2 Valve Relief vs. 4 Valve Relief - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-02-2004, 12:29 PM
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2 Valve Relief vs. 4 Valve Relief

This has got me wondering. On ebay under Racers Outlet I was looking for dished pistons for a 383. This guy is selling new dished Speed Pro coated skirt pistons with a 2 valve relief design for $174 for the whole set. In Jegs, they sell the same exact Speed Pro dished piston with a 4 valve relief design for $42 a piece or $336 for the set. Is that a money saving deal or is the 4 valve relief design that much better? What are the pros and cons of each? Or actually what is the exact difference? I plan on running vortec heads. Which design is better to run with these heads? What kind of rings are the best to run? Thanx for any input.

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Old 12-02-2004, 12:45 PM
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2 valve vs 4 valve

The 4 valve relief pistons can be used either way in the engine, where 2 valve relief pistons are directional and the reliefs have to match the valve pattern in the heads.

Given that all else is the same, the 2 valve piston will have nominally higher compression due to the 4 valve piston having an additional 2-4 cc of additional relief in the head of the piston. Depending on displacement as to how much the additional 2-4 cc of unswept area you have.

2-4 cc's will have more effect on compression in a 350 cubic inch engine than it will on a 454.

IE: a 4 cc unswept area could make a .4:1 difference in compression in a 350, and .3:1 difference in a 454.

a 2 cc unswept area would make a .2:1 difference in a 350, and .16:1 difference in a 454.

Last edited by Max Keith; 12-02-2004 at 12:45 PM.
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Old 12-02-2004, 01:14 PM
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your talking about kevin at racers outlet in indianola,iowa.i've been buying alot of stuff from him including a set of speed pro hypereutectic pistons with a dish and 4 eye brows that with my heads and engine will come out to 9.6-1 c.r. which is why i am buying them.i had an unfortunate mishap with a defective new balancer that trashed my crank and i have to rebuild my engine again which is what i had just gotten thru doing when the balancer split down the keyway while on the first test drive thru my neighborhood.since i had to rebuild again i decided the gas prices weren't going down soon and i was tired of paying for premium.i got new rod pistons ,valve springs,balancer and flex plate from kevin at racers outlet and love saving all that money.i live about 1 mile from one of jegs stores and have spent alot of money there.don't get me wrong jegs has treated me well thru the yrs. but they have all that overhead and kevin doesn't.there are many other stores on ebay where you can buy anything you need for your hot rod at a better price usuallybut not always.as anywhere else you need to pay attension.you need to decide if your motor is decked or what size your combustion chamber is to know what c.r. pistons you need no matter how many eye brows they have.you won't go wrong with kevin.but he is only there to take your order from 9a.m.-12p.m. M-THURS. iowa time central standard.tell him barry from columbus,ohio recommended him.
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Old 12-02-2004, 02:01 PM
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Where did you get the balancer the first time?

I bought some Valve springs from this guy:

http://cgi.ebay.com/ebaymotors/ws/eB...tem=7926620505

You know what Pioneer(the Manufacture) said about these "550" lift springs?

They are a .490" lift Z28 copy
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Old 12-02-2004, 02:07 PM
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rings

AS for your question about rings, chromolly rings are a wee bit more expensive, and harder to seat in but last longer as a rule. The cross hetching of the cylinder tends to be more critical with lapping in chromolly rings, where Iron rings are more forgiving, a little less expensive, and lap in quicker. The down side is that iron rings tend to not last as long. But when a set of iron rings will last well over 100K miles, and if you plan to keep the engine forever, I would say that cost is moot. Some pistons do require chromolly low tension rings, etc. The first question I would have is what the piston manufacturer recommends.
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