Autothority and weber jet sizing question
 

I've been playing around with the orifice sizing on my banjo bolt for the Autothority stg II chips. I was wondering if anyone knows what jet corresponds to what boost level? OR if someone knows how the weber jets are sized? I've been searching all day to no avail. It's more for curiosity sake.

I currently have a banjo bolt with a 145 jet and it makes approx 15-17psi. I also have a banjo bolt with a 1/16th hole drilled in it, and in 3rd gear I get a boost spike to 20psi before dropping to 14 by redline.

Again, mostly curious because the jets are so quick and easy to change it'd be the next best thing to an MBC.

how are you changing (or planning to change) the fuel/ignition maps to compensate for the different boost levels?

the jet only changes the dynamics of the boost regulation, it does not act as a boost limiting device. it regulates how fast the boost can change, not to what level it levels off at.

this is why you are getting huge overshoots in boost levels.

Nize - I'm not. By the looks of the AFR, (with the 145 jet installed) its plenty rich enough to support more boost. Even with the smaller orifice bolt installed, my AFR ran between 11.2 - 12.5 while on boost.

Cockerpunk - My understanding was that the orifice caused a delay in the KLR getting a true boost reading, causing the spike. Then it dropped off because the KLR resumed normal operation by triggering the cycling valve. Is that accurate?

exactly right

Few things to keep in mind:

The FPR does have manifold pressure on the back side of the diaphragm, so as manifold pressure increases, so does fuel pressure. When increasing boost, it does not necessarily lean out the mixture, since fuel pressure increases proportionally to boost pressure. But it is critical to monitor AFRs when tuning a car for higher than stock boost. EGTs are also good to watch. But you do need to know how to measure and interpret all the data thats collected.

The APE II ignition curves are mapped for around 1 bar(g) boost, so about 14.5 psig pressure, using premium fuel. If you increase boost above that, the risk of detonation increases (higher boost higher temp, but the same ignition timing). Chips mapped for very high boost will either require race fuels or they retard the timing to reduce detonation risks.

The APE II chips originally came w/ 5/64" and 3/32" jets, with the instructions to test the jet size in order to target 2 bar (abs) boost pressure. Due to variations in cars, there will not be a definite boost level for a given jet size. You will need to test your own jets and measure the boost levels reached for your own particular car. Make sure you have an accurate boost gage when doing this.

The cycling valve is a little solenoid valve that is used to control pressure going to the WG diaphragm. It does this by modulating flow/pressure from the intercooler pipe (banjo bolt) and directing some to the WG and redirecting some flow back to the inlet of the turbo (bleeds pressure off to the j-boot). The solenoid has a open/closed sequence mapped on the KLR chip, very fast cycling, so the piston in the valve assembly is nearly fluttering to modulate pressure to the WG.

The KLR does monitor boost pressure, but it is not a closed loop feedback/controlled system. It does not alter the cycling vavle duty cycle to adjust for deviations from stock boost. This is why you can shim the WG (increase pressure required to open the WG), or you can restrict airflow to the WG (jetting the banjo) which decreases the pressure going to the WG. Either will increase boost, although both are a somewhat crude means of doing so.

The primary reason that boost drops off at higher rpm w/ APE II chips, is that the k26 series turbos run out of breath (especially the -6, but even the -8 will significantly). If you were to use a K27 or other larger turbo w/ APE II chips and the jetted banjo, you would generate a somewhat flater boost curve.

Thank you for all that info! That was partially my reason for asking about this. I had a vague understanding of what was going on, but more knowledge is always welcome!

I see what you're saying about the turbo running out of breath. I have the -8 and when running a jetted bolt that provides 16psi it stays relatively flat, however anything higher tends to fade somewhat before redline.

**Double post**

Great thread, great info from many knowledgeable people. As time goes by I am getting a much better understanding of how this all works.

I have APE stage II, but mostly stock otherwise. I plan a Lindsey dual wastegate and MBC in the future.

Jeff

I'm planning to go to the A-tune, MBC, and probably Tial WG. In time anyways, but first I intend to keep reading and learning and ask questions when I can't find a good answer.

Thanks for not turning on the flames right away!