Guys I need some opinions real quick.
Can a 408 run on pump gas with 11.8 cr?
My build looks like this:

408
4.030 bore
6.125 rod lenght
-2cc flat top
(eagle kit)

232/236 595/602 114
1.75 rocker ratio should give 0.008 more lift
Dart Pro 1 225cc with 62cc chambers

Thanks

 

I think that you're pushin' it with 93 Octane. You can always retard the timing and run almost any compression without knock retard, but that's a loosing proposition. I'd run something like 10.8:1 and you'll have a whole lot more latitude in tuning and power production. Just my two cents.

Steve

 

I think if you had a 110-112 camshaft that would help bleed some off that off... But I think its a bit much with 11.8

 

Yeah, what these guys already said.


You can do it, but you're going to have to back off on something else to get her done...

 

I figured it up in an excel spreadsheet for finding compression ratio i founf off of ls1 tech. and according to it your dynamic compression ratio is 8.57 and that should definetly be do-able on 93 pump gas.

The only thing I'm not sure about is the deck height. I have heard different things from different people. Its either -.008 or +.006.

if it is the +.006: it makes you SCR 11.44 and your DCR 8.26

and 1.75 rockers on that cam changes the lift to INTK: .612 EXHST: .620

Results below:

__________________________________________________ _______________"Quick and Dirty Cam/SCR/DCR Calculator Spreadsheet
Modified and Simplified by PianoProdigy - PianoProdigy@gmail.com"
"Values that are green are standard stock LS1 values (if only swapping a cam, leave them alone).
The blue values are calculated and thus, are not editable. Compression values are orange (not editable)."

0.006 0.050 0.200
Intake Duration - ID (first number) 283 232 155
Exhaust Duration - ED (second number) 291 236 163
Lobe Center Angle - LCA (also known as LSA) 114 114 114
Intake Centerline - ICL (LSA - degrees of advance e.g. 114+2 = 112) 114 114 114

Intake Valve opens - IVO 27.5 2 -36.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC 75.5 50 11.5 ABDC
Exhaust Valve Opens - EVO 79.5 52 15.5 BBDC
Exhaust Valve Closes - EVC 31.5 4 -32.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL 114 114 114
Overlap 59 6 -69 degrees

Bore 4.03
ST = Stroke 3.622
RL = Rod Length 6.125
Number of cylinders 8
Deck Height (how much pistons come out of the hole) -0.008
Piston Dome or Dish (- for a dome + for a dish) -2
Compressed Head gasket thickness 0.054
Cylinder Head Chamber Volume 62

Static Compression Ratio 11.88 :1
Dynamic Compresion Ratio 8.57 :1
Rod to Stroke Ratio 1.69 :1
Bore to Stroke Ratio 1.11 :1

 

deck is -0.008 on the genIIIs

 

Ok, then he should be good to go with that set-up.

 

The stroke should be 4" also.

 

Thanks for the replies so far. This is what I thought also. I would be at 9.5:1 with the other Eagle kit with the -29cc pistons but I think this is too low...

 

what about if you set it up to run E85 that seems to be what a fair amount of people are going over too!

cheaper at the pump, less dependant on oil, 105 octane
down side....less gas milage but hell its a truck with a big cubed motor what do you expect...