Not boosting in all gears

[Jesus-Ninja]

So, I have this weird boosting issue. It's hard to tell when it started, as just before I smashed up the front end, the clutch was slipping on full boost. Then I smashed it. When I rebuilt it, I had to replace all the stock pipework, so upgraded the lot with 3". Clutch was still slipping of course, and worse, so wasn't able to really nail it. Clutch is done now, so lots of grippage :)

So, here it is...

In 4th or 5th pulling from about 2krpm, it makes good solid boost (about 16 PSI, which is a bit lower than I could get before), and it holds it well.

In 3rd or below, I can only make about 8 PSI.

I am at a loss.

The only thought I have is whether I should be able to make more or less boost in higher and loswer gears. The reason I say this is that my boost controller has an OverBoost protection which you set at something higher than your make boost (say 20 PSI) and if you hit that, it drops the boost to half of that value until boost drops off, then it resets. Of course, I'm wondering if I'm overboosting in lower gears and triggering that, but there's no spike on the gauge.

Frustrated, because rolling in 4th or 5th, it's never felt stronger, but in 3rd or below it's gutless. :(

[lathiat]

I'd check your boost controller settings. It might some have some gear, rpm, etc based settings.. or some other settings preventing it from working correctly.

[Jesus-Ninja]

Nope - only input is a vac/boost line. Everything else is power, external control, solenoid etc. Nothing as clever as RPM!

[Davezj]

Vr4 will boost stronger on a boost gauge in higher gears for the following reason,
When the engine is at say 3000rpm and you floor it in 4th or 5th gear the engine can not costume all the boost you are creating, as the engine rpm is too low, so the boost looks much higher than the turbos can actually produce.
when the engine rpm increases The engine will consume more and more air so the boost will drop off at the higher revs.
Well that is what my car is doing at the moment.

Is you boost controller an ebc?
I have a fairly cheap EBC (£150) and does have the over boost protection, but you can choose how much of the full boost you want to cut it by, boost limit value can be set from 0-100% so if you hit the overboost point you can set the limit to 100% and this will basically do nothing and allow the boost to build or set to say 50% and as soon as the overboost point is reached it cuts the boost to 50% of its set point for about 5 second, then returns to normal operation.

My point is can you change the boost limit value when the overboost point is reached.

Sorry if this is a bit of granny sucking eggs description but I thought I would share.

How quickly does your boost gauge change, and track the boost pressure change?
Is it a bit sluggish, I just wonder if you have a restriction in the pipe of the boost gauge. So when you get a big boost spike in 3rd gear which would be a hard power pull, the EBC hits overboost point very quickly, too quickly for you boost gauge to track.

You could test it by removing all boost control so no pressure goes to the waste gates and give it one boot full in 3rd gear to see if it builds full boost or if the boost remains low.
Then you will know if it is the boost controller issue or something else.

Just a few thoughts of mine.

[Jesus-Ninja]

Cheers Dave.

At 3000 rpm, the car is consuming the same volume of air regardless of gear - ie (3000rev/min)*((2.5/2)ltrs/rev) => 3750ltrs/min. Gear has nothing to do with it.

Boost controller is electronic, and I've never had this issue previously. The only changes are the boost pipework, a front end rebuild, a clutch change, and some larger bore downpipes (forgot to mention those!).

As well my separate boost gauge, my EBC itself has a digital gauge with a peak hold function on it, so I would expect to see the peak boost register on there, but it's never over what I can see on the mechanical gauge, so I'm now querying whether it's the OverBoost protection that's giving me this issue. I've also tried raising the OverBoost limit with no effect.

Checking out the pipework all the way from the plenum to the gauges is a good shout. Will have a nosey at that later :) Also like the suggestion of a careful run with no boost control, to see if its a turbo issue.

[Davezj]

Cheers Dave.

At 3000 rpm, the car is consuming the same volume of air regardless of gear - ie (3000rev/min)*((2.5/2)ltrs/rev) => 3750ltrs/min. Gear has nothing to do with it.

but that calculation is for a non turbo engine isn't it. we are feeding more air into the cylinder than 2.5L every revolution due to the boost pressure built, it is the same volume but it contains more physical air molecules because they are compressed.

the point i was trying to make (not very well I might add) is this, accelerating hard in a high gear gives you an artificially high boost pressure untill the engine catches up and starts to use up that extra artifical boost.
i believe to work in the follow way.
1. in 4th and 5th gear you will be accelereting much slower with you foot to the floor as you would if you were in 3rd from 3000 rpm.
2. you will be feeding the max amount of air into the engine and so more fuel will be going in, this creates a bigger bang, and more gases are expelled out of the exhaust port.
3. the turbos spin faster due to the bigger bang and more exhaust gasses and more boost is made. more and more each revolution of the engine.
4. however because you are in the wrong gear for the rpm to make the most of the bigger bang, the engine can not consume all the boost every cycle of the engine. some the boost climbs higher and higher each revolution of the engine. until a point is reached in the rpm band when the engine can consume all the boost and then the pressure stops increaseing (or Boost solenoide bedds it off), above this rpm the boost pressure drops off as the engine is trying to consume more pressure than turbos can generate, or the turbos are out of there most efficient range of boost productioon.

well that is how i see it.
however i could be wrong, but is what my car is doing at the moment.

[Nick Mann]

Dave, I think you are looking at the system if there was no control of the wastegates - i.e. you have set your boost controller to 3.0bar or you have welded your wastegates shut. Normally the boost control should cap the level of boost. I understand your point that if you spend longer at WOT in the efficient range of the turbos then you can potentially produce more boost pressure, but your control system should be sorting that out. On the VR4 the turbos most certainly do run out of their efficient range at high revs and high boost, so you do see a tailing off in pressure, but only because you have set your control above the limit of the turbos at that point. (Or the control is not actually controlling by that point.)

I have also got strange boost things going on. Sometimes my car makes 1.0bar of boost, others it will only be 0.8bar. Occasionally it only makes 0.6-0.7. I have yet to track the issue down, but things I have not done yet are check the continuity of the wire from the ecu to the boost solenoid and check the actuators/pushrods for the wastegates. Not sure if either of those ideas will help you, but you never know.

[Jesus-Ninja]

but that calculation is for a non turbo engine isn't it. we are feeding more air into the cylinder than 2.5L every revolution due to the boost pressure built, it is the same volume but it contains more physical air molecules because they are compressed.

the point i was trying to make (not very well I might add) is this, accelerating hard in a high gear gives you an artificially high boost pressure untill the engine catches up and starts to use up that extra artifical boost.
i believe to work in the follow way.
1. in 4th and 5th gear you will be accelereting much slower with you foot to the floor as you would if you were in 3rd from 3000 rpm.
2. you will be feeding the max amount of air into the engine and so more fuel will be going in, this creates a bigger bang, and more gases are expelled out of the exhaust port.
3. the turbos spin faster due to the bigger bang and more exhaust gasses and more boost is made. more and more each revolution of the engine.
4. however because you are in the wrong gear for the rpm to make the most of the bigger bang, the engine can not consume all the boost every cycle of the engine. some the boost climbs higher and higher each revolution of the engine. until a point is reached in the rpm band when the engine can consume all the boost and then the pressure stops increaseing (or Boost solenoide bedds it off), above this rpm the boost pressure drops off as the engine is trying to consume more pressure than turbos can generate, or the turbos are out of there most efficient range of boost productioon.

well that is how i see it.
however i could be wrong, but is what my car is doing at the moment.

The engine doesn't "know" what gear the car is in, the only difference is extra load in 5th owing to higher drag at higher speeds (3000rpm being a higher road speed in 5th compared to 3rd). By that token if I drove uphill in 3rd I should get more boost. I don't.

[Davezj]

i think my boost control is a bit off , my boost is controlled nicely in a 3rd gear pull from low rpm , set point 1.2 bar achieved 1.2bar quite happily, tailing off to about 1.0 bar at the red line. but in 4th and 5th from low rpm i get 1.4-1.5bar tailling off to 1.0bar at red line. i start hitting fuel cut at about 1.5bar as i raised to this point.

maybe i need to fiddle with boost controller, and do a boost leak test, to see if i have any leaks.

[Nick Mann]

1.5 bar doesn't point to a boost leak, it points to a hooligan in charge of the boost control!

[Davezj]

this is true, but that is why i don't think it is real boost, just a massive spike that never ends until the engine RPM catches up with it. the boost control is supposed to be set to 1.2 bar.
it could be due to exessively long pipe work to the to the boost control electronic box, which i have mounted in the arm rest cubby hole.
might be time to move it to test the theory.

i have got off topic here, but i have not been idle, i have been thinking about the original reason for this thread.
but i am stumpped for now.

[thegoose]

Better check my boost lol

[scott.mohekey]

Is it pulling timing for some reason?

[elnevio]

Just remember that in higher gears, the rate of change of acceleration is smaller (i.e. the speed your revs increase, decreases), so you can build more boost.

[Davezj]

isn't that what i have just said in a more flamboyant and drawn out way.

chers Nev that was much simpler

[Nick Mann]

Just remember that in higher gears, the rate of change of acceleration is smaller (i.e. the speed your revs increase, decreases), so you can build more boost.

I think everyone agrees with that.
Nicks point is that if you are going up a steep hill in third, your rate of engine speed change might be slower than if you are going down hill in fourth, so whilst there is a difference in gear, the engine doesn't care what the gear is.
My point is that if you are controlling your boost, the difference between gears should be minimal, as you are controlling the boost to a value based on load/engine speed but not gear.

[Davezj]

this is very true and very well put nick,
i have been thinking about Jesus-nijas lower boost issue, and it would probably be a good idea if he told us what sort of boost controler he has make and model. there might be some comon/collective knowledge about it.

As nick has just rebuilt the fornt end of his car, what would happen if he has connected it up the boost solenoid wrong way round the boost feed going to the wastegate port and the entry port going to the wastegate. i am not sure what would happen, but it woudl probably be odd.

could it be a knackered turbo that needs very high load to get it to spin up correctly, but it would have spun up correctly when going uo hill in third.

or has the boost controller been accidently set low to 8ps and the EBC is doing it's job correctly, but the start boost point or gain has been set wrongly and this is leading to a massive overboost under high load, which he thinks is the correct set point, but it is not.

did the boost contoler get reset back to default settting when he had his crash and has not been set back up.

or the ebc is just broken.

these are a bit random i know but i can't really think of anything that would cause this,
it is the low boost in 3rd gear when going up hill ptting high load into the turbos and no high boost, that is making everything i think of sound wrong to me.

[Kenneth]

Check the boost feed to whatever gauge you are using for boost.

I had a pretty poor feed to mine (I knew it wasn't the best, just kept putting off changing it) and it didn't respond well to fast boost changes and as a result I had a similar experience to you. I also didn't get any vacuum below -20inHg and idled at -18inHg which I know to be incorrect for my engine.

I got some aluminium tube from a hobby shop (think the OD is about 3mm) which I used to create a hard pipe to carry the boost signal between the plenum and the gauge sensor, using rubber hose only as joiners.

I idle at -22inHg and get full vacuum on deceleration now.