Mazda Rotary Club

Cars by Model Type => 3rd generation RX-7's => Topic started by: Andy J Conroy on August 31, 2008, 09:19:03 AM

Title: Who said Rx7\'s are really that bad on fuel....
Post by: Andy J Conroy on August 31, 2008, 09:19:03 AM
Did a nice long trip to newcastle this week and i was averaging 25mpg..... Not that bad really is it............. that was an average of 80mph with an afr of 14.6 to 14.8 on stoich...
Title: Who said Rx7\'s are really that bad on fuel....
Post by: m1tch on August 31, 2008, 09:34:30 AM
Oooo well done :) mine does 16mpg around town, I think someone managed to average about 28mpg, mine is stock and still drops to below 10mpg on boost lol
Title: Who said Rx7\'s are really that bad on fuel....
Post by: shaunwil on August 31, 2008, 10:42:31 AM
If you get around 70mph the tune may drop off to 16.5 with careful throttle control. Becomes a new game when you install a wideband :D

Will be asking pip if its possible to get it to do it a little faster like up to 80 !

Shaun
Title: Who said Rx7\'s are really that bad on fuel....
Post by: dthebuk on August 31, 2008, 12:19:07 PM
i manage 22 mpg on the motorway.
 
16 everywhere else....i don\'t even have a turbo!!
Title: Who said Rx7\'s are really that bad on fuel....
Post by: Kash_ on August 31, 2008, 12:56:28 PM
My best to date is around 180 ish miles on half a tank... mostly motorway with the ocassional a-roads... and this is a mixture of driving with a light foot and a heavy foot
Title: Who said Rx7\'s are really that bad on fuel....
Post by: FDAsh on August 31, 2008, 05:34:37 PM
I haven\'t found mine to be half as bad as people made out when I was looking to buy. I think it\'s yet another thing that armchair mechanics will blurt out because they don\'t have the finances or balls to take on an RX7 as a commitment themselves.

Just trying to imply you\'re making a poor choice.

Will see what mine can reach mpg-wise on the way from Germany to the UK, well, when the Autobahn\'s restricted anyway... :driving
Title: Who said Rx7\'s are really that bad on fuel....
Post by: DR SCHNITZEL on August 31, 2008, 07:02:30 PM
i get 40 miles on ten quid on a motorway and 35 ragging it around the back roads, 17.5 to 20 mpg with 350 hp. lets see what the new engine kicks out
Title: Who said Rx7\'s are really that bad on fuel....
Post by: marcusd666 on August 31, 2008, 07:09:47 PM
I managed to get to rotorstock on half a tank which was about 170 miles speed around 70 - 80 mph on the motorway
Title: Who said Rx7\'s are really that bad on fuel....
Post by: Grizzly on August 31, 2008, 07:28:28 PM
I found the cruise control helps get the MPG a little higher on the motorway, i set mine to 70mph and aim it in the right direction and i can quite easily get mid to high 20\'s
Title: Who said Rx7\'s are really that bad on fuel....
Post by: m1tch on August 31, 2008, 07:32:29 PM
I have got to 260 miles when using 2/3 of a tank, but then did 150 miles to about 50 litres on the next tank lol
Title: Who said Rx7\'s are really that bad on fuel....
Post by: m1tch on August 31, 2008, 07:36:07 PM
Think it might use more fuel if it used this rotor:

(http://tbn0.google.com/images?q=tbn:0HC8iZ6GRx-0YM:http://www.prime-mover.org/Engines/Images/cw_rotors.jpg)

That rotor is from a single rotar aviation engine, here is some info taking from http://www.rotaryaviation.com/rotaryhistory.htm#Part%203

We looked at the smallest Wankel in Rotary History 1, but who made the largest?  The answer is the US company Ingersoll-Rand, which became a Wankel licensee in July 1972 for compressor, pump, and generator assemblies.
 Early on, experimenters had been interested in finding the practical size limits of the basic Wankel configuration.  As early as 1960 pioneer Curtiss-Wright (C-W) had built a 31.5-liter (1920 ci) single-rotor engine intended to put out 1000 hp, but detonation problems prevented it from producing much more than 750 hp.  C-W had seemingly discovered the Wankel equivalent of a fairly well-known problem with large high-speed piston engines.  Generally, in such engines, above a bore size of about 100 mm (about 4 in) combustion cannot take place fast enough at higher engine speeds.  Weight and cooling also become problems.  Absolute limits hit at about 150 mm (6 in).  Obviously, engines with larger bores exist in applications such as ships, but they are limited to very low engine speeds.
 For the rotary, stratifying or layering the fuel-air mixture is one answer.  But Ingersoll-Rand (I-R) licked this issue by designing its rotary--originally derived from Curtiss-Wright--to burn natural gas, applying lessons learned from gas turbine operation, and limiting the engine speed to 1200 rpm.  The first I-R rotary began service in June 1975, a year before formal announcement of the program.  By 1978 I-R had logged 100,000 hours of field operating time.  The engine was available in 1- and 2-rotor versions rated at 550 and 1100 hp; it had a continuous 1000-rpm rating.  The basic design including the cooling system was roughly comparable to automotive Mazda rotaries before 1974, except that the rotor housings were cast iron instead of aluminum.  The rotor radius (-prime) x eccentricity x width (R\' x e x B) were 16.700" x 2.400" x 12.00" (424.18 x 60.96 x 304.8 mm), giving a displacement per rotor of 2499 ci (41.0 liters).  A person could easily crawl through an empty rotor housing!
 I-R\'s publicity stressed the rotary\'s fuel economy (brake  specific fuel consumption) in BTU/hp-hr in the normal compressor package compared to gas turbines and piston engines: at the time just around 9000 vs. 10%-30+% more for competitors.  The company offered users a comprehensive service and maintenance package including change outs as needed, though the expected lifetime of the rotary power module was at least 8,000 hours.  I-R was aiming for a lifetime of 24,000+ hours!  Correspondence in 1982 put the cost of a complete compressor drive at $400 per rated horsepower and a maintenance contract including change outs of $5-$6 per operating hour.  However, I-R ended rotary production by 1986.  My written correspondence to the company in 1997 asking about the program went unanswered.
 The market for this type of equipment was slow in the early \'80s recession.  At an industrial show in Norfolk in the late \'80s, an I-R representative who knew of the program told me that the market had become saturated by about 1985.  I-R\'s compressor packages, he pointed out, were used mostly to pump natural gas pipelines, using the gas itself as fuel.  Since fuel supplies were stable, few new pipelines were in the works by then.  But just suppose that were to change?
 POSTSCRIPT FOR INTERNET:  An I-R manager who was involved with the rotary program told me by e-mail in October 2000 that, to the  best of his recollection, 101 units had been built for gas compression and power generation.  Production of new engines had ended before 1985, but production of replacement modules for field support continued through then.  (SAE papers on lessons learned from the I-R rotaries appeared in 1986, implying that production had ended or was about to.)  According to the successor operation to C-W\'s rotary division, Rotary Power International (RPI), some of the I-R units ran for over 40,000 hours.  That\'s 4-1/2 years of continuous running, very roughly equivalent to 1 million miles (1.6 million km) on a car engine.  But the manager confirmed that the capability to make these mighty rotaries no longer exists.  The largest Wankel engine available as a production unit now seems to be RPI\'s 580 Series.
Title: Who said Rx7\'s are really that bad on fuel....
Post by: DR SCHNITZEL on September 01, 2008, 03:10:56 AM
wow id love to see a triple rotor one of them in the back of an old ford transit. woudl prob kick out about 8000hp, you would have to make it 4 wd though