mikevictor

If a piston engine's intake valve closes 70 abdc, it's an atkinson. I just drove 920 highway miles with my 6 ports wired open, and averaged 26 mpg. That doesn't smell like the 10% increase in thermal efficiency an atkinson is capable of. I suppose the double throttles would need to be wired open as well. Has anyone removed their auxilliary port sleeves and seen an increase in fuel economy?

j9fd3s

it seems port timing really doesnt have a big effect on mpg. couple examples.



my gsl-se and todds old rx3 would both do about 26mpg on the freeway. mine was stock ports/efi he had a big bridgeport with a holley. we were both running the same trans/rear gear. FB has better aero too....



our old FC race car with stock ports and all the 6 port junk removed got about 1 gallon/lap, or about 3mpg, the 787B got 4.6 mpg, despite it have double the rotors and making 4 times as much power. 787 has similar closing timing, but opens earlier



with my gsl-se i dont recall exactly, but i think without the 6 ports mpg wasnt that different, if anything it was a little worse

Lynn E. Hanover

What is an "Atkinson"?



Lynn E. Hanover

mazdaspeed7

A non-boosted version of a miller cycle engine. The intake is open well into the compression stroke, reducing the dynamic compression ratio, and therefore pumping losses, while only having a small effect on power since the expansion ratio is still high.



The problem with a rotary is the static compression ratio is too low to make good use of this to increase economy. The 6 port engines are already open a considerable amount into the compression stroke, and porting up only makes the engine less efficient. It moves the torque peak higher in the rpm band, and flattens it out.

mikevictor

9:1 is rather low, considering Prius has 13:1. You're probably right.



All I can report is that opening the double throttles results in more backfiring. I guess a negative data point is somewhat informative. I may be able to drive back to Memphis over spring break.



I wonder if an engineer at Mazda has tested renesis at 2500 rpm and light loading, with all ports open and egr almost high enough to miss. As far as I can tell, the only thing keeping the rotary out of mainstream vehicles is its lousy economy. Any improvement could be valuable.



I looked into Prius, and realised its aerodynamics are no better then my 7's. 0.26 cd x 24 ft = 0.33 cd x 19 ft. It rides on 195s as well, and is heavier, so rolling resistance ought to be similar.



If the old rotary could run at 18:1 afr, I might see 32 mpg, right? That would be interesting. Sounds like a respectable reason to buy an MSD.



I'd like to thank you for not telling me I'll lose torque with open 6 ports, or that rotaries aren't supposed to be fuel efficient. It can still spin on launch, but I'm not drag racing at the stoplight 500. And 14 mpg city doesn't really bother me. I'm only tinkering for the sake of tinkering.

Black91n/a

A true Atkinson cycle engine has a longer power stroke than it does a compression stroke. This isn't really practical on a conventional auto engine, so they simulate it with the afore-mentioned cam timing. This would work much better with direct injection, so you're not pushing fuel and air back into the manifold, which could combust and cause all kinds of problems.

j9fd3s

the prius has a 1 liter engine, the rotary is more equivalent to a 2.6l



the renny is different, but the "normal" 13b's are cruising around with a lot more exhaust gasses in the engine than just about any piston engine, "70% at idle" which is why the engine misses anyway



according to mazda's sae papers and the book "rotary engine" (google it, great read) once the exhaust gas reaches a certain percentage the mixture is unigniteable, more ignition does not help. but it does show that cdi does help. and you can run the rx8 spark plugs, which are better.



mazda's papers also make a convincing case that the 6 port style of porting is the optimal one for efficiency while having low emissions and keeping acceptable power. if it got better mpg with all the ports open they are smart enough to figure that out. although i do have to say that my buddies full bridgeport rx3 and my old gsl-se with stock 6 ports, got about the same highway mpg, 26ish. same trans/rear gears.



there is stuff you can do.



1. reduce pumping losses, #1 is the catylitic converter

2. the stock ecu runs on the rich side, plenty of fixes for this all the way from motec to super afc to a resistor

3. cdi ignition

4. rx8 leading plugs, these are like the racing plugs but in a "street" heat range.

5. synthetic oils...

6. the s5 higher comp rotors, small gains big expense



this is a cheap and easy stuff list....