OHV headers on SOHC

[JohnnyO]

@MSGia - fyi, I put a set of shorty headers on my sohc 2003 Ranger and dyno'd the truck before and after. The torque and power actually went down with the headers! Unless you have another reason to put on headers, I would spend the money on something else.

Guy who runs the Sport Trac board scored a deal on a used but unused set of JBA's still in the box. He dyno'd the Trac before and after and found a difference of less than 5 hp. It's not that the headers are bad, just that the stock manifolds are pretty good.

 

[RonD]

Yes, a lot of people find out that "bolt on" parts for better performance are not always "better" and can be worse

Car makers spend a lot of research $$$ on "bolt on" parts, and if its better then they "bolt it on", thats what they sell............performance

 

[JohnnyO]

Yes, a lot of people find out that "bolt on" parts for better performance are not always "better" and can be worse

Car makers spend a lot of research $$$ on "bolt on" parts, and if its better then they "bolt it on", thats what they sell............performance

Well, there's compromises and cost considerations. For example, I put a Gibson cat-back exhaust on my old Sport Trac. Gibson claimed 8 hp but I got it for better gas mileage (plus my sister got me a $100 gift certificate for Summit Racing, she only lives a few blocks away from Summit). Highway mpg was 3 mpg better than the EPA sticker but the noise level would be completely intolerable for 95% of people.

 

[sgtsandman]

Highway mpg was 3 mpg better than the EPA sticker but the noise level would be completely intolerable for 95% of people.

Kinda like it’s owner?

 

[MSGia]

@MSGia - fyi, I put a set of shorty headers on my sohc 2003 Ranger and dyno'd the truck before and after. The torque and power actually went down with the headers! Unless you have another reason to put on headers, I would spend the money on something else.
2msgia

Thanks for the reply, tell me more! What were the power losses? I was only considering replacing them because I’m replacing my entire exhaust system.

 

[MSGia]

I also like MPG and I’m trying to get the perfect exhaust note. Also, would aftermarket shorty headers not make room for tuning potential?

 

[RonD]

Headers are designed, like intakes, to get free extra power

Call "scavenging exhausts" been around since the late 40's early 50's on factory engines
That's where the MYTH of backpressure comes from

The way Scavenging exhaust works is simple to understand but hard to design yourself
This is a BASIC description not a "how-to", you can look that up

If you have air travelling in a 1" pipe and it is connected to a 2" then there will be a pressure drop when the air gets to the larger pipe, I know DUH
Well in the case of a V6 if you have three 1" pipes connected to one 2" pipe then as one 1" pipe's air(exhaust) reaches the 2" pipe it causes the pressure to drop in the other two 1" pipes<<< important
This pressure drop PULLS the exhaust out of each cylinder so piston doesn't have to PUSH it out, so it leaves more power on the crank
Free extra power

The design is based on engine size
The smaller pipe needs to be the right size to have a good Velocity, so you get a good pressure drop
Too large a pipe and not enough Velocity so no pressure drop
Too small a pipe and it restricts flow
Larger pipe needs to the right size as well, not to small and not too big, its called the Collector

And then there is the length of the smaller pipes, besides the sizes the length also decides when the lowest pressure occurs in the RPM band
Most factory manifolds have lowest pressure at mid-RPM band, 2,300-3,000rpm
Most off the shelf "headers" are designed for slightly lower RPM band, 1,800-2,500rpm for "off the line" power
Racing headers are higher RPM band, 3,500-4,000rpm

You can only pick one RPM band, lol


MYTH of backpressure
People would remove factory exhaust manifolds, and put on "freeflow" headers, larger pipes
Then go for a drive....................
"WTF!!! I LOST POWER, WTF!!!???
"This engine must need backpressure"

No 4-stroke engine can work with backpressure, they just lost the scavenged power from the factory exhaust manifolds
Stick a potato up the tail pipe see how engine does with backpressure, lol

Even straight pipes, one on each exhaust port can take advantage of scavenged power
The length and diameter of the pipe can have the same effect, the larger pipe is the OUTSIDE, lol, big pipe
As the exhaust exits the end of the pipe it will create a suction in the pipe and if exhaust valve is opening again then scavenged power


On intakes they use Runner Lengths to get a mini-boost
When an intake valve closes it creates a pressure wave that travels back up the intake runner, it then bounces off the end of the runner and heads back to the intake valve, if the reflected pressure wave hits the intake valve as it is opening again then it forces more air/fuel mix into the cylinder, mini-boost
Not much extra power but its free power just by a good design, and it is of course RPM band specific

 

[rubydist]

I was able to find the dyno graph for the 2 runs:

What was interesting is that you could feel that torque bump just before 3500 rpm with the JBA, so the "butt dyno" said they produced more power, but in fact they were just catching up to the stock manifolds at that point.

 

[ekrampitzjr]

In contrast to the older engines, automakers today don't miss too many tricks on manifold design. Racing Beat said after the Mazda RX-8 came out almost 20 years ago that it did a lot of experiments with the exhaust system and could pick up only a few hp—that's how good the stock factory setup was. It stands to reason that Ford would have a good manifold design by the time the SOHC 4.0 appeared.

For an idea of what was bad, look at the original 1950s–1960s iron exhaust manifolds for the small-block Chevrolet V-8s.

 

[MSGia]

I was able to find the dyno graph for the 2 runs:

View attachment 90905

What was interesting is that you could feel that torque bump just before 3500 rpm with the JBA, so the "butt dyno" said they produced more power, but in fact they were just catching up to the stock manifolds at that point.

Well, thanks for the dyno graph. Better save that 370$ for some air suspension…

 

[bobbywalter]

the dyno graph is good. congratulations with finding out the factory tune was spot on...

how far did you modify the air fuel and timing tables? did you go all the way with audible detonation or just fall off?


what you need to do is modify timing and fuel to take advantage of the available air flow potential to see if there was power available there....so how many tunes did you try? how far did you push the factory system and the headers?


ron is in the ballpark when he says the myth of back pressure..... but back pressure is just the harmonic of airflow labeled as backpressure. its not true backpressure...just the power pulse.


it is the reason you need to tune on the rollers with your exhaust and intake in place. and modify from there.

 

[rubydist]

@bobbywalter - it was a Bama Tune that I ordered telling him that I was going to put the headers on, so he had accounted for the headers in the tune. I had the same tune in both of those runs. Later I got the SCT Pro Racer s/w and did my own tuning, but that was after I added the supercharger.

Backpressure is completely different from the exhaust pulse pressure waves scavenging the cylinder.

 

[bobbywalter]

yeah....they get confused with scavenging, but often that is the exact reference. at least what they mean..most guys when i ask to explain back pressure...are referring to flow.

tuning the intake and exhaust together can really move a power curve . after seeing what went into the 3.5 ecoboost...it is amazing what can be done....and how well the oem system works.

do you remember what the tables were or have it still?? its a place where canned tunes screw people over a direct tune on rollers. there is base stuff that is close enough on most v8s...but the 4.0 is a finnicky sob with tuning. with higher octane i have seen 15 hp on tune with a 4.0 with better springs....the valve float was atrocious....the cammer engines do really well... but these things were never intended to go over 5000 rpm...


not alot on hp tuners for them...

 

[Josh B]

I shift mine at 2500, it seems to be at a good place there

Yall got me wondering about the exhaust on mine, and wondering if I have a better option with the Explorer exhaust. Well I just went and measured it at the tailpipe is 2 1/8" on the Ranger and a bit less on the Explorer, I didn't readjust the caliper but it looks like about an even 2"

I would have expected the 96 would had the bigger pipes, but could the 96 Explorer Exhaust manifolds have any advantage over the 93 Ranger exhaust manifold ? I'll be leaving the 96 Explorer intake behind due to the 93 Ranger wiring harness

 

[MSGia]

So, what do headers do for exhaust tone, deepen it, louder, etc... Because I am really chasing the perfect exhaust tone and (partially) engine bay looks. I keep changing my mind on everything