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Black from the waist down.
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Discussion Starter #1
I have two questions:

1. Is there a method for calculating exhaust pressures (or turbo inlet pressure)?

2. What two values does a Compression "Ratio" compare (numerator/denominator)?


Any help you guys could provide would be greatly appreciated (even a suspected range of exhaust pressure created by the R1/R6). As for the second question: I understand what a higher compression ratio denotes (higher compression of the air/fuel at top dead center) but have always wondered why it was given as a ratio as opposed to a singular value.
 

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Compression ratio:

Let’s define compression ratio, which is the ratio of the cylinder volume with the piston at the bottom of its stroke (bottom dead center or BDC) compared to the cylinder volume when the piston reaches the top of its stroke (top dead center or TDC). If we measured an engine with a cylinder volume of 45 cc at BDC and a cylinder volume of 5 cc at TDC, then 45 divided by 5 equals 9, giving us a compression ratio of 9:1.

that is a tiny motr btw.....lol
 

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Until it sleeps
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exhaust pressure? Im assuming u want volume too? Planning on hooking up a turbo sounds like. Well i can tell ya the R1 will never spool a T-66 :D
well ehaust pressure depends on your header, but volume should remain close to the same (at peak output).

Garret has variable vain turbos, Id look into those as it wouild help is spool at lower RPMs maybe something like a G15 or something that size, im sure a G25 is too big without a nice shot of NOS to try and get it to spool (Poor R1)

What size turbos do people put on Ford focus's (though they actually make less HP than our bikes). They could be a good comparison on turbo size.
 

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Black from the waist down.
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Discussion Starter #4
Thanks for replying to my post fellas. I'm sure the questions sound silly but I don't think that many people actually know the answers. I was pretty confident that a compression ratio was like you explained above MartinC but was unsure what the values/units were (pressure BDC/pressure TDC or volume BDC/pressure TDC). I thought that if the values were given in units of pressure that I could back calculate the exhaust pressure of the four cylinders with reasonable accuracy.
As for the turbo issue, I have been doing some research on how they work. One of the things that you mentioned, "spooling a T-66" is one of the limitations of the turbo that I was trying to overcome. It seems that the biggest problems/complaints about turbochargers involve the use of the exhaust gasses to pressurize the turbo's inlet (heat, slow spooling time, over spooling, etc.). It seems like the majority of time and money is spent trying to determine which turbo will work best with your motor output while trying to get around the limitations (custom fabrication, etc.) of having to re-route the system back to the exhaust manifold at a distance that will provide enough pressure. I always thought that turbo units where really expensive b/c of the high cost to buy a turbo "kit". You can buy a new or remanufactured Garrett Turbo for less than $500.00.
Anyway, after looking at a "electronic supercharger" site that MartinC posted some time ago I started wondering if you could purchase an electronic fan system that could be used to power the inlet portion of a turbocharger. I have been told "no way" but I can't ever remember not revving up my bike in fear of blowing gravel onto the cars behind me. I also can't remember seeing a top fuel dragster blow the header flaps off the exhaust. So what gives? Are exhaust pressures really that great?
Oh yeah...have you guys ever tried the "PowerDyn" computer program? It seems like a pretty good idea.
 

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So youre wanting to use an electric motor to turn the turbo. Your charging system wont handle the extra drain from that motor. What would it be? 8-10amps? Thats a lot on a bike. For short bursts (like 1/4 mile runs) it could work, but for normal driving I just dont think it'd be worth it.
 

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Black from the waist down.
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Discussion Starter #6
That's a good point. I guess you could always set it up so that it only comes on at full throttle or by a switch on the controls? You could also use the rechargable batteries that are made for RC airplanes.
 

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But if youre guna do that (come on at full throttle ect) why not just use N2O, plus u can keep your normal exhaust system without having to get some inefficient custom made piping. I say that because to get the exhaust to hook up to the header, they are all different lengths, tons of curves, not tuned ect..
 
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