I have a 1940 Chevy coupe with a 350/700R. I'm currently running block hugger headers going immediately into 2.5" exhaust. I feel that I would benefit from long tube headers with another 350 I'm working on, (350 LT1 W/a cam that is a little over .5" lift and 243/247 roller using 1.6 rockers. I'm using the most popular front suspension/steering conversion in place of the stock one so that puts the crossmember ahead of the engine and out of the way. This is such a popular conversion for our street rods I was wondering if there is a long tube header application that will fit my 40.
Headers are a compromise and are designed for the application. It is pretty simple physics. Header pipe length is designed for a peak response at a specific RPM. They give a boost at that speed and a sympathetic response at a speed double the design. The way they work is when the exhaust valve cracks open there is a strong pressure wave that enters the port. That wave travels at the speed of sound independent of the speed of the gas flow until it reaches the pipe exit (into a large collector). This exit sends a reflected negative pressure wave back up the pipe. At the design speed that negative wave reaches the exhaust valve just as it is closing, ****ing out more exhaust and ****ing in more fuel/air in the exhaust, effectively a mini-supercharge. On the negative side, headers can reduce efficiency at off-optimum speed for the same reason. P***enger cars use short, unequal length manifold runners to eliminate this peaky performance and smooth out the torque curve. All this works out that a street driven car wanting peak torque at 2500RPM to 3500RPM needs headers in the 33" to 36" range. Race cars need shorter headers since they run at higher speed.
Thank you much for the suggestion. I'm using a pair of their "Block Huggers" in my 1930 Model A coupe with a 440 Mopar so I know they make a good sound product for the money. I'll contact them to see if they can set me up with some long tube headers for the 350 SBC powered 1940 Chevy coupe.
Thanks for the information. If I find a vendor that can design and build these headers, I'll consider your information as well as theirs as a guideline. I like to apply all practicable tweeks here and there during car construction to salvage H P and efficiency along the way. Thanks again!
It is pretty well do***ented Small diameter stepped tri Y headers can sometime do VERY well below peak power. Perfect for non-drag racing, and maybe that too. Not messing up the carb with reversion is important, however I get it. Go over to Speed Talk, register and search for Calvin/exhausted.
I doubt you'll gain any serious HP swapping to long tube headers, but I understand wanting to get them. It's going to be nearly impossible for any company to build long tube headers for your car without having the car in their shop. Just to many variables to consider with custom V8 swaps. The only over the counter headers that might fit easily would be the universal "fat fender Chevy" fenderwell headers. But not every car owner wants fenderwell headers, and they may or may not fit the style of your build? I bought polished stainless fat fender Chevy headers for my '39 Chev coupe, and love the way they fit. But I put them on my SBC before I built motor mounts, so set my engine based on these headers.
Do you have room for the headers to drop straight down then turn 90 degrees backwards? If so, look at headers for a mid 60's Corvette.
We used Hedman #68300 on our '37-'38 Chevy's 40 years ago. I used them on my Coupe too . Look at them here at Hedman: Engine Performance & Vehicle Customizing Products From Hedman | Hedman Performance Group
Those aren't a very good buy compared to others on Ebay. I paid $107 for the same headers in polished stainless as shown above on my '39 picture. They're a little higher now, but still under $120. https://www.ebay.com/itm/EXHAUST-MA...045775?hash=item46c19da8cf:g:yLQAAOSwSwBgNI7E Yes, they're not quite equal length, but unless your engine is really built, it wont appreciate the difference.
All motors are different, Dyno time will tell you if you're looking for the max performance, torque @ a certain ""RPM ""or Wide Open. Other then that you are guessing. This is what it takes to fine tune , Dyno , $$$, large inventory of parts & experiment.
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