High Compression, What is to much?

[shovel89]

I purchased a 98 lowrider that has been put on steroids. It runs great, if you like a total hot rod. Question is, how much compression
can safely be used, as a daily rider before I end up buying many parts. I have had several evo's (fine motor) but usually only upgrade cam and maybe shave the heads with the thinner gasket. This one is up around 11 to 1, thoughts?

[stroker800]

  I don't like to go over 10.5-1,,,its hard to get good gas,,,extra temp from high compression,,,risk of ping and knock...My friends race bike is 17-1 comp,,,but only runs 10 seconds at a time..
Dave

[Hybredhog]

   My everyday bike (Dyna FXDXT), is at 11:1, but cranking presure is the bigger issue or decider. Mine is at about 220lbs, and I'm running just premium. Although I'm aware of pinging if it gets lugged, but I have to damn near be trying to make it do it, but I rarely let it go below about 2600rpms. good headwork, squash, and a good ignition goes a long ways. Bottom line is high compression if built & driven right isn't all that hard on motor, not to mention its more effecient, and you can make starting more effiecent too. Just look at the automotive wolrd, theres hardly anything under 10:1 now.

[shovhd]

11-1 comp is a bit of a PITA. It sure makes the starter grunt. I put in colder spark plugs and it allows me to run on 94 octane which we have up here in Canada (but a bit of octane boost still helps). Finding 94 last time I was down in the states was practically impossible. I'm running a Dyna-s igntion now and have ordered an Ultima ignition with computer link kit so I can try and tune it to run on 92 Octane. It runs great now, so I probably won't do anything with the comp until I need to do a teardown.

[Kevin]

Just keep good warm up habits. If it don't ping, ride on!

[bigtone]

I had 10.2 to 1 in my S&S 96 incher. It always pinged, no matter what I tried. Had to keep to rpms way up to try to avoid the pinging. I tried a 562 cam, it was slightly better. Still had about 215 psi cold cranking compression. Finally went with a crane cam witha  much later intake closing, knocked the cold cranking compression to about 170. Much better now

[d-dog]

I'm with Jeff - when he talks about cranking pressure, he's referring to the "static" compression as opposed to calculated compression.  You need to factor in your cam.  One with significant overlap, should crank fine with 11:1 but you're looking at a cam that develops it's power at the upper end.  One with little to no overlap could have problems with that ratio.
As they say - JMHO

Dog

[BikerJim44]

ShovHD, I am Soooooooooooooooooooooooooooooooo jealous. 94 octane? Paaaleaseeee send me a bucket of that stuff, did I mention Pleassssssssssseeeeeeeeeeeee? LOL Dang I haven't seen anything over 90-91 since I left New Hampster. Spidey.

[shovhd]

ShovHD, I am Soooooooooooooooooooooooooooooooo jealous. 94 octane? Paaaleaseeee send me a bucket of that stuff, did I mention Pleassssssssssseeeeeeeeeeeee? LOL Dang I haven't seen anything over 90-91 since I left New Hampster. Spidey.

LOL, come on up and help yourself. It's still cheaper than beer up here, of course beer is really expensive.

[Mark222]

Hey all:

I have been running +0.10 WEISCO 10:1 Pistons

Heads cut .040 and thin James gaskets

Head work performed with increased size valves

Crane H290   .581 lift cam

Roller rockers

Dyna 2000 ignition (single fire)

Mik 42 carb

Python III pipes

Upgraded starter to a Spike Unit and it has never even grunted, let alone slowed.


Gauge reads 245 - 250 when cranking coold with throttle wide open

Any thoughts?

Mark

[Cousin It]

 Dont really understand the question but if you want thoughts....
1    Does it run?
2   Are ya scared?
3   Ride It

Theres mine.  Anybody else?  LOL

[TheSwede]

Hi guys..
You can ride with a very high comp. ratio
it all solely depends of the cams intakeclosing,,
the higher the intake close on the piston way up
the less gas to compress in low RPM
overlap is not telling ,,,just intakeclosing

The price you have to pay is torque that's equal cylinderfill
before the inertia help fill the cyl. in high RPM

Best Regards
TheSwede

[lionsm13]

Hey all:

I have been running +0.10 WEISCO 10:1 Pistons

Heads cut .040 and thin James gaskets

Head work performed with increased size valves

Crane H290   .581 lift cam

Roller rockers

Dyna 2000 ignition (single fire)

Mik 42 carb

Python III pipes

Upgraded starter to a Spike Unit and it has never even grunted, let alone slowed.


Gauge reads 245 - 250 when cranking coold with throttle wide open

Any thoughts?

Mark

Yep; How's it run?
You never said.....

[Mark222]

Run's pretty strong, was thinking I missed a little something on the set up though.  I have seen less money spent produce more TQ where you can use it every day.  Some time ago I paid like $20 (maybe $40?) at an afternoon  Aces and Eight's  dealership event to pull the dyno for 2 runs.  It showed better than 80 / 80 if you believe the old traveling dyno 150 model.  I remember is was coming on strong from about 3200 up, but had drags on it at the time.

It does not ping, and it does not have comp releases.  Fires right off and has been 100% reliable for 25K miles or so now.

The Cam is a +4*  /  -4* type I have never pulled it back out and played with.  Intake closing is currently 43* in the stock gear position.  Thinking of moving the power band down about 300 RPM or so means adding more cyl compression, and I think I have all I need.  I have been told the evo sweet spot is closer to 220 CCP?  But never saw anything to back this up.  And I sometimes wonder what would happen if I moved the cam the other way, would it bleed off some pressure and build any more power where I want it?  At .581 lift and heads cut .040 I was concerned about just trying it without claying the set up for clearance, and did not want to tear the top off just to try it.

I have thought about trying a different cam but I have not had anybody tell me a cam that works well where the rest of the set up I have, so I have not messed with the current set up.  I ran the EV27 before and I would ping when hot.  Bob Woods hmmmmed and haaaawed a bit when I talked to him and and said I could handle the hi lift 6 and would like the other 6 too.  I has hoping he would clue me in on how to get the best from the compression I have developed, but stuck to "general" beliefs".


So I guess to sum it up, I am pretty happy with her in this form.  I have surprised a few buddies with newer (bigger CID) bikes with a mod or two, and yet like many others, always wonder if I left a little more "fun" on the table.  I now only put about 4k on her per year now that I have the 91 bagger.  So maybe I will do some experimenting again this winter.

Mark