On 12/7, I was at FLP and we used my car, a 2000 M6 Z28, for some solid data from the dyno. We wanted to see if the “Y” portion of the Y-pipe was actually a restriction or not. I was going to be replacing the Y with a (2) 2.5”-(1)3.5” Flowmaster Y collector. I had posted asking for data from people on this for a long time and never found or received any.
The test was to consist of the following:
2 pulls with the FLP Y w/ cats
2 pulls with the FLP Y w/ offroad pipes.
2 pulls with the Flowmaster Y w/ cats
2 pulls with the Flowmaster Y w/ offroad pipes

Mods relevant to this test are: 218/224/114 comp cam, LS6 intake, ported TB(removed the lip before the butterfly and smoothed the IAC hole, Stock de-screened stock MAF, FLP Long tube headers, 4” Mufflex w/ Flowmaster Race Muffler cat back, Strange 12 bolt w/ 4.11s.

***First of all, I would like to note that the HP/TQ numbers seen are somewhat effected due to the A/F ratio changing. It is still unclear why my A/F numbers were off. We don’t know why the air fuel numbers changed in the middle of the test but we don’t believe that the Y-pipe had any thing to do with it. My car was dyno tuned by Ed Wright in Tulsa about a year ago and the air fuel was perfect at that time. I have only changed the Intake, took the screen out of the MAF and removed the lip in the TB. My A/F ratio was 13.0-13.1 when it was done on the dyno. The weather changed slightly but we did not thing it was drastic enough to account for the change either. ANY info as to why the A/F ratios were so far off would be appreciated. ******

Here are the results in order of the tests performed (rwhp/rwtq-A/F):
2 pulls with the FLP Y w/ offroad pipes:345.4/346.4-12.0/12.2 341.0/339.4-11.5/11.6
2 pulls with the FLP Y w/ cats: 354.9/353.4-11.9/12.1 352.1/352.3-11.7/12.0
2 pulls with the Flowmaster Y w/ cats 362.3/360.8-12.5/12.7 362.3/361.3-12.3/12.6
2 pulls with the Flowmaster Y w/ offroad pipes 363.7/365.6-12.4/12.6 365.9/368.9-12.2/12.5

Some finial pulls were made with tuning by BV Performance that put me at:
374.2/374.2-13.5/13.1

So, now here are the questions:
Why did I pick up 9-11 RWHP when I put the cats on?
Why did my car dyno so low? It had 363/365 on Ed Wright’s dyno in Tulsa a year ago.
How much of the 7.4-10.2 rwhp (on the w/ cats tests) did I get HP from the new Flowmaster Y or change in A/F? Or both and if so at what ratio?
How did I pick up 18.3-24.9 RWHP (on the offroad tests) and change that much on the A/F?

The A/F issue seems to be the main culprit. These are SAE #’s. I would appreciate any info that could help clarify this data and then we can put the “collector restriction issue” to rest.

Finish Line Performance did an excellent job putting the new Y together. Don was like a magician. All mandrel bent pieces were used and it looks perfect. They are a professional shop that I plan to continue to do business with in the future.

 

Id have to go out on a limb and say its something to do with the a/f changing. There are lots of people who have tried 3" y pipes, 3.5" oval pipe ypipes, and 2.5" pipes and have seen no real difference. There is a marginal difference coming from the stock pipe that had been crushed from the factory. FLP has tested several different y-pipe sizes and noticed no power gains when going to a larger 3" pipe, maybe their test car was a small bolt on type car with smaller exhaust flow than a cammed car. Why your a/f ratio was changing is odd.. but people have noticed that when they put on a cutout their a/f ratio changes. Maybe your 4" mufflex is making a large enough difference in flowing that it can benefit from a larger y pipe. Still good numbers for the car, getting closer to 400 with stock heads. Nice car
-dan

 

When you dynoed the car, where did they put the A/F sensor? I know Ed puts his in the header or in the back o2 hole. If they put the sensor in the tail pipe of your car that might have a little to do with the A/F readings.

I am baffled as to why you would have gained that much power by installing the cats. I myself have dynoed the car in three stages: cats, no cats, and strait out of the headers. The car made more power in each step all the way through the RPM’s.

Jason

 

I didn't change the pipes on the y pipe, I simply changed the "Y" merge section on the FLP one. Just looking at it it completely looks like a bottleneck in the system. Supposedly MTI automatically does the conversion. I am not positive.
The A/F sensor was in the tail pipe of my mufflex. I can/will put in a bung to get better readings if necessary somewhere else in the system. Would this be beneficial for me to do??

The increas in HP with the cats was very strange. I think the af ratio changes had something to do with the nature of the pulls. I think hte car needed to be reved higher between gears while increasing the wheel speed to get ready to do a pull in 4th. Maybe the car needs to not be hammered until 3500rpm during a pull since it never sees below that at the track anyway??

 

both the finial pull w/o cats and the ones after that with new tunning were all higher than the previous runs with cats.

 

[quote]Originally posted by MBC Racing:
<strong>both the finial pull w/o cats and the ones after that with new tunning were all higher than the previous runs with cats.</strong><hr></blockquote>

I noticed that. But the 1st pull was w/o cats (cold 02 sensors), then with cats (nice and hot 02 sensors). The 3rd pull after the collector mod was with cats. The last pull w/o cats the 02s were probably already close to operating temp because of the previous pull. Remember this is just a guess based on observations some have noticed.

 

Makes sense. I wonder how long it needs to be running to heat them up correctly. How about when an engine is cold and the cars seem to run faster at the track? I have seen different results on this, but when Evan Smith would test the F-bodies, he got better times on a cold engine. AAAAAAAHHHHH more conflicting data that all has some sense to it.

Any more ideas?

 

The engine was cold but the cats held a lot more heat (I'm pretty sure he had cats on those cars), therefore heating up the 02 sensors faster. I think I read that operating temp threshold is around 600*F. Remember, the cats are designed to heat up fast and stay hot.

'Los

 

O2 sensors dont effect WOT A/F mixture. O2's are used for part throttle driving.

 

This is just a guess, but without the cats, your 02 sensors may not get hot quick enough to produce good readings. With the cats in place, the extra heat is there to put the 02 sensors within operating range quicker. Others have questioned this theory before, wondering why there seem to be 02 sensor voltage changes with the install of an off road pipe.

 

Well, I guess that throws out that possibility of the cats.

CAN ANYBODY TELL ME WHAT THEY THINK COULD HAVE HAPPENED????

I am getting a lot of good ideas, but still no dead set info.
Thanks