You don't have any pump gas issues with a dynamic of 8.9:1? If not, what's the secret?

I can't say I've ever tried to put one together that high, being a hobbyist, and all.

 

No secrets besides the typical stuff.... no sharp edges, maybe a step or two colder spark plug, tight quench, efficient cooling system & lower temp thermostat, etc..

I'm running right at 9.0:1 in my 383 LT1, ~575rwhp NA. Runs almost 10-flat 1/4 miles on a street suspension setup with no signs of any detonation. My buddy's Nova is a 421ci small block setup for 8.8:1 dynamic, this engine is making 673hp at the flywheel. Been together for almost 1 year now and no signs of detonation there either.

Most of the really strong engines I'm seeing these days are running between 8.5-9.0:1 dynamic compression. I think alot of the experimentation has spawned from events like Popular Hot Rodding's Engine Masters Challenge. Limitations are based around pump gas and getting the most avg torque and horsepower. The guys who've been in the top 5-10 in each round (small blocks and big blocks) all had setups with dynamic compression in the 8.5-9.0:1 range. No coincidence there IMO.

One thing about running larger camshafts that people always seem to misss is the change in dynamic compression. Magazines always run tests where they'll swap cams on the same motor, then make comments like "See, the larger cam only hurt the lowend and the liow-midrange torque suffered". Well sure... if you knock the dynamic compression to 8.0:1 or lower, the things gonna be soggy on the bottom. No big secret there, but people miss the details. Get the dynamic comp up and you regain alot of that low-midrange torque and shift everything higher rpm-wise for hp/torque.

I'm just a hobbyist myself, but I've spent enough money for services that I could pick the brains of some really good engine builders. All seem to concur with this dynamic comp range for pump gas street engines. The tuning and all the little details need attention but once it's setup correctly, the engine will need no more maintenance than any other high performance mill.

-Mindgame

 

Do you think the reverse-flow of the LT1 is a big factor in allowing the high DCR?

I'm getting ready to put together a 383 (Gen I SBC), and I was looking at hitting right around 8.5:1 DCR. I intended to run somewhere around 10.5:1, and about 22x* .050 on the cam. I'm just thinking I might be on the hairy edge of getting this thing to cooperate, using a carb and all. With the six-speed, I want all the low end I can get, and I have no real interest in spending the money to rev past 6200-6300.

Just curious. If I screw it up, that'll just force me to get off my wallet, trade out the old 63cc Twisted Wedge heads (first design) for some new 68-72cc AFRs.

 

The reverse cooling of the LT1 definitely helps things Todd. You're right.

The LT1 has that to it's advantage. One disadvantage it has is in being fuel injected and having a dry manifold. The intake is always higher in temperature than a carb intake because it can't take advantage of latent heat of vaporization in the plenum and port entries. So, those gains from reverse cooling are slightly offset by higher inlet temperatures.

Now, you can improve the cooling of a 1st gen sbc easily enough. Here's an example I found with a quick search to give you a general idea. Cooling System Mods

I've done this on a few of my own engines. Routing coolant to the area between the two exhaust valves is always a good idea on sbc's because that's where they typically get the hottest. Using a Brodix intake (or similar) that moves water from front to back also helps.

Sounds like a good plan to me. Just calculate your compression carefully and tune from rich to lean. If you can get some time on a chassis dyno with a wideband O2 sensor take it. Then fine tune the combination at the track.

Good luck.

-Mindgame

 

My brother is putting a 396sb in his 73 Camaro. Dart Iron Eagle 215cc heads, Herbert .567/.567 hyd. roller cam, Victor jr, 750 holley carb, TRW pistons (modified).. shortblock is done.. next week we put the motor together..

-Alex

 

Mindgame how do you figure static to dynamic compression? and would you give a clear example.

 

i say go the 406 route... as i did. the #'s below are 2 years old with an old "emissions friendly" setup. after emissions and i knew how much i could go, i changed out the cam and went to bigger injectors, ect.. and i (lowballing) expect 450RWHP and 500RWTQ (i was worried about emissions and had a really small cam in when i got these #'s) with the new setup.