Time for a dyno test

[49er]

Hi all

I have been reluctant to dyno the 850 because I couldn't find any previous records/results on Google or the GSR search feature.
I recently came upon dyno session results in "Two Wheels" magazine done in Sydney in '79 on a new GS850GN. The torque curve is very flat from 3500-5000rpm which would probably minic what many owners report, and that they really turn on from 7000rpm onwards. I now had a base line to work from.

Here are the links:

http://i155.photobucket.com/albums/s309/49er_photos/MainAnalysis.jpg

http://i155.photobucket.com/albums/s309/49er_photos/AussieDyno.jpg

http://i155.photobucket.com/albums/s309/49er_photos/TorqueHP-Speed.jpg

http://i155.photobucket.com/albums/s309/49er_photos/TorqueHP.jpg

The bike is stock with the following exceptions:

1. Capacity has been increased from 844cc to 894cc.
2. Compression ratio increased from 8.8-1 to 10.5-1 (JE Pistons)
3. Electronic Ignition installed - Boyer Bransden MP digital.
4. Cycleworks 4-1 exhaust.
5. Minor jetting changes made (Pilot circuit)

I asked my dyno man what scale the Aussie tests would have been done on. He thought that it in the day they would have been STD or DIN. He ran mine on both SAE and STD. I have based my comparisons on the SAE scale, which is 3% less favourable. Using the STD scale, my max HP at the wheel was 75hp.

I converted torque and hp figures from nm to ft lbs and Kw to HP from the Aussie dyno session. By comparison, I have increased max HP by 25% and torque by 38%.
Suzuki claims the 850's put out 77hp at the crank, so my rear wheel increase is significant.
They claim max torque at 7500rpm, mine is now at 6700rpm.

These results have been achieved whilst running the stock VM26SS carbs and stock airbox. I know that the "Pods Brigade" will tell me that I could have had 2-3 more hp by going down that track, but I'm certain that the torque curve wouldn't have been as attractive.

The engine has now done over 5k since the rebuild. For those who are interested, that annoying cam knock has not yet returned.

Ian

[tkent02]

38 % increase in torque sounds great...
Are these custom pistons? Can't find any reference to pistons for an 850 on the JE website.
Looking to do something similar to my 750, I have 850 cylinders waiting to go on...

[49er]

38 % increase in torque sounds great...
Are these custom pistons? Can't find any reference to pistons for an 850 on the JE website.
Looking to do something similar to my 750, I have 850 cylinders waiting to go on...

Yes, these are custom pistons. I supplied JE with moulds of the 850 chamber shape and the stock crown shape. I told them that I wanted to run 10.5-1 CR and gave them the chamber volume and new squish area needed to achieve that. I wasn't changing the cams, so stock valve pockets and squish areas were to be maintained. I asked them to supply the pistons as close as possible to the stock weights to help maintain good engine balance. They confirmed my calcs then got them to within 9 grams of the stock weights. I machined extra metal off the insides of the crowns and gudgeon posts to reduce the weights to stock figures.

If you were to fit these pistons to a 750, you would have something special. By using the 850 jugs, you can maintain a 2mm wall thickness on the sleeves when boring to these pistons. This allows better heat dissipation and superior rigidity on the barrel walls.
Most big bore kits supply pistons that are heavier than stock, so the engine balance is compromised unless the crank is machined. I wanted to maintain the smooth balance that my the 850 was born with without the hassle of splitting the cases.
PM me if you wish to go down this track. I can offer some guidance when it comes to the safe areas for removal of metal to maintain good balance.

[mac1170]

dyno

gday 49er, just wanted to know,you used the stock cams but did you dial them in to a differant lobe centre, to get better torque at that rpm, also when you did the rebuild did you clean up the ports at all, as they are pretty good figures, regards

[49er]

gday 49er, just wanted to know,you used the stock cams but did you dial them in to a differant lobe centre, to get better torque at that rpm, also when you did the rebuild did you clean up the ports at all, as they are pretty good figures, regards

Giday Mac
The stock cams are still timed at 110 degs. I did do a clean up grind to bring the lobs back to spec. These 2 valve cams have poor bearing support so the cams whip/flex at high rpms. This causes the lobs to wear to a tapered shape at their points. By doing a clean up grind, I have slightly advanced the opening and closing ramps. The valves also open and close slightly faster than stock. The lift is still stock as are the valve springs.

I have blueprinted the inlets. #3 port was slightly offset to the carb flange rubber. No clean up was needed on the ports. I did radius two inlet valve pockets that had rough ridged machining left by the factory. #3 had quite a bit of blending required to fix it. IMO, suzuki got it just right with their port finish. You need to maintain a slightly rough surface to optimise fuel atomisation. A super smooth/shinny surface will cause fuel droplets to form on them causing incomplete combustion.
I'm very happy with these results. HP wise, it now rivals a stock GS1000.

[49er]

gday 49er, just wanted to know,you used the stock cams but did you dial them in to a differant lobe centre, to get better torque at that rpm, also when you did the rebuild did you clean up the ports at all, as they are pretty good figures, regards

I've given the cause of the torque peak at a lower rpm from the factory figure, quite a lot of thought. I believe that it comes down to getting the balance of the mods right.

IMO, there are 3 significant changes from a stock 850 that have contributed to this.

1. The stock setup runs a 4-2 exhaust with a balance tube. There's not as much scavenging assistance with these designs. The design of my 4-1 has a signifcant influence on low to midrange torque without dumping power off at the top end. I believe the collector and slash design contribute to its great range of power.
2. The increase in CR to 10.5-1 provides more efficient combustion, increasing torque throughout the rev range. I run 98 octane fuel.
3. The fitting of a digital electronic ignition has enhanced the torque and power ranges for the following reasons. The '79 850's had points and a cetrifugal advance nechanism. Advance was all in by 2500rpm (37 deg).
I don't run the springs and weights and digitally now have advance all in at 4500rpm (39 deg).
I am sure that the retarding of the advance in the 2500-4500rpm area has contributed to the increase in torque in that part of the rev range and slightly above it.

All my carb tuning was done by feel and plug readings. The dyno session I have recorded here was the first time the bike has seen one, to my knowledge (a PO might have done so!!). The big advantage in testing on the dyno is that it confirms the air/fuel ratios that the engine is working in under loads. The ideal ratio is between 12.5/1 and 13.6/1 The closer to 13.6/1 that you can get, the more torque you can produce. Figures higher than this will produce more HP but at the expence of more heat and possible detonation. I did a second session a couple of days later, where I leaned the needle and increased the mains with slightly more air into the box. I lost 2ft/lbs of torque and 2 hp. The air/fuel ratios in the 7000-10000rpm range went down to 12.3/1

The present setup gives exellent performance in 5th gear, from 90kph(4000rpm) to 160kph (7000rpm). This is the range that most of your passing is being done.

Running 98 octane fuel has allowed me to add an extra 2 degs of advance. It also has meant that I don't get heating issues with the higher CR, and consequetly there is no need to run an oil cooler.

[mac1170]

dyno

gday 49er, what you were saying about the 4 into 1 exhaust, and the 98 octane, sounds fair, have you tried running colder plugs, on the strip this normally helps to pick up the mile an hour regards

[KiwiGS]

Hey Ian.
Just got back to work after the holiday.
Those figures look real nice. I should have taken up your offer of a ride!
Lucky for you I didnt though.
After I saw you I took the cbr to Palmy and crashed into a F*&king sheep on the way home. Not nice at all.
Anyway hope you are getting out in the great weather
Thanks for the beer to mate it was just the thing on a hot old bay day
Cheers

[49er]

gday 49er, what you were saying about the 4 into 1 exhaust, and the 98 octane, sounds fair, have you tried running colder plugs, on the strip this normally helps to pick up the mile an hour regards

Giday Mac,
Thanks for the feedback from your drag strip experiences. I haven't tried running colder plugs because the stock NGK B8ES are heading towards the colder part of the heat range anyway. I believe that you should run your plugs as hot as possible for road use. I haven't experienced any detonation at all, even when running 95 octane at the stock advance settings. Running 98 octane, I have tried up to 40 degs advance but found that I could feel a slight drop off in torque in the 6000-8000rpm range. I think that the engine was over advanced in this part of the rev range. I still had no audible detonation though!


The real benefit from the dyno session has been the ability to identify the air/fuel ratios at given rpms under load. I found that for any given set of revs, the AFR leaned by 1 full ratio while under 20% load. This isn't always obvious when relying on plug read feedback.
Cheers

[49er]

Hey Ian.
Just got back to work after the holiday.
Those figures look real nice. I should have taken up your offer of a ride!
Lucky for you I didnt though.
After I saw you I took the cbr to Palmy and crashed into a F*&king sheep on the way home. Not nice at all.
Anyway hope you are getting out in the great weather
Thanks for the beer to mate it was just the thing on a hot old bay day
Cheers

Jeez mate, don't tell the Aussies about the sheep!
Seriously though, how's the body and the bike? Those little woolly varmits can make a huge mess of bikes and cars, especially at speed. Carlos Sainz hit one in our National Rally at 190kph some years back. The front end of his Subaru and the sheep both disintegrated. He was quite badly hurt that day.
Good to catch up and share a beer. Get that GS1000 back on the road.

[Silvermachine81]

Ahhh, Hawkes Bay Summers.......Why did I ever move to Christchurch.......Oh Yeah, To get away from Flaxmere...Gang Members Staunching you out...The pay rates/lack of career options unless your a tradesman...and the fact that i'd spent my whole life there and wanted to see some more of the world!
I nearly forgot about that in that little dreamy moment remembering the good times!!

Now if only Chch could have Hawkes Bays summers, winters that didnt chill you to the bone, Friendlier people and a few roads that actually have some bends in them (apart from the Akaroa racetrack)!!!!

Guess you cant have everything.....

[KiwiGS]

Jeez mate, don't tell the Aussies about the sheep!
Seriously though, how's the body and the bike? Those little woolly varmits can make a huge mess of bikes and cars, especially at speed. Carlos Sainz hit one in our National Rally at 190kph some years back. The front end of his Subaru and the sheep both disintegrated. He was quite badly hurt that day.
Good to catch up and share a beer. Get that GS1000 back on the road.

The bike is not too bad the sheep is better and the body is a distant 3rd.

The left side of tank,left exhuast can, left side fairing, top fairing and blade are all scratched/holed.The front brake lever, back brake, pack rack and mirror are all broken.

The sheep ran away!

I had to ride for two hours with a disslocated shoulder, wrecked knee and various other cuts and bruises.
Just lucky I was wearing the right gear! The leathers are a bit sick and the helmet and gloves are thrown away.
Other than that it was a great holiday!
Cheers

[Silvermachine81]

I had to ride for two hours with a disslocated shoulder, wrecked knee and various other cuts and bruises.

Other than that it was a great holiday!
Cheers

Obviously you have huge testicular fortitude :-)

[KiwiGS]

Obviously you have huge testicular fortitude :-)

Nope. I'm scared of the dark:-D

[49er]

[quote=Silvermachine81;752926]Ahhh, Hawkes Bay Summers.......Why did I ever move to Christchurch.......Oh Yeah, To get away from Flaxmere...Gang Members Staunching you out...The pay rates/lack of career options unless your a tradesman...and the fact that i'd spent my whole life there and wanted to see some more of the world!
I nearly forgot about that in that little dreamy moment remembering the good times!!

Now if only Chch could have Hawkes Bays summers, winters that didnt chill you to the bone, Friendlier people and a few roads that actually have some bends in them (apart from the Akaroa racetrack)!!!!

"Unless you are a tradesman". Funny you should mention that I was in the early days. I still manged to leave HB and travel. Returned in '87 and havn't looked back. Even got interested in bikes again! We must catch up some time. I was last in Chch in November for the Steely Dan Concert.