heads. Mom's castings are from a good grade of cast iron (yes, there's many grades of cast iron) and are not soft like what GM used....and I'd rather deal with a valve that's trying to sink than a seat coming out.

I can't say what the big block heads look like running unleaded without changing valve seats, but I have a set of 72 318 heads that sunk all 8 exhaust valves pretty far in about 30,000 miles on unleaded.

 

[Cranky]

I can't say what the big block heads look like running unleaded without changing valve seats, but I have a set of 72 318 heads that sunk all 8 exhaust valves pretty far in about 30,000 miles on unleaded.

What kind of environment was this used in? Your Charger? Use a high performance cam with stronger springs? Normal running engine temps? Fuel used? E10 or more?

 

[72 Charger SE]

What kind of environment was this used in? Your Charger? Use a high performance cam with stronger springs? Normal running engine temps? Fuel used? E10 or more?

Used in my Charger while it was still my daily driver. Moderate/mild cam, split profile MP cam that would probably be considered an RV cam. Heads milled .030 to raise compression a bit, but it still ran fine on regular unleaded 87 octane. I was using stock valve springs since I had a mild cam and wasn't racing it. Never got it over halfway up the factory temp gauge. Don't think it ever got much gas with ethanol in it, but it could have. This was from 1989-96.

 

[Cranky]

I've heard of cases like that but heard of many more cases of the inserts coming out but now with those heads, you don't have a choice. I'm still from the thinking that I'm not going to install them unless I have to....but another alternative is to use a later model head. I assume the small blocks were treated the same as the big blocks with induction hardened EV seats? No worry about an insert coming out with those.

 

[SGTPaul]

Thanks for the input everyone. I picked up a set of 915 heads today with the smaller exhaust valves. Will probably have the 1.74" valves installed.

 

[Cranky]

Thanks for the input everyone. I picked up a set of 915 heads today with the smaller exhaust valves. Will probably have the 1.74" valves installed.

Score!!

 

[polyjohn]

Nice thread indeed!

I am a great fan of iron heads and pretty much have the whole collection lol.
As folks went over to aluminum, the iron heads got very cheap except for the 915 casting.
I have never run down the 1320 with anything but iron and 452 cubes, my best is 10.66.
Next plan is a stroker 512ci and with what iron head?
Probably the 906's as the flat tops I have would send the compression way too high...
I have sets ported by the 'great and the good', Koffel, Hauser and the best being Rob Loring!

Back to the 516 debate methinks?

 

[polyjohn]

There are different castings for the 516 I have found!
The worst being the 1966 ones for sure, very restricted exh-port...

The 64's and 65's seem much better cast in the exhaust area.
Plus I have a 516 undated casting without a Mopar CD stamp which appears to have the 915 Exh-port?

I have a 915 to hand and I will compare them both tomorrow.

 

[polyjohn]

Very strange indeed this 'un-logoed' 516 casting.
No casting date and no Mopar logo, plus an even better than 915 exhaust port TOO!

The roof is perfectly flat and maybe could take a re-shaping into a slight bowl as well...

Yes I know this thread is useless without pic's but my Samsung has broke!

I am a self confessed 'technophobe' and I can't load my old 'Kodak slides' on here either...

Kodak did have a 'Kodachrome Slide Lab' here in the UK (Wimbledon) and I was the 'engineer' there for a few years!
(Last Kodachrome film was processed in Kansas by Dwayne January 2011)