Headers, power and altitude

[alhnelson]

I'm considering replacing my stock 440 manifolds with Thorley headers sometimes in the future. In general, the info I've read and Clipper posts suggest that there is usually a noticeable improvement in performance. Just recently, I had someone tell me that there would not be a gain with headers at my altitude (generally between 5000 and 10000 ft elevation), due to the lower air pressure at intake at elevation. Does anyone have any experience or opinions as to header performance especially at higher elevations? Would also appreciate your general comments on the use of headers. I would probably special order the ceramic coated ones to reduce dog house heat.

Thanks, Al

[Plante]

The place I ordered my Thorley headers from said you cannot order them with ceramic coating.  But there are places that will coat them for you - at additional cost of course.  I am very pleased with the performance of my headers and the heat generated seems to be less than the stock manifolds.

[Charlie]

Another option for reducing the heat is to wrap the headers with Thermo Wrap.  When I put headers on my 67' Mustang with a 390 big block I used this stuff to wrap the headers and it is great stuff.  You can stick your finger on the wrap after the engine is hot and it won't burn.  I plan to install headers on my Clipper in the spring and I plan to wrap them first with Thermo Wrap.  Infact, just wrapping it around my present heat shields reduced the heat coming through the bottom of the engine cover and floor.

[EKS]

Be careful with the wraps. I've seen reference to them being a problem, causing headers to became brittle and fail prematurely. Some discussions are http://www.team.net/html_arc/mgs/199803/msg00739.html
http://www.se-r-list.org/new-archives/Week-of-Mon-20030224/012860.html
If I read it right the problem is the headers reach a higher temperature and the hot/cold cycling causes fatigue.
It appears that the thermal ceramic coating on the INSIDE of the headers is the most important because it keeps the heat out of the metal to begin with. Of course it is also the hardest place to do the ceramic coating. Do the research.

[alhnelson]

Thanks for the comments. I had read the post earlier about Thorley not coating them, however I have recently checked with Thorley and with SummitRacing and I've been told by both they can be order coated from Thorley, part # 109Y-C, but they are a special order. My research has also suggested that wrapping might have some long term negative effects as described in the previous post. Thorley recommends against any kind of wrapping on their website. I was especially curious about benefits at altitude. The Thorely tech people say their would still be a benefit but changing carb jetting may be necessary. I was curious as to what experiences people actually had.
Thanks, Al

[EKS]

Summitracing makes an air/fuel guage (P/N SUM-G2986 plus you also need a sensor). We put on one our Clipper that lives at 3000 feet of elevation (and higher) in Montana and is sometimes used for towing a horsetrailer. The rebuilt carb clearly runs rich and always has been rich. Getting it rejeted (or in this case finding different metering rods) is on the agenda. The exhaust pipe has always been black and the guage just confirmed the situation. We wanted to know where things were before we started making changes. There is a book `Motorhome and towing truck performance' by Roderick Lindberg where he documents (including graphs from dyno readings) the things he tried and what actually worked. After you get headers you probably want a low back-pressure exhaust system. Lindberg documents how with Headers, then 3 inch exhaust with a crossover/balance tube then Walker/Dynomax Mufflers then 3" glasspacks as resonators he only found .5 lb of backpressure and it was QUIET. It sounds like he had a problem with the fuel injection computer due to the low backpressure but that does not apply in our situation. See if you can find a copy of the book it is an interesting read. Be careful what you do if you have to pass smog (we don't have to do that here).
As a side note when we test drove our clipper without an air cleaner after installing the air/fuel guage the ratio was closer to what it should be than with the air cleaner. I've considered looking for a dual snorkel air cleaner and trying a K&N filter.

[alhnelson]

Thanks for the info on the air-fuel gauge and the motorhome performance book. Just ordered a copy through Amazon. I've been having fun and spending time playing around with the theoretical stuff trying to determine how well the new engine was meeting expectations. I've found a few handy online horsepower calculators and also set up a spreadsheet to analyze the rigs performance which I thought was substandard. I'm starting to believe that considering I live at 8500 ft and have to climb a 10% grade at 7500 ft coming up Boulder canyon, that there will be a limit. I've found that if I'm willing to bring the RPMs up to about 3500 in 2nd coming up the canyon, I can hold speed at 45. The performance at grade seems to be consistent with my spreadsheets and rated HP and torque when adjusting for normal drivetrain loses and altitude. I think the headers and high flow exhaust in the future should give a little extra push coming up the hills. Look forward to reading the book. Thanks, Al

[EKS]

Since power seems an issue research the difference in horsepower for various years of the 440 engine and what the differences were. I think you will find compression ratio a major factor. Check and see if there are other heads with smaller combustion chambers that would raise the compression ratio to something that would still work with available gasoline. I had a 350 chevrolet that I ported the heads on, not for horsepower but mainly to clean up the casting flash and irregularities. It made a huge difference. It shocked me when chunks of cast iron just projected out into the passages. If you're going to change manifolds it's not that much more work to change intake, timing chain (should be looked at depending upon mileage) and maybe the cam if research and budget supports it. Remember these engines were detuned (from earlier years) which cut power and mileage.

[alhnelson]

EKS - In reference to your comments regarding compression. I've just installed a reman engine in my Clipper which now has only about 600 miles on it. It's taken some time to work out the bugs from the installation but it's getting better. I have done extensive research on the Mopar engines (More than you can imagine as I am a research consultant by profession). I've looked at the various HP, torque, and compression specs for various versions of the 440 through the 70s. As to compression, after 1971 they usually had a comp ratio of 8.2 to 1. Pre-72 nominally had 8.8 (open chamber heads), or 9.5 (closed chamber heads). My Clipper is a 1979 with 78 chassis. Of course with a reman engine,it's impossible to spec it for any specific year however I do have the parts inventory for the engine build. It has the pre-72 higher compression pistons with the open chamber heads so theoretically it could be 8.8 to 1 comp ratio which would be a good thing especially at the altitude I am at and the overall loss in compression at altitude. If fact, with all the head and block milling that could occur in a reman engine, it's hard to have a specific comp ratio but I can guess that's it's higher than if it had gotten the later pistons. In the process of getting the engine up to power I've also done lots of research trying to determine the torque and power curve for this one. In the specs, some 70s 440 showed peak torque down at 2000 RPM and others showed it higher. I'm assuming there may have been different cams used. The cam in my engine is a stock spec cam. I checked with the cam manufacturer (Melling). They couldn't provide a power curve but based on specs, estimated peak torque should be around 2600 rpm which is consistent with other 440 specs I have seen. The biggest improvement in power I have gotten since putting in the new engine was from replacing the distributor. We found the old one wasn't advancing as it should so I replaced it with a Mopar performance which has a quick advance curve. At this point, I believe the engine is putting out close to what it should. Keep in mind that I live at 8500 ft elevation and climb a 10% grade coming up to our home. I had been hoping that the Clipper would fly up the hill in third gear but that may have been unrealistic. I did some further power and grade calculations and realized that even at factory spec torque and HP, this did not compute for the conditions and a 9000 lb vehicle. I find that if I am willing to bring the RPMs up to around 3600 in second gear, I can pull the 10% grade which is at around 7500 ft, at about a steady 45 mph. Of course, I drink several gallons of fuel in the process. I'm hoping that headers and exhaust in the future will make climbing those hills a little easier. The whole engine process is like going back many many years ago when I did my share of working on cars and engines and hot rods. Of course I didn't have the internet as a source of info then but I guess I didn't need it anyway.

[Guinnessecco]

May want to increase ignition advance.  I know fuel injected engines do this at increased altitude, as well as adjust for fuel mixture.  Also, if you set the engine lean, better keep another pair of metering rods or jets with you because running lean when you get to low altitudes will burn the valves.  If you can afford the bill, after market fuel injection would be nice, or swap fuel injection from a newer 440, then you do not have to worry about changing things with altitude.  Oh, heck why not just go with turbo charging?  This was done with some of the Executive RVs but the 727 automatic transmission seems only good for about 20,000 miles with that much power going into it.

[Charlie]

I read the comments made about wrapping the headers and suggestions to "do the research".  All of the negative that was stated seems to be second hand information from some other guy and basically just opinions without any experience using the product. Thorley would not recommend using wrap since they don't make and sell it.  I am not the smartest guy around but I cannot see how the headers would get hotter when wrapper.  They probably retain the heat longer but if you blow 1000 degree heat into a wrapped or non-wrapped header, both will only get up to 1000 degrees.  I have had a set of wrapped headers on a truck for 9 years and 88,000 miles.  I took it apart for a rebuild not long ago and I found no cracks, weakness or fatigue.  I wrapped them again and installed them.  I don't know what affect the wrap may have on performance but my suggestion for using it was to reduce the heat transfer into the engine cover and floor.  I'll let you all know how it works on the headers I will be installing on my Clipper in January.

[bigray]

Charlie,

I believe you have a chevy chasis with a 400 engine. I want to go with headers. I called a Throley shop yesterday and he says they don't show anything for a 1978 chevy van.

What did you get and did you have to do some modifications. Let me know!