negative split
07-19-05, 07:19 PM
#26
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depends on where in the map you are, around 0-150 mmhg there is a small mount of neg split, after that there is none. Ya my new motor is pretty stout, pinned the block etc. Next rebuild im gona do some grinding on my rotors simular to clr has done to theirs.
07-19-05, 09:51 PM
#27
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At high vacuum, you should have a high negative split. As you trail towards atmospheric, (zero vacuum, zero boost) you should be at no split or very slight positive split. At no point, under boost, should you be running negative split. As soon as you're into boost, go to positive split.
FYI, it took years of experimentation to get the CLR rotors correct. He had an "imitator's" rotor, someone who tried to duplicate what he did to his rotors. It came out of a granaded motor. They made a very big and easy to do error in machining the rotors. I'd have CLR do your rotors and not do them yourself!
FYI, it took years of experimentation to get the CLR rotors correct. He had an "imitator's" rotor, someone who tried to duplicate what he did to his rotors. It came out of a granaded motor. They made a very big and easy to do error in machining the rotors. I'd have CLR do your rotors and not do them yourself!
07-20-05, 01:14 PM
#28
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sounds like these guys at clr really know their ****. but if you have lower comp rotors, and have your ignition so finely tuned that you can hit full boost that quick, couldnt you benefit from a larger turbine housing? Great thread guys, learned a lot.
07-20-05, 04:46 PM
#29
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If you lug the engine at say 2000 rpm in third and just nail the throttle, full boost (I'm guessing 18-20psi) doesn't come on until around 4K rpm. It's when the engine is spinning and the egt's are already hot. Then there's virtually no lag. Doesn't feel turbocharged at all. Carlos thinks my hot side is too large now actually...I haven't even begun to discuss turbocharging with him yet, LOL. I think he believes in the small hot side, large wastegate theory, something I haven't really explored in depth. It seems like there are lots of people I've come into contact with in Florida that are using itsy bitsy hotsides and making 500 plus at the rear wheels.
CLR really does know their stuff...only recently have they taken on the lowly street guys like myself. In the past it was pro stuff only. In fact, they're working on a super top double secret project now! Of course I am sworn to secrecy! But Carlos has vast road racing experience including IMSA GTU stuff and most recently SCCA with his own car.
CLR really does know their stuff...only recently have they taken on the lowly street guys like myself. In the past it was pro stuff only. In fact, they're working on a super top double secret project now! Of course I am sworn to secrecy! But Carlos has vast road racing experience including IMSA GTU stuff and most recently SCCA with his own car.
Last edited by rx7tt95; 07-20-05 at 04:54 PM.
07-20-05, 05:17 PM
#30
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^hmm, i guess the neg. split wouldnt do much for a drag car then. since you dont really spend any time in vacuum, but for a street car its definately something i would look into.
07-23-05, 12:54 AM
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So in effect you are using controlled detonation in the form of two flame fronts coliding in order to create enough cylinder pressure so that the engine can run under extreme lean conditions? How would firing the trailing plug early pre-ignite the other rotor? The leadings are waste spark not the trailing.
07-23-05, 01:54 PM
#33
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Originally Posted by Bad2ndgen
So in effect you are using controlled detonation in the form of two flame fronts coliding in order to create enough cylinder pressure so that the engine can run under extreme lean conditions?
A normal burn cycle is smooth and controlled *burning*, propagating from the spark plug outwards. A common analogy is a grass fire set with a match in the center of a field - it more or less travels smoothly outwards. The flame heats up the fuel and oxygen immediately next to it, which burns, heats up the fuel and oxygen immediately next to that, etc.
Detonation is when everything *explodes* instead of burns. It's caused by too much heat and pressure, and everything goes off all at once. BANG. Your flame front is also expanding, and it is compressing the unburned air and fuel in the chamber... if it compresses it too much, it gets heated to the autoignition point (compressing a gas raises its temperature) and it all go boom.
You can have two flame fronts without detonation. Hell, all Mazda rotaries, technically, have two flame fronts, when leading and trailing ignitions are both active. Having two flame fronts just makes detonation more *possible* because the burn can happen too quickly and cause the excess pressure increase that results in detonation.
Rotary's main achilles heel is the burn happens too slowly, so anything we can do to make the burn occur more quickly is GOOD. Hence two or even three plugs per chamber...
How would firing the trailing plug early pre-ignite the other rotor?
BTW - Rotaries can run absurdly lean. I would consider 16:1 to be an excessively rich cruise mixture, even with grotty standard ignition timing. EGT is *not* a consideration at low power. Run lean enough and EGT's drop again, peak EGT is just lean of stoich and anything richer *or elaner* drops them off again. Probably not a good idea for runnign under boost, but it's great for getting highway fuel economy that makes people in econoboxes envious.
07-24-05, 10:01 AM
#35
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Dunno exactly...I usually gauge it by how much gas I use to make a run that occurs often. Usually jetting up to Tampa leaves me with just over half a tank at an 85mph cruise with the air on, windows closed. I was seeing just OVER 3/4 of a tank on my last run. So I was using about 1/4 of a tank to get to Tampa.
I did notice when I leaned out my a/f ratios initially I dropped my egt's slightly. Perhaps I should lean it out more (if the car is fixed, see my other CLR post for the bad news). I was initially worried about heat related wear to the turbo, etc...cruising with higher egt's. I guess it's really not an issue.
I did notice when I leaned out my a/f ratios initially I dropped my egt's slightly. Perhaps I should lean it out more (if the car is fixed, see my other CLR post for the bad news). I was initially worried about heat related wear to the turbo, etc...cruising with higher egt's. I guess it's really not an issue.
07-24-05, 02:08 PM
#36
I have lots of questions so bear with me here. When you say run larger negative split the farther you are in vacuum, exactly how much split are you referring to, -5 degrees, -10 degrees, more? Also when running this negative split, how much total advance are you running on the leading side? Also what rpm's do you do this at? Is it in vacuum at any rpm such as cruising speeds are is there an rpm cutoff point where you wouldn't want to do this above?
The RX-8 runs 5 degrees negative split at idle only. They have said this is for emissions and apparently they can run leaner because of this according to what you have said. Are you saying that negative split with a lean a/f ratio can give you great economy for cruising compared to traditional split timing and leaner a/f ratios? The key is in how much. I am curious as to trying this on a naturally aspirated car. Thanks for all the great info. If you can't give out specifics I understand but any neighborhood guidelines would be appreciated.
The RX-8 runs 5 degrees negative split at idle only. They have said this is for emissions and apparently they can run leaner because of this according to what you have said. Are you saying that negative split with a lean a/f ratio can give you great economy for cruising compared to traditional split timing and leaner a/f ratios? The key is in how much. I am curious as to trying this on a naturally aspirated car. Thanks for all the great info. If you can't give out specifics I understand but any neighborhood guidelines would be appreciated.
07-24-05, 02:41 PM
#37
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Originally Posted by rotarygod
I have lots of questions so bear with me here. When you say run larger negative split the farther you are in vacuum, exactly how much split are you referring to, -5 degrees, -10 degrees, more? Also when running this negative split, how much total advance are you running on the leading side? Also what rpm's do you do this at? Is it in vacuum at any rpm such as cruising speeds are is there an rpm cutoff point where you wouldn't want to do this above?
07-24-05, 03:50 PM
#38
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Originally Posted by Bad2ndgen
So in effect you are using controlled detonation in the form of two flame fronts coliding in order to create enough cylinder pressure so that the engine can run under extreme lean conditions? How would firing the trailing plug early pre-ignite the other rotor? The leadings are waste spark not the trailing.
07-25-05, 12:37 AM
#40
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The only way the trailing plug can ignite the next chamber is if the timing is so far retarded that the apex seal is between the leading and trailing plugs when they fire. The leading plug will fire into one chamber, the trailing plug will fire into the following chamber.
07-25-05, 08:31 AM
#41
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No, it's not a huge secret. I'll do a screen shot of my trailing and split maps and post them. I "think" I have my maps on the laptop. If not, I'll have to swing by the shop and download them. I've been waiting to tune on the local dyno which is/was waiting on parts for a rebuild (coils had to be rewound) so I have not dialed in timing as of yet so everything's conservative. I've mostly played around with logging fuel at WOT and various areas of cruise for better gas mileage as I drive the car daily. For those that do not know or have not read the last few CLR engine posts, I, more than likely, spun a bearing as a result of the oil pan incident a few weeks back. Anyway, wont' be working on the maps for a bit. Take a look at them when I post them and use as a rough guideline. My setup is very different from yours. If I remember off the top of my head, split starts out at about neg 25 and goes down from there. I'm pretty sure it's 25 at idle. I think I could probably go higher in areas but I haven't had time to mess with it nor bring the car to CLR for tuning. If/when the engine goes back together, it'll be one of my top priorities.
Originally Posted by rotarygod
I have lots of questions so bear with me here. When you say run larger negative split the farther you are in vacuum, exactly how much split are you referring to, -5 degrees, -10 degrees, more? Also when running this negative split, how much total advance are you running on the leading side? Also what rpm's do you do this at? Is it in vacuum at any rpm such as cruising speeds are is there an rpm cutoff point where you wouldn't want to do this above?
The RX-8 runs 5 degrees negative split at idle only. They have said this is for emissions and apparently they can run leaner because of this according to what you have said. Are you saying that negative split with a lean a/f ratio can give you great economy for cruising compared to traditional split timing and leaner a/f ratios? The key is in how much. I am curious as to trying this on a naturally aspirated car. Thanks for all the great info. If you can't give out specifics I understand but any neighborhood guidelines would be appreciated.
The RX-8 runs 5 degrees negative split at idle only. They have said this is for emissions and apparently they can run leaner because of this according to what you have said. Are you saying that negative split with a lean a/f ratio can give you great economy for cruising compared to traditional split timing and leaner a/f ratios? The key is in how much. I am curious as to trying this on a naturally aspirated car. Thanks for all the great info. If you can't give out specifics I understand but any neighborhood guidelines would be appreciated.
07-25-05, 11:19 AM
#42
fart on a friends head!!!
wow, this is EXTREMEMEMELY interesting. this negative split thing really does work eh? is it something that should only be tried on "scalloped" rotors? low comp rotors? or can it be done across the board? im in the midst of tuning so this is all VERY interesting. id love to check into it.
also, about the double throttle blades. . . michel. . . i totally forgot about that. i figured you had decided to give it up. i STARTED working on something and put it up. now, i wont be able to do anything for a good while. . . due to my untimely trip to afghanistan by the end of the year.
still. . . this is great. . . im really wanting to start doing this on my car. . .
now that i think about it. i had something happen while i was at a steve kan tuning event in alabama about a year ago. i hooked up my spark plugs BACKWARDS. negative split at 20ish psi was not cool (i had a wastegate problem as well). im STILL on the same engine w/no problems. i always thought that was funny. i even thought the kdr anti det device had something to do with negative split. . . . man, this is nice. geh. . . im excited.
paul
also, about the double throttle blades. . . michel. . . i totally forgot about that. i figured you had decided to give it up. i STARTED working on something and put it up. now, i wont be able to do anything for a good while. . . due to my untimely trip to afghanistan by the end of the year.
still. . . this is great. . . im really wanting to start doing this on my car. . .
now that i think about it. i had something happen while i was at a steve kan tuning event in alabama about a year ago. i hooked up my spark plugs BACKWARDS. negative split at 20ish psi was not cool (i had a wastegate problem as well). im STILL on the same engine w/no problems. i always thought that was funny. i even thought the kdr anti det device had something to do with negative split. . . . man, this is nice. geh. . . im excited.
paul
07-25-05, 10:05 PM
#43
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LOL, paul. You watch yourself over there in Afghanistan. I had a chance to go there and to Iraq and turned both down (photojournalist).
Negative split really does work. I think one could do it without issue if you do not have phase ported rotors (scallops). I'd think one could do it for any rotor but the split and timing would probably have to be optimized for your engine, just like any tuning.
Haven't given up on the double throttle. I have them hooked up now but they go open at WOT, even in vacuum. Will work on that a bit if I managed to come out unscathed with the whole oil pan incident.
Negative split really does work. I think one could do it without issue if you do not have phase ported rotors (scallops). I'd think one could do it for any rotor but the split and timing would probably have to be optimized for your engine, just like any tuning.
Haven't given up on the double throttle. I have them hooked up now but they go open at WOT, even in vacuum. Will work on that a bit if I managed to come out unscathed with the whole oil pan incident.
07-26-05, 08:53 AM
#44
fart on a friends head!!!
haha, ill watch myself. . . or try anyways. . . ill have my first son to come home to. . . so yeah, ill be careful. helicopter mechanics are pretty much on the safe list as it is anyways.
is there any way you could get a shot of your timing maps on the forum? id really like to see it in comparison. im having trouble figuring out what does what. trailing advanced? leading retarded? both moved in conjunction? does trailing take the place of the leadings original timing? im just a little confused on the placement of such timing.
about the double throttle. i had plans to modify a throttle body because i figured the double secondaries might cause a little bit of turbulence. . . maybe i thought into it a little too much!!!!
very very exciting
is there any way you could get a shot of your timing maps on the forum? id really like to see it in comparison. im having trouble figuring out what does what. trailing advanced? leading retarded? both moved in conjunction? does trailing take the place of the leadings original timing? im just a little confused on the placement of such timing.
about the double throttle. i had plans to modify a throttle body because i figured the double secondaries might cause a little bit of turbulence. . . maybe i thought into it a little too much!!!!
very very exciting
07-26-05, 10:18 AM
#45
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Since we know that Mazda uses the negative split during idle on my RX8 for economy benefits, I began to wonder why they didn't run negative split accross the board since the car is NA if it really helps the fuel economy.
My guess would be that the lean condition heats the EG up so much that at high RPM's it would burn the cat out to early, and Mazda has already had an issue with cat temps, hence the 11th 1/2 hour ECU flash port campaign as the cars came off the boat.
Kinda ironic that the car could get better economy if emissions weren't holding it back. Not to worry, if RG and I can get the Megasquirt working, we'll try a negative split and and see what happens.
My guess would be that the lean condition heats the EG up so much that at high RPM's it would burn the cat out to early, and Mazda has already had an issue with cat temps, hence the 11th 1/2 hour ECU flash port campaign as the cars came off the boat.
Kinda ironic that the car could get better economy if emissions weren't holding it back. Not to worry, if RG and I can get the Megasquirt working, we'll try a negative split and and see what happens.
07-26-05, 06:46 PM
#46
I decided to have a little fun and play with a crude form of negative split on my 1st gen using the distributer. The car is still nonturbo. I adjusted the split to 0. Total timing advance is set to 25 degrees. Then I hooked up the trailing vacuum advance to the manifold but left the leading vacuum advance disconnected. This gives me 15 degrees of negative split at idle and then it tapers off to 0 as load increases. Probably not as smoothly as rx7tt95's but it still does it nevertheless just to see what happens. It works. The car runs great. I no longer have the factory ecu so I can play with fuel trims. Because I no longer have the stock ecu, I also no longer have the vacuum actuators that limit vacuum to the advance below 1000 rpm. Without these you will have full advance at idle. Since I just have the trailing vacuum advance running straight to the manifold, I have 15 degrees of advance at idle on the trailing side. It does idle a little high and a little rough. If I were to use the vacuum switch, I could take care of the idle issue.
Overall the car still drives nice. I will have to see how well it performs in the long run compared to my standard 10 degree conventional split. I know this isn't a finely tuned and I have less control but at least I can see to a point if it works. Anyone with a distributer can do this. Disconnect leading vacuum advance. Set split to 0. That's it. Crude but testable.
Overall the car still drives nice. I will have to see how well it performs in the long run compared to my standard 10 degree conventional split. I know this isn't a finely tuned and I have less control but at least I can see to a point if it works. Anyone with a distributer can do this. Disconnect leading vacuum advance. Set split to 0. That's it. Crude but testable.
07-26-05, 10:47 PM
#48
Senior Member
Originally Posted by rotarygod
I decided to have a little fun and play with a crude form of negative split on my 1st gen using the distributer. The car is still nonturbo. I adjusted the split to 0. Total timing advance is set to 25 degrees. Then I hooked up the trailing vacuum advance to the manifold but left the leading vacuum advance disconnected. This gives me 15 degrees of negative split at idle and then it tapers off to 0 as load increases. Probably not as smoothly as rx7tt95's but it still does it nevertheless just to see what happens. It works. The car runs great. I no longer have the factory ecu so I can play with fuel trims. Because I no longer have the stock ecu, I also no longer have the vacuum actuators that limit vacuum to the advance below 1000 rpm. Without these you will have full advance at idle. Since I just have the trailing vacuum advance running straight to the manifold, I have 15 degrees of advance at idle on the trailing side. It does idle a little high and a little rough. If I were to use the vacuum switch, I could take care of the idle issue.
Overall the car still drives nice. I will have to see how well it performs in the long run compared to my standard 10 degree conventional split. I know this isn't a finely tuned and I have less control but at least I can see to a point if it works. Anyone with a distributer can do this. Disconnect leading vacuum advance. Set split to 0. That's it. Crude but testable.
Overall the car still drives nice. I will have to see how well it performs in the long run compared to my standard 10 degree conventional split. I know this isn't a finely tuned and I have less control but at least I can see to a point if it works. Anyone with a distributer can do this. Disconnect leading vacuum advance. Set split to 0. That's it. Crude but testable.
Grant
07-28-05, 09:02 AM
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I'll take a peek on my laptop today to see if I have my current map saved. I make it sound like it'll take a lot of effort because I use the Windows-based laptop for tuning only. Everything else I do computer wise is on a Mac. I literally have to go dig the laptop out, LOL. It's the wife's B-Day today so it's her day but I'll try to get to it. I know I have "something" on the computer, maybe a slightly older map. Won't be able to get to my car for a few days as it's at the shop.