I have to admit that when I added a Bassani X pipe to my car I really didn't expect to see any performance improvements. Well to my surprise I actually did see a slight improvement in HP and TQ on the dyno. The changes between the two runs were the addition of the Bassani X pipe and Corsa touring exhaust. Both of these runs were done on the same dyno…on different days. Both runs had the same correction factor of .98. Skeptics (like me) might say that dyno runs can easily have this much variation to them…true…. However, what I think is the telling difference is the shape of the curve. When you have variations in dyno runs the shape of the curve remains about the same…just the amplitude changes. In this case the change in curve shape represents a change in performance…although small. I compared the shape of the curves to other cars with similar mods, minus the x-pipe, and those curves matched my base curve pretty well. The conclusion I came to is that (to my surprise) the X-pipe does add a small amount of HP and Torque at higher RPM. You can draw you own conclusions from the data. :)

 

Hi,
Thanks for posting this data. However, I think this data shows no improvement. The baseline run (red) shows a spark knock event at ~5400 that pulled the timing and the power dropped. Between 4600-5400 the power is virtually identical, expect for the dip in the baseline at 5100. My experience with the available x-pipes on Vettes is that they can raise the backpressure which reduces power. Maybe we’re putting them in the wrong place.
Has anybody seen a good discussion of the theory of x-pipe? The NASCAR guys wouldn’t be using them if they didn’t have the potential to work.
Thanks,
Steve
:seeya

 

I lost 5 RWHP and 10 RWTQ plus a lot of good sound when I put the Bassani X pipe on a H/C header etc. setup. So I guess you can figure out where that X pipe is now.

 

:seeya I hear this argument time and again on the forum and I just can not believe that the x-pipe REDUCES power and torque. I added the TPIS headers ..pulled the cats and added an x-pipe "up close" to the header flange and gained nearly 41 lbs of torque and 29 RWHP. My car does not have ANY engine work..No cam or headwork at all.You can view my dyno sheet in the performance registry and view my videos on the c5 discussion forum under Bradenton..sweet victory.:yesnod:

I firmly believe that the cold air intake and a unobstructed and designed exhaust path "makes a significant difference" and you don't have to go into the engine to get great performance.If you wish to see the setup check out my homepage for full install pics of the exhaust:D

 

Your theory sounds plausible…..However, I don't think your right. The shape of my base curve is typical of an A4 car….and believe it or not almost all A4's show that dip. I don't know why? It could be spark like you suggest…but the M6 don't seem to have the same issue???? Below you can see a comparison to one of my stock runs. (I omitted the torque curves for clarity) I chose a run that didn't have the normal dip…and you can see the non x-pipe curve is pretty consistent with the curve in the first chart I showed.



In regard to the statement of lost power….You need to be really careful with dyno data. If you compared your raw (non corrected) data I am confident that it would show an improvement. Quite honestly the correction factors do the LS1/6 a great injustice. You can only get an accurate comparison of runs if they were done at the same correction factor. It makes a HUGE difference.

 

Go to http://www.drgas.com and get an education (from their viewpont) on x-pipes. I believe they supply a good portion of the NASCAR setups. Maybe even developed it.

See Ya
Easy

 

I dyno'd before I put on the TPIS headers and Magna Flow X pipe. While I'm still investigating the issues with cold weather dyno and high cf = .95, (stock 2001 and 2002 Z06's dyno'd way below factory HP)

My hp/torque gains were only 12.4 hp and 16.1 torque with the LT's & X pipe.

I do feel like I lost something somewhere. I was expecting much more! The dyno dude said I needed some more timing?

 

Not to say that their claims are untrue, but as their business is making these things you have to know that all their statements regarding X-pipes are self-serving. I think an independent evaluation of any possible benefits gained by the use of X-pipes would be more useful in coming to an unbiased understanding of them.

 

"(from their viewpoint)"

Exactly.

See Ya
Easy

 

Ok, so this is what I learned about x/h-pipes:
Our LS engines have a firing order that gives two sets of adjacent firing cylinders. There is one set on each bank for every complete firing cycle. This is a result of consecutive crank throws being 90 degrees apart. Only a “flat crank” solves this issue but the tradeoff is that the 90 cranks have better balance. When the two cylinders fire consecutively, they cause a higher backpressure in that exhaust pipe as they are flowing at nearly the same time.

An x/h-pipe tries to relieve this increased backpressure by joining the two sides of the exhaust system is some fashion. After joining both sides the average pressures are lower downstream going towards the mufflers. This has the potential to increase power.

H-pipes allow a cross-flow to occur between the sides. The passage for this cross-flow is restrictive because it is at a 90 degree angle to the main flow. This will restrict the balancing effect. The advantage to an h-pipe is that it does not add resistance to the main flow paths. The main exhaust pipes only have a hole in the side which does not cause a great increase in flow resistance. Straight pipes have lower flow losses then curved pipes.

X-pipes reduce the restriction of flow between the two main exhaust pipes by either curving them until they meet tangentially or actually crossing them. This geometry will maximize the transfer of pressure but may require many curves to be added to the system.

X shaped x-pipes simply cross the path of the pipes at some angle which could be as high as 90 degrees. This merge looks like the left-front-feeds-the-right-rear and vise verse. The turning angle for cross flow may be as high as 90 degrees (the same as an h-pipe) or something lower as the X angle is reduced. The downside of this configuration is the added turns and the addition of two holes in the side of each pipe.

Tangential x-pipes are turning the flow as it meets the merge area. This gives the flow a “push” into the opposite pipe which will maximize the cross flow, assuming that the pressure is lower over there at the time. The windows cut into the pipes were they merge can have a very low restriction to cross flow. There is an increased flow restriction due to the curves that are added in this configuration.

Plenum x-pipes dump the flow from both sides into a common chamber. The gases are mixed and the pressures are averaged in this space. The output from this plenum is a different set of pipes that then lead to the mufflers. Both mufflers see the same pressure and flow as they are now connected to this common source. The downside to this arrangement is that there is a loss entering and exiting the plenum. If the volume of the plenum is very big, the entry losses can also be big as the gasses expand. The exit losses can be minimized by having them shaped like a bellmouth, just like any good inlet. Rapid gas expansions make the exhaust system think that it has ended and a return pulse will be generated. If the timing of this pulse is in tune with the valve action, performance will be increased as in the case of long tube headers. The question is: where to put this expansion.

Where to put an x/h-pipe in a Vette:
X/h-pipes work by pressure differential. Max pressure is always forward of any restriction in the system (unless you add a pump). The back pressure in a stock Vette is about 6psi @ 6000rpm after the manifolds but before the pre-cats. The pressure drops to ~3psi after the main cats. Of course, the pressure will be zero at the exhaust tips as the gas escapes to the atmosphere. This means that the best place for an x/h-pipe is before the cats but after the headers. Unfortunately, this is not a smog legal mod. The O2 sensors are setup to adjust the fuel flow of only one side each. I know of no simple method to estimate were to put a rapid expansion in the exhaust to get a benefit in performance.

Summary:
H-pipes have a weak side-to-side transfer of pressure but nice straight main pipes. They are light and simple. Pop, pop.
X shaped x-pipes increase the side-to-side transfer but add curves and a couple of big holes in your pipes.
Tangential x-pipes increase pressure transfer but also add curves.
Plenum chamber x-pipes maximize pressure transfer but have the potential for the greatest pressure losses with curved pipes and entering and exiting losses to the plenum.
X/h-pipes work best in front of any restriction in the system.
Smog legal Vette x/h-pipes only see ~1/2 of the available backpressure.

Wild speculation based on one experiment and the above research:
My experiments with a plenum x-pipe showed a decrease in performance and an increase in backpressure of 1psi. Maybe if the losses into and out of the plenum were reduced a gain in performance would be available. I am contemplating this experiment.

I think that the “tangential x-pipe” has the greatest potential to increase performance. This is based on the expectation that the pressure transfer is effective and efficient and the pipe geometry can be reasonable. Sharp turns in the pipes must be held to a minimum.

Your comments are welcome,
Steve :seeya


[Modified by SNW Vette, 6:40 PM 2/14/2002]

 

The June issue of Hot Rod conducted an X-pipe test. They discussed how they work, then ran a car on a dyno, and the strip, with open headers; mufflers & pipes w/o a crossover; mufflers and pipes with an H-pipe; finally, mufflers and pipes with an X-pipe. These are the results:
a) Test Vehicle / 1970 Olds 4-4-2 w/350 block and modified
b) Where first seen / NASCAR guys began using X-pipes
c) X-pipe design theory - "By running the two exhaust pipes together in this fashion, the alternating pulses in each bank can work to create the same type of scavenging action in the other."
d) Works best on a V8 engine running 300-500 hp because the volumetric efficiency is not as great as on a 700-800 hp V8 engine.
e) Dyno pulls:
1) Open header - 430 hp @6850 rpm, 384 lb-ft @5600 rpm
2) 3" exhaust pipes w/Straightline mufflers and no crossover - 412 hp @6650 rpm, 371 lb-ft @5600 rpm
3) Same setup as #2 except with an H-pipe - 419 hp @6600 rpm, 378 lb-ft @5600 rpm
4) Same setup as #2 except with an X-pipe - 428 hp @6600 rpm, 391 lb-ft @5600 rpm
Strip tests:
1) Open header - 1.65 sec 60', 10.885 sec @123.89 mph
2) No run with the exhaust system w/o a crossover
3) Exhaust system w/Straightlines and full pipes and an H-pipe - 1.55 sec 60', 11.007 sec @121.33 mph
4) Exhaust system w/Straightlines and full pipes and an X-pipe - 1.62 sec 60', 10.897 sec @124.13 mph

This car, which used to run open headers at the strip, now runs with a dual exhaust system with an X-pipe. More details in the magazine, naturally, but very interesting, I thought.
Ed

 

Great thread! :cheers:
TTT

 

SNW vette,

First, I'm sorry about the large picture. I have no tool to resize the pic.

I found your post very interesting. You mentioned some drawbacks with the plenum style 'x-pipe'. I had a plenum type x-pipe made without knowing anything about x-pipes :crazy:

This plenum x-pipe has no bent tubes or any walls that can make the exhaust pulse to bounce back to the engine. It is made of four 3" dia. 5" long tubes and two oval 5" dia. 3" long tubes welded together. The plenum was polished inside before TIG welding the two halfs together to get rid of most edges from the welding. Under which of your descriptions would you place this type of x-pipe, is it a plenum style ? Would you recommend me to do any changes to the design ?

:cheers:




[Modified by seanr, 1:04 PM 2/15/2002]

 

I forgot to mention two things:
1) That was the June, 2001, issue of Hot Rod (great article)
2) I believe the X-pipe was mounted far forward in the car, just after the headers. There are some excellent pictures and a lot more data in the article.
Ed

 

I heard the best kept secret about x-pipes is the interface...and that if it is not at least 7", then it is not a performance enhancing modification...(info from motorolacup cars)

 

Charley Hoyt,
I can see from your second chart that the event at 4600 did not hurt the power at higher rpm’s but your first chart does not have a continuous curve like this one does. There is a definite downward step after the 5400rpm event in the first chart. Something is going on to make the engine loss power after this event. I don’t think this has anything to do with the transmission type.

VStella & C5Xtasy,
Both of your examples have the x/h-pipe up front where the pressure signal is the strongest. Maybe this is a clue to making them work well. HpCubed’s & mine where in the back.

Hi SeanR,
I like your x-pipe concept. It’s simple, gets good pressure transfer and looks like the flow losses should be low because the plenum is small. It’s even pretty close to Shinob’s97’s “mixing length” criteria of 7 inches. Please let us know how it works.

There is a return pressure pulse for every expansion or contraction of a duct. This is the mechanism that is at work in a tuned pipe. The strength is a function of the rate of the change. Each of your pipes feeding the plenum sees a 2-to-1 expansion at the entry. This will act like a header collector and return a pulse back upstream. You could use simple acoustic theory to estimate when the pulse reaches the exhaust valves (t = L/a) but it really is a complicated system that, for most of us, requires a test to evaluate the effect.

So, to answer your questions: I would call your x-pipe a “plenum” type, subspecies minimum volume. I do not know how to make it better. Testing may give you some insight as to how to make a model “B” for improved performance. I think this is a very interesting variation. Please publish your results.

Good luck,
Steve
:seeya
On resizing pictures. Do you have Microsoft Office? It comes with Photo Editor but it is not automatically loaded. Or, you could do a search on one of the many freeware web sites.


[Modified by SNW Vette, 4:40 PM 2/15/2002]

 

SNW Vette,

Thanks for your input :)

The pic shows the 'real thing'. I'm running without cats so the x-pipe flanges is bolted directly to the headers. I will rebuild this to the next summer to be able to use metallic race cats between the x-pipe and the muffler. I would say it's difficult to make any before/after dynos :(

Yes I know, I have not bothered to polish the X :D



:cheers:


[Modified by seanr, 11:16 PM 2/15/2002]

 

SNW Vette, The point I was trying to make is that all of the A4 cars have this shape curve. Here is an example of three diffenet A4 cars to sho how similar the curves are.



Here is another that shows two x-pipe cars.... Mine with a Bassani x pipe, and DougM's with a Magnaflow x pipe. Compare these to the shape of one of my stock runs.



The point I am trying to make is that the shape of the curve is changing....although the increase is minimal...there is a change in the shape of the curve.

I hope this info helps.