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Discussion Starter · #1 ·
I think it's time to throw some pistons at my motor in an attempt to bring the compression ratio above that of my lawn mower...
Question #1, is a 6.135 rod length the only option for a 9.8 deck tall block with a 4.375 stroke?? I'd like to get a better rod angle/ratio.
#2, with flat tops, what would my compression ratio be with 117cc chambers(prox). And is there a better piston choice for a 91 octane motor?
Q#3, are brodix bb2plus heads too small for my 557" bbc "under 6k motor"? (112cc runners)

#4 I'm at an altitude disadvantage(4500ft)...doesn't that mean a higher CR is in order?, and what does that do to head selection(size)??
thanks for your input....
 

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I think it's time to throw some pistons at my motor in an attempt to bring the compression ratio above that of my lawn mower...
Question #1, is a 6.135 rod length the only option for a 9.8 deck tall block with a 4.375 stroke?? I'd like to get a better rod angle/ratio.
#2, with flat tops, what would my compression ratio be with 117cc chambers(prox). And is there a better piston choice for a 91 octane motor?
Q#3, are brodix bb2plus heads too small for my 557" bbc "under 6k motor"? (112cc runners)

#4 I'm at an altitude disadvantage(4500ft)...doesn't that mean a higher CR is in order?, and what does that do to head selection(size)??
thanks for your input....

Save up a little extra and toss on a blower. That's the real solution for the lack of air...get something that forces it in. I know...not much help.

AP
 

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Discussion Starter · #4 ·
When I put this together it had some boost planned for the future....
I'm not certain what direction I'm going to go, but I'm leaning tword simple.
This is a "family" boat, not looking for huge #'s, just all I can get with pump gas with what I've got.:)sphss
Heck it runs 70 with an 8.4 CR, I'd be happy with 80.... plus spray:)grn
If I had to pick one question..... is the 6.135 my only rod choice?
 

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you could go 6.250... lets see u can get flat tops in 1.245 and 1.270 compression height so with 9.8 deck and 4.375 stroke you can use a 6.350 rod..with the 1,25 piston

About 9.5-1 with flat top and 117cc

problem is u pretty much need a custom rod to get this length..cause 6.385 is not gunna work :(

I dont like a 6.135 with that 4.375 stroke...IMHO just 2 much stroke for a short deck block

best bet may be 6.385 rod with custom flat top with 1.200 ch thats tight but would work..not the best but not many options
 

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Save up a little extra and toss on a blower. That's the real solution for the lack of air...get something that forces it in. I know...not much help.

AP
Blowers are for people who need a crutch :)LegHump

Get a set of good heads. :)bulb

S CP ;)
 

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I think it's time to throw some pistons at my motor in an attempt to bring the compression ratio above that of my lawn mower...
Question #1, is a 6.135 rod length the only option for a 9.8 deck tall block with a 4.375 stroke?? I'd like to get a better rod angle/ratio.
#2, with flat tops, what would my compression ratio be with 117cc chambers(prox). And is there a better piston choice for a 91 octane motor?
Q#3, are brodix bb2plus heads too small for my 557" bbc "under 6k motor"? (112cc runners)

#4 I'm at an altitude disadvantage(4500ft)...doesn't that mean a higher CR is in order?, and what does that do to head selection(size)??
thanks for your input....
BB2plus have an intake port of 312cc, chambers are 119cc, they appear to suit compression from about 12 & suit a roller cam. If you only want to rev it to 6k these may be ok particularly with the smaller 312cc intake runners. my02c:)bulb
 

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Discussion Starter · #16 ·
Kreg

Where did you come up with the 8.4-1 compression ratio? Shouldn't it calculate out to more like 9.5-1 with 117 cc chambers?

What's this about the 9.8" block,, you were working with a bowtie talldeck?
The pistons are reverse dome. I guess my machienist was smoking crack when he gave me this build sheet. Deck height says 9.7955. I hope the pos .065 quench is a typo also....
 

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DANG IT!!! Man i wish i would have known this before i bought the blower!!!! I could have built a N/A Big Block Ford otherwise! :))ThumbsDwn


AP
My 10:1, single carb 512" made as much as "most" blower motors and that was 18 yrs ago. :)bulb

Very good heads, roller cam and cubes go along way.


As to the OP..... bumping compression with the correct cam choice (roller) and having the heads working as good as they can will go along way. It does need a longer rod. A 557" should be great at the 6,000 rpm range if built properly.

S CP :D
 
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My 10:1, single carb 512" made as much as "most" blower motors and that was 18 yrs ago. :)bulb

Very good heads, roller cam and cubes go along way.


As to the OP..... bumping compression with the correct cam choice (roller) and having the heads working as good as they can will go along way. It does need a longer rod. A 557" should be great at the 6,000 rpm range if built properly.

S CP :D
Hey! Don't you have an oil leak to fix?????:D
 

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