overboosting versus diesel/gas for economy and power?

Submitted: Thursday, May 08, 2008 at 17:30
ThreadID: 57394 Views:2731 Replies:3 FollowUps:4
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Is increasing the boost achieving a similar result to diesel/gas?
Please check my logic here.

I have noticed a few posts on diesel with gas (LPG) injection.
The benefits being more complete combustion of the diesel, hence better economy and more power on full throttle. And a slight saving in the cost of fuel since some diesel is replaced with cheaper gas.
The cost is about $1500.00 after the government rebate.

However, I have been playing with boost on the pajero and increased it from 12 psi to 16 psi. I have installed a boost gauge and EGT. The fuel pump settings have remained stock factory settings. Boost obviously is only really higher at full throttle settings, but checking boost levels before and after increasing the boost at set speeds on the same section of road, at the same time of day, the boost is slightly higher (1 to 2 psi) at part throttle settings from 1/3rd throttle up.
I only use full boost ocassionally, maybe once a week or every 500 km, since I drive for economy.

During this experiment, I have noticed less soot, particularly on higher throttle settings. The pajero has an increased fuel setting on the fuel injection pump when boost rises. So I assume that getting more air into the engine has increased the efficiency of combustion. I am getting better fuel consumption, but only being able to check it from tank to tank during normal road use, it is hard to measure accurately, but a rough figure might be 5%. Maybe I am just driving more carefully. (Accurately measuring fuel consumption in every day use is open to many uncontrollable variables.)

Power has increased at the higher throttle settings, so also put this down to the efficiency of combustion.

So is the $50.00 spent on installing the manual boost controller a cheaper alternative to diesel/gas, giving almost the same result?

If diesel gas gives 10% saving in fuel bills, gas & diesel compared to just diesel, and I have already saved 5% with my simple modification, the $1500.00 gas installation will take about 170,000k, or 7 years at 25,000k & $1.70/l to pay itself back.

Sound about right?
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Reply By: Member - John - Thursday, May 08, 2008 at 17:41

Thursday, May 08, 2008 at 17:41
John, how do you now you have more power, have you dyno figures before and after the mods? John
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Follow Up By: Member - Oldplodder (QLD) - Friday, May 09, 2008 at 07:35

Friday, May 09, 2008 at 07:35

Before I started, I put new air & fuel filters in as a base for measurement.

I have a local steep hill, where I start off in 2nd gear at 1800rpm, and on full throttle used to only get to 4000rpm in 2nd at the top. I am now getting to 4000rpm and changing to 3rd before the top of the hill. About 10km/hr faster at the top.
My acceleration times in 4th gear from 60km/hr to 100 km/hr on the same stretch of road has also dropped.

Yes, as olcoolone suggests also I should dyno the car with the different boost pressures to see the difference.
FollowupID: 568944

Follow Up By: Member - JohnR (Vic)&Kath - Friday, May 09, 2008 at 07:52

Friday, May 09, 2008 at 07:52
Standard tests can work John, can't they. I have a stop sign and of course stop every time as cars and trucks come around the corner at you unsuspectingly.

From the stop sign to the second 80kph sigh is a good accelerative test or it used to be with Moses as it is on an incline too. Kath however can do my licence to that point. I won't say where my standard test is, though I know another member uses the same point.
FollowupID: 568949

Reply By: Member - Olcoolone (S.A) - Thursday, May 08, 2008 at 18:07

Thursday, May 08, 2008 at 18:07
It all depends on what is the maximum flow of the turbo is.

An inefficient turbo can show more boost but with the added problem of generation heat and lowering performance.

You have to find out what is the maximum flow of the turbo and go from there.

You may be able to get your turbo hi flowed to increase efficiency.

You may find you have gained 20% power up to 2500rpm but from 2500rpm to 4000rpm you have lost 30% power due to the turbo running out of puff and super heating the intake air.

The sure way is get it dynoed.

Regards Richard

AnswerID: 302736

Follow Up By: Member - Oldplodder (QLD) - Friday, May 09, 2008 at 07:37

Friday, May 09, 2008 at 07:37

Good point.

I do mainly drive in the 2000 to 3000 range, sometimes to 3500rpm.
I think you may be right in that there is less performance increase above 3000 rpm.
FollowupID: 568945

Reply By: pop2jocem - Thursday, May 08, 2008 at 21:44

Thursday, May 08, 2008 at 21:44
I assume you have increased the boost pressure at higher RPM,s by winding up the waste gate setting. I guess this would indicate the aneroid that proportions fuel to boost is seeing a higher value and increasing the fuel setting. Any turbo can only pump harder if the exhaust gas temperature and volume is increased. This pressure increase should, all things being equal, give you a power increase until the fuel pump max fuel setting is reached.
I would think that the only advantage the gas injection gives is maybe better effiiciency at lower RPM,s where the turbo,s effectiveness is not as good.
AnswerID: 302787

Follow Up By: Member - Oldplodder (QLD) - Friday, May 09, 2008 at 07:43

Friday, May 09, 2008 at 07:43

Point to ponder. Gas most probably does give more power lower down under maximum torque. Where my turbo is still spooling up.

I could have turned the fuel up to give more heat/power, but am also after economy, so thought I would try one step at a time. Getting 650 to 700 deg C before the turbo now, so didn't want to go any higher. The fuel injection pump is an old rotary mechanical, so there is no electrics to play with. Felt if I turned the fuel up, it would happen across the range, and give slightly less economy.
FollowupID: 568947

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