Whats your best lobe center numbers??

[Anonymous]

I was hoping you could all share with me your best experience on lobe centers for a 79 GS1000S or for that matter any gs 2 valve. I recently completely rebuilt (engine and frame) and the bike runs real well, great idle, strong mid range, but I am not completely satisfied with top end power. It's a little flat up there. I was hoping to feel the front wheel off the ground in first gear !

I currently have both intake and exhaust set at ---108--- on stock cams, a compression test shows 130 psi on all 4. I have been up and down the ladder with main jets.. ignition timing is on the stock marks.

Just in case it matters, I'll list the extras that may affect it, - 1085 Weisco kit, 82 gs1100 reworked cylinder head, -RS34 mikuni carbs-, Jardine 4-1 pipe, (welded crank, manual cam chain tensioner, oil cooler & billet clutch so it don't blow up) I hope..

Any advice on your best lobe centers, or any other comments would be greatly appreciated. 8)

Freddy

 

[KEITH KRAUSE]

My '79 GS1000E has it's cams set at 106. I really like the compromise between low/midrange torque and top end power. Nice wide powerband. Some of my mods are the 1085 pistons,V&H megaphone, K&N filters, DJ kit for the stock carbs.
108-110 is favoring top end over low end. Maybe the possible lack of power is'nt the cam timing?

 

[RacingJake]

You can always go down one tooth on the front sprocket. Doesn't cost much and is easy to do and if your chain isn't worn or stretched all you do is adjust the rear axle back. You should be able to feel the differance.

 

[Anonymous]

Could it be that the cam timing will not make that much difference?

I have heard that some of the newer bikes, 98-04 have stock cam timing of 105 exh and 114 intake and the stock GS had high numbers - 112 -116 on both intake and exhaust?

If I had a dyno to play with I would try all different numbers and share it but for now I think I'll try a lower exhaust and higher intake as compared to them being the same.

Yep... I'm just a gear head who can't leave it alone !



:idea:

 

[KEITH KRAUSE]

The cam timing makes a lot of difference. It has a lot to do with low end torque and top end horsepower. It's a mod' you can make with the way you ride in mind. Early stock GS's came with their timing set within a fairly wide range. Some bikes came to you set at maybe 102 and others came at 115+. You might get one with its cams set anywhere in between. This was the main reason two brand new bikes would differ in performance.
Setting the cams at 108-112 favors the top end but you sacrifice some low/mid-range power. If you set them at say, 114+, warm ups are slow, the engine runs hot, the carbs are difficult to tune and the powerband narrows. Mine are set at 106 each. The bike is just fun to ride. Lots of torque and plenty of top end.

 

[Anonymous]

Thanks Keith

Thanks Keith

Well your right it is fun to ride with lots of broad range power, but if I want maximum hp, for best 1/4 mile times, what do you think the best numbers would be?

 

[KEITH KRAUSE]

There are others here that drag race and they can answer that question from experience through actual testing. I just believe cam timing set up similar to mine is better for the street.
I would have to say that cam timing of about 112+ would be best for top end.

 

[cbxchris]

Typically the lower the cam timing the better the low end...same for higher lob centers with higher rpm. A 1150 typically runs good from 104 to 110. Just depends what you want...most are happier with lower lob centers. Aftermarket cams will degree in around 108-110 most of the time. The newer bikes like a hayabusa have very low lob centers. !02 -104 are very common with many going lower. A yamaha FJ 1200 was notorious for coming from the factory with 112-114 lob centers...drop them to 104 and a 1150 has a really hard time with a FJ. Got to add though when it comes to aftermarket the GS rules period.

 

[scotty]

I love this info so i did a search. i havent read any of these links yet though
http://www.google.com/search?hl=en&ie=UTF-8&q=motorcycle+cam+timing&spell=1

 

[Anonymous]

There is quite a bit of info out there that rehashes cam timing. looks like I found a few more .. thanks Scotty.

My new brainstorm, (which I'm sure no one has thought of 8O ya) is to keep the exhaust low...105 and advance the intake to 112. The low exhaust helps overlap while later intake may help cylinder charge. I did read that intake is more important/effective than exhaust. Sorry guys, but I just can't help myself from exploring this till I find more HP, or not.

Yep I'll be checking for valve collisions... greater than 50 thou should be safe.

Any others have thoughts on top end numbers ?

 

[scotty]

I noticed that the bike became nasty when the cam chain had worn to the max. i was going to take readings and see what the centers were set at under the worn conditions but got lazy and i have all the necessary tools. If the bike doesnt come on as hard after i have a new chain installed then i will go to adjustable gears and use some of the recomended timing settings.
This worn condition would produce a larger spacing between the inake and exhaust. The intake would be a bit later and the exhust later also. I dont have enough experience to imagine what effect this would have on an all out run.
any one have any comments???

 

[Anonymous]

I did read that intake is more important/effective than exhaust.

I have read that the intake valve closing point is the most important event in the entire valve timing sequence. So you should see the most effect there, if that is correct.

Mark