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 Post subject: Parasitic reduction: Pro/Con
PostPosted: Wed May 02, 2012 8:54 am 
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Joined: Fri Jul 29, 2011 9:08 pm
Posts: 30
In a recent thread started in a different section, the topic of veered away from the OP's intended discussion, and went into an interesting and opinionated discussion on the relative merits of using pulleys, EPS, EWP etc......

(I know you are all shocked, off topic discussion? strong opinions? On the internet? Oh my, such a rare thing!)

So, in an effort to continue the discussion, but not pollute the original thread, I'm attempting to capture the spirit of that discussion in a different thread dedicated to it.

There were some very interesting ideas presented there, perhaps worth preserving.

********* If I have copied anyone's notes, and they want them removed, just PM me, and I'll fix or edit as requested. I've gone back and gotten rid of the off topic fluff I put in that last thread on dwell tables etc... I would prefer that Simon's thread stay on topic and continue to be helpful to people wanting to learn about the pro-con(s) of using that function in the DTA. **********


Last edited by DTAS54 on Wed May 02, 2012 9:25 pm, edited 1 time in total.

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 Post subject: Re: Parasitic reduction: Pro/Con pg 1
PostPosted: Wed May 02, 2012 8:54 am 
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Posts: 30
The discussion began with a question revolving around alternator voltage, and how it varies. OP (Simon) had asked a question implying that he had voltages that were perhaps not always stable, admittedly without specifying that his car is a dedicated track car. What was missing in the OP's presentation was that he has a very aggressive over and under drive pulley system. Simon (OP) was inquiring about using a table that adjusted dwell by voltage.


stevieturbo wrote:
you seem to have a notion that voltage changes with rpm. Certainly on any car Ive ever worked at it does not.


DTAS54 wrote:
(Steve) your experience is invaluable. But it may also be limited to electrical systems running stock crank and alternator pulley systems with heavy duty batteries. A track car optimized for weight with a tiny battery and a virtually unstreetable set of pullies that will be fine between 4000 and 8000 rpm might not give you a stable voltage at idle or lower rpm. (of course you could argue don't use those pullies)


stevieturbo wrote:
TBH if you have an unstable electrical system, then you need to rectify that. There is more powered by electrics than just the coils. So why would you take risks ?
Lightweight is all good and well, but if it then poses a danger to the engine, is it really a smart move ?
Ive heard of other guys running lightweight alternators etc, and they seem to have a high failure rate. Surely a few extra kg's on a critical component for peace of mind is worth it ?
Or just buy a better specced lightweight alternator in the first place
A rock solid power supply is essential to any car IMO. Some people even use voltage regulated supplies on race cars to ensure it stays at 14v regardless, or else it all just stops.
Perhaps something worth considering, although it would add a little weight.


Last edited by DTAS54 on Wed May 02, 2012 6:19 pm, edited 2 times in total.

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 Post subject: Re: Parasitic reduction: Pro/Con page 2
PostPosted: Wed May 02, 2012 8:54 am 
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Posts: 30
Simon P. wrote:
The fact still remains that some of us are using VERY large alternator pulleys as well as or in addition to small crank pulleys and this is affecting available voltage quite a bit, especially in the lower RPM range . Sure, this is a choice but not one I'm willing to go back on. Reducing accessory drag to increase power is well established. There are even mechanical benefits to reducing accessory speed, notably eliminating water pump cavitation at higher sustained RPM's and less mechanical wear on some components like PS pumps (again, at sustained high RPM's). Does it have drawbacks? Yes. Is it for a daily driver with full stereo and power everything? No.
My own car idles around 1150RPM and actually can't recharge at that speed as the alternator ouput voltage is around 11V. There's nothing the regulator can do about that. Using the compensation table could help me here. Obviously what little time I spend idling I try and not use too many accessories. The cooling fan is actually all that I run at idle and even it's on a thermostat so not constantly running. Although I can't be 100% sure I think adjusting dwell based on my voltage range (11V idling, 12V at 1300RPM, etc) could help smooth out my idle enough to be felt. Running a fixed dwell may well work fine if your voltage regulator is doing it's job throughout your RPM range but as mentioned this isn't always the case.


lumley32 wrote:
and correct me if I’m wrong but....

if you very the speed that much then all you are doing is losing power from the alternator, as i understand it the speed affects the volts produced and then as you increase the amount of electrical load on the alternator the torque needed increases. Like an ac motor but in reverse, what I’m getting at is all you are doing is giving yourself an unstable voltage for no reason at all!

Don’t forget that your fuel pump will be dropping off with battery voltage as well!
I have my dwell times set as near as i can measure on a scope and they do very with battery voltage, but the only reason I have them set is in case of dips in voltage if the alternator fails. I would always ensure a stable voltage at all times!



DTAS54 wrote:
When one removes pulleys from an engine configuration, there is more power available to the rear wheels.

This is an undeniable fact.

If you ran a huge battery on an air-cooled engine with a manual rack for a drag race car, you'd make more HP to the rear wheels than if you bolted on hydraulic PS pump, water pump, alternator and AC compressor. Simple fact. Turning any pulleys = parasitic drag

When one realizes that a particular pulley set up is geared for a street car with full electronics, AC, radio fans, accessories like windows etc... AND must supply all those needs even at idle, it becomes immediately obvious that at higher rpm, the only rpm a track car "cares about" for stability, that we can under-drive the alternator dramatically, and still hit our target of a stable voltage and current from the alternator while in our target range of say 4000 to 8000 rpm.

Now, we still want to drive around the paddock, idle nicely, and have some safe drive-ability under 4000 rpm, so it does pay to consider the lower voltages and how to best run the engine with pulleys that we certainly would not choose for the street.

OP is smart enough to know he's compromising streetability by using small battery, possibly a lighter alternator (I don't think he's gone that far) and a pulley configuration that is optimized for higher rpm.

The "goal" is to get a fully charged coil, even at lower rpm/voltage. We don't need black magic to get there at low voltage situations, just the right duration of charging. Increasing the dwell won't affect our performance in the desired rpm range since it will only be at the lower rpm...even if it does slightly increase the drag below 4000


stevieturbo wrote:
If you're that concerned about parasitic losses, why even run hydraulic power steering ? Why run a mechanical water pump ?

And 8k isnt a huge ask of an alternator is it ? Plenty of road cars will see 8k, and they will still happily provide 14v at idle.
Same with running the smallest battery possible. To me it just makes no sense. Of course weight saving is good, but if it's at the expense of reliability or the ability to run the engine, then it makes no sense whatsoever.

What next, running the car without paint because it will save a few kgs ?

I really dont get the whole underdrive thing either. Just seems like clutching at straws and creating problems for virtually no gain.
Are the differences even measurable ? Maybe if you were turning a regular 10,000rpm or more yes, but 8k really isnt that high.


Last edited by DTAS54 on Wed May 02, 2012 9:36 pm, edited 3 times in total.

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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Wed May 02, 2012 8:55 am 
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Posts: 30
lumley32 wrote:
i agree that removing things will give you more power to the wheels, but if you need 300 watts to run an engine then you have to take 300 watts of power from the engine, its simple physics, energy cannot be created or distoryed!

i don't do street stuff, everything i do is for one thing, racing! my alunator runs at over 15 000 RPM and only just produces the correct current to run the engine magment, however it still has 14v at tick over!

......edited to keep on parasitic loss topic.....

3) what are you going to do about all the outer things that wont like running at 10v (fuel pump mostly)?


Simon P. wrote:
Pulleys are just ratios; increase one, reduce the other and you're just changing the amount of work needed to turn everything through ratios. My engine doesn't generate any more power, it just doesn't need as much to turn everything attached to the crank. Pretty much the same as changing rear end gearing. You're not making more power, you're just using a different ratio to accelerate your car.
One of the byproducts in the case of pulleys case is that changing the ratio changes the accessories speed, ie the alternator, PS and WP. And in my case slowing the alternator (not my intention, just a consequence of changing the pulley ratio) has created a situation in which at low engine speeds (below 1400RPM) I experience lower than "normal" alternator voltage which I feel may be affecting spark energy in my fixed dwell application. And thus the reason I feel adjusting dwell through the compensation table could be beneficial in my case. Certainly not to make more power, just to smooth out an already decent tune.


DTAS54 wrote:

You guys missed the point entirely. With under/overdrive pulleys, we are still fine at the higher rpm where we know we will drive the car. It was fine too with stock pulley configurations. Higher rpm was never an issue. Never. You guys would have a valid point if Simon chose pulleys that gave him less than proper voltage between 4000-8000 rpm...

BTW: My race car does use an electric power steering system, and in fact, it does run an electric water pump. I had the engine running with no pulleys at all for a season with the alternator off the driveshaft in the back seat.

Many pro-teams have even run alternators off axles to move weight back in the car as well as to drive them at lower speeds so there is less drag. There is never any need to spin an alternator at 8000 rpm.

BMW claims 3% improvement in fuel economy, and 3% bump in rear wheel HP in the MINI when they went to EPS for that car. Variable speed electric water pumps are becoming more and more common as they can precisely control coolant temperature without cavitating at high rpm, and using less energy, freeing it up for the driven wheels.


VR6Turbo wrote:
As for the pulley debate and what not. Is this not what race cars all about? The last tenth? Is that not what F1 is all about? The kers system giving just that little extra to get past an opponent?

It's easy to be dismissive but this is why we choose standalones in the first place. We don't want to be restricted to a locked down OEM computer, because let's face it, if we all had basic needs and no need to play around with dwell, why aren't we just using factory computers?


************************************************************

I have tried to capture the spirit of the conversation on pulley drive ratio changes to decrease parasitic losses, and also include whatever had to bear on the consequences of making those changes.

I had no intent to reinforce either side of an argument or make anyone look bad in the process of moving over the relevant posts, and I promise I'll add or subtract anything people think I left out, or don't want in the thread.

One participant asked that I delete his contributions already, anyone else, just let me know. I hope Jon is cool with that. I'm going to go back and delete my posts in that earlier thread and only leave reference to this thread until all notes are edited or removed so I can completely delete my off topic stuff over there. I invite others to do the same, and continue on this topic here.

Thanks for reading.... carry on!

Alex.


Last edited by DTAS54 on Sat May 05, 2012 12:35 am, edited 1 time in total.

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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Wed May 02, 2012 9:53 pm 
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Posts: 30
VR6Turbo wrote:
As for the pulley debate and what not. Is this not what race cars all about? The last tenth? Is that not what F1 is all about? The kers system giving just that little extra to get past an opponent?

It's easy to be dismissive but this is why we choose standalones in the first place. We don't want to be restricted to a locked down OEM computer, because let's face it, if we all had basic needs and no need to play around with dwell, why aren't we just using factory computers?


Precisely.

You get it.

I was going to say that it is like the old proverb,
Q: How do you eat an elephant?
A: One bite at a time.

Building a dedicated track car is a challenge where every 2-3 HP are in fact valuable, and every 10 lb you take off the car meaningful. If you find 2-3 HP three times, you've got yourself 10 HP. If you take off 10 lb ten times, you've got 100 lb off the car.

In the case of reducing parasitic drain on the engine, this is very, very tempting because if it is done properly (*), then it is virtually "free" HP vs making changes to the mechanical engine that might compromise longevity. Free in the sense that you have not caused a decrease in reliability... compared to say bumping to extreme compression/wild cams/higher redline etc....

The whole point of going to a standalone is to make these incremental changes possible in the first place, and still have a stable and well performing engine.

(*) btw, that is pretty much the whole point of the original thread of how to use a dwell vs voltage table properly and gain insight as to how people are populating it and how well it works for them etc


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Thu May 03, 2012 10:50 am 
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Joined: Tue Jul 26, 2011 12:20 pm
Posts: 100
ECU Model: S80 Pro
Firmware Version: 58
Regarding the alternator, you can do it the other way around; some aftermarket ECU’s(just like OEM ones) have the option to regulate the alternator themselves(current/voltage limiting, thus also drag limiting), or even shut them totally off(WOT).

Why not do something similar, turn of the power to the alternator field coils at say WOT, and put it back on below a certain level, but for 2-3HP is it really worth it?


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Thu May 03, 2012 3:08 pm 
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MarcoV6T wrote:
Why not do something similar, turn off the power to the alternator field coils at say WOT, and put it back on below a certain level, but for 2-3HP is it really worth it?



Who's to say we don't ? (wink)

And yes, if you can shut off the alternator at WOT and get any extra hp, without any deleterious effects.... it is certainly one of those incremental changes that adds up.

Similarly if I'm going down the front straight at full throttle, I'd rather have an EPS system at idle drawing nearly no current than a belt turning a hydraulic PS pump.

I think the harder decisions involve large expenditures.

Are stepped high performance headers worth $2500 if you only get 5 hp?. Are they worth it if you also then add a custom 3.5 inch exhaust behind it for another 5hp...

Paying so much for minimal incremental changes makes things like parasitic reduction a bargain if you dot your I's, and cross your T's to keep everything reliable.

How fast do you want to spend is a recurrent theme when one builds a dedicated track car.


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Thu May 03, 2012 6:06 pm 
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Joined: Mon May 10, 2010 5:09 pm
Posts: 214
ECU Model: S80 Pro
Firmware Version: 61
your still not getting it! there is "no" drag on an alternator! (apart from bearings) the only drag is when you draw current. the more current you draw the more power is sapped from the engine. changing the speed make no difference to the amount of energy drawn from the engine!!!

there is a very good reason to slow them down although, they can only handle certain RPM, if your keeping the engine at higher revs than there ment to be then you have problems! road cars run the alternators fast so that they charge at tick over, if you start reving the nutts of them then you have to slow the alternator down!

this is direct from one of the top loom builders in the country!

but im all for race engines and getting the last 0.1 hp out of them! just mapped an ZX6R 600cc bike engine that revs to 17 000 and kicks out a real 122BHP at the tire, comes out at about 132 at the crank! as we normley have about 11BHP losses in the tire and chain!


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Thu May 03, 2012 6:49 pm 
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Posts: 96
Location: Montreal, Canada
ECU Model: S100 Pro
Firmware Version: 61
Lumley32,
You're right that we're not creating anymore power with pulleys. But think of it this way;
It takes power to keep the accessories spinning but it takes "more" power to accelerate them. If you change the ratio (with different pulleys in this case) with which you accelerate your accessories, you're actually freeing-up some power. You're not making more, you just have some extra that you're now using to accellerate the car faster. Once you're done accellerating, the system speed restabilizes and you're back to using the same amount of power to turn everything no matter what ratio of pulleys you have.
To put it simply, reducing crank parasitic drag mostly gives results in the trasition phase of accellerating. In the steady state of "unchanged engine speed" the only "marginal" gain is in the slight reduction of friction drag the alternator, water pump and power steering pump give you from turning slower.


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 Post subject: Re: Parasitic reduction: Pro/Con
PostPosted: Thu May 03, 2012 6:50 pm 
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Location: New Zealand
ECU Model: S80 Pro
Alternators start flying to bits internally at above roughly 18,000rpm. Usually the rotor windings fly out and open circuit/short to ground.
They start charging at around 2000rpm, which is why they are geared roughly 2:1 on oem stuff.
Slowing them down can help the regulator out if you sit at high rpm all the time also.

Gearing 1:1 is a big step in the right direction for a racecar.

And yes, quite right about the parasitic loss though charging - if you want to see, give an alternator full field and see if you can turn the pulley by hand. Feels rock solid.
So giving less field current at certain situations will helop for sure - however of course dwell tables will need to be correct as the voltage may drop from doing this.

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