Dual exhaust - surprise increase or imagination?

Jack 34pu

Jack 34pu

Senior Member
I finally put duals on my 221ci 34pu yesterday. I drove it around town a bit and really didn't notice anything other than a sweeter sound. Today, I took it out on the 4 lane and I was shocked at the difference starting arounf 40mph and up. Is a fairly noticable increase in power and smoothness to be expected or is my mind playing games with me? Of course my wallet is somewhat lighter!
 
This is a question that JWL should be able to answer. Somewhere in the back of my mind he has tested duals vs single exhaust and found no real significant difference in performance.
 
Either way, it's worth it, isn't it Jack? Used to get at least 10hp just with a wash and Simonize, empty the ash trays and sweep out the mats as I recall. ..B.
 
Lawson Cox said:
This is a question that JWL should be able to answer. Somewhere in the back of my mind he has tested duals vs single exhaust and found no real significant difference in performance.
Click to expand...
You are right, Lawson. But it's the sound that counts.
 
Folklore has it there were three basic things a young hotrodder did 'back-in-the-day' to gain more power.
Dual Carburetors
Dual Exhaust
Aftermarket Cylinder Heads.

Dual exhausts should make a differance, after all the original Ford set up was pretty woeful so just about anything should (at least theoretically) be an improvement.
 
This is a topic I'm glad to see as I want to put duals on my 36 and wondered what improvement it would make. Anyone try putting headers on a 36 without modifying the battery box?

Phil
Chambersburg, PA
 
The dual exhaust didn't make much, if any, difference on the engine JWL tested in his book. However, it was an 8BA. Compared to a '34, the exhaust manifold passages of an 8BA are huge. I think there's a good chance you gained some usable HP, especially at higher RPM levels. Anyway, I'm sure the sound was/is worth it.
 
Fe26, is right on,did it as a teenager,and do now .not just for looks either,there is a power gain. Harold, central coast Ca.
 
On my '46 with a 59A running Fenton headers,dual exhaust with Smitties I definitely noticed an increase in performance over the stock single system.
In Roger Huntington's 1951 book "HOW TO HOP UP FORD &MERCURY V8 ENGINES" he notes about a 7% HP loss with stock system and up to 10 % gain in peak HP with headers,duals and less restrictive mufflers. Really only noticeable at higher RPM's.
These seem to be common figures among the Hop Up books of the '40's & '50's. How true is up for speculation.
 
There are MANY myths still roaming around out there. Some will never die. The thought that a tiny little 221 engine is going to become supercharged by installing a dual exhaust system is one to smile about. Either something was seriously wrong with the original system or someone changed the engine at the time the exhaust system was being worked on.
 
I really feel like I got an increase on my 8BA when I installed headers and dual smitty's. The lore is that you can't 'feel' a difference unless you add on 15 horsepower (to a typical V-8...) and I'm sure I got nowhere near that, but my seat-of-the-pants meter says she got a hitch in her get-along.
 
years ago i worked in a auto repair shop & the owner had us shine the hood when ever we worked on a car. he said the owner would think it runs better most of the time he was right
 
Logic dictates that duals with stock manifolds would provide a VERY small increase in revving capabilities, good headers would add a bit more, but actual hp gains will only come when the rest of the engine is modified to take advantage of the better exhaust. The whole point of a good exhaust system is not to sound good, but to give the increased duration of the cam a decent shot at getting rid of the increased quantity of fuel/air from the multiple carbs and better porting/valve flow. Of course, the better sound is just as important. :D
 
Thanks for all the reply's. Another thing I noticed - I'm running a separate temp gauge for each side and the pass side (where crossover pipes converged) was always running 15* hotter. I always thought it was a diff in the cheap gauges but after installing the duals, both sides now match in temp. It is a 221ci but a 1942 Canadian military - not the original. I drive "Lil Red a lot and know her qualities and it sure feels like she has an extra something above 40mph. But as noted above, a polished car also seemed to run better. Anyway, it was worth the effort and hope you all can enjoy your rides today.
 
As a kid with no $$, I asked in Pep Boys if a chrome exhaust extender added horsepower? The answer was YES: 5 HP.
I then asked how much gain wilth a rusty extension stolen for Jessie's Junk Yard in Cross Keys, NJ ...
clem
 
Only way to prove the point is on a dyno and measure the actual horse power before and after. My 35 rebuild has only just started but there is already a nice set of ceramic coated headers on the shelf that will supply dual exhausts. Expected HP gains? Who cares , we all know it will sound great!!
 
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