Exhaust, headers or cast iron, single or dual

[gary j zingle]

Arch,

Sorry to respond so late to this thread but I was out of town
without access to my "E" mail. Just catching up now.

If the exhaust system is built correctly even if hooked to mufflers etc.
a set of headers will still flow better than cast iron manifolds,

However I am not sure that I will go with headers on my GMC given my past=

experience.

In addition to the potential for increased noise, in many applications
since the headers take up quite a bit of space access for service
to other components can be made more difficult. I want to take a look
at a coach with headers before I decide.

Given the chassis I have not given any consideration to duals.

I don't think a single 3" tailpipe is the biggest restriction to flow.
I believe that to be in the exhaust pipes and mufflers immediately
to the rear of the exhaust manifolds/headers.

For power, economy and sound control, in the past I have had
good success with a cross over pipe. To do any good this
must be installed in front of the mufflers, but I don't know if there
is room with the mufflers up front to do a good job.

One that I have heard of but have yet to see is to move the muffler
to the rear. Think about this one:
- - Good free flowing big pipes ( 2 1/2" ?) into a "Y" into the 3" pipe
- - A 3" muffler mounted crossways behind the sewer tank
- - Tip of the exhaust out the side near the Onan exhaust

The big pipes and a smooth flowing "Y" into the 3" pipe functions
as the "cross over".

The big 3" muffler is as far back as practical..

Not as bold a statement as dual outside glass packs but maybe
a practical solution.

Of course issues related to sewer draining etc. may have to be
resolved for this to work.

Regards

Gary Zingle
1973 GMC 26 foot

 

[terry skinner]

One that I have heard of but have yet to see is to move the muffler
to the rear. Think about this one:
- - - Good free flowing big pipes ( 2 1/2" ?) into a "Y" into the 3" pipe
- - - A 3" muffler mounted crossways behind the sewer tank
- - - Tip of the exhaust out the side near the Onan exhaust

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
I just completed a system such as you describe. Thorly headers, 2-1/2 " then
"Y"ed together, then 3" pipe with 3" inside radius turns to get to the rear.
Flowmaster Type 70 muffler mounted crossways, then a 90 and three feet of 3"
pipe with a down turn at the end. I used existing holes thru the frame and
ended up with the same relationship to the bumper as before, only on the
left side of the coach. Sound is deeper but not enough different inside to
be noticeable. Just for Arch I started it up without the muffler. Sounded
like a school bus. The amount of heat in the engine compartment is
noticeably less. Gas mileage was 8.6 MPG, mostly in the mountains of Idaho.
All in all I am very pleased with the new system and would recommend it.
Pictures coming.........................................Terry
I used :
six feet of 2-1/2 pipe
nineteen feet of 3" pipe
four 90 degree, 3" inside radius 3" elbows
Thorley Headers, coated
one Flowmaster muffler, model # 70
PS buy the elbows separately. The ones bent at the muffler shop are too
restrictive

Terry & Diane Skinner
Webfooted in Washington
'76 Glenbrook

 

[jim bounds1]

The thing I really like is the lack of noise at most any speed. No muffler
rumble!

I am not sure if it improves the performance since I did not have the beast
mobile before the system was installed but I will tell you it performes
well especially at high speeds!

Actually, I used 2 1/2" all the way and put 2 3/4" "stinger" pipes at the
end. The 3" idea would probobly work well though.

I have no holding tank so you would have to get creative in routing the
pipe cross country to the driver side.

Someone else Emailed me some time ago & said they were going to run a
similar system, hey out there- did you do it?

Jim Bounds
- -------------------------

>

>
>to the rear. Think about this one:
>- - Good free flowing big pipes ( 2 1/2" ?) into a "Y" into the 3" pipe
>- - A 3" muffler mounted crossways behind the sewer tank
>- - Tip of the exhaust out the side near the Onan exhaust
> >>
>
>Check out Jim Bounds site: http://www.gmccoop.com/
>
>Not sure if he has a picture but he has a paragraph on the modifications to
>the "Dumpster" page and he can probably provide some more info to you if you
>need it as well as supply the parts.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>

 

[donald w. miller]

Jim,

Think I mentioned my setup to you quite awhile back.

Thorleys into a Flowmaster dual 2.5" to single 3" combiner up front, then a
3" run aft with a 3" large radius elbow into a 3" flow master muffler
mounted crosswise aft of my holding tank.

I have a macerator so the big sewage dump pipe was removed providing a clear
area for the cross mounted muffler.

Flowmaster also has a nice heat shield for their muffler which is probably
advisable.

I ordered Walker aluminized tubing and elbows through the local full service
auto parts store.

I am presently reworking the front components to free up the areas in front
of the fuel tanks so I'll have compartments there for additional tankage.

Don Miller
75 project
Shenandoah Valley of Virginia

> The thing I really like is the lack of noise at most any speed. No
muffler
> rumble!
>
> I am not sure if it improves the performance since I did not have the
beast
> mobile before the system was installed but I will tell you it performes
> well especially at high speeds!
>
> Actually, I used 2 1/2" all the way and put 2 3/4" "stinger" pipes at the
> end. The 3" idea would probobly work well though.
>
> I have no holding tank so you would have to get creative in routing the
> pipe cross country to the driver side.
>
> Someone else Emailed me some time ago & said they were going to run a
> similar system, hey out there- did you do it?
>
> Jim Bounds

 

[donald w. miller]

Hi Scott,

Tankage means most anything an active mind can think of.

How about liquid refreshments of your choice with a long straw ?

Your trapdoor idea sounds good too, because some of these guys need a better
place to hide their silver bullion when they travel.

In my case it means getting my leaking water tank out of the area behind the
rear wheels to help lower the CG and move some weight forward.

My notes for this project are:

MORE BELLY TANKAGE *****

Reroute forward exhaust to make room for 44 gallons or 272 pounds of water
nearly centered between bogies and front axles. Location is near optimum
for CG and handling moments.

A 25 gallon tank goes in cavity where mufflers were, 32" forward mid wheels
and 60" aft front wheels.

A 20 gallon tank goes in next cavity forward, just behind torsion bar
frame.

Tanks are welded from 1/8" aluminum or of fiberglass and epoxy.
24.7 gallon rear tank = 53"l x 20"w x 6"h
20" wide at bottom and 17.5" wide at top.

20.6 gallon front tank = 53"l x 17"w x 6"h
17" wide at bottom and 14.5" wide at top.

Tank aft walls slope 2.5" at top to clear bolt heads and top of cross
members. Aft tank bottoms rest on cross members. Straps hold up fronts.

Baffles reduce side to side movement
Tanks are pressure filled from top by city water supply.
Bottom outlets have a "T" with ball valves for easy draining.
Vents terminate near city water hookup so you can see when they are full.
Water stowage here requires provisions for engine heat and winter cold.

Don Miller
75 project
Shenandoah Valley of Virginia

> Hi Don!
> Does tankage mean gas/holding or stowage area available via trap door in
> walkway or under seats?
>
> Scott INSIDE GMC
> PHOTOS(sound on?)