Dave01GT

I have a Texas Speed 4.00 Stroke, 4.010 Bore, -10cc dished pistons, Patriot 64cc heads, and LS7S cam (242/250, .614/.614 114 LSA). I believe my compression is right at 10.6. I am new to LSX motors and have a few questions. With the large cam I am looking to get the most out of the motor N/A and up the compression to closer to 12:1. In order to do this, I ordered .040 Cometics and would need to mill the head down to a 56cc. Can 243 heads be milled that much (.048) or what is the optimum CC? Is flat or angle milling best? Would I have Piston to valve issues? Thanks for any input.

LSOHOLIC

Really not sure what your goals are......but....

Yes, a 243 can go to 56cc and yes angle milling is the key (the optimum chamber size and shape is dependent on the port and seat work and what the SSR likes). As far as compression goes, depends on how far the piston is in the hole for a credible calc. DCR is the number you should concern yourself with.

A lot depends on what fuel you intend to use.....

Lots of variables not discussed here, can make or break the "big" picture.

Good luck with your project.......

Dave01GT

Thanks. I'm hoping to use 93 octane. The heads are Patriot III 243's and not sure if they touch the chamber at all. I'm calculating my static to come in right at 12:1 with piston in .008 (from what I've seen searching), 56cc, and .04 gasket. I am confused how to calculate my Dynamic? I found a calculator, but how do you determine the Inlet Valve Closes ABDC? I saw that it should be between 0-90* but don't know how to figure it out.

LSOHOLIC

I dont know much about the Patriot heads but I can imagine you will pushing those heads to their limit with your bore and cubic inch. What size runners and valves ?? Any coefficient of discharge numbers ??

As you probably know...everything is and can be a trade off. You will probably lose a little flow (cfm) when the chamber is cut smaller (if the head was not designed around that small chamber). But there can be more power there if the optimum dcr per available octane is achieved....even with a little loss of cfm...imo. But the kicker is your heads are probably already on the "small" side for your cubes and cutting them will only magnify the issue.

About the piston location....most of the stock LS family pistons are somewhere between .005" to .008" out of the bore. This is not taking into consideration piston rock which can add an additional .001". But, most of your aftermarket pistons are in the hole....unless you have specifically decked the block to achieve the piston out of the hole. On your compression calculators the piston out of the hole is expressed in a negitive sign (-).

About calcing dynamic....you use the advertised duration number or the .006" number. Most cam companies will give you one or the other. The smaller the number, the quicker the intake/ exhaust ramps.
example...a 244@.050 lobe could have an advertised duration anywhere from 294 to 307 with the later being the "softest" ramp.

I have found 8.7 to 8.9 to be the threshold of "pump" gas in a LS combination.

Good luck with your project....

glenB

I think your head choice is wrong and if you want 12:1, why use a dished piston ?

Dave01GT

I bought the car with the motor in it. Just wanting to get the most out of it without pulling it. At least it has valve reliefs now that I've milled a good amount. Had the heads milled to 56cc today and will re-check ptv clearance.