Change of cranskshaft pulley to lightweight.

Change of cranskshaft pulley to lightweight.

Author
Discussion

Stan Weiss

260 posts

147 months

Thursday 19th January 2017
quotequote all
Mignon said:
It will show up as a "number" on a screen when a dyno is trying to do something that it's not been properly programmed for. To call that number horsepower is not even remotely correct though. Obviously when an engine is accelerating it is storing kinetic energy in its rotating and reciprocating components. That leaves less energy, or force, available to twist the torque arm on which torque is measured and in the absence of any correction for this stored energy will result in a smaller torque number compared to a steady state test.

However with any decent modern dyno software you should be able to correct for the moment of inertia of the engine component masses when doing an acceleration test. In fact there's a blindingly simple way of finding out what that correction factor should be even when you have no idea what the moments of inertia are.

Simply run the engine at two different acceleration rates. Adjust the inertia factor until both runs show the same gross torque numbers (measured torque plus inertia absorbed torque). That should bring you back very closely to what the engine will show at steady state and should of course now compensate properly for any other acceleration rate, even a variable acceleration rate.

The problem with trying to define any number showing on a dyno screen as being extra horsepower due to lighter components because of an accelerating run test is that this notional number will not show up at all when the engine is not accelerating. i.e. the car will not have a higher top speed which "proper" additional horsepower will clearly produce. It will not go any faster up a steep hill when acceleration rate is low or zero. It will not manifest much if at all in high gears.

All it will do is make the engine, and hence the car, faster accelerating, very briefly, in low gears. In fact if the vehicle is grip limited in low gears then it will make no difference whatsoever. By the time the vehicle is in a high enough gear to be able to take full throttle then the inertia effect will have dissipated anyway.
By your logic there would be no real difference in running a 10 pound flywheel verses a 50 pound flywheel.

If I ignore the torque / HP numbers shown on the dyno. The lighter flywheel will let the same engine complete a 600 RPM per second acceleration test in less time. Time is what matters to me in a race application. I could care less what happens on the highway at 75 mph in high gear when it goes WOT.

Stan

227bhp

10,203 posts

127 months

Thursday 19th January 2017
quotequote all
Stan Weiss said:
By your logic there would be no real difference in running a 10 pound flywheel verses a 50 pound flywheel.

Stan
No because a FW has a larger radius and that matters. The further away (radially from the crank) the weight is lost the more effect it has.

PeterBurgess

775 posts

145 months

Thursday 19th January 2017
quotequote all
Spot on Stan. The guy that worked the inertia rollers at Silkolene told me how they used it when he saw my new rollers in 2010 (wow, they are getting old now!). At Silkolene they altered everything they could, thinner chains, rubber contact, oil thickness etc to get the max power at the wheels, this translated to winning on the track even when the 'static' bhps were the same. The one that showed the best wheel power on the inertia was always quicker on the track than one that showed less even when engine dyno under equal operating conditions showed same power.
If Superflow say use same acceleration rate for all tests to be comparable it cannot be as easy as making a few adjustments to the software here and there, I would think Superflow would do it automatically if they could. Never mind, I will be happy running it the way Superflow tell me to. It has been hard enough sorting it all let alone thinking Superflow don't know what they are doing with acceleration rate stuff! Today we finally sorted all the input/output water pumps and set the return cistern float levels correctly (otherwise the return pump sucks air and doesn't self prime). We ran the water supply ( bypassing the pau) all day to check for flow and leaks. We now need to put two fresh 12v batteries on the dyno, check the starter motor system and do the initial calibration of the pau. My mate is making input adapters for various cranks for me. Another mate is fitting a girder system with block and tackle above the dyno so we can get the engines onto the dyno. I was hoping end Jan but looks like we will be late Feb early March to get an engine on it.
Pic shows windows98 all in one pc we have sorted for the dyno.

Peter





Boosted LS1

21,165 posts

259 months

Thursday 19th January 2017
quotequote all
^ So you're going to dyno engines in a jig now? Nice smile

Stan Weiss

260 posts

147 months

Thursday 19th January 2017
quotequote all
227bhp said:
No because a FW has a larger radius and that matters. The further away (radially from the crank) the weight is lost the more effect it has.
True @ 600 RPM sec acceleration rate 10 lbs @ 6" radius needs torque of 4.88 and @ 3" radius it needs torque of 2.44. HP will vary based on the actual engine RPM as will weight velocity but torque stays constant like rate of acceleration. So YES, the distance from the crankshaft center line and the amount of weight removed will vary the results seen.

Stan

________________________Rear______Aero____Rolling___________Rear_W__Accele___Time__Rate
RPM______MPH___Velocity__Wheel____dynamic__Resist.__Elapsed___Horse__ration__Differ__RPM
________________ft/sec__Torque___Drag_-_HP___HP______Time_____Power__in_G's__ential__Sec

__0.0____.000_____.000____0.00______.000____.000____.0000______0.00__0.0000__0.0000__0.0
500.0___8.925___13.090____2.44______.000____.000____.8333______0.23___.4882__0.8333600.0
_1000.017.850___26.180____2.44______.000____.000___1.6667______0.46___.4882__0.8333600.0
_1500.026.775___39.270____2.44______.000____.000___2.5000______0.70___.4882__0.8333600.0
_2000.035.700___52.360____2.44______.000____.000___3.3333______0.93___.4882__0.8333600.0
_2500.044.625___65.450____2.44______.000____.000___4.1667______1.16___.4882__0.8333600.0
_3000.053.550___78.540____2.44______.000____.000___5.0000______1.39___.4882__0.8333600.0
_3500.062.475___91.630____2.44______.000____.000___5.8333______1.63___.4882__0.8333600.0
_4000.071.400__104.720____2.44______.000____.000___6.6667______1.86___.4882__0.8333600.0
_4500.080.325__117.810____2.44______.000____.000___7.5000______2.09___.4882__0.8333600.0
_5000.089.250__130.900____2.44______.000____.000___8.3333______2.32___.4882__0.8333600.0
_5500.098.175__143.990____2.44______.000____.000___9.1667______2.56___.4882__0.8333600.0
_6000.0_107.100157.080____2.44______.000____.000__10.0000______2.79___.4882__0.8333600.0
_6500.0_116.025170.170____2.44______.000____.000__10.8333______3.02___.4882__0.8333600.0
_7000.0_124.950183.260____2.44______.000____.000__11.6667______3.25___.4882__0.8333600.0
_7500.0_133.875196.350____2.44______.000____.000__12.5000______3.49___.4882__0.8333600.0
_8000.0_142.800209.440____2.44______.000____.000__13.3333______3.72___.4882__0.8333600.0
_8500.0_151.725222.529____2.44______.000____.000__14.1667______3.95___.4882__0.8333600.0
_9000.0_160.650235.619____2.44______.000____.000__15.0000______4.18___.4882__0.8333600.0
_9500.0_169.575248.709____2.44______.000____.000__15.8333______4.42___.4882__0.8333600.0
10000.0_178.500261.799____2.44______.000____.000__16.6667______4.65___.4882__0.8333600.0
10500.0_187.425274.889____2.44______.000____.000__17.5000______4.88___.4882__0.8333600.0
11000.0_196.350287.979____2.44______.000____.000__18.3333______5.11___.4882__0.8333600.0
11500.0_205.275301.069____2.44______.000____.000__19.1667______5.35___.4882__0.8333600.0
12000.0_214.199314.159____2.44______.000____.000__20.0000______5.58___.4882__0.8333600.0

============



_________________________Rear______Aero____Rolling___________Rear_W__Accele___Time__Rate
RPM______MPH___Velocity__Wheel____dynamic__Resist.__Elapsed___Horse__ration__Differ__RPM
________________ft/sec__Torque___Drag_-_HP___HP______Time_____Power__in_G's__ential__Sec

__0.0____.000_____.000____0.00______.000____.000____.0000______0.00__0.0000__0.0000__0.0
500.0__17.850___26.180____4.88______.000____.000____.8333______0.46___.9764__0.8333600.0
_1000.035.700___52.360____4.88______.000____.000___1.6667______0.93___.9764__0.8333600.0
_1500.053.550___78.540____4.88______.000____.000___2.5000______1.39___.9764__0.8333600.0
_2000.071.400__104.720____4.88______.000____.000___3.3333______1.86___.9764__0.8333600.0
_2500.089.250__130.900____4.88______.000____.000___4.1667______2.32___.9764__0.8333600.0
_3000.0_107.100157.080____4.88______.000____.000___5.0000______2.79___.9764__0.8333600.0
_3500.0_124.950183.260____4.88______.000____.000___5.8333______3.25___.9764__0.8333600.0
_4000.0_142.800209.440____4.88______.000____.000___6.6667______3.72___.9764__0.8333600.0
_4500.0_160.650235.619____4.88______.000____.000___7.5000______4.18___.9764__0.8333600.0
_5000.0_178.500261.799____4.88______.000____.000___8.3333______4.65___.9764__0.8333600.0
_5500.0_196.350287.979____4.88______.000____.000___9.1667______5.11___.9764__0.8333600.0
_6000.0_214.199314.159____4.88______.000____.000__10.0000______5.58___.9764__0.8333600.0
_6500.0_232.049340.339____4.88______.000____.000__10.8333______6.04___.9764__0.8333600.0
_7000.0_249.899366.519____4.88______.000____.000__11.6667______6.51___.9764__0.8333600.0
_7500.0_267.749392.699____4.88______.000____.000__12.5000______6.97___.9764__0.8333600.0
_8000.0_285.599418.879____4.88______.000____.000__13.3333______7.44___.9764__0.8333600.0
_8500.0_303.449445.059____4.88______.000____.000__14.1667______7.90___.9764__0.8333600.0
_9000.0_321.299471.239____4.88______.000____.000__15.0000______8.37___.9764__0.8333600.0
_9500.0_339.149497.419____4.88______.000____.000__15.8333______8.83___.9764__0.8333600.0
10000.0_356.999523.599____4.88______.000____.000__16.6667______9.30___.9764__0.8333600.0
10500.0_374.849549.779____4.88______.000____.000__17.5000______9.76___.9764__0.8333600.0
11000.0_392.699575.959____4.88______.000____.000__18.3333_____10.23___.9764__0.8333600.0
11500.0_410.549602.139____4.88______.000____.000__19.1667_____10.69___.9764__0.8333600.0
12000.0_428.399628.319____4.88______.000____.000__20.0000_____11.16___.9764__0.8333600.0

stevieturbo

17,229 posts

246 months

Thursday 19th January 2017
quotequote all
I rather doubt the OP is at a level where he finally needs to fit a silly pulley to scrape that last fraction of performance to enable him to win races, having already carried out every worthwhile modification possible to get to this last ounce of desperation.

However...if he wants a shiny colourful pulley...go for it.

Boosted LS1

21,165 posts

259 months

Thursday 19th January 2017
quotequote all
stevieturbo said:
I rather doubt the OP is at a level where he finally needs to fit a silly pulley to scrape that last fraction of performance to enable him to win races, having already carried out every worthwhile modification possible to get to this last ounce of desperation.

However...if he wants a shiny colourful pulley...go for it.
Harsh but probably true.

PeterBurgess

775 posts

145 months

Friday 20th January 2017
quotequote all
Not for us to make a moral judgement on whether to purchase a pulley set or not. I think we have explained it will make a marginal improvement in acceleration capability. If the OP can be assured his engine will not disintegrate from unwanted harmonic imbalances exacerbated by crank pulley removal or suffer extreme NVH it must surely be his personal choice, mind you it is still his choice should it cause problems! Folk will be arguing over what colour next smile

Peter

Mignon

1,018 posts

88 months

Friday 20th January 2017
quotequote all
Ok so some people apparently want to see what bhp equivalent this lighter crank pulley might be worth. I programmed a generic 4wd sports car into my vehicle simulation software with 1300kg weight inc driver, 250 bhp, 5 speed gearbox, 1.1g grip off the line with really good tyres. Time to 100 mph was 12.487 seconds. I reduced the engine's moment of inertia by 5 lbs mass at an average radius of 2" from the crank centreline. New 0-100 mph time 12.460 seconds. I put the inertia back to stock and added bhp until the time was again 12.460 seconds.

The answer on a 250 bhp car is this pulley is equivalent to having an extra 0.53 bhp. If anyone thinks that's worth spending money on then by all means go for it.

PeterBurgess

775 posts

145 months

Friday 20th January 2017
quotequote all
So, at least the money spent would achieve something and not a total waste like some goodies are.
Don't forget what Inlineengine mentioned, reduce parasitic losses and bhp does go up. Most manufacturers will spec the water pump to give adequate flow under slow conditions. Use the care more spiritedly and not mess about in traffic jams and you can afford to slow down the water pump, especially to reduce cavitation at high rpms. Typically we see 2 bhp more on a race MGB when we run the water pump slower. So maybe 2.53 bhp on your 250 bhp engine. Reduce the losses due to A/C pump and power steering pump and you have even more of a gain......looks like the 10-15 could be achievable and not an instant gut feeling it wouldn't show more bhp?.....mind you the RCM kit does say it retains std pulley sizes smile

Peter

texaxile

Original Poster:

3,289 posts

149 months

Friday 20th January 2017
quotequote all
stevieturbo said:
I rather doubt the OP is at a level where he finally needs to fit a silly pulley to scrape that last fraction of performance to enable him to win races, having already carried out every worthwhile modification possible to get to this last ounce of desperation.

However...if he wants a shiny colourful pulley...go for it.
Ha ha, it's not about colourful pulleys stevie ( I'd have opted for black) and your are in fact correct, I'm way behind a level of such need. What I was actually trying to get the measure of were whether the spurious claims of 10-15 were true and if indeed the changing of a pulley would be detrimental to the harmonics and thus reliability of the engine. I was also interested in the possibility of getting a power gain via a relatively simple and easy route. It would seem that there are others here with some great insight and knowledge who have answered my question and saved me spunking cash on a bit of gucci engine bling.

There was no definitive answer that could be found elsewhere hence I asked here and I'm glad I did. Thanks to all those who replied.

Years ago when we were tuning and others were racing Starion and Lancer turbo's the trick was to get as much power running standard boost as possible, then we would look to increasing boost and fuel pressures etc , as increasing boost came with its own set of problems. In this case I was thinking along the same lines.



Mignon

1,018 posts

88 months

Friday 20th January 2017
quotequote all
Mignon said:
Ok so some people apparently want to see what bhp equivalent this lighter crank pulley might be worth. I programmed a generic 4wd sports car into my vehicle simulation software with 1300kg weight inc driver, 250 bhp, 5 speed gearbox, 1.1g grip off the line with really good tyres. Time to 100 mph was 12.487 seconds. I reduced the engine's moment of inertia by 5 lbs mass at an average radius of 2" from the crank centreline. New 0-100 mph time 12.460 seconds. I put the inertia back to stock and added bhp until the time was again 12.460 seconds.

The answer on a 250 bhp car is this pulley is equivalent to having an extra 0.53 bhp. If anyone thinks that's worth spending money on then by all means go for it.
Oops, I made a booboo. As well as reducing the engine's moment of inertia by 5 lbs at whatever radius I should also have reduced the actual physical weight of the base vehicle by 5 lbs as well because the lighter pulley is shedding genuine mass not just rotating inertia. Redoing the calcs with that accounted for the bhp equivalent rises to a lofty 0.88 bhp.

Mignon

1,018 posts

88 months

Saturday 21st January 2017
quotequote all
I just ran the same calculations on a more mundane vehicle. My own 109 bhp diesel shopping car. A 5 lb crank pulley weight saving made just 0.14 bhp difference to 100 mph. This is to be expected as the car is much slower accelerating than the 250 bhp sports car so the inertia energy loss is smaller.

I trust this has now put to bed any hopes that anyone might have had that a lightened crank, or even worse cam pulley which only rotates at half engine speed, make a scrap of difference to how a car goes. Something as big as a flywheel can make a difference if weight is removed at a large enough radius but that's about it.

stevieturbo

17,229 posts

246 months

Saturday 21st January 2017
quotequote all
Mignon said:
I just ran the same calculations on a more mundane vehicle. My own 109 bhp diesel shopping car. A 5 lb crank pulley weight saving made just 0.14 bhp difference to 100 mph. This is to be expected as the car is much slower accelerating than the 250 bhp sports car so the inertia energy loss is smaller.

I trust this has now put to bed any hopes that anyone might have had that a lightened crank, or even worse cam pulley which only rotates at half engine speed, make a scrap of difference to how a car goes. Something as big as a flywheel can make a difference if weight is removed at a large enough radius but that's about it.
For a while...Subaru did go from steel cam pulleys to plastic. Although with all the later VVT nonsense they had to go back to metal again

PeterBurgess

775 posts

145 months

Saturday 21st January 2017
quotequote all
You stick to your way Dave and I will happily go down the route of aggregation of marginal improvements. The current race stuff is going down the route of improving minutiae and if one ignores that one will be left behind. We have been watching it happen and non ultra light weight flywheels, rods and pistons engines get left behind! Folk are even microfinishing gearbox and axle internals. The early 90s are now 25 years ago!
http://www.mmsonline.com/articles/3-next-generatio...
Peter

Stan Weiss

260 posts

147 months

Saturday 21st January 2017
quotequote all
Mignon said:
Oops, I made a booboo. As well as reducing the engine's moment of inertia by 5 lbs at whatever radius I should also have reduced the actual physical weight of the base vehicle by 5 lbs as well because the lighter pulley is shedding genuine mass not just rotating inertia. Redoing the calcs with that accounted for the bhp equivalent rises to a lofty 0.88 bhp.
IMO, since we were talking about HP increase from the lighter part. The first calculate fits that better.

Stan

Stan Weiss

260 posts

147 months

Saturday 21st January 2017
quotequote all
PeterBurgess said:
You stick to your way Dave and I will happily go down the route of aggregation of marginal improvements. The current race stuff is going down the route of improving minutiae and if one ignores that one will be left behind. We have been watching it happen and non ultra light weight flywheels, rods and pistons engines get left behind! Folk are even microfinishing gearbox and axle internals. The early 90s are now 25 years ago!
http://www.mmsonline.com/articles/3-next-generatio...
Peter
Peter,
Watch some of those light weight internal engine parts. A part can be to light where it deflects and causes HP lose but yet not so light that it brakes. an example is wrist pins.

Stan

PeterBurgess

775 posts

145 months

Saturday 21st January 2017
quotequote all
I am very careful Stan, we don't run small pins in our Bs, we have dropped down to 17mm pins in our race A series. With regard to valves we do nut run 'skinny' valves. If we get lapped we may have to re think that smile
We were finding it hard to win races, cars creeping up like they had bigger engines when they hadn't, sorted when we went lightweight flywheel, rods and pistons.

Peter

Tango13

8,395 posts

175 months

Saturday 21st January 2017
quotequote all
Mignon said:
I just ran the same calculations on a more mundane vehicle. My own 109 bhp diesel shopping car. A 5 lb crank pulley weight saving made just 0.14 bhp difference to 100 mph. This is to be expected as the car is much slower accelerating than the 250 bhp sports car so the inertia energy loss is smaller.

I trust this has now put to bed any hopes that anyone might have had that a lightened crank, or even worse cam pulley which only rotates at half engine speed, make a scrap of difference to how a car goes. Something as big as a flywheel can make a difference if weight is removed at a large enough radius but that's about it.
Years ago the technical editor of Perfomance Bikes once wrote that the main benefit of lightening a crank was to the bank balance of the person doing the work.

I was advised by a bike engine builder not to lighten a crank due potential resonance issues at high RPM, the engine he built for me was low revving @9,700rpm but he had seen problems with IL4's running @14,000rpm+


PeterBurgess

775 posts

145 months

Thursday 2nd February 2017
quotequote all
I tuned an old P6 auto 3500 saloon today and it made me think of the marginal improvements.
We did some initial runs then played with the ignition timing and recorded the blue power line with the lowest torque and bhp. We noticed there was little effect above 2000 rpm playing with the timing so we looked for a bottle neck. Someone had messed with the inlet tube attached to the drum-type air filter housing and it no longer had the small radiused entry to the pipe. We tapped it back into shape with a ball pein end of a hammer and a nylon mallet. The resultant improvement is shown in the middle dark red torque and power line, only a little more power but all welcome. The higher tourquoise line was what would be achievable with K&N cone filters straight onto the entrance of the SU carbs. The owner decided to go with the original filters (middle lines for torque and power) to keep the car original.

Peter