426 Hemi 
starting engine build seeking help ....
starting engine build seeking help .... ok my qeuston is i am running a cc 503 got my heads at the shop and i need to know what would be best vavle set up my pistons are trw forged with 100+ dome.. stock heads and the 503with these pistons should i stay stock vavle or go bigger ? it will be a 355.. i plan on porting these heads ... anyone run this combo? i know i am goin to clay my pistons to e sure but i am wondering if this will be a good setup ... i appreiciate any advice 
For the most part, aftermarket pistons are very forgiving with valve sizes. Majority come with big enough reliefs to not have to worry about it. The piston manufacturer should be able to give you some idea also. At minimum you should be able to hold the 2.02/1.94 valves.
Since you have it apart I would definatley get some work done to those heads. The power is made in the heads, you build the bottom end just to hold it. Not sure your budget, but might be worth consulting AI or LE to see what they think on the porting options.
Since you have it apart I would definatley get some work done to those heads. The power is made in the heads, you build the bottom end just to hold it. Not sure your budget, but might be worth consulting AI or LE to see what they think on the porting options.
For the most part, aftermarket pistons are very forgiving with valve sizes. Majority come with big enough reliefs to not have to worry about it. The piston manufacturer should be able to give you some idea also. At minimum you should be able to hold the 2.02/1.94 valves.
Since you have it apart I would definatley get some work done to those heads. The power is made in the heads, you build the bottom end just to hold it. Not sure your budget, but might be worth consulting AI or LE to see what they think on the porting options.
Since you have it apart I would definatley get some work done to those heads. The power is made in the heads, you build the bottom end just to hold it. Not sure your budget, but might be worth consulting AI or LE to see what they think on the porting options.
I have never seen 1.94" exhaust valves...OP. Send your heads out to get them ported and set up for 2.00" int/1.56" exh valves.
I'd send your heads out to Ai.
yea i know this and i would love to let them do my heads but i am bugeting and have sum experience in porting ..so my machinist wants me to stay stock valves but i want a bigger valve... but i am worried about clearance with that big dome and a cc503 with 1.6rr since i am uping the compresson i want to move air more freely
yea i know this and i would love to let them do my heads but i am bugeting and have sum experience in porting ..so my machinist wants me to stay stock valves but i want a bigger valve... but i am worried about clearance with that big dome and a cc503 with 1.6rr since i am uping the compresson i want to move air more freely
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COMPRESSION RATIO
Compression ratio is a term that all of us are familiar with, but very few of us really understand. Whether we are milling down stock heads, swapping for some aftermarket ones, changing the stroke, the pistons or just simply using a thinner head gasket, changes to you engine combo have a profound affect your compression ratio and, consequently, on overall performance and drivability. With that in mind, I developed and easy to use formula to calculate compression ratio.
Compression ratio is defined as "the volume of the cylinder at BDC (bottom dead center) divided by the volume of the cylinder at TDC (top dead center).
CR = (Vbdc/Vtdc)
Without getting into too much detail, we can expand this to the following equation:
CR = [{(B/2)^2 * S*Pi}+Vcc+Vp+{(B/2)^2*Pi*(DH+TG)}]
[{(B/2)^2*Pi*(DH+TG)}+Vcc+Vp]
Where:
CR= Compression Ratio
B = Cylinder bore (Stock LT1 = 4.00in)
S = Stroke (Stock LT1 = 3.48in)
Vcc= Combustion Chamber Volume (Stock LT1 = 58cc = 3.539 in3)
Vp= Piston Volume (Stock LT1 = 4.5cc = 0.274606 in3)
DH = Deck Height (Stock LT1 = 0.015 in)
TG = Head Gasket Crush Thickness (Stock LT1 = 0.05 in)
Pi = 3.1415
As long as all other variables remain constant, you can change a single variable (for example larger/smaller combustion chamber size) to determine your new Compression Ratio.
*Convert Cubic Cenimeters (ccs) to Cubic Inches (in^3) using the following formula
in^3 = (CCs/16.387064)
Keep in mind that the above is how you calculate your SCR (static compression ratio). You need to take into account your valve events to calculate your DCR (dynamic compression ratio).
P.S. Just changing a couple things in the above formula like piston volume (aftermarket flat top pistons), gasket thickness (thinner gasket), and chamber volume (milling heads) can increase your CR to a nice streetable CR that can run on pump gas.
Last edited by ss.slp.ls1; Jul 9, 2009 at 02:15 PM.
Keeping all things stock and just using a GM Impala head gasket (.028" compressed height, stock is .051") you get a compression ratio ~11:1.
Now factor in a set of aftermarket forged aluminum flat top pistons with 5cc valve reliefs (I don't see how that wouldn't yeild a smaller piston volume) and your compression ratio will be higher still. You can even do a slight mill on the heads. Choising wisely you can get a compression ratio ~11.5:1. The fact that our engines are reverse cooled allows us to get away with higher CR without detonating. So you have to determine how high of a compression ratio you want and if it suits your build plans.
I'm not sure but I don't think you will be using pistons with a .100 dome on an LT1 and run pump gas. The most common is a flat top with 5cc valve reliefs. You better be checking to PTV clearance if you decide to use the pistons you have.
