I have ran both, they definitely change the sound, both with different in that regard. I am thinking an H pipe as the sound is good as is a tiny bit quieter will be fine. Will there actually be any noticeable gains on a 400 HP motor? I have 1 3/4" primary tube stainless headers into dual 2.5" cats then dual 2.5" stainless pipes into dual Flowmaster FX stainless mufflers into 2.5" dual tail pipes out the back. I found a reasonable source for the stainless H Pipe and will go with Amazon stainless U bolt clamps. I can probably get them within the 18" that supposedly is most effective.

 

Right from Hedmann, who makes both;
H pipe typically improves power below previous peak, X pipe improves power above it.
I like the sound of the X pipe more, but that’s just me.

 

To me neither are worth the hassle. Yep, dyno test show some gain, but not enough to be worth it. I've never seen an x-pipe that fit good and sat tight. Its a case of keeping up with the jones's. Total PITA if the trans needs to be pulled other work needs done.

 

If you have a mig welder, skip the U-bolts and buy V-bands. Stainless welds really easily with a mig and the V-bands make install/ removal super easy with a better seal than U-bolts or band clamps. The first time you need to pull the exhaust you will be happy you did it.

 

It is true, it does make servicing everything harder. The H pipe is probably more for my goals, maximizing low end power. I would have to get my Daughter's boyfriend to weld on the nice V band clamps.

 

I agree totally.

jerry

 

The H pipe actually should fit nicely right at the double hump cross member. The pipes are less than 2 feet apart there. I shouldn't have to touch the 4L80E, U joints or the Type O 12 bolt for years. I may try the lap joint stainless band clamps to hold the H pipe in place.

 

I put an X pipe in my 71 98 with Hedman headers. It fits great, there's plenty of room behind the transmission.

 

I really liked my 88 with the X pipe. My 70 was either too loud or too quiet when I had the X pipe. I ordered the H pipe, like the down low gain. I am running big 200cc port aluminum heads, mild 2100 stall 4L80E and 3.08 gear. I plan on swapping the 28" tall 275/60R15 to a 225/70R14 Radial TA or maybe 27×8.5 R14 General Grabber RWL A/T tires on the 14x6 aluminum rims😃.

 

Perfect, should be right in line with your racing preference. Seeing that you are a 1/8 mile guy.

 

If you do turndowns in front of the axle with slip fit or v-bands at the headers, it's super serviceable. The headers hold up the front with hangers in the back. I gave up the X for overdrive. I like the way they sound under load.

 

I wish our local track didn't shut down, first year I had my 70S, why I never raced it. I would have ran the Challenger too, I remember someone running in the mid 10's with new Camaro. I laughed my *** off seeing that time. Betting my heavy, V6 AWD Challenger would have been a full second faster in the 1/8. Also this motor should be really strong in the mid range, probably won't be much stronger down low than it was.

 

Full 2.5" tail pipes out the back. Should be easy to install it at the front U joint in the crossmember humps. My exhaust is full length 1 3/4" Chinese stainless headers, dual stainless cats with 02 bungs built in, dual 2.5" 304 pipes about 3 ft long into straight through dual 2.5" Flowmaster FX stainless into aluminized local bent 2.
5" crimp bent tail pipes. For the price, I should have bought the Flowmaster stainless pair of tail pipes.

 

Any noticeable performance improvement?

 

No, there was no change on the butt-dyno. It did change the sound some, but headers and Thrush glass packs make for a pretty loud exhaust note. I've actually considered changing to Dynomax turbo mufflers.

 

I just saw an Engine Masters episode dealing with this performance question. The quick answer is an approximate 4 ft/lb increase and no change in HP were seen on the dyno for a 360 hp motor.

 

I just had an H-pipe install on my car with 375 sbo stroker. I have Hooker headers, dual 2-1/2" race cats, 20" long DynoMax SuperTrubo mufflers and a pair of resonators in the tailpipes; I know, it's complicated. Before the H-pipe the exhaust note was loud with a sharp, "poppy" sound; with the H-pipe the "poppy-ness" is gone and the exhaust has a more mellow rumble. It still gets pretty loud when I step on the gas but overall I think it improved the sound. No noticeable change in throttle response or perceived power.

Rodney

 

Yeah, that is how I remember the last time I ran a H pipe.

 

My butt dyno (and the tach) notice reduced power with tailpipes, even 3 in.

 

4 ft/lbs on a chassis dyno is not a measureable gain. Way too many variables will gain or lose that without even popping the hood.

 

Yeah and mine aren't mandrel bent, which hurts even more. Either way the exhaust tone will change with no crossover and a roller cam. The H pipe is basically to maximize scavenging for my system as is.

 

One more variation for serviceability with X or H pipe. Longer term, with stainless pipes, only the mufflers are apt to rust out, so this makes each segment of the system convenient to R&I, or replace. Similar to V bands, just different.

 

I always used an H pipe to eliminate the drone.

 

It was surprising to me that after adding the H-pipe my system actually picked up a bit more drone above 2000 rpm than it had before the H-pipe. It's very minimal but I didn't expect this.

Rodney

 

the TQ increase was greater than 4 down lower..the difference at peak TQ was only 4. look at the graph… it looks more like 6 to 8 at 3800

the crossover made more TQ right from the start through 4300 the whole average TQ was better

 

That what I thought, closing in on 10 ft-lbs of torque is significant. Either way, an easy add in and will be done.

 

all gains are incremental..wether it’s exhaust, ignition system, tuning or anything else. never discount any gains, especially when they’re over a wide rpm range.
then you multiply those gains by the TQ converter stall ratio X the gear ratios in the trans X the rear ratio…that 6 or 8 from the hit to 4700 is way more actual TQ at the wheel.

 

Yes, all gains make a difference. My Quadrajet is fully tuned with an AEM wideband, high 12's WOT, 14's idle, 15's part throttle. Very easy to change the tune as needed. l plan on running 40 total timing plus vacuum advance on 91 non ethanol. Will try to bring it all in as early as possible. Mark made max power with basically the same compression but more cam at 40 degrees. Going with a bit shorter tire as well, either 26.5" or 27" vs the current 28" height. My lowest goal for the head and cam swap is the same low end performance with much stronger mid/higher rpm performance. Another huge bonus from these new heads should be, no pinging. It only did it here and there in just the right conditions. I will take a nice gain throughout the rpm range, especially down low, which this H pipe should provide.

 

hopefully you’ll get it to the track to get some real numbers.

 

It would be nice, would tell me what the actual power output is or at least a better ball park figure. Pretty sure the closest track is 4 hours away in Saskatoon now, a long ways to go. I still have Mickey Thompson ET Street bias ply 26×10.5-15. I have the snell rated helmet as well. Unfortunately both are probably aged out, it would depend on the inspectors. I would be a leisurely cruise at under 2500 rpm, I may consider it.

 

Thanks for posting that dyno plot. Area under the curve(s) indicate the gain is lot more significant than one value delta (4lb-ft) at a distinct speed.
I run an H-pipe on my 442 and have for years. I prefer it over the 'X' style but either one is better than no cross-over.

 

Back in the day when I built the 64 F-85, I went with 3 inch mandrel all the way with Flowmaster 44's . I got a great deal on the exhaust system at the time or I would have purchased the 2.5 inch. Turn downs were right behind the rear wheels. Wasn't looking for any performance gains..

 

What about a Z pipe?

 

Hmm, the Z pipe is interesting. One thing mentioned on the G body site that makes sense to me is to make the crossover pipe, as large as possible. I may actually make it 2.75" over the 2.5" OD duals.

 

Maybe I missed it in the video with the Z pipe. They picked up 30 odd hp but they also removed the cats. I would like to see the Z pipe with the cats for an apples to apples comparison.

 

I have a 3” Hooker complete dual stainless system going on my 84 H/O . I’ve used two of these Hooker G body systems before....they sound absolutely fantastic and fit perfect.

all hung with rubber hangers and stainless band clamps come with it . Polished straight through mufflers with sound packing insulation. The X crossover is just a big open chamber,,not like the typical X style
I’ll post pics later.. the 3” system is a few hundred dollars less than the 2.5”

 

That is what I am getting at, to be clear, keep my 2.5" exhaust system and just enlarge the crossover section between the two H's to 2.75". Then added into the existing 2.5" exhaust pipes.

 

So my 304 Staunless H pipe pieces showed up, they look really nice. Unfortunately they are all 2.5" OD, not ID like I hoped for the H pipe pieces. It didn't say and not the end of the world. I ordered 6 of the much more expensive but should better and firmer, 2 layer 2.5" butt joint stainless 304 band clamps. Should be here next week.

 

So measured and cut with my Milwaukee reciprocating saw with new Dewalt 6" blades. I used my impact and my tail pipe expander on all the pipes to get as good a seal as possible.

 

You have 10 clamps in 2' of pipe work. I'm not busting your chops but you might get some of that welded.