Using a supercharger map

[Sumner]

I was wondering about using a smallish charger.  Rotrex make a C8-8 in a CCW version that will give me a 1.8 PR at about 10psi boost (probably as much as the BSA can stand, maybe more) which is about a 50% boost in hp, but it is close to the surge line.  Still, I could start with less of an overdrive to begin with.  The CCW is attractive in that I can drive it direct from the crankshaft.  And it is a small package with its own built in oil pump.  But, the intake is only 34mm and output 28mm??  Sounds small for producing up to 75hp.

75 HP would be ....



http://www.vespalabs.org/@api/deki/files/1353/=rotrex_c8-8_compressor_map.png

.... in the neighborhood of .0625 kg/sec of air and that is way over on the right side of the map and getting into the 50%-60% efficiency area so probably producing very hot air.  You really need to use one of the calculators to see for your motor were the plotted point would be and see if it even falls over there or off the top or right side.  2 different motors (different displacement, rpm, etc. ) won't necessarily plot the same point at say 75 HP output in your case.  75 HP with that compressor is probably going to be hard.  Looks like you need to think larger where the 75 HP isn't right at the compressor's upper limit,

Sum

[JimL]

I'm working on 2.0 pressure ratio at 300 Cu/Meter per hour on this map (650cc engine, 10,000 rpm 4-valve twin).  Looks like about 13,000 rpm on the blower with ice water intercooling.  That 2.0 pressure ratio is not so much boost at 6000 ft density altitude, I was told.  I suspect I will need full bypass up to at least 3500 engine RPM....or more?

my oh my...so much to learn.
JimL

[Robin UK]

The AISIN AMR500 is worth a look. Often used by the VeeDub people and I've seen them fitted to Harley's as well. Compact and they often pop up on eBay at reasonable prices.

Cheers

Robin

[Koncretekid]

A week ago I couldn't even read a supercharger map.  Now with the aid of online formulas I can run thru the numbers and actually see what comes out, more or less.  Unfortunately, the more I learn, the less I seem to know about this subject.  It's going to be a slow learning curve, especially for those of us who have been basically out of the loop for 40 years or so, not to mention age related learning issues, constant access to the beer cabinet, and naptime.

[Sumner]

I'm working on 2.0 pressure ratio at 300 Cu/Meter per hour on this map (650cc engine, 10,000 rpm 4-valve twin).  Looks like about 13,000 rpm on the blower with ice water intercooling.  That 2.0 pressure ratio is not so much boost at 6000 ft density altitude, I was told.  I suspect I will need full bypass up to at least 3500 engine RPM....or more?

my oh my...so much to learn.
JimL

MatchBot shows the engine needing about 390 cu/meter per hour for the engine at a 2.0 pressure ratio,

Sum

[JimL]

Sum, is that at 12 psi base atmospheric pressure? 

Thanks for whatever you can figure.

My 2.0 target is only 11.5 psi after the intercooler, at Salt Flats air density.  I know the blower can do it, but the engine cant take it.

JimL

[Sumner]

Sum, is that at 12 psi base atmospheric pressure?  

Thanks for whatever you can figure.

My 2.0 target is only 11.5 psi after the intercooler, at Salt Flats air density.  I know the blower can do it, but the engine cant take it.

JimL

Here are my inputs and the outputs.  Ignore the turbine inputs/outputs.

I was mainly figuring the air requirements for the engine at that rpm, altitude, etc..  Guesses on intake restrictions, ve, etc..  

Load...

http://www.3k-warner.de/en/aftermarket/matchbot.aspx

... the calculator and play with it with what you feel are realistic numbers and take the air flow and pressure ratios and plot them on your map of choice after printing it out for different rpms and boost numbers.  

You have to change the m3/sec to m3/hour for the air needed (multiply by 3600).  Also click on the link under the picture to enlarge it so you can see it.  I didn't spend much time on this so errors are probable  .  It does look like the compressor you showed could handle the air requirements.



http://purplesagetradingpost.com/sumner/bvillecar/jiml-1.jpg

Good luck and does the 125 HP sound close to what you would be expecting,

Sum

[JimL]

Thanks, we are pretty close with numbers.  This blower was made for 500cc-1200cc engines (typically small cars).  I have a bit more flow capability than typical production small car engines, and I am able to run at extremely low (less than 150F) cylinder head temperatures for several miles.

Because I can absolutely prevent over-boost, I can run higher compression pistons than might be used with a turbo.  I want to preserve as much as possible the gains made, to date, while picking up what we can get without stealing it all back from the end of the crankshaft.

125hp would be more than 50% increase in power from the engine that is currently running this bike 160-165 mph.  I think that could be another 10 mph?

Or it might break badly....

JimL

[Sumner]

Thanks, we are pretty close with numbers.  This blower was made for 500cc-1200cc engines (typically small cars).  I have a bit more flow capability than typical production small car engines, and I am able to run at extremely low (less than 150F) cylinder head temperatures for several miles.

Because I can absolutely prevent over-boost, I can run higher compression pistons than might be used with a turbo.  I want to preserve as much as possible the gains made, to date, while picking up what we can get without stealing it all back from the end of the crankshaft.

125hp would be more than 50% increase in power from the engine that is currently running this bike 160-165 mph.  I think that could be another 10 mph?

Or it might break badly....

JimL

If 83 HP is getting you 165 mph then 125 HP gets you 189 mph, on paper  .  That is getting pretty close to 200  .  200 mph needs 148 HP.

Since the MatchBot calcs are based on a turbo the gains might not be the same HP wise as what is charted there if you are using up HP with the crank driven compressor???  If it was the turbo they are showing turbo shaft HP as 13.8, but are taking that into consideration when figuring the net HP of 125 if I understand it right.  Not sure how to figure your HP figures to drive the compressor,

Sum

[Stainless1]

... 125hp would be more than 50% increase in power from the engine that is currently running this bike 160-165 mph.  I think that could be another 10 mph?

Or it might break badly....

JimL

My guess is you will be riding 5 miles instead of 3 if you want to, and it might stay together....
It is all part of the fun  
Sumner beat me to it

[JimL]

First note here...I screwed up a supercharger reply to Tom and put it on the other thread in this section.  Sorry fellows, now you have to fish it out of the wrong thread....but when you read the big goof up I made on that supercharger system, it'll make perfect sense how I could put the little story in the wrong place.

Thanks for the calcs on speed, however, based on how much work/modifications it took to go from 150 to 165 I think it wont get anywhere close to 190 and probably not even 180.  I've been able to easily feel the power gains, in recent years, by how this thing can spin up the rear wheel in 2nd and even 3rd gear.  It used to be mostly a 1st gear issue, even with lower gearing and less weight.

It is hard to believe how the last 20 years have slipped by.  Back when Dan and I started on that Modified Roadster we thought we'd have it figured out in a few years.  Didnt happen and we never got past about 180-185 despite more boost, bigger injectors, and finally a Pectel fuel injection.

The point is, expectations get lower even when you work harder than ever at going a tiny bit faster.  That 200 is someone elses world, and certainly not available to a 650 pushrod twin, but it would be fun to run long course again!  We will see what happens.

Thanks again, JimL

[Sumner]

....The point is, expectations get lower even when you work harder than ever at going a tiny bit faster. 

Yep easy paper HP makes easy paper speed.

I just modified my HP needed spreadsheet that I attached above and attached the modified one.  It now lets you also enter the new anticipated HP and calculates the new anticipated speed base on know speed and HP.

To use it download it and save it then you can enter numbers,

Sum

[JimL]

Here is an interesting experience driving superchargers with multi-rib belts.

Years ago, I built a 3.4 V6 Corolla with my son, Matt.  In order to make room for "stuff", I chopped off the original fan coupler pulley mount (on front of engine).  I then built several belt drive systems that didn't work while running his blower at 9.5 lbs (sea level).  Note that I converted from 4-row belt to 6-row (by using a crank pulley off a Camry aluminum V-6).

It kept spitting belts when trying to run the blower above 15,000 rpm.  I tried multiple positions of a tension idler, on the "slack side" of the belt.  One day, I lucked out and caught the belt partially walked off as I shut down the engine.  It was walking off on the straight run "pull" to the crankshaft.

After more experimenting, I learned the belt liked a back side tension roller, just after it left the blower pulley (see pic below).  I suspect this reversing of bend, under highest load, was restraightening the web inside the belt.  The tension idler position ended our belt problems with this car.  It was a cute car, and BAR certified legal...anyway, this belt system worked for years and almost 80,000 miles after the conversion.

Perhaps it will work for my new project, as well.