Hemi Killer

iTrader: (6)

I think I might have too much. Here is what I have:
-383 Ls1 ( 4.00" stroke,bored to to 3.903" and 10 out of the hole)
-Mahle 3.903" pistons w/ -6cc valve reliefs
-patriot stage II 5.3 heads (62cc)
-stock GM mls head gaskets (0.560")
-F13 cam (230/232-.595/.585-114+8) yes, the guy that built my motor thought I wanted it advanced because it it was going in a truck. He was supposed to have fixed it, but the dyno peaks at 5600 and falls on it's face, with a ported 90/90 set-up. I plan on putting some trickflows on it this year, so I will fix it then.
So can anybody tell me what my DCR might be and if it is too much? The SCR should be at 11.1:1. My tuner couldnt run much timing, it would knock and ping its *** off.
Made 394/408 locked in third gear. Should have a lot more in it.
Thanks.

mark21742

You need to know your intake valve closing point after bottom dead center, then goto Wallace racing calculators and find = dynamic compression... punch in all your numbers and it will give you your dynamic compression. 8.5:1 dynamic is high, but safe, and I know a few people running close to 9:1 still on pump gas.

Your 11:1 static ratio is good, but you might need to retard the can back closer to 0 if your numbers are too high...

For instance I'm running 12.56:1 compression on my 408 but with my cam the intake valve closes at 85 degrees abdc, so I have a good safe 8.25:1 dynamic compression....on 92-93 octane I have 0 knock

disc0monkey

iTrader: (10)

I'm running more than that on 93 with a stock chamber and runs fine

disc0monkey

iTrader: (10)

That much advance is insane

Samer

I have a 383 with almost the same specs but I thought that my Mahle pistons are 0.010 IN the hole?? Have you measured your piston to deck clearance and verified this number?

I estimated your DCR to be ~8.9:1 which is a bit high. Just retard your cam to have 2 degrees of advance instead of 8 and your DCR will be fine.

I have seen people with 9:00 DCR and they still using 93 octane but I think that they are at the danger zone.

Improving your quench (piston to head clearance) will help your engine tolerate more SCR and DCR. This can be done simply by going for a thinner head gasket (0.040) but in your case (0.010 out of the hole) it won't be recommended as it will put your quench at 0.030 which is a tight quench.

Go for a bigger cam man !!

FlamingTA

iTrader: (8)

You might be running too much head gasket also. Even if your pistons come out of the hole .010 that still leaves .046. I think to run a high DCR and SCR you need to be around .035 area. I could have it wrong tho and I'm sure someone will correct me.

mark21742

Nope, your right....035-.045" quench is optimum. The closer you get to .035" the better and makes it less prone to detonation.

I have 0 deck height so I went with a .040" gasket....Cometic can make just about any thickness head gasket you need....takes about a week + shipping time.

mark21742

I agree. I like to have alitttle safety cushion just incase you get a bad tank of gas...daily driver 8-8.5:1 dcr..... track car only, who cares, just run race gas

Sales2@Texas-speed

iTrader: (5)

If he said it was a 224º intake duration cam with a 112LSA+3, would it have still been insane?? That would have the same IVC event timing Look past the advance number and check out the valve events....they mean alot more. *disclaimer*not saying I would have suggested advancing it that much, just trying to get people to look past the .050" specs *disclaimer*

Correct, their compression distance of 1.105" will put the piston at 9.230" in the block, so on an unshaved 9.24" deck height block you'd be .010" in the hole.

Sales2@Texas-speed

iTrader: (5)

OP: You're about 10.8:1 static according to my calculations (I put pistons in hole .010" based on the pistons specs and assuming you didn't have a custom set made with a different compression distance). That'd make your DCR about 8.6:1, which depending on climate and tune could be just fine! Always remember there's alot more to running pump gas than just DCR!!

chrs1313

iTrader: (24)

yeah that quench is pretty huge with the piston in the hole and that big of a head gasket