My head hurts from trying to figure out Pats CR page. If I give specs can anyone tell me where this combo comes out.
.004 deck
.041 gasket
4.166 gasket bore
4.030 bore
3.75 stroke
72cc camber
6cc valve reliefs
I come up with 9.9 static CR

My cam is 296 in 308 ex
232/242 @50
.500/.518 1.5 ratio
108 LS
12.0 btdc IO
40.0 abdc IC
53.0 bbdc EO
9.0 atdc EC
installed on a CL of 104

its a hydrolic flat tappet
How does this look with iron heads?

Thanks
Richard

Assuming a rod length of 5.7", I came up with a DCR of 7.51 .

A little too big a cam for a static of 9.9...IMO.
Something in the 280/288 adv. range might be better.

Yes, I have 5.7 rods

Well I already have the cam. Its been in the motor for 3 years. A new set of Dart Iron Eagles with a smaller chamber are going on in a few weeks. I am at 9.5CR now with no detonation issues but I was a little worried about the 72cc chambers. What is a safe number for iron heads when it comes to DCR.

Originally posted by gearheads78:
What is a safe number for iron heads when it comes to DCR? Generally below 8.2 is fine for 93 pump gas. Some of the more efficient chambered heads (Vortec, etc.) can stand a little higher.
Also depends on the quality of gas available in your area and condition of your cooling system..

The max's for DCR and pump gas are 8.5, 8.3, and 8.25. Under the proper conditions and a carefully built engine, 8.5 will work. David Vizard recommend 8.3 as the practical limit for street use. Personally, I'd stay below 8.25.

I got the same SCR and DCR as Bill. 7.5 will work but that is leaving a lot on the table. With 10.8 SCR (64cc chambers), the DCR goes to 8.16.

Your intake valve is closing at 72 ABDC so yes, the cam is MORE THAN A schosh big to make 8 to 1 DCR..

You will need an intake valve closing time of about 63 ABDC, imho which puts you in the 278 advertised duration range ground and installed at 108/104. Or at 108/108 you will need about a 270 to 272 advertised duration cam!!

How far off am I Pat???

pdq67

Sounds right. A smaller cam or more compression is the way to go. You've got a pretty good handle on this, PDQ.

Its funny how things change. In early 2001 when I was first building this motor I had a different cam selected that was quite a bit smaller. I was second guessing myself and posted on this board. The guys that were here talked me into the bigger cam :rolleyes: :D Oh well with 76CC camber 882 it has been as fast as 8.07 and consistant 8.30's.

OK a couple more questions. I have been collecting pieces for a nice 406 shortblock but I just don't have the $$ to finish it now. I got these Darts that I will use for the 406 in the future but for now they will go on the 383. I want to make due with the shortblock in there now as it is.

Looks like according to above I can mill these some to bump CR and still be safe.

First of all does nitrous effect the max DCR I should be shooting for? I don't have it now but may in the future.

Second I want to run the specs of the 406 to make sure if I cut these down I am still safe on 93.

4.155 bore
3.75 stroke
4.190 gasket bore
.041 thickness
.000 deck
5.7 rod
cut the heads down 66-68cc range
pistons 5.4 cc dish

cam
solid flat tappet
283/296
252/264 @50
.600 1.7in .018 hot lash/.597 1.6 ex .020 hot lash
lobe lift .353/.373
LS 112
intake CL 108
IO 18 BTDC
IC 54 ABDC
EO 68 BBDC
EC 16 ATDC

This is a custom grind that Dave Crower himself came up with to run good on motor and fly on the bottle. I will run good gas in a small second cell when the bottle goes on the car.

i get 11.2 SCR and 8.64 DCR. for the 406. For use on the 406, I'd keep the heads at 72cc's for a DCR of 8.2. Can't help on the nitrous question, I know nothing about it except that it likes a lot of exhaust duration.

If you are serious about using these heads on the 406, I'd suggest setting up the chamber size for that and live with the lower DCR in the 383. If you want to max the 383, cut the heads and use larger dish pistons in the 406 to set the DCR.

If you are serious about using these heads on the 406, I'd suggest setting up the chamber size for that and live with the lower DCR in the 383. If you want to max the 383, cut the heads and use larger dish pistons in the 406 to set the DCR. [/QB]Thanks Pat thats good information.
That is what a may do. I don't have the pistons yet for it so I could change to a dish and kill some CR.