Compression and such
Thread Starter
|
Cruiser
Joined: Mar 2006
Posts: 204
Likes: 0
From: Scottsdale, AZ
Compression and such
Generally speaking, with what static compression would you want to start using compression releases?
Also, generally, what would be the maximum static compression when using 91 octane fuel, assuming 2000 ft altitude and outside temps in the low 100's? (Phoenix AZ area)
Also, generally, what would be the maximum static compression when using 91 octane fuel, assuming 2000 ft altitude and outside temps in the low 100's? (Phoenix AZ area)
Road Captain
Joined: Mar 2006
Posts: 741
Likes: 11
From: West Central WI
RE: Compression and such
This will depend greatly on the camshaft you choose, an earlier intake closing number will build more cylinder pressure, IMHO, anthing around 190 ccp and up is release territory. You can find a great ccp calculator on the BigBoyz cycles website.
Thread Starter
|
Cruiser
Joined: Mar 2006
Posts: 204
Likes: 0
From: Scottsdale, AZ
RE: Compression and such
RR525 or RR615 cams (gear drive)
95"
R&R stage 2 1/2 heads
Power Commander locally tuned
Rinehart TD's
SE A/C
SE billet cam plate and new pump
I'm leaning towards a ccp of 10.1:1 or with the RR615's 10.4:1 (although with the RR615's, 10.8:1 is recommeded). I'm just concerned with the lower octane gas here (91 is best we have) and with the high heat. 10.8:1 might be too high.
95"
R&R stage 2 1/2 heads
Power Commander locally tuned
Rinehart TD's
SE A/C
SE billet cam plate and new pump
I'm leaning towards a ccp of 10.1:1 or with the RR615's 10.4:1 (although with the RR615's, 10.8:1 is recommeded). I'm just concerned with the lower octane gas here (91 is best we have) and with the high heat. 10.8:1 might be too high.
Sponsor
Joined: Dec 2007
Posts: 12,084
Likes: 829
RE: Compression and such
If this is an R&R package, perhaps a call to those folks would be in order.
Trending Topics
Thread Starter
|
Cruiser
Joined: Mar 2006
Posts: 204
Likes: 0
From: Scottsdale, AZ
RE: Compression and such
Absolutely agree to that. And, Randy has responded with good info. All I am trying to do is gather knowledge from a wider base...kind of like a doctors second opinion. It never hurts to build on knowledge and with several engine builders on this site, it makes for understanding more before pulling the trigger. As one person has in their signature, "knowledge is power".
Compression releases area a definite starter/battery saver. But, they really wouldn't be needed until some reasonable number. I "suspect" once one hits about 10.5:1, they would begin to be desireable and at 11:1, probably a necessity. But, just my WAG having never been above maybe 9:1.
I also understand that as compression goes up, the need for higher octane goes up. This is even more true as the temperature increases. So, I was curious as to what people have seen with motors they built at higher compressions and especially in hotter areas. This would help me to compare apples to apples (even tho the apples may not be the same type, they are in the ballpark).
Compression releases area a definite starter/battery saver. But, they really wouldn't be needed until some reasonable number. I "suspect" once one hits about 10.5:1, they would begin to be desireable and at 11:1, probably a necessity. But, just my WAG having never been above maybe 9:1.
I also understand that as compression goes up, the need for higher octane goes up. This is even more true as the temperature increases. So, I was curious as to what people have seen with motors they built at higher compressions and especially in hotter areas. This would help me to compare apples to apples (even tho the apples may not be the same type, they are in the ballpark).
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Road Warrior
Joined: Dec 2006
Posts: 1,530
Likes: 0
From: Diamond Bar, California
RE: Compression and such
Well, I did a 10 to 1 HQ being unsure of the Cali gas, but Im confident now that I could go 10.6 without much fan fare.
Elevation plays alot too, My home town of Salt Lake City, Ut is around 4200 ft above SL, and my bike as it is right now would lose close to 15 lbs of cylinder presure if I rode up there today, so I know I would have to add some compresion to get the same power up there.
Scott has a good point about calling R&R to find out how much cylinder presure is needed to make either one of thoses cams run properly, and pick the parts that match the best and your riding style and overall bike weight.
Elevation plays alot too, My home town of Salt Lake City, Ut is around 4200 ft above SL, and my bike as it is right now would lose close to 15 lbs of cylinder presure if I rode up there today, so I know I would have to add some compresion to get the same power up there.
Scott has a good point about calling R&R to find out how much cylinder presure is needed to make either one of thoses cams run properly, and pick the parts that match the best and your riding style and overall bike weight.
Ultimate HDF Member
Joined: Feb 2006
Posts: 5,939
Likes: 3
From: TX
RE: Compression and such
Along the lines of your Dr's analogy... follow the recommendations of the "Dr"! If R&R tells ya to go with 10.8:1 because that what makes the cams (actually the package) happy, then do not try to re-engineer it.They have good stuff, but like any other package... it has to be setup and installed properly ~ as "prescribed" in order to get the most out of it.
From a purely "starting" perspective, those cams are easier on starting than many others based cam timing, but even so... GET THE COMPRESSION RELEASES!
"Typically", 9.7 ~ 9.8:1 is a good level to start seriously considering compression releases, but as was mentioned, cams do play into the equasion. If for no other reason than insurance on your starter, it will be $$ well spent.
Regarding temps, altitude, & octane, you should again follow the advice of your chosen motor guy.
From a purely "starting" perspective, those cams are easier on starting than many others based cam timing, but even so... GET THE COMPRESSION RELEASES!
"Typically", 9.7 ~ 9.8:1 is a good level to start seriously considering compression releases, but as was mentioned, cams do play into the equasion. If for no other reason than insurance on your starter, it will be $$ well spent.
Regarding temps, altitude, & octane, you should again follow the advice of your chosen motor guy.