Close Chamber or Open Chamber Heads?

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2doorswinger

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Im going to be ordering a set of Edelbrock rpm performer heads for my 1970 340. Currently has stock pistons in it, may go to a stock bore, forged piston. I believe the 1970 340 had a compression ratio of 10.5:1? Is this correct? Can I use the closed chambered heads with the stock pistons or a set of forged pistons? (looking for 10.5:1 compression)
Also, what kind of horsepower can be expected out of the motor with a set of out of the box edelbrocks, 10.5:1 compression, Edelbrock rpm air gap intake, 750 cfm carb, a good size cam (.520ish on lift) and a set of TTI stepped headers? Thanks guys.
 
Most guys buy the closed chambered heads and then adjust the head gasket thickness to get the proper "piston to head" clearance. Stock early 340's tend to have pistons protruding somewhat above the deck, but you really have to measure it after all the machining is done at mock up.

As far as power from your "paper" combo.......A solid 400hp would satisfy me.......As long as you're willing to gear it right & use the proper torque converter?
 
Gears in the rear of the car are 4.10's with a sure grip and its a 4 speed car! Would i just have to get a much thicker head gasket? And how would 500 be obtainable?
 
2doorswinger said:
Gears in the rear of the car are 4.10's with a sure grip and its a 4 speed car! Would i just have to get a much thicker head gasket? And how would 500 be obtainable?
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Nice gears & the 4spd is good :D. Whatever gasket can get you in the .035" clearance range is optimal. 500hp will be a stretch without aftermarket heads, or at least well prepped/ported stockers. The Eddy's cleaned up would probably do the job. The cam would be next in line. Heads, cam & compression are where the big numbers are made.......along with a supporting cast of bolt on's.

And then there's the streetability question, and what type fuel.....pump gas?
 
Buy the closed chambers and do as Rick mentions.

The open chambers will provide ZERO quench which is helpful in keeping detonation from occurring. You want quench. The only way you will get any quench with a stock 340 piston is if the piston is above the deck .060-.070... good luck with that!

That build well tuned will make an easy 430hp.
 
Jeez Louise , I have 0.038 piston to head clearance , that be good enough ? And I have a similar build and did not hit the magic 430 hp , torque yes , still looking for HP
 
jerry6 said:
Jeez Louise , I have 0.038 piston to head clearance , that be good enough ? And I have a similar build and did not hit the magic 430 hp , torque yes , still looking for HP
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You might have .038 at the areas the deck surface has material, not any quench with the parts that were used. The open chamber has ~.060 step and there is no way to do anything with it unless you use a quench dome piston. .012 out of the hole, .050 gasket and open chambers is really irrelavant to a quench discussion with that extra .060 step.

I'm guessing he may be looking at something like the Comp XS282s camshaft. My friend had one 10:1 340, eddies, 282s, victor and a 750 or 950dp. Made 455hp and about the same TQ.
 
Looking for 91-94 pump gas! That should be obtainable with 10/10.5:1 compression with aluminum heads right? Should i change out the pistons or keep the stickers?
 
2doorswinger said:
Looking for 91-94 pump gas! That should be obtainable with 10/10.5:1 compression with aluminum heads right? Should i change out the pistons or keep the stickers?
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1st question; Yes

2nd question; if you have the positive deck height pistons in a 340, then you should get the "340" heads with the piston relief in the heads chamber. The pistons themselves are fine if not a bit heavy due to the dome.

If you have any other engine, the stock slugs can be replaced and should be if a high compression ratio is desired.

In my 360's, I like to zero deck the pistons and run a .038 head gasket with the Edelbrock RPM heads. Not there 340 head. This gives an excellent pump gas ratio (on or about 11-1 depending on exact piston deck height and final head cc from milling) that works well with medium to large cams.
 
I put some open chambered edelbrocks (65cc.) on a basically bottom end 340 (other than rods lightened w ARP bolts, and heavy forged 2316 TRW pistons) rite around 10.2:1 comp, a comp XS282S cam .520/.540 solid, with rpm air gap and a holley 750. 273 adjustable rockers. Made 428HP @ like 5800 RPM. Was going to go closed chambered, but pistons stuck above the deck and at the time I did not want to use a thick head gasket. Looking back I would get closed now (better quench) and run the thicker gaskets.
 
Even with a positive deck height piston stay FAR away from the Ede 340 head.

Ask guys like, RAMM, Brian at IMM, MRL, IQ how they would do it. I doubt any of them would choose the open chamber over a closed chamber with a zero deck or slight positive deck piston set up. Only time to take an open chamber is if the piston is so far below deck that achieving quench is not possible.

Pick your parts, pay your money.
 
crackedback said:
Even with a positive deck height piston stay FAR away from the Ede 340 head. Ask guys like, RAMM, Brian at IMM, MRL, IQ how they would do it. I doubt any of them would choose the open chamber over a closed chamber with a zero deck or slight positive deck piston set up. Only time to take an open chamber is if the piston is so far below deck that achieving quench is not possible. Pick your parts, pay your money.
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+1 All you need to know right there... there's a reason all 2-valve cylinder head designs since the late 1980s have been closed-chamber. LS engines, Magnums, heck even the '09-up Hemis now have quench pads on the sides. Not to mention basically all aftermarket heads are closed.
 
crackedback said:
Even with a positive deck height piston stay FAR away from the Ede 340 head.

Ask guys like, RAMM, Brian at IMM, MRL, IQ how they would do it. I doubt any of them would choose the open chamber over a closed chamber with a zero deck or slight positive deck piston set up. Only time to take an open chamber is if the piston is so far below deck that achieving quench is not possible.

Pick your parts, pay your money.
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I'm with yea here. Those stock 340 slugs are a bit above deck. I'm not sure if I would want a thick gasket and a open chambered head. I did have to do just that on one long ago with a 360 that had +.012 slugs and the heads were the closed Edelbrocks. To solve the problem I used a .050 (IIRC) thick gasket.

I forget where the OE 340 slugs sit above the deck.
 
OldmanRick said:
Most guys buy the closed chambered heads and then adjust the head gasket thickness to get the proper "piston to head" clearance. Stock early 340's tend to have pistons protruding somewhat above the deck, but you really have to measure it after all the machining is done at mock up.

As far as power from your "paper" combo.......A solid 400hp would satisfy me.......As long as you're willing to gear it right & use the proper torque converter?
Click to expand...

This ...
, a good size cam (.520ish on lift) ..
What came options are open to you? Hydraulic flat lifter,solid flat tappet/ hydraulic/solid roller ? For out of the box Edelbrocks & 500 ponies camshaft will need to be more aggressive. A zero deck flat top piston ,63 c.c. Edelbrock head is best. Professional head assembly /porting brings the price and reliability,on the heads up. The expected here: A good hot rod machinist, will match those heads ,with a correct can. It's that experience your paying for. The reliability & street abilities, make it worth it. Sorry about the long post.
 
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