I have a buddy's car I was tuning at the track and we seemed to have a big boost fluctuation in certain gears. He has a Precision Billet 6765 (Anti-Sruge H Cover with 0.96 A/R) with a Turbosmart 48mm wastegate and if I remember right an HKS manifold. It seems through 3rd and a bit of 4th, the boost is fluctuating downwards. I was thinking it might be the wastegate but its fluctuating downwards instead of spiking up like you'd expect when its a wastegate problem. He is using the FJO boost control solenoid to control boost and I had it set to run the same duty cycle across the whole RPM band (the problem doesn't seem RPM related anyway). Has anyone experienced this before or know a possible cause?

The only other thing I can think of is a failing wastegate as opposed to too small of a wastegate but it ONLY does it in 3rd and a touch of 4th, never in the higher gears. Also, it was working fine last year with his old GT35R with everything else exactly the same. Nothing was changed but the turbo this year.

Here is a graph of exactly what is happening. It's a pull down the back stretch at Mosport, 2nd - 3rd - 4th - 5th. This was taken in the morning when it was only running about 1.15 bar. I forgot to save the logs in the afternoon when we had it close to 1.3 bar (turbo really starts coming alive here ).

Red - boost
black - AFR (included to show its not the cause of the problem)
green - RPM



thewird

 

pic doesn't show up.

also, can you explain how the plumbing is hooked up? What size hoses are being used?

 

Plumbing for for what?

Here is the pic again... Not sure why it didn't show.



thewird

 

I'm a half idiot lol. I just realized I still had the last log open on my tuning laptop when I tried to turn it off, it asked me if I wanted to save it. So here is the 1.3 bar log. Same back stretch at Mosport. Notice the problem still happens in the exact same spots and gears even with the higher boost.



thewird

 

Is there a sensitivity setting on the boost controller? I know on my turbosmart there is a sensitivity setting so that it doesn't try over-compensating too much. It sounds to me like a boost controller issue.

It would make sense that it needs adjusting over the 35R, because when this thing comes into boost, it comes into it harder, flows more air.

 

The only type of boost control allowed with the FJO boost solenoid is a 16x16 cell with TPS vs RPM for duty cyle. I just fill all cells with the same duty cycle %. With the old 35R, I would ramp up the duty cycle at high RPM since it was losing boost up top (probably due to the 0.82 A/R) but with the 6765, boost is flat all the way to redline so there is no need to ramp it.

I was thinking about the same thing over the 35R and if it was overboosting or spiking it would make sense. But its doing the opposite by spiking down, in essence losing boost. And to make it even more curious its perfectly fine in 2nd, half of 4th and 5th gear >_>

thewird

 

That's weird, so it does not reference manifold pressure at all? I'm not familiar with that controller at all. I'm just thinking, 100% throttle, 4200 RPM in 4th gear would seem to me to be loaded much differently from 100% throttle, 4200 rpm in 3rd gear, you know? You'd be getting more mass flow in the 4th gear pull, and require less duty cycle in 3rd to maintain boost, that's all.

 

It's integrated with the water injection system so if the water pressure drops, it shuts off the bosot. I need to laptop to make any changes. The only other boost control variable is the max boost setting which I had set at 20 PSi. If it kicks, it shuts off the boost completely until you flip the switch on and off so thats not it. Yah, neither I or Jim understand the whole thing either which is why I opened the thread hoping for different perspectives

thewird

 

Spring pressure versus desired boost level can also play a factor. If you're running a 13lb spring and are trying to run 20lbs in some instances you will get fluctuations like that. That said I'm guessing your not really doing that, as it would seem you're having the problem around 15psi. I would first remove the boost controller entirely and run it and confirm the gate itself is ok. If so I would start looking at BC settings.

~S~

 

Oh yah, I should have probably mentioned it doesn't do anything unexpected with the boost solenoid off running wastegate pressure. Zero R, like I mentioned before your controlling solenoid duty cycle directly and there are no other settings that affect boost. With the boost controller off it does this... That's a 3rd gear pull to 7,700 RPM when I was initially tuning it on the street.



thewird

 

The wastegate and the solenoid. Are you using the top port of the gate? If so, what is the pressure source for the solenoid/top port and the pressure source for theside port? Are they tee'd off the same source or are they separate? Are they coming before or after the intercooler?

 

The boost port on the turbo is being used for the bottom part of the wastegate. There is a port on the IC pipe between the turbo and the intercooler that is used for the boost control solenoid. The lines are the size of the ports on the solenoid and wastegate.

Hmm, after typing that is it possible the pressure at the turbo and the IC pipe may be different in certain conditions causing the fluctuations in those specific spots which makes it seems like its in certain gears only? The rate of change of RPM somehow changes the pressure at the turbo and the IC pipe even though its before the intercooler?

thewird

 

I don't have an answer to that. I would suggest playing with the pressure sources for the wastegate though. It couldn't hurt right?



Maybe try hooking the solenoid and thus the top port of the gate to the compressor outlet of the turbo. Then hook the side port to a source after the intercooler.

 

I've read that you're better off using manifold pressure source for the bottom port of the wastegate, it's a cleaner source. I think it was Sean that mentioned that...

 

If you do that you'll run into overboost issues unless you ment to say the top part of the wastegate (where you hook up the boost control solenoid).

thewird

 

I don't think there's necessarily one best way to hook up an external gate. It depends on a lot of factors, especially target boost vs. spring pressure.

 

If you do that you'll run into overboost issues unless you ment to say the top part of the wastegate (where you hook up the boost control solenoid). At least, thats what I always believed. Don't quote me on that

thewird

 

Another option to try if you can't figure it out is to hook the solenoid up to the wastegate like an internal gate, using the side port only. Here is an example shown with a Perrin solenoid:





Your solenoid duty cycle is then your ratio of ON (venting wastegate side port) to OFF (pressurizing wastegate side port) position.

 

i feel your pain. after a fair amount of trying to get the boost control part of the FJO AI module to work i gave up on the boost control part of the setup. i forget the exact problem but FJO was saying that they were going to fix it.

i reinstalled my AVC-R and am a happy camper. (love the other FJO stuff)...

good luck,


howard

 

Howard,
Did you have random boost issues with the FJO boost controller? This problem only happens in 3rd gear.....2nd, 4th, 5th boost hits 19psi and holds.....Why just 3rd gear?

 

Hay Canadian Guys, you should contact Streetpower @ streetpower.ca. He sorted out the same boost controller and the same turbo set up on my car.

 

We're gonna try putting in a Profec B boost control with the exact same connections to find out if that is the cause. Would kinda suck if thats the problem since that would eliminate the failsafe for the AI.

rx7rocks, if Shawn has any input, the thread is open to the community.

thewird

 

I think I used an old Mazda vacuum solenoid.
Barry

 

I think you might have that backwards or I wasn't clear which is very possible. Best possible source for gate control is the shortest allowable line .25" id from compressor cover to the WG bottom port.


~S~

 

Thanks for the clarification Sean, it was a while ago, I must've got it backwards. Makes sense, since it should be the highest source of pressure in the intake.