H-pipe vs. x-pipe vs. no cross over

The truth in this test of a 360 hp LS motor is that any cross over pipe is better than none.

Also, contrary to what many believe, the x pipe is hardly better than an h pipe and probably not worth the extra time and money in fabrication for 1.3 hp gain and basically zero torque for a mid 300 hp motor.

 

What was the base line with stock exhaust and straight pipes?

 

Straight pipe here. You'll have to watch the video. The peak torque and hp are only part of the story. There's gains from the cross pipe at lower RPMS as well.

 

Watched that last nite myself, Im pretty much done with X pipes anyway due to serviceability and divided pipes just sound better imo. Not like us big block guys need another few ftlbs , got too much as it is

 

Thanks for sharing this. We never got into to these because of the serviceability and the few I have been involved with never felt they did what they hopped for. But I will say every combination is a little different. I do feel some may see more improvement than this test provided depending on there combination. Open headers work great.

 

Good points. Thank you.

 

One thing I don't like about x-pipes that you can't tuck the exhaust like you can with straight pipes or an H-pipe. You can't simply swivel them up,because the joints are at 45's. Those who have done both would understand. When I ran my 3" Torque Tech,I installed an H right after the collectors. I was able to make that whole system disappear under the car. I can't do that with an X. I am now changing to a 3.5" system,and I can still tuck it,but not if I run the X. I may need to fab a 3.5" H,or just run neither. A properly built and tuned header,with the correct primaries,lengths,and collector,will produce greater results. It's not necessarily just large primaries. Yes,you can get some production-built 2" headers that will breath well and make power,but sometimes there is still more left in the table. One of my sets of custom headers has 4 steps. 1 7/8" to 2" to 2 1/8" to 2 1/4" into a 4" can,tapered to a 3.5" collector. Those headers increased my HP & TQ 30-40 over the production 2" headers. I did this with engine dyno pulls as well as chassis dyno pulls,but the same 3" full exhaust stayed on there. It's no different that any other performance part. Everything needs to be hand-picked for maximum results.

 

I do not like the sound of an X. Too rapsy and "blatty" for my tastes, like a 6 cyl UPS truck. H sounds lower and deeper.

From wave tuning theory (or pipe organs), the H halves the frequency (makes it lower), compared to plain dual exh.

 

it's a lot of money for a small horsepower gain. use that money elsewhere.

 

Jim Hand did extensive testing on his test vehicle with crossovers. So, like the video, limited variability in testing conditions. His takeaways for Pontiac engines are here:

http://www.pontiacstreetperformance.com/psp/exhaust2.html

http://www.pontiacstreetperformance.com/psp/exhaust3.html

 

Interesting article. So many variables at a track between runs and throughout the day. How many runs did they do with each setup? And when did they test the next exhaust? Unless there are huge differences, you could never really statistically separate this all out.

 

Are H pipes supposed to be that long?
I wonder what the results would have been with an H pipe 1/3 the length of what they used.

 

Mr. Hand did hundreds of runs(probably better to say thousands) with that vehicle and carefully documented each and every change, track and weather conditions, etc. So, I think among the Pontiac community, most take his comments on what affects performance at face value. There are still several Pontiac engine builders who stick pretty close to his recommendations when it comes to using factory cast iron parts.

I did have his book for a while, I bought it for $20, someone offered me $75 after it went out of print and so I sold it. Now, if someone would offer me 3.75 times what I have in one of my Firebirds, but that's another story. I would add that he was very liberal with his charts. Very minute differences(tenths or hundredths of a second even) would be blown up to look like major differences. And we know they aren't.

Another comment I would make is that the other work I've seen done with cross overs shows while only making very minor improvements tend to have them over the entire rpm range. As was noted on the video there is some tuning that can be done location wise. A few people I've read said that you can feel a difference in the air flow by using pipes of different lengths and measuring temperature/air flow at exit. I don't recall at what point you were supposed to locate the X/H pipe in that flow, but they did claim a difference. Likely that point would be different on any given vehicle based on the bends/size of pipe/engine power(i.e. airflow) of that particular engine. And of course the underside of the vehicle would impact that cross over location.

 

My thoughts exactly. Look at the new GT 350R. Makes 526 horse and only 429 torque but it makes for a great balance on an actual street car. My tires will never hold the torque my BBB will make on the street when I hammer it. Learning how to get that thing to launch should be fun.

 

Exhaust systems using headers don't need crossovers, since the vast majority of the pulse gathering effect is happening inside the headers themselves.
Exhaust systems using manifolds need all the help they can get.
Exhaust pipe size relative to power output is also important.

 

For those of you who wish to squeeze every ounce of power out of your machine and still maintain good ground clearance (or clearance for merging) , perhaps oval tubing is the answer.

You can get mandrel bends of all kinds with oval tubing.

Here are a couple of charts I snagged off the internet to be used as reference tools for calculating custom exhaust configurations:

 

I would like to see numbers for tail pipe location. Some like the extensions that stick out past the bumper, some hack em off just past the muffler. the main thing I think abuot the X pipe is it is quieter.

 

The functional point of an "X" or "H" pipe is that each exhaust pulse can squeeze through BOTH mufflers. Given a large enough/low restriction crossover (either X or H) you could almost double the muffler volume. Most crossovers have some resistance to flow, so in practice I suppose it's like having ~150% of the normal muffler volume.

Additional muffler volume makes the total exhaust restriction less. It's also reducing the noise, and changing the pitch/tempo to something that sounds quieter to people than it actually is--a nice acoustical trick.





The same sort of "sharing" goes on, on the intake side. A fully-divided intake manifold forces each cylinder to run from half the carburetor. An open plenum allows each cylinder to draw from the entire carb. A two-plane intake manifold with the divider cut down is analogous to n "X" or "H" pipe, where there's some amount of restriction in the communication between planes of the manifold.

 

Test the numbers on your own car for tailpipe location.
Sensitive Magnahelic type vacuum gauges are all over the web.
Talked about decades ago for high speed circle track racing.

 

Very tough to use a dyno to test things at part throttle without some sort of standard protocol or use generic or invalid engine parameters and have any sort of conclusion.
It's as silly as saying, "On a chevy..." or "on a Pontiac".
As it's already been addressed, borrowing engineering from other areas of use do require some thought into how it would fit the overall paradigm of your own build.