What's best on a 355 domes and open or flatop and closed? Runnin 93 oct - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-05-2012, 06:21 PM
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What's best on a 355 domes and open or flatop and closed? Runnin 93 oct

On a High Horsepower 350 pump gas what is better?
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Old 11-05-2012, 07:25 PM
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Originally Posted by Billgt63SS View Post
On a High Horsepower 350 pump gas what is better?
Flat top pistons combined w/the chamber volume needed to get your target compression ratio is the best formula in nearly every case.

There may be an argument made for an inverted dome piston combined w/the chamber volume needed for the target CR, but generally speaking a FT w/a smaller chamber will give better flame propagation and a cleaner burn w/better quench/squish action than an open chamber and a dome.

The shape of the chamber is also an important part of it all. A heart or kidney shaped chamber having a larger area quench pad and a more central spark plug location biased towards the exhaust valve (like on the Fast Burn and Vortec heads seen on the right, below) will give a better quench/squish action and detonation resistance than even the earlier small chamber SBC heads (like the fuelie heads, left below) w/FT pistons.

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Old 11-05-2012, 08:01 PM
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Still there is a case for not going much over a 8.5 DCR.
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Old 11-06-2012, 01:10 PM
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Originally Posted by cobalt327 View Post
Flat top pistons combined w/the chamber volume needed to get your target compression ratio is the best formula in nearly every case.
^^^^times 2
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Old 11-08-2012, 06:01 PM
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Originally Posted by Billgt63SS View Post
On a High Horsepower 350 pump gas what is better?
Depends a whole lot on where in crankshaft degrees the cam shuts the intake. A high horsepower engine usually means a really big cam, this looses a lot of torque off the bottom end that needs to be restored; the method of recovery is through higher than expected compression. Obviously 93 unleaded does impose an upper end to the squeeze, but none the less you're probably going to be shoved to push the limits.

Gearing including the result of tire size and vehicle weight as well as the end use of the machine will also impose restriction or open possibilites. Stiff gears and light weight combine to let you run more compression than what would otherwise be expected. Drag racing will let you may even require you to push the limits harder. Round track especially in the dirt will also let you push harder. Paved round track and road course will force a back off of the upper limit because of the better traction and the possibility of hauling the revs up in the wrong gear which will overload the engine and push the detonation limit sooner. A hot street engine will also have to be more conservative on compression, especially if you mix it with higher gear ratios. Off road tends to use large diameter tires, these unless you really hang some nasty gears in the rear end, will also drive a more conservative compression solution.

So to be of any real help I'd have to know a whole lot more of what's in-store for this high ouput 350.

Bogie
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