zukirf

going to turbo my motorcycle its a 94 suzuki rf900r the motor is based off the 93-98 gixxer 1100w. its stock with 11.3:1 compression. i'm gonna try and find some turbo pistons to lower the compression to liek 9.5:1 or 10:1. if i want to run 93 octane gas how much boost can i run without detonation? i had a guy that builds cuctom motorcycles tell me the motor can hold 15psi before i start breaking internals but i know it'll detonation before that

TorganFM

Depends on dynamic c/r, timing, etc.

Slo_crx1

Well, he already gave static compression so dynamic(or effective) c/r can be found out from that.
Check out this link for a little article that explains some things...http://hondaswap.com/turbo-informati...ression-29102/
The article deals with Honda car motors, but the principles are the same for any motor.

TorganFM

But I thought it wasn't that simple, like cam overlap figures into dynamic c/r and not just a formula involving static (in the cylinder as if no valves opening), or will cam specs determine the static compression? I know it's in there somewhere.

zukirf

wow i was expecting to get flamed instead of getting answers lol but thanks guys

i did the math on that ----

9.5:1 at 9psi =15.3 effective compression

10:1 at 8 psi = 15.4

11.3 at 5psi = 15.1

i tried to keep them at about the same as what that guy said was ok for that honda motor. how high can you go? or do you want to try and stay around 15.3? it is a daily sriver like the honda.

why can you run a turbo at 15.whatever:1 compression on pump gas but not an n/a? is it becuase your only at full boost for a short period of time?

Slo_crx1

Cams can have an effect on effective c/r, but usually only to lower it. Once cam overlap is introduced it decreases the effective c/r even if it increases the cfm flow into the cylinder head (because it also increases cfm out of the head). Cam lift will increase the amount of air that can be pushed into the head, but cylinder pressure + "x"psi will always produce the same effective c/r. Cfm flow has little to do with c/r's and cylinder pressure.Pretty much got it. There are some tricks used to be able to run higher pressures on high c/r motors, larger exhaust a/r's to aid in reducing backpressure, reduced (but finely tuned) timing in boost, etc. I run a b16a (10.4:1 c/r that's listed) and I run it at 14-16psi. Lower boost pressures like mentioned don't need as much fine tuning to run them safely. I would suggest tuning both for AFR's and EGT's and listen for detonation. Too high a timing curve can produce higher than wanted egt's and detonation, but beware of too little timing...it too can produce high egt's which can damage your pistons very quickly.

zukirf

AFR's and EGT's ? school me im a noob

Slo_crx1

AFR=Air Fuel Ratio. Stoich is 14.7:1...that is NOT what you want for a turbo motor in boost. Around 12.5:1 is better in boost to give a safety margin.
EGT=Exhaust Gas Temperature. You can get an egt gauge with a probe and put it in one of the runners on your turbo manifold. Think of it like a temp guage for your exhaust.

zukirf

gotcha thanks teh egt gauge is called a pyrometer by the way my buddy bought one for his diesel

Slo_crx1

Yes they are. Diesel guys use them alot, as do aircraft. If you want an extremely accurate and reliable pyrometer, get one for use in aircraft. Avoid any of the AutoMeter gauges if you can...very inaccurate and unreliable units.