TURBO

[Bennybloke]

Talking of the supercharger vs turbo debate, my busa is supercharged, my bosses busa is turbo'd, both make the same sort of peak power, but his makes more torque, ESPESCIALLY in the mid range, factor in how many horsepower a suitably sized (for the engine) supercharger would take to drive it on a trx, you'd gain maybe 15 ponies at the most, so a turbo is definately the way to go for grunt. And if it's matched properly to the engine (efficiency, gas flow rates, rpm etc etc so on so forth and a shedload of other brain melting maths lol) lag is non existant, the delivery is fat and smooth, and providing you're not trying to boost a standard engine it'll be reliable power to. For example the turbo I'm going to bolt to mine isn't massive, in fact it's actually pretty small, but should give approx 115-130hp and about 75-80lbsft, with the majority of that being made before 6000rpm... but as I said in another thread just now the turbo's unfortunately on hold for a while (money and paitince have run out lol) and I ended up spending today at work knocking up a new exhaust and starting to put it back together. I think I have some pics of the turbo's progress somewhere, if I come across them I'll stick them up

[devlin]

That prompted me to read some more and came across a few things. This seemed to sum up most of what I read......

http://www.ststurbo.com/turbo_vs__supercharger

This is what I was thinking of using ......

http://www.rotrexsuperchargers.co.uk/Ro ... d_C15.html

after I had seen it used on this.....

http://www.youtube.com/watch?v=BQslEkcwu7o

but may have to do some more research. Yes I know I could just go and buy an R1 and still have a faster bike. That's not the point though.

[Bennybloke]

Hi Devlin, there are a fair few things wrong with STS's comparison, in fact someof the points they've made sound more like a salesman lying than an engineer describing lol, the rotrex is what I'm running on my 'busa and there isnt anying like the amount of noise they're describing. The rotrex systems are basically a turbo's compressor mounted on a belt driven gearbox, in fact theonly noise ou dont get from a standard bike that this system creates is BOV noise, very quiet 'chuffy' flutter on idle and the characteristic hiss when you roll off or change gear. It's the roots type superchargers (two counter rotating helical vanes) that make the loud-a*sed whining that they speak of, the type usually used on cars.
Now this is the boring bit, STS's comparisons...
Controlling boost on a turbo with an elctric switch? Yeah esy, but to have a switch, you will need a remote wastegate (a good one is very pricey) some kind of switchable flow solenoid and a digital boost controller (again, pricey), it's far simpler and cheaper to use a standar type integral wastegate thts preset to the level of boost you'll require.
As for turbo's running cooler? Lie, outright lol. Like I've said on previous threads again usung mine and my boss's busa's for comparison, the supercharged engine runs way cooler, the heat emanating from under the turbo bikes fairings at traffic/town speeds for example is intense.
And as for the up pipe cooling the charge before it enters the engine? If you've put an intercooler inline and are moving at speed yeah it will, without it though the boost pipe will get hot, air does that when its compressed, wether its by a turbo or a supercharger, boostpipes get very warm indeed lol
You don't need to change pulleys on a rotrex to change boost, it can be controlled with check valves, BOV adjustment, pulleys only need to be changed if you want to adjust the MAX available boost, and a C15 will deliver a MAX of 16psi, plenty...
If it throws a belt, it's either misaligned ('charger not installed correctly usually) or the owners been slack on they're maintennce schedule...
I reckon that's probably enough ranting for now lol, generally speaking, if they're installed and set up properly a supercharger and a turbo will deliver the same thing, with a turbo maybe giving more torque (i know that sounds odd) so it just depends what youwant from the bike

[devlin]

Agh, I only skimmed the sales pitch. I went back a read it properley and now I can see what your saying. It looks like they are comparing it to the roughest supercharger set up rather than a refined system like the Rotrex. The one thing I do like about the Rotrex is keeping the exhaust heat away from the induction impellar and path. Has there ever been a turbo where the two impellars have been seperated with a connecting shaft? Is it really an issue for normal applications? Also, why does the turbo produce more torque? Is it because you can get the impellar spinning faster lower down in the rev range rather than wating for the motor to spool the supercharger up?

[Bennybloke]

Thats the only thing you have to remember when looking at a reatailers site, at the end of the day they're trying to sell their product lol, but yeah, it's like they're comparing a factory fit turbo to a supercharger cable tied to an engine by some muppet in a shed :/ And you say about keeping exhaust heat away from a supercharger, next time I have the fairings off of my busa I'll take a pic to show you how close the exhausts are to the intake pipe on the unit...
And to be honest I'm not sure how that would work unless someone built a turbo more than a foot in length as the two impellers are seperat and connected via a common shaft, I know I said that the boost pipe heats up but thats just what happens when you compress air, cooling it down again and getting the air density back up again is where an intercooler comes in. And a turbo making more torque doesnt have a simple answer lol. This is probably gonnaturn into an epic-long post but these are my conclusions from experience with mine and my bosses bikes (both busas).
I'm running the rotrex supercharger, C15 (different impeller and housing machined to suit) running up to 16psi, no intercooler. Boost on idle is negligable, and due to the lowered compression ratio the power (actual horsepower, torque, delivery etc) is actually softer, or more docile if you like, than the standard bike. Over 1800 revs boost builds progressively and linearly in line with engine revs to 16psi at 10750 (raised rev limiter), the power and torque curves on the dyno not far over standard, at 2800rpm the torque curve goes skywards and the horsepower curve starts to chase it, they rise near vertically until the torque peaks at 140lbsft (the curve doesnt drop off however, it actually stays pretty much horizontal at this level until the limiter cuts in) and horsepower keeps climbing to 280hp, both curves very smooth and very progressive, add an intercooler and that would easily reach 320hp, BUT, without the mechanical drag needed to drive the charger that could be as much as 400... Like you say the fact that the 'charger can only spin up as fast as engiine speed and the gearing on the pulleys will allow, is probably why the torque and power curves look the way they do and why (combined with the lowered compression ratio) the low down delivery is so soft.
My bosses turbo 'busa is running a garret gt35/71 (the numbers are designations for the compressor/turbine impellers, it was explained to me what they mean at one point but i've since forgotten lol). Running on 8psi (the bike has the facility to run at 28psi as well but thats another story lol) at 10500 (standard rev limit). Now this thing is running an even lower compression ratio than my bike (standards 11:1, mines running 9.8:1 and his at 9:1) Boost hovers between 0.5 and 0.75psi on idle, and ramps from that to the full 8psi by 3000rpm. If our dyno had facilities to plot a 'boost curve', my bike would draw its line nice and straight from 0 to 16psi, the bosses turbo bikes boost curve would be a steep ramp up from half a psi(ish) at idle to a 8psi at 3000rpm and stay as a horizontal flatline til it hit the limiter. The turbo get's to 8psi's worth of revs as soon as the engine is pumping out enough gas to get it there, then the wastegate (a sort of bypass valve either built into the turbo's tubine housing or mounted externally in a seperate exhaust pipe) opens and bleeds the excess eshaust gas away from the turbine to stop the boost rising further. This bike's torque curve builds almost vertically from idle to a max of 187lbsft at 6800rpm (the supercharged bike peaks with its 140 at 6500rpm, but the turbo's alread making about 15lbsft more) and levels out, holding horzontal til the limiter. Horsepower ramps up slowly at first, only passing a standard bike's power curve at 3900rpm, the steepens and gains power rapidly (4000 to 5000rpm see's it go from 85hp to 135hp...) and keeps building at a similar level of brutality tilabout 7800rpm, then gains slower until peaking at 274 at the limiter.
So like I say, similar peak horsepower between the two systems, but the turbo make more torque, a lot sooner. Lag is non existant on either of them, the supercharger because of the very manner in which it's driven, and the turbo through good design and careful choice (of turbo). Lag with a turbo comes about generally through chasing unrealisticly high power outputs, like bolting a turbo on thats too big for the engine, it can't make enough exhaust gas to spin it up quickly enough, or poor design like placing the turbo in the inlet side of the engine, the exhaust gas then having to travel around the outside of the engine giving too much time for 'pulsing' pressure waves in the gases before they actually reach the turbine. Personally I also have other reservations about putting the turbo behind the engine, but that's getting away from the point. So long as the turbo is properly matched to the engine it's going to be fitted to, and the whole thing is set up properly after it's installed, it should be just as smooth and driveable as a stock bike, make just as much power and torque as a supercharged bike (although as you can see in the examples above it's usually more) all while running lower boost, better fuel efficiency and reliability to boot.
Hope all this helps, and if any of it's confusing I apologise in advance lol, seriously though just say if I haven't explained something properly and I'll try and do it better

[devlin]

I reckon that's pretty good explaination. I understood some of teh principles and you've filled in a lot of holes in my knowledge. They sound like two animals of bikes that I don't think I would want to ride. I would imagine the SC bike would be very easy to ride around town what about the turbo bike? Also with the lower begining output of the TRX I would imagine that the turbo wouldn't neccesarily make it a difficult bike to ride.

Interesting conversation.

[Bennybloke]

Cool I'm glad I've been of some help and to be fair both of them are pretty easy to ride around town or just 'ride normally' in general. Admittedly riding normally is using throttle openings that are tiny, 40mph in top gear on mine is very little more than just putting tension on the throttle cables lol. And neither do I, I worked out a while ago that with the turbo I want to use on my TRX power output should be between 115 and 130 horsepower and around 75lbsft, with an emphasis on low down grunt and midrange power. With the weight of the bike it shouldnt be any harder to ride than an average 600, just with more stomp.

And I'm glad you think so, usually if I start talking like this outside of work people start yawning or making excuses to go and be somewhere else lol

EDIT: sorry about the spelling mistakes in ths and my last post, I havent slept for about 19 hours now lol

[billy budge]

This page has taken me an entire huge mug of coffee to read and I must say....its feckin awesome, a very riveting read.

Always been a fan of whizzy bangers (turbos) and had planned to do an old skool suzi gsxr 7/11 turbo but after collecting all the bits, I had to sell it for sad reasons. That and the fact that some of the calculations still fry my head even though I work in aerospace engineering.

I have the upmost admiration for you chaps (Bennybloke+Devlin) on tackling these things and for sharing your knowledge. Had never even thought of sticking one on a TRX......I will watch with interest.

[Bennybloke]

Thanks for the kind words and encouragements Billy I'm afraid my own trx turbo will probably only be next year now, the money ran out lol, but on the plus side I've spent the last couple of days putting it back together to run normally aspirated still here if anyone else needs some pointers on 'charging of any kind, and once my turbo's back on track expect pics and updates as it goes along lol

[billy budge]

yippee!!