wcbcruzer

Can your truck make boost if you free rev it in park/neutral? I can make up to 5 psi at about 2200 rpm.

Video clip:

http://www.youtube.com/watch?v=O847tnHUQzw


Reason I ask is because it seems some people can't. Maybe someone has an explanation.

Yellow Yota

Max of 5, but not normally that much. Seems like it'll come up a few pounds, then fall off a bit after the motor spins up.

Dartmouth 12V

Yes, you should be able to make boost in neutral. A heavily modified truck that puts out more fuel(heat) and spins more rpm will make more but all of our trucks will make a little.

JohnX

You meant to say almost all, right?

Mine makes no boost just the way it sits now, made just enough to get the needle to flicker before i did the turbo.

infidel

Both my trucks are around 350 hp and will just barely move the boost gauge floored in N.
Of course it's not something I've tried often, hate burning fuel without moving.

sleepr tsi

Mine doesn't make any boost without load.

cumminsdriver635

I can get mine to 10psi by revving it hard, letting off and stabbing it again when it gets back down to about 2k rpm. Thats even with my hx40. The 4k helps too im sure.

wcbcruzer

So what could cause some trucks to make boost, and not others? I have my #10 plate in the stock position. Starwheel hasn't been messed with. Timing is still stock as far as I know. My egts don't go over 1150 degrees. Truck doesn't smoke unless I rev it real quick from idle. The gsk I did is the washer mod. I get 14.7 mpg city and about 20 hwy. My city boost levels are 7-13 psi average on take off to keep up with traffic. Hwy boost levels are about 7 psi at 70 mph and 10 psi at 75 mph.

Dartmouth 12V

Think about what boost is and what your turbo does.

Boost is a measure of pressure in your intake. Since it is pressure, it is a function of both the restriction of the intake and the amount of air being rammed in there. This is why people port their heads, so that they can move more air with less boost pressure. Any time air is being forced into an engine, there is some "boost" it just may be very little. A naturally aspirated engine actually has negative boost since atmospheric pressure is greater than that in the intake and the air is sucked in rather than forced in.

Your turbo is a thermodynamic device that takes the energy of your exhaust and uses it to turn a fan that forces more air into your intake. The more BTU's that come out your exhaust, the more air it will force in. At idle, there is very little energy lost out here so the turbo is barely spinning. It may actually be that a stock truck has negative boost at this point, I am not sure, it depends on whether the turbo is moving more air than is being sucked into the engine. When doing a free rev, you put out a little bit more energy in the exhaust so it still won't spin the turbo a lot but you will build a little boost, even on a stock truck. When you put the truck under load, a lot more energy comes out the exhaust which makes the turbo build a lot more boost.

The factors that play into how much boost you can make are related to airflow restrictions(whether the head is ported, # valves, etc), the turbo, the rpms, and how much fuel you are injecting.

JohnX

Thats a nice explanation, but it doesn't really explain why some people never get boost revving a stock truck, and some people do. When my truck was stock, needle wouldn't even twitch. With the 330 injectors it would only twitch to maybe one psi. Now with the new turbo, plate, and gsk...absolutely nothing.

Maybe the difference is in the gauges.

Diesel Dave2

Same here....No boost in N....at 2200 RPM...

murphy41

Wouldnt elevation have an affect on that ? the lower you are the more dense the air is ??

BigErksG2

true as well... there is more oxygen in air at 0psi at sea level than 0 psi above sea level (4000 ft) so the same amount of air modifications and the same amount of fuel would produce more exhaust energy to be transferred to the turbine wheel in the turbo at sea level.

clm12valve

i can hit around 10 psi but before the gsk 2 psi

infidel

Perhaps some folks see no load boost due to restrictions in the exhaust system in relation to power mods added.
Stock exhaust or a plugged up cat would make a big difference.