915 Heads On 383

[FirstPolara]

I have a 1970 383 that is all stock except a 750 edelbrock carb, 727, 323 suregrip. I have access to a set of 67 915 heads with 2000 miles on them since a rebuild. I can buy these for around $350. After extensive reading, it seems to me that most would say that the 915 head is superior to the 906 head.... but here is my question. Without touching anything else on this engine, my plan would be to buy these heads swap them with the 906's and while I'm at it put on a performer intake. Will I notice a difference or am I wasting my time and money by doing this? Does this price seem reasonable?

Sorry for creating another thread about 906 vs 915 heads but after breaking the bank on the rest of the car I am looking for the cheapest way to get the most out of my 383. Thanks in advance for any replies.

 

[FirstPolara]

Also, if it makes a differece the casting number on the heads is 2780915.

 

[cwhubb]

I'm not an expert on head flow or cfm's but my experience has been at right around 15 hp increase give or take, I can feel, seat of the pants wise, a difference. You'll deff feel a difference. with those gears and the new heads, and manifold you'll feel the motor keep pulling past where the stock set up started to level off. nice and smooth like when an airliner takes off. the price is good if they are as new as you say plus you will never get stuck with them if you dont like em, they are a hot item.

 

[cwhubb]

Oh and by the way my friend had a 70 super bird with the 440 comando, same gears as you some head work done, at a dead stop it felt just like a take off, (if he didnt rev and punch it) nice and smooth at first then it just kept pulling and pulling we hit 120 and it still was pulling, yea, you'll like it

 

[FirstPolara]

Thanks for the input. I was wondering if it would make a difference off the line as well. Sounds like this would be a good investment for me as I'm not looking to race but would like a good result when I decide to put my foot into it.

 

[RustyRatRod]

They'll raise compression by more than one point. I think it's a good comparison to call them closed chamber 906s.

 

[FirstPolara]

ok, sounds like a good idea for me to give it a try. I will confess to being very green....with that being said what should I look for on these heads when I go to buy them to ensure they are in good condition as he claims. Overall they look good but is there anything I could be missing?

 

[RustyRatRod]

Other than being able to disassemble them, there's not a lot you can verify. Unless of course they look like crap. I would rather see heads with light and even carbon deposits than see perfectly clean heads. That would mean they had been cleaned up. People try to hide things sometimes. Look to make sure the valves have a good margin. The margin is the part of the valve face that sticks up into the combustion chamber....in other words, the edge of the valve face should not be flush with the combustion chamber. It should be slightly above it. If they are flush, or even sunk into the combustion chamber, that's a sign the valve guides are worn and have allowed the valves to beat the seats out in the heads. It can be repaired with new guides and seats, but that's not an inexpensive repair. You can also look for obvious cracks. Prone spots are right off the deck surface going into the chamber, or right in between the valves. If you see any cracks, I would pass. I don't care what anyone says, cast iron is a double barrel bastard to repair right. Plus, it is very expensive to repair cracked cylinder heads correctly. In that case, you'd be better off going aftermarket heads. But lets be optimistic. They may be in great shape. Good luck and keep us posted.

 

[IQ52]

The difference you will get with the cylinder head exchange is mostly going to come from the "rebuild" of the 915 heads versus the condition of the original 1970 906 heads. It would cost you more than $350 to rebuild the 906's.

If the 915's and the 906's were in the same condition, I would guess the chamber size difference in the heads will raise the compression on a 1970 383 from 8.3:1 compression to 8.9:1 compression or about a 6 horsepower increase.

The biggest horsepower increase, from your contemplated changes, will come from the intake manifold swap, even though the Performer is the least effective of the present Edelbrock manifolds available. I guess I might as tell you why. The stock factory cast iron intake will limit the flow through a factory iron head that has been ported to 300 cfm, to down around 208 cfm. So because the 906 and 915 heads flow the same in stock form, about 230 cfm, the manifold will choke the flows on either head so that the only increase from the head swap will come from the compression increase, or 6 hp. No matter what, change the manifold.

For hp/$, if your 906 heads are in good shape, you'll be ahead by changing the intake manifold only. Otherwise buy the heads and the manifold and make the swap, but don't expect earth shattering results.

 

[FirstPolara]

Thanks for the info. Now that I know what to look for, I will go check them out tomorrow. I can't even begin to tell you guys how much this site has helped me and the wealth of knowledge that is available here is greatly appreciated!

 

[FirstPolara]

IQ52... I do beleive my 906's to be in good shape as the engine runs strong but I don't have anything apart to confirm that. Maybe I should leave well enough alone if the best bang for $ is in the intake manifold. As a side thought... if you don't like the performer what would you recommend?

 

[IQ52]

Didn't say I don't like it, said it is the least effective. It is closer to the stock manifold than anything else Edelbrock has to offer, and is therefor the most restrictive to airflow. If you ever plan on further performance enhancements, I would step up to the Performer RPM manifold as it will yield larger results now and still be able to keep up with more performance upgrades later.

The biggest restriction to airflow now is the intake manifold. Then it is the heads, in the valve size and the throat and bowl shape. Then it's the port shape. Best of all, save your money so you can get an aftermarket aluminum head in the future. Well, that is IF you plan on anything else in the future.

 

[Garys1969RR]

When you say "Performer" intake, are you talking the 383 performer, or the RPM Performer? I believe the RPM Performer is a better design, and a more modern intake. My son is running a street dominator single plane intake on his 383 with stock 915 heads. And it runs real well. Good luck.

 

[Garys1969RR]

Ok 52, you just answered my question. Thanks!

 

[STREETREBEL]

I swapped my 906's for 915's and I could feel the differents big time!
And they where both new heads.

 

[65 Plymouth Satellite 426]

Damn...Didn't I Just Answer Someone's Posting About 906-915 Cylinder Heads?

 

[Meep-Meep]

I ran 915's on a 383 with zero deck pistons and they were great. I didn't have anything to compare them to but I believe getting the higher compression due to the closed chamber was better than getting the same higher compression with a domed piston. It's usually best to keep an unrestricted chamber for good flame travel. 915's on a 383 will not raise the compression all that much so you should also run the steel shim gasket, but only if you end up with no less than a .040" quench distance. The smaller chamber and the steel shim gasket may get you .7 points but on a 440 it can get you closer to one full point.

I'm running 915's on my 440 now with a small cam and I had a factory iron intake on it with a 750 AFB. I won't say the iron intake wasn't holding me back but I will say my 440 would pull hard to about 5700 RPM and easily go to 6000+. My 3700 lb car runs 12.80's @ 107 with the cast iron intake and full exhaust. I now have a factory iron six BBL and have noticed a substantial seat of the pants difference. That said, and depending on your cam and compression combo, I doubt you will notice an earth shattering difference between the factory iron 4 BBL vs. the standard performer.

$350.00 for a good set of 915's is a good price and if you do get them I'd plan on a small makeover rather than just swapping one component. 915 heads for more squeeze, mild cam, exhaust and intake. Job done!

 

[RustyRatRod]

Really? So that's about all huh? I always thought a little more. Thanks for the info. 6HP. Heck, just spin the 906 motor a few more revs. LOL

The difference you will get with the cylinder head exchange is mostly going to come from the "rebuild" of the 915 heads versus the condition of the original 1970 906 heads. It would cost you more than $350 to rebuild the 906's.

If the 915's and the 906's were in the same condition, I would guess the chamber size difference in the heads will raise the compression on a 1970 383 from 8.3:1 compression to 8.9:1 compression or about a 6 horsepower increase.

The biggest horsepower increase, from your contemplated changes, will come from the intake manifold swap, even though the Performer is the least effective of the present Edelbrock manifolds available. I guess I might as tell you why. The stock factory cast iron intake will limit the flow through a factory iron head that has been ported to 300 cfm, to down around 208 cfm. So because the 906 and 915 heads flow the same in stock form, about 230 cfm, the manifold will choke the flows on either head so that the only increase from the head swap will come from the compression increase, or 6 hp. No matter what, change the manifold.

For hp/$, if your 906 heads are in good shape, you'll be ahead by changing the intake manifold only. Otherwise buy the heads and the manifold and make the swap, but don't expect earth shattering results.

 

[detmatt1]

If they're the non hp 915's you may want to have the bigger exhaust valves found in the hp version.

 

[Garys1969RR]

While on the subject of 915 heads, I read that the Stealth head is an aluminum version of the 915 head. But with slightly larger combustion chambers at 84 cc. Has any one looked at/compared the port shape of the 915 to the Stealth? I believe the Stealth has the 2.14 intake, 1.81 exhaust valve sizes. I am still trying to decide whether to port a set of 915s, or go to an Alum head. Thanks for any ideas.