Can't breath!

[Manhattan]

my GW that is. I have detemined that my pinging problem is exhaust related. The new 360 runs great - for about 30 minutes. Then it runs like $*it! The temp gauge stays right at 190 and yet it runs like it's at 240. The gauge has been confirmed correct.

The culprit - an old cat!

So, I'm going to replace the exhaust system from the manifolds back. I don't want headers. I want dual exhaust. I'm actually going to buy two new (gulp..) catalytic converters, new mufflers and do it by the book and keep it legal.

I need help:

Will duals fit? (gas tank on drivers side)
What kind of cats should I buy?
Should I go 2.5"?
Will an "H" pipe make much difference on a stock (RV cam, 2 bbl... ) motor?
What kind of mufflers? (thinking 3-chamber Dynomax) I don't want it loud - at all, but do want the power.

Thanks!!!
Mark

[This message has been edited by Manhattan (edited September 06, 2000).]

[joe]

Mark, a plugged cat will definitely cause poor performance. Don't know about causing a pinging prob though? Problem with dual or any freer flowing exhaust is that with less restriction/back pressure the motor will run even leaner. I can't see if it's pinging now that duals will help but I really don't know. If it still does ping after the swap you may have to go to the next size bigger jets for the carb.
This dual-vs-single exhaust has recently been kicked around here and my personal vote on a "GW specific" exhaust is a single 3" system. Just for the fact it's a cleaner/easier install/routing because of the plastic fuel tank. So far as legality goes check with your state smog Nazis. In some states if the rig came with one cat and you add duals with two cats it's just as illegal than one exhaust with no cat. If it came with one cat that's all you're allowed. I know it's stupid but that's the way it is in some places. Some states don't care how you meet smog regs so long as you do it. Some require it meets the stock visual inspection also. Good luck, hope you get some other advice on this also. That was my two cents anyway and I'm off to the airport... http://www.cs.colostate.edu/~zeimet/ubb/smile.gif See you all in a couple of months.
-joe

[BobBarry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Manhattan:
my GW that is. I have detemined that my pinging problem is exhaust related. The new 360 runs great - for about 30 minutes. Then it runs like $*it! The temp gauge stays right at 190 and yet it runs like it's at 240. The gauge has been confirmed correct.

The culprit - an old cat!

So, I'm going to replace the exhaust system from the manifolds back. I don't want headers. I want dual exhaust. I'm actually going to buy two new (gulp..) catalytic converters, new mufflers and do it by the book and keep it legal.

I need help:

Will duals fit? (gas tank on drivers side)
What kind of cats should I buy?
Should I go 2.5"?
Will an "H" pipe make much difference on a stock (RV cam, 2 bbl... ) motor?
What kind of mufflers? (thinking 3-chamber Dynomax) I don't want it loud - at all, but do want the power.<HR></BLOCKQUOTE>

Others will note the possible legal difficulties of replacing one cat with two. I'd be more concerned about the physical difficulties. On a GW, it is nearly impossible to get two pipes over the rear axle, due to the track-bar bracket.

A single 3" flows more than two 2.25" pipes, and nearly as much as two 2.5" pipes. Any of those will flow more than enough to let a stock or mildly-modified 360 breathe easy with no exhaust restriction.

My GW never sees over 4000rpm; for it, a single 2.5" exhaust with high-flow cat and muffler *DRAMATICALLY* improved performance! I too had a clogged converter; replacing it made the most difference.

As for "not-too-loud", well, good luck. Even the quiestest Flowmaster will wake the whole street when you start it up in the morning. Best bet would be a 3" stock-type muffler, if you're looking for peace and quiet.

------------------
[B]Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[Manhattan]

Joe,
Thanks. The guy who is going to do the exhaust is checking on the legality of true duals on the '88 GW - it doesn't look good. He also said that doing duals into/out of one cat will not yeild much additional flow - some, but not worth the money and hassle involved with routing around the gastank.

Should I worry about the brand of Cat?

[Manhattan]

What about the brand of Cat? Where do I get a "high-flow" cat?

Thanks!
P.S. This forum is amazing! You guys have saved me countless hours of hunting for information and countless dollars in going with bad or missing information!!! - thanks

[Ralph]

Exhaust discussions are common here, and dual exhausts have been brought up a few times. The thing is, you have a big dang gas tank along the driver side of your frame, not conducive to exhaust plumbing. And you have nice factory heat shielding along the passenger side of your frame, where a singular exhaust will do all you relaly need.

The OEM exhaust system is 2.5" starting at the Y-pipe (just before the cat converter).

I don't believe dual exhaust makes that much of a difference until you get into higher rpm ranges.

As for a catalytic converter, I got a Dynomax high-flow unit from Jegs. It's commonly available from speed shops, Summit Racing, even JC Whitney. I bought Edelbrock's biggest muffler, also from Jegs; other guys have realy liked the Flowmaster D50.

[Manhattan]

Ralph,
I think I'm going to go with a 2.5" or 3" single system with a Hi-flow cat and muffler.

What does your system sound like? Are we talking stock Mustang GT loud, Chevy Z71 pickup loud or hot rod loud?

I just don't want a "hot-rod/redneck" GW, my CJ filled that order already (built 360, headers, glass-packs...)

Thanks!

[Veepster]

I just started for the first time my Thorley header, hi flow cat, Dynomax race welded muffler, all of these being 3 inch and all tubing being 3" mandrel bent aluminized.

IT SOUNDS AWESOME!!!

perfectly quiet at idle, very low tone when driving...and if you floor it...it wakes up and sound great.....I would even call it classy.

------------------
Peace.............BartG

78 Chero
360 2v, 400 QT with low
almost drivable:
4" skyjacker
33x12.50 BFG KO's
Thorley headers, 3" exhaust
Infiniti power leather seats

[Manhattan]

WHERE ARE YOU GUYS GETTING HI-FLOW CATS!?!?!?!

I have found tons of mufflers but no cats!

Any help would be great

[Veepster]

all my parts were purchased through Summit

------------------
Peace.............BartG

78 Chero
360 2v, 400 QT with low
almost drivable:
4" skyjacker
33x12.50 BFG KO's
Thorley headers, 3" exhaust
Infiniti power leather seats

[BobBarry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Manhattan:
WHERE ARE YOU GUYS GETTING HI-FLOW CATS!?!?!?!

I have found tons of mufflers but no cats!<HR></BLOCKQUOTE>

I spent the big-bucks for a Random Technology high-flow unit that bolted in place of the stock converter. See them at http://www.randomtechnology.com/ . Pricey, but well-constructed. Even with that and a Flowmaster muffler, a complete exhaust replacement on my truck cost half of what a custom-bent 3" would cost, using lower-quality parts. And I don't know if I would have had any better performance.

------------------
Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[SlickKipper]

I got my hi-flo cat from the Louisiana Muffler Mart www.lamuffler.com. (http://www.lamuffler.com.) Also got my flowmaster 70 there. The products, and company, have been good to me.



------------------
1989 GW,
K&N air filter,
Flowmaster 70 Series muff,
hi-flow cat

D'Wag (http://hometown.aol.com/hebbarts/myhomepage/photo.html)

"ahh, i love the smell of 11 year old differential oil in the morning"

[Manhattan]

SlickKipper,
How does your Wag' sound? Is it loud?

[SlickKipper]

Sounds...sheik. I highly recommend it. Loud? Nah. Just makes a fsj sound better. You certainly won't take center stage with a Flowmaster 70. If you're like me, you'll often wish it was louder, and never wish it was quieter, if you get one.

Hope that helps
-Kip