pulley kit and other basic mods comparison

[wparsons]

Originally Posted by nikitopo

What do you mean if the launch was the same? It is a plain simple full throttle 2nd gear pull. It is not a launch! You log the parameters and you calculate the acceleration based on the timings. Weather conditions were the same and there was no wind. Road was the same and level.

What's going to be faster 50-60km/h, starting at 50 and flooring it, or starting at 30 and flooring it? The rate of acceleration is going to be significantly faster from 50-60 if you floored it at 30 vs flooring it at 50. That's why more than just the time from 40-103 matters.

How sure are you that there was no wind at all? You're talking about differences of 0.01s, even a tiny little bit of wind can make that difference.

Originally Posted by nikitopo

Doing two pulls is not enough? Ok, but I wouldn't expect a 40-100 km/h timing to be THAT different on a 3rd or 4th pull. Maybe some small differences, but not THAT different.

High sampling rate and longer period of collection make the data better. You can't change the sampling rate, so you need to collect data over a longer period. Easiest way to do that is to use a higher gear. It most definitely makes a difference. Hell, if you read the documentation for virtual dyno it even tells you not to use 2nd gear because it's too short and makes for inconsistent data.

Do five 4th gear pulls on the same road back to back and you'll have a much better sample set to look at.

[Spuds]

Originally Posted by wparsons

Do five 4th gear pulls on the same road back to back and you'll have a much better sample set to look at.

I'm not entirely sure his car can reach the top of 4th gear with his fd... I usually use 3rd gear and find it adequate for logging. Not as good as 4th, but isn't an excessive speed up top for a highway.

[churchx]

wparsons: and in your example i'd double those 4th gear runs to be performed in both directions. Exactly to cancel out possible wind impact.
But also yes, 4th gear is a bit excessive, at least on public roads. From memory when i recently was on track where at end of longest straight i for first time was able to redline 4th, speed IIRC was 170-180kmh on speedo. Speeding ticket at such might be .. a bit on costly side

[NoHaveMSG]

Originally Posted by Spuds

I'm not entirely sure his car can reach the top of 4th gear with his fd... I usually use 3rd gear and find it adequate for logging. Not as good as 4th, but isn't an excessive speed up top for a highway.

Same here. With 4.1 FD I think the top of 4th is over 105mph. Not trying to get a felony just for the sake of logging.

[Ultramaroon]

Originally Posted by Spuds

I've offered to do the math on pulleys twice now and will repeat it here. Math does not lie or exaggerate. It has no motivation. It simply is. I just need stock numbers for the model.

My offer to check your math stands.

[Tcoat]

Originally Posted by Ultramaroon

My offer to check your math stands.

He means it. Checking math is like porn to him!

[humfrz]

Originally Posted by Tcoat

He means it. Checking math is like porn to him!

Some "porn" for @Ultramaroon ........


humfrz

[nikitopo]

Originally Posted by wparsons

What's going to be faster 50-60km/h, starting at 50 and flooring it, or starting at 30 and flooring it? The rate of acceleration is going to be significantly faster from 50-60 if you floored it at 30 vs flooring it at 50. That's why more than just the time from 40-103 matters.

How sure are you that there was no wind at all? You're talking about differences of 0.01s, even a tiny little bit of wind can make that difference.



High sampling rate and longer period of collection make the data better. You can't change the sampling rate, so you need to collect data over a longer period. Easiest way to do that is to use a higher gear. It most definitely makes a difference. Hell, if you read the documentation for virtual dyno it even tells you not to use 2nd gear because it's too short and makes for inconsistent data.

Do five 4th gear pulls on the same road back to back and you'll have a much better sample set to look at.

Originally Posted by Spuds

I'm not entirely sure his car can reach the top of 4th gear with his fd... I usually use 3rd gear and find it adequate for logging. Not as good as 4th, but isn't an excessive speed up top for a highway.

I have also logs with 3rd gear and the results in virtual dyno are a bit better in the range of 198 whp. For me it doesn't matter if it is 194 or 198, but that they are much higher of what a stock car would give. You cannot really attribute these figures on the catted +17 OEM header or the tune. Something else must contribute to these numbers!

[nikitopo]

Originally Posted by Spuds

I've offered to do the math on pulleys twice now and will repeat it here. Math does not lie or exaggerate. It has no motivation. It simply is. I just need stock numbers for the model.

Math do not lie, but you have to model the problem correctly. You asked twice about total weights and diameters. A total weight and diameter is enough ONLY for the solid pulley. On the OEM pulley you have two different pulleys the one inside the other joined together with a rubber. You need the diameters of both and the weights of both. No one can really provide these numbers, unless someone takes apart the pulleys and measures the two weights. Then you have to create a model that the inside pulley is rotated by the center hub and the outside pulley is rotated by the inside pulley. With such model you would find that the rotation inertia is MUCH BIGGER and it not only relevant to the weight difference. As said before it is a complex problem and there are unkonwns in the equation (i.e. the weights of the OEM pulleys). It is much easier to make some measurements and see how the car behaves with standard tools like the virtual dyno app.

[nikitopo]

Originally Posted by churchx

wparsons: and in your example i'd double those 4th gear runs to be performed in both directions. Exactly to cancel out possible wind impact.
But also yes, 4th gear is a bit excessive, at least on public roads. From memory when i recently was on track where at end of longest straight i for first time was able to redline 4th, speed IIRC was 170-180kmh on speedo. Speeding ticket at such might be .. a bit on costly side

For me there isn't any issue to speedup on 4th or 5th gear. I am in Germany and I am doing the tests in autobahn. The real issue is that reduction on weight of rotation parts doesn't contribute so much after the 3rd gear. Especially with a longer fd like the one I am using. However, this is another discussion and let's stay on what "gains" you can see with such mods on 1st, 2nd or 3rd gear.

[Ultramaroon]

Originally Posted by nikitopo

Math do not lie, but you have to model the problem correctly.

Have you ever done this kind of modeling? Because you sound just like someone who has read enough to talk about it but have no practical experience.

[nikitopo]

Originally Posted by Ultramaroon

Have you ever done this kind of modeling? Because you sound just like someone who has read enough to talk about it but have no practical experience.

Of course I have done this many times and published results in scientific journals. It is very common when you are modeling a problem mathematically to verify somehow your conjectures or even have an expert from another area that will check the results and tell you if they make any sense or not. There exist even journals that will not accept any theoretical model without additional practical evidence or some kind of application.

[Spuds]

Originally Posted by Ultramaroon

My offer to check your math stands.

It's in an MS Excel sheet (didn't want to actually write code for it lol). If you got Excel, I can send you it. I'll probably post it when complete, but I want to test it out first and rain is getting in the way .

[Spuds]

Originally Posted by nikitopo

I have also logs with 3rd gear and the results in virtual dyno are a bit better in the range of 198 whp. For me it doesn't matter if it is 194 or 198, but that they are much higher of what a stock car would give. You cannot really attribute these figures on the catted +17 OEM header or the tune. Something else must contribute to these numbers!

And I'll repeat my question. What is the actual weight (well, mass really) of your car at the time of the run, and how much fuel was in it? I'm pretty sure virtual dyno follows an equivalent energy strategy to calculate output. For that you need an absolutely accurate mass.

A heavier vehicle takes more energy to accelerate to a given speed as a lighter vehicle. If that acceleration is over the same period of time, the heavier vehicle will have had greater power applied. Virtual dyno probably starts with the acceleration numbers and back calculates the amount of energy that must have been put into the vehicle using the kinetic energy model. If your mass is off, your power output calculations are off.