How to get more torque from a 4g93 SOHC 16v

Hey all, newbie to the forum here.

I have a 92 Expo LRV Sport AWD 5-speed that I picked up cheap a while back with a bad tranny. It only had 84k on it and the problem was that, in 2nd gear (only), as long as you kept your hand on the gearshift it would stay in gear just fine - but if you didn't it would jump out of gear if you let off the gas quickly. 1st-2nd syncros were also bad so it would grind if you didn't hesitate a split second in neutral during the 1st-2nd shift.

I drove it like that for about 15k miles but finally got tired of nursing the tranny along. So, I recently picked up a low-mileage replacement at one of those "engines imported from Japan" places and installed it. Now it shifts and works perfectly. I have absolutely fallen in LOVE with this little micro-van as my daily commuter - all over again!

There is only ONE thing about it that I DON'T love about it. It is in SERIOUS need of more low RPM torque. I don't like how high I have to rev it and how much I have to slip the clutch to get a smooth takeoff - especially when starting from a dead stop going uphill (a common situation here in Seattle).

I've read that advancing the cam will improve torque in the lower RPM ranges, so I'm thinking about installing an adjustable cam gear/sprocket to see if that will help. I'm also thinking about doing the IAT-resistor mod to make it run a bit richer for a bit more power. Anybody got any other suggestions?

Keep in mind that
1) I am a very capable mechanic and fabricator (I do the Jeep thing and have built all my own suspension modification and body protection parts)
2) I'm not really looking for big HP gains
3) I'm not concerned about having more top-end power either, and
4) I'm on a pretty tight budget (would I be driving a 13-year old car every day if I weren't?).

Any suggestions are welcomed.

Thanks,
Bob

Boy that's a good question. I'd start with possibly airflow or like you said, advancing timing just a little bit. Not much though.

quote:

ORIGINAL: patsevo8

Boy that's a good question. I'd start with possibly airflow or like you said, advancing timing just a little bit. Not much though.

Thanks for the reply, but I'm not really wanting to advance the timing - at least not in the traditional sense of advancing the distributor. That contributes to pinging problems and the need for higher octane fuel. Can you say S-P-E-N-D-Y?

What I'm thinking about advancing is the camshaft timing. Of course that will advance the ignition timing too, since it is driven off the camshaft, but I'm thinking I'll probably need to actually retard the timing at the distributor to compensate.

I figure if I advanced the cam say 6 degrees, for example, and the stock ignition timing is supposed to be say 4 degrees BTDC (don't know what it really is without looking it up) I'll probably have to set the timing at the distributor (or at least the reading of the timing from the crank pulley) for 2 degrees ATDC in order for the ignition spark to happen at the same point in the piston stroke. Or maybe somewhere in between 2 degrees ATDC and 2 degrees BTDC. I'll just probably have to play around with it a bit and figure out what works best by trial and error.

As for making it breathe better, I have already given that some serious thought too. Making the air flow better on the intake side always benefits both HP and torque. Things like porting heads, boring throttle bodies, swapping fuel injectors, high flow intake manifolds, free flow filters and such are all good for performance across the whole RPM range. Unfortunately though most of the benefits are gained at the high end of the RPM range - not at the low end, which is what I'm really looking for. Also there is the fact that most of those kinds of mods are anything but cheap.

On the exhaust side, making it flow too freely will actually reduce low end torque by moving the torque peak into a higher RPM range. At low RPMs torque actually benefits from some backpressure. Of course as the RPMs increase you reach a point where backpressure builds up enough to start robbing power, and at that point you need more flow capacity.

I know that there is no "magic bullet" to get what I'm after. I'm just hoping that others around here may have come up with some low-buck mods I can do that will individually make some small improvements - and just maybe collectively make enough gains to overcome the little Mitsu's one, slightly unpleasant performance characteristic.

Did you replace the japanese sensors with the ones off of the older engine? When I swapped a jap engine into my wife's little 90 eclipse 4g93 1.8L I was dissapointed until someone suggested that the sensor parameters were not the same because of the different emission restrictions programmed into the ecm. Other than that, have you thought about going irridium? NGK's are $8.00

quote:

ORIGINAL: FireDoc

Did you replace the japanese sensors with the ones off of the older engine? When I swapped a jap engine into my wife's little 90 eclipse 4g93 1.8L I was dissapointed until someone suggested that the sensor parameters were not the same because of the different emission restrictions programmed into the ecm. Other than that, have you thought about going irridium? NGK's are $8.00

Sorry FireDoc, but I may have been a little unclear in my first post. I haven't swapped engines - only trannys. I still have my original US-spec engine.

Now that I'm back to driving it every day again, what I'm trying to figure out a way to do is to improve my low RPM torque so I don't have to rev it so high and slip the clutch so much in order to start it rolling from a dead stop.

I've been thinking about doing some minor ignition system upgrades too - they can't hurt and might even help gas mileage. I take it you like the irridium plugs. Are they that much better than Platinums? I've been thinking about getting a set of the Bosche +4 Platinums or maybe even trying some Splitfires.

Any other specific recommendations/suggestions? Better plug wires? Hotter coil maybe? Even looking for anybody to make specific recommendation of brands/part numbers of anything that has worked well for them....

My mistake on the engine bit, I assumed when you were looking for torque you had done a complete swap. As far as Iridium plugs go, they are far superior to platinum because the have much less resistance, harder metals, higher temp tolerances, etc. Here's an article that explains it. http://ducatigarage.netfirms.com/denso.html It doesn't sound like I have to explain all the benefits to you, as far as other ignition parts go you probably know all the good companies that make what you want, of course finding an application for your "Not so popular to modify" engine that isn't just going digital (as you mentioned budget) may be more difficult. I'll keep my eyes open.

quote:

ORIGINAL: FireDoc

As far as Iridium plugs go, they are far superior to platinum because the have much less resistance, harder metals, higher temp tolerances, etc. Here's an article that explains it. http://ducatigarage.netfirms.com/denso.html

Thanks for the link - I'll check it out

quote:

ORIGINAL: FireDoc

..........as far as other ignition parts go you probably know all the good companies that make what you want, of course finding an application for your "Not so popular to modify" engine that isn't just going digital (as you mentioned budget) may be more difficult.

Yeah, that's what I'm running into all right. Not a very common vehicle or the most common engine Mitsubishi ever built. That's why I'm soliciting info from the "been there, done that" folks around here

OK, here's an idea and a bunch of questions for all the experts out there.

I was just down at the wrecking yard looking at and comparing two wrecked Expos.

One was a 92 with a 4g93 SOHC 16v (1.8 liter) just like mine.
One was a 94 with a 4g64 SOHC 16v (2.4 liter).

I noticed that the intake plenum and throttle body on the 94 were significantly larger, but otherwise seemed to be set up EXACTLY the same. Connectors all seemed to be of the same type and size and all seemed to be located in the same places. Throttle linkages & their mounting brackets even looked interchangeable.

This gave me an idea. So, here goes with the barrage of questions.....
Does anyone know if the intake for the SOHC 4g64 will bolt onto the SOHC 4g93 head?
If not, how about the throttle body?
If it is possible to do either of these swaps, would I also need to swap the airbox so that the MAF sensor is matched to the intake?
What about the ECU? Are they mapped differently? Would it be necessary - or even possible - to swap them as well?
Or would it be easier/better to swap all my sensors & such over to the new intake & throttle body?

I'm thinking that I might be able to scrounge the parts off one of the scrap-pile engines in one of the larger yards for really cheap. On the surface, this looks like it might be a pretty easy swap. Just wondering if anyone has tried it and if so, how well it worked and what are the pitfalls. I've been calling around trying to get my hands on the intake and throttle body gaskets for both to compare them, but no one seems to have them on hand (surprise, surprise!). May have to just order them compare them and then pay the restocking fee if I decide not to acutally buy them.....

Well, I read several posts by a number of people in various import car and "tuner" forums who vigorously maintain that modifying the IAT is pure snake oil. In one forum it was even listed in a thread called Crap that Doesn't Work - right along with fuel line magnets and the "tornado" intake inserts. SO, I read up on it some more and really got my head around exactly how the IAT mod works. I also read a few articles on aftermarket "piggyback" performance chips, and replacement programmable ECUs. From this I determined that modifying the signal from the IAT is one of the tricks that both these devices employ to enhance performance. Based on my research, I decided to go ahead with giving it a try.

Reading the IAT diagnostic procedure in my Chilton's manual told me that the IAT's resistance at an ambient air temperature of 32 degrees should be around 6000 ohms, and at 68 degrees it should be around 2700 ohms. The wiring diagram showed me which pins on the combined MAF/IAT to measure to check it, and sure enough, the resistances were right about what it said they should be. My wife thought I was nuts when she saw me putting the airbox in the freezer to get it down to 32 degrees for the test! So, at this point I had all the info I needed to proceed.

Rather than pay some eBayer $5-$40 for a five-cent resistor in the 3k-5k range and a set of instructions I decided to do it a little differently and make mine adjustable. I bought a 5k linear potentiometer, 5 foot of 18 guage speaker wire, and a 5-pack of snap together male/female "bullet" connectors at Radio Shack - all for about 6 bucks total.

I cut the wire to the IAT (red & black wire - pin 6 on the 7 pin connector to the airbox MAF sensor) and installed a male snap connector on one end and a female snap connector on the other end. I figured that, if it didn't work, I could just plug the two ends of the wire back together to UN-do the mod quick & easy. Next I threaded the speaker wire through one of the rubber grommets in the fire wall and put a male snap connector on one wire and a female snap connector on the other wire and plugged them into the ones I put on the IAT wire. Next, inside the cab, I soldered the two ends of the speaker wire to the center and end terminals of the potentiometer. VIOLA' - an adjustable IAT!

With the potentiometer turned all the way down to zero it is like nothing has been done. The ECU reads the actual resistance of the IAT. This a good thing for those of us who live in areas where passing an emissions "sniffer" test is required to renew your tabs. With the potentiometer turned all the way up, the ECU reads the combined resistance of the IAT and the 5k potentiometer - roughly 7k-8k of resistance. This translates to the ECU getting a signal telling it that the air temperature is somewhere in the 10-15 degree range.

Since colder air is denser air, the ECU adjusts the pulse width to the injectors to hold them open a tiny bit longer - to push through a little more fuel and try to maintain the correct air/fuel mixture. But, since the engine temp sensor is telling the ECU that the engine is fully warmed up, it doesn't advance the igniton timing - like it would if it were running in open-loop (warm up) mode. This is very important because one of the problems I was experiencing was knocking and pinging when engine was pulling hard at low RPM with the throttle wide open (a.k.a. "lugged down"). When taking off from a dead stop - especially uphill. I was having to rev the engine up into the 2000 RPM range (that's just an estimate - since it doesn't have a tach) and then slip the clutch to avoid "lugging" the engine and having it ping and lurch etc.

I took it for a test drive and the difference/improvement was quite obvious. IT WORKS! Not what I'd call a dramatic improvement, but definitely noticeable. I went over to the parking lot at my son's school to do a little low-speed testing. The lot is set up with two parallel parking lanes about 100 yards long with a row of parking stops in between, and it is on a slight hill. I did about a dozen "laps" around the row of parking stops in 2nd gear to test it at various settings of the potentiometer. Everytime I came around the end of the row I let it slow all the way down to just under 10 mph, and then as I started the uphill run I'd floor it. With the potentiometer set to zero the car would lurch and ping very badly and barely manage to accelerate to 12 or 13 mph by the end of the row. With the potentiometer set to the middle setting (~ 2500 ohms) it was a little better, and with the potentiometer turned all the way up to 5000 ohms it was MUCH better. Barely pinged or lurched at all and it accelerated to 15 mph!

Next I drove it around the neighborhood doing multiple starts from dead stopped with various potentiometer settings. My "seat of the pants tachometer" tells me that if it takes 2000 RPMs to get a smooth startup with the dial set to zero, then it probably only takes 1500 RPMs to get a smooth startup with the dial set to 5000 ohms. That's a BIG improvement. I'll probably hook up a tach to test it and get some actual numbers, but there is no question, based on the old "butt dyno" that there is a definite improvement.

As my last test I decided to do a high-speed hill climb. We live on top of a hill that is about 600 ft high, and one route to the top is a 3/4 mile long, divided, 4-lane street, that is a 6% grade. I hit it in 3rd gear at 40 mph with my foot on the floor and the dial set to the 5000 ohm position. Initially I was accelerating up the hill, but as it got steeper it stabilized at around 50 mph as it got into the long steepest section in the middle (50 mph is the speed limit on that road BTW). After a couple of seconds I spun the dial to the zero ohm setting to see what would happen. The engine almost instantly started to ping and ever-so-slowly loose speed. After a few seconds I then spun the dial back to the 5000 ohm position and, just as quickly, it STOPPED pinging and started slowly regaining the speed it had lost! Heck, for my money, that would be worth the 6 bucks and 3 hours invested (including tracing the wiring, testing the IAT, and the trip to Radio Shack) right there!

So, now the only thing that remains to be seen is the mod's effect on gas mileage. The eBayers claim up to a 20 HP gain and equal or better mpg from this mod. Now, I know that the boost is less than that - 20 HP added to an engine that only has 112 HP to start with would be a MUCH more dramatic-feeling improvement. However, I'd be willing to believe that it is somewhere close to 10 HP, give or take a pony or two. If that means I don't have to floor it quite so often, then just maybe the mileage won't be negatively impacted - or at least not much. Of course, I do have the option of turning the mod off every time I get on the freeway if I like, so maybe I can just get in the habit of turning it on and off depending on how and where I'm driving. Or maybe setting the dial at the halfway point to get a balance between the max power boost and max fuel economy will be the answer. Who, knows? We'll just have to see how it goes.

I'm still looking for other suggestions, looking for an adjustable cam gear, and wondering about the manifold & throttle body swap though. So, if you're reading this little book I've written, and have some more suggestions for cheap mods, or info about the intake swap idea, then bring 'em on! I'm not satified just yet - but I wanted to share what I did and what the results were with anyone who might be interested.

WOW! I can't believe that there isn't more activity around here. From what I've read, the 1.8 liter and 2.4 liter engines in the Expos are the same ones that were installed in Mirages, Lancers, and Diamantes. I would have expected the resident experts to be coming out of the woodwork around here by now. Instead I kinda feel like I'm talking to myself......

Oh well, here goes anyway. FWIW I took it one step further today. I went back to Radio Shack and picked up a 10k ohm potentiometer, a knob to fit on the shaft of the potentiometer, and a small project box.

I replaced the 5k ohm pot with the 10k ohm pot and put it inside the project box. The box is just the right size to wedge into the open space right under the stereo (where the factory equalizer would go - if I had one). Then I put the knob on it and wedged it into place. VIOLA', now my adjustable IAT is complete, easy to use, and even looks nice!

I fiddled around with it a little and it seemed to work best with the potentiometer set to around the 2/3 to 3/4 mark - around 7k ohms. Combining that with the approximately 3k ohms from the IAT (at about 65 degrees) it is basically telling the ECU that the ambient air temperature is around 15 degrees below zero Farnehiet. Cranking it all the way up to 10k ohms for the ECU to get a signal totaling around 13k ohms (again, at 65 degrees) would be telling the ECU that it is -50 degrees outside. That might be a little too much - but we'll see. I plan on drving it for a week at the 1/4 setting, then for a second week at the 1/2 setting, and a third week at the 3/4 setting, and finishing up with a week at the max setting. That way I can compare gas mileage, driveability, etc. to see what works best.

I think I've taken this mod about a far as I can go with it, now it is just a matter of fine tuning it to see what setting works best. FWIW, I went ahead and ordered the intake and throttle body gaskets for both the 1.8 liter 16V SOHC engine and the 2.4 liter 16V SOHC engine at the local auto parts store. When they come in I'll probably buy them both, take a few days to compare them, and then maybe return one or the other for a refund. That ought to tell me if the intake and or throttle body transplant would be a direct bolt on or not. I'll report what I find out after they come in later this week.

Don't know if there is anyone even reading this, but if so, I hope someone sometime will find it helpful. I'll continue to report results if there seems to be any interest.........

Some intital results.....

After installing it I took a 150 mile highway drive to another town on the other side of the mountians (business trip). I had the IAT mod dial set to about the 3/4 mark ~ 7k on the potentiometer and 3k from the IAT. Same signal to the ECU as if it were only around -15 degrees outside.

Wish I had filled up the tank before starting out just to see what the mileage was. I had already driven about 60 miles around town before doing the install, which influenced the gas mileage. Got about 18.5 mpg in mixed driving. Not great, but only a little less than the previous average of around 19-20 mpg for mixed driving.

I decided to dial it down just a little. Set it to the 1/2 way point ~ 5k on the potentiometer and 3k from the IAT. Same signal to the ECU as if the outside temp were around 10 degrees. Filled it up for the return trip and filled it up again after I got back. I couldn't believe it, but it got 26.7 mpg! Of course about 140 of this 150 miles was straight highway driving, but it also included climbing TWO 4,000-5,000 foot mountain passes! 26.7 mpg is better mileage than it had EVER gotten since I bought it! Only about 2.3 mpg lower than the EPA highway estimate of 29 for the rig when it was brand new! Needless to say I'm VERY excited about this!

Edit: The 18 liter and 2.4 liter intake and throttle body gaskets came in today. The intakes are TOTALLY different (bummer) BUT the throttle body gaskets are identical (whoohoo!)

Soooo, looks like I need to locate one of the slightly larger throttle bodies for a 2.4 liter as my next mod to try and pump it up some more.....

You make me wish I was still stuck with my wife's little 90 eclipse 1.8. It sounds like you've come up with something applicable for lots of different vehicles with Natural aspiration. I'll forward this thread to a few guys who have similar needs.

quote:

ORIGINAL: FireDoc

You make me wish I was still stuck with my wife's little 90 eclipse 1.8. It sounds like you've come up with something applicable for lots of different vehicles with Natural aspiration. I'll forward this thread to a few guys who have similar needs.

HEY! Thanks for replying FireDoc! I was beginning to imagine that I heard an echo in here ;)

I can't really take credit for "coming up with it". It was actually developed by someone else and eBay has a bunch of sellers offering several variations. They are usually advertised as "Up to 20 HP boost for your <insert make & model name here>" or something similar.

They range from under $10 for a 2-cent resistor and an instruction sheet on what wires to hook it up to, all the way up to a fully adjustable potentiometer in a small enclosure with install instructions for around $40-$50. I just built the more sophisticated and expensive version myself for about the price of the cheapo version.

I'm pretty excited about the improvement and am looking forward to further documenting the results and fine-tuning it to get the best performance/mpg balance. I drive quite a bit for my job, so I should be able to gather data pretty quickly. I'm even MORE excited about the possibility of the throttle body swap and what kind of gains that may produce.

Again, thanks for the encouraging reply and I'll continue to report results as I gather them.

I work 3 days on, 4 days off , so I only get to reply thurs thru sat. All other time is spent on the water pretty much. But I, and others are reading.

HMMMN, 3 days on and 4 days off and your handle is FireDoc, hmmmmn....

Wouldn't happen to be a fire department EMT, would you?

It depends on the day, We rotate if we are certified to do other jobs. Mainly I am an Engineer.

Engineer? As in holder of a BS in an engineering discipline? Or as in the guy in charge of a (fire) engine?

I'm a Computer Engineer and MCSE myself.

BTW, still not having much luck finding an adjustable cam gear. The only one I've found is made by RPW and the freight for the new gear from Australia, and to return mine to them as a core, is around 80 bucks! Add that to the $100 price tag and it starts looking a bit steep as an "experiment". Anybody got a line on any other cam gear that will work on the 4G93? The same engine was used in the 93-96 Mirage, but none of the big names seem to make one for it. I'm actually starting to think about picking up a junkyard cam gear and try making my own!

To that end I pulled the cam gear cover off to take some measurements and discovered something VERY interesting. Somebody made a mistake and installed the timing belt 1-notch off. The cam gear was already advanced too much! Since it is a 48-tooth gear, advancing the gear one tooth on the notched belt had the cam advanced 7.5 degrees (360 degrees / 48 teeth = 7.5 degrees per tooth). I corrected that and reset the timing and it is already running much better. Pulls MUCH stronger at low RPMs. I can get a smooth launch at around 1000 RPMs now.

I did a number of full throttle runs up that same 6% grade hill mentioned in my earlier post. I made slight timing adjustments between each run to get my base timing set to maximum advance for the best power and torque without pinging. Got it pretty much perfectly dialed in and it is running great. I can top that same hill in 4th gear at 55 mph whereas before it was 50 mph in 3rd.

Its still no low-end torque monster, but it is certainly much better. Apparently 7.5 degrees cam advance was TOO MUCH. I still want an adjustable cam gear to see how it does with about half that much advance - around 3, 4, or 5 degrees or so. I'll continue reporting how it goes as I make changes and adjustments.

BobC92, I just got back from being away 10 days for a cataract operation. Just want to let you know I read (can now see) and enjoyed your entire post. A good learning tool for me. I wish more posters here would be courteous enough to respond with the results of suggestions made to solve their problems. Seems most jump in as newbies, post once and are never heard from again. The people trying to help and learn hardly get any feedback. I hope you stay Bob.
I have a question. since you are fooling the computer into thinking the air temp is lower than actual, the air is actually less dense. Do you know if you are getting complete burning of the fuel mixture? It would be interesting to use an exhaust gas analyser with different pot. settings to see what your air/fuel ratio is like?? Have you looked at the plugs to see how they look? Rich mixture could be hard on cat?

quote:

ORIGINAL: pc
.......I have a question. since you are fooling the computer into thinking the air temp is lower than actual, the air is actually less dense. Do you know if you are getting complete burning of the fuel mixture? It would be interesting to use an exhaust gas analyser with different pot. settings to see what your air/fuel ratio is like?? Have you looked at the plugs to see how they look? Rich mixture could be hard on cat?

All excellent questions, PC. Unfortunately I don't know the definative answers to most of them at this time! I did just check my plugs over the weekend and they looked fine - no soot or other signs of fuel loading.

I also know that the exhaust doesn't smell rich, for what that's worth. Also the mileage I've been getting supports it running lean enough. My supposition is that the "normal" air/fuel ratio is probably just slightly on the lean side of the "perfect" stoichiometric 14.7:1 air/fuel mixture - in the interest of maximizing fuel economy. When you think about it the difference in the density of air that is 65 degrees, and air that is 10 degrees below zero, it is really pretty small percentage-wise. I'm thinking that it is unlikely that the modifications I have made to the IAT result in an air/fuel ratio any richer than 13.5:1 or, more likely, 14:1.

Therefore, given all that, along with the condition of the plugs, no excess fuel odor in the exhaust, and good mpg I'm pretty confident that it isn't doing any damage. I'd sure like to take your suggestion and have the exhaust gas analyzer results to back that up though. I just don't know anyone who has one to use without paying them for the priviledge.

Progress report (sort of). I've created a spreadsheet to track my gas mileage. So far I'm averaging around 19 mpg in the city, and 27 on the freeway.

Seems like the thing that makes the most difference in mileage - maybe even more than city/highway or the setting of the IAT sensor adjuster is my use of the AC! In mixed driving I seem to get around 25 mpg with it off, but as low as 15 mpg with it on!

I spent $23 on eBay for an oiled gauze filter (K&N knockoff) and a MAF adapter to install it. I'm looking forward to seeing what kind of benefit I get out of it.

I took a gamble and bought a good, tested, used throttle body off a 92 Expo with the 2.4 liter engine. Found it at a wrecking yard in PA for $50 including shipping. It isn't much of a gamble because I'm about 90% sure it will fit. The big question is how will it work with the 1.8 liter's MAF. I found a 2.4 liter MAF locally for just a few bucks - just in case I need it.

At this point I'm planning on doing just one mod at a time - with a week or two to evaluate in between. That way I can see what gives the most bang for the buck. I'll keep reporting back - just for the heck of it.

Really interesting stuff. I wonder if you would pass emissions with all the changes. When I bought my Montero I knew it was underpowered (3.0L) but the truck had so many other good features that I bought it anyway. The purchase has done well for me as I have had zero problems with this SUV other than normal wear and tear. Your tinkering has paid off as you seem to be accomplishing your goal as evidenced by the uphill runs. From 3rd and 50mph to 4th and 55mph is impressive for the dollar input. The trade offs, aren't there always, seem to be acceptable for you. I look forward to your next post.

quote:

ORIGINAL: pc

Really interesting stuff. I wonder if you would pass emissions with all the changes. When I bought my Montero I knew it was underpowered (3.0L) but the truck had so many other good features that I bought it anyway. The purchase has done well for me as I have had zero problems with this SUV other than normal wear and tear. Your tinkering has paid off as you seem to be accomplishing your goal as evidenced by the uphill runs. From 3rd and 50mph to 4th and 55mph is impressive for the dollar input. The trade offs, aren't there always, seem to be acceptable for you. I look forward to your next post.

Well, all I've really done so far, other than set the cam back to its stock position, is the IAT mod - but there's a lot more to come!

As for the emissions question, particularly in regards to mods I'm doing, here is my logic on what I expect (hope?) to find....

1) The IAT mod shouldn't affect emmissions testing since before going to the testing station I can simply turn the dial to its zero ohms setting and the IAT signal goes back to stock.

2) The cam gear mod shouldn't have a negative inpact on emmissions either. It recently passed emissions with flying colors - even though the cam was advanced a full tooth - making it 7.5 degrees too fast. From that I conclude that an adjustable cam gear and 3-5 degrees cam advance isn't going to hurt anything in terms of emmissions.

3) The low restriction air filter is going to allow it to draw in a greater volume of air more easily. However, the air will still all pass through the Mass Air Flow sensor (MAF), which is what tells the ECU how to pulse the fuel injectors to deliver the right amount of fuel to mix with the air. So, the air fuel ratio, and therefore the emissions, shouldn't be affected by that either.

4) Swapping the throttle body may present a little more of a challenge - but then again it may not. If I use the original MAF, then the effect should be about the same as the air filter - little or nothing emmissions-wise. However, the smaller original MAF won't net me as much potential airflow benefits as the larger one from the 2.4 liter. At that point it would be the most restrictive bottleneck in the intake system.

5) Swapping the MAF is even a little more likely to present some challenges - but again, it may not create any issues either. It all depends on what approach Mitsubishi took. This is where I've had to do a fair amount of research. I have done a LOT of pouring over the MPI and engine bay wiring diagrams for my 1.8 liter and for the 2.4 liter. In all critical respects, the two are identical. Wiring colors, connectors, pinouts, and the connections to the temp sensors, ECU, TPS, MAF, IAT and IAC motor are all the same. The testing procedures for the individual components, and the test values for them, are all the same as well - at least for the ones that the manual lists a testing procedure. In fact, several of the procedures are listed together as being "for the 1.8 and 24. liter engines".

The big difference between the two is that, due to its displacement, the 2.4 liter needs to suck in a larger volume of air every revolution than what the 1.8 needs - 1/3 more to be exact. The 1/3 larger volume of air has to mix with 1/3 more fuel to maintain the correct air/fuel ratio. There are several possible ways that Mitsubishi could have designed the system to deliver this increased fuel. This is where some serious thought and logical deduction comes into play. The alternatives as I see it (listed in the LEAST-likely-case-first order) are

A) Make the two MAFs pin compatible, program the ECUs the same, and use the same fuel injectors, but make the MAF output signals (for a given airflow volume) different - to make the ECU pump more fuel through the injectors.

B) Make the MAF output signals (for a given air flow volume), and the fuel injectors the same, but program the ECU to control the injectors differently so that they push more fuel.

C) Make the MAF output signals (for a given air flow volume) and the ECU programming the same, but use larger, more free - flowing, fuel injectors.

D) Make everything the same except the diameter of the MAF. I think (and hope) that this may be the case - for a few different reasons.

First, the system uses a MASS Air Flow (MAF) sensor to measure airflow. This makes me think that the output of the MAF is proportional to the absolute quantity of air that passes through it - not the speed or pressure of the airstream. The larger MAF can have the same output signal as the smaller one when flowing the same quantity of air - if it is truly measuring the total amount of air sucked into the engine. The air just has to move more quickly through the smaller diameter MAF to get the same volume per unit of time as the larger one, but they should both give the same output because the same amount of air has passed through them both - it just moved faster through the smaller one.

As long as the fuel injectors have sufficient capacity, then an ECU with the same programming controlling the same fuel injectors should maintain the same air fuel ratio with two different sized MAFs flowing the same volume of air and giving the same output. The benefit of the larger MAF would come from the fact that it requires less vacuum for the engine to suck an equal quantity of air through it. Creating less vacuum means less power wasted on sucking the air through the intake - which equals more power available at the wheels. Kind of like the difference between sucking a drink through a skinny little coffee straw versus a regular straw. You can get the same volume at the same rate, you just don't have to suck as hard on the regular straw.

Second, since the TPS and IAT test procedures and values are the same for both of them, and the IAT is incorporated into both of the MAFs, it would make sense that the rest of the MAF electronics would be the same. Making the two of them different would just create a needless increase in R&D, tooling, and manufacturing costs. Same is true for the TPS.

Third, the same idea applies to the ECU programming. Creating two different fuel and timing curve maps would mean a fair amount in R&D costs, an expense that could just as easily be avoided by making them the same and changing something else if necessary.

Basically, the most economical thing for Mitsubishi to do from a manufacturing standpoint would be to make everything identical if possible. If that weren't possible, then the most likely reason would be that the injectors for the 1.8 liter couldn't push enough fuel to mix at the right ratio with the increased air volume of the 2.4. In that case the simplest solution would be to upsize the injectors and be done with it.

So, based on my research, my understanding of how the fuel injection system works, and what I know about manufacturing economics, I'm hoping that my deductions are correct and swapping to the larger throttle body and MAF won't have any major negative effects on the emmissions either. I expect that, at worst, it might create a lean condition that can be easily corrected by modifying the MAF signal, or swapping the fuel injectors. Kind of an application of the Occham's Razor principle. The simplest explanation (or solution) is the most likely one for Mitusbishi to choose.

Sorry this ended up being so long, but that's a problem I'm known to have - making long-winded explanations. At least I know that if anyone read all of this then they really MUST be interested....

More and more this "experiment" is sounding like a project car.

quote:

ORIGINAL: FireDoc

More and more this "experiment" is sounding like a project car.

Well since "tinkering" (as PC called it) with cars is one of my hobbies, I guess (by your definition) you could say just about every rig I've ever owned was a project car, FireDoc. I just get a kick out of seeing what I can do to make a rig better. Especially if I can figure out how to do it for cheap

BTW, FWIW, once I do the air filter and throttle body mods (even if I replace the MAF), and then fab my own adjustable cam gear, I'll still have spent less than $160 total. Unless I have to replace the fuel injectors to make the throttle body/MAF mod work the way I want it to. That would add some to the cost.

I only spent $1800 for the car around 3 years ago, and just put another $900 into it for the tranny, the clutch set, and the clutch hydraulics rebuild kits. $2700 total investment. In the meantime I've gotten a couple of years use out of it and put 25k miles on it, so I figure I'm still WAY ahead of the game with this rig. KBB says it's retail is $4,600 and wholesale is $3,000 for one that is in "good" shape. I have less than that into it, and it nearly fits the definition of what they would consider "excellent" shape.

So, if I spend a couple of hundred on playing around with it, then its no big loss. I should be able to recoup it if I ever sell it. If I don't, then OH WELL, at least I had some fun with it

I see nothing wrong with your goals. I, however, Will spend $ whatever the cost if it is what I have to do to get the best results I can with my ability level. I guess that is also why I have a hard time getting rid of ANYTHING I modify, too much sentimental value. A victim of my own device!