Modifying M-Tronics or Autotune saws...

[MCW]

Hi guys.
This is a question for some of the more technical minded guys here in regard to porting and modifying some of the later computer controlled saws. If it has been covered before on AS then apologies.

Firstly we all know that these saws have certain parameters they need to operate under. If anything goes outside of those parameters I assume that the management system cannot compensate for this so the saw either runs poorly or starts having issues under load etc etc.

What are some of the problems that builders/porters have come up against when modifying these saws based on the management alone?

The main thing that has brought this to my attention is a piped 576 doing the rounds on the Australian race scene built by a guru out of Europe that has all of the Autotune gear removed. Therefore the systems obviously have limitations but I'd like to know what.

Hopefully somebody here can tune me in.

Before anybody winds up this isn't a shot at these systems but I'd just like to know how much is known about the parameters they are designed to operate under. I know there are some pretty awesome saws around with both AT and M-Tronic but they don't strike me as being much more than mild-moderate porting. There has to be a point where these systems can't cope anymore.

I'm sure Stihl and Husky didn't design the system to handle extensive porting and high compression but I could be wrong

Any thoughts? Thanks in advance.

 

[Stihlman441]

opcorn:

This is going to be interesting.

 

[7sleeper]

If I may add a question is "What I always wonder is, how much does the MM or porting decline it's usability in higher altitudes like we have in the alps?"

7

 

[MCW]

If I may add a question is "What I always wonder is, how much does the MM or porting decline it's usability in higher altitudes like we have in the alps?"

7

Well I've run my ported 7900 and 390XP at 10m above sea level and at 1600m above sea level. They seemed to run the same (OK OK I know it's probably significantly lower than the alps but anyway...).

 

[7sleeper]

Well I've run my ported 7900 and 390XP at 10m above sea level and at 1600m above sea level. They seemed to run the same (OK OK I know it's probably significantly lower than the alps but anyway...).

Obviously I was misunderstood. I feared so. The saws you mentioned have conventional carbs where adjusting altitude adjusting is no problem but how is it with the AT & MT carbs after modification?

7

 

[deye223]

opcorn:

This is going to be interesting.

:agree2:

 

[XSKIER]

Perhaps consider that a 576xpat carburetor is not large enough to feed a race saw anyhow. something like a mikuni super BN 38?

 

[MCW]

Obviously I was misunderstood. I feared so. The saws you mentioned have conventional carbs where adjusting altitude adjusting is no problem but how is it with the AT & MT carbs after modification?

7

What? You can adjust them? That's crazy talk.
I agree on the AT and MT.
My concern is that they may end up getting modified beyond their ability to cope. The reason I started this thread is that I've never read much about the operating parameters of these systems and am curious to know just how far they can be pushed before they can't compensate anymore.

 

[XSKIER]

Like an 044 carb on a 026?

 

[sachsmo]

Good thread,

i often wondered if there is enough adjustability built in to handle say e85?

 

[MCW]

Perhaps consider that a 576xpat carburetor is not large enough to feed a race saw anyhow. something like a mikuni super BN 38?

I fully agree. However even if it could feed a race 576 would the electronic part of the system be able to handle it?
For your information the actual black plastic intake of this particular saw is not far off of stock but it is creaming piped saws nearly 20cc larger.

 

[7sleeper]

What? You can adjust them? That's crazy talk.
I agree on the AT and MT.
My concern is that they may end up getting modified beyond their ability to cope. The reason I started this thread is that I've never read much about the operating parameters of these systems and am curious to know just how far they can be pushed before they can't compensate anymore.

Somehow I have the feeling your yanking my chain!? I was taking reference to your example of the 7900 and 390. Those you can adjust. But what would happen to a highly modified AT or MT saw in higher altitude. Would it run out of auto adjustment tolerance?

7

 

[MCW]

Somehow I have the feeling your yanking my chain!? I was taking reference to your example of the 7900 and 390. Those you can adjust. But what would happen to a highly modified AT or MT saw in higher altitude. Would it run out of auto adjustment tolerance?

7

Yes I am I'm with you but I'm actually wondering what the limitations are on a highly modified AT/MT saw at any altitude. Surely somebody knows the limitations of these systems? I mean can the H jet solenoid adjust over the full range like a normal screwdriver can?

 

[mweba]

opcorn:

 

[sachsmo]

With Brazil being the epicenter for old growth logging, it would be very interesting to hear from some of the loggers/mechanics down there.

Surly there are some members from there, or a Spanish speaking member who could find where these guys' hang?

They use Ethanol almost exclusively down there at the pump. Are they using pure Petro in their saws?

If not, what are they using?

I do know they can buy saws that have been long discontinued in other parts of the World.

SORRY, just thinking out loud.

 

[XSKIER]

So that particular 576xpat is running a regular 576xp carb? Most fuel delivery systems I have experience with are about maxed out for sea-level, -20*F operation. From there, the ECM will pull fuel with increased temperature, altitude, or in the case of a saw, rpms.

 

[MCW]

So that particular 576xpat is running a regular 576xp carb?

Actually not much is known about the mods done to this saw. It came with some pretty specific instructions including one that states "do not pull this saw apart, ever"
I think it is a 576XP carby though but what's been done to it is anybody's guess.

 

[T0RN4D0]

I can't see why high altitude would cause problems- higher altitudes mean less air and the car actually needs to dump in less fuel to make a proper mix. If it can control low enough flow for a stock saw (and im sure they tested that) than a modified should be less of a problem. The problem there could occur if the carb/air filter doesn't let in enough air to make the most possible power, but that's another issue not really related to autotuning.

So the range could be an issue at sea level, and i've read here somewhere that an auto carb dropped enough fuel to compensate for an air leak, so it looks like it has decent flow capacity for some mods. I'm sure you can take mods far enough that that it will become a problem for it, but my guess is it will just become the weak link.

 

[XSKIER]

I speak in very broad generalities, because I don't know enough about the specifics of M-Tronic or AutoTune. It seems as only the designers have it down, as a result of some of the customer/dealer interactions over malfunctioning saws that have been discussed here. Technology will sure bring some exciting things to OPE in the next 15 years, the hurdle will be getting the consumer to pay for it. $32 earthquakes aren't helping the cause either. Perhaps one day Baileys will offer a "hypertech power programmer" for the next wave of injected saws?

To answer the original question I believe any of the electronically enhanced carbs will flow enough fuel to support their own Venturi size. Lowering the air velocity by boring the Venturi on one of these carbs would likely have negative results.

 

[rmh3481]

Here is a view of a 575 built at Husky, it looks to have the same intake and carb although I do not think it uses the A/T system;
The chainsaw guy shop talk Husqvarna 575 XP Racing chainsaw Modified - YouTube