Muffler?
 

We used a 3" Summit Racing muffler to chassis dyno the car this weekend. The reason for the muffler was to get a better wide band O2 reading at lower rpms, the O2 sensor is in the collector about 8" from the end. So it doesn't read well below 4500 or so.
This is a chambered muffler not a straight thru design.
We have a loss of HP and torque starting at 7100 rpms. and continuing downward at about a 45 degree angle.
We adjusted timing and fuel mixture. Was able to take power away but not add any.
This happened at the same rpms using 2 different intake manifold setups and tunes.
Thought it could be my hydraulic lash adjusters pumping up. But the cam manufacturer says that if that were the problem the car would misfire when backing off the throttle.
Noticed that when we first dynoed the car (inexperienced operator) a year ago there seems to be the same problem. But due to the circumstances never paid any attention to the sheets.
The first motor I built (less compression, less cam) made increasing power to 8100.
Other than cam and compression the only big difference was the first motor had an pretty intricate crank scraper. While the new one only has a windage tray.
Try to narrow down ideas.
Thanks.

Re: Muffler?
 

So it ran better with the other cam and no muffler. What's confusing you? :)

Re: Muffler?
 

No I didn't say that. I said it made power to 8000. 218 hp to be exact. That motor had smaller cams and less compression.
This motor (bigger cams and more compression) makes 233 hp but at 7100 it noses down. If it could make power to 8500 it should be close to the 240 mark.
Just wondering if a muffler could be the cause of the down turn? I realize the muffler might hurt perfomance some though the range. But to just go to a given rpm and lose power. It still turned 7700. No breaking up, just down on power.

Re: Muffler?
 

You don't have the cam advanced to much do ya?

Re: Muffler?
 

We played with cam timing on the dyno last year. And I retarded the intake cam at the track in a test session one day, To try to get the cylinder pressure down (compression test =300pounds) It slowed up a bunch.

Re: Muffler?
 

Art,I would try a straight thru design such as
a Max-Flow,MagnaFlow or a Borla.The cars we dyno
have usually picked up power over a chambered muffler
setup with the same id size.
Any reason you didnt use the crank scraper on the new
unit?

Re: Muffler?
 

I don't run the muffler on the track. I just needed something to steady the O2 signal at low rpms. I want to know if the chambered muffler would make the hp nose down at a certain rpm. Or would it just restrict it throughout the range.

The crank thats in this motor doesn't have any counterweights. I would have to have built it from scratch and didn't have the time. I will do one this winter, if nothing else gets first priority. Last year I had to figure out and fix the trans brake, and put and paint a new front end on the car.

Re: Muffler?
 

Art, you can have a muffler shop make a 24" extention with a 45 degree bend in the middle and clean up the wide band numbers down low just as well. Cheaper and takes up less room under the car or in the shop. I always took it back off for higher RPM work.

Re: Muffler?
 

Yes thats probably what I should have done. I figured the muffler would be dual purpose, and easier on my neighbors ears. Hoping I don't have to put the car back on a dyno to see if it was the muffler. Or if there is something else.
There are a couple of other things I'm looking at. Hoping to get to a track next weekend to test it out.

Re: Muffler?
 

Art, I have run dynomax ultra flow welded on my 70 challenger and picked up HP versus the headers.

They are street legal 3 inch inside pipe and come in oval and round. Part # 17220 Oval, 17223 round center in and out. Assuming you have a collector with a 3 inch piece on you can build your bolt on kit with adj length and turndown from Jegs for cheap and easy. True straight through and they flow like none other.

For your data file if you ever do the muffler thing again, or decide to drive you Super Stocker to the track!