Raise Compression

[vej]

Well, after I changed the rocker box gasket and fixed that oil leak, I noticed I had a leak from the bottom of the cyclinder! DAMN!!! So, looks like I"ll be pulling the cylinder off to replace the gaskets. I figured if I was going that far down, maybe I should go ahead and deck the cyclinder to raise the compression... nothing crazy, just take it from the stock 9.0/1 to somewhere between 10.25 or10.5/1

Was wondering a couple things about that.

1) how noticable HP / Torque gain would I get out of that (my 117 is stock other than .585 cam, and S&S Dual Runner intake).

2) I plan on doing all the assembly / disassembly... so, how do I know how much to have the machine shop take off? (didn't want the added expense of taking the bike to them and having them break it down).

Thanks!

 

[john sachs]

Will be a noticeable difference in power, and torque.
You need to know a number of things before you figure out how much to mill off the heads.
How many cc's in the combustion chambers.
How far in the hole is the piston, or are they at "0" deck.
What thickness head gasket is going to be used.
With the answers, and using the 117 cubic inches, and .585 cam, you can figure out your existing compression ratio.
Figure how much higher you want to go, mill the heads to get there.(-.007") usually = 1cc. 0r
you can send them to me, give me the above info, and I'll set them up for your combo with NO pms.
For no further oil leaks, change the base gaskets as well anytime you remove the heads.
John

 

[FrankBDPS]

Well Eric you just got free advice from one of the best in the business. If you want it done right take it to Johns shop. Good lu k.

 

[vej]

Will be a noticeable difference in power, and torque.
You need to know a number of things before you figure out how much to mill off the heads.
How many cc's in the combustion chambers.
How far in the hole is the piston, or are they at "0" deck.
What thickness head gasket is going to be used.
With the answers, and using the 117 cubic inches, and .585 cam, you can figure out your existing compression ratio.
Figure how much higher you want to go, mill the heads to get there.(-.007") usually = 1cc. 0r
you can send them to me, give me the above info, and I'll set them up for your combo with NO pms.
For no further oil leaks, change the base gaskets as well anytime you remove the heads.
John

Thanks John... you actually aren't "too far" from me, I live over in Land O Lakes, a suburb of Tampa. My original thought was to take it apart, drop the cyclinders off at a local machine shop, pick them back up in a day, then get it all back together... Still up in the air on exactly "what" i'm going to do, just know I have to stop the oil leak, so it only makes sense to bump compression at the same time (as long as it doesn't make the engine less dependable).

Thanks!

 

[Th3InfamousI]

Thanks John... you actually aren't "too far" from me, I live over in Land O Lakes, a suburb of Tampa. My original thought was to take it apart, drop the cyclinders off at a local machine shop, pick them back up in a day, then get it all back together... Still up in the air on exactly "what" i'm going to do, just know I have to stop the oil leak, so it only makes sense to bump compression at the same time (as long as it doesn't make the engine less dependable).

Thanks!

I'd just unbolt the engine and take it to John complete and let him do all the measuring.

Some of you guys are a lot smarter but I'm not sure I'd trust my measuring skills.

Sent from my 831C using Tapatalk

 

[john sachs]

After 32 years in So. Fla. I bought a home in Deltona(4 miles east of I-4). Still doing work down here, should be in business up there end of June or middle of July.
No need considering to send the whole engine. Can do the work with simple measurements, and accurate info.
John

 

[Jwooky]

Will be a noticeable difference in power, and torque.
You need to know a number of things before you figure out how much to mill off the heads.
How many cc's in the combustion chambers.
How far in the hole is the piston, or are they at "0" deck.
What thickness head gasket is going to be used.
With the answers, and using the 117 cubic inches, and .585 cam, you can figure out your existing compression ratio.
Figure how much higher you want to go, mill the heads to get there.(-.007") usually = 1cc. 0r
you can send them to me, give me the above info, and I'll set them up for your combo with NO pms.
For no further oil leaks, change the base gaskets as well anytime you remove the heads.
John

Curious, wouldn't all the 117's be the same, combustion chamber, deck height etc?
Why would you have to measure every one?

 

[BadDawg Bill]

After 32 years in So. Fla. I bought a home in Deltona(4 miles east of I-4). Still doing work down here, should be in business up there end of June or middle of July.
No need considering to send the whole engine. Can do the work with simple measurements, and accurate info.
John

I just bought a home in Deltona too.... Small world...

 

[KaptinAmerika]

Curious, wouldn't all the 117's be the same, combustion chamber, deck height etc?
Why would you have to measure every one?

Once you start getting in to high performance everything becomes critical.

 

[john sachs]

Once you start getting in to high performance everything becomes critical.

!00 % true.
Just like women, no 2 are alike.
Between core shift, machine tolerance, mileage, rebuilds, no 2 are the same.
I only deal in being 100 % correct, that's why I need all the info. I stay too busy to wonder if they're all the same.
John

 

[Nཛ͢ཀཇཧ༏ཧי]

Just out of curiosity, how high of compression can you go before you start sacrificing the bikes usability. I know with cars anytime we went over 10.5:1 we started having issues with premium pump fuel, and needed to mix racing fuel.

 

[liferider]

I decked the heads on my 88" EVO .010, but I sent my heads to Kendal Johnson. I called and talked to Kendall for an hr about what I had and what the bike was going to be doing and what I expected out of the finished product. he did the head work and supplied me with all the products and I assembled. But we decked the heads, new adjustable push rods, high compression piston port & polished intake & exhaust valley's, new bigger cam, new crank, power commander and new bigger injectors plus a 2 into 1 thunder header. I went from 55hp to 98hp! That's huge! If your in Florida call Kendall. He is in Winston Salem. Call him and tell him what you have and that it is a BigDog motor. S&S set these motors up very different than stock S&S motors. S&S told me that 3-4 yrs ago. Anyway call Kendall and tell him what you have and what you want as a final product to be. He will tell you what you need. Plus your only 9 hrs from him, you might want to just bring him the bike and let him do the work.