Minimum sensors needed.

[stick004]

So I've done a bit more homework. But I can't seem to narrow it down.

(idea) Project recap: 8hp Kohler single cylinder engine (K181). 6psi supercharger. MicroSquirt running fuel and ignition. I've successfully gotten 37hp (10hp block) to the ground on alcohol garden tractor before using a carb. But alcohol has been ruled out. It's time to raise the bar and go EFI with a S/C.

I've seen the superbike down the page running on only the TPS, buts whats the minimum sensors that are needed to be used on in engine to assume accurate control of the engine (with Micro Squrit) and which ones can be simulated with the tables in Mega Tune?

It's mostly a space concern. With my little 8hp, the intake/throttle body is basically a 3/4" tube with a butterfly in it. I will be able to use a TPS, a remote MAP (connected with vaccuum tubing), a HAll or VR sensor for timing, an 02 sensor in the exhaust, and IAT sensor.

(I can probably get a coolant temp sensor in the head, but being air cooled, I'm afraid I'd overload or melt the thing with the head temps well above 500degrees at the end of a run. I could put it in the block close to the cylinder but then I don't know if it would warm up fast enough. Testing is in order I assume.)

Is there anything I will need to make room for? I think I've got it all covered. But I don't know... As far as I'm concerned. It never hurts to ask.


I know there are a few guys running 1-cylinders on here and the MegaSquirt forums, maybe a few suggestions could be kicked my way. I've seen one Kohler K301 running a Garrett Turbo and Megasquirt on the web, But have never seen him on here. I've searched but all the Briggs stuff are older threads and mostly over my head at this point.

BTW: I've got my fuel system nailed down using a PICO 19lbs/hr injector, running on 30-35psi of fuel. (maybe less) I want to use the PICO style because it's only 1/2" the size of your standard Ford/GM injector. Also, my pump, regulator, fuel tank, and lines have been selected. As soon as I figure out the theory how to make the thing fire with only one cylinder (it doesn't exactly say "Do this " in the Mega-manual), I will be ordering parts! I also have to convince my wife I need to spend nearly $1000 on cool parts and stuff to make my little tractor do it's thing.



Edit: Also, no one around my area and in my club is goign this route. Plus I'm keeping it Top Secret to the guys I pull with. So the forums are the only place i have to spit out ideas. THANKS GUYS!

[efahl]

For your purposes (racing engine) the "coolant" temp sensor is merely window dressing. In a street engine, you'd use it to tune the warmup enrichments (WUE), but with your engine you can probably just use the after start enrichment (ASE) to provide enough fuel to get it running for a few seconds and then warm the motor up statically without any WUE.

So, what do you need? Tach input, MAP or TPS (your choice) and IAT. If you go with TPS (Alpha-N fueling algorithm) then you can use a MAP sensor open to the atmosphere to measure barometer and do auto correction, or you can just calculate an altitude density number at the track and tweak the required fuel number to "change the jets" based on just barometer (not temperature, as that will happen automatically).

Eric

[toon2]

you will need some form of CHTS as it's a fundamentalmeasurment of micro S.

I might be possible to use a CHTS biased resistor style that is made for air cooled motors and download easy therm.

EDIT: nevermindLOL

[stick004]

I thought a TPS was required to direct the injector(s) duty cycle.

Ex: at 50% throttle they would only be injecting half as much fuel then WOT. determined by throttle position not MAP pressure.

I thought a MAP sensor was used to determine mainly the timing curve. (espescially in a boosted application where combustion temps can sky rocket.) But I can use it to direct the injector cycle too? Cool. See I'm learning more everyday. Although, it makes sense to me to use a TPS also so I'm not depending on only boost pressure to determine my fuel curve.

If I only need a MAP, why do most GM cars have a TPS and MAP sensor? I know from first hand experience, when the TPS goes out on a GM TPI injection setup, the car doesn't run.



After reading my question more carefully. I should have asked if I needed any more sensors that I was already using. I'm happy to know I'm not required to run a temp sensor. If I can't get it to warm up quickly with one, I'll cross that bridge when I come to it.

An AIC valve or PWM style idle control was my last concern. But those are basically a "choke" device right? In my application I can merely do that manually. so I shouldn't need one.


Thanks for all the help guys! I've started to plan where I will be mounting all my stuff and running my wiring harness. I'll get some pics up sooner or later a this progresses.


Nic

[Matt Cramer]

Microsquirt needs at least one load sensor. There's three types of load sensors - the TPS, MAP, and MAF. Normally, Microsquirt uses the MAP for main fuel calculations and the TPS for acceleration enrichment.

There are cars, both Megasquirted / Microsquirted and OEM, that run around with only one load sensor. For example, a lot of 1980s era BMWs and many early 1990s Mazdas use just a vane air flow meter and do not have either a variable TPS or a MAP sensor.

[efahl]

I thought a TPS was required to direct the injector(s) duty cycle.

Ex: at 50% throttle they would only be injecting half as much fuel then WOT. determined by throttle position not MAP pressure.

Nic,

I'll go into some details below, but first I'll address this. The load sensor's electrical output (any of the three sensors that Matt mentions) typically is not linear with flow. Raw TPS is the least representative of actual load, so 50% throttle rarely if ever flows 50% as much air as 100%. Most throttle bodies are sized for some minimal restriction at maximum RPM, so if you are at, for example, 1000 RPM and open the throttle 20% the flow is exactly the same as at 100%.

If I only need a MAP, why do most GM cars have a TPS and MAP sensor? I know from first hand experience, when the TPS goes out on a GM TPI injection setup, the car doesn't run.

Hmm, that's contrary to my experience and one of the diagnostics I've used on GM cars. Usually you can unplug either of the MAF or TPS and the car still runs fine. 1) This is redundancy, so you don't strand your customers. 2) It's diagnostic because when you unplug the bad sensor the car usually runs better.

An AIC valve or PWM style idle control was my last concern. But those are basically a "choke" device right? In my application I can merely do that manually. so I shouldn't need one.

Those devices are both just idle stabilization parts, and are not needed on a race engine at all (just set the idle high enough that it doesn't stall and you're done). "Choking" is only needed on a mechanical system (carb) to generate more vacuum and pull in more fuel. With EFI you simply pump in more fuel based on some sensor input (usually head/coolant temp).

Ok, to expand on what Matt said above as briefly as I can...

There are three basic algorithms for computing both fueling and timing.

1) Alpha-N (TPS=Alpha, RPM=N). Use these two variables to figure out how much air is flowing through the motor. Simple, but hard to tune and not as accurate as MAP-based load due to inability to take into account barometer and such.

2) Speed-Density (RPM=Speed, MAP=Density). Instead of estimating manifold density from TPS, this uses the MAP reading directly to estimate the flow. Typically easier to tune than A-N, but can have problems with lumpy cams at low load where the MAP signal jumps around wildly.

3) Mass Air Flow (MAF sensor alone). If you really want mass flow, why not measure it directly? Because the "turn down" ratio is not as good with MAFs as it is with the other algorithms. Typically a MAF sensor only has a narrow dynamic range, so if you size it small to get resolution for low loads it chokes at high loads, but if you size it big to eliminate the choking then it doesn't measure accurately at low loads.

All of them have strengths and weaknesses, so the choice is sometimes not clear. For a race-only engine, A-N works just fine because you are willing and ready to retune the engine all the time anyhow, barometric correction can be part of the at-the-track setup. SD is much better for a "consumer vehicle" (your daily driver) because you don't have to retune it, and MAF is even better unless you are seeking driveability AND big HP in which case that dynamic range stuff may bite you.

I could go into the use of each of these type of sensors for transient compensation (when you change the throttle or RPMs), but I'm too lazy and this is all probably in Lance's fine manuals anyhoo.

Eric

[stick004]

Wow! thank you.

That clears things up signifigantly.

I think I will try to use Speed-Density first with the MAP sensor detecting the little boost (6psi) I will be using.

If I have any problems with low or crazy signals at low load, I'll try the Alpha-N setup since I will then have a MAP sensor to read the baro.

I'll get back to reading the manuals now. I want to better understand using a TPS (if at all, of course) for acceleration enrichment.


I'll read more before I get into that.


Thanks alot guys! always very helpful.

Nic

[frogpirate]

I think I will try to use Speed-Density first with the MAP sensor detecting the little boost (6psi) I will be using.

Thanks alot guys! always very helpful.

Nic

Great thread, as is pertinant to me. I am building a 1 Cyl motorcycle for racing, and it's nice to see that some of the things I've sussed out for myself others agree with (CLT not really needed, a-N is fine etc.)

So Nic, how are you building that 6PSI boost? I am having trouble identifying a turbo SMALL enough for my 585cc, I can't imagine what your using!

Ken

[stick004]

I am using a "special" blower. It is technically a supercharger, not a turbo. It is a converted electric blower now pulley driven. (built by me.) It looks just like a mini ATI procharger.

I guess I'm alittle emberassed by it's previous use. It was a pool line blower.

The specs from the original blower (when it was electric.) were max output of 146 in/water (5.3psi) at 2500rpm. So I can slightly overdrive it to get about 6psi. I can't remember the CFM though.

It's not a "leaf blower" of anything like that. It was specifically a centrifugal blower designed produce boost to pressurize plumbing lines. It just happen to be electrically driven. Now it's belt driven. The pressure build has been bench tested and seems to build nicely with rpm increase. Now I have to get an engine to run with it. Hence... MegaSquirt! (or microsquirt in my cases.)

It was manufactured by GG Interprises. (now owned by a spa company.)

Here's the only link I have found to the original blower.
http://www.poolcenter.com/winter_suppli ... ty_vac.htm

The thing is cool. I've used one for years. And it creates usable boost! It doesn't just give up when you plug off the end like a leaf blower. I took it out of the yellow case, and with the sealed block off plate/bearing support and pulley I used it's less than 4" thick. makes getting it in my puller alot easier.

[efahl]

Nic,

Wow, that's pretty cool! Back in my youth I tried to use a GM vane-type emissions air pump as a supercharger on a lawnmower motor (this was way back, mid-'70s?), but never got it working. Your setup looks like it will work great, hopefully the blower has good efficiency and you'll get a big HP kick out of it.

If you have an extra input to spare, you might want to wire it up to another IAT and put one on each side of the blower. If you have the temperatures on both sides, then you can calculate compressor efficiencies directly and plot them as a function of boost or RPM or whatever.

Eric