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Evolution of a HotRod - Part 6 Flywheel (Read 152 times)
DragBikeMike
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #45 - 07/21/21 at 20:20:45
 
Acceleration improved slightly in the lower gears, but slowed down a bit in fifth gear???  In addition, maximum rpm in 5th gear dropped by 250 (6050 rpm vs 6300 rpm).  What’s goin on here?

This is a big single-cylinder engine with a power curve that flattens out right about 5500 rpm.  My previous dyno pulls with this cam show the engine makes good power past 5500, but that power really isn’t increasing.   It’s flat from 5500 to almost 7000.

Aerodynamic drag goes up by the square of the bike’s speed.  The amount of horsepower required to power the bike increases by the cube of the increase in speed.  We have a flat power delivery struggling against an exponentially increasing power demand.
 
With a single cylinder engine, you get one shove (power stroke), followed by three parasitic strokes (exhaust, intake, compression).  That one shove, the power stroke, must provide enough motive force to sustain rotation through the remaining three strokes, plus overcome all the parasitic losses (friction, valve springs, pumping exhaust, compression, etc.), plus overcome the exponentially increasing counterforce presented by the wind.  Without the energy stored in the heavy flywheel, the rotating assembly can’t maintain forward motion, it loses ground to the wind.
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DragBikeMike
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #46 - 07/21/21 at 20:22:15
 
Is the light flywheel worth the effort and expense?  Depends what you are looking for.  If you are into stop-light drag racing, you might like the small flywheel.  If you spend a lot of time on the open road where you want the best top gear performance, the heavy wheel is for you.

I was surprised that the 3rd gear acceleration numbers didn’t show a bigger improvement.  We took a lot of weight off that rotating assembly.  Seemed like it should have made a bigger difference.   But the stopwatch don’t lie.
 
It will be interesting to see what happens when I add more compression or displacement.  I don’t know if these old bones have enough gas in the tank to get into the regimen of swapping flyhweels with every engine combination (head, cam, & CR).  We’ll see how things shake out.
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DragBikeMike
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #47 - 07/21/21 at 20:24:45
 
This completes the flywheel portion of the project.  The 3” flywheel was a wash.  It provided a small improvement in the lower gears but a slight loss of performance in top gear.  The 3” flywheels don’t grow on trees; you won’t find one on Amazon or eBay.  It was not hard to install but required some special tools.  I would say that most of the Savage crowd would find little benefit from this modification, and some would be disappointed.

Performance remains about where we left it at the conclusion of Part 5.  Moving forward, I will leave the small flywheel in place until circumstances dictate another look.
 
Next stop on the Power Train?  Cylinder head.  Let’s see what happens when we slap on a head with significantly better flow-bench numbers.  Part 7 will install a ported head.

At this point, I have done 174 WOT acceleration pulls to dial in the different combinations.  There’s a little over 2450 miles on the engine since it was restored to box-stock configuration.  The old girl is still holdin up good.  No leaks.  No ugly noises.  Not using any oil.  Just a bit of oil accumulating in the catch-can.  It’s still a solid motor.

I hope some of you find this project informative and can use the data I collect to help make decisions on your own project.  If you have suggestions or comments on my test methods, post a reply so we can discuss.   As mentioned earlier, if you have a particular component or modification that you would like to see included, let me know and we can collaborate.
 
Best regards, Mike          
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zevenenergie
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #48 - 07/22/21 at 03:39:07
 
Great howto...

I'm not really surprised at the result.
I did the same with a 70cc 2stroke engine.
I replaced the steel centrifugal coupling on the crankshaft with an aluminum one and made the flywheel 70% lighter.

It gives a better throttle response in neutral.
But with acceleration on the road no difference at all.

What was clearly noticeable was that the braking distance became shorter.

The acceleration is mostly determined by power and the weight of the bike and various resistances.
The engine therefore accelerates too slowly to be bothered by the inert flywheel.

The braking decereration take place in a shorter period of time. And especially at high revs there is a lot of energy in the flywheel.
Which then has to change relatively faster in rotation than when accelerating.

(Sorry for my poor englisch).

I'm curious how your flywheel brakes.
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Armen
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #49 - 07/22/21 at 04:30:37
 
Thanks for the detailed write up!
Have to say, I'm surprised at the results. I remember Dave got some significant measurable improvements with the lighter flywheel.
Hmmmm
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LANCER
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #50 - 07/22/21 at 10:08:45
 
When doing your timed runs how do you start and stop your stopwatch ?
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #51 - 07/22/21 at 12:41:58
 
As Armen stated, my timed runs did show a pretty big drop in my 0-60 mph time.  I did about 5 runs with each flywheel using my GPS that records 0-60 times. I did the runs with the big flywheel in the morning and the runs with the small flywheel later that same day.  My times with the larger flywheel were around 5.5 seconds, and I got them down to around 5 seconds with the lighter flywheel.  Perhaps some of that difference was me just getting better at leaving the line and shifting gears.........with my tall gearing I only have to shift once as I reach 60mph in second gear.

The weird thing was that my 1/4 mile times were almost identical with either flywheel.  I did not understand if my data was accurate....or if I could not leave the line as aggressively - it was weird as it just didn't seem to be logical.

In order for my 0-60 times to be better - but my 1/4 mile times to be equal.....that would require the bike to be slower somewhere after I got to 60 and was going to the from end of the 1/4 mile!  (I am not home right now where I can see what my MPH was at the end of the 1/4 mile).

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DragBikeMike
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #52 - 07/22/21 at 15:52:51
 
Zevenenergie I think you articulated the braking issue quite nicely.  That's something I hadn't considered, but it is certainly a valid point.  The absence of flywheel should most certainly improve compression braking.

Lancer I do the timing off videos.  I record my runs using a GoPro camera and then do the timing in the comfort of the climate controlled DBM laboratory.  It works great.  All the pulls are done on the secret DBM closed-course test-track, in exactly the same location for each gear.  I try to always do the tests under similar atmospheric conditions.  Not perfect but the best I can come up with.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1577664388/0#5

Armen I agree.  I was actually very surprised.  I figured the lighter wheel would make a big difference.  After I did the timing pulls, I decided to see what I could dig up on Google.  I kept finding discussions where gearheads spoke about other gearheads loosing top speed when they installed a lighter flywheel, but I could never find a direct link to the source.  The discussions always wandered around with a bunch of theoretical back & forth.  I could never find the "horse's mouth".  Apparently, there are others who have experienced the same phenomenon.  Dave's experience, in a way, mirrors mine.  His 0-60 dropped, but 1/4 mile ET remained unchanged.  That indicates he accelerated faster in the low gears, and slower in the high gears.

Dave it would be great if you could find that old MPH.  
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #53 - 07/22/21 at 21:31:44
 
DBM:  really appreciate all of the work you are doing to develop this engine. Here's my quandary: going through my 10 years of 'motorcycle classics' , I constantly wonder why 500 singles, GoldStar, Manx, G50, Velo, 2-valve heads, are shown with higher HP and much higher top speed, compared to our 4-valve head, higher volume lump?
All of these bikes are internationally known, S40 not so much.
The only modern single with greater output is KTM, especially the '390r' which is leading the MotoAmerica novice class against Ninja 400s.
What makes these older singles so powerful?
It's not all due to CR !
Cheers!  Cool
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #54 - 07/22/21 at 22:37:05
 
Don't get fooled by the HP numbers of older bikes. They used to measure HP at the crank instead of at the wheel so those numbers will be higher than if they were measured at the wheel.
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zipidachimp
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #55 - 07/22/21 at 22:46:37
 
Manx 500....130, 140 mph ?
1. https://en.wikipedia.org/wiki/Norton_Manx

1961 Matchless G50 specifications
Type: Air-cooled SOHC single
Capacity: 496cc (500cc)
Bore & Stroke: 90mm x 78mm
BHP: 51 @ 7200rpm
Maximum speed: 135mph
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Re: Evolution of a HotRod - Part 6 Flywheel
Reply #56 - 07/23/21 at 04:09:36
 
zipidachimp wrote on 07/22/21 at 22:46:37:
Manx 500....130, 140 mph ?
1. https://en.wikipedia.org/wiki/Norton_Manx


I just finished reading a book about the Norton Manx 350 and 500 race bikes.  The factory worked very hard trying to get more performance out of the bike, and each year they seemed to find one or two more HP.  The book stated that in 1961 they were up to 53HP.  The bike was a true race bike and had a very narrow rpm range where it ran well - it had to be wound up to make power and be competitive.  They were able to find a few more HP - but only a few riders could use the extra power productively and keep the engine revved up where it made the extra power.....most riders were faster around the track with the 53HP engine.

The Manx engine is not an engine that can be ridden on the street from what I have read.  It is a race engine and it has horrible manners when out in public.  The engine has to be kept up in the power band to run well.

I believe the cylinder head is the limiting factor in the design of the Savage.  When I look at the intake and exhaust ports of engines that make big HP they are smooth and straight in comparison to the Savage.

The DR650 engine is very similar to the Savage engine - but it was able to make 46HP in some countries (in some countries it was detuned to 34HP likely to comply with restrictions).

I believe Suzuki was engineering a small capacity Cruiser type motorcycle that was not a performance bike, and they intentionally designed it with good torque values and made it easy to ride.  It is likely the Savage was designed to be a low HP entry level bike that was in compliance with the restrictions on power/size that are required in the places where the bike is sold in larger numbers (The US is only a small fraction of the world motorcycle sales).  It is also very likely they didn't want to make if faster than their bigger and more expensive V-Twin bikes.

The Savage engine can be made to run really nicely and be noticeably more powerful if you follow Drag Bike Mikes excellent threads - but it will never be able to make the kind of HP that a modern performance engine can make.   My Cafe' bike has a Wiseco Piston, Stage 3 cam, some head work, intake and exhaust improvements,  and a lightened flywheel.  The bike weighs about 320 pounds and accelerates about the same as an 883 Sportster up to legal road speeds.....and that is quick enough to satisfy my speed needs.  Sport bikes can easily leave me behind - but I still have plenty of power to keep my happy and with my increased power and taller gearing I can cruise at 75mph easily.
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