Cupcar

Take a look here for a little explanation and be sure to click on one of the "X-design" links within the web page http://www.burnsstainless.com/theory.aspx

Bill Verburg

Sort of, inline 4s often use a Tri-Y exhaust because it's easy to construct and package, the pairing of primaries depends on the firing order, 2 alternately firing cylinders will be paired on one section and the other 2 which are also alternately firing cylinders will be paired in another section, then the 2 sections will be merged, this is essentially what *** does only they pair the left alternate firing bank, pair the right alternately firing bank then merge the banks, the lengths of the primary and secondaries are carefully selected so that the gas flow and acoustics of one cylinder are used to enhance the flow of another paired cylinder, the goal is to spread and enhance the torque curve, as opposed to totally separate pipes or 4 into 1 collectors used on odd fire engines which generally are tuned for max hp but only over a very narrow rpm range, this design can also be used on V8s

inline 4s can have various firing orders depending on the crank design, a typical 1-3-4-2 using a tri Y will pair 1-3 and 2-4 primaries,
so they go B-S into the one collector then B-S into the other collector than the 2 collectors are merged, into a B-S-B-S what happens w/ these is that the acoustic signal that enhances exhaust port flow occurs at 2 separate rpm pts because of the 2 separate merges, this smears the enhanced torque curve over a wider range than a single stronger signal generated by a solitary collector which only affects a single narrow section of the rpm curve

swmic

Thanks Bill, you are truly an asset to have on this site.

Cupcar

I used to have a 1998 Integra Type R (4 cylinders). The USA R version used a 4-2-1 cast iron header and the Japanese market R had a 4 -1 tubular header. I did dyno runs with both in a before and after test. The results were exactly as Bill says, the USA version had a broader torque curve and the Japanese version produced a peakier torque curve with about 2-3% higher horsepower than the USA's.

Also, the Japanese version had a shorter CAT with only 1 element in the system while the USA version used 2 of the same elements in series, both in the same B pipe position. The car barely passed NOX in CA smog testing and had to be really hot to pass.

Cupcar

I have decided to take a drive to the Dansk factory tomorrow and will return with a full report of their program.

Bill Verburg

I should have pointed out there there actually 2 different Tri Y configurations commonly used on inline 4s
The one I described above is called non-sequential, there is another called sequential where consecutive firing cylinders are paired, so one branch gets B-B-S-S then the other gets B-B-S-S then the 2 branches are later merged into BB-SS. This is a compromise between, the max torque spread of the first set up and the max hp at a specific rpm of a 4 into 1 collector. The consecutive B-B doesn't load the collector as in the V8 because the firing pulses are 180* crankshaft degrees apart in the 4 and only 90* apart in the V8, the flat 6 is blessed w/ 120* crankshaft degrees between firing cylinders so the typical collector only sees one firing every 240*

Cupcar

I went to Dansk muffler in Viborg, Denmark yesterday and found the factory, really called JP Group a/s a huge manufacturer of a lot of different auto parts. I was given a factory tour and pictures will follow later.

I ordered their Cat bypass pipe system, part number 93.400S, for track use shown below. It is all stainless steel and mandrel bent from one piece of tubing with one O2 probe bung for a '95 Bischoff exhaust system:

FSCCA

Great info here. Maybe I missed it, but is there any benefit to an X-pipe over the straight pipes in the pix for our cars?

Bill Verburg

That's what I use, w/ stock turbo mufflers it's barely legal at LRP

Cupcar

Perfect.

Cupcar

After all the discussion here of even firiring versus uneven firing engines, and noting that Porsche has never used a crossover system in any of their dedicated racing 911 cars, I figured an X pipe would probably do no good and may do harm.

Ed Hughes

Read the thread-it's all there.

vincer77

The correct pairing would be 1-4 and 3-2 to get the even firing pulses. I have never seen any other firing order in inline 4s that would have an alternative pairing. Flat 4s (VWs and 914 - like I said VWs ) require that cylinders be paired across banks and makes it difficult to build a properly paired tri-y header. I like 4-1s for these applications.

That said, for a 4-cylinder, I do not believe that a 4-2-1 is better (from an exhaust standpoint) than a properly designed 4-1 system due to the even fire nature of the engine. Tri-Ys can be lighter, and as said, package nicely, particulary in FWD applications.

Who is ***?

BTW, is there a difference in the exhaust note between the Bischoff and Gillet exhaust?

vincer77

Sorry for the double post, but how would this setup look? I do not see how you could have B-B-S-S in the final collector.

Never say never. Pics taken at Daytona 24. 997 RSR exhaust

Bill Verburg

There are different ways to configure the exhaust
here is 1&2, 3&4 pairing


here 1&3, 2&4 pairing


here a 1&4, 2&3


Which you use depends on firing order and hoe you want to affect the torque curve

non sequential tri-y has the widest torque spread, 4 into 1 the narrowest but also the most peak hp, non sequential tri-y is in the middle

When I raced Honda MC we played around w/ this a lot, I see that current 4 cyl inline superbikes are also playing w/ crank variations to further alter the torque curves