Fabio421

I'm shocked that a BOV or a recirculation valve isn't part of the kit. That seems like an odd place to cut corners. Maybe the idea was that since there is such a long run from the compressor to the throttle body, there would be enough volume that you wouldn't see comp. surge during shifts, only when you close the TB for extended periods. In an auto car like this one, I guess a BOV is less necessary than on a 5 speed. I've never really thought of it like this before but I guess I can see the logic ( if I'm even remotely on point ). Still, a BOV is better than none.

Keep giving us the updates. Its coming along nicely.

ptuomov

Is the wastegate reference pressure from the manifold pre or post throttle plate?

Imo000

There are factory turbo cars that run 10psi and never came with a bypass valve. At only 5psi nothing will happen to the compressor. My Paxton SC kit for my Trans Am didn't have a bypass/blow off valve either.

atb

The P9 guys had one one their test mule for a long time. It was part of a pretty elaborate system up in the engine compartment with a custom made alumimun air box etc. I don't think it ever actuated at 5 psi so they left it out of the kit.

killav

Tuomo,

The boost reference is taken directly from the outlet of the compressor (there is a fitting here). The STS manual stated that I could run a boost reference line up the manifold, or a short one (about a foot long) from the compressor outlet directly to the wastegate. If I remember correctly, I think the manual stated that you would see slightly less boost at the intake by using the short method, but the boost pressure is monitored more accurately.

Running a long line from the turbo in the back to the engine might be a cheap way to see a little more boost at the engine without changing wastgate springs-the trade off being slower wastegate response.

I can not remember at the moment, if the manual stated (if running the line to the manifold) to install before or after the throttle body. I think it was after the TB.

killav

I do plan on going a little higher with the boost, so I thought I would go ahead and install one now. The compressor surge I am hearing is very mild, not like you would hear on some 25 psi Supra with no BOV

As far as the BOV not actuating, I can't see how it couldn't. I have an 11psi spring in the BOV but it does not open at 11 inches of vacume. I tested it with a mighty vac, and it pops open at about 22 inches of vacume with no pressure on the other side. My engine pulls about 17-18 inches of vacume at idle, about 19-20 inches when closing the throttle at speed in a lower gear. Add the boost pressure on the other side once the throttle is closed shut and 19ish inches of vacume on the other side and I have to believe that this thing will pop right open.

88 928 Turbo

It definitely doesn’t hurt to add a blow off valve, although it’s not all that necessary on an automatic. On the other hand, a BOV is necessary on a 5 speed car allowing the compressor to continue to spool or “free-wheel” between shifts. This allows the 5 speed car to be at boost, and “free-wheel” during a shift in order to decrease the spool up time after the shift eliminating turbo lag. On an auto you just don’t have the constant on-off-on boost of a 5 speed.

Mike - I have been running my auto for a few years now @ 7-9 psi without a BOV and have yet to have any issues. As an automatic your BOV will mainly actuate when you are at boost and abruptly lay off the throttle, otherwise you probably rarely actuate it under most driving conditions. On John’s auto, which is running upwards of 14 lbs of boost we do have a BOV installed. This helps with compressor surge at the dragstrip and on the dyno, once again, when he or I abruptly lift off the throttle.

You are on the right track for tuning the BOV, a vacuum gauge is a must. Just be sure when all is said and done that you check to make the sure that the BOV is staying closed while in gear at idle. Then have someone watch your BOV while on the dyno to make sure it is opening properly.

Similar to all of the STS kits (which typically come as a base without BOV’s) a BOV can be added to the p9 kit for 5 speed cars.

ptuomov

At 5 psi WG spring and the WG referenced to the compressor outlet I am guessing that it's going to be safe to run it without a bypass valve. If there's a slow pressure surge in the long pipe, I am thinking the wastegate may open and slow down the turbine and compressor. My understanding is that the compressor surge is a danger only at high pressures, but I may be wrong.

It would be better to have a bypass or blow-off valve, of course.

You should fit a manual ball valve boost controller to the WG reference line so that the WG doesn't crack open too early. Maybe you already have one. If you don't, it's probably $25 or something.

I am running 18 psi with an early '87 stock long block at high rpms. Even without intercoolers, I think you can go higher than 5 psi at top end. You might want to consider adding a eboost2 electronic boost controller that allows you to tailor the boost profile separately at each rpm point. That controller is worth about 50-100 peak whp on the Kuhn twin turbo system.

killav

Ok I took the car out again last night, and something just wasn't right. (It's funny how quickly your brain gets used to boost). I was more agressive with the throttle, but I was only seeing about a pound/pound and a half of boost no matter what I did with the throttle. Plus, the spool up just did not sound right, it was very quiet compared to the day before.

I went home and started looking for the problem. Turns out that I had a joint pop apart under boost the day before. The crossover tube that runs up along side the engine is made out of two peices of carbon fiber. The Kit comes with about 2 feet of silicone hose that you cut to fit in order make all of your connecting pieces. I cut the one holding the carbon fiber pieces together to short-it was barely holding on to the tube on each end. I was pretty happy that this is all it was.

Edit: I had a long piece of silicone hose left over, more than enough to make much longer piece to connect the two carbon fiber pipes.

killav

Here is a video of what the exhaust sounds like. The crossover was disconnected at this point (unknown to me at the time). If you listen carefully, you can hear the turbo spool up, but the boost gauge is still in vacume. I really had to lay into it to get that pound of boost on the highway LOL.

http://www.youtube.com/watch?v=Db700ZNH-c4

Tom. M

Nice find... that's much better than heading down I5 to Sharktoberfest a few years back....doing something resembling triple digits dicing it up with a few 928's and 911..when all of a sudden you hear a phuuuuuump!!!!...and the hood lifts slightly in the back..and all your power is suddenly gone!

Was able to limp the car to the next off ramp..thinking I blew it up... seems the boot holding the airbox/blowoff valve (I had the old style setup...not the carbon fiber one) had come off the MAF... after a few minutes letting it cool down.. the boot was back on..and we were on our way...

killav

I wanted to give an update for those who are following along. I finally got the tuning to the point that I felt comfortable getting on the throttle a lot more last night. All I can say, is this kit is worth every single solitary penny. I am thoroughly impressed. Getting sideways at 25 mph going up hill on an on-ramp is why I shelled out the money for this. It has been said before on this board, it completes the car.

Anyone that has any reservations about turbo lag with a rear mounted turbo need not worry. There is virtually no lag. The torque of the V-8 gets things moving along very nicely before boost hits at 2300 or so and is all in by 2600-2700 rpm give or take a few. I am still recording zero knocks so there is still room for improvement. My initial EZK map was backed way off. I am back to about 5 degress retarded at the point where boost hits maximum so the rule of thumb (1 degree per pound of boost) is working for me so far. I have the timing backed off even further at the upper end of the load/rpm range.

The blow-off valve is working however I need to change the spring out to a 9 psi spring. The Tial unit was supposed to have the 9 pound spring, but it has an 11 pounder installed. I get a couple of chuggs from the compressor turbine on abrupt throttle closing before the BOV opens up. It is louder than I expected too. Hearing that Pshhhhh is pretty friggin cool.

John Speake

Great fun :-) Thanks for the update.

AO

Rock on, Mike!

killav

Here is a plot file from last night. The AFR was about 11.7 to 1 on the one pass that I made with the WOT switch activated (See yellow dots on lower right hand side). The car was still not floored, about 8/10 throttle or so. I changed the WOT cells in this area to 50 before the pass in order to make sure it was on the fat side for my first attempt at more throttle.

I had one knock finally in the 4800 rpm cell(you can barely see the small x on the far lower right of the plot) but this is not a BIG X therefore within tolerance I assume. This is a small sampling from about 30 minutes of driving last night. There are a lot of log files but not very many data points. I kept stopping the logging when I was just idling or at cruise on the highway. I need a lot more data to finalize the base maps but this was a start none the less.

All of the rich/lean cells were fixed (auto-adjusted), and the new map is already loaded into the PEM. Amazing stuff.