Over boosting

Submitted: Thursday, Aug 07, 2008 at 21:15

ThreadID: 60589 Views:2768 Replies:4 FollowUps:6

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Member - Luke (SA)

G,day everyone

The last few weeks I've been thing about the Patrols boost pressures.

Some of you already know I have fitted a factory Nissan turbo to my non-turbo 4.2. The factory turbo models have a boost compensator mounted above the injector pump, I didn't put one on. I also didn't put the blow off valve on either, so I have nothing to keep the boost down or to tell me what it's doing!

I though about fitting a temp. boost gauge to see what it's doing at different times then taking it out, but who has the time to look at a gauge constantly while negotiating 4wd tracks (I could imagine driving flat chat up a sand hill looking at a gauge lol).

Should I fit a boost compensator? I am going to fit the blow off valve as from memory I was told they let go at 12psi (I think). Is this enough?

Am I worrying about nothing??

Thanks in advance

Cheers Luke

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Reply By: qubert - Thursday, Aug 07, 2008 at 21:17

Thursday, Aug 07, 2008 at 21:17

the turbo must have a waste gate.

AnswerID: 319647

Reply By: GerryP - Thursday, Aug 07, 2008 at 21:35

Thursday, Aug 07, 2008 at 21:35

Hi Luke,

While I own a 'cruiser with aftermarket turbo, I don't imagine yours would be very different to mine, but the amount of boost is generally controlled by adjusting the rod from the actuator which controls the wastegate. Generally, this is set to control the maximum boost at higher revs under load. I guess a blowoff valve would do the same, but is not really necessary.

The boost compensator adjusts the amount of fuel delivery based on current boost pressure. This is basically to prevent over fueling under low boost conditions. While a boost compensator would be nice, you can do without one and most aftermarket installations do just that. Fitting an EGT (exhaust gas temperature) gauge will allow you to keep an eye on EGT to prevent engine damage due to over supply of fuel.

I guess, in summary, I would install a boost gauge and an EGT gauge, then adjust the wastegate actuator to operate at the whatever maximum boost you decide on. That is really all you would need to do. I must say that it is somewhat comforting to have both the boost and EGT readings there during those long, hard climbs when towing as it is sometimes easy to overdo it with EGT rising rapidly.

Hope this helps.
Cheers
Gerry

AnswerID: 319654

Follow Up By: Member - Luke (SA) - Thursday, Aug 07, 2008 at 22:34

Thursday, Aug 07, 2008 at 22:34

Thanks Gerry

I thought the opposite about the compensator. I thought it acted as a regulator and kept the boost at a constant pressure. It makes more sense (what you said) that it sits on the injector pump.

Maybe if I fitted a boost gauge and a EGT gauge I could play around with the waste gate actuator and I could see what's going on there. The only thing I don't have is the dyno to see what the power is there and when.

Cheers Luke

FollowupID: 586279

Follow Up By: GerryP - Thursday, Aug 07, 2008 at 23:03

Thursday, Aug 07, 2008 at 23:03

Luke,
If you want to do it yourself, first play with the waste gate adjustment so that your boost does not go beyond a certain pressure while under load at high revs, say giving it the boot up a hill. The maximum boost is something you need to decide on - for my 1HZ 'cruiser, 8 psi is the limit as they don't like to be boosted too much, however I would suggest the Nissan would comfortably take 11 to 14 or thereabouts - others more in the know about Nissans may wish to offer their thoughts on this.

Once you have that set, then tweak the fuel (small adjustments only!) to keep the EGT within safe limits, once again under load, but lower revs (labouring a bit). This would be somewhere around 520 degrees maximum taken after the turbo (at least that is what it is for my 1HZ). However, be aware that as you increase the fuel, you will also increase the boost as the extra combustion will work the the turbo a bit harder. So it's all a bit of a balancing act, but not difficult, just fiddly.

Of course, your other alternative is to find a good diesel joint with a dyno, pay them a coupla hundred smackaroos and let them do it for you.

Good luck mate
Gerry

FollowupID: 586283

Follow Up By: Member - Luke (SA) - Sunday, Aug 10, 2008 at 23:48

Sunday, Aug 10, 2008 at 23:48

Thanks Gerry

I think I will fit a boost gauge and maybe one day fit a EGT as it seems everyone recommends them

Cheers Luke

FollowupID: 586864

Reply By: qubert - Thursday, Aug 07, 2008 at 21:49

Thursday, Aug 07, 2008 at 21:49

i have a friend who runs his nissan 4.2 diesel at 23psi. thats a fair bit, remembering its no good having the air go in without fuel for the bang. it puts out 300hp at the wheels. once you get up to the big ones like that there is other stuff to change too like radiator , more tyres , intercooler etc. if you can find the balance between power and economy thats all you need.

AnswerID: 319661

Follow Up By: Member - Luke (SA) - Thursday, Aug 07, 2008 at 22:37

Thursday, Aug 07, 2008 at 22:37

I don't think I will be needing 300hp in the 4wd, now if it were the Monaro then I would be disappointed :)

Cheers Luke

FollowupID: 586280

Follow Up By: Nomadic Navara - Thursday, Aug 07, 2008 at 23:58

Thursday, Aug 07, 2008 at 23:58

qbert said "remembering its no good having the air go in without fuel for the bang" - have you had your injection pump recalibrated? If you are not putting extra fuel in to take advantage of the extra oxygen in the cylinders then you are wasting your efforts. You will just be getting extra pressure in your cylinders for not much extra advantage.

PeterD

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FollowupID: 586286

Follow Up By: Member - Luke (SA) - Sunday, Aug 10, 2008 at 23:46

Sunday, Aug 10, 2008 at 23:46

Yes Peter the injector pump has been recalibrated. It was done a couple of years ago before I fitted the turbo (I had the turbo sitting here waiting to go on). Injector pump was reconditioned, 6 new injectors and glow plugs all at the same time.

Cheers Luke

FollowupID: 586863

Reply By: Member - Olcoolone (S.A) - Friday, Aug 08, 2008 at 09:59

Friday, Aug 08, 2008 at 09:59

Luke the load compensator if for fuel supply when the vehicle is on boost and the blow off valve you are talking about may be a over boost safety valve....different to a blow off valve, blow off valves release pressure in the inlet when the throttle is closed and the over boost safety valve releases inlet pressure when the boost gets to high if something happens to the waste gate.

A lot of mechanical systems use them whereby on most electronic systems the ecu will control it

A boost compensator will give you more go as it will supply more fuel under boost.

Your fuel delivery at the moment may be mapped at a ratio 1 to 1 and when you fit a boost compensator it will still be 1 to 1 with no boost but when you come on boost your fuel delivery may be mapped at a ratio of 1 to 1.3 giving more fuel.

AnswerID: 319723