Thread: What do you pros think??

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With that comp ratio, Ive decided to do a little more work. I just got a Hughes SFI flexplate, ARP bolts, ARP harm balancer bolt and a few other goodies and sent needed parts to machine shop to be decked, balanced and line bored. In the long run, I hope to have a better big block, even if it is 11.5:1cr and running on strictly race gas. Hopefully it doesn't take them long, as I've never done any business w/ them. 11.5 to 1, 584/588 lift cam screams POWER to me. I hope it works. Paul, what gear ratio do you suggest, if not 3.89? Email is parpartgene@gmail.com. 406-939-1079 (MT)

I predict that you will be sick of this motor within 30 days. Once you wake up and realize that you will have to feed it race gas for the rest of its life, you'll probably be tearing into it to change either pistons or heads.

OK, the block deck height is 10.320" The stroke radius is 1.925". The rod is 6.605". The piston is 1.752". The stack adds up to 10.282". Deducting the stack from the block deck height leaves us with a piston deck height of 0.038".
Here are the values:
cylinder 4.390" x 3.850", 954.9cc's
head 75cc's
piston 4.2cc's
piston deck height 4.390" x 0.038", 9.4cc's
gasket Edelbrock 7314 4.5" x 0.048", 12.5cc's
Total suckin' 1056
Total squeezin' 101.1
Divided equals 10.445:1 static compression ratio with 0.086" squish.

What would I do? I'd cut the block decks to zero and have the thickness of the gasket as the squish dimension. Then I'd use enough cam and the 95cc heads to get the motor into pump gas territory and make a scary fast motor.
Zero deck, 0.048" squish, 95cc heads, 9.55:1 static compression ratio. CompCams 34-711-9 solid roller cam, custom ground by Comp to reduce lift to 0.700" so you could use the springs that Edelbrock assembles on the heads (0.700" lift limit).
http://www.compcams.com/Cam_Specs/Ca...csid=1032&sb=0

RPM HP TQ
2000 171 450
2500 220 463
3000 281 492
3500 360 541
4000 440 578
4500 513 600
5000 568 596
5500 602 575
6000 612 535
6500 591 477
7000 548 411
Peak volumetric efficiency 97.3% @5000
Peak BMEP 193.8 @4500
These numbers were achieved with 0.700" lift on the DynoSim. If you would prefer a hydraulic cam, call Comp and see if they can grind you a hydraulic roller that is close to the specs on this solid roller. In my opinion, using a flat tappet cam in this day and age is just insane.

Help me test my app -

Oppps - posted before I saw tech's reply - let me try it with those numbers - great test case - thanks.

I was beta testing a java Compression Ratio applet I am developing and get these results, which is close very to the Crane advertised DCR of 9.5 for the cam.

What was your planned deck height and gasket thickness? With those numbers I could run it again. I assumed 0 deck height, .038 compressed gasket thickness (assume the same diameter as piston), flat top pistons and rod length of 6.8.

Also if those pistons have a valve relief, that volume should be added to the displacement volumes for a more accurate number.

Parameters:
Cylinders: 8
Bore: 4.39 in (.030 over)
Stroke: 3.85 in
Chamber: 75 cc
Deck Height: 0.0 in
Gasket Thickness: 0.038 in
Intake Closing ABDC: 68.0 degrees

Result:
Total Displacement: 466.20865373389995 ci
Cylinder Volume: 58.276081716737494 ci
Deck Volume: 0.0 ci
Gasket Volume: 0.5751924948664999 ci
Dynamic Stroke: 2.884533605675133
Static CR: 12.31140988142115
Dynamic CR: 9.4748420598766433

Using the numbers tech gave and a closing angle of 68 degrees ABDC for that cam -
My chamber needs to be adjusted for a floating point number - so I rounded to 79cc with valve relief added in.

Looks like that combo will take pump gas.

Cylinders: 8
Bore: 4.39 in
Stroke: 3.85 in
Chamber: 79 cc
Deck Height: 0.038 in
Gasket Thickness: 0.048 in
Intake Closing ABDC: 68.0 degrees

Total Displacement: 466.20865373389995 ci
Cylinder Volume: 58.276081716737494 ci
Deck Volume: 0.5751924948664999 ci
Gasket Volume: 0.7265589408839999 ci
Dynamic Stroke: 2.884533605675133
Static CR: 10.518149583509192
Dynamic CR: 8.131278529214296

Need to adjust my calculations for gasket diameter.

954.9 in the cylinder
95.0 in the chamber
4.2 in the piston
0.0 in the piston deck height
12.5 in the gasket

1066.6 total suckin'
111.7 total squeezin'
divide the larger by the smaller and find 9.548:1, rounded to 9.55

Ok - I have a couple of questions.
You guys have years experience - I'm just an engine theorist crunching numbers.

**************
With 95cc chamber,
4.2cc piston relief
0 deck
cam intake closing at 68 degrees ABDC

Dynamic stroke = 2.88 in
Dynamic CR = 7.4:1

**************
With the 75cc chamber
4.2cc piston relief
0 deck
cam intake closing at 68 degrees ABDC

Dynamic Stroke = 2.88 in
Dynamic CR = 8.8:1

***************
Isn't a dynamic CR of 8.8:1 well within the pump gas range?
Thanks for the info to determine the piston to deck height given overall deck height.