Dome VS Flat Top

[norton]

Gee, Warpspeed, your query didn't mention cost being a factor

Given all being equal how much is a flat top piston worth, as far as hp, over a domed piston. (If any at all?)

Bottom line, we all agree. Since you are working with the antique 23-degree SBC stuff (this from a Studebaker-Packard V8 guy, but we've got 12-degree valve angles) you now say cost is a factor then, as Joe says, a domed piston would be your answer. However, if ultimate horsepower is the goal without regard to cost, current best science says small chamber/dish or flat top.

thnx, jack vines

not saying that cost is a huge factor here. (But I am not going to run out and spend thousands on new heads when mine are sufficiant for what i am doing) What I am saying is that I already have the dart 64cc head and I am going to a bigger bore over the winter so since I will be getting pistons just trying to determine dome or mill the head??

[PackardV8]

At the risk of being accused of taking the side of theory over practice, the earlier the ignition point, the more cylinder pressure the piston has to overcome on its way up to TDC. Yes, an individual engine may make more horsepower with more advance, but in general, designs which need less ignition advance have a more efficient combustion chamber design and usually can make more net horsepower.

To Joe's point, when working with what ya' got, give it whatever ignition advance makes the most horsepower, write it down and go on to the next one. When designing a clean sheet engine, find the combination which requires the least advance for best power.

thnx, jack vines

[David Redszus]

David: do you have a picture of that Porsche piston.

As a matter of fact, I do. I took a picture of the piston with my phone today.

Now if someone will teach me how to post JPEG graphics, I'd be happy post them.

[3V Performance]

At the risk of being accused of taking the side of theory over practice, the earlier the ignition point, the more cylinder pressure the piston has to overcome on its way up to TDC. Yes, an individual engine may make more horsepower with more advance, but in general, designs which need less ignition advance have a more efficient combustion chamber design and usually can make more net horsepower.

To Joe's point, when working with what ya' got, give it whatever ignition advance makes the most horsepower, write it down and go on to the next one. When designing a clean sheet engine, find the combination which requires the least advance for best power.

thnx, jack vines

X2 well said jack

[bigjoe1]

I have seen some engines that the owner would not try more advance than 35-36 degrees, and when I keep advanceing it, the engine picked up 55-60 HP. Can you believe that someone would be that stubborn that they wont even try it, It is true though.

JOE SHERMAN RACING

[nitrous small block]

my last motor i had, the one in my sig: 355 with afr 210 box stock heads, had 76cc chambers with an 11cc dome piston. picked up 20hp from 34 degrees to 40 degrees, didnt try anymore because it was a fight to make it happy for nitrous and n/a.

[2xmod]

Does everyone but me think it is important to run less timing-- like 34 instead of 40 to get the most HP..I do see some engines will want way more timing than others, but I have also seen where the one making the most HP wants the most timing.. Am I all alone here ?

JOE SHERMAN RACING

Not at all,we have a low buck 350ci single 4bbl altered on alcohol with flattop pistons 461 fuellies & 9.9-1 comp it has gotten faster with each timing increase up to (& we've not gone further) the 43* we currently run.Guess that the engine will tell what it wants,if we listen

My 355 Alky with 461 heads lovess at least 40 degrees. It just screams at 42 degrees,at 36...its just not the same. Everyone thinks Im crazy running that much timing.

[axegrinder]

My last three motors look like this. All very similar and racing in the same class.

1: 14to1, flat mill aprox .100, 6cc dome .375 tall,41dg timing $15,000=748hp
2: 14.3to1, angle mill 1dg, 3cc dome .250 tall,41dg timing $17,000=762hp
3: 14.9to1, angle mill 2dg, 3cc dome .220 tall,37dg timing $23,000=806hp


These motors were not identical otherwise but close. All run on the same dyno all had CP pistons hand finished domes by me and Iron Eagle heads fully ported by me.

Basicly the numbers are backing up what everybody is saying on this thread. Myself, I hate big domes but I will use them if cost is an issue. BUT I will always hand finish them and there will be nothing left sharp on the piston. A half inch tall dome with a sharp peak is sh*t! That is asking for 48dgs timing and less power in the end. (in a 23dg sbc) And yes Joe I always run what ever timing the motor likes.