Gernby

EDIT: Here's the big discovery that sandbagged the test of the 70mm exhaust with 70mm TP. I eventually repeated this test and discovered significant gains ... later in the thread.!

I made an irritating discovery yesterday while reinstalling the stock cat on my car. The gasket that I used between the 70mm test pipe and 70mm single was 4mm smaller in diameter than the 2 pipes it was joining! That means that there was a 2mm ring of obstruction. Since I don't really know how much that would reduce performance, I'm going to have to repeat that test.

I have completed a modified version of the "Stock Equivalent" calibration that generates the same AFR curve with my 630cc injectors as it did for my stock injectors. The tentative results with the stock cat and 70mm single might show an increase over the stock exhaust, but I won't know for sure until I reinstall the stock exhaust. However, the stock cat still causes a HUGE dip in power between 4500 and 5500 RPMs if I try lowering VTEC below 5500.

H22toF20

I bet that makes you want to

I knew there had to be something.

Harpoon

Gernby

I repeated the tests with the OEM catalytic converter installed. The results were the same, and there was no significant change in torque or AFR.

Red is the 70mm and green is my modified stock exhaust. I had to return the unmodified exhaust I borrowed. VTEC engagement was 5500 RPMs.





I also performed the tests using a "stock equivalent" tune that I made for my larger injectors. I didn't feel comfortable running quite as lean as the true stock tune did with stock injectors, so I added a bit of fuel for the high cam.

Red is the 70mm and green is my modified stock exhaust. Yes, this test showed the oem exhaust slightly better than the 70mm single. Basically, they were both within margin of error.





I also verified that the optimal VTEC engagement didn't change by tuning for VTEC at 6400 (blue), then tuning for 3500 (green). The red plot is from the 70mm single with 60mm test pipe with VTEC set at 3500. The optimal VTEC engagement with the OEM cat is clearly 5500 RPMs. It's amazing how little the OEM cat reduces the peak numbers, but it's a real shame that the midrange losses are so enormous.

rjones

I would really like to see the internal silencer with the stock cat and 70mm exhaust.

s2konroids

Good stuff Chris.

How to do you think a HFC would compare to a stock CAT?, in terms of performance.

The berks CAT is almost hollow inside , in the UK our smog/MOT test showed that my car passed literally by a toads ball!

Gernby

I'll find out how an HFC compares in the next couple days, but my guess is that it will perform about like the stock cat (on my car anyway). The flow on my stock cat seems to be comparable to that of my test pipe. The only thing that seems bad about the stock cat is that it screws up the harmonics of the exhaust pipe, and creates a "band stop" for the high cam at 5K RPMs. I don't see any reason to think an HFC would be any different.

Gernby

Who's Chris?

s2konroids

Greg sorry

Not a particularly brilliant/accurate test but I dyno'd the car at 350BHP with a testpipe and it was 347BHP with a HFC (about the same throughout the rev range), however this was about two month's later and it was a slightly warmer day.

Vitt

[QUOTE=gernby,Jan 19 2011, 03:31 PM]I'll find out how an HFC compares in the next couple days, but my guess is that it will perform about like the stock cat (on my car anyway).