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edelbrock rpm performer heads 350 vs 383

29K views 13 replies 8 participants last post by  idontdrivericeieatit 
#1 ·
Ok i bought a used set of rpm performer heads "hope I did good" and im looking to build a bottom end for my camaro would I be better off with a 350 instead of a 383 with those heads a little confused about the specs on the heads there marked 6073 on the outside and 6061 inside but i think there 70cc with 170 or 185cc intake i want a good cruiser, kinda hotish, like 400hp range low compression motor. I know its not going to be good on gas but i want it to be efficient for what it is so 350 or 383 pros cons on ether
 
#2 ·
For mileage you want the highest compression you can run with whatever cam you're looking at- but you also need to use a cam with low duration (which lends itself to lower compression).

If I were in your shoes, with those heads and a 383 I would go with a 10:1 compression and a cam in the 215º range with all the lift you can get (hyd roller with 1.6 rockers).
 
#5 ·
i was planing a 383 build but doing research on my heads alot of people are saying they are not enough for a 383 idk but like i sayed i want around 400hp but i dont want to go over board with it cause i do plan on driving this car alot gas mileage is not my most concern but i do want something i can drive
 
#6 ·
If you need to get a new crank then there is no reason to not go with a 383. If you're on a tight budget and can reuse your crank then a 350 can hit 400hp pretty easily with those heads.

It comes down to budget and what you have. A 383 will have more torque BUT a well built 350 can easily provide the power you're wanting.
 
#8 ·
I can't say from experience, and perhaps I shouldn't say anything for that reason, but I'm going to through my two cents in anyway, and if anyone disagrees please correct me.
If I were you I'd start with a 87'-92' roller cam block and use the stock lifters/spider retainer for considerable cost savings. The stock type lifters/"dogbones"/spider retainer for roller blocks can be purchased in a kit for almost 1/2 the cost of retro-roller lifters alone(used in older blocks).
As far as the heads you have(I have the same) I would disassemble them and do some pocket porting/chamber blending/polishing. Mine had sharp edges where the valve seat inserts were cut, and seats installed too deep IMO, that might have caused hot spots for detonation. Get two used valves from the machine shop you plan to use, and insert into the chamber that your working on to prevent damage to the seats before grinding. I used a dremel with a flexible wand, and sanding rolls as I didn't have an air compressor for a die grinder. I'm sure most wouldn't recomment a dremel, takes alot of time and not the proffesional way to do the job, but I think it worked ok for me.
I'd then get the machine shop to check the valve guides to see if there ok before getting a valve job done. After the valve job have them milled just enough for clean-up of the deck for gasket sealing. Then cc the chambers and equalize them for consistant compresssion and CR calculation(mine measured an average of 72cc +/-.3 after all the work).
I'd also get some beehive springs/retainers/seat inserts to work with a roller cam. I used Comp Cams behives pn 26986-16 springs, pn 795-16
10*retainers, and pn 4694 spring cups, and all fit withouut maching the heads.
This is probably alot of over kill for a 400hp, low compression engine, but I would at least do the valve job, guides checked, springs checked, deck shaved, and cc'ed. Use the springs recommended by the manufacturer of the cam you use. The springs on mine were not spec'ed for a roller cam. Being that your talking about a low compression motor smoothing the chambers may not matter, but it wouldn't hurt and may be whats needed to equalize the chamber volumes. I can't guarantee it, but I'm bettting mine will support a 383 making 425-450hp. I'll have to wait and see if I lose the bet.
I'd also use a Scat crank and rods, for a six inch rod as you can get it internally balanced(with exception of flexplate if using a one piece rear main seal used in roller blocks). I don't like an unbalanced dampner on the crank snout as the front main bearing has enough of a load as it is with the accessory drives(alternator/pwr steering/ AC). I have heard some negative rumors lately about Scat cranks, but I bought mine directly from Scat awhile back, and it checked out good with my mics. I also got the Pro comp rods that have the ARP 7/16"cap screws that didn't require any clearancing on the block. I haven't checked cam clearance yet.
For lower compression I'd use a piston with a 12cc "d-cup" and a zero decked block with a head gasket of 0.039" thickness(Felpro pn 1010 has a preflattened copper ring for alum. heads) for a 0.039 squish/quench distance to ward off detonation. I can't guarantee that it would be able to run using 87 octane, but with 72cc chambers it comes to about 9.5:1 static CR, and with a Comp 270 roller cam the dynamic CR comes to about 7.8:1. According to Comp's camquest software it comes to 437hp and 480ftlbs torque.
Ignore the groves in the chamber pics. I'm using a flat top with 5cc valve reliefs and the CR comes to 10.2:1, so I'm trying to get every bit of detonation resistance I can. Don't know if they work anyways.
Just some things to think about!
FWIW
ssmonty
 

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#10 ·
HCOMPTON,
The ridges around the valve seat inserts were not swirl devices. Some chambers on the head had them and some didn't. It was left from the machine operation at the factory to install the seats. I believe a machine operation be it by CNC, or manual mill, or something else was used to cut the bore to the same depth for each chamber relative to the table height of the machine. However each chambers casting depth wasn't consistant thus the ridge on some chambers and not on others.
If your refering to a vane downstream of the valve guide, there wasn't one on these heads. I did reduce the diameter of the guide bosses to reduce air flow restriction although it won't make that much of a difference, similar to the reduced valve stem diameter of the Manley "Pro Flow" valves I installed. I figure every little bit helps as far as beating the next guy.
If your refering to a swirl vane in the chamber such as a raised boss around the spark plug location, there wasn't one in my heads.
As far as a "Rule of thumb for aftermarket heads is only port them if you have too by class" thats the first time I've heard of that. I have heard of no porting allowed in certain classes. As far as I'm concerned I had the spare time and the will to try to make them better than stock before I installed them on an engine vrs removing them to do the same later.
Just MHO.
To each his own,
ssmonty
 
#9 ·
Hello Munchigan,

My 1977 Nova had a professionally built 383 with 60899 heads, mileage on longer drives was about 18 mpg, about what the original 350 got.
Engine had Comp 280H flat cam, dynoed at 430 Hp(5500rpm) 470 torque-nice engine, easy to start and drive. 60899 are 64cc straight plug RPM. I sold this engine and moved up to a 420 Dart. This car is a summer drive/cruise car, hasn't been to the drag strip. Engine was built and tuned for premium (91 octane) pump gas.

Here is a location to search your 6061 and 6073 heads:
Edelbrock.com

You have 4 digits as opposed to newer Edelbrock numbers of 5 digits, so your 6061 will be 60619 and 6073 will be 60739. You will see that both are 70cc, straight plug but 6073 is for solid flat tappet and hyd roller. You will have to do a bit of searching to find spring rates.

Hope this helps,
Regards,
Meldrum
 
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