Going to Megasquirt, More questions |
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Going to Megasquirt, More questions |
bbrock |
Sep 11 2021, 10:46 AM
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#1
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914 Guru Group: Members Posts: 5,269 Joined: 17-February 17 From: Montana Member No.: 20,845 Region Association: Rocky Mountains |
After about 1,700 miles of driving my freshly restored car with rebuilt engine, I’ve decided I’ve had my fun with Weber carbs and distributor-based ignition and am ready to step up to modern EFI and coil on plug ignition. Even with the jetting that came out of the box leaving the carbs running rich, the performance has been fantastic. What is not fantastic is the garage stinking of gasoline, no compensation for altitude, and being generally too fiddly to set up for my taste. My trials with the ignition are documented in another thread. Yes, I know a 1-2-3 would solve those problems but for the money, I’d rather invest in modern COP ignition as part of an EFI upgrade.
My goal is a smooth, efficient, and reliable street machine that I can drive from sea level to 11,000 ft. without starving or choking on fuel. Efficiency is at least as important as performance. As long as I can get at least the stockish 100 hp, I’ll be happy and beyond that, I’d like to wring as many mpg out as possible. The engine is a mostly stock euro-spec 2L engine. The only mod is a fairly mild Elgin 6048 camshaft with 256 duration for the carbs. A source of pride of this build is this custom 911/914-6 inspired air cleaner I made which I think looks cool and really silences the carbs. Now for the questions: • Single throttle body or ITB? I think I’ve made a decision but still interested in thoughts. I was thinking about welding injector bungs onto the carb manifolds and using my carbs as throttle bodies. The main appeal is that I would keep my cool air cleaner to make the other kids jealous. However, it seems the stock throttle body would greatly simplify the conversion. Also, even though the custom intake is designed to allow access for servicing and easy air filter replacement, it does crowd an already crowded engine bay and makes working in there just that much more of a challenge. My stock TB needs some TLC and might have to be sent for professional refurbishing. I think I could sell my carb setup to cover that cost but not sure. The upshot is that I’ve all but decided to go back to the stock TB, but curious what others think. • N Alpha, Speed Density, or MAF? I’ve been reading up on this and think I understand pros and cons, but still a little confused about sensors needed. With my efficiency goal, I think MAF is the way to go. It looks to me that cutting off the tube connecting the stock air cleaner to the TB and replacing it with a MAF could be a really slick way to add MAF in stealth fashion. Has anyone done this? If not, how does one find the right MAF to use? Other than dimensions, what else needs to be considered? Another question is about MAP + MAF vs MAF only. I’m a little confused about advantages or when a MAP sensor is needed if you have a MAF. • Barometric correction – this is an important feature for my location, but the hardware needed to implement it is a little confusing. It seems like if you are running a MAP, then barometric correction is obtained by adding a second pressure sensor (another MAP?) to read reference atmospheric pressure to make corrections to the fuel mixture. How does it work with MAF? Do you only need one pressure sensor to read atmosphere? Or do you still need to reference it against manifold pressure? I assume a lot of this is done in the software but I haven’t looked to far into the tuning part yet. I’m more trying to figure out a shopping list for parts at this point. • Anyone running a CAM sync and sequential spark and injection? Again with the efficiency goal, this is appealing. Looks like Mario is working on a new version which isn’t available yet, are there alternatives available? It seems people say you still need a crank position sensor even with a cam sensor in the mix. It isn’t entirely clear why though. Lastly, and this is mostly just curiosity, but is it correct to think that the lifespan (in miles) of spark plugs are cut in half with wasted spark? I have many more questions but this is already too long so will save them for later. TIA |
falcor75 |
Sep 13 2021, 11:14 PM
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#2
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
I went the ITB route for my 2.3 but my car isnt built for daily driving or milage. Its more of a autocross and country road dasher. I got the camsync for mine and its installed and hooked up but we didnt end up using it. The reason is that the car drives fine without it in Alpha-N and wasted spark. My yearly milage between april and october is around 1k or less.
What I'm most happy with my set up is the noise and the crisp response and the bluetooth monitoring that allows me to display engine data in a tablet on the dash. What I'm not happy about is the low idle at startup for the first minute untill the engine heats up a bit. With my ITB's I would need to add an idle air control valve to really sort that out. |
GregAmy |
Sep 14 2021, 06:00 AM
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#3
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Advanced Member Group: Members Posts: 2,390 Joined: 22-February 13 From: Middletown CT Member No.: 15,565 Region Association: North East States |
What I'm not happy about is the low idle at startup for the first minute untill the engine heats up a bit. With my ITB's I would need to add an idle air control valve to really sort that out. I spent a lot of time managing startup, controlling the AFR with WUE and idle RPM with ignition timing control (Idle RPMs Advance Timing)...and mine starts foot-off, with no aux air valve, and pretty much cores it. It can be done w/o an idle control valve. |
jd74914 |
Sep 14 2021, 07:10 AM
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#4
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Its alive Group: Members Posts: 4,813 Joined: 16-February 04 From: CT Member No.: 1,659 Region Association: North East States |
What I'm not happy about is the low idle at startup for the first minute untill the engine heats up a bit. With my ITB's I would need to add an idle air control valve to really sort that out. I spent a lot of time managing startup, controlling the AFR with WUE and idle RPM with ignition timing control (Idle RPMs Advance Timing)...and mine starts foot-off, with no aux air valve, and pretty much cores it. It can be done w/o an idle control valve. (IMG:style_emoticons/default/agree.gif) The key is controlling idle speed with timing as Greg said. A bit of ignition trough to settle the engine in works quite well, particularly if you increase the map resolution a bit in that range. Note that while optional with a TB/plenum you really need to do this with ITBs unless you want a lot of plumbing complication. Since you have a really nice air box, I would highly recommend using a Bosch TMAP (temperature/map sensor) installed in a boss for the barometric correction. They aren't too expensive, hide well, and are very robust. If you want to go really crazy... some motorcycle MAP sensors, 1 per cylinder, with a IC used to pull the max manifold pressures would give a really good input to speed density. From what I've seen, the failing of most ITB speed density is that a physical signal average (4 tubes from each manifold running into a plenum) is a) highly damped and b)biased downward so it's not really a true MAP representation. Someone used to make a board to do that processing, though I haven't seen one in years. |
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