fuel economy

Just had a chance to test my 110 fuel economy on a biggish run, took tests for 2 tanks, 1300km approx all up, towed a 8x5 trailer from Hobart to Swan hill, then through Healesville back roads to Traralgon, then back to Melbourne, city driving in traffic then back to Hobart again.

Average is 12.5l/100km.

Turbo intercooled, .996:1 gears and 235/85/16 A/T tyres.
Trailer empty on way up, 80% load on way home, bulky not heavy.
sat on 95 to 105km/h, overtook a few times up to 120km/h.

Overall very happy considering engine has almost 600,000km and no recorded injector or pump maintenance other than fuel filters every second oil change, cleaning of sediment bowl and periodic added fuel treatmenst from when donor vehicle was bought new in 1988.

JC

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Originally Posted by 85 county

cool, so if I put a turbo in my oven it will spool up? No.Mass X volume velocity, less backpressure and lack of scavenging.

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To put it simply, the turbo enables you to get more air in than NA, and do it more efficiently than would increasing capacity, but this increase does nothing for you until you burn more fuel. The exception to this would be if you are already overfuelling - in this case, certainly, fuel economy may improve slightly, but only if you do not increase fuelling.

John

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Originally Posted by justinc

Just had a chance to test my 110 fuel economy on a biggish run, took tests for 2 tanks, 1300km approx all up, towed a 8x5 trailer from Hobart to Swan hill, then through Healesville back roads to Traralgon, then back to Melbourne, city driving in traffic then back to Hobart again.

JC

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It's all up and running then? I've got some questions on the performance of that factory Isuzu turbo you are running.

Hi Dougal,

It's a TB25 Garrett, (are those factory?) anyway, manifold is similar to factory one I believe, it is wastegated but that is plugged up and the boost set to 15psi at manifold using the fuel screw. max egt has been about 600 upstream at these settings. The only irritating issue is the idle speed is a bit higher than I would like, and the idle stop screw is out quite far enough, but makes no difference.

Running factory Td5 defender exhaust system from engine pipe back, flows pretty well and is quite quiet.

As I said, I am very happy with overall performance and economy, allround it is a very good set up.

JC

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Originally Posted by justinc

Hi Dougal,

It's a TB25 Garrett, (are those factory?) anyway, manifold is similar to factory one I believe, it is wastegated but that is plugged up and the boost set to 15psi at manifold using the fuel screw. max egt has been about 600 upstream at these settings. The only irritating issue is the idle speed is a bit higher than I would like, and the idle stop screw is out quite far enough, but makes no difference.

Running factory Td5 defender exhaust system from engine pipe back, flows pretty well and is quite quiet.

As I said, I am very happy with overall performance and economy, allround it is a very good set up.

JC

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Justin, your turbo is the factory fitted item from the 94-98 4BD1T and 4BD2T engines. It's a T25 with an Isuzu specific turbine, and a 0.67 A/R turbine housing with a T3 flange.

Should have a 54mm compressor fitted from the factory and I'm looking into upgrades for it, there are a lot of owners in the US of 4BD2T engines who run this turbo and need an easy upgrade for the next step. I have a plan and it should be plug and play.

Can you tell me what the minimum rpm is that you can pull 10 and 15psi boost?

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Originally Posted by Dougal

Justin, your turbo is the factory fitted item from the 94-98 4BD1T and 4BD2T engines. It's a T25 with an Isuzu specific turbine, and a 0.67 A/R turbine housing with a T3 flange.

Should have a 54mm compressor fitted from the factory and I'm looking into upgrades for it, there are a lot of owners in the US of 4BD2T engines who run this turbo and need an easy upgrade for the next step. I have a plan and it should be plug and play.

Can you tell me what the minimum rpm is that you can pull 10 and 15psi boost?

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ah, good info thanks. when i was looking at turbos waaay back 7 or so years ago, i contacted turboglide who did kits to suit 4bd1 in motorhomes etc. this was the turbo they recommended and the manifold was one of theirs but i have discovered genuine isuzu ones are almost exactly the same, and cheaper. i don't have a tacho, but at these fuel settings and a hill infront of me, i can see 15psi at about 2600 to 2800rpm, and 10 is easy at around 2000 to 2200, under load. these are approx, based on gear that i am in. i will try and get closer numbers by staying in 4th gear for all these tests, watching road speed and hooking up the boost gauge again if it would be helpful? should be easy to calc revs then :)

i am interested in a plug and play solution for more boost, i feel trying to get more out of mine feels as though the little compressor is overspeeding. i could do with a little more as i have a ginormous front mount ic with 3" pipework and could easily take 20+psi....:)

jc

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Originally Posted by JDNSW

To put it simply, the turbo enables you to get more air in than NA, and do it more efficiently than would increasing capacity, but this increase does nothing for you until you burn more fuel. The exception to this would be if you are already overfuelling - in this case, certainly, fuel economy may improve slightly, but only if you do not increase fuelling.

John

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So does a NA Isuzu have around 20% unburnt fuel post combustion or is this not true and is this figure much the same for a tubo motor? If it is and LPG increases the fuel burnt as claimed then doesn't this increases the engine efficiency and hence economy?

If I understandit right a turbo adds more air so you can add more fuel to burn with each compression cycle, but the efficiency of the motor to burn the air/fuel mixuture does not alter greatly just the volume. Is this a fair comment?

regards
Garry

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Originally Posted by garryseries3

So does a NA Isuzu have around 20% unburnt fuel post combustion or is this not true and is this figure much the same for a tubo motor? If it is and LPG increases the fuel burnt as claimed then doesn't this increases the engine efficiency and hence economy?

If I understandit right a turbo adds more air so you can add more fuel to burn with each compression cycle, but the efficiency of the motor to burn the air/fuel mixuture does not alter greatly just the volume. Is this a fair comment?

regards
Garry

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20% unburnt fuel would see huge plumes of smoke. If you believe that I have a bridge that may interest you... LPG fumigation is simple fuel addition, some adiabatic cooling, and possibly some changes in flame fronts and or flame propagation, however there is no independant research to prove the latter.


Fitting a turbo will be the best mod you ever did...

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Originally Posted by justinc

ah, good info thanks. when i was looking at turbos waaay back 7 or so years ago, i contacted turboglide who did kits to suit 4bd1 in motorhomes etc. this was the turbo they recommended and the manifold was one of theirs but i have discovered genuine isuzu ones are almost exactly the same, and cheaper. i don't have a tacho, but at these fuel settings and a hill infront of me, i can see 15psi at about 2600 to 2800rpm, and 10 is easy at around 2000 to 2200, under load. these are approx, based on gear that i am in. i will try and get closer numbers by staying in 4th gear for all these tests, watching road speed and hooking up the boost gauge again if it would be helpful? should be easy to calc revs then :)

i am interested in a plug and play solution for more boost, i feel trying to get more out of mine feels as though the little compressor is overspeeding. i could do with a little more as i have a ginormous front mount ic with 3" pipework and could easily take 20+psi....:)

jc

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That's the one. I suspect turboglide were selling the genuine Isuzu parts. Quite a good and easy move on their part. Another guy in the US was selling the same Isuzu manifold and turbo for toyota 3B engines, just slotting the holes so the manifold kind-of fit.:(

There is a turbo used on the Isuzu 4HE1 motors which uses the same turbine but a different turbine housing and a bigger compressor. It should fit straight into the turbine housing from the turbo you've got and provide more boost throughout the rev range with no loss of top end. Oil supply/drain are the same but air piping might need small modifications.

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Originally Posted by garryseries3

So does a NA Isuzu have around 20% unburnt fuel post combustion or is this not true and is this figure much the same for a tubo motor? If it is and LPG increases the fuel burnt as claimed then doesn't this increases the engine efficiency and hence economy?

If I understandit right a turbo adds more air so you can add more fuel to burn with each compression cycle, but the efficiency of the motor to burn the air/fuel mixuture does not alter greatly just the volume. Is this a fair comment?

regards
Garry

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Turbocharged engines are more efficient across the whole operating range than non-turbo engines. Even at part load.
In addition, turbocharging allows you to pull higher gears and run lower rpm which can further save fuel.
IMO the only reason non turbo engines are using similar amounts of fuel, is because they are slower and make savings through wind resistance because of this.

The 20% unburnt fuel claim by lpg mongers is complete and utter bollocks.

Quote:

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Originally Posted by garryseries3

So does a NA Isuzu have around 20% unburnt fuel post combustion or is this not true and is this figure much the same for a tubo motor? If it is and LPG increases the fuel burnt as claimed then doesn't this increases the engine efficiency and hence economy? ....

regards
Garry

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Unburnt fuel on a NA is very low, probably well under 1% even at full throttle unless you have the fuelling incorrect. And remember that there is already (a lot of) excess air at all smaller throttle openings, which is where most of your driving is done (well, most of mine, anyway!), so that adding extra air by fitting a turbo will not burn any more excess fuel. I don't know where the 20% came from, but that figure is ludicrous!

LPG may slightly improve fuel burn, but it can still only burn fuel that is unburnt, less than 1%.

John