Too much boost=bad

[Hey]

As you know, I have build an electronic VNT controler.

I have played with the setting a lot these pas days and I came across something very interesting.

I was able to have the boost vary all the time. For example from 3 to 10psi on the highway.. continuously.

What I saw is this.. at 10psi, I could feel the car slow down... at 5psi I could feel the car going faster.. etc. Same thing happened at low speed. So.. having too much boost is bad for torque/hp/consumption.

THis is why the A4 tdi do 5.5l/100km in town and the A3tdi do 6.1l/100km in town.. the turbo is less restrictive on a VNT.

So for those that runs a lot of boost... be sure it is necessary.

[Jay]

Not enough fuel for the amount of boost?

[Rabbit on Roids]

think of it, boost is slowing down the piston. it takes force to compress the air. we are already running 24:1 compression.. and with boost you add 1 point of compression for every pound of boost. so you guys running 25 psi are pretty much running effectively 50:1 compression or so. thats gonna take more effort to push the piston up. thats the only reason i can come up with...
-edit-
anderw posted at the same time i did, so he might be more accurate.

[Turbinepowered]

So how do ECO engines, with no fuel compensation for their boost, improve mileage?

[rallydiesel]

That's why it's so nice to have a boost gauge measuring exhaust manifold pressure. It's all about flow, not necessarily pressure. The northern European diesel tuners have been able to get impressive power by focusing on increasing flow and not really worrying about pressure. It's also how you keep the head from lifting.

[rabbitman]

I totally enjoy reading this kind of stuff , makes perfect sense not to pump more air in than necessary.

[Hey]

I knew you would like that!

I have gained A LOT of HP since my controler has been installed.. and this is all due to a good ratio boost/fueling. I had too much boost when accelerating slowly.. I could feel the car slow down...or I can now... because I feel like 3200tr in accelerating slowly is very fast coming... I never shifted there before but now it all goes by itself. I need to re-educated myself to wait less time before shifting.. lol!

For those who have mechanical controlled VNT .. adjust it so you have 0-2psi at 100km/h and only about 5-7psi when accelerating slowly in town driving.

[jasonsansfleece]

Can you explain Rallydiesel's point about the  gauge measuring exhaust manifold pressure?
Guy

[Rabbit on Roids]

I knew you would like that!

I have gained A LOT of HP since my controler has been installed.. and this is all due to a good ratio boost/fueling. I had too much boost when accelerating slowly.. I could feel the car slow down...or I can now... because I feel like 3200tr in accelerating slowly is very fast coming... I never shifted there before but now it all goes by itself. I need to re-educated myself to wait less time before shifting.. lol!

For those who have mechanical controlled VNT .. adjust it so you have 0-2psi at 100km/h and only about 5-7psi when accelerating slowly in town driving.

i still have no control, but thats about what my turbo puts out anyway... i have about 3.5 psi at 60 (100 kmh) and when im accelerating, say pulling out onto the highway, i get about 5 psi, unless i really stand on it.

[saurkraut]

at 10psi, I could feel the car slow down... at 5psi I could feel the car going faster.. etc. Same thing happened at low speed. So.. having too much boost is bad for torque/hp/consumption.

This must be a VNT only situation.  I'm running k24 turbos with the waste gates disconnected, so the more I push on the pedal, the more boost i get, and the faster I go.  My cruise boost is at around 7 PSI.  If I touch the go pedal, boost climbs rapidly past 10 PSI, and the engine starts pulling noticeably stronger.  Full throttle boost is around 30 PSI and it really goes nuts at full boost.  So my torque/HP are noticeably better with more boost.  My fuel consumption, eh, not so good.

Perhaps you should edit your post title to reflect that this is a VNT issue.  For my stuff, more boost is always better.

[jtanguay]

As you know, I have build an electronic VNT controler.

I have played with the setting a lot these pas days and I came across something very interesting.

I was able to have the boost vary all the time. For example from 3 to 10psi on the highway.. continuously.

What I saw is this.. at 10psi, I could feel the car slow down... at 5psi I could feel the car going faster.. etc. Same thing happened at low speed. So.. having too much boost is bad for torque/hp/consumption.

THis is why the A4 tdi do 5.5l/100km in town and the A3tdi do 6.1l/100km in town.. the turbo is less restrictive on a VNT.

So for those that runs a lot of boost... be sure it is necessary.

sounds to me like you need to open up your exhaust 

[saurkraut]

No problem.  I know I’m not achieving the best efficiency out of the fuel.

My hart burn is with the title of this post "Too much boost=bad" and the comment that “having too much boost is bad for torque/hp/consumption”.  And the we have 10 PSI mentioned as the point that things fall apart.    I’ll give you that the consumption is an issue, but the torque and HP are great.  Its a little tough on transmissions though.

[Rabbit on Roids]

tough on transmissions? im pretty sure im never going to have to stray away from an 020 in my car. i just dont think there is enough car there to hook up the tires good enough to break poop. a 1600 pound car just doesnt seem like it would be hard on trannys. i dont doubt it tho, im not saying you are wrong, just saying that i never have enough traction to break anything.

[saurkraut]

Try driving on twisty roads at high speed with allot of throttle.  You'll bust trannies.

[Rabbit on Roids]

i do drive like that often. have had good luck with my gasser 5 speed.