Let's Talk Compression Just a Little
Road Master
Joined: Jul 2006
Posts: 1,229
Likes: 20
From: Illinois
I have a mild 95 SE performance heads with some port and polish, 10:5.1 and a 257 cam PING PING PING, I never realized how bad the gas was around where I am at until the last ride of the current season. I was out about 100mls west and bought some true 93 bike ran great and solid had a much deeper tone and no ping.
I have tuned most of the ping out but still deal with some depending on the weather. I am going to change out my cams on the advice of Doug from HQ, he tells me that I am loosing velocity with the SE heads and cam I am running.
If this new set up doesn't work I will tear it all out and do a completely new set up crank to heads.....
I have tuned most of the ping out but still deal with some depending on the weather. I am going to change out my cams on the advice of Doug from HQ, he tells me that I am loosing velocity with the SE heads and cam I am running.
If this new set up doesn't work I will tear it all out and do a completely new set up crank to heads.....
Last edited by tgaetto; Dec 11, 2008 at 02:14 PM.
Grand HDF Member
Joined: Sep 2007
Posts: 4,122
Likes: 44
From: Boise Idaho
When using higher compression with todays gas I have found that if you use a complete kit like from Head Quarters or any other good builder will work just fine with up to 10.75. If you hodge podge something together you can end up with problems and as much as enerything cost you are money ahead to get a complete kit from one source.
Proper squash size and cam selection is very important to stop pinging and make starting easy.
Proper squash size and cam selection is very important to stop pinging and make starting easy.
Ultimate HDF Member
Joined: Nov 2005
Posts: 5,926
Likes: 138
From: NE Ohio
Like everyone else has been saying, a little more compression isn't going to hurt a thing. I'm running HQ's touring package with their porting, 0039 cams and compression set at 10.1. My cranking compression is at 195 on both front and rear cyl. This summer I did a 3600 mile trip out west with no problems that I didn't create myself. I've run everything from 93 octain to 87 octain, the only rattles I had was a touch when I had the 87 in the tank and the outside temp was in the high 80's and I was riding 2 up in the hills of PA. I've since made a couple changes that have the bike running cooler so I don't think I'd even have much rattling with the 87 now. The trick with running higher compression is the right build components and a good tune, choose wisely and a **** eating grin will be your reward.
Road Master
Joined: Oct 2007
Posts: 1,117
Likes: 4
From: Log home in SE Michigan full time. Log cabin in east TN, Smoky Mountians part time
Compression ratio is a calculated number. If you buy 10.5/1 pistons does not mean that you will have 10.5/1 compression ratio. You must calculate the stroke, cylinder diameter, head gasket thickness, piston dome height, subtract the valve relief area from the piston, and cylinder head chamber volumn. With that information you have to either presume worse case for deck height, which would be zero or measure the deck height to get the actual number. You really should be measuring deck height too. Deck height is how far the piston is in the cylinder bore at top dead center (TDC), optium would be zero deck height for MOST builds. The TC88's were pretty good at being zero, the TC96's are all over the board, usually the piston is DOWN in the bore, meaning you dont have as much squish at TDC....you still have cylinder volumn if the piston is not at the top of the bore, meaning also you WILL have less compression if you calculated it at being at the top of the bore.
You need to calculate deck height on EACH cylinder.
I dont have the numbers here at the key board but I'll repost the formula on how to calculate compression ratio. Simple to do.
You need to calculate deck height on EACH cylinder.
I dont have the numbers here at the key board but I'll repost the formula on how to calculate compression ratio. Simple to do.
Thread
Thread Starter
Forum
Replies
Last Post
