Triumphrat

ohiorider · 10-27-2007

I posted some of this in August, but would appreciate some opinions from you motorheads about the results:
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A couple of months ago, while I was changing shims on my valves, I decided to re-index the cams. I had already worked through what these changes would do to the timing. Jojje had confirmed that moving a cam one tooth would change the timing 15 degrees when measured at the crankshaft.

First I had the bike dyno'd with the cams in the stock position. Although the air/fuel ratio showed the bike to be running rich, I didn't want to fool with the jetting before a second dyno run with the cam timing changed. I was trying to see what making this one change would do.

Next, I advanced the exhaust cam one tooth (15 degrees at crank) and retarded the intake one tooth (15 degrees at the crank). Per my calculations, and using the cam timing specs for the 790 and 865 engines, this change would make the timing milder (like the 865), and therefore I expected to see the torque and hp curves change dramatically, hopefully providing more torque at a lower rpm. One would think that changing the valve overlap from 39 degrees to approx 9 degrees (similar to 865) would be a significant change.

The dyno results "before" and "after" were practically identical, which left me at a loss. I guess I would have expected either much worse or much better results, not same/same.

I did not attempt to calculate dynamic compression ratios for stock and modified versions, so I may have improved one area and worsened another with this mod.

Since the modified engine performed so much like the stock engine, I reinstalled the cams back to stock timing after riding it modified for approx 1000 miles.

Here's the two dyno runs for comparison. As stated before, both indicated a too-rich mixture.

http://s115.photobucket.com/albums/n...ent=Slide1.jpg

http://s115.photobucket.com/albums/n...ent=Slide1.jpg

Bob

bonnieblackinfl · 10-27-2007

Bob, what is it you would like to know? I will run your setup through my dyno software, if you are looking for the best setup.

Greg

ohiorider · 10-27-2007

Greg - I guess what I'm trying to understand is why such a major change in cam timing made little or no difference in the dyno results. Attached are two slides. The first represents stock 790 timing, the second represents a comparison between the modified cam timing on my 790cc and stock 865 cam timing (I wanted to see them side by side). I created these slides using data from the Triumph Service Manuals.

http://s115.photobucket.com/albums/n...mTiming007.jpg

http://s115.photobucket.com/albums/n...mTiming010.jpg

And here's the entire file (13 slides).
http://s115.photobucket.com/albums/n...0Cam%20Timing/

I appreciate your taking a look at my info.

Bob

mikeinva · 10-27-2007

thats a very good test you ran.I think we need to use a deg. wheel and a indicator to find out what are cams are realy doing I bet there not all the same.even same years bikes.I dont think we will make more HP with out getting some new grinds .

SCCTrim · 10-27-2007

I think it's important to note that...( in my own experience )...differences seen on paper from a dyno and differences felt by the seat of the pants are 2 different things. When I altered my cam timing I only advanced the exhaust cam, leaving the intake in it's stock position.

The difference on paper was almost negligable, but by the seat of the pants the difference was certainly noticable. The bike pull's harder down low now, with a little noticeable loss on top. A little difficult to notice the loss as with so many mods the bikes pull's like hell anyway.

But there was a definate change for the good down low. For the street I'd only advise advancing the exhaust cam on the 790 powered bonnies.

ohiorider · 10-27-2007

Quote:

Originally Posted by mikeinva

thats a very good test you ran.I think we need to use a deg. wheel and a indicator to find out what are cams are realy doing I bet there not all the same.even same years bikes.I dont think we will make more HP with out getting some new grinds .

Mike - I was using an image of a degree wheel only as a background to paste up where valves open and shut. I agree, it would be interesting to use a degree wheel on a cam along with a dial indicator, to get some actual measurements. Amazingly, the guys out of N Zealand that sell hotter cams don't publish their cam specs. I'd think if I was in that business, I'd measure stock cams and publish that data side by side with my hotter cams.

Bob

ohiorider · 10-27-2007

Quote:

Originally Posted by SCCTrim

I think it's important to note that...( in my own experience )...differences seen on paper from a dyno and differences felt by the seat of the pants are 2 different things. When I altered my cam timing I only advanced the exhaust cam, leaving the intake in it's stock position.

The difference on paper was almost negligable, but by the seat of the pants the difference was certainly noticable. The bike pull's harder down low now, with a little noticeable loss on top. A little difficult to notice the loss as with so many mods the bikes pull's like hell anyway.

But there was a definate change for the good down low. For the street I'd only advise advancing the exhaust cam on the 790 powered bonnies.

The bike felt like it pulled harder at lower rpm, but I wasn't sure if it was actual or the placebo effect.

Bob

bonnieblackinfl · 10-27-2007

Bob, I ran every combination possible in the program and it says that the advanced exhaust cam is the best combo. The I=R and E=A combo you had won the HP in the upper rpm range after 7k, but lost the TQ war throughout the band.

Granted this program is a few years old, but it really does make for a nice tuning device. The numbers aren't too accurate, but they aren't that far off either.

You may want to try 5 points less on the mains.

Greg

ohiorider · 10-27-2007

Greg - thanks for running the numbers for me. Leaving the intake alone and advancing the exhaust goes along with what SCCTrim said in his response. I'm dropping the mains a step at a time. I've taken step #1, which is dropping from 125 mains to 122 mains. Better. Especially since the outside temps have dropped a bunch. She felt really strong yesterday, which makes me think I may leave the 122 mains until warmer spring and summer weather in 2008. I have a set of 120s and 118s on hand. Redbird (Larry) previously suggested dropping main size (done) and that I pull the shim off each needle, but I haven't gotten around to that yet. That'll be next.

Bob

bonnieblackinfl · 10-27-2007

Bob, no problem man. If I could figure out how to copy a screen image I would put the results up so you could see the differences. I find that visual is always better.

If someone could show me the way, I think it would be benefical for everyone to see.

Greg