No!! Did Richard just do the unexpected? He just speculated on the horsepower gains of his forced induction kit. Do we all know what this means? Richard is bound to drop off the face of the planet for the next year! Why? Because every other vendor on this forum that has claimed figures has done so. Usuallly within 24hours! I want to be the first to call dibs on Richards workshop! :p

Here's an air density calculator, if one wants to see how much air density and therefore power output can actually change depending on temperature, pressure and humidity of the surrounding air.
http://wahiduddin.net/calc/density_altitude.htm (scroll down to the purple thingy)

So a power claim or a dynosheet is really only useful if these 3 parameters are also stated.

For a Dyno to be standards compliant (i.e SAE), it is supposed to apply a correction to the measured figues using the current atmoshperic conditions. The corrections are designed to standardize the figures to a standard temp, pressure, humidity.

That said, it seems you still make more corrected power on an ideal (cool, dry) day.

Cheers,
Hymee.

I don't know about some of these chassis dyno's but modern engine dyno's take this information into the correction factor. On my Superflow it colected the borometric pressure and temp by itself. The vapor pressur is put into it by the operator after using a sling psycometer. I don't know how it's spelled.

This is a wet bulb dry bulb instriment. Did yoou guys see the operator swing an instriment around in the air and put some input into the dyno? If not then the dyno didn't know all it needed to know for corrected read outs.
There are units that can read this by themselves though so you can't be sure.

The point is that this is an input and you don't have to use it yourself. The dyno does it for you befor it gives you the numbers. Without this being used in the calculation there would be no reason to even compare power readings like you guys are doing. Don't even post them, they're worthless except to see on the same day if the weather doesn't change to see between runs if you have made any more power. you may as well read out in any sort of numbers. Like one dyno could read out in four digits while another in two. I have 2754 units of power in my car. You have 110 on the same car but a different type dyno.

Dynos have to be able to compare with each other, that is why they calabrate them. It's a simple thing to do. Just hang a known weight at a known distance from center and read lbs of torque. Then you know if it is right. You check it with several different weights to check the range.

I think it was Engle that had a dyno built using one of those big scales that they used to have to weigh yourself on in public places by putting in a dime. Except this one was so old it took pennys. "Ready to make a run, someone go put a penny in the scale" True story from the late '50's early '60's. (No I was in high school then.) They probably stole the scale from a bus station. :rolleyes:

Now they just use a strain gauge. Cheap and accurate. The dyno probaly can print out in Std or SAE though. Since Std reads higher everyone uses that.
The car companys use SAE. Which brings us o another point. Mazda is claiming Their rating in SAE and no one else can even get it to read their numbers using Std! Whats up with that??

So, the HP reading depends on many parameters like the accuracy of the strain gauge, the accuracy of the pressure, temperature and humidity reading and when they were last calibrated. Then the actual HP production of the engine depends on the temperature of the intake, water and oil temperature and probably even more.
I wonder what the total margin of error is? Can you even reproducibly measure power within 5% taking all correction factors into account, assuming one dyno is for instance in Denver and the other one in San Diego?

You bet, probably within 1%

Yes the power output depends on the temps in the engine. In fact for every10 degrees of water temp there is 1% gain. That's hotter guy's. The hotter the more power, NASCAR engines run about 220f. They can go up to 260f before they get into trouble. You get 3 degrees extra temp before boiling for every psi over atms. Meaning for a 25lbs cap the coolant say water will boil at 212+75 or 287f. Add some antifreeze and it goes up from there. But antifreeze is not as good of a coolant as water.

You can make water a better heat transfer medium by adding a "Wetting" agent. This breaks the surface tension of the water and lets it get closer to the metal surface. If I remember right it adds another mole of oxygen and therefore becomes more corrosive.

So this is why racers monitor the temps closely. It's always faair because all race cars are in the same condition at the same time. Now the team that can adjust their engine for conditions has an edge.

not this car Richard- Racing Beat's Jim Mederer has shown with his ecu test bench that if the car see's coolant temps rise above a limit set in the pcm the car starts pulling timing. the longer its stays at that higher temp or the more the temp goes up the more timing is pulled. then it starts lowering your rpm limit and other things to try to get the temp back where it wants it. that limit is well below boilover.

OK Not this car. The rotary I have come to find is already running hot. This is something I must think about. Since there is so much heat in the exhaust why is there no moore heat in the water? Or is the water doing a balls out job just trying to keep the thing from welding itself together now?

dont forget - oil is doing alot of the cooling work. hence why we in the states have 2 oil coolers stock.

Yes ant that is one of the reasons I'm trying to find my old materials professor. He has developed coatings for the hot section of APU's. I want to see if these can be applied to the exhaust ports.

But that doesn't mean that the engine couldn't produce more power if it would run hotter without affecting its timing. If the rotary engine could be built out of some exotic ceramic material it could probably run hotter and increase its power and efficiency.

For instance silicon nitride (well if it just wasn't that expensive to manufacture, there's certainly enough silicon and nitrogen around).
http://www.azom.com/details.asp?ArticleID=53

This talk about comparing different dyno's... I have a couple of views on this. First and foremost, I don't think the primary purpose of a dyno is to compare power outputs between different dynos. The primary use is to compare changes made to a daseline - readings taken from the same machine.

The dyno is but one of the tools used by the tuner. Yes - a tool. There are lots of variables. And one car will make different power on the same dyno on different days. I have seen so many dyno-war threads, it is silly.

Dyno Dynamics try to have a standard testing sequence and accredited testers for what they call the "Shoot-out" mode, to try to make for an even playing field. It has some merit, but the cinical amongst us would see it as a clever way to try to create demand for the product.

Strain gauges. That sounds a bit like something off the ark! All the modern dyno's I have experienced in Australia (chassis and engine) are electronically controlled, and use electromagnetic "brakes" to measure the power.

Cheers,
Hymee.

some of us have been preaching that for years on this forum , thanks Hymee:)

Hymee, you have your componants confused, The braking of the dyno can be done with many types of resistance. Most engine dynos use the "water brake". Some use Eddie Current. That's a wonderfull thing as you get to sell the electricity back to the power company.

Now the strain gauge is just a link between the engine and the frame. It electronicly sends the info to the computing componant which in turn converts it into a number we use called Ft/lbs. Then utilizing this number and the one it gets from the speed sensor gives us the HP. It can compute SAE readout or Std corected. Just tell it which you want.

In the case of the Superflow it reads fuel flow and airflow by turbine. Using numbers you put in it gives A/F by weight. It uses direct not corrected HP to come up with these answers. It then gives you BSFC and BSAC. Brake specific air and fuel consumpsion.

You see that it needs you to weigh the fuel by specific gravity (a hydrometer or by weighing 100 cc's on a scale) and air by RH, temp and baro in inches of Hg.

That is the only way you can get the proper corrected figures. I can't picture the chassis dyno operators going through all those hoops. So if you (Hymee) say that you see higher numbers even after correction between cold and hot days on your dyno runs then this is the reason. ;) To do it right you need to treat it like you are conducting lab tests for atom bonbs. All the details must be factored in.

As I said the formulas have been accepted around the world by race engine builders and car factories alike. Only on the RX 8.com club forum have they been called suspect. But then there is the mom who looks at the army on parade and says "look my son is the only one in step". How can you argue with her. :rolleyes:

Now I'm very carefull not to argue with people who hold decades old practice in their hand. Why? Because there was this saying carved into the entrance of one of the many academic building from which I was evicted. "Where a little knowledge is a dangerous thing" ;)

Richard,

I'm not making an argument with you. All the "modern" engine and chassis dyno's I have seen in this land use the electro magnetic brake thingy to measure the power dissipated it. No strain gauges anywhere. And from the power the torque is derived by a simple calculation, as you know, the only other factor being the RPM.

The power measured is determined by the relationships between the resistance, voltage, current.

And the air/fuel ratios are read from a very accurate O2 meter. And the Dyno cells typically have a weather station on the wall, so the SAE correction factors can be entered fairly simply.

Perhaps I have been lucky to see modern stuff! The most common ones around here are DYNOLOG(IC) and DYNO-DYNAMICS.

http://www.dynologic.com.au/index.html

http://www.dyno.com.au/

Cheers,
Hymee.

That dyno dynamics engine dyno looks nice.

But, But, But Hymee, what do they use for load mesurment a "load cell"
That is the same sort of device as a strain gauge. not using the electricity developed by the electro magnetic brake. The load cell can work with a 5 volt input same as strain gauge input.

Some load cells are buttons, some are s shaped thingies.
They can be made to take enormous amount of weight.

So how much are these things compared to the Superflow??

Nighty night, Thecrankyoldbastard :cool:


Edit) oh yea, they take baro and RH and temp automaticly.

BUT, they say they correct to SAE. Now if that's the case what do the systems used over here cor to. anyone know??

I remember a few months back someone posted a little table showing simple boost curves of different supercharger setups. It looked something like this.
Rpm Boost Pressure
Centrifugal
Positive displacement
axial flow


The numbers were filled in obviously. I was wondering if someone could post that again, I can't remember exactly how it went, but I think the centrifugal was exponential in nature, the PD was full boost from 0 rpm but I dont remember how the axial flow went. Thanks to whoever posted this before and to whoever can help answer my question.

(it may have been me)

This is the way it works...

Centrifugal - boost is roughly proportional to the square of impeller speed. 2 x RPM = 4 x boost.
This means, that for a blower designed to give 12 PSI boost at 9000 engine RPM, it will give 3PSI at 4500 RPM.

Axial Flow - Roughly linearly proportional to blower speed. 2 x RPM = 2 x Boost.
That means at the same design of 12PSI boost at 9000RPM, we get 6 PSI boost at 4500 RPM. So at 4500 RPM, you got twice as much boost as the centrifugal.

Positive Displacement - roughly constant boost at all blower speeds. 2 x RPM = same boost :( . Also mean 1/2 RPM = same boost :)
That means for the same design parameters of 12PSI at 9000RPM, you will get 12PSI at 4500 RPM. And 12 PSI at 2000, 4000, 6000, 8000. So at 4500 RPM you got twice the boost of the Axial flow, as 4 times the boost of the centrifugal.

The advantages of the Centrifugal are compactness. It is also what a turbo uses for it's compressor - the difference being the shaft speed (hence boost) is more or less based on engine demand (exhaust pressure), not engine RPM. You can also get higher boost pressures, so you can get more max HP. But you have to wait for it!

The advantages of the axial flow is it is fairly compact, and apparently takes less HP to spin, and puts less heat into the charge. Hence you get more useable power. Richard showed me some graphs on the axial flow for the heat it puts into the charge. And also how it made more power than other other systems for the same PSI.

I have charts showing lab tests for the HP required to drive a twin-screw, and also how much heat it adds. You cant get away from adding heat to air when you compress it. It is just a matter of physics, no matter how efficiently you do it. After all, that is how a diesel works, right? It compresses the air so much it gets hot enough to ignite the fuel.

Bring on forced induction!!!

Cheers,
Hymee.

You've got the explanations for PD and axial confused with each other.

Thanks a lot Hymee :) I think I got it now, thanks for replying so quickly.

Holy fat fingers batman, how did I manage that? I'll fix it!!!

Sorry if my little mistake confuses it even more!! But what you said the first time in your question is correct. I just tried to expand.

Centrifugal = "exponential" boost
Axial Flow = "linear" boost
Positive Displacement = "constant" boost

Thanks again RG for pointing out my error. I should have checked it properly!

Cheers,
Hymee.

Oh, OK. Sounds good, everyone's human so you're forgiven Hymee. :D

Afsc
 

Okay another daft question from a really keen scotsman.
Firstly the 3 posts that I have posted so far dont actually seem that enthusastic about this project.
I would just like to say that RP and everyone else involved with this project has done an excellent job so far in designing this supercharger.
I am eagerly awaiting the finished product.
Only one thing, when thinking about the engine management system for this project please forget about the canzoomer module.
I am sure 99% of canzoomer customers across there are delighted with his work and the power increase that they got. As for myself the unit dropped my total horsepower by 20hp running with 0 map. From this conclusion my self and two tuning garages decided that is was unsuitable for the UK Spec RX8.
The UK spec runs with the larger spark plugs as standard equipment.
As for RP's comment about better fuel for more power, could you please explain a bit more what you mean by "better fuel". I make the stuff across here for a very small company called BP.
Our standard fuel is RON95 with the better fuel being of Ron 97-98.
I know from previous trips to the states that you guys can run from about, please correct me if I am wrong, 86 - 95.
So in theory for the better petrol I can be running about 101 octane level across here. Never tried it yet with the RX8 but the old nissan almera loves the 101 octane blend. By the way to get the 101 I have added octane boost which is about 107 octane, 2 bottles off.
Now that that is out of the way, will porting the rotary engine in association with the supercharger make a difference, or will the supercharger design already be at the limit. Is this supercharger going to be slightly over designed for future expansion is probably the question that I am trying to ask here.
:cool:

This question may have been answered before in this thread, but honestly I have forgotten 2/3'ds of it already.

But by "linear" boost increase, does the boost above atmospheric start at 0 at 0 rpm, or at idle, or somewhere higher in the rev range?

Also, how does linear vs constant boost translate to driving characteristics of the engine?