915 vs 452 heads on 383

Brett350 · Jun 5, 2020

Thought I'd get an opinion before I toss my engine back together. The 915s from 67 have the smaller exhaust valves and closed chambers. The 452s are open chamber but have a bigger exhaust valve. Curious if the 452s would be more beneficial with the bigger exhaust valve despite a drop in compression or if I should stay with the 915s. Compression is right around 9-1 on my 383 with the 915s. I have headers, performer rpm intake, kb pistons, and a lunati 226/234 @ .050 cam. Thoughts?

Jerry Hall · Jun 5, 2020

Brett350 said:
Thought I'd get an opinion before I toss my engine back together. The 915s from 67 have the smaller exhaust valves and closed chambers. The 452s are open chamber but have a bigger exhaust valve. Curious if the 452s would be more beneficial with the bigger exhaust valve despite a drop in compression or if I should stay with the 915s. Compression is right around 9-1 on my 383 with the 915s. I have headers, performer rpm intake, kb pistons, and a lunati 226/234 @ .050 cam. Thoughts?

I don't think the loss of compression will offset the bigger valves. 8 valves and 8 seats installed in the 915's and you have the best of both.

33 IMP · Jun 5, 2020

Are the KBs the quench dome pistons or flat tops? Quench domes most likely won't work with the 915s unless its way down in the hole. If they are flattops, the best answer is putting bigger exhausts in the 915. I think i would stick with the 915s, even with the small valves.

1 Wild R/T · Jun 5, 2020

452 has bigger valves and better ports... But I'm still a big fan of 915 heads... Also I hate low compression pig motors....

PRHeads · Jun 5, 2020

For that combo, use the 915’s.

Nate S · Jun 5, 2020

If you were doing something else with the engine that might allow the compression to stay up I’d go with the -452’s those hardened valve seats can be nice and it’s got the bigger exhaust valves with no work. If it’s really already that low though you might just stay with the 915’s. Have you measured deck height? A proper calculation is pretty easy at this point.

67MPRFAN · Jun 5, 2020

I just went through a similar situation, I changed out my 906 heads with 2 inch Super comp headers to a set of 516 heads and smaller headers and you can tell a seat of the pants difference

wyrmrider · Jun 5, 2020

915's came with either 1.6 or 1.75 ex valves
for a mild buid 1.6 works fine
putting in the 1.75 gives you new seats
the larger 2.15 intakes make a bigger difference but the 2.08 work fine unless they are sunk in the heads now if you are porting, similar to the 902 (do I remmember that right?)
If the 452's have already had a valve job chances are you are through the factory hardening anyway
915's can be used with many 0 deck pistons (6 pack compression height) and later aftermarket heads
no future with the 452's

cryplydog · Jun 5, 2020

I put 915's on my 68 rr engine and took the 906 off many many moons ago. I don't think the 383 will mind the smaller exh. valve you have a good exhaust.

Brett350 · Jun 6, 2020

33 IMP said:
Are the KBs the quench dome pistons or flat tops? Quench domes most likely won't work with the 915s unless its way down in the hole. If they are flattops, the best answer is putting bigger exhausts in the 915. I think i would stick with the 915s, even with the small valves.

Running the kb400 pistons to keep compression up. Tough with the short stroke of the 383. This was a budget build for a street car. Pistons are about 50 thou in the hole. Was running before with the 915s before I had to tear it down. Calculated compression pretty much bang on 9 to 1

wyrmrider · Jun 6, 2020

good to go
mr gasket .028 gaskets
you do not want to drop your compression
agree on the exhaust unless seats are gone
you can probalby find take out 1.74's if you shop around
if you have time post a wanted
the exhausts can have chrome stems wheras the itakes ususlly do not

915 vs 452 heads on 383

Brett350

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Jerry Hall

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33 IMP

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1 Wild R/T

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PRHeads

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Nate S

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67MPRFAN

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wyrmrider

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cryplydog

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Brett350

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