killav

I have been shark tuning on an 86.5 mid mount turbo for a few days now and have ran across an anomaly I cannot explain. When under full throttle, the car will reach 6lbs of boost by 3k rpm's, but steadily drops off to a low of around 4lbs by 6k rpm. The sharkplotter map clearly shows this. I forgot my laptop today, but will screen plot the latest map that I have to show what I am seeing.

The load reaches the 1000 range on the MAF load around 4k and then steadily the MAF volts drop as the RPM rises, following the drop in boost and reduction in airflow into the engine. I would suspect it is just a simple leak somewhere but I am not sure. The sharktuner tuned right around this. Car runs really good, and is pulling strong even though the boost is dropping off. The sharkplotter/sharktuner adjusted the fuel for the dropping airflow. But, if I get this fixed, the mixture will be lean again.

Thoughts.

James Bailey

Would not the air flow into the engine at 6,000 RPM be about TWICE the airflow at 3,000 RPM. So boost/pressure at 3,000 RPM has more resistance due to the lower air flow. Then at 6,000 the greater needs of volume might cause the pressure drop. Perhaps has much to do with the sizing of the turbine and compressor wheels. Much like camshafts you can pick the RPM where they work best BUT you can not have both high and low RPM performance.

Speedtoys

Turbo too small? What's the flow map for your shooter?

hacker-pschorr

Was it always doing this or did it just start happening?

I cannot remember if you had this car on the dyno, did it do the same there?

Have you pressurized the intake with an air compressor to make sure no leaks? I had an issue way back in the first days of my supercharged setup. The leak didn't show itself until the upper end of the boost scale. Ended up being an intake gasket at the head. Once I reached a certain level it bled off any additional boost.

Lizard928

Either the turbo is too small and not able to supply the air needed (which means that it will be overrevving too), or you have a wastegate issue.

killav

Ok, I just spoke with Sean who installed the turbo kit. The kit comes with a boost controller that I am not familiar with. The car does have a vacume leak issue at least in the HVAC system. When opening the throttle enough for the engine vacume to drop, you can hear the fresh air flap open and the air gets much less cool-the heater valve is probably opening at least partially as well. According to Sean, this boost controller does have vacume from the engine running to it. It could be as simple as a vacume leak.

SeanR

Vac leak at the boost controller.

Turbo is a 62mm.

killav

That size turbo should be good for HP levels way North of 500.

As a side note, somewhere along the way, the digital boost controller lost the 6lb setting, which I did not notice unit last night because I was tuning in 1000 rpm increments as to not blow anything up. Last night was the 5000 to 6000 range session (read go to jail tuning). Anyway, I was seeing boost numbers up into the 8lb range (nowhere near redline) and the ST was doing a wonderful job of adding an enormous amount of fuel to compensate. So I know the car will get up into higher than 6lbs of boost which leads me to further believe the issue lies in the vacume source to the boost controller. I don't know why, but I did not notice the boost dropping off as mentioned above until I reset the controller to 6lbs. Not sure why, but the car was still building boost when I let out of it so if the car ever reached whatever boost level it was set to then it probably would have started dropping off maybe.

Oh yea, the car is a beast at 8lbs with proper fueling!

Cosmo Kramer

Where did you T in the vacuum line for the boost controller?

A turbo that size should support 450 - 500 hp so size is OK.

killav

Ted I am not sure as I have not traced that down just yet. Sean might chime in and shed some light.

SeanR

I think I've got it T'd off the 3 way at the brake booster. It was back in December when I did that so I may be wrong. I do know I tried to keep each system that was on vac separated.

SeanR

Hey Mike, a thought.

You said the boot on the cold side of the turbo blew off right? The boost controller and vac source line is locate real close to that. There is a chance that when the boot blew, it took those connections out.

Just got off the phone with Pele, he's bringing the car in for a top end refresh first week of next month, coil overs will go on at the same time.

killav

Yes if your standing facing the car the left (passenger side) boost tube blew apart upon throttle lift on the way back to John's. The BOV just doesn't seem to be blowing off very rapidly, even more evidence of vacume issues.

Re:top end refresh. Cool. I plan on burning a chip tonight where I am at now and then we can finalize after the top end refresh.

SeanR

I"m talking about down at the turbo.. That boot.

Tom. M

Does Mark R's kit relocate the Maf to the intake side of the turbo?