inceased compression ratio

Forum rules
Please do not start new topics here, but here: New Panhead and Flathead topics
Post Reply
Guest

inceased compression ratio

#1

Post by Guest » Tue Mar 25, 2008 3:09 am

I have a 4-1/2 stroke x 3-7/16 bore motor It has s&s 2800 ser. 8.5:1 CR pistions .I works well with the exception of occational hard starting due I think to the long duration cam I would like to Increase CR to 9;1 or 9.5:1 any thoughts?



Cotten
Posts: 6911
Joined: Mon Aug 26, 2002 9:09 am
Location: Central Illinois
Has thanked: 100 times
Been thanked: 268 times

#2

Post by Cotten » Tue Mar 25, 2008 2:27 pm

Guest!

My first thought is that something else makes it hard to start than compression: My second thought is that you would have a hard time finding decent fuel for the higher compression.

....Cotten

rrhawg
Posts: 93
Joined: Wed Feb 20, 2008 4:59 pm
Bikes: 59 Pan, 65 Pan, 45 Wl, 46 UL, 41 Chief, 48 Chief, 50 Chief, 53 Hummer, 53 Simplex, and misc. others
Location: Newport, Oregon
Has thanked: 2 times
Been thanked: 2 times

Re: inceased compression ratio

#3

Post by rrhawg » Tue Mar 25, 2008 2:55 pm

Anonymous wrote:I have a 4-1/2 stroke x 3-7/16 bore motor It has s&s 2800 ser. 8.5:1 CR pistions .I works well with the exception of occational hard starting due I think to the long duration cam I would like to Increase CR to 9;1 or 9.5:1 any thoughts?
You can run a higher compression with the longer duration cams, as they won't build their peak compression until the higher rpm's. Depending on what you run for an ignition can also make a difference in weather it will ping or not, and how much.
Rich

Guest

#4

Post by Guest » Tue Mar 25, 2008 11:50 pm

Thanks for replys, The bike does run well,I have electronic single fire ignitionand dual plugged heads.I have tried differant timing setting via timing light.I have never had problems with pinging.But the bike does seem to kick start rather easily considering the longer stroke

Guest

#5

Post by Guest » Wed Mar 26, 2008 12:09 am

In my last post I said kick starts easy I should have said kicks over easy
But like like I said before, the bike runs well,I just think it could run better

rrhawg
Posts: 93
Joined: Wed Feb 20, 2008 4:59 pm
Bikes: 59 Pan, 65 Pan, 45 Wl, 46 UL, 41 Chief, 48 Chief, 50 Chief, 53 Hummer, 53 Simplex, and misc. others
Location: Newport, Oregon
Has thanked: 2 times
Been thanked: 2 times

#6

Post by rrhawg » Wed Mar 26, 2008 12:39 am

It sounds like your on the right tract. There is nothing like compression for building power. You might look at putting a VOES switch on also if your ignition has provisions for it. With the dual plugged heads you should be able to retard you timing about 5 degrees also.
I have a panhead running 10 3/4 to 1 compression and it runs great.
What about the head work? Flowed heads make a world of difference. Along with a free flowing exhaust. Consider it a air pump, the more air you get into and out of the cylinders the better it will run.
Rich

Guest

#7

Post by Guest » Wed Mar 26, 2008 1:18 am

I posted once on this forum a while back I dont remember my user name or password. I cannot log in because It says me email address is invalid .the posts I reply as a guest keep being kicked out HOW can this be fixed?

panhead
Site Admin
Posts: 2560
Joined: Wed Dec 12, 2001 9:17 pm
Bikes: 1954 FL
Location: Holland
Has thanked: 7 times
Been thanked: 54 times

#8

Post by panhead » Wed Mar 26, 2008 8:48 am

I posted once on this forum a while back I dont remember my user name or password. I cannot log in because It says me email address is invalid .the posts I reply as a guest keep being kicked out HOW can this be fixed?
You are registered as rrennchh. I emailed you a new password.

fourthgear
Posts: 1391
Joined: Mon Apr 11, 2005 1:12 pm
Location: north florida
Been thanked: 4 times

#9

Post by fourthgear » Wed Mar 26, 2008 1:41 pm

I'm running KB pistons @ 9.5-1 and they run & start fine . My motor is stock displacement . One kick starts , warm or cold.

Guest

#10

Post by Guest » Tue Apr 01, 2008 12:42 am

I was thinking of boring to 3.5 and using 4.250 pistons with stroker plates to dial in compression ratio

Guest

#11

Post by Guest » Tue Apr 01, 2008 12:53 am

Ok maybe I can post as a guest I should have added stroke before 4.250 I think the plate and base gasket should add up to somthing like .125

Post Reply

Return to “Motor”