Bama99z

iTrader: (7)

So I am wondering what is a safe compresion ratio for pump gas build that I am working on? Due to my 59cc heads I have ordered the Wiseco -15cc dish pistons. That should put me a little over 11:1 is that ok or should I of went with a piston with less dish which = more compression? 408 street build with cometic .040'' head gaskets? Suggestions!!!!!!!!

Austin95

iTrader: (22)

That should be fine on pump gas with the right tune. As always, its in the tune.

ckpitt55

iTrader: (4)

static compression is only part of the story. your cam profile and dynamic compression play more of a role in what octane you can run safely

Knight-Z06

tms is building my 408 at 10-7 , i have prc 227 heads with 60cc chambers my static comp will be 11-3

dr_whigham

iTrader: (49)

11.7 static here, with an 8.5 dynamic. 59cc head with GM MLS head gaskets.

.051 I believe? Runs great on 93 and 93 only. But then again, who the hell runs on 87

Bama99z

iTrader: (7)

Well how do I accuratly figure both the Static & Dynamic Compression? I can still change the pistons to -8cc If I need too.

Cam Info
Cam- Competion Cams
ADV Duration Int/Exh
285/291
Duration@.50 235/242
Lift 620/.610
Lobe Sep 113.0 +2

JakeFusion

iTrader: (7)

0.006
Intake Duration - ID 285
Exhaust Duration - ED 291
Lobe Center Angle - LCA (also known as LSA) 113
Intake Centerline - ICL 111


Intake Valve opens - IVO 31.5
Intake Valve closes - IVC 73.5
Exhaust Valve Opens - EVO 80.5
Exhaust Valve Closes - EVC 30.5
Exhaust Centerline - ECL 115
Overlap 62


Bore 4.03
ST = Stroke 4
RL = Rod Length 4.125
Number of cylinders 8
Deck Height -0.006
Piston Dome or Dish (- for a dome + for a dish) 15
Compressed Head gasket thickness 0.040
Cylinder Head Chamber Volume 59

Displacement 408.178356
Static Compression Ratio 11.3086936
Dynamic Compresion Ratio 8.836847103

If you run it with GM MLS gaskets you'd be fine with the 15cc pistons. You'd end up with 11.01: SCR and 8.6:1 DCR, which is acceptable for 93 octane. The 8.83:1 DCR with the .040" Cometic is a bit much. Also, since it's iron block, you can't run quite as much compression/timing due to the thermal properties of iron from what I've seen. A .045" gasket would be a happy medium between them...