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I have an EFR7670 running on E85 currently, but it is honestly a huge hassle especially since I have another E85 car I have to keep up with. What are the downsides of going back to 91? I want to keep the car as reliable and smooth running as possible, not so much chasing big power. It is a track car and driving to the track while dealing with E85 is kind of a pain as well.
Ever thought about running a mix ? E50 gives you 90+% of the octane that E85 does and E30 gives a great octane boost as well . I do E30 because it's an easy % to get : 3parts E10 plus 1 part E85. On a trip to the track you only have to take a few gallons of E85 (assuming you can't get it at the track)to keep you going for the day. The difference in consumption from petrol is negligible as are the extra fueling requirements.
Now that we have a frame of reference let’s take a look at our turbo rotary:
Rear Wheel Power
(Mazda lists displacement at 80 cubic inches. There are a couple of legitimate ways to derive displacement. In order to be conservative I am going to use 160 cubic inches so as to better compare apples to apples.)
1993 Mazda RX7 OE 217 rwhp 1.36
1993 Mazda RX7 350 rwhp 2.19
1993 Mazda RX7 400 rwhp 2.5
1993 Mazda RX7 450 rwhp 2.81
1993 Mazd a RX7 500 rwhp 3.13
1993 Mazda RX7 550 rwhp 3.44
1993 Mazda RX7 600 rwhp 3.75
This is profound. A “lowly” 350 rwhp RX7 is within spitting distance of the highest output boosted motors offered for 2018!.......
2.19 V 2.23
Given that even at "lower" power levels our single turbo setups are around the same levels as current "supercars" it is easy to see the interest in running alcohol as a base fuel. lots on this board do it, including me for a couple of years.
While E85 might work dandy in a piston engine i have 5 13B-REWs that show otherwise in the rotary.
Our engines have a borderline lubrication problem running on gas. Rotor housings never look really good after usage. The problem is getting enough lubrication between the apex seal and rotor housing. The best partial fix is pre-mix however Mazda understandably didn't want potential buyers to confuse a $44,000 sportscar with their lawn mowers. So the "solution" had to be the external oil pump... two major problems... it was going to have to use oil from the motor, not 2 cycle, and it was not the best way (pre-mix) to partially fix the problem. and it didn't. just take a look at the Renesis... Mazda initially doubled the number of oil injector ports per housing and then later added a third. and OBTW, the 3 port Renesis still has a horrendous rotor housing wear problem.
So the single turbo 13B-REW has a fundamental wear issue between the apex seal and housing... what does that have to do with this thread?
the title is way wrong... instead of "downgrading" to pumpgas you are upgrading. upgrading because gasoline in itself is a lubricant.
it is pretty simple: rub gasoline between your thumb and forefinger, it feels oily. do the same with alcohol, it feels "dry."
my problem with alcohol is not power, my problem is with the loss of lubrication.the lube loss is not initially evident as while wear is greatly accelerated the two pieces conform to each other and compression is fine. the problem is the wear is greatly accelerated.
wear expressed in three ways:
increased chatter
decreased chrome
flatted leading edge of the apex seal
another issue with alcohol as a base fuel are tar deposits. i am not a chemist but i have consulted with numerous high level Scientists at various major oil companies as well as the usual smaller racing oriented oil companies as to why these bothersome deposits occur. no doubt they are from some interaction between the ethanol and premix. of course plan B would be try another premix. been there done that. no difference. the tar coats the rotor face and the sides of the rotor that face the intermediate plate as well as the primary port runners. the secondaries also show some tar but since they are used much less there isn't as much deposition.
as i mentioned i have 5 motors that i disassembled upon which i base my wear and tar conclusions.
4 of the 5 were running perfectly and were taken apart at the end of the summer so as to install stud kits.
two of the motors were my own. one had lost 20% compression when i lost a fuel pump fuse in the middle of a run at the Texas Mile. only internal problem was flattened corner seal springs.
three were customer motors run one summer on E85... making 500, 550 and 613.
two different excellent tuners
three different apex seals
six different well selected pre-mixes (Redline 2 cycle Alcohol Oil, Valvoline (2) special blends specifically for me, Klotz Benol, Klotz Super Techniplate, & Amsoil)
all with the same problems.
out of the norm rotor housing surface wear and matching apex seal wear
tar
here are the three rotors from the customer motors. the one on the right was very low miles, the center was the most miles and 613 hp.
the substance appeared to have no solvent. acetone did nothing to remove it. i had to blast it. compare these rotors with the rotor that came out of my car after four years. prior to taking the picture i did not clean or touch the rotor:
the motor was run on gas around 500 hp. it also benefited from alcohol but only in boost. i do love alcohol but as they say on T V, in moderation.
As was correctly posted earlier in this thread by Brettus, the benefits of alcohol are not linear with the amount. i use a maximum of 900 CC in boost. i end up with clean low wear motor internals as well as no knock at 585 with 93 pumpgas and methanol.
if you are running with a lower power objective water will deliver exactly the same benefits... no knock and clean low wear internals.
i have an engine that has been running for a few years at a touch above 500 on 91 octane (Tucson, Az) at 4000 ft with just water.
sorry for the longish piece here but my view is that you are upgrading not downgrading when you switch to gas. in your situation 91 octane and a simple AI system running water and you are set.
Last edited by Howard Coleman; 05-08-19 at 10:17 AM.
gasoline and Walmart 2 cycle as premix. 1 oz street, 1.5 oz track.
during the 4 years compression rose about 15%. the reason i decided to disassemble it was to see how much sideseal clearance had opened during the 4 years... approx 1 thou.
Last edited by Howard Coleman; 05-08-19 at 08:25 AM.
Howard ...... maybe running 30% Ethanol would yield similar results to W/I on both counts (power and gunk/wear) ..... I don't have any long term teardown results to go by however.
one valuable observation is that gasoline does not in any way dissolve the tar.
the only liquid i found that made even the slightest dent in the tar was... penetrating oil. so i doubt that the tar situation will be negated by running a large dose of gasoline as base fuel. i do agree that you will probably get all you need as to knock resistance w a modest amount of ethanol in the base fuel. i still think that you will be losing a great deal of lubricity and the engine needs way more than even a steady intake of gasoline as base fuel provides.
one valuable observation is that gasoline does not in any way dissolve the tar.
the only liquid i found that made even the slightest dent in the tar was... penetrating oil. so i doubt that the tar situation will be negated by running a large dose of gasoline as base fuel. i do agree that you will probably get all you need as to knock resistance w a modest amount of ethanol in the base fuel. i still think that you will be losing a great deal of lubricity and the engine needs way more than even a steady intake of gasoline as base fuel provides.
I kinda already learned this the hard way ..........
Renesis turbo at 400whp level running omp only on gas+W/M = ok
Same power with 30% ethanol + omp only = bent apex seals from overheating
Same power with 30% ethanol + premix at 100:1 = ok
However .... I trust the ethanol more than I do the W/M for knock suppression .... also learnt the hard way
Footnote edit : The Renesis omp pushes through a ton of oil at WOT and I suspect much of it is in an effort to get the oil to push into the middle of the housing on an S1 . This seems to be sufficient under boost on straight pump gas but not when you introduce a fuel with no lubricity.
Howard, were the 3 engines you posted rotor photos of or any of the engines you are seeing 3 patterns of excessive wear run with the combination of e85 with premix and the use of an OMP or e85 and premix only?
BTW, was talking to Cam Worth this afternoon... i asked him what his experience was w E85 motors and his direct quote was...
"it tears them up." asked for more specifics... he said the rotor housings get raped...
sort of like this one:
they all look the same: circumferential striations varying only by degree. this housing was in excellent condition prior to being run on E85 for a summer.
here's 585 rwhp on 93 pump and 900 cc of methanol...no knock, no drama. alcohol used right, only when needed.
top to bottom
RPM 7722
boost 24.9
knock reading 20 front 30 rear... real knock is around 200
Ignition lead 12.9
Methanol (AI) pressure 132 psi
i do think that if your power goal is above 600 that some sort of alcohol as a base fuel is advantageous, it is just that you will be challenged as to rotor housing lubrication.
for sub 600 power gasoline is your base fuel. if you are wanting to run in the 300-425 range water (or water meth) is your answer. above 425 i suggest 100% methanol as AI and your go to system is made by Alkycontrol. i have run my Alkycontrol system since 2003. it features stainless steel braided lines and is more thoughtfully engineered as it should be since methanol can burn your car to the ground. for water or water meth (which isn't flammable) the newly re-designed AEM system is fine.
BTW, was talking to Cam Worth this afternoon... i asked him what his experience was w E85 motors and his direct quote was...
"it tears them up." asked for more specifics... he said the rotor housings get raped...
sort of like this one:
they all look the same: circumferential striations varying only by degree. this housing was in excellent condition prior to being run on E85 for a summer.
I had the same thing when running a combination of softish apex seals (e&j) with an ethanol mix. It didn't do that when running the OEM seals however.
the motors had Goopy, Super Seals and Rotary Engine seals, there was no difference. i would never run OE seals in a anything but a stock motor as they are too brittle and break with knock taking out the internals and the turbine wheel. pick your poison.
wow thank you for the detailed analysis of this topic. you have me convinced to go back to 91. this motor has about 10k miles on it and has been run on E85 by the previous owner about 5k miles. hopefully things haven't suffered much...
E85 does not tear up rotor housings in my experience. I opened an engine with 2-3 years of run time at very high boost( 31 psi), mainly road course driven, with a fair amount of dyno time also. E85 only, 1:1 premix( no omp), with OEM apex seals, and it was MINT inside.
it is possible that the harder OEM seals work O K w E85. they don't work O K when you have knock. of course none of us will ever encounter knock.
From my learnings I came to the conclusion that any knock was going to do damage anyway so better to avoid it with use of high octane gas. I've actually had a few instances on E30 when things have gone wrong and been very surprised not to hear any knock . One time my fuel pump starved and I saw afrs in the 15s at 14psi ....no knock at all !
BTW, was talking to Cam Worth this afternoon... i asked him what his experience was w E85 motors and his direct quote was...
"it tears them up." asked for more specifics... he said the rotor housings get raped...
sort of like this one:
they all look the same: circumferential striations varying only by degree. this housing was in excellent condition prior to being run on E85 for a summer.
E85 definitely is not the cause of the rotor housings being torn up. That is most likely caused by the apex seal choice and/or inadequate lubrication.
Recent teardown of my motor after 4 years at over 40psi (street car, so it's driven every week) and it had zero issues with rotor housing wear. Same as my last teardown, no wear issues.
"E85 definitely is not the cause of the rotor housings being torn up."
"most likely caused by the apex seal choice and/or inadequate lubrication"
since you have all the answers, how about being helpful to the community.
since i state that there were three brands of apex seals (Goopy, Super Seals and E&J) and you are talking apex seal choice just what apex seal is going to solve the problem?
since i stated that five well selected premixes were used just what is your lubrication solution?
I've personally seen Super Seals, ALS and E&J do that same kind of damage on pump gas even with the usual premix lubrication amounts. I don't have any experience with Goopy seals though.
I do know that It's not E85 dependent for this type of damage to happen, E85 will just require a different type of lubrication as standard premix does not suspend/mix in E85 for long. OMP may work ok without premix on E85 but I haven't tried it.
I've personally seen Super Seals, ALS and E&J do that same kind of damage on pump gas even with the usual premix lubrication amounts. I don't have any experience with Goopy seals though.
I do know that It's not E85 dependent for this type of damage to happen, E85 will just require a different type of lubrication as standard premix does not suspend/mix in E85 for long. OMP may work ok without premix on E85 but I haven't tried it.
Copeland, just so you are clear i, and i assume others, are looking for answers as to what, if anything, can work w E85.
you say "E85 will just require a different type of lubrication as standard premix does not suspend/mix in E85 for long."
as per my post 5, "six different well selected pre-mixes (Redline 2 cycle Alcohol Oil, (2) Valvoline very special blends specifically for me, Klotz Benol, Klotz Super Techniplate, & Amsoil)...
no differences. and for sure the premix was getting into the motor as the interaction between it and the ethanol is what caused the tar deposits.
i am just looking for answers. so far the only interesting comment was made by Turblown. he had no significant rotor housing wear with a motor that was running OE seals. For me, that isn't a solution as they are too brittle for higher power motors.
05-06-19, 04:36 AM
