200. dome sbc pistons with heart shaped chambers? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-09-2010, 02:51 PM
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200. dome sbc pistons with heart shaped chambers?

i am rebuilding the top end of my high comp 355.. i have speed pro power forged 30. over pistons with a 200. dome.. i am looking at the procomp aluminum heads.. they are 200 cc intake 2.02 1.6 valves and the have cncd 64 cc combustion chambers.. also they are heart shaped and the seller is saying they may need to be dremeled out about 50thousanths right on the flat surface at the point in the middle of the valves .. does anyone have any intell on this as i do not wanna purchase heads that will not work with my pistons.. im also ganna run atleast a 555 lift flat tapped cam ..so can i run 200 dome with heart shaped combustion chambers?

pistons Sealed Power #844-L2252AF30

here is the heads
http://cgi.ebay.com/ebaymotors/ws/eB...=STRK:MEWAX:IT

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Old 12-09-2010, 04:21 PM
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Quote:
Originally Posted by 355guy
i am rebuilding the top end of my high comp 355.. i have speed pro power forged 30. over pistons with a 200. dome.. i am looking at the procomp aluminum heads.. they are 200 cc intake 2.02 1.6 valves and the have cncd 64 cc combustion chambers.. also they are heart shaped and the seller is saying they may need to be dremeled out about 50thousanths right on the flat surface at the point in the middle of the valves .. does anyone have any intell on this as i do not wanna purchase heads that will not work with my pistons.. im also ganna run atleast a 555 lift flat tapped cam ..so can i run 200 dome with heart shaped combustion chambers?

pistons Sealed Power #844-L2252AF30

here is the heads
http://cgi.ebay.com/ebaymotors/ws/eB...=STRK:MEWAX:IT
If you're building a serious race engine a much smaller chamber with a flat top piston is the better solution, I'll offer this as an example from DART: http://www.dartheads.com/products/ai...itfile_id/122/

The reason being that extremely small chamber heads with a flat top piston has much better flame propagation and a faster burn thru the mixture than a larger chamber and pop up piston. This nets more power, a lot more power than you can ever get from forcing the flame front around a dome on a piston crown.

I recommend you reconsider your configuration plans.

Bogie
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Old 12-10-2010, 06:56 AM
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Originally Posted by oldbogie
The reason being that extremely small chamber heads with a flat top piston has much better flame propagation and a faster burn thru the mixture than a larger chamber and pop up piston. This nets more power, a lot more power than you can ever get from forcing the flame front around a dome on a piston crown.

I recommend you reconsider your configuration plans.

Bogie
Strictly speaking, the net gain from a dome to flat-top isn't as big a one would think. The dome itself does increase swirl in the chamber, which, in itself, also aids in combustion efficiency. Bottom line is, to get a desired compression ratio, using a dome to get there isn't that bad an idea.

tom
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Old 12-10-2010, 07:36 AM
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I agree with Old Bogie. I guess it depends if you're really talking about a true high rpm race engine, or not. I mean like 14 or 15:1 plus compression and over, lets say, 7500 or 8000 rpm- a flat top is much better than a dome. First, you don't have time for as much timing advance, which a dome usually needs. Second, a dome piston is heavier. Flat tops make for a very light piston, which aids in rpm. I think there is a formula somewhere that says that the forces a piston sees from changing direction go up exponentially with rpm. So at very high rpms, you are trying to push and pull the pins right through the pistons. Piston weight is a huge deal in those scenarios. My sprint car engine-tight little 36 cc chambers with 2.200 and 1.580 ti valves, very short flat top pistons, and just over 15:1. Best at 28-30 degrees timing. Any more will burn off the electrodes on the plugs. Will happily sing along wide open @ 8500 plus.
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Old 12-10-2010, 10:55 AM
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Quote:
Originally Posted by machine shop tom
Strictly speaking, the net gain from a dome to flat-top isn't as big a one would think. The dome itself does increase swirl in the chamber, which, in itself, also aids in combustion efficiency. Bottom line is, to get a desired compression ratio, using a dome to get there isn't that bad an idea.

tom
I would not agree that the approach with a dome provides as much benefit as a small chamber and a flat top, but that depends.

From analysis we've been doing domes actually dampen the swirl, while they do a great job of increasing mixture density which increases the potential of the spark stating a fire that should burn faster because of the density it ends up that the dome adds burn time. This looks like a combination of conditions where the dome actively is in the way and it adds surface area which pulls heat out. One could say there is an anti-detonation element in that, but the loss of energy to the surface pulls a lot of potential power out. There's always the classic solution of more advance but that has it's own set of problems.

I think both the factories and certainly NASCAR builders have been showing the way ahead since the days of the SB2.2 of really small chambers, very tight squish/quench, big valves and ports, and flat top pistons.

In this specific case of a modern heart shaped chamber and a dome, I feel the dome interferes with the intent of the chamber at the same time, I experience shows me that a dome will work better with an open chamber. So my choices would be a smaller modern heart shape chamber with a flat top or a larger open chamber with a dome. My basic rule for a rough determination as to where to start with an engine configuration is that a normally aspirated engine on gasoline always gets a small chamber and flat top or D dish piston. An engine using a blower, or alcohol, or nitrous, or nitro-enhanced fuels gets an open chamber and a flat top or dome depending on final CR selection. My thoughts here are that where a lot of volume is being pushed into the cylinder that a more open area around the valve aids in getting all that stuff in. This decision on chamber size and piston crown is also dependent on valve angle where the typical 23 degree is more likely to follow the scenario above while flatter angles that open the valve into a larger area within the cylinder reduce the need for a large chamber to provide the extra clearance around the valve for lots of stuff to get past.

Anyway my thoughts on the matter. I suppose this makes my brain look like a skid road alcoholic that's staggering along the curb looking in the gutter for butts to smoke and whiskey bottles with a swallow still in 'em. Yes I don't live far from First an Pike, those of you that have visted this fair city and went to Pike Place Market will understand this view.

Bogie
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