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Mazda CX-7: Bring the diesel version to the USA!

22 messages,  Last post on Mar 01, 2009 at 12:14 PM

You are in the Mazda CX-7 Forum.

What is this discussion about? Mazda CX-7, Diesel, SUV

Messages Page 3 of 3

#13 of 22 Re: Madza CX-7: Bring the diesel version to the USA! [lineman] by mark4biodiesel

Apr 02, 2008 (9:47 am)

Replying to: lineman (Jun 15, 2006 9:04 pm)
Clean diesel, ULSD, is way over priced as of April 2008, in western NY state, diesel was selling for exactly $1 per gallon more than gasoline. It was higher than even the weekly Federal EIA report shows by 29 cents per gallon at $4.399. Even though the federal and state taxes are less on diesel than gasoline, diesel should have been selling for a max of $ 2.90 per gallon taxes included. The major oil companies are screwing the american public as they have finished making all the heating oil for the winter season over one month ago. There is not the demand for diesel/heating oil because truck shipping volumes are way down due to the slow economy as well. This proves the oil companies are as guilty as sin. Time to start using home made fuel such as ethanol which can be made in your backyard and mixed with normal gasoline at a 20 percent rate with no starting problems. Or save even more money by using propane which sells for 2/3 the price of gasoline and just over half the price of diesel.

#14 of 22 MPG/DIESEL by mazdacx7

Feb 12, 2009 (4:39 pm)

How is going to be the MPG with Diesel.???

#15 of 22 Re: diesel with manual please. [ktl2] by wwest

Feb 15, 2009 (9:42 am)

Replying to: ktl2 (Dec 06, 2007 1:16 pm)
For the average american driver a manual transmission in a FWD or F/awd vehicle cannot be considered safe. But help may be coming...
 
VW has just introduced a FWD vehicle with a stick shift using a technique that automatically up-revs the engine to prevent loss of control should the driver inadvertently downshift the transmission to a level that results in loss of traction due to poor roadbed adhesion.

#16 of 22 Re: Madza CX-7: Bring the diesel version to the USA! [carlitos92] by wwest

Feb 15, 2009 (9:50 am)

Replying to: carlitos92 (Mar 21, 2008 7:35 pm)
Your thinking is outdated, TOTALLY outdated.
 
Modern day engine computers use EFI/SFI PWM timing to simply ENRICH the mixture if detonation, not due to lugging, occurs. The computer uses the crank position sensor and the new non-resonant wide-band knock sensors to determine if the fuel combustion initiated upon ignition or prior. If timing is already fully retarded it simply enriches the mixture.

#17 of 22 Re: Madza CX-7: Bring the diesel version to the USA! [carlitos92] by wwest

Feb 15, 2009 (10:06 am)

Replying to: carlitos92 (Mar 21, 2008 7:35 pm)
You're ALL missing the point.
 
The turbocharger is the primary reason the CX-7's I4 engine gets such HORRID FE.
 
In order to provide for the "rise" in effective compression ratio as the boost comes up the engine MUST be derated in normal off-boost mode. Otherwise the DISI (DFI, Direct Fuel Injection) engine could have a native compression ratio of 12:1 and give you more decent FE when cruising along at relatively constant speeds.
 
The real answer would be to extend the range of the current VVT system such that the native compression ratio could be raised to 12:1 as in other DFI applications and then use delayed intake valve closing to gradually reduce the compression ratio as/when the turbo spools up and provides more and more boost.
 
Even better yet, make the native cylinder compression ratio 15-16:1 and then use the valve timing to bring in down to 12:1 under normal driving conditions. Then gradually transition to <10:1 as boost rises. High FE Atkinson cycle mode off-boost and then transition to Miller cycle mode as boost rises. Even eliminate the wastegate this way, the delayed intake valve closing could be used to limit the turbine speed.

#18 of 22 Anyone interested..?? by wwest

Feb 26, 2009 (6:08 pm)

I went by the Kirkland Mazda dealer today to look over the CX-7 and collected a brochure. Before I actually buy one to experiment with/on I was wondering if anyone in the Puget Sound region might be willing to participate in an experiment to improve the FE of the CX-7, possibly substantially so.
 
What I would like to do is mill the head of a CX-7 engine to get a compression ratio of 12:1. 12:1 has become typical for a DFI, Direct Fuel Injection, engine, but since the CX-7 is turbo charged the factory's "native" compression ratio is, as it must be, quite a bit lower in order to provide for the additional "compression" from the turbocharger as it spools up.
 
During the experiment the wastegate would have to be "wired" open so the effective compression ratio could not rise (much) beyond 12:1.
 
If anyone owning a CX-7 is interested I would be will to pay the costs purchase and install a new factory head once the experiment is complete.
 
I suspect the off-boost FE improvement might be in the range of 50%

#19 of 22 Re: Anyone interested..?? [wwest] by tidester

Feb 26, 2009 (11:14 pm)

Replying to: wwest (Feb 26, 2009 6:08 pm)
I suspect the off-boost FE improvement might be in the range of 50%
 
What would be the basis for your suspicion? Is it just a hunch or are there real world numbers behind it?
 
tidester, host
SUVs and Smart Shopper

#20 of 22 Re: Anyone interested..?? [tidester] by wwest

Feb 28, 2009 (3:17 pm)

Replying to: tidester (Feb 26, 2009 11:14 pm)
Well, first, this engine uses DFI, Direct Fuel Injection, for which 12:1 compression ratio is now typical. But in order to allow for the increased "effective" compression ratio as the turbo spools up the "native", off-boost, compression ratio is only 9.5:1.
 
So "off-boost" this engine is quite heavily derated/detuned and runs in that mode 95-98% of the time.
 
Cadillac just happens to have two V6s in the market at the moment, one with DFI and one without. Compare the two and you get my theory.

#21 of 22 Re: Anyone interested..?? [wwest] by tidester

Feb 28, 2009 (10:59 pm)

Replying to: wwest (Feb 28, 2009 3:17 pm)
But you're suggesting that a 26% increase in compression ratio (9.5 to 12.0) will lead to a 50% increase in fuel efficiency. I don't see how that follows.
 
tidester, host
SUVs and Smart Shopper

#22 of 22 Re: Anyone interested..?? [tidester] by wwest

Mar 01, 2009 (12:14 pm)

Replying to: tidester (Feb 28, 2009 10:59 pm)
The power increase from CR would result in less turbo on-boost time......
 
The turbo wastegate could be held open for low to moderate levels of acceleration.

Messages Page 3 of 3

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