Someone asked about power.   I dynoed the GS at 42 Hp stock at 14.7~ psi(Rear wheel SAE Horsepower, adjusted to sea level).  Since horsepower is directly porportional to intake pressure for a given compression ratio, and I have increased the ABSOLUSTE pressure to ~45 psi (30 psi gauge), the engine should produce in the area of  120 hp at the rear wheel.   :mrgreen:

HOWEVER, friction loads increase with higher compression...so I will estimate that I am probably getting about 105-110 hp.  For a few seconds.  

If you guys do want to turbo your bikes, I would suggest you stick to 10-15 psi (gauge).  My team and I did quite a bit of stress anaysis on the shape of the plenum, and the associated parts to handle that psi, Unless you had our exact model and built it just the way we did, you might end up cracking your plenum or worse.  10-15 psi will get you 65 to 80 Hp.  

My seat of the pants dyno says that this is about right for the bike.  I haven't dynoed it with the turbo on...maybe I should do that sometime.  Anyway, the thermodynamics are correct (They gave the team our sheepskins, right?) and I would be very suprised if the bike didn't make those numbers.   :dunno:

And Last:  I run 105 octane in the bike.  I mix a blend of Toulene and Xylene with 93 octane and this gives me at least 103~105 octane.  Don't try to run 15 psi without a much higher octane.  I'm not kidding, unless you want to paste your ass to the moon, on the back of your skyrocketing heads.  

I will check my files and maybe send a test file in a couple of days.  Please give me time as these documents are big, hairy, and have my name on them.  


Bling!

if your running the hight boost like that why wouldnt you want to run race gas? i guess my question is why cant you run the higher octaine with 15psi of boost?

turbo boost isn't the same as increasing compresson in the cylinder...turbo engines don't require race gas but engines with high cylinder compression have to use race gas

i'm still not understanding why it is so bad to run the high octane gas in this situation.

I can host the files.. PM me..

you don't have to run race gas to increase turbo boost....i'm not a turbo guru but i know some thing about turbos....me and my friend took his VOLVO turbo and increased the boost from 5 to 24 PSI and he was running 91 octane gas....it would backfire from time to time but it ran good

There's a good chance that the compression in that Volvo wasn't too high.

If the GS makes more compression (without the turbo) it will need race gas or else it starts knocking. The Turbo pumps more mixture in the cylinder wich means that the compression will also get higher. If it gets too high the engine will start knocking. That's why the standard compression on Turbo-engines is often a bit lower.

you *do* need to run higher octane gas with more boost, otherwise you will get knock.  the reason your friend could get away with using 91 octane is because his car had a knock sensor, which can retard the timing automatically to reduce knock.  if he were to run higher octane gas, he would be able to run more advance and make more power safely.  

it's NOT bad to  run high octane gas.  in fact, what he's saying is you NEED to run higher octane gas.

and for whoever asked about race gas, toulene and xylene are common components in race gas.  you can pick them up at most hardware or paint stores.  they both have octanes in the 114-117 range i believe.  if you were to mix one of those with 94 octane in a 1:1 ratio, you'd end up with about 104-105 octane, though personally i wouldn't do more than 3:1 gasoline to toulene/xylene.  also, they have a tendency to make rubber gaskets and hoses deteriorate much faster than regular gasoline.

fwiw, i OWN a turbo car, and i run about 18-20psi.  stock was ~14psi.  and yes, there is a noticible difference when running 93 octane vs. ~96 octane.  i haven't tried anything higher than that.

Quote from: LarsThere's a good chance that the compression in that Volvo wasn't too high.

If the GS makes more compression (without the turbo) it will need race gas or else it starts knocking. The Turbo pumps more mixture in the cylinder wich means that the compression will also get higher. If it gets too high the engine will start knocking. That's why the standard compression on Turbo-engines is often a bit lower.

good point but volvos compression is 8:1 and gs500's is 9:1
not a big difference but probobly makes a lot of difference

Hey all,

Sorry I can't reply as often as I like, but I do have to work

Two things.  One: compression is compression.  Since turbos provide pressure by compressing the flow of air, this must be multiplied by the engine compression to get true compression. Ex: a turbo blowing 15 psi gives a compression of ~ 2:1.  This goes into an engine that compresses the mix 9:1.  Therefore, the true compression is 2/1 x 9/1 = 18/1 or 18:1 compression.  

Since this vapor pressure of fuels is dependent upon the absolute pressure, and atmospheric is 14.7 then 18:1 compression gives a before ignition pressure of roughly 260 psi absolute.   AND using the approximation of the Ideal gas law (yes I know air is not ideal, but close enough) this also gives a temperature of the mix, prior to ignition, of approximately 600 deg F.  This is localized temperature within the gas cloud, and is only an ESTIMATE.  I am not going to get into an arguement about the Gauss-Seidel iteration process required to find the true temperature and pressure.......Whew!.  

Okay.  So a higher octane fuel does nothing other than resist knock by resisting spontaneous combustion at higher temperature.  Higher octane = Higher knock resistance. Easy.  Turbos create lots of heat and pressure, see above, and as a result, to avoid knock you must use high octane fue.   Q.E.D.  

Second, the formula's work backward.  If you have the specs on your engine, you can estimate the octane you need. There are a couple of places on the net where you can get formulas for high octane. The basics are this:  A large portion of actual fuel, mixed with Toulene which is an accelerant, not a fuel, and a portion of Xylene which is a "light fraction" of the fuel.  The trick here is that the toulene increases the flame front propogation across the head, allow normal combustion to occur before knock can start.  As a hard example of this, in the 80's formula one teams used to get 1500hp from their turbo engines by running 70 PSI and using tremendous amounts of toulene.  This "rocket fuel" was later banned, and now the engines are in the 900-1000 hp area.  

I think the formula I use requires 4 oz. of toulene for 1 gal of 93 octane.  

Jiggersplat was right.

Bling!

Where'd you learn all this crap Bling? I can turn wrenches like nobody's business, but you start throwing equations and shaZam! at me like that and I get a frickin' headache!

Also the volvo was water cooled wasn't it. Air cooled is basically like playiing roulette compared to water cooled. Steady temp, no uneven hot/cold spots and a well defined range of temperature.
Cool.
Srinath.

Ah.  Well....I'm a mechanical engineer with a specialy in dynamic systems of pneumatics and hydraulics. I work for an Aerospace company as a manufacturing engineer.  But, mainly I trained under Proffessor Bob Woods at University of Texas at Arlington.  An outstanding professor with an drive for racing.  Under his guide, the UTA racing team has won more of the Formula SAE competitions than the rest of the world combined.  

Enough said?

Bling!

Bling-  What is the ideal gas law approximation that you used to find the temp... I follow you through the explanation, I just want to know the formula.  

So what temp is the exhaust gas?  And doesn't that temp effect the the temp of the compressed air (reasoning behind intercoolers) which enters the engine?

later,

Hi-t

Without refering to my books, the Ideal gas law is PV=NRT or expressed in word form, pressure times volume = the numbers of moles x the universal gas constant x the temperature.   With a given quantity of gas, it can be summarized as PV=RT.    (a mole is a quantity of molecules, not a ground rodent)

Please note this is an approximation which closely resembles air and other gases, but is not specific.  There are adjustments to the formula for each gas: air, nitrogen, helium, etc. but for this type of discussion it's fine.

Hi-T, I think that there may be some confusion about intercoolers.  In a turbo system, intercoolers work as an Air to Air heat exchanger, flowing compressed and hot INTAKE air inside, and cooling air outside...much like a radiator, only intake air instead of water.  

The heat of exhaust is usually between 1200 and 1500 deg, depending on the original fuel/air ratio.  Most turbo systems make big efforts to keep that heat from affect the relatively cooler intake air.  The biggest heat transfer occurs at the turbocharger, itself, through the casing and through the turbine spindle shaft.  This amount of heat is minor when you consider that compression of the intake air alone causes temps to climb to 350 Deg F or higher.  

In a thermodynamic sense, heat and pressure are interchangable.  A turbocharger thus exchanges pressure and heat of the spent exhaust gases for pressure and heat of the incoming gases. When doing this turbochargers can commonly see efficiencies of 50 to 60%.  Quite high.  

Bling!

Holy cow ... what an edumacation we are getting!  Just kidding!  It's a refreshing change from talking about carburator jets.  Sounds like you know what you're talking about Bling!  Thanks.

Rob

I would also imagine you have a Cap on the octane you can run, higher the octane the hoter the burn yes?  Figure there is a point to which its the pistons start mushrooming, and heads start drooping do to heat.

The higher the Octane the hotter the burn = NO.   High Octane does not burn at higher temperature.  In fact, High Octane fuels have a greater portion of the "light fractions" of fuel, or in other words, have a greater portion of the fuels that evaporate faster, thereby igniting at lower temperatures.

These ligher portions are known mainly as the "Aromatics" because they are the ones you normally smell the most.  They increase octane by vaporizing faster and allowing the burn to occur faster.  

Gasoline is a chemical mixture of up 23 different chemicals.  Refineries mix each fraction of chemical to suit the climate and law of the state or town that the fuel is going to.  Also, the Petroleum pulled from the ground is much different from site to site.  Therefore, the 93 octane I get from the station is NOT the same formula you may be getting.  In fact,  since most gas stations do not have octane testers, unsruptulous companies make profit by providing 91 octane instead of 93.  Buyer Beware.  

An Octane Limit?  Short answer: I don't know.  

However, since high octane fuels cost lots of $$$, this is usually not a problem.  

"The higher the octane, the hotter the burn" comes from the fact that many racers who run high octane also have high compression engines, thus encouraging engine knock and higher cylinder temps.  And THAT leads to holed pistons and toasted valves.  

Bling!

So simply put, gas is gas (from the pump)- regardless of the octane # it should burn and produce the same amount of heat or energy.  As compression increases, the temp inside the cylinder increases meaning that a higher octane gas will withstand the higher temp resulting from the higher compression/pressure and have a higher flash point.

So, an engine that runs lower octane and higher compression risks a trip to the moon because detonation can occur before the engine is ready for it... and with a higher compression you're dealing with more than just an average knock.

Now a gas molecule can only store so much potential energy- so by increasing the compression, we increase the number of potential booms (or molecules) that can fit in the cylinder... then by increasing the octane we control at what temp the boom occurs and make it more likey that all the booms occur simultanueosly.

Do I get it? ( really... Is this a sound understanding?)

So an intercooller is primarily used to cool the intake air into the engine.  How much difference does this make?  At what temperatures are there significant changes in air density?  I assume there is a differance considering must turbos do have an intercooller.  

Thanks  Hi-T

i believe the of BTU's released during combustion per unit of fuel is what determines how much power you get out of gas, not the octane, but the rest sounds more or less correct to me.  i'm sure our expert, bling, will chime in though.