Fuel injection, rev limiting methods

[ChrisBennet]

Originally posted by DRD
A few comments about igniton rev limiters. I have found that most igniton limters that drop out the igniton, in time end beating the hell out of the rod bearings. The unloading and loading on the rods beat the bearings. Cuting off the fuel seems to be a better way. Everyone taks about running lean, but when you cut the fuel off,there is no fuel, just spark, you can't burn gas that is not in the chamber.
Darren

Darren,
Killing the spark compeletely would seem to beat stuff up like you said.
Thinking out loud, when you cut off fuel, the injectors stop sending fuel of course but AFIK there is still a fuel "cloud" behind the valve and coming off the intake port walls that gets sucked in. That would result in a lean mixture if only for a little while.

Chris

[DRD]

I have never hit the rev limiter in my p car to clarify. I come from a very wide range of engine building history. And I will refer to MSD boxes for droping out the spark. These boxes limit the revs buy droping cylinders like warren had said in a few post ago, when you hit the limiter, the engines back fires from all the gases built up in the cylinders, imagine if the cylinder runs through its cylce a few times and then sparks, you have a few cycles of fuel in the chamber, creating a hydralic conditon, putting stress on the bearings.
You cut the fuel and it stops making power, you drop rpms, the fuel comes back on , and it fires as normal.
The lean conditon might be true for a split second, but you would have to run it lean for more than a few seconds to burn a valve.Maybe I am talking a bunch of crap, but just sharing some of my experiences.
Darren

[RarlyL8]

Seems to me that a rev limiter that shuts off the fuel is no different than just lifting off at high RPM.
The cylinders are still sucking, the plugs still sparking, but the gas volume is way down.

[ChrisBennet]

Originally posted by RarlyL8
Seems to me that a rev limiter that shuts off the fuel is no different than just lifting off at high RPM.
The cylinders are still sucking, the plugs still sparking, but the gas volume is way down.

But the air volume is still way up.
-Chris

[dean]

To answer a question a few posts ago. The rev limiter on my 81SC is located under the hood behind the master cyl. It is about 2"x1"x1" black box with maybe a 5 wire connector on it. It works in conjunction with the tach and it opens the circut to the fuel pump.
Dean

[jluetjen]

Darren;
I've got an MSD with a 7000 RPM rev limit in my car and I've hit it a couple of times. (By the way, this is less then the 7200 RPM factory limiter in the distributor) It doesn't backfire, it just starts to run a little rough - like I said, it feels like the valves are floating and stops pulling. The MSD Soft-Touch rev limiter is far more gentle then the factory limiter which essentially turns the motor off.
I also used to race a Mazda 323 (SCCA-ITB) which had the factory fuel shut-off rev limiter. I only had to hit that once in a race to know that I didn't want to do that again because you can definitely feel the car "bouncing" against the rev limiter.

Having used and experienced all 3 versions, the Soft-Touch spark cutting strategy is the method that I prefer.

[ChrisBennet]

Many thanks to all of you!
-Chris