[wolf]

One of my local tracks just announced mandatory mufflers going forward. My cars (stick cars) launch foot to the floor using MSD (spark limiting) 2 steps to hold launch RPM. Anyone have any experiences doing that with mufflers? I'm concerned my mufflers will become bombs when they fill with unburned fuel while "on the chip"...

[adam woodmancy]

I have 3" dynomax super turbos that dump in front of the axle and I have never had an issue using the 2 step with a transbrake. I am by no means an expert, but so far so good

[Mike S]

I have been running mufflers and a 2-step for 10+ years with no problems. I have an X pipe and straight perforated tube mufflers dumped in front of the rear axel. I have the 2-step set from 3000 to 4000. Usually have it set at 3800.
You shouldn't get raw fuel in the mufflers because of the 2-step.

[wolf]

Originally Posted by Mike S

I have been running mufflers and a 2-step for 10+ years with no problems. I have an X pipe and straight perforated tube mufflers dumped in front of the rear axel. I have the 2-step set from 3000 to 4000. Usually have it set at 3800.
You shouldn't get raw fuel in the mufflers because of the 2-step.

Auto or stick trans Mike? I don't think you can compare a completely unloaded stick car engine on the chip @6000 RPM to one loading against a converter - there's WAY more fuel going into the exhaust with the stick since the engine is not making any power with no load.

I have full exhaust systems (with tail pipes out the back) on my cars too BTW, so that probably makes things even worse, for combustible exhaust capacity. Cut outs after the header collectors have always been opened when using the 2 steps.

My concern is based on a previous experience where I literally blew the muffler open on my old truck when a bad connection caused the ignition to cut out for a few seconds at highway RPM (and I didn't get off the throttle quick enough), then when it came back on...BOOM!

[Mike S]

It's an auto but using a trans brake. Basically like dumping a clutch. I run a 1050 holley with 50cc accelerators pumps. It dumps a lot of fuel when I go on the 2-step. Never had a problem with fuel in the mufflers .
I don't really understand why load or no load would change anything.

[wolf]

Originally Posted by Mike S

I don't really understand why load or no load would change anything.

If the engine is under load, it's making power, which means it's burning fuel, not just sending it all out the exhaust.

[455 pontiac]

I have 3.5" dynomax mufflers and leave at 3500 on the brake with 1100 dominator, never any issues.

[bad69bird]

Vibrant makes "mufflers" that are lightweight and no real performance loss.

https://www.summitracing.com/parts/v...iABEgKsofD_BwE

[wolf]

Originally Posted by bad69bird

Vibrant makes "mufflers" that are lightweight and no real performance loss.

https://www.summitracing.com/parts/v...iABEgKsofD_BwE

Thanks for that link. I might end up bolting something like those onto my cutout flanges - if the packaging fits. I don't want to replace the street mufflers outright with race mufflers, for a bunch of reasons. We don't have the dB limit yet, so I'm not sure if that idea will be quiet enough though.

[goathead455]

I use a 2 step on a stick car with full exhaust.
Never any problems with unburned fuel in the mufflers.

[Tom Vaught]

During the Road Race years (14), when I was a National SCCA Scrutineer, Flow Master used to make mufflers that would pass any sound check. And the DB limit was high in those days, and still is: (Noise limits of 98 decibels at 50 feet from any track edge), so I would not worry to much about losing performance with running mufflers.

Same deal with "fuel in the exhaust system". Lots of On/Off the throttle (slow down and then back at WOT), never happened for the typical racer.

Tom V.