Alan 91 C2

I bought the S car about two years ago. Boost was ~ 1.6 bar indicated max.

The car had LR boost enhancer and Autoauthority chip.

I removed the boost enhancer and chip, as part of the troubleshooting. Still poor boost. Found the cat pipe was badly collapsed, and inspecting the Porsche waste gate showed the valve was not fully closing on the seat. The valve was slightly bent, cleaned up with valve grinder, touched up seat with valve seat stone. No more leak in the WG.

Bang! Boost to ~ 1.8. Re-installed the Autoauthority chip, still ~1.8 bar.

Took apart the LR boost enhancer, all good, field calibrated with compressed air to open at ~ 14 PSI.

WOW, boost to 2.0 bar indicated. Backed off the BE, 1/2 turn for boost at 1.9+. (Too keep the boost gauge in the operating range, I was not sure if I was over 2.0 bar as the gauge only shows 2)

Now I need to install a boost gauge, and air/fuel ratio, before I up the boost. As I have 2.5 Bar fuel pressure.

But the car pulls like crazy on boost!!

User 52121

Definitely don't trust the gauge on the dash. Install a good aftermarket gauge ASAP.

I know the Autothority chips tend to give a lot of boost - I'd hesitate to run both an LBE *and* the autothority KLR chip, especially if you're seeing higher peak boost. If I were you I'd (a) get a real boost gauge and (b) remove the LBE until you can confirm peak boost with the LBE is no higher than without.

jackkthemackk

My 86 with the stock k26/6 seems to JUST hit 2 BAR of boost on the dash with just the Autothority Stage 2 chips. Pulls hard but I've never driven a different 951. I'll be installing a pretty PODI boost gauge in the spring to get the exact boost measurement then. Is it suppose to get all the way to 2 BAR stock with just the chips?

333pg333

.....it's not 2 bar. Well let's say it's not 29 psi. It's 2 bar absolute. Subtract approx 15psi (1bar) and you're about right.

User 52121

Keep in mind that the only AFM chip that has viewability into actual boost pressure is the Rogue A-Tune. So for these Autothority chips, the KLR chip controls boost level, and the KLR/DME chips are expected to work together. The DME chip expects the exact boost curve that the matched KLR chip will deliver. By increasing boost above what the KLR chip does, you're now exceeding what the DME was tuned for, the DME has no idea you've increased boost.... and you wind up with fueling and ignition timing for lower boost levels than you're running.

Plenty of people have gotten away it.... but IMO it's not adviseable. Especially since I'm pretty sure it's the Autothority chips that have a reputation for running things on the lean side.

Willard Bridgham 3

I have a calibrated aftermarket boost gauge and the stock gauge and they agree completely. The stock gauge is fine but is hard to read.

Josh B

Hey Alan - hope things are going well. We are planning a great year here in Atlanta. AutoX, DE, Caravan to 944 Fest, some parting parties and mtn runs - lets be sure to keep in touch!

CO951

My stock gauge matches my aftermarket gauge, too.

Omni, you've described some things very different than the way Josh (Rogue) explained them to me when I was testing his original A-Tune for him, but I am not an expert, so I don't want to say some thing is wrong.

The key about the LBE is that it was not meant to be used as a boost controller (physically it is a boost controller). It is suppose to be set below the max stock boost level (cycling valve still controls max boost), strictly to help build boost faster. (It prevents the building boost from partially opening the WG while still well below max.) If it is boosting higher with the LBE than without it, it is set too high and is causing a boost spike. The 14psi it was set to is too high for the LBE, it is suppose to be something like 11 or 12 psi, so it opens before max and you don't get spikes.

grenadiers

Lindsey chips require a 3.0 bar FPR to prevent the engine from leaning out at high boost. You might want to consider one.

CO951

The chips are set for different FPRs, don't just change the FPR without changing the chip.

lart951

We have gone through this a zillion times, 1 bar on the stock gauge is atmospheric pressure so there is not such thing as 2bar on the stock gauge

Alan 91 C2

Thanks for the good discussion.

Yes, the boost gauge is absolute pressure. I am happy with the performance and may turn the LBE down an additional 1/2 turn for around 1.9 bar indicated.(close to stock max of 1.85) I know my boost gauge is quite close as in Duluth we are at 1,100 feet above sea level, and my boost gauge reads about .9 bar, absolute (versus .95 bar at std atmospheric pressure actual.) with the key on engine off.

I will watch for the 944 run in Atlanta, should be fun.