Triumphrat

ohiorider · 08-22-2007, 11:39 PM

I'm in the process of adjusting the valves on my 2003 T100 (790cc). While I'm at it, I may reinstall the cams so that timing is one tooth off from stock (exhaust advanced, intake retarded). The goal is to hopefully develop more torque in the lower rpm range where I normally ride the bike, down in the 3500-5500rpm range. More torque and more hp down low would be a good thing for me and how I ride, as long as the bike doesn't run out of steam at 5000rpm.

Will it work? I'm not sure. But based on the documentation I've worked through, it doesn't look like my 790cc engine (re cam timing) will be much different than the stock 865cc Bonnie engine. The question is .... will it run like a slightly smaller 865, or fall on its face?

The bike is currently running so well I'm almost inclined to return the cams to stock position and be happy with the fact that I got the valves adjusted. But my curiosity is getting the best of me, and I want to know if doing something as simple as moving the camshafts one tooth (15 degrees crank movement) will make a different bike out of my T100.

Without putting a bunch of $$ into the bike for CR carbs and big bore kit, I'm thinking I might be able to do a low-budget thing that will put the torque down into the rpm range where I ride. I rarely rev the bike over 6000 rpm.

And if I don't like the performance, it'll be no more than a few hours to return it to stock cam timing.

(can we paste url links directly now? .... hope so, or you'll have to cut and paste this link into your browser address bar).

http://s115.photobucket.com/albums/n...0Cam%20Timing/

The link will take you to Photobucket. I'd view the information as a slideshow, and hit your F11 function key to open up a full screen. Click on pause to view any slide that catches your interest, assuming any do.

I had the T100 dyno'd stock a few weeks back, and if it feels at all like the cam changes are doing what I hope for, I'll have it dyno'd again and add the dyno charts to this information.

Regards,

Bob

bonnieblackinfl · 08-22-2007, 11:51 PM

By retarding the intake cam, you gained power up top, not down low. To increase torque in the lower rpms, advance the intake and put the exhaust cam back. I think you will like this configuration better.

Greg

ohiorider · 08-23-2007, 12:07 AM

Greg - I'm going to try this configuration first. I've documented it, and can plug dyno data into the documentation once I have the bike dyno'd. If it doesn't do what I would anticipate, it'll be a simple matter to return to stock or give your configuration a try.

However, I'm not sure why my configuration, which includes retarding the intake cam timing, and advancing exhaust timing, would add power at the top, since I'm reducing valve overlap at TDC from 39 to 09 degrees, essentially eliminating the scavenging effect that I associate with making power at high rpms. Help me out with this one.

Summary - what I'm attempting to do is see how a 790cc engine performs with what is essentially 865 cam timing, except for the fact that the 790 cams have a few more degrees of duration.

Bob

bonnieblackinfl · 08-23-2007, 12:27 AM

True, I understand the thought process behind it and you are right, basically you are "decamming" the engine. However, you are opening the intake cam later and closing it earlier, and opening the exhaust earlier and closing it later. You will have more of a gain by increasing the intake charge and leaving the exhaust alone. I don't think our bikes have a problem with exhaust scavenge, we need to fill the chamber sooner to build dynamic compression, which build power.

Try it both ways and let us know.

Greg

ohiorider · 08-23-2007, 05:16 PM

Quote:

Originally Posted by bonnieblackinfl

............. However, you are opening the intake cam later and closing it earlier, and opening the exhaust earlier and closing it later ....................

Try it both ways and let us know.

Greg

Hi, Greg, I reread your post, and wanted to clarify what is happening with this proposed change. There isn't any way I can physically open the intake later and close it earlier, since that would require changing camshafts to ones with much shorter duration. What's happening is that the intake is being opened later (4 degrees BTDC instead of 19 BTDC, and is closing later, at 58 degrees ABDC instead of 43 degrees ABDC. Both opening and closing are retarded by 15 degrees. As for the exhaust .... the valves open sooner (51 BBDC vs 36 BBDC) and close sooner (05 ATDC vs 20 ATDC). There is no way I can change the duration of the cams without changing cams.

Anyhow, I have the correct shims, and am ready to reassemble. I'll let you know what the dyno numbers look like once I have it dyno'd within a week or so, if the results aren't too embarassing. I've already had the bike dyno'd with the stock cam timing for comparative purposes.

Bob

agro · 08-23-2007, 09:15 PM

Bob, if you have the time and money, get a dyno test with the exhaust only advanded and a dyno a dyno test with the intake retarded and the exhaust advanded.

It would be interesting to see the difference.

Bob, this link below is for free dymo simulation demo:

http://www.proracingsim.com/download...ynoSimDemo.EXE

Have used this with the Triumph cam timings, to get an indication of how timing changes affedt hp and torque. The only problem with this demo is the bore and strokes are fixed, but all other variables are adjustable. This demo indicated that advancing the 790 ex cam made more torque and hp, and advancing the ex cam and retarding the intake cam, made even more torque and hp than the standard 790 cam timings!

I have as set of 790 cams, purchased from Bonneville Performance, they had 1500 miles on them and were from a '03 790 cc T-100.

Initially installed the 790 ex cam, at standard timing, to my '04 Thruxton, had problems mainataining an idle with the stock carbs, figured out that the air jet in the stock carbs was too small and did not want to drill it out, fixed the problem by using vacuum hoses to connect the intake manifolds and carbs.

However lost a bit of bottom end power with this setup, therefore not wanting to refit the Thruxton exhaust cam, I advanced the 790 Bonney ex cam, 1 tooth, got back the bottom end power and more.
Have run this setup for 18 months now.

Run a 19 tooth CS sprocket, gutted stock airbox, 135 mains, 40 pilots,4 turns out, Unifilter, Madaz open stainless mufflers, bike pulls hard to 7000 rpm each gear and comfortable to 180 km/h before tapering off in power.

One day i'll get around to fitting the 790 intake cam.

SCCTrim · 08-23-2007, 10:00 PM

By simply leaving the intake cam in its stock configuration and advancing the exhaust cam 1 tooth you can expect a 2 to 4 ftlb increase in torque, and about a 5 hp loss on the topend.

I dunno that I would retard the intake, imo it would kill the topend more than I personally would want.

Something I noticed as well was that I get a very mild engine ping when very low in rpm's with the exhaust cam advanced. Probably upped my cr over the 10.5:1 by advancing the exhaust.

Looking forward to your dyno results....

ohiorider · 08-23-2007, 10:30 PM

Well, it seems to run just fine. First things first. Thanks to all you guys who gave me confidence to twist on those abomitable, tightly stuck cam cap bolts. I did the valve adjustment, and I'm happy with the results. The exhaust came out exactly where I calculated them, the intakes are within spec, although one is a loose .20mm gap. Not taking it apart for that. The adjustment really quieted down the valve train ... I almost miss the thrashing, I got so used to it.

Re the cam retiming .... sort of understand how the guys must have felt at Los Alamos in 1945 when they pushed the button .... like, what's gonna happen?

I did advance the exh and retard the intake per the info I posted in this thread. Seat of the pants, the bike appears to have much more torque just off 3000/3500 rpm, and I swear I thought I felt it coming on cam at around 4500. Since it was dark, and we have bunches of deer leaping around our roads, I thought I'd wait until tomorrow for a real road test.

I'd be interested in hearing from any of you who opened my photobucket link, if you'd let me know if the graphics were understandable. I had to do that just so I would understand what was happening inside.

I don't see how this retiming could hurt anything, but I've said that before. Only some time will give me that level of confidence.

Bob

LT · 08-23-2007, 10:43 PM

There are several threads about this at Delphi and other places, can't find any right now. Essentially, best results have been had by advancing exhaust cam 1 tooth, leaving intake alone. BTW, only works on 790cc, 360 degree engines. Tried it on my America, didn't work.
Edit- found one http://www.bonnevilleamerica.com/for...rue#Post192219

bonnieblackinfl · 08-23-2007, 11:02 PM

Rider, after reading my post I understand the confusion. The fact I was trying to make is the trade off in the opening and closing points with the modified/stock timing combonations. When I re-read it, I knew what I was talking about, but it came out wrong....sorry.

I am meerly suggesting that advancing the intake cam only, I think would give you a broader low-mid powerband. I believe you will gain more by packing the cylinder earlier, not later.

Your photobucket pics are right-on! I hope you don't mind that I saved them for myself. I started creating a very crude version of what you have when I started dabbling in cam timing for our bikes. You saved me a hell of a lot of headache

Good luck with the dyno, and if you get a chance..run the intake advanced and the exhaust stock.

Greg