Megasquirt question

[mikey]

Will dual throttle bodies work with a megasquirt setup??? Sounds like it would be a great setup.

Mike

[lapuwali]

Sure, all it takes is fabrication and money. The dual throttle bodies are relatively expensive, and you'll have to do all your own plumbing. The chief advantage of using MS on a 914 is the car is already injected, so all of the plumbing and much of the electrical work is already done. All you're replacing is the ECU with a nicely programmable unit and the MPS with a much more reliable solid-state unit (well, and the throttle switch with a real TPS).

[mikey]

What does the MPS get replaced with?

[lapuwali]

A solid-state MAP sensor, which will probably outlive the car. The MS has one on-board. You run a vacuum tube from the manifold all the way to the MS box.

Note that getting a good MAP signal is one of the problems with individual throttle bodies. In a single throttle setup, the MAP signal is from all cylinders, so it's "averaged" over the cylinders, and tends to be smooth. The MAP signal from each throttle on a multi-throttle setup, however, tends to be choppy. This gets worse as the cam gets wilder. This can be fixed by plumbing all of the manifolds into one small plenum just for the MAP signal, or by reprogramming the MS to only use the TPS signal, and not MAP, as the load signal.

As I said, it's considerably more work than just swapping the D-Jet ECU and MPS for the MS, retaining the OEM throttle, manifolds, injectors, etc.

[mikey]

Shoot....maybe I will just keep the d-jet plumbing then. I was just planning to run 96mm pistons, and a cam which is a little wilder than stock. Will the stock injectors be ok for this application too? Are you using the megasquirt yourself? If so I would like to pick your brain a little.

Thanks,
Mike

[lapuwali]

I'm not using the MS, yet. I have a couple of unassembled kits that will be going together over the next few months. Go to the 914 club board (www.914club.com). There are at least three guys over there running MS on D-Jet hardware.

FWIW, I believe the stock injectors will work fine on an even heavily modified engine. They're WAY oversized for the application, and one of the problems with trying to make MS work on a nearly stock system is the injectors are so big that getting a narrow enough pulsewidth for a good idle is actually something of a problem.

Search on that board, esp. for stuff by DNHunt. He's done a lot of work getting MS to work well on D-Jet plumbing.

[ViolentBlue]

I'm going to be running a MS setup with a supercharger on my fresh 1.7l, a single throtlebody will be in order, but I understand people have had good results running a small vacuume caniser with a tube running to eash TB and a single line to the map sensor, the canister volume tends to smooth the vaccume pulses of the individual TB's for the map sensor.

as for injectors, I found that toyota 4AGE injectors slip right into the injector bungs, use the supercharged ones for a little extra flow. you just have to make your own fuel rail, which I did bu using two toyota units, one for each side redrilled and cut down.

[Dave at Pelican Parts]

Originally posted by lapuwali
Note that getting a good MAP signal is one of the problems with individual throttle bodies.

So just ignore the MAP signal, and run it alpha-N. ("Alpha" meaning throttle angle, "N" meaning RPM.) That way, it will be an electronic approximation of MFI, where throttle position and RPM are the two major determinants of the amount of fuel injected.

Throttle position is a less-precise approximation of the load on the engine than MAP is, but it's better than nothing. And you can make it work reasonably well...

--DD

[lapuwali]

"So just ignore the MAP signal, and run it alpha-N. ("Alpha" meaning throttle angle, "N" meaning RPM.)"

Yeah, I said as much. Alpha-N setups tend to be more finicky, and you typically end up with things like flat spots when doing unusual things like starting from a stop heading up a steep hill (not so unusual in SF, pretty unusual in Iowa).

MS also doesn't do Alpha-N out of the box. I believe there's some code floating around to get it to work, but reprogramming the microcontroller isn't for everyone. The TPS signal in the stock MS code is only used for acceleration enrichment and open-loop selection. Most people who resort to Alpha-N are doing so because they simply can't get a reliable MAP signal, such as running a very wild cam in a race engine. Some of the EFI motorcycle setups (and compared to cars, all bikes have really wild cams, and all have individual throttle bodies) will use both. Alpha N below a set engine speed, then speed-density (revs and MAP) above that, when the signal as typically stabilized.

As for needing to use Toyota injectors, the stock 2.0 D-Jet injectors are 380cc/min, which is HUGE, good enough for something like 250hp. If anything, using smaller injectors will aid in tuning, esp. at idle.

[Dave at Pelican Parts]

D'OH! Sorry, I read right over the "ignore the MAP" sentence in your post.

Good point on having even more DIY if you do go with alpha-N. And also a good point on the bike systems; I didn't realize they already did that but it makes sense to set things up that way.

--DD

[3D914]

MIke,

I'm currently running MS on a 2.0L with the WEB #73 cam. I abandoned the stock FI because it just wouldn't adjust enough to accomodate the web cam.

I'm using the stock plenum, but have considered your idea. The advice so far is the same I concluded. Currently its just a matter of the money - but isn't it always!

The WEB 73 cam with MS on the dyno yielded 95hp at the wheels. You can also tune for econo or performance. A recent cross-country trip yielded a high mpg of 35 and a low of 25 (w AC running).

Enjoy!

[mikey]

Is it smooth through the entire RPM range?? What sensors were you running? Just the MAP and the throttle position sensor? What was the total cost of getting the MS running??

Thanks,
Mike

[mike mueller]

my MS install cost:

MS box=120 or so
new GM air temp sensor= 15 (stock one can be used from the D-Jets, not the L-jets, or at least not very easy)
new TPS (forget what brand) = 45 (used available from autowreckers or eBay, cheap enough to put on a new one)

I used my stock 1.8 injectors (will upgrade to 2.0 soon when the turbo goes on)

stock CHT instead of coolant sensor (same thing)

no O2 sensor right now, but these range from dirt cheap (used, wouldn't recommend it) to a few hundred for the better wide band units

free laptop

[mikey]

Does the stock 2 liter plenum have enough air space for a 2.1 liter with mild cam??? I was thinking of ditching the stock air filter as well and putting on one of those K&N cone filters on the throttle body.

Mike

[mike mueller]

biggest motor that I've seen using the stock intake plenum is a 2.4, so your setup should work just fine.....pretty much any combination you can think of intake manifold/plenum and throttle body wise will work with the megasquirt....you'll just have to do some homework 1st.

[lapuwali]

If by 2.1 liter you mean a 2056, yes. There are people running 2056s with the stock D-Jet, even. Converting to MS using the D-Jet hardware will allow you to run a wilder cam than you could with the D-Jet setup.

[mikey]

Awesome!!!! I cant wait!!!! I am good with electronics so that will be no problem. All I need now is MONEY!!! Heheheheheheehhe!!!


Mike

[3D914]

Mike,

I use a universal K&N for AutoX and DE with Porsche club. The calculation page they have doesn't result in a very big filter, but it has no intake restrictions and I like the responsiveness. I also found a vacuum T to connect two of the remaining vacuum hoses to the top of the filter. I'll have to dig up the number somewhere. One of these days in all my spare time I'm going to get all this stuff down on paper, in one place.