| Author | Message | ||
     M1combat |
Can we change the cam timing in an XB to make more power or at least to shift the power curve around? Is there even enough room so we could move them one tooth over and not bash a valve? What would be the repercussions to the FI system? Just curious  . | ||
| Fullpower |
moving your cams a tooth would be a rather large deviation from a very well engineered cam profile. you will notice the torque curve is a relatively gentle mound, and that the horsepower is still climbing at the rev limiter, i propose that the factory cams are about ideal for the application, unless you find a way to rev these XB engines substantially higher. | ||
| Leftcoastal |
I don't have an XB model, but I'm sure the cams are set up virtually identical to tube frame Buells and Sportsters. Since the cams each drive off the one next to it, how would you move any of the cams "one tooth" without throwing the next one out of time, compounding the problem. It's hard (at least for me!) to describe but you would have to move each cam lobe in relation to it's own drive gear in order to achieve any usable cam timing change. (Something that cam grinders and racers do, I'm sure) I wouldn't suggest attempting "Moving them one tooth over" unless you enjoy the sound of bending valves and denting pistons. It's not a pleasant sound - take my word on this! AL (Message edited by leftcoastal on July 16, 2005) | ||
| M1combat |
"Since the cams each drive off the one next to it, how would you move any of the cams "one tooth" without throwing the next one out of time, compounding the problem." Understood... I think I said "them" as opposed to "it". "I wouldn't suggest attempting "Moving them one tooth over" unless you enjoy the sound of bending valves and denting pistons." So you're absolutely certain that rotating either the exhaust or intake cams (or maybe both) either way would most CERTAINLY result in a bashed valve or in valve interference? | ||
| Fullpower |
well the exhaust cams would be easiest to experiment with, they are both outboard, and at the respective ends of their drivetrain. | ||
| Rocketman |
If you work out how many degrees one tooth (or however many teeth for that matter) is then arm yourself with your cam specs you can easily do the math to see where moving your favoured amount of degrees gets you. I think what you are trying to suggest is optimizing your cam timing by dialing the cam in to its most accurate setting. To do this you would need to have all the cams on variable key ways rather than each cam keyed in a fixed position offering no adjustment. I'd hazard a guess and say if it were worth the gain someone would be making variable cams for just this purpose. Hey maybe someone does? Consider also that cams are a black art in many respects but their manufacturers be it Andrews Red Shift or whoever will have put a great deal of effort getting close to perfection I'd imagine. More so when we take into account these are four cam motors which I imagine gives the cam profiler more scope for accuracy over a single cam operating a single valve when manufacturing to a suitable tolerance. To put that into perspective my old TVR motor runs one camshaft so the compromise for optimum profile is worked into 12 valves operating in 6 cylinders. I have about the best cam in there for fast road \ race use without compromising street drive-ability. As with my particular TVR, a 1977 Taimar, no one made cams specifically for them. What was \ is available were all reground using the original Ford cam. Consequently these cams can run as much as 8 degrees out. Mine's out 4 degrees but I'm not that bothered to want to spend a couple of hundred quid on a variable timing pulley because I'll never feel the extra 4 degrees in performance gain given I've already gone from 138bhp to over 200bhp with everything else I've modified. I guess what I'm saying is one can get far to involved and yes I'm one of them but there comes a time when reality strikes and the reality is the reward sometimes isn't worth the effort unless you're out to win a trophy or something. Rocket | ||
| Steveshakeshaft |
Yeah, but Rocket, if you've degreed the camshaft and it's definitely 4 degrees out. Then making a new keyway @either 176 or 184 degree (as required) opposite the stock one is a piece of cake! | ||
| M1combat |
Well, I'm mostly just trying to start conversation. What if the exhaust cams can be turned one tooth over and there are massive (or even moderate I don't care ) gains that Buell can't talk about due to emissions regs? I hear we already lift .550? | ||
| Rocketman |
Bloody hell Steve I can't tell you how many times I've looked at that steel timing gear and thought of how to modify the key way by 4 degrees without risking destruction of the existing woodruff key position. I shouldn't admit it here but anyway I never thought to turn it around 176 or 184 degrees and start again. Thank you very much for the awakening. Something to do with staring at it for far too long is my poor excuse! Consider it done and I'll happily take that 4 degrees ta. Combat what's required in your scenario is a set of cams that have the camshaft itself fastened to their respective drive gears in a manner that allows the camshaft and drive gear to rotate around one another. The rotation need only be a few degrees in either direction which would give scope to fine tune each cam. Perhaps some kind of centre bolt fastening - I don't know. Is there enough room to make such a cam? If so it would need to have the drive gear and camshaft lockable once ideal positioning was achieved. Perhaps pin locks would work. Good luck. I'm sure such finite tuning would give some reward given how some tuners require ultimate power. If you make any money when you take 'em to market remember where you got the idea from  Rocket | ||
| M1combat |
I'd thought of that (like the adjustable cams for the Cosworth engines of days gone by), although if I do I'd be happy to whip up an expenses paid trip over here to an Oktober or Spring fast ride ). I was totally accepting of the constraints I would have... That being that I can only adjust the cam the same number of degrees that the pitch allows me to. Anyway, I suppose if I want to check it out, I'll need to be doing the same thing as I have done with the XB9 ECM  . | ||
| Tomd |
M1, Advancing the exhaust event works best for engines that need a lot of help in the exhaust department like your Ford. By advancing the exhaust cams only your going to decrease the overlap in the engine, (the amount of crankshaft rotation where the exhaust and intake are open) resulting in shifting the power band slightly lower. You may also decrease the power stroke event length as the valve will pop open sooner, (remember the cam pops the exhaust open before the piston reaches BDC on the power stroke)this may result in performance and HP decrease. Cam timing is not just dependent on the timing of the valve open and closing, you have to take into account the mass of air your trying to move in and out of the engine. Cam designers spend huge amount of hours trying many variations in order to get the best compromise. Remember street engines need a nice wide power curve in order to be fun to ride, race bikes are work to ride. Playing around with cam timing is best left to applications that will run in a predetermined RPM/power range like drag racers. The can set the car up to stage at a specific RPM and leave and shift at it's optimum RPM. Since the engine essentially sees one RPM, you can tune the entire package for that. Tom | ||
| Steveshakeshaft |
Rocket, you are more than welcome. You're obviously a happy man, so I'm happy too. Seeing the "obvious" in a machine is something much more difficult than you might imagine. I run my own business on that basis. Please post the results of the 4 degree correction when you've done it. (BTW, for smaller corrections a stepped key can be made). HTH. Regarding the degreeing in of camshafts, sometimes you will see a device where the hub has (say) 30 holes and the corresponding shaft has (say) 29 holes. The hub is locked to the shaft at the nearest matching set of holes corresponding to the desired timing. Such a device is known as a vernier adjustment, named after the principle of the vernier caliper. HTH. Steve www.shs-consulting.co.uk | ||
| Rocketman |
Steve I considered making a stepped key - then thought twice. The effort wasn't worth the gain. With enough money spent on the whole already cam and steel timing gear in this instance I decided there was no need to increase the budget by going down the vernier route but I will let you know the results of your suggestion when and as soon as I get time to rekindle the TVR project. Thanks again Steve. ps; are you doing the Black Bear ride to Linc's on the 30th? Rocket | ||
| Steveshakeshaft |
Rocket, I've sent PM to you. S | ||
| M1combat |
So if I wanted to shift the powerband towards the upper end I would retard the exhaust timing... I hear there's already a good deal of overlap (I can hear it in the exhaust too). Anyone know how many teeth are on the exhaust cams? | ||
| Tomd |
M1, Hi, I think these are better reading about cam timing tech than I have time to type up. Tom http://www.sportrider.com/tech/146_0306_art/ http://www.compcams.com/Information/Tutorials/ http://www.wallaceracing.com/cambasics.htm http://www.iskycams.com/degreeing.php http://www.auto-ware.com/combust_bytes/valvetiming.html | ||
| M1combat |
Thanks . | ||
| M1combat |
Well... I learned a couple things from the Isky link . It still seems that if you can get away with retarding the exhaust cams relative to the crank (by that I mean starting their event later) that you may be able to get more power on the top (assuming you won't bash anything...). In effect reducing overlap. I'd like to know just how much you'd have to sacrifice in the middle and on the bottom if you did this... Don't turbos/superchargers typically like less overlap too? That would be one way to get some of the lower end power back and maybe get some large gains at the top... Maybe one of these days I'll check it out . I'll probably build a good grenade at the least . | ||
| Rocketman |
Steve no mail. I'm at seanpepper@gmail.com Rocket |
