7.4l tune-up

[wanderingeye]

We bought Hedman headers from Summit Racing. There were only two brands that have a 3/8" flange. These things are hell for stout and fit perfectly. The ceramic coating cut down the heat in the dog house considerably. One unexpected benifit was the noise reduction. Free-flowing exhaust gasses make less noise than the original restrictive castiron manifolds. Cheers Tom

[ralley]

I, too bought some hedman's a few months back, but haven't put them in yet. Looks to me like I will have to re-plumb the exhaust to make them work, and I haven't done my homework about where to buy exhaust fittings and which ones to buy. Maybe at my next tune-up when the plugs are out....

Is there a proper thread about doing this job--? I may have missed it.

Rob

[wanderingeye]

Ralley It might be worth your time to check your headers with the manufacturer's web site, Hedman.com. Under Hedman Elite (extreme duty/ motor homes) you will find your engine and chassis year. The reason for caution is that these headers are one of only two brands that I could find with a 3/8" flange. I cannot remember another automotive product that rated so high on the cost/benefit curves. They fit perfectly and fortunately all the original bolts came out. We threw the cast-iron manifold and air injection in the dumpster. The original manifold was spauled, like crumbling concrete from excessive heat. Depending on elevation changes and wind speed (it's hilly and windy here in the NE), we're getting up to 11 mpg. Our headers were $275 from Summitt Racing with $10 shipping.
Cheers, Tom

[GlenCoombe]

Tom, if you think the Headmans are stout wait till you pick up a Flowmaster 70 muffler. I was very much surprised at how heavy and well constructed they where. They really "round" out the sound too. At normal throttle opening they are quite tame, however when you dip a bit deeper the big block signature sound is very nice indeed. The temptation is to drive a little more with the drivers window open and your foot a little deeper if you like that kind of sound.

[ralley]

Originally Posted by wanderingeye

Ralley It might be worth your time to check your headers with the manufacturer's web site, Hedman.com. Under Hedman Elite (extreme duty/ motor homes) you will find your engine and chassis year. The reason for caution is that these headers are one of only two brands that I could find with a 3/8" flange. I cannot remember another automotive product that rated so high on the cost/benefit curves. They fit perfectly and fortunately all the original bolts came out. We threw the cast-iron manifold and air injection in the dumpster. The original manifold was spauled, like crumbling concrete from excessive heat. Depending on elevation changes and wind speed (it's hilly and windy here in the NE), we're getting up to 11 mpg. Our headers were $275 from Summitt Racing with $10 shipping.
Cheers, Tom

Thanks very much. I'll check this weekend. Headers are still in their shipping box under the bed in the Zeppelin, so will requires some excavation to get to the paperwork for model #, etc.

Rob

[ralley]

The Hedman part number for my configuration is 69820. It is the "elite" with the 3/8 inch flange.

Thanks for the heads up............

R

[swebster]

ralley,
You'll have to "marry up" the old exhaust to the new headers but I'm with Glen, this is a good time to consider replacing everything. New free flow mufflers, an H pipe and 2.5 pipes will help those headers do their job.

I use flex connecters to transition the 3" header outputs to the 2.5 pipes, then into a three foot pipe, back to an H pipe kit from Jegs. From there two more 4 foot pipes lead into Jegs mufflers then more sticks to the back, two 90 degree mandrel bent pipes then out the sides. I also added SS exhaust tips for that extra 5 hp!

Went and used all new hardware, handers, everything. My exhaust was a mess from the manifolds back so this complete replacement made the decision easy. I have to think the replacement process would be easier than trying to connect up to your existing system.

[dinoburb]

Greetings,

I have a recommendation that is slightly counter to most of the previous suggestions. If you are going duals than the 'H' pipe is a must, however, a single 3" or 3.5" pipe will provide the necessary flow improvement at towing RPM (with a slight torque improvement over duals) but not quite as much horsepower at 5000 rpm (which you'll probably never hit)! Remember, most items designed to improve HP usually do it at the expense of low end torque. Even most torque improvements claimed by dual exaust proponents are at a higher RPM than the original numbers. When Gibson exaust talks torque and towing in the same breath they talk a single pipe system ex: Summit Racing Parts (This example is for my R-2500/454 Suburban). Quality headers such as the Hedman 69820's are also a must. If the vehicle requires a catalytic converter you'll also need a high flow converter to match the improved breathing provided by the headers and large exaust.

Hope this helps.

Take care,

Sean

[ralley]

Gentlemen: Thanks very much for the sage advice. Duly noted and saved against the time that I need a new exhaust system.

For the time being, I will install the headers and join up with the existing 3 inch pipes, and await failure of the existing system (which appears in very good condition). I can lay up parts against the inevitable.

Best,

Rob

[rvlover]

I want to join Rob's post, this is very helpful. My engine work is complete except for distributor and headers. Searching now for the right Hedman. Thanks for the usual great forum help. joe

[wanderingeye]

Alansd, Peter-79MH, FrankR, OutofControl, Swebster, GlenCombe, Ralle and Dinoburb
Gentelmen, Your posts on this forum have made owning an Airstream more pleasant than it might otherwise have been. I am not a mechanic! My wife says I have a 51% success rate of dissassembling something then reassembling it and having it work again. She may be right....my orphan parts jar is as full as my spare change jar. Our '84MH is in magnificent shape considering it's age. I beleive in renewing rather than repairing. For instance, I have completely replumbed the fresh water system. We have 77,000 miles and I am looking toward the day when I may have to reengine. This (attached) engine has been offered to me at a reasonable price. This would be a preemptive maintenance. What do you think? Tom

[outofcontrol]

You might have to cut a hole in your doghouse for that blower.

You might as well just remove the doghouse so you can look and listen to that jewel while you punch it.

-Kevin

[GlenCoombe]

Sweet!! So now the questions. At 77,000 miles how many miles do you put on annually? Have you done a compression test and or a leak down test to determine the condition of the internal engine components of your existing engine?
I wonder if the drag of the blower drive will compensate for the lack of cooling fan drag. Electric fans intrige me.
With so many engine options that one would have to be a real bargain to get me to make a big dent in my wallet and start the long process of making the switch.
Frankly I'd ditch the blower... you could sell it on eBay!

[swebster]

Is that a big block? I'm no expert but those rocker covers make it look like a small block. Either way I'm not sure a roots style blower would make sense in a motorhome. It is cool - but rather impractical.