a displacement calculation that does not work using a web calculator
Thread Starter
|
Road Warrior
Joined: Jun 2009
Posts: 1,943
Likes: 3
From: NYC
a displacement calculation that does not work using a web calculator
ok, who can help solve this.
tried it on a few web calculators and it didn't work.
if I have a 103 as a result of a 4.38 stroke and 3.875 bore
and I replace the flywheel with a 4.625 stroke (4 5/8)
difference is .24 in stroke.
whats my new displacement.
Can I add a .25 thick cylinder base gasket to raise my cylinders to avoid changing my valve to piston clearance while keeping my compression intact?
tried it on a few web calculators and it didn't work.
if I have a 103 as a result of a 4.38 stroke and 3.875 bore
and I replace the flywheel with a 4.625 stroke (4 5/8)
difference is .24 in stroke.
whats my new displacement.
Can I add a .25 thick cylinder base gasket to raise my cylinders to avoid changing my valve to piston clearance while keeping my compression intact?
Last edited by speakerfritz; Dec 17, 2011 at 09:47 PM.
Elite HDF Member
Joined: Nov 2010
Posts: 3,846
Likes: 173
From: Simi Valley, CA
109 CI.
0.7854(Bore sq) x Stroke x 2 = Cubic Inches
No you cannot add a .25 spacer to the bottom of the jugs. How would you fit the intake? Or exhaust?
0.7854(Bore sq) x Stroke x 2 = Cubic Inches
No you cannot add a .25 spacer to the bottom of the jugs. How would you fit the intake? Or exhaust?
Last edited by 2black1s; Dec 17, 2011 at 10:46 PM.
Cruiser
Joined: Apr 2010
Posts: 105
Likes: 0
From: Kennesaw, Georgia
The additional volume (displacement) per cylinder is found using the formula for the volume of a cylinder = "pi" times R squared times H, where
"pi" = 3.1416 (approximate)
R = 1.9375"
H = 0.24"
That calculates to 2.83 cubic inches per cylinder = 5.66 cu inches total
To check the calculation, original R is bore / 2 = 1.94 so::
3.1416 x (1.94)(1.94) x 4.38 = 51.8 cu inches per cylinder = 103.6 cu inches
(Note that the measurements and the value of pi are "rounded off" to the calculation is only approximate)
"pi" = 3.1416 (approximate)
R = 1.9375"
H = 0.24"
That calculates to 2.83 cubic inches per cylinder = 5.66 cu inches total
To check the calculation, original R is bore / 2 = 1.94 so::
3.1416 x (1.94)(1.94) x 4.38 = 51.8 cu inches per cylinder = 103.6 cu inches
(Note that the measurements and the value of pi are "rounded off" to the calculation is only approximate)
Thread Starter
|
Road Warrior
Joined: Jun 2009
Posts: 1,943
Likes: 3
From: NYC
yes...I initially thought that as well.
Thread Starter
|
Road Warrior
Joined: Jun 2009
Posts: 1,943
Likes: 3
From: NYC
good question. all the intakes I seen have an open bolt hole on one end and a close one on the other. and if the spacer only needs to be .125, maybe this would not be impossible.
Road Master
Joined: Sep 2007
Posts: 1,184
Likes: 0
From: The Peoples Republic of Massachusstts
Trending Topics
Road Warrior
Joined: Aug 2010
Posts: 1,268
Likes: 8
From: Detroit, the asshole of America
Why not just buy a set of pistons for it instead of trying to add base spacers, longer pushrods, and a new intake? Would be cheaper and less hassle. And either way you slice it, the compression ratio changed because the cylinder volume is different.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
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
Southpaw Super Glide: A Left-Hand-Drive 1979 Harley FXE Built to Fit the Rider
Verdad Gallardo
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,897
From: Bedford UK
If it was OK to do that, that would be the way it is usually done, which it is not! There are a lot of competent engine builders out there who do it the 'normal' way and that seems good enough for me! When I stroked my Evo my builder used shorter pistons.
Thread Starter
|
Road Warrior
Joined: Jun 2009
Posts: 1,943
Likes: 3
From: NYC
Thanks, thinking out loud here, I can play with the head gasket to tweak the compression back to where it should be.....the longer push rods are OK, thought of that....don't think I need new pistons, have some new cast and new forged...new intake , I think that any changes to intake surface mating spacing as a result of raising the jugs can be compensated for by adding gaskets between existing intake and existing jugs. i'm mainly after keeping my valve to piston clearance within limits after the new flywheel is installed. Raising the jugs should do that....there's plenty of cylinder wall available...certainly .125 to .25. don't need a whole lot and raising the jugs is easier in my mind than cutting the valve grooves on the pistion surface deeper. I could cut into the forged ones...but don't think there's enough meat on cast ones to go that route.