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View Full Version : Differences between an X and H pipe



benoit
07-09-2006, 08:36 AM
I've pretty much narrowed my exhaust system down to a LT headers, 3 inch pipe with dynomax ultra flo welded mufflers and some type of cross over pipe.

my question is should I go with an X pipe or H pipe and what are the characteristics of both?

Thanks!

BADVELLE
07-09-2006, 10:32 AM
I always look at this question in the form of exhaust flow/equalization. I always lean towards the "X" pipe design due to ease of exhaust transmission. Both of these pipes are working to equalize the exhaust flow through the system, with a "H" design, there is no smooth transition between the two pipes.

chicane67
07-09-2006, 12:24 PM
How about a primitive, hacker, stick figure picture ??

The only challenge's to this is the execution and packaging. But, the basic 'X' does much better than a standard 'H' any day of the week.

Blown353
07-09-2006, 04:17 PM
For the original question: X from a performance standpoint, definately, but there are always those with mixed opinions on the sound they produce. I for one love the higher pitched and smoother wail an X system puts out but some don't like it and miss the lower-pitched "grumble" that an H-crossover puts out (which admittedly is more tame and smooth than a straight-dual setup.)


How about a primitive, hacker, stick figure picture ??

The only challenge's to this is the execution and packaging. But, the basic 'X' does much better than a standard 'H' any day of the week.

That is very intriguing. How does the "true" X compare both in sound and HP/TQ gains (estimation only obviously) to the "abbreviated" X that everyone sells/runs?

I can see why vendors only sell the partial-X since it's cheaper and simpler to fab & install-- would adding the additional piping around both legs of the X be worth the efforts? I have plenty of room and it wouldn't be hard to mod my current system by adding the 2 pipes around my Dr. Gas X junction.

chicane67
07-09-2006, 06:22 PM
I found the sound quality to be of my own liking. It has a lower, more subdued idle and the higher pitched wail under loaded RPM. It was experimented with until the results were reached to tone down high HP cars. We were trying to tone down the system so that you didnt stick out like a sore thumb to the local 5 oh's. It was quite at idle and very punctual off of that. Mind you that the muffler used were 'experimental' FlowMasters of their 3-chamber race family... which became their DeltaFlow models some 10 years later.

My estimation of values between the true and abbreviated X ?? I am sure they will be a lot closer than that over a comparison to an H system. I too think that it will have more of a sound signature change than that of a huge hp/tq number change.

Adding tubing to the existing X in your system might not gain you what you might think. The additional (for lack of better words) "plenum volume" I think will be too much. I have found that the 'X volume' is actually pretty critical to CID. If it is too large it will slow the gas speed down and hurt scavenging.... to small and it will increase pressure too much.

The 'true' X was designed and built by the very same gentleman that designed and sold the 'abbreviated' X rights to Dr.Gas. After a few years of system testing (instrumented pressure, temperature and sound) the true X is what we ended up with. Since then (1987-1988) some things have changed for the better, product-wise. I would love to do a true X with the engine/drivetrain that is going into the 67 now.... but I am more weight conscious now than ever. Plus I just want something simplified.... because a 3.5" system is a little tougher to build.

Blown353
07-09-2006, 08:29 PM
Very good point about proper sizing and crossover volume to maintain velocity, too big can definately hurt things.

I'm intrigued enough to experiment. For a bit of info, my current system is 1.75" primary hooker super comps (3" collector) to a 3" Dr. Gas X, back into Ultraflows, then 2.5" tailpipes out the back. Probably smaller than optimal for my engine when "on boost" but like anything it's a series of compromises based on packaging, cost, what's available, and my own skills.

If I were to experiment my plan was to cut in and fit additional 3" pipe around the X and the way my bends are it would be almost a straight shot. Based on your educated guess... would it be worth trying? Is there a certain "plenum" volume you feel would be too big? I can make a pretty good approximation of what the volume of the piping and X would be between the bypasses.

On a similar note, what do you think about MAC's "Pro Chamber"? It seems to be a big open box that both sides dump into with two outlets. Wondering what your opinion is on it. Not looking to necessarily try it, just wondering what you think.

Linky: http://www.macperformance.com/store/product1.cfm?SID=3&Product_ID=30

redss86
07-12-2006, 07:47 AM
This would be interesting to learn more about. I hope to see more info on this setup. One problem I might have doing this is fittin it into the confined room/space I have available for exhaust. Wouldn't you have to run this setup on a full exhaust system all the way out the rear? I probably wouldn't work properly on a setup that exits infront of the rear tires, would it?

chicane67
07-12-2006, 07:21 PM
Give me a day or so..... cuz I need to sit down and write an intelligent answer..... and my schedule isnt supporting that time right now.

redss86
07-18-2006, 06:32 PM
Any thoughts yet?

Blown353
07-22-2006, 04:37 PM
Report back soon... I couldn't stand it anymore and decided to plow ahead.

This afternoon I cut and fit the new "bypass" pipes around the X, going to cut out the main exhaust tomorrow and weld the bypasses in. I'll let you know how it turns out. Wanted the bypasses to extend aft a bit more to reduce the angle they merge back in, but I'm limited by floorpan clearance back there.

Teaser pic:

https://static1.pt-content.com/images/noimg.gif

Blown353
07-23-2006, 01:31 PM
Finished.

Initial thoughts/observations:

- Idle tone / free rev tone & volume behind the car pretty much unchanged from before with just the standard X (meaning I really like it.)

-Interior noise at idle, light acceleration, and cruise quieter by a very noticeable amount and the overall sound that you still hear inside is smoother. This is a BIG plus, reduced interior noise is good IMO. I used to have a little "noise peak" / resonance about 2000-2100 rpm at steady cruise, it's still there but SUBSTANTIALLY reduced in volume now and the tone of it has changed to a less irritating note. It wasn't horrible before but it's much improved now.

Don't have any impressions yet of how it sounds when beating on it either from inside or outside the car, it's 110F outside right now and I didn't get into it for fear of detonation. Once it cools down I'll do some datalogging and see if my A/F ratio has been affected any.

Unfortunately I didn't bring my digital camera to my friend's shop, but another plus is it looked way cool standing against the wall after it was done. Had a couple friends looking at it and scratching their heads. :razz: It does take some time to cut, fit, and blend all the piping to have nice smooth transitions, and the way I did it meant there was quite a bit of bead to lay down, my approach is definately not ideal from a fab standpoint but it was the best way to integrate it into my current system. A better way would be to bend the two main pipes from the header collectors back to the mufflers then fit in the X, much less cutting and welding to do. I probably have ~8 hours in the job total and could have done it in 6 if I had the plasma cutter yesterday, using the plasma today was much quicker than the sawzall and angle grinder yesterday...

ProStreet R/T
07-23-2006, 03:15 PM
Neat, so what you did was basically turn it into a really big straight dual setup so it can kill all the exhaust velocity.... well done.


I have a ton more to post on this from an engineering/physics perspective but no time. Will get back at it tonight.

Blown353
07-23-2006, 04:42 PM
Neat, so what you did was basically turn it into a really big straight dual setup so it can kill all the exhaust velocity.... well done.

Whoa, I think my sarcasm detector is vibrating. Yep, sure is.

If you had posted only a couple hours earlier I would have stopped and waited to hear back from you, but oh well. Live and learn. I did it anyways.

I'm sure the velocity is substantially decreased (which obviously isn't good from just about any perspective) and I knew this going in. Tom alluded to this earlier (i.e. the total volume of the X and the pipes leading to it from the main pipes is important based on engine CID and he thought my "plenum" volume would be too large.) I was hoping he would chime back in with some numbers and a target volume to shoot before I plowed ahead but I got impatient and bored... so I had to try it.

I can always re-do it later, aluminized pipe is cheap and the Dr. Gas X junction can be very easily removed and salvaged. Until then I'll drive it for a bit and see what happens.

I'm sure things are stagnating at light load which does absolutely nothing for scavenging, but under wide open and full boost things probably aren't too bad (I could very well be mistaken here, exhaust design is not my forte!) Also, my cam has minimal overlap (supercharger oriented grind on 114 LSA, I remember the overlap being 20 degrees or so @ .050) so that probably lessens the negative impact of my modifications.

Still, gave me something to do yesterday afternoon and this morning.


I have a ton more to post on this from an engineering/physics perspective but no time. Will get back at it tonight.

I am really looking forward to what you have to say, honestly. Hopefully Tom will jump back in if he gets a free moment and bash my experiment too. :hand: Bash away guys, I'm all ears. Seriously. Hopefully I'll learn something! Probably should have picked up a book before the welder. LOL!

ProStreet R/T
07-24-2006, 11:44 AM
haha yeah that should have thrown the sarcasm meter right into the red zone.

Ok let me see if I can explain this so it can be understood without giving everyone a headache.

The principle behind an X-pipe is to help the left/right pulses scavenge each other, and with that balance try to retain as much velocity as possible.

See you can't think of exhaust flow like water coming out of a hose. Everything is in pulses, and on a V8 alternating pulses in the R and L banks. Now on my viper for instance it wouldn't do much of anything as it has paired cylinders firing on the L & R banks, also why they sound kinda funky given their displacement.

So basically when the exhaust pulse from one header comes down the pipe and hits the X, it doesn't just cross sides and run on it's marry way out the tail pipe. That single pulse is somewhat split between the two pipes where they cross. Now normally doubling the volume would kill the velocity and such but with how the pulses merge it's not the case.

H pipes work in a similar fashion but to a much lower degree as the pulse transitions between the two tubes is minimal. Personally I feel H pipes are a waste of time, either keep everything separate or run a nice X.



Also why run 3" collectors into 2 1/2" pipes? Run 3" all the way out with a decent set of mufflers and it will sound great. If you want to change the tone do it with the muffler. I've been pretty pleased with the stainless magnaflow straight-thru stuff. Nice and quiet till you really stand on it. Or just use the ultimate muffler, a Turbo :headbang:

Blown353
07-24-2006, 05:20 PM
haha yeah that should have thrown the sarcasm meter right into the red zone.

Ok let me see if I can explain this so it can be understood without giving everyone a headache.

I thought you'd like the sarcasm detector comment. LOL!

And... I *WANT* a headache! Looking for good books now. I've read serveral EAA papers on aircraft exhaust and collector design (dB readings, wave speed & pressure, overall backpressure, BSFC numbers, temperature & altitude effects, adustable megaphone collectors to maintain scavenging as altitude increases, etc) and that's what I really want. I'm an engineer, I like painful reading, although sometimes I put the fab work before the research :jump:

Good info you posted but it's too "topical"; I understand the "fluff" and general theory behind the X pipe, looking for more of the hardcore "exactly why it works with numbers to prove it" kind of stuff.

Tom earlier alluded to the standard X we all see (and what I was running before) is actually the simplified version and what I have changed to is the REAL version (although my "retrofit" is probably far from ideal and is hurting velocity too much because of excessive crossover volume and increased sizing/x-sectional area at the transitions slowing the velocity.)

Don't know if you were referring to me or not, but I'm not running 3" collectors into 2.5" pipe. System is 1.75" primaries, 4 into 1 collectors, 3" collectors into 3" tubing all the way back to 3" Dynomax Ultraflos, then 2.5" mandrel bent tailpipes out the back. I could definately benefit from a purpose-built tri-y setup with merge collectors (as nearly everyone else could who is not running them) but that's not an expenditure I have in mind at the moment.

Let's keep this going, this is fun.

I'm convinced that 99% of the "hot rods" out there don't have too much actual design work put into the exhaust. We buy what headers are on the shelf and are known to fit, buy what mufflers we like the sound of on other people's cars then connect the components with piping. I want to go beyond that and want to know what is required to do it correctly. I never intend to be an expert in this field (that's what guys with PhD's in fluid mechanics and acoustics are for) but I'd at least like to know enough to point myself in the right direction and then run it by some experts.


Or just use the ultimate muffler, a Turbo

That's still "on the list." The Procharger, while nice, is just a layover on the trip to TurboTown. Those neat little spinning mufflers also make the exhaust design downstream of the wheel much, much simpler. LOL!

ProStreet R/T
07-25-2006, 07:55 AM
Ahh I should have looked at your profile, I get so used to people getting a preverbial deer in the headlights look when I try to explain some of this stuff, it's just habit to dumb it down.

I don't have any hard core (SAEish) data on the X/H pipe data but let me see what I can dig up.

You're pretty much correct, 99% of all cars have pretty pathetic exhaust systems. It's amazing that most will drop crazy $$$ building the car and use some lame generic headers.

At the same time i've kinda stumbled on some info that really made me think. A certain super stock racer is running a pretty generic small block mopar, production heads, normal rpm, 360ci, but using 2" primaries :screwy: Turns out going from 1 3/4 picked up .15 and 3mph in the 1/4. It really doesn't make a whole lot of sense, given the engine size/rpm/compression, those SHOULD be detrimentally big. I know mopars like a lot of breathing room but SHEESH.

hahaha yeah after the little wheel it does get a whole lot easier. Just run a 5" pipe off each turbine and out the side sills. At least thats how i'm doing it :evil:

Skip Fix
07-29-2006, 08:53 AM
From my personal experience on my high 10s TA a 3" Dr. Gas X system into welded Ultraflows and tailpipes ran the same as open headers with no exhaust system on the car (ie about 50-70 lbs). A 3" H pipe with 2 chamber loud a$$ resonating Flowmasters was about .2-.3 slower uncorked WITH the tailpipes and mufflers still on the car. So I'm a firm believer in an X pipe for sounds and performance. I'm too old for open headers. It's nice and quiet when they see my taillights!

DeltaT
07-30-2006, 04:55 PM
I hate the Flowmaster hi-freq 'ringing' and their resonation, but have always had excellent results with their products. In this latest iteration of my sleeper's drivetrain, I modified some Hedman 1 3/4" Huslers (lowered the bolt holes .2" to deal with my raised exhaust ports, a little clearancing, Jet-Hot) and ran them into a dual 3" Torque Tech exhaust with 3" Flowmaster Deltaflow 50's, and 3" tailpipes that exit behind the rear wheels.

To deal with the ringing and resonance, I added Summit's 3" crossover H-pipe, which quieted down the car inside and out.
I wrapped the Flowmasters in Longacre Racing's HD aluminum backed ceramic batting. The seams are at the bottom for moisture drainage. Then I wrapped over it with Thermo-Tec's black header wrap:

https://static1.pt-content.com/images/pt/2006/07/4dr_exhaust_tackedthrumufflers_071604-1.jpg


Then I wrapped the system the same way:

https://static1.pt-content.com/images/noimg.gif


And added the header wrap to the system:

https://static1.pt-content.com/images/noimg.gif

Now the sound that comes out the tailpipes is pure, lo-freq rumble, until I really get on it, then the system wails!

I know from testing and reading - David Vizard did a lot of testing on H-pipes - and my own experience, that the H-pipe does help with sound reduction and usually adds some torque. I haven't tried an X-pipe yet. I wanted the removable H-pipe for servicing reasons.

Good thread!

Jim

My Site: http://home.mindspring.com/~jim_fisk/id1.html

chicane67
07-31-2006, 01:36 AM
First of all, Jim..... that is one f 'in baddass sleeper. :headbang:

Sorry it took me so long to get back to this. Nice job on the fab side of things.... by the way. No bashing required either. Cuz ya never know, until you experiment and try things.

Thoughts... since you have a procharged small block with 3" tubes, 2.5" tails and the noted LSA, I dont think it killed anything. With the 2.5" tails acting on the system as a convergent duct, it will evacuate the system better, even if the overall volume of the X is a little bigger than optimal. The only way I can sorta tell if the system is close physically, is if you were to feel the exhaust as it comes out of the tail pipe with your hand. It should feel like it is just falling out of the pipe and have near, no pulse to the gas movement. Another thing to observe is when you cover one outlet with your hand, it should not push your hand off. These were things that we noticed during our development.

The only way to really tell you what is actually going on would be to instrument test points and take measurements. Its not to hard to pull off. A gaseous k-type thermocouple, a simple guage and some welded fittings or (the prefered) press fit pressure taps and some spagetti tubing.

Funny you would bring up the MAC pro chamber, it is very much like something I got to play with years ago. While working for Guldstrand, I did some development work with flowmaster in the early 90's on their ZR-1 system. The factory exhaust system utilized a 'resonator' and flowmaster basically made one up with the same technology as their mufflers. I'll tell you what, if I could fit one of those into my exhaust system, I wouldnt think twice about it. It sounded totally bad@ss. You can see the resonator they came up with in this picture (http://www.flowmastermufflers.com/products/images/17115_ztn.jpg) the only real difference is its size compared to the MAC unit.

In this picture (http://www.t56kit.com/projects/simmons/28.jpg) you can see the what we finally came up with for the engine package being used. Its kinda similar to your end result considering the amount of tubing used.

I guess you like the same abusive reading material that I do. I wish I could just whip up some PDF's of some of the stuff I have, but some of the engineering reports are a little page heavy. I have an aero/thermal back ground in gas turbine engine R&D.... so I have a whole bunch of dry, PhD speak, math heavy material for those days I really feel like I need a nose bleed. I dont know if you have run across these tech articles yet, but there its a good read: burnsstainless (http://www.burnsstainless.com/TechArticles/Theory/theory.html)

This can give you an idea into how the rod ratio can effect things: stahlheaders (http://www.stahlheaders.com/Lit_Rod%20Length.htm)

I have some great stuff on advanced combustion, power and thermal cycle optimization, developments in hi temp materials and coating tech advancements..... but I have no idea on how to get this much material into something I could link or send at a moments notice. I guess that will be another project to add to the list.

Id say the next thing to read up on would be wave theory, engine cycle analysis, material selection and T.B. Coating's with the intent on a better understanding of enthalpy..... and maybe something to brush up on the effects of temperature and pressure when dealing with mean gaseous flow...... and maybe something on pressure vessel dynamics on top of that.

Blown353
08-14-2006, 11:20 AM
Tom, thanks for getting back and as usual more good info. Time to start doing some research on my own when things slow down a bit anyways, it's been crazy between normal work and after-hours work-- I've been doing a lot of EFI work lately for other people and haven't had much time for my own stuff.

After all was said and done I still think the "experiment" was worthwhile as I really like the reduced SPL of the exhaust. I'll do the generic "hand test" of the exhaust flow soon, maybe by taping a piece of paper to the bumper to swing in front of the exhaust tip as that will easily demonstrate either linear or pulsating flow. I'll try more in-depth instrumented testing if/when I can borrow the data acquisition stuff and transducers/tc's from our lab here at work.

I am due for a muffler change though, I was stop drilling some cracks in one of my Ultraflo's yesterday and even though I poked the drill about 3" into the cases I didn't get ANY packing out on the drill bit. Nothing at all. Couldn't fish any out with a small hook either and I couldn't see any left in the cases. When I change the mufflers (probably going to 18" case Magnaflows with Flowmaster taper reducers on the back of them) I'll hack apart my Ultraflos and see how much (if any) packing is still left in them. The lack of packing would probably explain why my mufflers have become real "poppy" over the last year.

And Jim, if you want to do an X-pipe I suggest you put flanges or v-bands in front of your mufflers, that way you can drop out the entire exhaust from the header collectors all the way back to the mufflers. Makes tranny work a piece of cake!

paul67
08-14-2006, 12:20 PM
What hedders are you running 4-1 or 4-2-1 as the 4-2-1 is better for the getting the pulse out but must be set to the firing order of the engine.

Blown353
08-18-2006, 10:58 PM
Yay, all done with new mufflers (18" Magnaflows)

https://static1.pt-content.com/images/noimg.gif

Final result is rather "docile" sounding at cruise... in fact, it's very very quiet. Just what I wanted. It will still chirp car alarms when idling by but the idle volume is very reasonable and so is light/medium acceleration rates around town. WOT is very smooth sounding and still has the trademark X-pipe wail to it but the volume level is much quieter than you would expect given the HP in front of it.

Very, very happy with the end result. Glad I went out on a limb this time. Tom, you're a bad influence.

My friend who owns the muffler shop was cursing me today when I brought the car in to install the new mufflers. He threatened to beat me if anyone else saw my exhaust and came to them asking for a similar setup. I bought the 3" tube a while back and I told them it was for a "project"-- and there were all dumbfounded today when they saw what I did with it. LOL.

Interesting point of data... with no other changes besides the exhaust (true X and new Magnaflows) while doing some datalogging in very similar ambient conditions to previous datalogs with the old exhaust setup (standard X and the smaller Ultraflo's) the engine is now running 5% leaner according to the wideband from 4200-6600 rpm under WOT-- so something is definately working right. I did several passes last night to make sure it wasn't a fluke and the A/F changes repeated every pull.