I have been playing around with using negitive split in vacum and am impressed with the results.

in my p rows i have have a basic split of
p1 -31
p2-28
p3 -25
p4 -19
p5 -15
p6 -11
p7 -6
p8 -2
p9 0
p10 i incress gradually to a +15 deg split at 12psi. So my p1 trailing timing is 70ish degrees.


I have noticed a large incress in low end torque and i use less inj duty cycle during steady state cruise. You can putt the car around at 1300 -1800 rpm with out bucking and hesitation. The combustion is cleaner. I don't smell as much of the unburnt fuel smell.

Any one else do this thats willing to talk about it. I got the ideavreading sumthing from a guy that actully road races rotary powered cars wrote on this fourm a few years ago, it just didn't make sense at the time. Seem to work awesome.

 

crickets...

 

From what I've heard the RX-8's uses negative split from the factory in certain conditions. It would be interesting to see a back to back comparison on a dyno to verify your butt dyno findings. I'd like to see some more input from other members as well.

 

I just started running negative split in vacuum since last week and am pretty impressed. The Motor is a lot quieter and smoother in the low end. Also you can run slightly leaner. I'm running around 25 degrees split at idle and up to 35 negative at higher vacuums. I found about it on the thread named "negative split". I would recommend anyone with a power FC or other ECU that lets you run negative split to try it. I can post my split map if you tell me how to post it.

 

yeah please post some pics

 

You can post your map by taking the .dat file and compressing it into a zip file that allows you to post it on this forum. If you want just post a screen shot you can do an image capture on the Datalogit window and upload the image on the forum.

 

Here is the trailing map that I use showing the split. I may add a little more negative split further down the P rows and see how the engine responds.

 

i use -3 split and its deff smoother cruise, i am not too sure about your aggressive split but i guess it works for you

 

I have run -17 at idle, and -3 for most of the cruise area for a few years.
Larger port engines tend to need even more negative split for low power areas of the map.

Helps in better mileage, and allows leaner mixtures to reduce carbon buildup.

 

Hmmm

 

I haven't tried it yet. I've been waiting on finishing this next setup and hitting to rollers to see the effects. I cringe at experimenting without a dyno to give me some sort of readout. I'm entertained, please give me more to read...

 

I wish I had the time and money to play with the equipment.

It seems to smooth out combustion when you are at like say 7,000 rpm in 2nd gear in vacum...holding steady state throttle... then slighty incress the throttle and it is smooth...not bucky or jerky. Over all part throttle accereration is smoother than it was. Car just drives smoother than it ever has. I have had it for 10 years, changed to this split 3 or 4 weeks ago.

How does one upload my map.

I can monitor injection duty cycle and see a difference, seems lower, I have had a pfc on the dash of my car since 2003.

As far as the dyno, that would let you tune the curve to see where you need to come to 0 split. The neg split is most effective in high vacum. When You get to your constant load cells the split needs to be closer to zero. I am still playing with it.

 

you should do some searching on Rx8 club, its hard, but people do post logs and maps.

anyways, to make it simple the Rx8 works 2 ways. @zero throttle, Leading is -5. Trailing is RPM dependent, so at idle its 10 degrees or so (it moves a little), and @8000rpm it can be like 35-40, and it comes down with rpm. its a bit weird because it should be in fuel cut at zero throttle, but it does do it.

when you apply throttle the idle split of 10-15 goes away really fast, so by 1500-1800rpm and maybe 15-20% throttle its gone. mid rpm cruise split is close to zero, but its positive. high rpm high load split is 15.

i will grant you the stock Rx8 is different from a modded Rx7, but it never sees any real load with negative split

 

I like the idea of what the rx8 does, I was unaware of this,

 

Here we go, just open the zip file. FYI this is a 550cc 1300cc map with a large streetport. I'm not sure what MAP sensor is used so PLEASE do not load this into you car and start going (I have to say it). I won't have time to comment as I only did a "features" look but here's the file

 

Its a gm 3 bar map sensor, turbo is a T-3 35r with a 1.06 exhaut housing, no AI, big v-mounted ic, large streetport. Engine has 24,000miles on it

Thanks for posting the file. I tried in the manage attachment but it kept sayin invalid file.

 

Compared to my maps and others, that would blow my engine.
Rows 16/17 for 16 psi is more than even the stock map for P20.
Something is wrong here.

 

What exactly do you think is wrong??? too aggressive timing? it runs, pulls hard all the way up to 8500rpm. I am more concerned about the negitive split aspect of it than whats going on at 16psi.

Its actually based around a map of yours I got from barry 4 or 5 years ago. I changed the scaling so it reads up to 8800rpm and added a few pressure cells. Its been tuned by me for my for my car over those years

I drive and boost my FD every day and have for almost 2 years now, engine has closer to 25,000 mile on it now. This engine is on its 3rd transmission, i keep breaking 3rd gear. 1.3o bar. 98 percent duty cycles with 1300cc injectors, that doesn't work either from what every one online says, but i disagree. Anyone want to post sum of my data log, as you seem to think sumting is amiss.

I just get so annoyed by people telling me this or that won't work, or its wrong, . I am willing to share how I came to this, and have data to show exactly what the ecu is telling the engine to do.

I have a randome Question?? Does any one know how they were able to keep the exhaust turbines cool on a F-22 engine so they can super crusie. How were they able to get the metal(exhaust turbines) to sustain constant temps in the 3000 deg f range???

 

and if you notice the map is called negivitesplithightiming. As in it is my most aggressive timing map for the car, I have ton's of maps with different timimng curves, this one feels fastest

 

Tell me what boost you are running and in what P row it uses.

 

Chuck, for 12 Psi, it can work with conservative AFR's but any higher then 12, it starts getting aggressive. Its definitely not ideal but it can work. His restrictive turbo limits the torque which allows for a more aggressive timing. Its not our generally accepted as correct way of tuning but will work. I wouldn't take it on the track like that but for weekend spurts, I wouldn't worry about it too much unless the boost goes up.

seandizzie, are you logging your pulls? I might be a little concerned around peak torque which be around 6,000-6,500 RPM

thewird

 

Calibrated GM 3 bar setting; 43500/0 for FD3S or 6525/0 for Universal.

Calibrated direct plug in APEXI DENSO DPS-310-2000A (949940-6270 5 volt) 3 bar map sensor: 45200/3300 for FD3S or 6780/3300 for Universal.

His values do not match either??

Using straight PIM conversion, 12 psi would use P rows 14/15. That is way too hot for a T3 GT35R with 1.06 turbine with large street port. I have that turbo and it flows very well.

As I said ealier, something is wrong??????

 

Yes I am logging my pulls, i would post the data logs, but can't get them to load. I will email them if anyone wants to see them I have a couple, I would love to post them. I hear your concern and understand that I am pushing what is safe. If my fuel curve wasn't spot on it wouldn't work, It took for freaking ever to get the fuel right at elevated boost pressures, it barly works, not a safe map, do not load this map in your car and try to use it, especially if you have stock apex seals... but damn it pulls hard

Chuck I am running around p-18-19 a l. Around 18-20psi. 1.3x bar.


So what do you guys think of the negitive split in vacum.

 

O and does anybody have the answer to the f-22 super cruise question?? It involves using air off the compressor to create a cushion of kool air around the turbines... Growing metals in a lab, using electricity to create millions of microscopic holes in the surface of the turbine blades, Pressurize these holes with air from the compressor and you keep the heat of the jet exhaust from melting the blades, super cruise, I have held the prototypes in my hand... and i have the uneducated retard version... Just a random question to create thought and share sumthing I find really cool.. that a really cool old guy shared with me...

 

Interesting, it sounded like you were only running 12 psi. I'm assuming your using some sort of auxiliary injection then? I bet the Florida humid air isn't hurting either

thewird