Why does this car like so much timing?

[NeedForSpeed]

Actually, the svx has a long rod, effectively. The stroke is very short, under 3". The bore is very large, 3.8+" in 3.3L, 3.9+" in the 2.5L.

Some imports do have much longer con rods, but also much longer strokes and significantly smaller bores.

The 3.3L svx rod/stroke ratio of the svx is 1.74. [5.137 rod/2.953 stroke]
The 2.5L sti rod/stroke ratio is 1.65 [5.137/3.110], same rod length, but 'effectively' shorter.

Mitsu engines have a long con rod, 5.906", but the stroke is a long 3.465".
Thus, the Mitsu rod is 'effectively' shorter [r/s 1.7] than the Subaru svx rod.
The Mitsu pistons are 3.346" in diameter.

The BIG FACTOR in needing more ignition advance is the large Subaru bore. The flame must travel much farther to reach the cylinder wall, so more advance is needed, comparatively.

svx pistons are larger than Chevy 305 pistons, which measure 3.766".

The eg33 can be fitted with 4.0" pistons. That's the standard size of most small block Chevy and Ford V-8s!

Originally Posted by oab_au

Gid'ay Tom, yes the length of 130mm is short. 145mm would be about the norm, but they did need to keep the engine width down to fit in.
The shorter the rod, the faster the piston moves across TDC. This causes the compression space to change, through the burning phase. The longer rod keeps the combustion space, pretty much the same during the burn.

The shorter rod length, suits the high speed, high compression engine, better than the longer rod.

The ample squish area provides the turbulence that is needed to keep the burn time reducing, as the engine rpm increases, otherwise we would need to keep advancing the spark timing as the engine speed increases.

Harvey.

Shouldn't you be putting sheets up on your erection?

[Trevor]

Originally Posted by oab_au

Gid'ay Tom, yes the length of 130mm is short. 145mm would be about the norm, but they did need to keep the engine width down to fit in.
The shorter the rod, the faster the piston moves across TDC. This causes the compression space to change, through the burning phase. The longer rod keeps the combustion space, pretty much the same during the burn.

The shorter rod length, suits the high speed, high compression engine, better than the longer rod.

The ample squish area provides the turbulence that is needed to keep the burn time reducing, as the engine rpm increases, otherwise we would need to keep advancing the spark timing as the engine speed increases.

Harvey.

Shouldn't you be putting sheets up on your erection?

There appears to be confusion here regarding bore stroke ratio and connecting rod length.

Quote ----”The shorter the rod, the faster the piston moves across TDC. This causes the compression space to change, through the burning phase. The longer rod keeps the combustion space, pretty much the same during the burn.”

Harvey, this is indeed interesting. Could you please explain on the basis of geometry, how at any given RPM, a variation in rod length, as opposed to length of stroke, has the effect you describe.

[Pure_Insanity8]

Originally Posted by Phast SVX

I have the same dillema. I have always wanted to buy a supra when i graduated college, now i have secured a full time position for january but i a mgoing to be proposing to my GF in the next few months, so there goes the supra...its ok though, it would be rediculous to have 3 cars, two of which are money pits. Ill just have to focus on the SVX and not be rediculous and buy a 18-25k car that i couldnt drive very often anyways.

phil

Are you including her car as the 2nd (without a Supra)? What is the daily driver when the SVX is in storage?

C'mon Phil, marriage or a Supra... which has a higher benefit to cost ratio (and you're too young for marriage anyway)? How is the married life going for Rob (since he isn't here to answer for himself)?

[svxfiles]

Originally Posted by Trevor

. Could you please explain on the basis of geometry, how at any given RPM, a variation in rod length, as opposed to length of stroke, has the effect you describe.

Hi Trevor.
I have read tests comparing longer and shorter rods used in the exact same engine,(abet a chevy 350) with the same compression ratio, and the same weight of the piston and rod.
The longer rods gave a little more power.
Part of the articles explanation was that the piston had more "hang time" at TDC.
My thinking at the time, was that there would be less side loading and less friction.
Here is a link, not to the lost article I spoke of, but one I found today.
http://www.grapeaperacing.com/GrapeApeRacing/tech/connectingrods.pdf#search='connecting%20rod%20leng th%20vs%20hp'

All of this is WAY COOL!

[Trevor]

Originally Posted by svxfiles

Hi Trevor.
I have read tests comparing longer and shorter rods used in the exact same engine,(abet a chevy 350) with the same compression ratio, and the same weight of the piston and rod.
The longer rods gave a little more power.
Part of the articles explanation was that the piston had more "hang time" at TDC.
My thinking at the time, was that there would be less side loading and less friction.
Here is a link, not to the lost article I spoke of, but one I found today.
http://www.grapeaperacing.com/GrapeApeRacing/tech/connectingrods.pdf#search='connecting%20rod%20leng th%20vs%20hp'

All of this is WAY COOL!

l

Certainly a lot of interesting points have been made. However your thinking is exactly in line. A longer rod is more efficient as you point out, but other aspects concerning engine bulk and reciprocating weight come into the equation and the end design must always be a compromise.

[Trevor]

Originally Posted by svxfiles

Hi Trevor.
I have read tests comparing longer and shorter rods used in the exact same engine,(abet a chevy 350) with the same compression ratio, and the same weight of the piston and rod.
The longer rods gave a little more power.
Part of the articles explanation was that the piston had more "hang time" at TDC.
My thinking at the time, was that there would be less side loading and less friction.
Here is a link, not to the lost article I spoke of, but one I found today.
http://www.grapeaperacing.com/GrapeApeRacing/tech/connectingrods.pdf#search='connecting%20rod%20leng th%20vs%20hp'

All of this is WAY COOL!

l

Certainly a lot of interesting points have been made. However your thinking is exactly in line. A longer rod is more efficient as you point out, but other aspects concerning engine bulk and reciprocating weight come into the equation and the end design must always be a compromise.

P.S. The words "hang time" I would suspect have been used as there is no way to accurately describe that which can not be defined as a measurement. Crank throw will effect piston speed and time through a distance over TDC could be broadly termed as a factor, "hang time", but to be specific, measurements would require defining. The important point is that rod length is not the major part of the equation.

[cdigerlando]

A lot of interesting points are raised here. But I would like to point out that a lot of other 4 cyl. subarus w/similar bores are running a lot less timing. Is there negative advance built into the 3.3 motor? Does the cam profile allow more agressive timing?

How many licks does it take to get to the tootsie roll center of the tootsie pop? Anyone know any Owls?

[sicksubie]

Can msd ignition controllers be used with the SVX?

[BackWoodsBob]

Could someone possibly get me pointed in the proper direction on learning how to tune these ECU's or Megasquirt 2?

The DIYpnp megasquirt 2 seems like it would work fine with our engines. But I'm far from an expert. I read some of their technical documents, it seems easy enough to get the car started, but I'm lost after that .

Any help would be appreciated.

[icingdeath88]

Originally Posted by BackWoodsBob

Could someone possibly get me pointed in the proper direction on learning how to tune these ECU's or Megasquirt 2?

The DIYpnp megasquirt 2 seems like it would work fine with our engines. But I'm far from an expert. I read some of their technical documents, it seems easy enough to get the car started, but I'm lost after that .

Any help would be appreciated.

I have done some looking into making a MS3x work with these. Definitely doable. I'll post more about it in the morning, it's bedtime.

[BackWoodsBob]

sounds about right for those of us on the east coast too.
Thanks for the quick reply

[icingdeath88]

Ok, so the reason I know it's doable is that it's been done 3 times with megasquirts to date. dynomatt has been running his race car with one for years, the EFI logics car was using a motec ECU, but they sold it and switched to a megasquirt, and it has been running. And another guy (2006eg33) with an EG33 swapped into an impreza used one as well, but I don't know how well it was running, I just know that he got most of the way through it.

Ok so the MS3 is MAP-based, and has a built-in MAP sensor, to 2.5bar. Plenty for what you and I are trying to do. The other sensors it will need are crank/cam sensors, coolant temp sensor, throttle position sensor, and O2 sensors. It needs to be able to control the IACVs, the injectors, and the spark. Those are just to get it running, to work normally it will also need to control the IRIS valve, and probably a few other things.

So because it's MAP-based, you no longer need the MAF. You just run a vac line from a port on the intake manifold to the port on the megasquirt. An IAT sensor will help get a more accurate airflow reading as well, but I think it's not necessary.

Dynomatt set his crank sensor setup by using the 12-tooth wheel on the crank sprocket and the corresponding sensor, by removing one of the teeth, and telling the megasquirt that it's a 12-1 wheel. Easy enough, but because you have to actually remove one of the teeth, it makes it a lot less plug-and-play friendly, and you can't switch back to the stock ECU without changing the crank sprocket back. The other toothed wheel, which has a strange arrangement of teeth, is unused, and so is the cam sensor, and the engine is run as wasted-spark. Not ideal, but it works easily enough. Now I'm not sure Matt's reasons for not using the cam sensor, but I was going to do it this way because looking at the cam sensor setup, it appears that it reads the 5 spokes of the crank sprocket. The only cam sensor arrangements I could find the MS to support were 1 or 2 tooth cam wheels.

However, 2006eg33 said that he was using the cam sensor and that it's only read as a 1-tooth wheel, not 5. Which makes a huge difference, but I have not been able to confirm this independently. Maybe Harvey or someone already knows. I am hoping the ecutuner SSM software will let me figure it out. (Ordered it, hasn't arrived yet.) Haven't had a chance to get my eyes on a crank sprocket to check visually whether the back of one of the spokes (probably the one with the arrow) is different from the others, which would also support this.

Now, the other sensors, and IACV I should be able to get working by starting with dynomatt's tuner studio files and seeing how they are setup. There are even some that have the IRIS valve working. (On a side-note, with a turbo setup you might be able to gain more torque in different rev ranges by adjusting the RPMs that the IRIS opens and closes. So having the control over it that the MS will give you is beneficial.)

For spark I was planning to use LS coils, because they have built-in ignitors, and getting them to work, controlling dwell times, etc is pretty well documented online. Also they are cheap, but pretty powerful. You could mount them on either side of the engine like this, but I was thinking to mount them under the intake manifold. Should have some room once the EGR and emissions stuff is gone.

It's also a good idea to put in an intake air temp sensor, and a wideband O2 sensor. Not checked into those too much yet. Should be easy to find regular O2 sensors that would work though. Even stockers I bet will work.

The only thing I'm still pretty lost on is knock sensors. Seems like most people running megasquirts don't use them. Not too sure how important they really are, but it would be nice to have them. Seems doable from my brief research into it.

If I had the spare cash I would have ordered a MS3x and started playing around with it, but currently all my money is tied up in trying to buy a house. :/

So if you want to play guinea pig and try it out, I can help get you started. I have a bunch of files that Matt emailed me that I need to upload so other people have them as well.

I would also advise starting with a more-or-less stock engine, getting it running on the megasquirt and then turboing it. I am hoping that with this new info about the cam sensor, and getting a DIYBOB (there is one that matches our ECU) it would be possible to plug in the Megasquirt, fiddle with it for a little while, and then switch back to the stock ECU so the car can still run normally. Right now I need both cars to be daily driveable.

[BackWoodsBob]

*edit*
Just found another link on their site that will probably answer a lot of questions that I have. I'll read and come back if I have questions.
http://www.megamanual.com/index.html
*edit*

Wow hell of a write up thank you .

I' have a more or less stock EG33. Its been ported mildly by myself, full intake and exhaust. I would love to be a guinne pig, but aside from getting the car to start, I have no idea how to read those addresses the DIYPNP site lists .

I did find SVX rom files that have been broken down, but again, I have no idea what those addresses do or how they affect things. Before I order 500$ worth of material (the guy with the swapped 06 is on rs25.com and is willing to sell me his ecu adapter so I can switch back and forth quickly) I would like to know what I'm getting into.

I read their tech files on how to get the engine to start, and that alone seems easy enough, but I just don't have enough knowledge about this sort of thing to actually attempt it with my only engine. I would however, be doing as you suggest. Tuning it on an 'stock' engine, then later going boosted and re-tuning.

I've seen Harvey post his timing maps, is he running a PNP or custom roms on an Eprom chip?

[icingdeath88]

Originally Posted by BackWoodsBob

I've seen Harvey post his timing maps, is he running a PNP or custom roms on an Eprom chip?

Harvey is on a stock ECU.

I hear you about not wanting to be a guinea pig. I'm going to try to free up some cash so I can get started on mine. There have been a few people who've posted asking about the megasquirt and I'd really like to have some definitive answers about what will work and what won't. I don't know your timeline, but maybe I'll get mine going soon enough that you can follow along.

There is a lot to know about this stuff, but there is also a ton of reading out there that will get us there. Get to reading lol.

[BackWoodsBob]

Oh I am reading! It's finding stuff for beginners that's proving difficult!

I'm hoping by tax return time I'll have enough saved to order the PNP MS3 kit with the 3.0 revision for 6COP ignition support.

So, about 4 months. At which time I'll make a thread for tuning and for my build. I don't mind being the Guinea pig, but I'd rather have an idea of what I'm doing, before I jump feet first.

I realize the learning curve is going to be steep, but it was just as steep when I was teaching myself to do wire harnesses . And that turned out really simple, I can only hope this will prove as easy once I bite into it!