25thannivZ28

I'm in the process of putting an engine together (Either a 355 or a 396sb), but before I go and buy all the internals and plan on machining the block, I am wondering how much compression can I get before I have to use race gas 100% of the time? For example, if I got 13.5:1 compression, can I still use 93 octane pump gas? Or would I have to stay on the lower side 11.5:1? Obviously, i'm hoping to use pump gas but want the compression to be higher. According to my dynojet simulation software, that difference between the two is 34 hp & 25 tq at the fly.

AlkyIROC

Each engine is different. You only need enough octane to prevent detonation under load.

At 13.5 compression, anything less than VP C12 will probably have detonation.

8urv8

yeah, most of the time anything over 11:1 or 12:1 will need higher octane fuel to prevent detonation. Another thing that will affect it is the head design and piston top design.

25thannivZ28

My thoughts were to zero-deck the block and get flat-top pistons. I'm working with a local race shop and they haven't raised any flags about that idea.

I have Trickflow Twisted Wedge heads, 2.02/1.60. I planned on porting them out & doing a valve-job, they're almost 5 years old now.

8urv8

ok. Well, I run the 3.1L V6 with ported and polished heads, Crane .425 (Int. & Exh.) cam and 98mm custom throttle body and if I run anything less than 93 octane, it runs like a leaf blower.

25thannivZ28

Assuming I go with the lower 11.5:1 (give or take), which engine would you choose? The 396 or 355? Also, which one do you suppose is cheaper?

Though it would be pretty cool to tell someone you have a 396 under the hood, the 355 is a pretty close competitor It has more hp but the 396 has more tq.

I tried to attach the "print screen" pics of the dyno chart, but the .jpeg comes up way to blurry. I put the figures below, all rated at the flywheel.

355: 4.030 bore x 3.4780 stroke
533hp at 6500.
488tq at 5000.

396: 4.030 bore x 3.875 stroke
532hp at 6000.
519tq at 4500.

the zander

Unless fuel economy is a major concern i see no reason not to go with a 396. it provide you with more "area under the torque curve" which is what i would consider one of the best indications of 1/4 mile ability. As far as the cost in concerned that depends entirely on if you already have components you want to use. If your going to be purchasing everything new, the cost will be almost the same. Check out ohio crankshafts website, the difference in price between a 3.480 and 3.875 stroke 4340 crank is $20 (insignificant really). The cost between 5.7 and 6.0 rods is $0.

http://ohiocrank.com/hbeam_rods.html
http://ohiocrank.com/chevysb_cranks.html

-Z