Ari Jay Comet

Two friends of mine and I got into a discussion about boost levels. They both own nicely modified (250-350HP) Mitsubishi Eclipse AWD cars. They run about 12psi and 16psi, respectively.<p>Anyhow - the discussion was the boost levels of the TT. My better friend said he had heard that the 180HP TT ran 16-18psi of boost, and that the 225HP version runs 25psi.<p>There was some discussion of running 25psi over atmospheric, the possibility of doing so, and then also the likelyhood of a stock car doing it.<p>Does ANYONE know what the stock boost levels for the Audi TT are? Preferably, I'd like to know both stock for the 180HP and -ALSO- the 225HP model!<p>As a side note, www.audi-usa.com lists the boost as "Max. boost = 1.8 bar" - but what does the "max" mean in that clause? Hmmm..<p>Thanks ahead of time for any info...

Jim Torongo

A turbocharger is a bootstarp device; the more charge it sends to the engine, the more exhaust volume there is, making the turbo blow even harder,and so on. Were there no control in this circle, it would push your engine straight into detonation and failure. The usual control device is a boost regulator. It measures the boost pressure going to the engine. If that pressure exceeds some set point, the regulator opens a valve that diverts some exhaust gas flow around the turbine, straight to the exhuast tailpipe. this reduces the boost back to the set point ( maximun boost), preventing overboosting. The valve is called a wastgate. lets talk about the 180hp motor which has a boost above atmospheric pressure (1 bar) of about .8 bar. At sea level one bar is about 6.6lb's so a boost of 1.8 bar would result in aprox 12psi way short of the 18psi your friends quote. JIM<br>

Jim Torongo

Ever talk or write without thinking, I do...you would understand if you knew me. Anyway, air pressure at sea level is 14.7 not 6.6 so 1.8 bar is 26.46psi or Aprox 12lbs of boost. Right anwser wrong way to get there (read origional post). So the TT has .8 bar of boost above 1bar or 11.76psi boost above atmosphere for a total of 26.24psi. I apologize of the brain fade. JIM

Dr. Lane

You are absolutely right, except at sea level 1 bar equals 13.7lbs/boost.<br>These numbers are important for turbo enthusiasts because when forcing more air into the engine, you need more fuel to burn. Personally, I run a max of 14.385 lbs/boost in my 3KGT Spyder VR4 because over 15lbs you run the risk of over detonation. In other words, you crack the heads and demolish the pistons. So, when I recieve my 225TT I plan on boosting the turbo pressure within in nornal limits of course!

Bruce R.

It's always been my understanding that a pressure boost is just that, a boost. I believe your numbers are correct with one exception. The 1.8 bar boost is in fact 26.46 psig. gauge pressure, not psia.(absolute). The SLK has a .5 bar boost which equals about 7 psi(g). That would be a negative pressure in the manifold by your method, and I know that's not right.<br>This is a question, not a flame....

Jim Torongo

Bruce, the .5 bar boost for the SLK is 7lbs Aprox which is added to the one bar of natural pressure of 14.7psi for a total pressure of 21.7psi(g). Of course pressure at sea level can vary as you know so I use an average number (at least I believe it to be) Dr. Lane's figure is different however our method is the same, I think. Remember thr TT's boost is .8 bar not 1.8 bar so we are on the same wave lenght. JIM

Jim S

I've had my TT on the dyno and it maxed out at 11-12 (cant be exactly sure from the boost gauge). So, stock its running approx .8 bar (above atmospheric pressure of course). Dont know about the 225's since they will be using different turbos and intercoolers, so they could surely push more. probably not more than 14-15psi because the 225's have significantly improved exhausts over the 180's. The KKK 03 04 turbo's dont seem to do much better with boosts higher than 1.1 bar.<p>Jim S.<br>silver/black 180

Dr. Lane

The only reason why I stand behind my numbers is because I have a manual boost gauge feed directly through the wastegate soleniod. Therefore, when my HKS boost controller is set at 1 bar, my boost gauge reads 13.7. I then have an overboost of 1.11 bar for 3 seconds which my manual boost gauge then reads 15.02 lb/in.<br>I strongly feel that for any turbosharged car, a manual boost gauge should be mandatory. It's a shame that Audi didn't provide one for us enthusiasts.<br>I hope this has provided some insight.<br>

Ned

Jim had it write, Audi measures absolute boost. My S4 ran a 3.0 bar sensor, meaning my ECU was mapped to 29psi, not 44. I did however, run 25psi under certain conditions. Mind you, my S4 was modified. The stock TT will run 12 psi and fade out to about 10psi at the higher rpms. The 225hp TT will run at 1 bar (2.0 bar by Audi standards) or 14.7psi. <p>Ned