Hey guys, I've been experimenting w/ zero split in vacuum lately and as a result I've made some changes on my publicly available Split tables. Basically IIjust re-created one that fits all the 13B's instead of the two I had up for Stock/Extend Port and Bridgeport respectively. Give these a try and see what you think.

http://bdc.cyberosity.com/v/Technica...72008_vex.html

http://bdc.cyberosity.com/v/Technica...72008.jpg.html

B

 

Wow, that new timing map is quite radical from anything I've seen. Any reason for this? I mean, 38 - 46 degrees of advance in the ENTIRE vacuum area from 20 - 80 kpa, even at idle??
Also, I'm guessing that running 0 split in vacuum everywhere will help with torque (but worse gas mileage), or the other map where running up to 19 degrees of split will help with smoother driveablity and better gas mileage?

Maybe I'll try both and find out (as you stated of course )

 

That sounds like the bridgeport table and not the regular one. I do run progressive advance in vacuum at lower RPM's on the bridgeports because of a theory I have concerning the negative effects of overlap being greater at lower RPM's.

Give the zero split one a try and see what happens. So far so good over here. I know some folks have been doing it for awhile but up until a few weeks ago I'd not paid much attention to split stuff in vacuum. Always felt it's effects were marginal at best.

B

 

in theory, zero split (or approx zero split, based on the location of the trailing plug) should be the most efficient since combustion would be closest to constant-volume, so whereever its possible to run it without knocking (such as when boosting), its probably beneficial. It would be a secondary effect acting with overall spark timing, but every little bit can help.

In addition, the stock maps that i've seen run 0 split at low loads approaching prob approx 80 kpa (rough estimate)

 

I wonder where Brian got this idea!

 

Gee, it wasn't Fred or anyone.

 

Btw, along with the zero split table update, I also zipped up those along with the other tables (and screenshots) into a nice, single file that can be downloaded from here:

http://bdc.cyberosity.com/v/Technica...82008.zip.html

B

 

Keep in mind that ms2/extra supports negative split as well, although right now only up to -20 degrees

Ken

 

^^^ When I was trying to get ms2 1.0.2 to work reliably on my brothers car months back, I had set the split table at -20 degrees throughout the whole rpm range and below 80 - 85 kpa and then tapered to 0 degrees at 0 vacuum and then progressed to +11 degrees at 175 kpa. I noticed a huge improvement at idle and the throttle response was incredible. It just overall ran soo much smoother and better. Needless to say, the current ms1 setup doesn't compare. Too bad I couldn't get it to work reliably (too much noise and consistent table corruption)

 

I wish the older Haltechs allowed negative split. I'd love to experiment with negative split in vacuum as I've heard the same thing before. Thanks for the numbers, 2lucky2tha7. I may make a negative split table here and see if anyone would like to try it. Should be real easy.

B

 

Just an FYI for those interested in negative split. Compression ratio affects how much negative split you can run. A low compression ratio such as 8.5:1 may be able to run up to -75 degrees of split at points!!! A high compression ratio such as a 10:1 Renesis can functionally only go up to about -40 of split. Now that I've probably got everyone scratching their heads about this, go have some fun!

 

darn too bad i sold my MS

negative split sounds like it may do some well in crisper throttle.

 

Can someone school me on negative split?
To my understanding, zero split means L and T fire at the same time? Am I correct? So negative split, do you guys mean the T would fire before L??? I thought that was a big no no.


EDIT: I ws just thinking about it. i think I had it backwards. So for ex: -15 degrees split = T will fire 15 degrees after L

 

Negative split means trailing fires first.

It's a very "black art" in the rotary world and there isn't much info about it except what comes from the few people who are brave (stupid?! ) enough to try it.

 

I'd def be willing to play with it in vac, once i get the MS2 chip in there and working. See if there are any fuel economy improvements on my bi-monthly 600 mile drives

 

If you'd like, I can make something up according to 2Lucky's numbers and try that out. Just listen for any kind of engine ping down low while in vacuum and part throttle. It won't be damaging but if spark is firing too hard ahead you'll know it. Plus water temps may shoot up.

B

 

Interesting....so what are the benefits of running negative split in vaccum? smoother idle, less fuel consumption?

 

The corruption problems in 1.0.2 are usually caused by somewhat flaky usb->serial adapters or built-in serial ports. There are things you can do in the ini file to make it more reliable.

As far as noise issues go, I've never had an issue with 1.0.2 once I added a .01 uF cap across G+ and G- going into my lm1815 board.

I know people have had some issues with 2.0.1 on the rx7 though. For 2.1.0, I'm going to be working on the second trigger code until I can crank and start the engine, and drive it through my whole rev range on at least 2 cars before releasing it. I'm going to be working on trigger masking and filtering in combination along with James, so we'll be able to get it working as well as, or better than polling in 1.0.2.

The corruption problems that are seen by some in 1.0.2 don't seem to happen in 2.0.x either.

Finally, if I have time, I'll try to add negative split support up to -50 if I can. If not I'll make it go as far as it can reliably go.

Also, I'm not sure if the "running smoother" stuff was because of negative split. One of the rx7's I've been working on lately just switched to ms2/extra 1.0.2, and it runs EXTREMELY smooth (the engine doesn't shake at all on idle), and we're running positive split on the whole table.

Ken

 

Well, it'll probably be another month or so before I convert over to MS2, and even then its not difficult to make up a split table and play with it (altho determining the effect without a dyno may be more difficult on a finer scale) Hopefully i'll be able to get an EGT sensor to keep an eye on it that way too.

 

Negative split will do some interesting things and you can't base your opinion solely on EGT's. Negative split when done right allows you to run really lean when cruising. So lean that your EGT's will register as higher as you lean it out but will then go back down when you keep leaning it out to where it needs to be.

 

Hi guys, quick question almost on topic (!). I've been looking at Megasquirt and also VEMs but VEMs doesn't seem to have many people doing rotary. It also doesnt support trailing plugs. Is it effective to run just the the leading plugs if you didn't have a way of firing the trailing ? also how about firing L and T at the same time or is this a no no? really appreciate any help as I need to make a decision fairly soon and have a lot of learning to do !

 

you can do that as long as you're not running boost, and are a little more conservative with WOT timing... this may not help your power though. Plus, why give up the capability to run split if you dont have to?

 

Just to wake up a REALLY old thread... I just started using negative split with my ms3 today... it makes a HUGE difference in smoothness and how lean I can run.

This is on my fairly tired S4 NA.

Previously I couldn't run much leaner than 14:1 without the engine feeling like it was running rough and less powerful. Negative split has allowed me to go to 16:1 so far on cruise, and it still feels fine, and revs very quick.

Whoever came up with this idea it's a good one!

I totally forgot about making the range of negative split allowed larger, so I'll probably work on that soon if I have time (writing rotary sequential fuel code on ms3 this weekend which is more important for being able to really lean out low load for me).

Ken

 

RX 8s use it,, Mazda has tried just about everything known. dont work to well with boost.

but if it makes you happy go for it.

 

It's a good thing you can set split positive or negative in our split table then!

It's only for use off boost... but it helps a lot there.

Ken