EXHAUST SYSTEM

 

Date: Wed, 29 Oct 1997 14:05:54 -0800

From: Gary Ohst <garyo#globalpac.com>

Subject: Re: GMC: Exhaust System

Gcbr#aol.com wrote:

> 2. I also want to put in a 3-inch exhaust system, any comments?

Larger diameter tubing might be better it it does not drop the exhaust gas flow speed. High gas speed provides better scavenging of the exhaust gasses. High performance motors need larger tubing due to increased rpm and gas flow capability. It's not so much back pressure that is important, but good gas flow speed. If the tubing is too large, low rpm performance will be hurt, but higher rpm performance will be increased. For a low RPM motorhome, larger tubing may not be neccessary.

Gary

 

From: "Skid" <Not_here#gte.net>

Subject: MY $.02 on the header issue...and another question!

Date: Tue, 17 Mar 1998 22:44:43 -0800

Yo!

Having had several sets of headers in my past, and particularly a longer haul experience with a full Banks kit on my last P-30 moho, believe it or not I'd tend to agree with Arch: save the $$ on the headers - just make sure that you get a superior job done on the system aft of the manifolds.

We just had to replace the original manifolds on our '76 Eleganza (a 455, but most of you know that!), and the problem was that the beautiful, almost new 3" exhaust system was only put on very recently by the previous owner. So the original manifolds had cracked on both sides, in several places. We were pleased to find out that Cinnabar still has some NOS 455 manifolds, and in spite of UPS strike (the work was done last summer), they were able to get them to us in less than 4 days.

 

Date: Wed, 18 Mar 1998 09:38:43 -0600

From: Rich and Dottie Major <bmajor#worldnet.att.net>

Subject: Re: GMC: Re: GMC Open discussion of Upgrades

Paul,

I achieved the same performance you are talking about, but without the headers. I installed Flowmaster Mufflers, an MSD ignition with a "spark box" and an open element air cleaner. The engine breathes better and all the fuel is burnt in the cylinders with the new ignition. An added benefit with the MSD is the engine now starts much easier.

I have had headers on several other cars and I would not want to install them on a motorhome. I was replacing header and collector gaskets continuously on these cars. Due to the nature of headers, they burn gaskets and I would not want to be replacing them on the GMC too often.

Rich Major

'78 Kingsley

 

Date: Sun, 22 Mar 1998 20:06:01 -0811

From: Scott Woodworth <myvair#lemoorenet.com>

Subject: Re: GMC: [Fwd: cylinder heads for 1976 Palmbeach]

Rich,

The GMC motorhome shop manual does not show the use of exhaust manifold gaskets. There's a good reason not to use them in this application.

Motorhome service causes a great amount of heat. The engine is under a moderate to heavy load most of the time. I'd be willing to bet that the exhaust manifolds can get dull cherry red during long hill climbs. Using gaskets will insulate the exhaust manifolds from the heads. That leads to overheating and cracked manifolds.

The best solution is to take them down to a good machine shop and have the checked for cracks then have them surfaced. Make sure that they take off only as much metal as necessary.

Reinstall the manifolds without gaskets and torque the center bolts to 25 foot pounds. Then torque the outside bolts to 15 foot pounds. That allows the manifolds to expand lengthwise when they get really hot. That way, they won't crack. Leaving the gaskets out will allow the water cooled heads to sink more heat from the manifolds. This tip comes from the book Trailer Life's Rx for Rv Performance and Mileage by John and Estes, Bill Geraghty. (Out of print)

Note: Do not use galvanized bolts on your manifolds if you ever plan to remove them. Please use grade 5 or grade 8 bolt and put anti seize on them or dip them in plain unflavored Milk of Magnesia.

- -Scott Woodworth

P.S. The 403 heads are 4C.

 

Date: Wed, 25 Mar 1998 00:20:33 -0500

From: "Thomas G. Warner" <warner#borg.com>

Subject: RE: GMC: [Fwd: cylinder heads for 1976 Palmbeach]

Rich, excellent idea but I would not put them on without a gasket. The original GMC engines did not use gaskets as you indicate but they did use a substance similar to pyro putty to ensure a good seal. I believe Clarence Buskrk uses solid copper gaskets to both seal the manifold to cylinder head, and provide better heat conduction to the water-jacketed cylinder heads.

 

Date: Wed, 1 Apr 1998 10:29:45 -0500

From: "Bartz, Paul" <s9d3452#mail.drms.dla.mil>

Subject: GMC: RE: Project enlarged to include Muffler/Tailpipe. Looking for suggestions/recommendations.

Heinz:

A year ago last December, I replaced my entire exhaust system at the time I needed a new muffler.

Went with Thorley headers, Flowmaster mufflers (big block series) and three inch exhaust pipe after the Y-pipe on my 78 with a 403 ci engine. Had a muffler shop custom bend the piping between the mufflers and the Y-pipe.

Prior to installing the system, I sent the parts to Hi Performance Coating to be coated with an aluminum-ceramic coating. I was after longevity and as a bonus the coating acts as an insulator and keeps the engine compartment cooler.

When I assembled the joints, I used band clamps vs. the usual U-bolt style, which put a crimp in the metal and make it difficult to separate later when needed.

In conjunction with the 3.42:1 ring and pinion gear installation, I now have better hill climbing ability on the highways than a stock 455 ci engined coach.

In case you're not already aware, there is another alternative in addition to the Jardine system. A fellow in Ontario Canada makes a stainless steel system. He usually advertises in the GMCMM magazine in the want ad section, however I didn't find it in the March issue.

Paul Bartz

> From: Heinz Wittenbecher [SMTP:heinz#bytedesigns.com]

> Sent: Sunday, March 29, 1998 8:11 PM

> Subject: GMC: Project enlarged to include Muffler/Tailpipe.

> Looking for suggestions/recommendations.

>

> My new Thorley Headers are not quite sliding in as a direct replacement which means some cutting and welding is going to be necessary.

>

> Since my tailpipe past the muffler is 10+ years old and the mufflers are of the Muffler Shop variety done as an emergency replacement I'm considering to treat the ol' gal to some new ones.

>

> When the Muffler Shop installed the last ones everything got welded. Is that really necessary? recommended?

>

> I've seen Flowmasters mentioned/recommended in this list before. I presume that's the mufflers?

>

> I would also assume that complete kits are available and while I've seen Jardine exhaust kits advertised I've not been paying the greatest of attention as there hasn't been the need :-)

>

> So... what is going to be my best bet if replacing new from back bumper to Thorley Headers?

>

> Any suggestions/recommendations/experiences greatly appreciated.

>

> Heinz

> '76 Transmode, Vancouver BC (actually Langley).

 

Date: Mon, 13 Apr 1998 21:47:08 +0000

From: Homebase#atcon.com

Subject: Re: GMC: Exhaust manifolds - 455

> Subject: GMC: Exhaust manifolds - 455

> Date: Mon, 13 Apr 1998 18:18:27 -0500

> Reply-to: gmcmotorhome#mailinglists.org

> I have warped exhaust manifolds on my 455. Does anyone know of a repair or >should I just bite the bullet and buy a set of headers? Your comments are >requested. Thanks

>

> Russ Bethel

> San Antonio, Texas

>

> My suggestion......

Take the manifolds off, take to a machine shop and have them planed. While you are waiting the two days or so, order a set of ceramic gaskets from Mondello. Put it together, and as they say around here; Bob's your uncle !!

MikeB

 

Date: Tue, 14 Apr 1998 09:55:00 -0600

From: Robert Shimanek <robshim#up.net>

Subject: Re: GMC: Exhaust manifolds/anti-seize 403/455

Added note on exhaust gaskets. I was constantly replacing my gaskets on the 403 engine. Had the manifolds machined which helped somewhat. Had one manifold cracked which was replaced.

The gaskets had to be replaced too frequently so I doubled the gaskets on each side. This helped temporarily.

After approximately one year of replacing gaskets engine began running rough at idle and power appeared to be reduced. Compression check revealed two right cylinders were low. (engine mileage 92K)

Removed the heads, had the valves and seats reground, and two exhaust valves replaced. To my surprise I noted that the exhaust port surfaces on the heads were eroded causing my gaskets to blow even though my manifolds were machined. I completely forgot to check the heads during my gasket replacing.

So it is important to insure the head surfaces are checked and don't operate the engine too long with blown gaskets because it will erode the head-- then your problems will start.

Too bad someone doesn't manufacture a solid copper gasket for the manifold to insure a good heat sink for the manifolds

The recommended use of anti-seize on the exhuast bolts is a must. I would stay away from the anti-seize with graphite as the base component. This may cause cracks expecially on stainless steel.

I use the anti-seize with a copper base on all exhaust components and sparkplugs. When you apply it to the spark plugs only apply to the first two (2) threads. When you have to remove the manifolds or any part of the exhaust including the spark plugs this will be the payoff on the ease of removal.

Just think if you break off a spark plug or bolt what happens next?

You can usually purchase the ant-seize at any auto parts stores.

Hope this gives you some input

Bob

 

Date: Mon, 20 Apr 1998 19:11:31 -0500

From: "Gilbert R. Bethel" <rbethel#txdirect.net>

Subject: GMC: Mufflers??

I have ordered headers from HPC in Salt Lake City and upon inspecting the mufflers they look like they are getting thin on the outside. I think I may have to replace them soon. What mufflers should I run with the ceramic coated headers. I would like to keep the noise to a minimum.

Russ Bethel

1976 Glenbrook

------------------------------

Date: Mon, 20 Apr 1998 21:50:14 -0500

From: Rich and Dottie Major <bmajor#worldnet.att.net>

Subject: Re: GMC: Mufflers??

Russ, you want a free flowing exhaust system. I just installed Flowmasters on mine and there was a noticeable increase in performance. It's not noisy at all.

Rich Major

'78 Kingsley

 

Date: Tue, 21 Apr 1998 08:49:50 -0400

From: Zachary Zehnacker <zakz#erols.com>

Subject: Re: GMC: Mufflers??

I'm not sure I can agree with this recommendation. The Flowmaster mufflers we got for replacing the Dynomax ones that came with our 3" Jardine exhaust system were VERY loud. Flowmaster uses noise cancellation and has no packing material whatsoever. The back of the motorhome was unusable while traveling the exhaust was so loud and pulsating. They are built like tanks, however, and would probably outlast your motorhome. Unfortunately for us, we ended up taking them off to put Dynomax mufflers back on. The Dynomax mufflers are only loud in one RPM range instead of the entire range like the Flowmasters were. The Dynomax mufflers are built pretty cheaply, however, and do not last much over a few years. The next time we do it, we will probably look to some stock type mufflers which are not free flow at all. At the RPM's we turn our motor (usually less than 3500 RPM) and with two mufflers, we just don't think the better flow is worth the noise it creates. I have seen ads for a new muffler from Walker (same company as Dynomax) that is supposed to be a little more free flowing than stock, but not as free flowing as their Dynomax brand mufflers. These might be a better compromise for flow and noise.

Just our experiences,

Zak

PS - All our travel is done while towing a trailer, so our noise experiences might be different from others. Our motor is under a much heavier load at all times which might account for our Flowmaster/Dynomax experience. The motorhome, however, was silent (inside) when it still had the stock exhaust system even when we were towing.

------------------------------

Date: Tue, 21 Apr 1998 08:45:18 -0400

From: Marcus McGee <crsalert#frontiernet.net>

Subject: Re: GMC: Mufflers??

Try Summit or Jeggs for the Flowmasters.

Summit has a Net store or you can get the catalog. Also Jardine has a good muffler if you are looking to go to the 3" pipes.

Marcus

 

Date: Tue, 21 Apr 1998 11:49:30 -0500

From: Rich and Dottie Major <bmajor#worldnet.att.net>

Subject: Re: GMC: Mufflers??

Zachary/Russ

When I had the Flowmasters installed I was looking to increase the preformance from the 403 CID motor. I must admit that no one travel in the rear of our motorhome while I am driving so we can not comment on noise back there. However, there is no noticable noise from the exhaust system while seated in the front of the coach. In addition, Flowmaster has 3 types of mufflers with different sound levels for various applications. I made sure I purchased the most quiet muffler they had. I do use a louder Flowmaster on my 31 Ford, but that was intentional and it is loud.

Flowmasters can be purchased from Summit Racing in Ohio, Tel 1-800-230-3030. Summit is very large mail order supplier of automotive performance parts. And they have the best prices. You can also call Flowmaster at 1-707-569-9929 and discuss your application and they will recommend the correct part number.

Rich Major

'78 Kingsley

 

Date: Sun, 31 May 1998 21:57:20 -0700

From: Jim Bounds <jimbounds#sprintmail.com>

Subject: Re: GMC: Water Consumption

L.J. CHRISTOPH wrote:

>

> I have noticed in the past few trips that I am using water in the radiator. >It seems there is a leak somewhere and I am having a hard time finding it. >Changed the thermostat and also the short bypass hose. I have looked for >water leaks and I can't find any. Is it possible that I have a head gasket >going? How can I tell if it is a head gasket?

Christopher,

If you think you have a blown or suspect head gasket problem, pick up a cooling system presurizing pump with a guage. Snap it on the water cap inlet and pump up the system. If it holds pressure, the leak could still be there but small. Heat the engine up and test again, there may now be a leak down. Next, turn on the engine and see if there is cylinder pressure coming from the water inlet. If water is being forced out the inlet, only while running, you may have a leaking head and or gasket.

Good luck on your search.

Jim Bounds www.gmccoop.com

 

Date: Sun, 31 May 1998 23:52:49 -0400 (EDT)

From: "Thomas G. Warner" <warner#borg.com>

Subject: Re: GMC: Water Consumption

L.J. need more details.

1. Do you have a temp gauge that reads numbers or are you using the factory one? What is it reading ie; is the engine overheating and are you losing coolant out of the overflow?

2. have you replaced the radiator cap with the correct one?

3. Have you run a compression check on the engine?

4. (easiest) Have you filled the radiator with coolant to the top of the neck, let the engine get up to temperature and watched the coolant for bubbles from the exhaust. Optionally get a pressure tester to pressurize the radiator and see if it will hold pressure. If it does not you either have an external leak( you already said that you cannot find any external leaks) or a head gasket.

 

>LJ.........The "Okie" method of checking for a leaking head gasket works every time. Run your jewel up to a sturdy phone pole until it is touching. Pull off the radiator cap and fill the radiator to the top so the water is easy to see. Have someone put the transmission in high gear and then slowly increase the engine speed. As the engine goes under load, if you have a bad head gasket, the water in the radiator will bubble up. To find which side is bad, drive around for a while and then pull the spark plugs. Usually the plug nearest to the leak will be clean looking in relation to all the other seven. Don't do the phone pole thing too long or your burn up the tranny. If you knock down the phone pole, get the hell out of the area! Apologizies to anyone from Oklahoma

..Jim Davis

 

Date: Thu, 18 Jun 1998 16:25:13 -0700

From: Chuck Will <willa#impulse.net>

Subject: To Coat or Not to Coat!

Greetings. I was wondering if any of you out in the GMC world have taken to the Ceramic Coatings for the Doug Thornley Headers or some orther brand of headers. I purchased the headers from "Mondello's in Paso Robles" and have read a lot about the coating. The ceramic coating cost is $ 220.00 plus the freight each way. Is it worth this cost? The Thornley headers comes with a "Jet Hot" Industrial coating on the outside. This coating however, does not cover the entire inside of the headers.

In addition, the copper gasket supplied by Mondello (at an additional cost) has two cylinder exhaust ports together in the center. Is this correct or should the center ports be welded shut. I am confused here. I thought the idea from the header was to keep all the exhaust ports separated so they would increase the flow of the exhaust gases independently of each other. If this is the case does it not seem reasonable the thick copper gasket should be closed in the center for this application? Need some Technical Help. Thanks Chuck

 

Chuck:

If by the "two cylinder exhaust ports", you are talking about the passages to the intake manifold, there was also previous discussion on that. If you want to pursue that, the ports have to be plugged and then you need to substitute an electrically operated choke on the carburetor for the original choke. Same as above, if you don't have access to the earlier discussion, let me know and I'll e-mail it to you.

Paul Bartz

 

 

Date: Fri, 26 Jun 1998 13:42:47 -0500

From: "Russ Bethel" <rbethel#stic.net>

Subject: Re: Biggest Bang For the Buck

I have a stock 1976 Glenbrook. I installed Doug Thorley ceramic coated headers, free flow mufflers, and 3 inch tail pipe. I still have the 3.07 final drive. I tow a 16 foot double axle trailer with a Jeep Grand Cherokee on it. I also have a tool box and 12 gallons of gas (for emergency use) on the trailer. I estimate that I am pulling about 4,000 lbs. I do not have any problems on interstate highways. If I were going to be in mountains I may think of changing to the 3.50 conversion using the different ratio between the torque converter and transmission.

I think the first thing to do is the exhaust system with headers. That will get rid of the exhaust manifold problems plus improve the performance. Then install a good transmission cooler and larger lines from the transmission to radiator. After that I would evaluate the situation to see what kind of dollars I would spend vs improvement gain expected.

Russ Bethel

rbethel#stic.net

 

Date: Wed, 12 Aug 1998 07:59:10 -0400

From: pete <pete#blakechevy.com>

Subject: GMC: gmc exhaust

Tom,

Call Jardine Performance Exhaust in Jackson Hole, Wyoming. I put their headers and complete exhaust system on my coach. It's all top quality stuff and is much better than the OEM. 1-307-733-7473. It's custom made.

Pete Blake

pete#blakechevy.com

 

 

Date: Thu, 13 Aug 1998 00:16:39 -0700

From: Jim Bounds <jimbounds#sprintmail.com>

Subject: Re: GMC: Exhaust System Repair and Replacement

Tom,

By this time, many components of the original exhaust system are dead! I have found that replacing the entire system is many times the correct answer. It fall back on the old saying," Don't fix it for just today, fix it for the future"! There are so many other things that you need to watch on a GMC that there is no need in partially repairing the exh.system and watch to see when the other components go south! I use Gibson & Jardine complete exhaust systems usinf 3" alumised pipes and Doug Thorley headers. The kits are very complete and a bolt in proposition. If you would like more info, give me a toll free call at 1-877-275-4462.

Jim Bounds www.gmccoop.com

>

>Need some info Anybody know the exact size of the OEM mufflers ? I'm planning to replace current glasspaks with Flowmasters or Hemi-style.I plan on using new stock engine pipes, and Y pipe. I need to know diameter as well. ...

>>Mark

>>'77 Palm Beach

>>

Call Juanita at FlowMaster 1(800)544-4784; She knows; I would suggest that you locate a local muffler installer that has an RV lift and who will install others products. BTW; Jardine has the complete package, all ready to bolt up, headers etc. I used FlowMaster, with stock manifolds, 2-1/2" down pipes to FlowMaster Mufflers to performance "Y" then out of "Y" with 3" two 90s and down through frame out factory path with 3". I would suggest using their mandral 3" 90 deg. ells, your installer should be able to modify them for a perfect fit.

Very happy with the results.

JRBiava

----------------------------------------------------------------------

Date: Fri, 26 Jun 1998 13:42:47 -0500

From: "Russ Bethel" <rbethel#stic.net>

Subject: Re: Biggest Bang For the Buck

I have a stock 1976 Glenbrook. I installed Doug Thorley ceramic coated headers, free flow mufflers, and 3 inch tail pipe. I still have the 3.07 final drive. I tow a 16 foot double axle trailer with a Jeep Grand Cherokee on it. I also have a tool box and 12 gallons of gas (for emergency use) on the trailer. I estimate that I am pulling about 4,000 lbs. I do not have any problems on interstate highways. If I were going to be in mountains I may think of changing to the 3.50 conversion using the different ratio between the torque converter and transmission..

I think the first thing to do is the exhaust system with headers. That will get rid of the exhaust manifold problems plus improve the performance. Then install a good transmission cooler and larger lines from the transmission to radiator. After that I would evaluate the situation to see what kind of dollars I would spend vs improvement gain expected.

Russ Bethel

rbethel#stic.net

 

Date: Tue, 15 Dec 1998 20:19:31 EST

From: Gplymate@aol.com

Subject: GMC: Exhausting Advice?

One muffler has sprung a leak. Got gashed going over a protrusion in the street.

Midas sez it can put on a new muffler for $77. There's been so much talk about getting rid of exhaust gas lately, I'm wondering if a Midas muffler will be o.k.

Advice, comments, and sympathy needed. TIA.

Glenn

78K OR

------------------------------

Date: Tue, 15 Dec 1998 21:45:42 -0500

From: John Wright <powerjon@tm.net>

Subject: Re: GMC: Exhausting Advice?

Glenn,

You need to get rid of the stock type mufflers. Flowmasters would be a

good replacement, a little more noisy, but they will flow about twice

the stock mufflers and reduce the back pressure. I am sure other GMCer

will have suggestions for you also. Review them all and make your choice.

J.R. Wright

77 Eleganza II

 

Date: Wed, 16 Dec 1998 09:27:46 -0500 (EST)

From: "Thomas G. Warner" <warner@borg.com>

Subject: Re: GMC: Flowmasters or Edelbrock Exhausting Advice?

I have decided to go to the Edelbrock stainless steel mufflers. they are

almost as quiet as stock but flow as well as the flowmasters which are much

louder than stock. Lost my part # for the Edelbrocks and have to find it.

anyone else have the Edelbrock #?

In my JEGS catalog they have the Edelbrock heavy duty 409 stainless steell

lifetime muffler with 3" center in/out part # 350-5526 for $108.99 each.

they may work.

------------------------------

Date: Wed, 16 Dec 1998 09:27:46 -0500 (EST)

From: "Thomas G. Warner" <warner@borg.com>

Subject: Re: GMC: Flowmasters or Edelbrock Exhausting Advice?

I have decided to go to the Edelbrock stainless steel mufflers. they are

almost as quiet as stock but flow as well as the flowmasters which are much

louder than stock. Lost my part # for the Edelbrocks and have to find it.

anyone else have the Edelbrock #?

In my JEGS catalog they have the Edelbrock heavy duty 409 stainless steell

lifetime muffler with 3" center in/out part # 350-5526 for $108.99 each.

they may work.

 

Tom and J.R.,

Thanks for the muffler comments. The idea of reducing back pressure is

appealing, and I like the prospect of that as well as quietness in the

Edelbrock muffler as suggested by Tom. But, wouldn't such a change involve

installing new pipes as well as new mufflers? It's not just a simple matter

of yanking out the old stock mufflers and sticking in new upgrades is it?

And, Tom, you can chalk me up as being a hopeless (helpless?) do-it-

yourselfer. But, exhaust systems are beyond my calling, and I don't have a

30,000 lb lift at my disposal. Don't I wish! :-)

Work on the exhaust system will be left for others who have the equipment to

do it. Gee, it's tough to admit there's something I can't do........... ;-(

Glenn

Noisy GMC OR

------------------------------

Date: Fri, 18 Dec 1998 10:45:01 -0500 (EST)

From: "Thomas G. Warner" <warner@borg.com>

Subject: Re: GMC: Exhausting Advice??

Glen I have worked on my exhaust system without a lift. jack up the front

of the coach, put stands under it, take off both front wheels and liners,

and you can work on the exhaust manifold, headers and mufflers quite easily.

Tom & Marg Warner

Vernon Center NY

1976 palmbeach

 

Date: Sat, 19 Dec 1998 11:18:06 -0500

From: Ted Schurman <tedsch@erols.com>

Subject: Re: GMC: Exhaust wrapping , Engine Compartment Heat?

I have seen information from Doug Thorly not to wrap the headers and that it would void any warrentee. Guess they get too hot.

Ted Schurman

73 Glacier VA

 

Thomas G. Warner wrote:

>

> The material is available from Summit 1-800-230-3030 50' for $24.95, part #

> DEI-010101.

>

> AM 12/10/98 -0500, you wrote:

> >Would it be of any value in reducing engine compartment heat to wrap the

> exhaust manifolds/down pipers with insulation material designed to withstand

> hi-temps? If anyone has done this, where did you get the material? I suppose hotrod/racing shops would have it but I haven't checked yet.

> >

> >Someone suggested that would be enhance performance since the hotter gases

> would improve engine breathing. Any thoughts? Thanks.

> >

> >Ralph Edelbach, '74 Glacier

> >

Tom & Marg Warner

> Vernon Center NY

> 1976 palmbeach

 

Date: Fri, 11 Dec 1998 15:44:58 -0500

From: Zachary Zehnacker <zakz@erols.com>

Subject: Re: GMC: Ceramic Coating

Chuck

The view of Jet Hot vs. HPC is the other way around in the racing world. Most racers view Jet Hot as the more desireable GMC of coatings :). This is probably due to Jet Hot's advertising and contingency payouts though and

may not have anything to do with which product is better.

Zak

 

At 09:01 AM 12/11/98 -0800, you wrote:

>is pretty to look at. But cost a bit to have removed. It is not a Jet

>Hot Coating it is a High Performance Coating. There is a difference.

>Sort of like our GMC and the rest of the coaches runing around on our

>highways. Give Cory a call he will answere all your questions. ONE

 

Date: Mon, 18 Jan 1999 02:12:28 -0500

From: Zachary Zehnacker <zakz@erols.com>

Subject: Re: GMC: Exhaust

Do these larger exhaust sizes really fit well? We have a 3" (stock is 2.5") and it just fits through the original exhaust silicon rings. Any larger would definitely require removing those mounts and some other mods I would think. I can't see bigger than 3" being much of an improvement. Does anyone here have experience with larger than 3"? We will probably be redoing our exhaust in stainless soon, so we are interested in any new info on this topic. By the way, does anyone here have any experience with the stainless exhaust advertised in the GMCMI newsletter classifieds? We were considering getting that system (with the 3" upgrade), but if we can't find anybody that has experience with it, we will probably just fabricate our own.

Zak

 

At 12:54 AM 1/18/99 EST, you wrote:

>I know alot of people have been using 4" exhaust pipes--is there some

reason for using the 3.5 in.?

>Scott Adohen@aol.com

>

Date: Mon, 18 Jan 1999 02:24:28 EST

From: Adohen@aol.com

Subject: GMC: Subj: Re: Final drive thread

Thanks Zak!

Should have said 3"--- going to bed--thunder and lightning--melting--

Scott Adohen@aol.com

Date: Mon, 18 Jan 1999 08:28:50 EST

From: HLBF@aol.com

Subject: Re: GMC: Final drive thread

In a message dated 1/18/99 0:14:26 AM EST, srchrls@gateway.net writes:

> a 3.5" exhaust system

> and recently added a transmission cooler that sits in the wheel well

Where did you route your 3 1/2" exhaust pipe? Where is the oil cooler located

in the wheel well?

Lanier

 

Date: Mon, 18 Jan 1999 18:45:51 -0500

From: John Wright <powerjon@tm.net>

Subject: Re: GMC: Final drive thread

I haven't heard of anyone using a 4" exhaust, you can't get it down thru the frame rails unless you cut the frame cross members and I wouldn't recommend that, and you sure don't want it hanging down underneath the frame. The 3" exhaust is the largest that will fit right down the frame rail holes without any problems. Any thing larger than a 3" system and Hi-flow type mufflers is money not spent well. I myself have a 403 with 2.5" flowmaster into the stock 2.5" exhaust tail pipe. When I got rid of the stock 2" mufflers the larger piping and higher flow mufflers (220 cfm each compared with 110 cfm stock) my fuel mileage went up from 8.9 to 10.8 mpg. (I run 67-68 mph on most X-ways with the cab air on). Would probably be even better if I ran more towards 62 to 64 mph. The 403 is approx. 20% smaller in displacement than the 455 and the 3" is marginal change. The 455 really likes the 3" tail pipe and larger mufflers. Header are an options that you need to decide if you really need them. I keep after my maintenance on the motor and do not have exhaust manifold leaking problems. I use a Fel Pro #1439 gasket along with the high temp copper silicone. I also use grade 8 cap screws type bolts with liberal amount of high temp nickel never seize. I use a torque to tighten the bolts (25 ft/# and do a quick check of them every 4 to 5 thousand miles. I just installed a 3.55 final drive this fall and do not have enough data to determine how much if any the fuel mileage will drop. The new gearing gets the motor up into its power band and doesn't lug anymore (should burn the fuel better). Used to slow down 10 to 15 mph on some hills with the 3.07 gear, but with this

3.55 the mph did not drop off at all. The cruise kept it right at 64 mph. Better quit, getting too wordy.

J.R.Wright

GMC Greatlaker

77 Eleganza II

Michigan

 

Zachary Zehnacker wrote:

>

> Do these larger exhaust sizes really fit well? We have a 3" (stock is

> 2.5") and it just fits through the original exhaust silicon rings. Any

> larger would definitely require removing those mounts and some other mods I

> would think. I can't see bigger than 3" being much of an improvement.

> Does anyone here have experience with larger than 3"? We will probably be

> redoing our exhaust in stainless soon, so we are interested in any new info

> on this topic. By the way, does anyone here have any experience with the

> stainless exhaust advertised in the GMCMI newsletter classifieds? We were

> considering getting that system (with the 3" upgrade), but if we can't find

> anybody that has experience with it, we will probably just fabricate our own.

>

> Zak

 

Date: Mon, 18 Jan 1999 15:30:21 -0500

From: Zachary Zehnacker <zakz@erols.com>

Subject: Re: GMC: ZaK's Website

JR,

The most important thing is that it is very difficult to find OEM style replacement tie rod or ball joint boots. These polyurethane ones avoid having to buy new tie rods or ball joints just to get new boots. They are also much thicker, so they should not split like the OEM boots do so easily when putting in new grease. These new ones should last a long time without splitting. They also look much better than stock IMHO and give the whole job a much more clean and race-like look.

Most polyurethane sway bar end link or bushing companies probably make them. Ours are from Energy Suspension. We got them from JEGs, but any Energy Suspension dealer should be able to get them. JEGs sells them in red or black for $4.00 for 2 tie rod boots or $8.00 for 2 ball joint boots.

Other places might offer them in other colors.

Zak

At 10:04 AM 1/18/99 EST, you wrote:

> <<< We used Energy Suspension tie rod and lower ball joint boots.>>>

>

>Nice job Zak. Could you tell me about the boots? Manufacturer, where they

>were bought, and the advantage over originals. Thanks.

>Take care...........JR

------------------------------

Date: Thu, 21 Jan 1999 22:47:48 -0500

From: John Wright <powerjon@tm.net>

Subject: GMC: Exhaust Gaskets

Fellow GMCNetters,

Recently solid copper exhaust manifold gaskets have been available for the 403 and 455 motors. Several of our parts suppliers have offered these for sale. A company call Specialty Competition Engineering make these but I am asking if anyone has a Phone number for direct buying.

J.R. Wright

 

Date: Thu, 21 Jan 1999 23:40:15 -0500

From: Zachary Zehnacker <zakz@erols.com>

Subject: Re: GMC: Exhaust Gaskets

J.R.,

You can get the Mr. Gasket Copper gaskets from Jegs, Summit, or any other place that carries Mr. Gasket products. Jegs even lists them in their catalog ($31.99 a set for part #720-7170). These sources seem cheaper than the prices I have seen advertised by the GMC suppliers I have seen. I don't know if there are any differences between the Mr. Gasket ones and the ones sold by the GMC suppliers though.

Zak