We decided to make our own exhaust X-pipe to replace where the CATs go for when racing.

To me the X pipe should be close to where the bends are that trap gases and not further back where pipes are straight.

We also made slip flanges for the CATS so they can be easy swapped with X-Pipe when need be

We'll post more scanner data of test results to see what differences there are.

Three inch slip fittings for Collectors or Headers and 2 1/2 fittings to stock mid exhaust pipe.

Gut feeling is the exhaust pulses are better, exhaust sounds smoother, more low end torque and requires a PCM tune as O2s report leaner with the X pipe installed but further analyzing the scanner data should give the results

Here is the results of the 1st testrun with the X-pipe
No tuning changes were made so that we could see what the cause and effects of the exhaust change was

Engine leaned up about 5% more so assume better exhaust flow and you notice at idle (cell 19) was way more leaner so the X-pipe allowed this engine makeup to move out the exhaust better in cylinders.

Rearwheel gains look to be about 10/10 HP/Tq and shows the claims some vendors make of 30 HP is bogus.

Gutted CATs Left graph - Xpipe Right side

Here is a compare of launching to 120 MPH with the G (gutted CATS)
Then with the proper placement of our X-pipe

And then a superimposed scanner data of both as to HP and Tq.

You notice with the front placed X-pipe HP and Tq come on much faster and have aboust 3 MPH faster then G-Cats at the same distance

Here is 2nd round of testing.
Tests spread across 2 days but weather the same for both days at about 50 degrees.
Two tests with X-pipe done today to then compare the tests of yesterday which was one run with gutted CATs and one run with X-pipe.
Keep in mind the vette has 3.73 rearend gear with 335/30/18 tires with limited traction but all testcases are equal with that issue.

Also when values go negative that is due to wheel spin and standing start and having to make 4 manual trannie shifts.

Same road used in all tests.

Again X means with X-Pipe and C is when gutted CATs were used.

Clearly correct placement of X pipe ( using 3 inch to collector but then 2 1/2 inch pipe to exhaust pipes) as you see the first 7 seconds from dead launch X pipe is winner as to HP, Tq, and MPH

For this test we retuned the PCM for a perfect fuel trims around zero and WOT AFR at 12.8:1.
Also changed radiator fans coming on at 200 degrees to 185 deg

With the tune horsepower increased from 475 to 513 flywheel.

This makes it easy to see the difference as what happens for the 1st 7 seconds from launching.

As seen when the Xpipe is used the HP and Torque quckly increase and when Xpipe is used it gets to red line sooner so shifting to 2nd gear happens about 2 seconds faster

It looks great, JR. Quick question I have is did you have to alter your oxygen sensor locations at all?

No changes to any of the 4 O2s,

I designed this so rear O2s and their bungs stay in stock locations.

I wanted as little changes to the mid pipe as possible so only the front of pipes were cut shorter and rest of mid pipes stay in stock placement.

How would you think your design fairs against the Stainless Works setup I already have? I don't have cats, so the headers go into a section about 1 foot long, then another about 2 foot long that the rear O2's plug into, then into the X-pipe. So clearly your x-pipe would bring the x-pipe at least 3 foot closer to the headers, if not closer. I was just wondering if I could somehow just swap some of the parts around to make it happen, but I see with my current pipes I'm going to have to do some serious rearranging to get the O2 sensors where they need to be. I don't see how I can post a picture of my setup on this venue, but I can sent it to you privately.

Thanks,

Read this first

Exhaust flow

Good example Rick K reminded me of

Some years ago Rusty Wallace in Nascar out of the blue began winning several racers. The exhaust sounded different.
Others did not know why until he crashed and car ended up lying on one side and everyone then saw the exhaust design.

The closer the X is to the heads the easier it is for it to draw the exhaust out of the heads leaving better makeup of air/fuel burn.

Further back the X is means there is more exhaust volume backed up to where the X is.

The center of X is open which allows the exhaust flow of one head to pull the flow of the exhaust in the other sides echaust pipe.

Better image of X-pipe to collector of Headers and rear O2s in stock location