MCPaudiTT - DEFCON 1

I finally spent some quality time with my homebrew boost machine (BM) this weekend:

<img src="http://images7.fotki.com/v141/photos/4/435091/1703560/PolishedandAssembled-vi.jpg">

Note that the check valve is backwards in this photo, and I did correct that before ever installing it...

I do have a couple questions, as this is the only BM equipped car I have driven/ridden in.

1. I am seeing spikes that settle in quickly at every gear change. I thought the BM would stop that (Revo programming if that matters)? They are much less severe than they were without the BM. I hit 22-23 psi peaks and settle in to 16-17 psi after a second or two in every gear (the peak and settling psi use to be different in every gear and more radical). Do others see a similar "wave form"? Or do I just not have something adjusted correctly? Or do I have a leak?
2. If 1. is normal, it looks like I can increase the boost so that I peak at 24-25, which should settle at 18-19, right? IIRC, 26 will set a CEL, right? However, I thought others were setting the BM to settle at 21-22 psi, which for me would spike at 27-28 psi - that would set a CEL, wouldn't it?
3. Boost is coming on much more evenly and much sooner (and without WOT), so I think the Norgren pressure relieve is working well.
4. Notes to other self-builders, the plugs on the Norgren valve were both unsealed from the factory, and were the only leaks I found when I tested the system offline. Another note to homebuilders, the plugs on the MetalWorks valves are NOT 1/8 NPT. I am not sure if they are 5 mm or 1/8" BSP. I was able to get ones that match at work, but the bin was unlabeled... I will update if/when I find out what they are.

Thanks for any input/feedback you can give...

TTschwing

Mike...

1) Spikes are short fast rises in Boost pressure that occur as the turbo spools quickly, and before the N75 gains control over the air signal to the wastegate. The Boost machine will basically smooth those and allow normal N75 control and not let those overboost pressures past the valves...You'll still have a slight bit of lag time before all those kick it. It will smooth some more as you put a few miles on the set-up. What you're calling Spike, is really max boost. The car will never hold that, and it really shoudn't. As long as there is an N75 in the system, boost will bleed down with a rise in RPM's so you'll always see a natural taper down to a certain point. Pressure is being diverted to the Wastegate to open it, determined by the duty cycle of the N75 (controlled by the ECU).

2) you can set Max boost at 24-25 if all condidtions are right and the car will typically settle in at 20. Keep in mind, you're making a LOT of heat at that pressure. It's really better for the car to make 22 or so your max pressure..You'll find that's plenty of boost and as get things a little more tuned, you'll find that boost isn't everything...Just one part of the equation. As to when you'll go limp, each car is different...There are a lot of sensors feeding data to the ECU....If all are optimized, you're levels are higher.

To best illustrate spikes and BM control before and after, these two graphs are best. Quicksivas stage 3 just before, and just after a BM install essentially with no tuning of the valves. We guestimated the turns, threw it in there and it was about perfect. Keep in mind, stage 3 programming has a different N75 duty cycle plugged in, the the turbo is pumping much more volume. There is not as big a need to taper boost on this set-up because of the big turbo..

Before you can clearly see the spike:
<img src="http://images2.fotki.com/v21/photos/7/7305/191484/roachpreboost-vi.jpg">

After, see how it's smoothed and elevated:
<img src="http://images2.fotki.com/v21/photos/7/7305/191484/roachpostboost-vi.jpg">

Command pressure is what the ECU is telling the car it wants. IC pressure is actual Boost pressure as measured by the MAP sensor between the IC and the Throttle body. Manifold pressure is a calculated number using MAF signals. Vag will not read any higher than 2550 milibars (or 22.7 PSI or so).

MCPaudiTT - DEFCON 1

boost 1-2 psi, right?

TTschwing

Driveability, Feel, comfortable power levels etc...You're close.

MCPaudiTT - DEFCON 1

Get the feeling I won't see many/any TT's there. If I do, I will be sure to snag a shot!

Not sure I will get a chance to install the modTTallica **** before I go, either... I want to butt feel the change when I put it in, so I need a few days after I put it in to feel the delta...

ITALSKIER

nice explanation,steve.......)

FAN OF F1

If so, then mine is working correctly. I kept trying to get it to go to 22 psi and stay at that boost level all the way through the rev range. I have the upgraded spring in my DV, SAMCO hoses, ect and could not figure why I was seeing this bleed. If what you are saying is that this is normal, I will be very happy. The car runs great with the BM, ****, TTDA and FPR upgrade. The boost issue was just puzzling me. For those wondering what it feels like...I have an APR 93/100 octane chip. With the above upgrades, it feels like the car is on 100 octane when I am running the 93 set-up. I have not driven it yet with 100 octane since the upgrade to see what that is like.

blackfnTTruck

Yup, just what I was going to say....................NOT, very informative, as usually, Steve

MCPaudiTT - DEFCON 1

pressure regulator, so I thought it would hold at what I call a peak, too. I thought the N75 would bleed off any pressure that the regulator passes (anthing over the set value of the regulator). Hence my original question. I don't have any complaints about how it is working now, just wanted confirmation that it is normal, which I feel I have now received. It sounds now like that pressure must pass by the regulator and on to the N75, and the N75 must see the excess pressure before relieving it (at least that is my current understanding).

Now waiting for my **** (BAMM) to get here this week, and I will have a full ModShack Stage III in place...

Thanks again, Steve, for your informative response, and your willingness to help with a home-built system!

TTschwing

Since the regulator is before the N75, it sorta Clamps the pressure pulse at whatever setting you dial in. It then is passed to the N75 which is purely mechanical also, but controlled by the ECU. The Duty cycle of the N75 solenoid starts out at 96-98% (all air going to the intake hose) and gradually, with RPM's drops to 60% or so with the difference going to the wastegate to crack it open and bleed boost. Duty cycle is duty cycle. I'm not sure if there are any other inputs besides RPM, but it appears to be pretty consistant...

<img src="http://images8.fotki.com/v132/photos/7/7305/191484/turbo_schematicvicopy-vi.jpg">