'98 T5 Max Boost <3000 RPM

Post by **boosted5cyl** » 20 Mar 2011, 10:06

Ive noticed a few people have mentioned that you should not exceed x amount of boost under 3K RPM with these motors. Is this due to detonation, rod bending or boost spikes?

Some said 7psi and others said 10psi is the figure to not exceed <3K. Which is it? I'm thinking of setting my wastegate actuator pressure that number -1 or 1.5psi to see how the car performs. Currently its set to stock: 30Kpa (4.35psi, call it 4.5psi). Basically im looking to give the car a bit more pep on partial throttle.

Also, while I think of it. How is the TCV solenoid controlled in this car? It doesnt have a MAP/pressure sensor so what determines the boost. MAF reading? Load?

Post by **jimmy57** » 20 Mar 2011, 11:13

If you have auto trans the boost is reduced in lower two gears to reduce stress on final drive and to prevent BAD torque steer and very touchy throttle.
The motor really doesn't care, Volvo does nothing to hold it low on manual trans models.
There may be some reason to play it cool on a really pumped motor with nitrous or other radical mods.
The TCV control 98 and older is a mostly fixed program with overboost monitoring via MAF vs RPM. If MAF signal exceeds diagnostic program amount it is contrued as overboost if the oxygen sensor V is also within acceptable range.
Some regulation based on computed torque (from TPS-MAF-RPM) to attempt to keep torque even over the broad range of rpm.
If you set base that high you'll set codes. The TCV won't be able to bleed enough wastegate feed to keep it within max allowed.

Post by **jblackburn** » 20 Mar 2011, 12:52

They do have a MAP sensor just behind the washer fluid tank; but I'm not sure how much it contributes to the whole air/fuel equation.

Adjust that rod too much and you'll screech tires from a stop and have an extremely touchy throttle. I shortened mine by about 1 1/2 turns, and it takes off nicely now without lurching.

Post by **boosted5cyl** » 21 Mar 2011, 06:35

I plan on any adjustments I make being measureable (pressure V # turns) and gradual. Any thoughts on the max PSI below 3000. 7? 10?

Post by **jblackburn** » 21 Mar 2011, 07:09

I think as long as you're still using the turbo control valve (read: not a manual boost controller) the ECU will automatically limit the boost to ~7 psi or so in 1st gear off the above stated concern with the auto transmissions. After that, most times when you floor it above 30 mph the RPM will be close to or above 3000 and it will boost to the full pressure of whatever you set it to.

Post by **boosted5cyl** » 21 Mar 2011, 08:41

Cool, ill play around with it and report back......

Post by **jimmy57** » 21 Mar 2011, 10:57

jblackburn wrote:They do have a MAP sensor just behind the washer fluid tank; but I'm not sure how much it contributes to the whole air/fuel equation.

The sensor many call MAP on later is the Boost sensor and is not used as atmospheric sensor since one is built onto the circuit board of Mot 7.01 ECM's.
The violet colored sensor on your car is an ambient pressure sensor and has very little to do with boost.

Post by **jblackburn** » 21 Mar 2011, 11:03

I figured as much; mine went bad and I could tell absolutely no difference in the way it ran.

Post by **Juan62** » 28 Mar 2011, 17:36

I highly reccomend a HD Turbo Control Valve and a Compressor Bypass Valve (install the red spring) from IPDusa.com Also, they have a video (FEB or MAR 2011) new letter titled "Turbo 102." Watch the video... They also have a boost gauge tester to adjust your wastegate. Hope that helps. P.S. On Sale now!!!!!!