View topic - what does a boost compensator do, and are they worth it?

what does a boost compensator do, and are they worth it?

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what does a boost compensator do, and are they worth it?

im about to put an axt turbo kit on my 1hz cruiser and have heard talk of boost compensators. what do they exactly do and is it worth fitting one when i get my turbo on?
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Unread postby 100_cruiser » August 14th, 2008, 2:05 pm


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My explanation may be a little on the naive side but basically the boost compensator is a manifold pressure activated fuel regulator.

In effect when you sink the boot in the compensator "should" recognise the difference between on and off boost and fuel up to match..

Essentially I think the most benefit you would get would be a bit less black smoke off boost with the foot down...

The factory turbo has a compensator and I think it is just another thing to need adjusting to be tuned properly so if you can get away without one I wouldn't bother.
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Unread postby Sea-Dog » August 14th, 2008, 3:09 pm


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If i had the money i would fit one. I havnt heard of them needing adjustment any more nesacarily than the rest of the pump at a tune up. The compensator just means when your at idle your not using extra fuel but when the boost comes on it winds up the fuel pump to deliver more fuel to match the boost so to speak. With out one they just set the pump at the ultimate boost level the turbo will run.
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Unread postby Muckinhell » August 14th, 2008, 5:00 pm


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They are expensive to retro fit to a non compensated pump and personally I can't justify the money.
However, they will make a difference to you fuel economy (depending how you drive) and potentially allow more power as it won't overfuel when off boost
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Unread postby Patrolling Paddy » August 17th, 2008, 8:39 pm


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What year model is it ??? it may already have one on it, mine is a 2001 model and it has one. Not sure what models came with one, might be worth asking the turbo mob??
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Unread postby DX80 » August 25th, 2008, 12:16 pm


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Think you'll find it's an altitude compensator. I've got one on my 1hz 105 cruiser.

Unread postby HiCountryCruisr » August 25th, 2008, 8:07 pm


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I got a Quote for a turbo a while ago, and the turbo guru told me i didn't need a boost compensator because it already had one.
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Unread postby DX80 » August 26th, 2008, 8:07 am


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100_cruiser wrote:im about to put an axt turbo kit on my 1hz cruiser and have heard talk of boost compensators. what do they exactly do and is it worth fitting one when i get my turbo on?


There has been a few explanations that are almost there. This, I hope, may help. The boost compensator or air/fuel ratio controller (Catterpillar's name for this device) is used to reduce the production of black smoke when the throttle is opened with little or no boost pressure. It does this by restricting the amount the fuel rack (inline injector pumps) moves to allow more fuel to the injectors untill the turbo starts to produce pressure in the manifold. The rack is then progressively allowed to 'open' as the pressure rises up to a set maximum fuel setting at a specific boost pressure.

All of this is to reduce emissions and it is importantant to note that the maximum fuel setting is NO different at a particular Kw output regardless of weather a boost compensator is fitted or not.

You might now be wondering if it's only to reduce emissions than why bother fitting one? Well there is another problem with black smoke. Untill a turbo is making enough boost for any particular fuel setting, it actually acts like a restriction in the inlet manifold, making the fuel mixture rich and in a diesel unlike a petrol this can lead to high exhaust temps. This is where the boost compensator helps most at lowish rpms and high load. It is also where the altitude compensator performs a similar role. The 'boost' pressure in this case is atmospheric air pressure (high at sea level and low at high altitude) so the fuel rate is reduced as altitude increases.
Your Cruiser has one of these fitted which may be able to be used with a turbo but I suspect the sensitivity to pressure much above atmospheric would be too fast for any sort of progressive fuel rate increase. also the diaphragm might not be designed for even moderate boost pressures (10 psi). This is something a Diesel tuning specialist would be able to answer.

Sorry for the long winded answer but hope it helps a bit:thumb:
Cheers
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Unread postby D.R.eos » August 27th, 2008, 1:11 am


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I got one fitted when I had my 1HZ turboed, as the guy that did it (Ray at TEC) said that if you don't, it can damage your engine by overfuelling when off boost (i've since heard this from others).

I've heard some horror stories about smoke plumes that you get without one (off boost), but with mine on, it runs beautifully, and never blows smoke either on or off boost.
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Unread postby marki » August 27th, 2008, 1:07 pm


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D.R.eos explanation is pretty accurate but i will add that a boost compensator or aneroid is it actual name, Is not only for emissions but also engine responsiveness and fuel economy.
On After market turbo kits without an aneroid the technician will wind the fuel rack stop out allowing the injector pump to supply more fuel at full throttle which is ok providing the boost is there at full throttle, but without a dyno and a exhaust temp gauge this adjustment can be an educated guess to much extra fuel can cause excessive exhaust temps which can melt pistons an aneroid will allow the fuel delivery to rise only when the boost is there. Yes they aren't cheap but as a diesel mechanic i would recommend the fitment of one.
But if you find that the price is out of your reach ( as it would be for a lot of us) an egt gauge would tell you if your temps are excessive and these can be fitted for a few hundred $

Unread postby cooter » August 30th, 2008, 12:19 am


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cooter wrote:pretty accurate but i will add that a boost compensator or aneroid is it actual name,


The correct name for a boost compensator is "boost compensator".

This device compensates for changes in boosted induction pressure, by changing fuel pump output according to the boost pressure.

An aneroid contains a set of brass bellows containing a partial vacuum, as the name suggests, that is, anerobic means "in the absence of air". These bellows are much like the bellows found in a barometer.

The aneroid or Diesel Altitude Compensator (DAC) as Denso calls it, compensates only for changes in atmoshperic pressure by changing fuel pump output, but to a much smaller degree than a boost compensator.

Some German and Yank OEM`s keep calling boost compensators, aneroids but they are completely different devices with different jobs to do.

The "series two" 1HZs found in the 100 series and the 70 series of the same era have DACs fitted to their pumps and these cannot be modified to work as a boost compensator.

The 1HZ fitted to 2003 onwards 70s and 100s have a boost compensator fitted to their pumps.The compensator in this application changes fuel output in accordance to the duty cycle of the EGR system by switching a vacuum to the underside of the boost compensator diaphragm to pull the compensator in and out of the pre-set maximum fuel delivery.

These compensators can be easily set up to work as true boost compensators when these engines are fitted with after-market turbo kits.

IMO a boost compensator is a very good thing to have on an after-market turbo install for reasons given by Cooter and D. R. eos. If it is installed correctly it should never need "adjusting to be tuned properly" after the initial set up.
Cheers, Dakar61

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Unread postby dakar61 » August 31st, 2008, 8:45 pm


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Excellent post Dakar!

That cleared a few things up for many of us. Learn something everyday.............;)

Unread postby DJR96 » August 31st, 2008, 10:25 pm


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Hi all,
I'm not sure where to begin, I can expain how the boost compensator works and the dac works perfectly, just need to know what part of it you are lost on cause alot of people have said alot stuff, so i don't wanna leave info and make you more confused, but I work in fuel injection . IF you have a question just ask.

Unread postby kungfukid86 » September 8th, 2008, 7:43 pm


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dakar61
sorry mate i stand corrected i did my time on cummins diesels and always referred to then as that

Unread postby cooter » September 11th, 2008, 9:51 pm


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Dont apologise Cooter.:thumb:

Cummins have been confusing the issue for years.:D
Cheers, Dakar61

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Unread postby dakar61 » September 12th, 2008, 1:54 pm


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