Lethal Locost goes MegaSquirt

After two seasons with the car, I became annoyed with some of the limitations of the OEM fuel injection. It ran very rich for most of the time, and pig-rich at full throttle. The engine was fun below 4500rpm (the removed T-VIS switch point), and then something changed in the tuning and was a whole lot more fun from there to the redline.

I decided to go MegaSquirt. For a control-freak like me, having full control over everything excites me.

I ordered MegaSquirt II, V3.0 from DIY AutoTune and was very happy with their service as well as the product. Since I was going MegaSquirt, I might as well go to town, so I bought a set of GSX-R/600 Independant Throttle Bodies (ITB's) off eBay for about $60, and bought all the Ford EDIS stuff from Pick-and-Pull for about $30 more.

The MegaSquirt took about 10 hours to assemble, taking my time and checking everything every step of the way. I wired it for Ford EDIS, a GM stepper IAC (not installed) and flyback circuitry for low-impedance injectors (though I am using a resistor block with low-impedance injectors).

The EDIS parts were thieved from an early 90's Ford Escort. I machined the unused power-steering pulley grooves off the crank pulley, and machined the EDIS 36-1 wheel bore to a 0.0015" interference fit. I put the pulley in the freezer, and boiled the wheel, and then quickly got it into place by gentle tapping with a dead-blow hammer.

I made a sensor bracket that mounts on some unused engine block bosses, and places the sensor roughly horizontal, even with the crankshaft. The trigger wheel was placed with the missing tooth 90° ahead of the sensor.

A metric-size frost plug was also pounded into the old distributer hole in the cylinder head using Aviation Form-A-Gasket as a sealer.

Modifying and Mounting the ITB's

I lopped the plenum off my previously fabricated intake manifold, and tweaked tubes #1 and #4 to match the spacing of the GSX-R/600 ITB's. I had to machine spacers to spread TB's 1 & 2 from 3 & 4 about 3/4", and I made longer bolts using 1/4" rod - I welded a nut on one end, and threaded the other for the metric threads inside the Suzuki TB's. I've seen people use Redi-Rod and some cobbled-together nuts and washers for that, but personally I think it looks like poo when it's done that way.

The secondary air-valve thingies were removed, as were the GSX-R injectors (since the 4AGE injectors are in the head). The holes were filled with "Quick Steel" epoxy putty, after cleaning them thoroughly and cutting threads into the holes for the putty to grip. The 4AGE throttle cable rotating thingie was cut off and welded to the ITB's as the GSX-R one was too small.

Air Filters

I used bulk straight rad hose to connect the ITB's to the intake runners, and some hand-made trumpets to the ITB's. K&N has air filter #RC-3510 for a Legend/Dwarf cars running Yamaha FJ1200 motors - they fit perfectly onto the hose I used to attach the trumpets. The trumpets were made out of exhaust tubing, annealed and pressed over a die I machined to the same taper as the TB's, the correct length, and as hefty a radius as I thought I could get away with.

Mild steel trumpets: $5

K&N filters: a bit more than $5

Re-wiring

This is where I regretted trying to use as much of the Toyota harness as I did. That was a stupid, stupid move. It made the MegaSquirt rerofit needlessly complex. I followed the factory wiring harness diagram, and matched it as best I could to what MegaSquirt needed. Luckily (or, masochistically), I really enjoy electrical.

Tuning

I had almost zero success finding base maps to begin with. The few that I found either didn't make sense to me, or not at all for a blue-top 4AGE. For an engine with such a wide fan-base, I was surprized that nobody had anything available.

You use MegaTune to set up the engine, and then use MegaLogViewer to datalog what's happening and you can let it adjust things, or you can make adjustments. I did both.

Oh yeah, you're really going to want a wide-band O2 sensor. I bought an Innovate LC-1 as it was relatively inexpensive and seemed versatile.

Many websites have mentioned how difficult it is to tune ITB's. Many give up trying to run Speed Density (MAP/RPM-based) and tune to run Alpha-N (TPS/RPM based). Other more adventurous sort run blended tables (a bit of both worlds). I'll keep you posted with where I end up. Keeping in mind this is not my daily driver, and I can afford to compromise some driveability for the sake of "fun."

I set up fuel using the default "Generate" feature of MegaSquirt, and ended up richening the "cruise" to 14.7 to get rid of some surge and stumble under light throttle, I shifted the "lean cruise" area higher in the RPM (based on the rpm ranges I previously cruised at), and had to richen up quite a few cells to smooth out the acceleration.

As of this writing, here are my tables so far (March 2009):

Volumetric Efficiency Table

Air Fuel Ratio Table

Spark Advance Table

Assessment So Far

Two words: Awesome!

Whle I wouldn't say the tuning is perfect yet, and there are still some low-speed stumbling going on, it's better! The engine has far more torque than before. The ITB's are freaking loud. It's a very different beast to drive, you need to be much more gentle on the throttle - it's hard to be smooth at low speeds (I may need to build a more "progressive" throttle wheel).

I love the ability to tweak the tables and see improvement. I'm a tweaker and a control-freak, and this is candy for me. It will be interesting to see how this progresses.

You need to get a video of the engine running with the ITBs. Loud is good.

This thread delivers.

I don't know how you find the time - I've got kids and a fultime job just like Mr. G, and my latest Megasquirt build is at 8 months and counting.

Also, I was looking at your AFR table - if you're having an off-idle stumble, try leaning out the low RPM /high vacuum bins to about 16:1, that cured mine on my last build.

awesome man :) just awesome... then again i've got a thing for a locost, 4ag, and MS... it's just all over when you put em together...

well, you just cemented my engine plans for the fiat

I think I have tables for 4age MS. I will have to look around. If not I think I know where to get some but you seem to have things under control. There was a a guy that was making a plug and play MS to replace the ECU on MK1 MR2's. I did some additional work on this as it was perfectly legal to make this mod running ALPHA N in SCCA IT class. You had to set it up using alpha n as at the time the MS could not use the AFM and the SCCA rules did not allow for the addition of any sensors, wires or vacuum lines to the stock ECU housing. Ohay those were some fun times. I wonder if with the new technology that the microsquirt has to offer if a MK1 MR2 could be made competitive in IT. Hmmmm.

Looks good. Your VE table looks somewhat familiar. How are the injectors/rail moutned?

I just love art in motion. Beautiful, would love to see some video.

Just got done checking out your web site. What an awesome build!! Two thumbs up!!

I did start with your VE table, Dr.Hess, as it was closest to what I was doing - 4AGE and ITB's, although not a 16V. I changed some VE bins ever so slightly, and may modify it a bit more. What I'm ending up with is quite a bit different though....

It ran, albeit poorly, which I attributed to nasty default SBC timing, and nasty default AFR's. Once I sorted those out, MLV did the rest of the fiddling with longer and longer datalogging. Depending on what happened, what it sounded like, and how it pulled, I would go back and tweak the AFR's the most - the timing I have right now is pretty conservative. It's pretty reasonable to drive right now.

The injectors are Honda 235cc out of a '92 Accord I found at the wreckers. They dropped right in place of the 187cc bluetop injectors (in the head, not the manifold), and even used the same connector, the same fuel rail and everything.

Brilliant! And I agree with RexSeven, a nice 'n loud ITB video is necessary.

What's your idle kpa, I'll let you know if you should switch to Alpha-N or not. I tune more ITB'd cars then not anymore

Also you may or may not want more bins for spark past 4k, it's not like you need a locked advance. Some motors pick up with more/less timing then where a normal distro would run flat.

Glad MS is working out for you though.

My idle is around 42kPa, and pretty steady, too.

My spark advance is pulled completely out of my bum. It seemed like a reasonable shot at something that would work, based on my antiquated experience with carbs with mechanical & vacuum advance.

I'm always keen on input!

fifty wrote: try leaning out the low RPM /high vacuum bins to about 16:1, that cured mine on my last build.

I've been thinking on that - how does this work>?

SkinnyG wrote:

fifty wrote: try leaning out the low RPM /high vacuum bins to about 16:1, that cured mine on my last build.

I've been thinking on that - how does this work>?

I'm not sure if I'm answering your question correctly, but my thought is that the fuel atomizes poorly at idle, so it puddles on the walls of the intake. Once you get on the gas it enters the air stream and creates a rich condition.

Changing those bottom left-hand bins worked well for me and won't harm the engine (no load). Just save your current map so you can flip back to it if needed.

Oooh. That makes sense. I'll give it a whirl. Thanks.

Man, you guys are really giving me the incentive to finish my MSnS conversion on my ITB 240Z!

KA or SR 240???

I think we need the video and a few more pictures!

definatly need video,, with good sound

4cylndrfury wrote: KA or SR 240???

I would never put a 4 cylinder in a 240Z, not even an SR20DET. It's just wrong.

This is an L28 block w/N47 head running the original Dual SU manifold converted to dual 55mm ITB's with 2 750cc injectors and a basic MSA 6 into 1 header.

ww wrote:

4cylndrfury wrote: KA or SR 240???

I would never put a 4 cylinder in a 240Z, not even an SR20DET. It's just wrong. This is an L28 block w/N47 head running the original Dual SU manifold converted to dual 55mm ITB's with 2 750cc injectors and a basic MSA 6 into 1 header.

I'm thinking 4cyl fury must have had "SX" instead of "Z" on the mind.

MrJoshua wrote:

ww wrote:

4cylndrfury wrote: KA or SR 240???

I would never put a 4 cylinder in a 240Z, not even an SR20DET. It's just wrong. This is an L28 block w/N47 head running the original Dual SU manifold converted to dual 55mm ITB's with 2 750cc injectors and a basic MSA 6 into 1 header.

I'm thinking 4cyl fury must have had "SX" instead of "Z" on the mind.

indeed...look at my name...its the way Im wired sorry