KB237s compression check...

[davidcam69]

Bought back my 69r/t 440 in 2009. Rebuilt my numbers matching engine shortly after and then decided to do a total resto. I'm getting near the end. I built a cradle to install my eng and tranny under the car and to double as a test stand. Joined this forum after I put my engine together. Read the posts about building a turd 440 and have been wondering what I've got ever since. My goal was to build a basically stock street pump gas engine (not a turd) that run as good as it could with stock heads and exhaust manifolds, not wanting to take a chance of hurting my numbers matching eng with a higher end build.

When I put this eng together, I was thinking it was going to be a 9.5 to 1 and more concerned about having to much compression than not enough. I didn't check how far the kb237s went down in the hole. I just don't know. This is what I do know.

40 over 440 uncut block
906 uncut heads new guides valves and harden exhaust seats (no work on heads-stock)
comp ex268h cam kit(springs, retainers-stock rockers with adjustable push rods)
stock exhaust manifolds
ch4b intake with 750 Holley DP(I have the org carb and intake but couldn't resist this combo for now)
Chry electronic ign- 20 int and 36 total
KB237s-40 over
.40 fel-pro head gasket
4 speed-3.54 dana
compression check (eng hot) 160 psi average- 157 lowest-162 highest
15-17 inches of vacuum at 800 rpms


What is my compression ratio? What would it be with a .20 head gasket? What do you think of this combo?

Thanks, Dave

 

[John_Kunkel]

Without knowing the exact block height and combustion chamber dimensions you can't compute the precise CR but, with 88 CC chambers, a .040" gasket and .015" in the hole you'd have 9.61-1 With a .020" gasket it would be 10.03-1

Bore: (diameter) 4.36"

Stroke: 3.75"

Cylinder Head Volume:  88 CC

Effective Dome Volume: Use (-) for Dome and (+) for Dish.   +5

Deck Clearance: .015"
 
Compressed Gasket Thickness:  .040"

Number of Cylinders:  8
     
Compression Ratio : 9.61 : 1

 

[BSB67]

I like your build.  I would do the cam and carb a little different, but I still like your choices.

John has the pistons at 5 cc, I see them as 9 cc. 

If it is 9 cc and depending on the head volume and the piston distance below the deck your CR will be in the range of 9.1 to 9.4.  Based on my experience using dynamic cylinder pressure calculators, your cylinder pressure and cam specs supports this static compression ratio range too.

Going to a 0.020 head gasket will increase your compression ratio by about 0.4.

How does it run?  Did you have any problems sealing the intake to the head?

[davidcam69]

Thanks John, hope your calculations are correct. That's what I was going for back when I put it together.

BSB67, it runs really well on the engine stand. I've probably got a couple of hours running time playing with it. Never run that much initial before (20 degrees). No kicking back on starter, nice idle. The intake fit great, nothing has been milled. One thing I don't understand is the plugs are running black or sooty. Started out with 72 and 82s with 6.5 pv. Idle mix screws didn't like anymore than a half turn out. Kept leaning it out and are at 68 and 78s with the plugs not looking much better and the idle mix screws still not liking much more than a half turn out. Running NGK5 plugs that some seem to recommend. I can tell the engine is running leaner account my eyes aren't watering as much. I'm curious what cam and carb you recommend. Thanks for your input.

Do the stock blocks vary that much in deck height from block to block? Sounds like I should just pull the heads and do it right and see what I've got. Not much of a job on the stand. So glad to hear my pistons are going to work.

Thanks again, Dave

       

[BSB67]

Thanks John, hope your calculations are correct. That's what I was going for back when I put it together.

BSB67, it runs really well on the engine stand. I've probably got a couple of hours running time playing with it. Never run that much initial before (20 degrees). No kicking back on starter, nice idle. The intake fit great, nothing has been milled. One thing I don't understand is the plugs are running black or sooty. Started out with 72 and 82s with 6.5 pv. Idle mix screws didn't like anymore than a half turn out. Kept leaning it out and are at 68 and 78s with the plugs not looking much better and the idle mix screws still not liking much more than a half turn out. Running NGK5 plugs that some seem to recommend. I can tell the engine is running leaner account my eyes aren't watering as much. I'm curious what cam and carb you recommend. Thanks for your input.

Do the stock blocks vary that much in deck height from block to block? Sounds like I should just pull the heads and do it right and see what I've got. Not much of a job on the stand. So glad to hear my pistons are going to work.

Thanks again, Dave

       

If the block was not decked, the piston will be about 0.020" down in the hole.  Head cc estimate of 88 is as good as any, maybe 90.  Grinding seats and valve increases ccs, new exhaust seat and new or larger valves can reduce volume.  Just hard to estimate.  If the valve pockets are 9 cc, you compression will be less.

[davidcam69]

Thanks BSB67, probably couldn't tell the difference between 9.1 and 9.5 with this mild build. Still thinking of pulling it down.

[BSB67]

Personally, I would not pull it down until after it is in the car, you drive it a bit, and then determine that there is a reason to that.  It might be perfect now and then who really cares where exactly the piston is?  You might have a detonation problem now, or performance might be less than hoped for.  Then you can tear into it with a plan.  

[Challenger340]

The 237's are fine.
Nice build

[davidcam69]

Thanks (John, BSB67, 340, Ron, coonhunter and others) for sharing information and for any advice. Always look forward to reading your posts.

Dave