Thread: Ideal boost at cruising speed

depends on the load and operating conditions.

I cruise around the tdi300's at 10-11 psi boost at 105kph in the disco.

IMHO your boost pressure at cruise is too high. And will most likely be hurting your fuel consumption though too high a ration of drive pressure to boost pressure.

Ideally you want the variable nozzle to open (and therefore reduce drive pressure) when you lift your foot to cruise and close when you push it down to accelerate hard.

This involves extra complexity with the accelerator position here is a link to what someone has done on a merc diesel I have see other solutions, a LR Tdi for example, but have lost the link unfortunately.

I agree with John...for example my boost at cruise was around 7-8psi and max boost was 30psi with a exhaust A/R of 0.50 on a turbo that is not suitable for what I wanted....I havnt played with the vnt's however sounds to me as though something is not quite right with vane position.

Thanks guys. Looks like I have some playing to do.

At cruise my boost is around 7psi, with max boost around 18psi (conventional T25 turbo).

Steve

Originally Posted by inside

Thanks guys. Looks like I have some playing to do.

The first thing I suggest, is to measure the drive pressure (pressure in the exhaust manifold) also commonly called TIP (turbine inlet pressure).

If this pressure is less than the boost pressure, then don't be too concerned.

However if the turbine nozzle is causing to much restriction (which is how it increases TIP so the turbine can develop the torque necessary to drive the compressor faster), then you are loosing power and wasting fuel for no good reason.

the grubb on here was building a programmable controller for his VNT turbo and others have done the same - see this link This is the most flexible way to get the best from a VNT.

What is your cruising rpm?

Originally Posted by Bush65

The first thing I suggest, is to measure the drive pressure (pressure in the exhaust manifold) also commonly called TIP (turbine inlet pressure).

If this pressure is less than the boost pressure, then don't be too concerned.

However if the turbine nozzle is causing to much restriction (which is how it increases TIP so the turbine can develop the torque necessary to drive the compressor faster), then you are loosing power and wasting fuel for no good reason.

I see what you're saying but it just doesn't sound like fun.

My problem I think is the vacuum on the actuator is too strong so it's not moving away even when boost increases. If I fix the strength of the vacuum I think the actuator will be more free to move.

Originally Posted by Dougal

What is your cruising rpm?

The Ashcroft calculator says 1872 at 80kph and 2340 at 100kph.