So, I finally bought some long tube headers and high flow cats.

Many years ago, I purchased some JBA shorty headers because my stock manifolds were very rusted and I had several bolts that had broken off at the head. I got a smoking deal on some “titanium, ceramic coated” shorty headers and bought them. I couldn’t afford long-tubes, so, I just went for the shorty headers.

Fast forward to “sometime in 2020” and I started hearing a loud banging/rattling/quasi-dinging metal on metal sound. It would come and go. I made a few feeble attempts to figure it out and nothing.

Well, about a month ago I started up the H2 and the sound was very pronounced and consistent. No longer a random, or intermittent type thing. So, i devoted an afternoon to figuring out the source of the noise.

Turns out, my passenger side cat was broken. The interior guts had cracked and were rattling all sorts of crazy!

After some substantial research on catalytic converters and their cost, I began to consider some long tube headers WITH catalytic converters.

I purchased a set made by Dynatech. A set of headers along with matching high flow cats. Their cats only mount up to their own long tube headers. All stainless and with the O2 sensor bungs to maintain some degree of factory setup.

Observations:
The drive is NIGHT AND DAY!!! Just the way the H2 responds to gas peddle input is totally different. More instant/rapid; a lot more obvious; the H2 doesn’t grunt nearly as much...I can actually hear/feel the engine breathe soooo much better that the acceleration delivery is noticeably different.

I don’t hammer my H2 with the gas peddle, after all it’s a 3 ton refrigerator on wheels....mine has a 6” lift with 38” tires....not a “fast” vehicle by any means.

Still, after installing the headers and cats, I am just amazed at how smooth the engine and transmission work together now. I don’t feel the shifts, hardly at all. Mind you, I keep the rpms at 2,500 or less. The torque delivery is the most noticeable....I man, the thing “moves” when you press the gas vs “delayed and then moves.”

At highway speeds 65-75, the H2 no longer spends as much time in 3rd gear. It actually feels like it’s cruising vs trying to gear down to make it up small incline. Just nuts!

I didn’t do any WOT pulls or try and pass anyone. But this thing held very well at 70mph, nowhere near the sluggish nature I have grown to “accept.” H2 was always shifting back and forth between 4th and 3rs, gets to be a pain when you’re trying to relax and just drive. Tonight’s drive.....totally relaxed.

Some disclosures:
I inflated my tires to 60 PSI
I have stock muffler
Engine is remanufactured and bored .030
Transmission is a reman as well
Stock tuning
87 octane fuel
Aftermarket mesh-type air filter

Now, some questions, more of a survey type:
Anyone else experience this kind of improvement with their long tunes?

Any ever see their gas mileage improve?
mine went from 8.2-8.6mpg to 11.0mpg all while using 87 octane. I did the math by hand and got 10.8mpg, but still......long tube headers and high flow cats increasing mpg?!?!?

What PSI do you guys run? I had a patch done on a tire and the shop inflated mine to 60. After I installed the wheel, I noticed the H2 “sat up”
higher. So, I increased the PSI on the rest. H2 ride very well. I have fox shocks with reservoirs in the front and dirt logic shocks in the rear. Suspension felt great on the highway!

 

My guess is that your MPG/ Performance gains are from the new cats, I bet they flow more than the OEM cat and there is a good chance your original cats were plugged up. I bet it sounds really good with the new headers.

p.s. 60 PSI in your tires? I run 35

 

I went with a lower end brand and got the stainless OBX long tubes with high flow cats. Those connect to a full stainless GMPP (GM Performance Parts - made by Borla) cat back touring setup. Yeah, it made a significant and noticeable difference and sounds great. I did keep the stock airbox and filter as they are already a top notch cold air intake setup from the factory but I did change out the air tube for an Airaid tube. Then I did a custom tune, I did one for running 93 octane for about a year which was pretty sweet but the fuel costs got to be a bit much so I cut the timing back a few degrees so I could run 87 octane again without knocking and still very very happy with the performance although the drop from the tighter timings and 93 octane was noticeable. Prior to those I did replace the plugs with new ACDelco iridium, new wires, new knock sensors, and cleaned the MAF. When I got it I also changed it up to Amsoil synthetic oil.

Also of note - the OBX high flow cats are not terribly effective. The exhaust is a bit smelly and l got a check engine code so I had to reduce the downstream O2 sensor ratios in the tune (not a big deal for me since I have a full EFILive which lets me tweak things as much as I want). I have a 2" lift and run 37x13.5 (Cooper STT Pro mud tires) and currently have been running them at about 44psi. I need to do a patch test to get my ideal pressure though. I'm sure higher would help economy a bit but at the expense of ride quality and of course the contact patch is really what will determine the ideal pressure be it higher or lower. Prior to the tuneup and exhaust I was averaging around 9.8mpg and now overall average around town about 11.2mpg so yeah I did get a bit of a boost in economy. I attribute that to all of the work though, not just the exhaust.

Shorty headers, generally speaking, offer little to no performance increases over the stock manifolds. About the only use for them is if the price is right and the stock manifolds are cracked and you dont want to bother with long tubes. Good choice on going with full long tubes!

If your stock cats were rattling it is possible they were also getting restricted flow from their age which can severely degrade performance and economy so some of your economy gains are probably due to those just needing replaced anyways.

 

how did you like the JBA shorty headers? how have they held up? was it a direct swap? i have your original issue. manifolds are cracked as well as a few studs. looking for replacements but do not want to purchase new jba shorty's as they cost practically the same as long tube setup

 

Dynatech cats have 349cfm of flow vs stock has 257cfm.

I would have never imagined such a change in economy!

psi is nuts, I know.....I usually run 50. I tried 35-40, but my tires are very wide...15.5” and they were waaay too grabby at the lower psi

 

After reading some of the replies, sounds like the high flow cats are the main contributors to gains.

349cfm vs 257cfm stock, considering they were 16 years old and 1 was rattling, definitely a big change. This is one of the reasons i went for the long tubes....”i need to replace both cats anyway”

 

The JBA shortys were a perfect and direct fit! Better flow than OEM, but nothing when compared to long-tubes.

Very easy to bolt up! They look good too! The ones I bought were ceramic coated and made a HUGE difference in underhood temperatures.

Mine can be reused, so, if you’re interested let me know and we can work out a deal. I can send plenty of pics to show condition.

 

sounds like a plan... i am interested. i need some any ways. i had noticed there is a difference between the California flanges and the federal emission ones. i do not know what my stock 03 ones are.

 

What year is your H2? Do you know what item # you purchased for the cats?
I just checked Dynatech's website for the headers and cats, and they show the cats are for the 6.2L. Item # 715-14320.
I have an 07 H2 and would love to upgrade to long tubes with high flow cats.

 

Highflow cats: 715-84220
long tube headers: 715-84110

Double check the arrangement of your cats. Mine split off before the muffler and are considered a 2 into 2. Two separate tubes go into muffler.

There is another style that is combined. Has a different Dynatech part number.


https://www.carid.com/dynatech/super...ification_mail