standalone rev limiters and T5

THE place for technical discussions concering the construction and preparation of SAABs for all forms of motorsport, Rally, Road Racing, Auto-X etc....
tirediron
Posts: 148
Joined: Mon Oct 08, 2012 10:22 pm
Number of Saabs currently owned: 7
Location: NH

standalone rev limiters and T5

Postby tirediron » Tue Jan 12, 2016 12:08 pm

I don't suppose anyone has done this, but I am looking into if it is possible to run an adjustable external rev limiter in conjunction with T5. most devices are for use with traditional distributor/ coil systems but some are available to be used with coil on plug. I guess my question is as to what each wire to the DIC is used for. the wiring diagrams that I can get show the circuits between ECU and DIC, but do not specify their purpose.

best I can tell, these aftermarket limiters just interrupt the spark signal at a given rpm. I am not sure if it is possible to do so with the saab DIC.
-matt

User avatar
Jordan
Site Admin
Posts: 4057
Joined: Fri Oct 13, 2006 2:38 pm
Number of Saabs currently owned: 6
Location: Vernon, CT
Contact:

Re: standalone rev limiters and T5

Postby Jordan » Tue Jan 12, 2016 1:26 pm

I guess what would be the reason, since you'd either have to adjust the limiter out of T5 anyway since it is coded into it? The RPM signal is generated by T5, so you can't really circumvent it. As for the DIC wiring basically you have the 4 coil trigger wires, 2 combustion sensing wires that share alternating cylinders, knock signal wire and power/ground. You could also use a external rev limiter to just cut the fuel pump which is how LH works, but that is a bit harsh.

User avatar
squaab99t
Posts: 1121
Joined: Wed Mar 28, 2007 5:43 pm
Number of Saabs currently owned: 4
Location: Shoreline Wa

Re: standalone rev limiters and T5

Postby squaab99t » Tue Jan 12, 2016 3:00 pm

The motorsports ECUs I have seen have a two stage rev limiter, Soft and hard. I believe it is to prevent the LH fuel pump cut effect where it is totally on or off. The soft limit pulls spark from certain coils and only fires maybe every other or every three from the standard cycle. This will drop the torque and give the driver indication to take your foot out of it, and/or a natural lost of power and the engine will slow down in the case of a constant load. The hard limit will to just that, cut all spark to all coils.
Cutting the fuel pump is not as smart, cheap for an OEM, but it runs the risks of running lean and a potential for pre-detonation.
I set my soft and hard at 6800 and 7000 respectively. I've never felt the hard cut.

tirediron
Posts: 148
Joined: Mon Oct 08, 2012 10:22 pm
Number of Saabs currently owned: 7
Location: NH

Re: standalone rev limiters and T5

Postby tirediron » Tue Jan 12, 2016 5:16 pm

it isn't for a performance benefit, it's to pass tech. :fuckyou:

tech is checking limiters to ensure it's factory, so I am looking for something switchable. I think I can use one of the aftermarket units being that there is an input wire to each individual coil.

on the LH topic, I am a bit unsure how LH uses the fuel pump to limit RPM? I hardwired mine to try an eliminate the limiter and it still hits at 6250. I don't know how it could drop pressure rapidly enough to work anyways, I was under the impression the LH fuel map just ends at 6250.
-matt

User avatar
squaab99t
Posts: 1121
Joined: Wed Mar 28, 2007 5:43 pm
Number of Saabs currently owned: 4
Location: Shoreline Wa

Re: standalone rev limiters and T5

Postby squaab99t » Tue Jan 12, 2016 6:24 pm

I think lh is boost limited, when too high, switch and relay cut power to the fuel pump. Not sure if there is a rev limiter on the stock arrangement?

User avatar
Jordan
Site Admin
Posts: 4057
Joined: Fri Oct 13, 2006 2:38 pm
Number of Saabs currently owned: 6
Location: Vernon, CT
Contact:

Re: standalone rev limiters and T5

Postby Jordan » Tue Jan 12, 2016 8:12 pm

No fuel, no RPM, pretty simple, the pump just cuts out....ever run out of gas under full load?

Since you can live tune t5 through the CANbus, the slick way to do it would be to set the base RPM limit as standard and then update the "active" program with the new limiter in the car. Active program is stored in volatile memory, in other words, when you cut power (flip the kill switch off and on) it would reset to the hardcoded standard value.

This is the method used in the software style "launch control" that is part of the t5 dash. Basically it resets the rev limiter to your desired low max (say 3krpm) and then some input (clutch release or brake pedal release) resets the ecu back. Something similar could be accomplished with the right code, although some type of computer would probably be needed in the car to activate this as well as the communication hardware.

tirediron
Posts: 148
Joined: Mon Oct 08, 2012 10:22 pm
Number of Saabs currently owned: 7
Location: NH

Re: standalone rev limiters and T5

Postby tirediron » Tue Jan 12, 2016 8:46 pm

I get it, I am just saying that ive hardwired the fuel pump to ignition power to try an defeat the LH limiter, and it still exists. under free rev I would think rpms would continue to increase for a few milliseconds after the fuel pump is shut off due to residual pressure in the rail, similar to a carbureted vehicle running with fuel in the bowl. that and time to build fuel pressure in the pressure depleated system would in theory take a second or so to resume power, which LH does not exhibit a delay as such.

I don't know, ive done zero research to support this other than my own experience. I just don't understand how, if it does in fact use the pump.

Jordan, ive got to admit anything using T5 suite to vary a limiter is over my head. that's why I send my ecu's to you :thumbsup:

dennis, I don't know about a boost limit based system, everything I own is N/A.

that being said my LH experience is limited to 2.4.2, maybe 2.4 is different?
-matt

User avatar
Jordan
Site Admin
Posts: 4057
Joined: Fri Oct 13, 2006 2:38 pm
Number of Saabs currently owned: 6
Location: Vernon, CT
Contact:

Re: standalone rev limiters and T5

Postby Jordan » Wed Jan 13, 2016 8:31 am

LH has both fuel cut and ignition cut like squabb mentioned. But it does both for different reasons. You probably get that lag becuase a) turbos are thirsty and b) maybe your not under load. Anyway back to your original question. What external rev limiter do you have? That would help to know what kind of input output it has. That way you could trigger power cut to the DI maybe through the main relay.

User avatar
Crazyswede
Team Turbo Troll Crew
Posts: 4387
Joined: Fri Sep 22, 2006 3:53 pm
Nickname: Mongo
Number of Saabs currently owned: 97
Location: Rutland, Vermont
Contact:

Re: standalone rev limiters and T5

Postby Crazyswede » Wed Jan 13, 2016 10:33 am

my rev limiter is attached to my right leg ;)
I am the 73%

tirediron
Posts: 148
Joined: Mon Oct 08, 2012 10:22 pm
Number of Saabs currently owned: 7
Location: NH

Re: standalone rev limiters and T5

Postby tirediron » Wed Jan 13, 2016 11:24 am

I don't currently own one. on my carbureted vehicles I just use an MSD 6al which uses resistance chips for limiter adjustment, but that obviously wont work in this situation. standalone limiters can be had for about 150 bucks, but there are a few different types. I would think one designed for coil on plug ignition would work because you can tap into each coil wire to the DIC individually. something that just opens the power circuit to the DIC at a given rpm may work too? I was just worried if I wired it that way it may just kill the engine when the limiter in engaged. maybe it wouldn't piss off the ecu though? I suppose I could try it with a toggle switch to momentarily cut power and see what happens.

probably could tap into the injector power circuit too, although I dunno whats better for the motor.
-matt

User avatar
Jordan
Site Admin
Posts: 4057
Joined: Fri Oct 13, 2006 2:38 pm
Number of Saabs currently owned: 6
Location: Vernon, CT
Contact:

Re: standalone rev limiters and T5

Postby Jordan » Thu Feb 18, 2016 8:06 pm

I've been working on setting up this hardware to work with t5. https://www.autosportlabs.com/product/racecapture/ It's basically a pretty sophisticated piece of racing hardware that can does lap timing, data logging and telemetry. I have the "pro" version hardware which has some extra inputs and outputs for additional sensors , the non pro version is still in pre-production. But the magic is that they both have a CAN Bus interface and a way to program custom functions for it. It sounds complicated, but once the code is cracked (I'm almost there) , you can easily set something like if speed=0 set the rpm limit to 6250 else set rpm limit to whatever you want. It should work in theory at least :) For the money it could be a great companion to t5 On the race track


Return to “SAAB MOTORSPORT TECH”

Who is online

Users browsing this forum: No registered users and 1 guest