Compression vs/ Octane???
- Thread starter BigIQ?
- Start date
Rucky
Active VIP Member
NICE SLED...more pictures are welcome 
- Thread starter
- #3
Thanks, She's had a little makeover since that pic....This is why i was asking about the compression, not sure waht to turn it to, to run half and half race, premium......squeeze more ponies out of it....
Chopped the front suspension, re-nicasil, blueprinted and coated pistons, 04 AC 900 carbs.....only been able to ride twice this year, so still a little tweaking to be done...Also have to (home fix) my ekholm susp...i guess i'm too hard on things...lol
Chopped the front suspension, re-nicasil, blueprinted and coated pistons, 04 AC 900 carbs.....only been able to ride twice this year, so still a little tweaking to be done...Also have to (home fix) my ekholm susp...i guess i'm too hard on things...lol
- Moderator
- #4
Rucky
Active VIP Member
AGREED ^^^^^
- Thread starter
- #7
- Thread starter
- #8
cey800
Active VIP Member
- Joined
- Nov 12, 2006
- Messages
- 451
- Reaction score
- 7
What's the hp on the 950 psi, nice sled!!
Dude if that thing only has 130lbs of comp in each cylinder it may aswell only be running on one cylinder, Not bashin ya but premium fuel is about all that will run on. Remember that to good of fuel can rob hp. If I were you id bump that comp up and run some race fuel to get the full effect of that engine.
- Thread starter
- #11
Well...When i talked to Bruce...he mentioned that it should run 190-200 hp...depending on your tuning skills....and with race gas...i assume.Not bad for an older motor....But then again..he quotes all hp with the use of bigair carbs and psi pipes....I run AC carbs and Jaws twins...i know that if it has any hookup...i'll jerk your arms near off...
Oh ya did i mention that this thing weighs something like 420lbs dry...if my calc's are anywhere close...
Oh ya did i mention that this thing weighs something like 420lbs dry...if my calc's are anywhere close...
Rucky
Active VIP Member
TEST RIDE!! I want that sled lol. I want an IQ mod sooo bad, too bad money is being spent elsewhere
- Thread starter
- #13
Thanks for the info Deano670...but that is what i was trying to get at...i want to run the compression up..but not sure where to stop at...i guess if i can't pull it over...= too much compression....lol...i've ran it at 130...because i didn't know what to set it too...and in this case i like to error on the side of caution...than chaos...
- Thread starter
- #14
Thanks Rucky...actually..whenever i've been out with it...the guys that i ride with will not take it for a rip...not sure why...but if i ever get home...i'll see if me and Nosrx1 are going for a ride...and your welcome to give her a squeeze...lol
- Thread starter
- #16
Right on man...well if 130=premium, and 140= 50/50, than 150= straight race gas....or there abouts.....well i sure appreciate all the help guys....
If any of you guys are around the end of march when i get home...i'll be in the market for some riding....
Cheers.
If any of you guys are around the end of march when i get home...i'll be in the market for some riding....
Cheers.
Garryese
Active VIP Member
Compression is not a good indicator of actane needs. Seen engines detonate at 140psi on premium and seen engines run fine one regular with 180 psi.
Compression ratios are moderatly useful in guestimating fuel needs, but still has room for error. 10.5:1 or less should be good with regular. Up to 12:1 should be good on premium. Anything over 12.5:1 I recommend a race mix.
Piston crown design, piston material, head design, head temperature, exhuast and intake design, fuel/oil/air ratios, squish velocity/area/clearance, etc all have an effect on detonation and thus octane needs. This is why you are getting conflicting advise.
A complete list of engine mods with the compression ratio of the pistons would help us guess your fuel needs.
Compression ratios are moderatly useful in guestimating fuel needs, but still has room for error. 10.5:1 or less should be good with regular. Up to 12:1 should be good on premium. Anything over 12.5:1 I recommend a race mix.
Piston crown design, piston material, head design, head temperature, exhuast and intake design, fuel/oil/air ratios, squish velocity/area/clearance, etc all have an effect on detonation and thus octane needs. This is why you are getting conflicting advise.
A complete list of engine mods with the compression ratio of the pistons would help us guess your fuel needs.
True, true very true, keeping inmind the above highlighted items all have an effect on one common factor COMPRESSION, which for the common rider is what he is going to read on his gauge. In my eyes YOUR engine builder should be able to tell you EXACTLY what kind of fuel to run in your MOD ENGINE!!!!
My two cents
Ancient Sledder
Active VIP Member
I don't want to sound like a jerk, but in the picture of the sled I think I see an EGT setup. You should be able to keep from melting a piston by watching that. The other fellows are right in saying that there is more involved than compression pressure for determining the octane needed.
Garryese
Active VIP Member
EGT is a good tool to use to prevent a piston melt down, but melt down is not a octane issue. Melted pistons are usually a result of incorrect fuel/air ratios. Octane controls detonation; detonation can crack a piston or erode a hole into the piston crown. When detonation errodes enough of the piston crown away, the crown overheats and then melts. So, you can have safe EGT and still burn a hole through the piston.
One has to be careful in diagnosing the root cause of piston melt down. Detention will cause to piston crown and/or head to appear sandblasted with possibly broken rings or cracked piston skirt. If in doubt it is best to have a mechanic inspect the piston, cylinder head and spark plug.
Similar threads
