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Originally Posted by kahren' date='Dec 26 2003, 02:13 PM
it will blow if u really ping it hard under load
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Originally Posted by TheAntiChrice' date='Dec 27 2003, 02:25 PM
Ohh.. Okay.. then you learn something new everyday... I'm just going by what I've read and heard about rotaries that a good ping will pop a seal. So wait.. how resilient are these motors anyways and what would the ideal CR be for pump gas and moderate boost?
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Had to bring this subject back https://www.nopistons.com/forums/pub...#>/biggrin.png This is the way I see it. I think using the Renesis rotors in a boosted application could be very beneficial provided with good tuning. Here's an example:
Lets build 2 Fd engines to produce 400hp. Both engines will have the exact same setup(same upgraded twins everything). One will use it's stock rotors while the other will use the higher compression Renesis rotors. To make the 400 hp, theoretically both engines will experiance the same pressures and tempuratures inside the combustion chamber. Lets say that the engine with stock rotors makes its hp at 17psi. With the added leverage the higher compression rotors of the other engine, this engine should make that same hp but at a lower boost (14psi just guessing). That psi differance alone means the turbos are more in their efficiancy range. And we all know that a turbo running in it's efficiancy range mean that it's not heating the air like crazy. Also the less the air is heat decreases the chance of detination. I personally think this would be an excellent advantage of running the higher compression rotors in the older turbo engines. Overall drivability should be improved. |
Cept higher compression makes for detonation because the air is allready twice a dense at 15psi, you then compress it down 9:1 and its effectivly 18:1, ren rotors would be like 20:1,.. just my impression of it,.. may be wrong. On the other hand on the aus rotary forum and the rx8 forum I have heard of someone running stock rx8 seals in a PP motor in austrilia without problems,..
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Youre forgetting that increasing the compression will increase the VE, and spool a large turbo faster than lower compression, while having better off boost response.
Drago, your math on the chamber pressures is way off. You need to use absolute pressure. 2 engines both at sea level and 90% VE, one running 9.0 CR and one running 10.0. 14.7 PSI on the 9.0 CR motor will have the same chamber pressure as the 10.0 CR motor running 10.5 psi. |
Someone build a high C/R and try to make 400+ horse on pump gas... I dare you.
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Originally Posted by RONIN FC' date='Apr 29 2004, 09:46 AM
Someone build a high C/R and try to make 400+ horse on pump gas... I dare you.
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Originally Posted by mazdaspeed7' date='Apr 29 2004, 07:12 AM
Youre forgetting that increasing the compression will increase the VE, and spool a large turbo faster than lower compression, while having better off boost response.
Drago, your math on the chamber pressures is way off. You need to use absolute pressure. 2 engines both at sea level and 90% VE, one running 9.0 CR and one running 10.0. 14.7 PSI on the 9.0 CR motor will have the same chamber pressure as the 10.0 CR motor running 10.5 psi. Yep I forgot to mention those benefits as well https://www.nopistons.com/forums/pub...#>/biggrin.png So based on the above info thats 4.2 psi differance. This would mean that the higher compression engine has much lower intake temps. Seems like a no brainer to me! Ronin Fc, Don't get the impression thats it's not possible. Overall unless someone experiments with this we may never really know how well the engine performs in the long run. Thats why I'm keeping a very close eye on the turbo and supercharged Rx8's that are in development on the Rx8forum. Remember low compression is always refered on a factory boosted car because it leaves just enough of a safety blanket for those people who choose to use a lower octaine gas. Low compression is more user friendly for the average Joe. Thats doesn't mean that it's better than high compression for someone who can tune it properly(which should be done anyways). |
Here is a really excellent post form the Rx8forum about this subject:
With lower compression, you have the ability to run greater timing advance as well as the ability to get away with lower octanes easier than you can with higher compression. On higher compression engines you need to run less timing. There is always a tradeoff. Everything is tuning based. Manufacturers know that not everybody treats their cars as they should. They go for performance numbers that are very conservative. They will also do this with the biggest margin of error that they can get. They understand that some people will use the cheapest gas they can find that has the least resistance to knock. When you are upgrading the performance of your vehicle, it is just assumed that you are accounting for this. When the '87 Turbo II RX-7 came out, Mazda claimed that they could not run any more boost or higher compression due to the risk of detonation. Then in '89 they upped the compression and the boost which totally countered their previous statement. In '93 they redesigned the engine to flow more air, slapped 2 pathetic little turbos on the car, made the coolant system less efficient, raised the boost, and still gained power. When do the reasons to do something stop? It really comes down to margin of safety vs their tuning abilities. With the stock Renesis tuning and it's frequent updates, do you trust Mazda with forced induction on this engine? FWIW: Rotary Performance has used the 9.7:1 compression rotors in streetported single turbo 3rd gen RX-7's and put out over 400 rwhp. It is all in the tuning. Don't try it on your stock ecu. There does come a point in forced induction where you really do want to run lower compression since the higher compression engine will need so much timing retard that it is no longer gaining in power. This number is quite high though and realistically out of the range of a street driven car. Use the high compression. Just tune it.[/B] Also keep in mind guys if the 3rd gen if felt stock it will easily go over 100k miles with its poor factory setup. Mine has 79k with original vac lines and runs damn near perfect. I'll give Rotorygod much props for the above info. |
Originally Posted by The Ultimate 7' date='Apr 29 2004, 05:47 PM
I'll give Rotorygod much props for the above info.
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Agreed! I especially like the way he explains all the details and doesn't flame people who ask so called stupid questions.
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sorry bout the wrong math,..
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Originally Posted by Drago86' date='Apr 30 2004, 01:10 AM
sorry bout the wrong math,..
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Originally Posted by The Ultimate 7' date='Apr 29 2004, 01:47 PM
Here is a really excellent post form the Rx8forum about this subject:
Why would someone with a street car take an REW motor, capable of 400+ stock block run 10.1 rotors? To run low boost, while on the fringe of destruction? For off boost response? Seems hardly worth it. I can see some methanol fueled race car that gets torn down every couple of races needing higher C/R to combat the lag from a tremendously large turbo. I think most people forget they drive street cars. |
Originally Posted by RONIN FC' date='Apr 30 2004, 11:04 AM
I think most people forget they drive street cars.
Anyway, I have to rebuild my S4 motor soon and I wanted to put better rotors in it. I have a set of S5 counterweights and one good S5 rotor. I have access to a machine shop so milling isnt a big issue. From my understanding, to get Renesis rotors, I need just the rotors and the counterweights. In your opinions, would it be better to just buy one more S5 rotor, or should I get the Renesis rotors? And what is the cost of each solution? Thnx Andy |
If I were rebuilding an NA engine, S4 housings etc, minimal or no porting, would using the stock FE seals work fine? All the concerns I see above seem to be centered around applying boost to the seals, but sticking with the compression ratio they were designed for, in different housings, they should be fine, yes?
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Your better off with S5 rotors and counterweights. The machineing and balancing makes it not worth it.
The rens apexs need to be machined out to take a conventional seal. The rens apex cant take the heat from the peripheral exhaust, and isnt designed to cross an opening. |
problem with the renisis seals is that the apex seal will flex when passing over the exhaust ports. if you run renisis rotors just use some old apex seals...
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Originally Posted by The Ultimate 7' post='514288' date='Apr 29 2004, 02:47 PM
Here is a really excellent post form the Rx8forum about this subject: Also keep in mind guys if the 3rd gen if felt stock it will easily go over 100k miles with its poor factory setup. Mine has 79k with original vac lines and runs damn near perfect. I'll give Rotorygod much props for the above info. my fd has 93k on everything too, its had rear brakes, a clutch and a radiator, everything else is factory. part of that is how the thing had been used. the fd doesnt have the cooling to do much more than short bursts.... |
Originally Posted by Robbomaz' post='395619' date='Nov 24 2003, 03:47 AM
We probably could have used the renesis seals, but this was not something I could be definate about, given that we knew the seals did not cross a port as designed. The renesis seals may well be fine but that was not a risk I wanted to take with this guys motor. He is an unsponsored racer (apart from our discount price https://www.nopistons.com/forums/pub...IR ) and needed a season + package so it was decided to machine the grooves to take proven seals. I'm sure someone will use the new seal in an old motor soon. I believe the gas edge is better sealing on renesis seals. i think you may have chosen correctly with that one. i was at mazdatrix a few months ago and they told me how they warped the apex seals in the rx8 rotors. i think they were also spinning it in the neighborhood of 10kish rpm though, so i'd wonder if the seals could tolerate the life of a turbo streetcar-which would peak out closer to the 6500-7500ish rpm range...and not have to stay in that range for 20 minutes at a time... just a thought. |
Originally Posted by j9fd3s' post='514133' date='Apr 29 2004, 09:56 AM
no way its happening on california pump 91 were you talking about higher than 9:1, or renesis rotors? i've got a high compression engine in my fd... i'll see what i can safely extract from it, but i bet 400 shouldn't be a problem. and yes, on shitty california 91 |
Originally Posted by guitarjunkie28' post='771763' date='Oct 22 2005, 04:55 PM
were you talking about higher than 9:1, or renesis rotors? i've got a high compression engine in my fd... i'll see what i can safely extract from it, but i bet 400 shouldn't be a problem. and yes, on shitty california 91 good luck! |
Just out of curiousity, what is your goal behind running high comp rotors?
Are you running 9.7 or the rens 10:1? |
my goal is more low end without the twins. i wanted more instant power when i mashed on the gas pedal--even before the turbo spooled. fuel economy too. i don't have much answers on how well it works yet, other to say it feels great and is getting 20+ mpg (tuning not quite dialed yet). when i actually do more testing, dyno, etc, i'll be able to form a little more intelligent and educated opinion, but for right now, all i can say is i like it.
goals are pretty conservative. ~350-400ish whp on 91 pump gas before the water injection. 450-475 whp on 110 octane. it's at 10 psi right now and there's ~1600 miles on the motor so far. it's about dyno time. i'll get back to you with results. |
Originally Posted by RONIN FC' post='772356' date='Oct 24 2005, 03:17 PM
Just out of curiousity, what is your goal behind running high comp rotors? Are you running 9.7 or the rens 10:1? they started life as 9.7's, but i dished them and polished the faces. when i cc'd the chambers for balance, they came out to be 9.49:1 CR |
Oh, so your compression isnt so high. Hope you didnt cut those rotors too thin, that will be another aspect to worry about.
You seem confident all will be well, Post a dyno chart when your done. |
i'm not confident...i just don't care.
if it blows up, whoopity-******'-doo. i'll build a new one, and at least i learned something. |
Originally Posted by guitarjunkie28' post='774591' date='Nov 1 2005, 02:12 PM
they started life as 9.7's, but i dished them and polished the faces. when i cc'd the chambers for balance, they came out to be 9.49:1 CR i bet the polishing helps, also 9.49 is better. |
there was some debate on the polishing...
one argument would be that more heat gets reflected and turned into movement. another would be the question of atomisation and the fuel sticking to the face of the rotor. i dunno which is the more correct, but i'm in the process of finding out i guess. |
Originally Posted by guitarjunkie28' post='774910' date='Nov 2 2005, 01:44 PM
there was some debate on the polishing... one argument would be that more heat gets reflected and turned into movement. another would be the question of atomisation and the fuel sticking to the face of the rotor. i dunno which is the more correct, but i'm in the process of finding out i guess. i polished the faces of the rotors on my t2, cant say i noticed a difference, id like to think theres less chance of having a hotspot/stuck carbon and thus less chance of detonation. |
oh yea... that was another thought too. no carbon buildup.
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Originally Posted by guitarjunkie28' post='774910' date='Nov 2 2005, 04:44 PM
there was some debate on the polishing...
another would be the question of atomisation and the fuel sticking to the face of the rotor. i dunno which is the more correct, but i'm in the process of finding out i guess. |
Originally Posted by RONIN FC' post='774957' date='Nov 2 2005, 05:25 PM
I cant see the fuel droplets sticking to something that hot and moving. that was my argument. but i dunno... we'll see |
Originally Posted by RONIN FC' post='514126' date='Apr 29 2004, 09:46 AM
Someone build a high C/R and try to make 400+ horse on pump gas... I dare you. Have been doing that since the late 80's. It's all in the tuning and combination. One of the most important factor in running high compression would be to keep everything cool. As a matter of fact in my experience it don't matter if it's high or low compression if you're trying to run high boost on low octane(93 pump) if your combination will not support it. Always remember heat is a rotary #1 enemy be it by coolant or air intake temps. A lot of people don't realise how much impact coolant temps can effect total psi on low octane fuel. Ever wondered why 3rd gens are more likely to experience knock on low octane. Even with the biggest most efficent I/C it's added benefits would be deminished by high coolant operating temps resulting in high underhood temps leading also to high intake air temps. That's only a part of the problem. This from my experience is what is responsible for majority of the problems in that high coolant temps leads to high rotor housing temps which also leads to high spark plug tip temps which results in pre-ignition which I believe is what rotaries sufffer mostly from especially around the trailing spark plug area. Everyone is always trying to blame compression and low octane as the killer. Sure it's easier to have less mistakes running high octane and low compression but why suffer all the ill effect of doing that when there are other methods that can be done to obtain positive results. A balance must be acheived somewhere in the combination. You got to choose which of the following will do so and also most important in which order of importance. Just a small list off the top of my head. Air intake temps. Coolant temps. Oil temps. Spark plug heat range. Rotor housing coolant passage modifications. A/F ratio. Total ignition timing. Fuel octane. Compression ratio just to name a few.https://www.nopistons.com/forums/pub...IR#>/smile.png |
good info..
i've got a dual oil cooler setup i made, aluminum oil pan (9 qt total system capacity), 5" thick intercooler, 2-pass radiator, good ems to control everything... i'd say i've got all the ingredients to make things work. but then again, just because you have all the ingredients in your kitchen doesn't mean you can bake https://www.nopistons.com/forums/pub...R#>/tongue.png |
Originally Posted by crispeed' post='776236' date='Nov 7 2005, 06:47 AM
Have been doing that since the late 80's. |
Hi, assuming a stock S6 fd3s running rx8 rotors stationary gears and standard factory ecu,
will the ecu knock sensor/ignition retard be quick enough to protect the engine? Or is there an addon unit to improve the speed/response/effectiveness enough to make it work with a margin of safety with the std ECU? Or should you go straight to an aftermarket system? Thanks Michael |
You cant run rx8 stat gears without a rx8 eccentric shaft. The oil journals for the main bearings are in different spots.
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Really? I was unaware of that........
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They are off by about 1/16th of an inch.
If you use the rear stationary gear from a Renesis on a 13B, you need to run a bead of gasket sealer around it. The older stationary gears had an o-ring at their base that sealed them to the rear housing. The Renesis rear gear does not have that o-ring or the groove for one. The o-ring is actually on the rear housing. This is why you need sealant. Lots of little differences between engines. |
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