Advice req - Differences between similar diesel cars & chipping

Discussion in 'Diesel powered automobiles' started by Eddles, Feb 23, 2011.

  1. Eddles

    Eddles Well-Known Member

    Hello all,

    Sorry for the long post and the use of UK units, but wanted some of your opinions... I know it's all UK stuff, but the theory should be the same no matter where you live so please bear with me.... ;)

    I used to have a 2001 Opel Astra ECO4 which was specially designed to reduce fuel consumption through an underbelly pan, skinny and really big fuel saver tyres (175/80/14) on steel rims, spoiler and wide ratio 4th and 5th gears. I found mention that Opel *might* have programmed the computer to use less fuel and had lowered the suspension but I couldn't find firm confirmation of this.

    It had a 1.7 Isuzu DTI engine with a distributor type fuel pump with simple injectors giving 75 BHP. I got an average combined fuel consumption of 74 MPGuk out of that compared to a rated combined figure of 64.3 MPGuk - see my sig below. Someone pulled out in front of me and I ran into her, writing off the car. Oh well. Eventually, I decided to buy another Astra, but due to the extreme rarity of the ECO4 and that it doesn't come with ABS as standard, I decided to get a non ECO4 diesel Astra with ABS. This car comes with the exactly the same engine as my ECO4, but with common rail injection and, I believe, a lower pressure turbo. The engine produces 80 BHP and much cleaner emissions. However, I'm getting about 61 MPGuk out of that out of a rated combined figure of 61.4 MPGuk, so I'm rather disappointed with this.

    Now, I haven't driven an Astra DTI or an Astra ECO4 CDTI so it is difficult to tell whether the higher fuel consumption is due to the common rail injection system or the modifications Opel did for the ECO4. I have been seeing reports online that the CDTI engine uses up more fuel than the DTI engine but I tend to be suspicious of those sort of reports[1], however if this is true, I suspect that Opel increased the power of the CDTI engine as it's much cleaner than the DTI at the expense of fuel consumption mainly because, to be honest, the engine is pathetically weak[2], and 80 BHP "sounds" better than 75.

    The government says that the CDTI engine gets *exactly* the same fuel consumption than the DTI which lends credence to the fact that the ECO4 modifications helps a lot, however the government figures show little difference between the ECO4 and the standard Astra - only 3 MPGuk combined, but I am getting 13 MPGuk combined less on my new Astra.

    I have already planned to swop the alloy wheels (195/55/15) on my new Astra to have exactly the same wheel setup on the ECO4, that should gain a couple MPG. Unfortunately it won't be realistic for me to get the wide ratio 4th and 5th gears from the ECO4 and fit them on my car. I'm not bothering with the spoiler as I'm not really convinced that it really helps.

    I am seriously considering getting the engine chipped to attempt to reduce the power and hopefully increase fuel consumption but I wanted your opinions. I can't see much options beyond getting an standard Astra engine pan however it's rather pricey second hand. The additional ECO4 underbelly pan bits will be next to impossible to get as no-one know about those.

    Thanks for reading this far! :D

    [1]"I only get 50 MPG out of my car, while the government tells me I can get 75 MPG!" "You've been doing 90 MPH on the motorway, haven't you?" "Err... yes? So?"
    [2]The 68 BHP Fiat 1.2 diesel engine found in some Opels run rings around the Isuzu 1.7 diesel engine.
  2. ILAveo

    ILAveo Well-Known Member

    I suspect that you are right that they traded efficiency for power and emissions reduction.

    I'm far from an expert on chipping, but chips also strike compromises that you may not think about when you buy them. The subcontractor I work with who chipped his turbodiesel truck to get more power to pull around his big iron ended up replacing his turbo a few times. I'm not confident that chippers are careful about the long term effects of their reprogramming and turbo's require extra care.
  3. I don't think you want to reduce power to gain mpgs.

    The higher HP tune is making the engine operate more efficiently. Lower HP tune, engine is working harder to move the car.

    I have the option to switch tunes on the fly. 6 tunes by pushing a button. Stock up to 140 HP over. The 2nd highest tune dynoed at 441 HP at the wheels vs stock tune of 360 at the engine. I get on the highway, turn the tune up to that level, but cruising at highway speeds I'm not using 441 HP. I get better mileage running the high HP tune vs stock. Where the high HP tune kills economy is if you drive like a Tard.

    I've had the tuner on truck over 300,000 miles with no adverse effects. A lot depends on the people doing the tuning and the person driving it.

    edit - remembered a great comparision -

    Back when my truck had just under 100,000 miles on it a friend bought the exact same truck. Exact - both were 2007 Silverado, crew cab, long bed 2wd 3500 single rear wheel. And we were within a couple thousand miles of each other on the odometer.

    The only differences in the trucks were: 1 my was tuned. 2 - I had an aftermarket cat back exhaust, his was stock. 3 - I had 115 gallon auxillary tank in bed, he had nothing (so with fuel I was carring about 1000 pounds more than he at the beginning of the trip), 4 - Tire brand. I had Michelins, dont know what he had, but we did have same size tires.

    We both leave town and go to a camper dealer, and hook up to the exact same 5th wheel campers going to WY, delivering to the customers house, 2 blocks apart. We both fill up in Indiana, so now I have 1000 pounds more than him, and we leave for WY.

    He is behind me, I am leading the way the entire trip. We have to stop every 300 or so miles for him to top off on fuel, but I didnt add any until after we get to WY.

    After the trailers are delivered we both fill up. All said and done, I used 10.5 gallons less for the trip than he did.

    Contribute the mpg differences to, tire brand (maybe some of it) Driving style (maybe a little, but it was both of us going the same speed, both of us using cruise, and very little traffic slow downs), And a tuned, more efficent operating engine, maybe?
    Last edited: Nov 27, 2011

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