Turbo boost adjustment

[fenlon]

When increasing boost don't you need to adjust the fuel or is that just in gasoline engines? Sorry still learning about diesel.

[Roscoe]

Gday Fenlon, First of all, the speed at which a turbo spins is determined by the amount of heat generated in the combustion chambers. The more heat generated, the more air expansion and volume you get and the faster the air flows through the turbine wheel.

The snail like housing on a Turbo is called the "Volute" and this reduces the diameter of the exhaust manifold outlet down to the inlet of the turbine, This increases the air velocity into the turbine.

The rpm of a turbo can range from about 5,000 rpm up to around 80,000 rpm at the same engine speed, this is determined by the amount of fuel being injected into the combustion chambers, You compensate for load by giving it more throttle, more fuel, more heat, more heat, more air volume and because the pistons are pumping the air out, the velocity has to increase to compensate.

The more air you pump into the engine, the more power you will get up to a point. This is sometimes called the "smoke point" The only way to play with the injector pump calibration is on a dyno, the engine needs to be placed under full load and the fuel increased until you start getting black smoke then back off the fuel until the smoke stops. Some places have "smoke meters" which are more accurate at determining the maximum settings.

With the increased velocity, you can then get flow restriction probs through the exhaust system which is why a lot of people increase the pipe diam size down stream from the turbo.

Be warned, more fuel means more heat to be absorbed by the cooling system and sometimes the cooling system design limits can be reached after doing this, especialy on a long hard climb etc.

Hope this has helped, cheers

[fenlon]

RoeDao, You said anymore than 16 psi could do damage and Graham said no more than 14. Is the boost gauge for this connected near the turbo outlet or at the intake manifold? Also you mentioned I/C temp, is that intercooler? What temp is too high? Thanks in advance for helping with the newbie questions. I just ordered the boost gauge and I don't want to kill a perfectly good MU because I put it in the wrong spot.

Jim

P.S. Thanks for breaking that down Roscoe

[Stu]

Dad's 3.1 Bighorn Irmsher currently peaks at 14.8psi under full load which is essentially 1bar. He's running a Norgen regulator and pressure relief valve setup which means the wastegate actuator will only see boost once the regulator pressure reaches the set level instead of stock where the actuator can tend to progressivly open as boost increases. The setup is identicle to the one shown in the Audi article on Autospeed. Cost around $70nz in parts.

With the factory top mount intercooler, we found there is some sort of boost relief that opens around 14.5 psi and dumps any further pressure. Even with the wastegate wired shut we couldn't get anything more than 14psi. Now the top mount is binned, and the norgen setup installed, boost can be raised well above 14psi with relative ease. We have yet to do so as the turbo drop pipe (quite restrictive) is still standard, as is the rest of the exhaust for that matter, and I'm considering throwing an external wastegate for a laugh.

Hopefully we'll have the new stainless exhaust made in a few months which should make a fairly significant difference. As it is, towing our 6m boat up the Bombays is almost a 5th gear affair although we sit in 4th so as to not strain things too much.

Hope this helps

As a side note, anyone know how many 3.1TD Irmshers came out with a front LSD standard?

[James W]

There is on the inlet manifold a spring loaded valve. This I believe will thus limit inlet manifold pressure, i.e. a pressure releif valve.

Also there is between the turbo and inlet manifold a vacume operated butterfly valve, I don't know this but I would imagine the engine management system would act to close the valve on over presure.

[Roscoe]

Interesting James, On my 4JX1 Engine, there is a butterfly valve on the boost side of the turbo as well but in this case its electrically activated with a position sensor. More computer controlled electrickery.

I must learn more about this engine, even as a Diesel Mechanic, Ive lost track of some of this modern technology. Its more a matter of experiance now because in the past, everything was pretty much the same.

[MattMU]

James, the relief on the inlet? Are you talking 3.1 or 2.8?

I run the 2.8 turbo on my 3.1 and with the undersize of the turbo I doubted it would over boost (we run 3.9 4BD1T isuzus with no wate gate at work all day pulling 6 ton!) even without the wastegate.

My boost controller just bleeds of pressure to the waste gate as described above, but I dont like the concept. You have now created an airflow that was never there, the origional just transfers pressure down the line without a continuous flow. The guaze in the controller was blowing small amounts of oil (PCV and maybe a little turbo seal) even after I fitted a PCV filter. So some oil has to be travelling down the hose to the waste gate diaphragm....not a good thing if it starts to fill the diaphagm??
Anyway,
It definately spins harder after 3000rpm, you can hear the whistle or the extra RPM and the car is livelier at the top end, but I havent pushed it. Dont have the a boost guage connected, so I will play on the weekend with a home made one!
Hence why I was asking bout the presure relief, I just cant see anything in the manifold that could be that on my 3.1, it would be a good safety valve for overboost!

I uess this is the only time a blowoff valve on a diesel would be a benifit, would protect the engine and keep the spool up if nothing else!!

Matt.

[James W]

The relief valve I'm talking about is on the 4JB1. It's to the rear of the inlet manifold between the rocker cover and inlet manifold. It's about the size and shape of a 'C' size battery, sorry to photos right now. It is however if I remember corectly plumped via a hose into the breather system, that is the rocker cover and air filter box. So I may have been misleading you now that I think about it some more, it may not function as I previously suggested. It is however defiinetly a spring loaded valve with flow from the inlet manifold outwards, one would assume out to the air fillter.

"My boost controller just bleeds of pressure to the waste gate"

I assume you mean the control line for the waste gate, which forms part of a feedback loop. Pressure in the control line balances out with the waste gate diaphram return spring.

[MattMU]

Nah James I have fitted a boost controller, this bleeds the pressure off the wastegate line, tricking the wastegate into staying closed longer. Thats why I dont like the setup, it now has manifold pressure air travelling (very minute) down the hose to the valve. If there is oil in the air (small) over time it will build up in the line.

Thats why I have disconnected the wastegate line altogether to see what sort of pressure I run since I have a 2.8 turbo on the 3.1 motor. I can get away without the wastegate and maybe just fit a modified blowoff (relief) valve to prevent over pressure!

Matt.

[RoeDao]

i could only manage about 11.5 psi of boost pre-intercooler and with the wastegate blocked..... i unblocked it when i had it dyno tuned a couple of weeks ago and it would go no higher than 10.5 psi on the dyno....... he got some more neddies in the rear wheels and a HEAP of torque..... i went home and plugged the wastegate line and wound the needle off the end of my 15psi gauge......... although the turbo screamed it ass off (it does that even at 10.5psi) it didn't go a lot better because it was tuned for the boost available. I am going to make a hand control to hold back the wastegate so that it produces 12 psi before opening, when i make my dash pod, i will buy an adjustable boost controller. Once i have 12 psi i will again get it dyno tuned for that pressure. It made a heap of difference after the last retune, the next one will see it go even better!!!

[namic69]

I installed a VDO boost gauge and then install a boost controller between the pick up and the waste gate diaphragm, this unit has a spring loaded gate that is adjustable so the waste gate is not getting any pressure until the pressure I set is reached. End result is faster spool up more torque. Nice.... The unit and gauge cost me $145.00

[MattMU]

Namic, how about some details and some pics??

I have a little adjustable boost controller, but it is a bleed offone, so it tricks the wastegate into thinking the pressure is low. Dont like the fact its continuously bleeding off manifold pressure and creating a flow of oil/air down the wastegate line!

Matt.

[Jimmu]

Yeah Namic69 Send some pics...

Sounds just like what I want to go with the intercooler fit up...

Also what brand boost controller? Where did you get it from?

Jimmy.

[namic69]

No problem just give me an email address to sent pics to The boost controller is from GFB (Go Fast Bits) www.gofastbits.com.au

[namic69]

I got the parts from New lynn and I think you can get them from Repco too. I went for Go Fast cos I think they are better quality.

[andy]

There are a wide range of boost taps out there ranging from simple fishtank valves for $2 to all out electronic boost controllers for $800+.

Personally i grabbed a Racepro gated bleed valve off trade me for $45 and that allows boost adjutment to within half a pound.

Any tap should have pretty much the same effect as its only bleeding off a little pressure to fool the wastgate into staying closed for longer. Another recommended type is the Norgren pressure regulator as used in compressed air appliances. You can also add in a Relief valve which controls the speed at which the wastegate senses pressure to allow for more precise boost control i.e it doesn't creep past your desired boost level and then jump back down again.
Personally i find my bleed tap perfectly adequate with only about half a pound creep from 12.5psi back down to a steady 12 throughout the rev range
Andy

[adrian]

Today i eventually got round to trying to sort out the boost pressure on my bighorn 3.1TD.

i hooked my boost gauge up to the turbo side of the intercooler. there seams to be some vaccum operated valve there that does something? and a nice convenient bit of pipework to put a T piece in.

i drove it for a few miles but could get no higher than 0.75Bar (10.5psi) (it is japanese import into uk, with auto box)

so i thought i would just alter the wastegate actuator, something i have done on petrol turbo cars i have had many times in the past.

but it is so difficult to see the bits you need to adjust, and even harder to get your hands near them.

is there any special technique? or just dive in there.

can i just check what i read also, that you can run the car, without the wastegate connected, without any problems?
as if this is the case then i may try this?
i know it definately isnt something you should ever do on a petol turbo car, as it will go bang very quickly.
(i to am still learning about diesel engines)

i also noticed that there seams to be a large diameter tube running round the back of the engine, connected to 2 what seam like something to do with the emmissions perhaps?? attached to the inlet manifold, but dumping carbon rich gas to the atomosphere??
any ideas what they may be for? and would performance increase if i removed them, i would need to find out local emission laws though.

i know the car is never going to be as fast as a scooby-doo, so that isnt what i'm after, just a little more power for when i'm cruising on the motorway.

adrian

[geeves]

That large pipe connects to the exhaust and is Exhaust gas reticulation and bleeds exhaust back into the inlet to reduce nitros oxide emmisions. You deffinatly get more power disabling it but may fall foul of local emmisions laws

[geeves]

Just picked up a boost gauge at Repco at a good price $24.49 (normal price
is 34 but they have a 30% off special) which seemed a good price.
The results on my 2.8 bighorn was 8psi at 1500rpm 13 at 18 and 13.5 from2000
all the way to 4200.This was at full throttle with lower readings at part throttle This is with the gauge conected to the tap at the inlet
end of the intercooler. Do these figures sound right for a belived stock
engine with 180000km on the clock?
Also is teeing into the pipe at the front of the intercooler that goes to the fuel pump a good idea

[Graham]

Geeves, that's a bargain price for a boost gauge! I'm jealous - after shopping around a lot I had to pay about $70 for mine

My 3.1TD used to show 0.9bar max boost, around 12.5psi. Now that I have blocked the EGRs its dropped a fraction.

IMO yours sounds a little high, but I really don't know if 13.5 is normal for the 2.8 or if it should be closer to 12 like my 3.1 is.

Plus there could be differences in the readings from the boost gauges - really, for an item this price, I don't think there's a guarantee about it's accuracy

Ciao! Graham.