Exhaust tubing reducers

I'm in the process of attempting to fabricate headers for a 3.8L Ford V-6. It's a special use engine that will be powering a homebuilt airplane using a prop speed reduction unit. This means that the engine will be running most of the time at around 3,900 to 4,000 rpm while in cruise.

The information I'm getting is that the exhaust header tubing diameter should be 1.5", not 1.75. Using 1.75 works fine for an all out competition engine, where it's run at maximum rpm all the time, like at the drags or at a circle track, but for my application, using 1.75" makes the engine peaky and tough to tune the carburator and causes uneven mixtures in the combustion chambers. Since the 3.8 already has a less than perfect manifold for this purpose, it's important to pay attention to information about proper header design.

The exhaust header flanges I have are cut for 1.75" tubes. That's the way most of the header flanges are manufactured, and custom header companies just install cones, or reducers to bring the tubing size down to the proper diameter to run the rest of the tubing.

So I'm trying to find a source for these reducers. Ideally, the reducer should have about half an inch of length at 1.75" before the reduction begins, then about another half an inch at the 1.5" diameter so as to facilitate mating to the rest of the 1.5" tubing.

Any ideas on a source?

Thanks, Corky Scott

Reply to
Corky Scott
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On Wed, 11 Feb 2004 14:59:44 GMT, snipped-for-privacy@greetings.dartmouth.edu (Corky Scott) wrote:

|I'm in the process of attempting to fabricate headers for a 3.8L Ford |V-6. It's a special use engine that will be powering a homebuilt |airplane using a prop speed reduction unit. This means that the |engine will be running most of the time at around 3,900 to 4,000 rpm |while in cruise. | |The information I'm getting is that the exhaust header tubing diameter |should be 1.5", not 1.75. Using 1.75 works fine for an all out |competition engine, where it's run at maximum rpm all the time, like |at the drags or at a circle track, but for my application, using 1.75" |makes the engine peaky and tough to tune the carburator and causes |uneven mixtures in the combustion chambers. Since the 3.8 already has |a less than perfect manifold for this purpose, it's important to pay |attention to information about proper header design. | |The exhaust header flanges I have are cut for 1.75" tubes. That's the |way most of the header flanges are manufactured, and custom header |companies just install cones, or reducers to bring the tubing size |down to the proper diameter to run the rest of the tubing. | |So I'm trying to find a source for these reducers. Ideally, the |reducer should have about half an inch of length at 1.75" before the |reduction begins, then about another half an inch at the 1.5" diameter |so as to facilitate mating to the rest of the 1.5" tubing. | |Any ideas on a source? | |Thanks, Corky Scott

Why don't you just expand the ends of your tubing? Standard procedure. Any muffler shop will do that for you, just cut some tubes and take them by.

Rex in Fort Worth

Reply to
Rex B

I'll ask the local Midas shop. Thanks for the tip.

Corky Scott

Reply to
Corky Scott

Reply to
Mike Behnke

| You'll do better at a custom exhaust shop. | |Corky Scott wrote: | |>>Why don't you just expand the ends of your tubing? Standard procedure. |>>Any muffler shop will do that for you, just cut some tubes and take them by. |>>

|>>Rex in Fort Worth |> |> |> I'll ask the local Midas shop. Thanks for the tip.

That's for sure! Look for an independent who caters to car builders. Stay away from the franchise shops. Any departure from their standard menu will yield unpredictable results. Rex in Fort Worth

Reply to
Rex B

In general, I'd agree, find a shop that does custom work, not just factory replacements. The Mineke (sp?) shop here in Dallas did some work for me that worked out great. I just told them exactly what I wanted and watched them as they did it. I needed some custom plumbing for a supercharger aftercooler installation and it's held up fine for 2 years and I don't expect to have a problem for quite some time.

-Bruce

Reply to
Bruce Chang

Easier said than done. This is the upper Connecticut River Valley, northern Vermont and New Hampshire. Aren't too many rod shops around here.

I'll do some checking though, there is an engine building shop where I know someone. They build race engines for the northeastern circle tracks up here and in Canada.

Corky Scott

Reply to
Corky Scott

*Any* muffler shop can open up our pipe.
Reply to
Stephen Bigelow

|On Wed, 11 Feb 2004 11:03:35 -0600, Mike Behnke |wrote: | |> You'll do better at a custom exhaust shop. |>

|>Corky Scott wrote: |>

|>>>Why don't you just expand the ends of your tubing? Standard procedure. |>>>Any muffler shop will do that for you, just cut some tubes and take them by. |>>>

|>>>Rex in Fort Worth |>> |>> |>> I'll ask the local Midas shop. Thanks for the tip. |>> |>> Corky Scott |>

|Easier said than done. This is the upper Connecticut River Valley, |northern Vermont and New Hampshire. Aren't too many rod shops around |here. | |I'll do some checking though, there is an engine building shop where I |know someone. They build race engines for the northeastern circle |tracks up here and in Canada. | |Corky Scott

There are some manual alternatives that might do if you don't find a local shop that is cooperative.

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Rex in Fort Worth

Reply to
Rex B

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They're also a huge pain in the butt, but yes, they are an alternative.

-Bruce

Reply to
Bruce Chang

At this point, I may go an entirely different route. A friend of mine pointed out that McMaster Carr has a number of stainless steel tubes along with various bends and reducers that could be purchased and would work very well as exhaust tubing. The wall thickness is .065" as opposed to the .049" material that most kit header manufacturers utilize.

The only downside is that the header kit guys procued U bends of a fairly narrow radius while McMaster Carr does not carry U bends. But they do carry 90 degree bends. They also carry the reducers I need.

The cost of enough material including the bends is about what I'd pay for the same material in mild steel.

I don't own a TIG machine, but stainless can be welded with an O/A torch, or I might be able to borrow a friend's TIG.

Corky Scott

Reply to
Corky Scott

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