Springer, doesn't the big bore kit come with SE flat tops? I thought those were listed at 9.4:1 so maybe a little less cuz of the combustion chamber size? School me oh wise one.......springer- said:There technically isn't enough information to answer your question. You would also need to know your deck height, head gasket thickness and actual combustion chamber sizes.
But on a guess, assuming 85cc combustion chambers, a deck height of 0 and stock gaskets would be about 8.6:1
Assuming larger than spec combustion chamber (typical) around 8.4-8.5:1
This is static compression.
Wasn't paying attention ... numbers are corrected to reflect a 95"adlerx said:Springer, doesn't the big bore kit come with SE flat tops? I thought those were listed at 9.4:1 so maybe a little less cuz of the combustion chamber size? School me oh wise one.......
Here's the thing... :roflback:adlerx said:Springer, doesn't the big bore kit come with SE flat tops? I thought those were listed at 9.4:1 so maybe a little less cuz of the combustion chamber size? School me oh wise one.......
springer- said:Here's the thing... :roflback:
I can't make HD numbers come out right based on their published specification. For example....
Stock engine says 8.9:1 CR
If you use 3.75" x 4.00" (bore x stroke)
Head Gasket 3.85" x .052" (bore x stroke)
Deck height = 0.00"
Piston head volume = 0 cc
Combustion chamber volume = 85 cc
I come up with 8.63:1 CR. Add to that, the pistons have valve reliefs and the combustion chamber typically run larger. You could be adding on upwards of 6 cc's !!! That brings it to around 8.2:1 CR. Also keep in mind that when the engine is hot it grows slightly and that reduces the CR also.
The stock head gasket after crush measures about .045 and barely makes a difference in the CR.
I can't get any of there Compression ratio's to come out right, they're all lower than what HD claims.
If I am wrong in figuring this out, maybe someone (Doc) can correct me. But I think my numbers are right. :dunno: :dunno:
OK, so I'll assume what you and Hippo say is correct. By your calculations, what would the Hi Comp Cast ones come in at with stock (bigboyz) heads. Hope you see where I am going, don't really wanna mill my heads but still trying to get to that magic 9.8-9.9:1 comp ratio. I know without ccing my heads it is hard to figure. I just don't want to put the hi-comps in there and end up with the SE claimed 10.25:1 but from your calculations (I flunked math) it sounds like i'd be fine running the hi-comps with my 37g cams. Guess I should have had bean cc and match my heads when I had em there but I really knew absolutely nothing(even less than I know now if that's possible) about any of this stuff when I sent em in last spring. I already have the flat tops but that's like the cheapest part of the build, I can get the hi-comps and put the flat tops on ebay.springer- said:Here's the thing... :roflback:
I can't make HD numbers come out right based on their published specification. For example....
Stock engine says 8.9:1 CR
If you use 3.75" x 4.00" (bore x stroke)
Head Gasket 3.85" x .052" (bore x stroke)
Deck height = 0.00"
Piston head volume = 0 cc
Combustion chamber volume = 85 cc
I come up with 8.63:1 CR. Add to that, the pistons have valve reliefs and the combustion chamber typically run larger. You could be adding on upwards of 6 cc's !!! That brings it to around 8.2:1 CR. Also keep in mind that when the engine is hot it grows slightly and that reduces the CR also.
The stock head gasket after crush measures about .045 and barely makes a difference in the CR.
I can't get any of there Compression ratio's to come out right, they're all lower than what HD claims.
If I am wrong in figuring this out, maybe someone (Doc) can correct me. But I think my numbers are right. :dunno: :dunno:
I have to make a couple of assumption, piston head volume is unknown, deck height = 0, combustion chambers = 85 cc, stock head gasket. Using reverse calculations I can only assume the piston head volume is around -8.5 cc (can anyone confirm this?).adlerx said:OK, so I'll assume what you and Hippo say is correct. By your calculations, what would the Hi Comp Cast ones come in at with stock (bigboyz) heads. Hope you see where I am going, don't really wanna mill my heads but still trying to get to that magic 9.8-9.9:1 comp ratio. I know without ccing my heads it is hard to figure. I just don't want to put the hi-comps in there and end up with the SE claimed 10.25:1 but from your calculations (I flunked math) it sounds like i'd be fine running the hi-comps with my 37g cams. Guess I should have had bean cc and match my heads when I had em there but I really knew absolutely nothing(even less than I know now if that's possible) about any of this stuff when I sent em in last spring. I already have the flat tops but that's like the cheapest part of the build, I can get the hi-comps and put the flat tops on ebay.
Any input welcomed
thanks, plm
Yes, but IMO your stock heads can be made to out perform the SE heads for half the cost.TNHARLEY said:SPRINGER
with the build that I have now if I add the SE heads this winter will it help much. Mike