Well, I was so careful in "designing" my recent 396 rebuild for street duty and was sure that my CR, not DCR, would be around 9.7 in order to run 92 pump gas, but now, I believe that it just may be higher than that. Here is my combo data for figuring static CR only........

396 (.060 over)
4.156 cyl. bore
3.76 stroke
4.25+/- gasket bore
.039 gasket thickness
.025 deck height
96cc chamber vol. (closed chamber ovals)
TRW2240NF60 replacement piston(9.6 CR, .182" dome w/21cc)

Running this in Pat Kelly's DCR program, I come up with a CR of 10.3, which I think may be representative of what I really have. However, running the same data in the 'Virtual Engine 2000' CR calculator, I get a higher CR of 11.2!

Shouldn't I really be in the 9.7 range like I originally thought based on the above info and parts????

Thanks for any help. Charles

I say 10.3 is close. the stock 325/350 horse engine with closed chamber heads yeild an advertised 10.25:1 compression ratio. I have run this combo on the street on 92 octane with no problems

im running a true 10.2 to 1 comp 396 bored .090 over on 87 octane with no ping problems, timming is set at 42 total and 22 initial, im even running 2.41 posi

Charles,i have the same setup you do with .030 396,L2240nf30's,and closed chambered 98cc chambers.

I was also worried about the comp being too high esp when i checked the cranking comp,apporox 210-220psi,OUCH.

But i have not had any detonation issues YET,we will see as i get more miles on the mill and when it carbons up a little i am afarid it may start to act up them,but time will tell.

What cam & specs are you running?

My cam is CC hyd flat tappet:
222/226 @.05,.525/.525,112 deg L/S angle. I am running approx 18 deg btdc initial & 38 deg btdc
including mech for the timing.

I now wish i had run a little more cam to bleed off a skosh more compression and to take advantage of the good compression i had.

Hopefully you will be ok with you setup like am.

Scott

Scott, I hope you're right. I don't want to go pinging around the neighborhood when I get it on the road in the spring.

I have the Crane 278 Powermax hydraulic in my 396. It's a split duration cam with the following specs:

278/290 Adv. (very long exh. duration!)
222/234 @.050
.529/.525 lift
114 LSA

I thought that this would be the perfect mild-mannered street cam with the wide 114 LSA and still able to provide decent punch at the strip with small tube headers, TH400, and a B&M 2400 stall.

Charles