LSxManiac

First of all, you can't use a 2-bar map sensor without A LOT of calculations because the PCM is designed to operate with a 1-bar sensor. Second point, depending on the amount of air the engine is using, you may not need to convert to speed density. If MAP goes to 100 kPa and the MAF is maxed out, you can just crank up the PE table values to add more fuel. At this point, the system is functionally in speed density mode because the MAF (being maxed out) is no longer supplying relevant information. This may not work at high boost pressures, or if you're marginal on injector size, but I've tuned a bunch of supercharged cars (including some 86-89 models) using this method. You should be able to do everything you need with Tuner Cat.

RealQuick

Major purpose of switching to speed density should be for boosted vehicles. Setting up for the 2 bar MAP is the big issue that people havent figured out. I just scored a FAST system with White's racing harness and WB O2 setup for 600 shipped... no more scewing around..

blkchevyz

cheater.

RealQuick

STSturboLT1

This is a pretty old thread, but I just thought I'd share that I recently got my car running a 1.5 bar tune in SD mode with the stock LT1 PCM.

I achieved 1.5 bar by using a 3 bar MAP sensor with a 2X voltage amplifier circuit I added. The reason I did this was to retain more resolution within the tables since I'm only running 7 lbs. of boost. I could have gone with a 2 bar sensor instead, but I wanted the extra challenge. I'm weird like that.

Here's what I did to modify the tune... All of the MAP based constants I divided by 1.5. For the VE tables, I moved the columns accordingly: for the 30 kPa column, I used the cells from the original 45 kPa column (30 x 1.5 = 45). For the odd numbered columns like 35 kPa, I averaged the values from the closest columns: in this case, the 50 and 55 kPa columns (35 x 1.5 = 52.5). I did this for the whole table, and for columns 70 through 100 kPa, I just re-used the values from the 65 kPa column for now. Next, I realized that 100% is the limit for the VE cells, and when in boost the values needed could be higher than 100%. So I divided all VE cells and the injector constant by 1.5 (somewhat arbitrarily chosen). I used the same basic approach for the spark advance tables, except they were easier since there was no scaling involved, just moving columns around.

Once all the tables were adjusted, I started the car up. It fired up right away and ran fine. I drove the car for a few miles, and could tell the fueling wasn't ideal since it had hesitation at times, and large fuel trims confirmed it. After several iterations of logging and adjusting the VE tables, the tune is almost dead on for normal driving. I used some runs at the track a few weeks ago to dial in the WOT tune, and it's pretty close to perfect. I had an LC-1 wideband to do my WOT logging.

I went to a speed density tune because the car has better throttle response compared to using the MAF. Plus I'm sick of always having to clean the MAF, and the fact that it's just a restriction, albeit small, on the intake. I just thought some of you might be interested.

engineermike

That's cool. I thought about the >100% VE and I really don't think it's needed. Correct me if I'm wrong, but the fueling goes up according to the MAP reading. In other words, if your MAP reads 30 psia (15 psi boost), then the ECM will supply twice as much fuel as it would for 15 psia (0 psi boost, or NA). The VE is simply how much of the pressure in the intake manifold actually makes it into the cylinder. I've read that turbo motors VE is actually very low at full boost due to the exhaust expanding and taking up space.

Mike

STSturboLT1

The problem is that the stock PCM can't recognize boost, it only recognizes up to atmospheric pressure. The new MAP sensor fools the PCM into recognizing boost as being within the 100 kPa limit. Additional trickery is needed by scaling the injector constant, to make the PCM add more fuel than it intends. I originally planned to tune WOT strictly with the VE table, and set the PE values to 0, but I ended up hitting the 100% limit in the VE table (and still running lean) so I ended up using PE anyway. In order to get the VE values under 100 at WOT, I would have to further lower the injector constant, which I don't plan to do at this point. Maybe I'll re-visit that after I get my new motor installed next year.

Not sure how to respond to the exhaust in chamber comment. Shouldn't it be almost completely expelled after the exhaust stroke? My understanding of VE is the percentage of air that enters the cylinder compared to a cylinder full of air at atmospheric pressure. In any event, it drives great, and it was a fun and relatively easy project. As a side note, I will probably switch to a 2 bar MAP at some point, as the circuit I added is a bit of a kludge and I'm concerned about the long term reliability.

VK

Thanks for the new info! Even tho my car is down and out atm, i'll have her running again soon and starting thinking about what i was going to do about tuning.

engineermike

No, especially not on a turbo motor. The exhaust pressure will typically run twice the boost pressure. So, at TDC after exhaust, you have a combustion chamber full of 20 psi exhaust gas (assuming 10 psi boost). You have to expand that down to 10 psi during the intake stroke before boost can start entering the cylinder. So, you give up the first part of the intake stroke totally, thus lowering the VE.

Mike

STSturboLT1

Okay, I see what you're saying, and I agree. However, it shouldn't take much piston movement on the intake stroke to drop below the intake boost level. By the time the intake stroke is complete, there should be more oxygen in the cylinder than there would be at atmospheric pressure due to the boost. I agree that the exhaust remnants will decrease it somewhat, but I don't think it would be that significant. I could be full of hot water, as I'm not a turbo expert (or tuning expert for that matter). All I know is that at VE=100% it was still lean at WOT.

dookie454

Another 2 Bar LT1 Stock PCM success story here... 2 bar is definately worth putting the work into if you plan to run lots of boost (over ~7 psi) and you have heads/cam work which allows the MAF to max out early on, once the MAF maxes your left with only PE enrichment which is a blind fueling addition based on RPM alone, and even that maxes out quickly - I had 38% (near maxed) at 6200 rpm with only 7 psi and 83lb injectors 50% DC).
My thought was if I change my pulley and add a second fuel pump.. how will I get the PCM to add more fuel since everythings maxed out and it cant measure the additional air/pressure? (or what if my blower belt/hose pops off at WOT with all that fuel being blindly dumping in????)
So.. either mess with a mechanical FMU and huge fuel pressure/pumps or modify the PCM for free.... hmmm

By the way someone said the MAP also inputs the barometric pressure when the key is first turned on and now that's off by 1/2... SO WHAT!! your "calibrating" everything to the 1/2 off reading so unless you drive in extreme different elevations regularly you wont even notice (but the 02's will correct for it anyway)

Well.. I just did mine (SD, Closed Loop, 2 bar, 83lb injectors) thanks to finally reading someone else had success (STSturboLT1), thanks STSturboLT1 for posting!! I spent the time simply because you said it works - most say it cant work (but they didnt try apparently)

For me it all started from trying to figure out how to do two things:
1) Ramp up to 15psi (currently at 7psi on a Forged 383) simply because my MAF maxed out at 5400rpm (I plan to spin to 6500+) and PE table is only good for ~40% which is about where I was at at 6300rpm with only 7 psi...
2) Get my 83lb'ers running ok (suffering from lean tip-in for about 6 months now - best I could get it to run was with MAF and Open loop.. Closed loop it was a mess.... long story but 42lbs ran fine and 83lbs were lean only on tip in - like the pump shot was broken)

Year ago I wanted to try 2 Bar MAP but everybody all over the web said "dont do it", "it cant be done..." "not enough resolution" all that but actually from what I've learned there's plently of resolution for a 2 bar tune AND a decent cam (234 duration) and still idle at 700 rpm.

All I had to do was:
1) Buy a 2 Bar Map and cram the connector into it
2) I didnt have the VE's dialed in from the previous tune/engine/cam rebuild since I relied on MAF (which now Im thinking is what caused my problems with the 83lb injector lean tip-in) so I had to make a whole new VE/KPA MAP table by moving all KPA values down about 1/2 (some of the low end KPA werent quite half since it's not a linear change between the sensors)
3) Since my MAF was maxing out I decided to run SD and save alot of headaches in the future.. therefore to enable a full 0-15 psi boost refence VE tables I had to cut the injector size in 1/2 as well so there's enough VE percentage left over for 14 psi (1 psi is at about 60kpa and 14psi is at 100kpa).
4) Once I got all this roughly input, it would start but only barely idle... if I pressed the throttle it wouldnt rev up.. just continue to idle.. it was running lean but I was beginning to think the 2 bar setup wouldnt work until I increased the VE in the proper tables then it began to actually rev up when I hit the gas.... WOW

5) From here I re-enabled closed loop operation (to get the 02 feedback logging in datamaster) and ran it until it warmed up and entered closed loop.. it ran like comeplete garbage at first (too lean, then too rich..) but after a few VE MAster runs it smoothed out but was still too lean and still had the Lean tip in that I always had with the 83lb injectors... so I lowered the injector size from 40 (1/2 of 83lb) to 30... and for the first time ever all lean tip in stumble was GONE!!!! The car runs BEAUTIFUL now only after 3-4 VE master datalogs and finding the right injector flow rate.. you have no idea how happy I am about this... I tried everything with the 1 bar tune but because everything was scaled properly I didnt bother changing things like injector size so I never would have fixed this problem if not going to 2 bar.

6) Now, datamaster reads about 70-75kpa at 7 psi manifold pressure, right in line for 14 psi, running a little rich at WOT so I could either put -# in the PE table but since I'm in the VE tables all I have to do is reduce the VE in the RPM and KPA of WOT to "calibrate" the VE cells.
Also noticed my combo likes about 32-45 degrees of timing from idle to WOT, so losing any resolution in the idle/low rpm high load area's dont seem to be a problem at all since my 1 bar timing table values were all so close together (stock they varied alot but never understood why - perhaps for emissions??)

Another big benefit of the 2 bar tune is the fact I no longer have my last line of 100kpa timing reduced so far (since with 1 bar anything over 100kpa was boost but has to be setup for timing at max boost since 1 bar doesnt know how much boost)... this means power delivery is much smoother and there's no more ~10 degree drop from 95-100 kpa like there used to be.

It really runs good. I'm really suprised.

STSturboLT1

I'm glad that it worked out for someone else too! Hopefully others will find the info useful as well.

sean-k94z

Interesting, I tried a 2 bar sensor about a year ago and could never get things to work well(Lean tip-in and so on), despite all the rescaling efforts. What I found is that the stock PCM (94 in SD mode) seemed to use a SD/alpha-N blend. If you don't believe me unplug the maf and the map sensor and your engine will run fine. I would be curious to see a working bin file. If anyone with a working 2 bar bin has time send a copy to sean-keys@keystoneis.com

dookie454

"Interesting, I tried a 2 bar sensor about a year ago and could never get things to work well (Lean tip-in and so on), despite all the rescaling efforts."

I had this same problem with the stock 1 bar setup when I switched to 83lb injectors from 42lb injectors. Never got the problem to go away until I rescaled for the 2 bar MAP. Still had the problem with the 2 bar until I continued to lower the injector size quite a bit beyond 1/2 way... to 30lbs from 83lbs).

So you say the LT1 PCM uses the TPS and RPM alone for fueling? I'd think the VE tables have to be right for this to work... VE uses %TPS under 340rpm it's probably extended out for the higher rpms with MAF and MAP disconnected.

1982z28with18s

I never thought about it, but this would work PERFECT in conjunction with using megasquirt to control the fuel side for me. So I could ramp my timing in with 35 degrees of timing up to zero vacuum, then down to say 25 at 5lbs of boost, 20 at 8lbs of boost, 18 at 11lbs, and 16 at 14lbs or more. This would make it so much smoother than just having the 16 degrees at 95kpa+ like I have it right now.