Headers on a 4.0 SOHC

[Flash]

Has anybody done it? Have you logged any real results?

Usually I'd just go ahead and do it but parts for Explorers aren't that common here so I'd have to import them.

I'm asking because none of the headers I've seen in any ads look that great.

 

[Greg_DonWindsor]

Yes. I bought the Gibson ones. It was absolutely worth it.

 

[Flash]

Yes. I bought the Gibson ones. It was absolutely worth it.

Can you elaborate please?
Improvement in power, economy, driveability?

Thanks.

 

[Greg_DonWindsor]

There was a very noticeable improvement in power, sound, idle, and economy (when on cruise and not hammering the throttle of course). I would not recommend installation of headers if you do not already have air delivery upgrades upstream, as in a cold air intake, larger MAF sensor, and throttle body.

 

[Greg_DonWindsor]

http://www.explorerforum.com/forums/showthread.php?t=389587

This thread i posted a year ago contains mpg and 0-60mph data before and after the install. I already had all upstream air delivery upgrades, and the gibson cat-back at the time I installed the gibson headers, and a new set of magna flow cats.

 

[Flash]

http://www.explorerforum.com/forums/showthread.php?t=389587

This thread i posted a year ago contains mpg and 0-60mph data before and after the install. I already had all upstream air delivery upgrades, and the gibson cat-back at the time I installed the gibson headers, and a new set of magna flow cats.

D'oh, I had already come in on that thread way back then but didn't see your updates.

It was my understanding that none of the intake components were any impediment to airflow and could supply a lot more horsepower than was required.

Last thing: the reason I was asking if anyone had any actual experience with these things was that those Gibson headers look like neither tuned length nor interference type.
Now doubt they'd flow better than the standard manifold but I didn't think they'd give much extractor effect.

 

[2000StreetRod]

exhaust restriction

In my opinion the worst exhaust restriction in my stock system were the bends in the downpipes upstream of the cats.

I retained my stock manifolds but upgraded everything downstream and my max power only increased by 10 rwhp. I would be surprised if any header that will fit in the space available would increase power by more than 2 rwhp. 4pointslow has headers on his 98. He may have measured the improvement.

 

[Flash]

In my opinion the worst exhaust restriction in my stock system were the bends in the downpipes upstream of the cats.

I've noticed those bends and the tortured path the exhaust takes to get into the cats.
I've spoken to a custom exhaust shop abouting routing the pipes differently.

With the headers it's not so much flow as whether or not the design will produce the pulsed extractor effect.
None of the designs I've seen look very good.

 

[2000StreetRod]

downipes

My 2" dia. downpipes were cut to a short length and expanded to fit 2.25" dia. high flow cats.

The cat output 2.25" dia. pipe was expanded to fit the input of a 2.5" dual in/3" single out Y.

You have to be careful modifying the exhaust system to reduce flow restriction to increase max power or you will lose low speed torque. My torque actually increased slightly and I think that was due to the Dynomax VT muffler.

It has a spring controlled variable flow valve.

 

[Flash]

Rod, do you keep a photo log of everything or do you throw your car up on a hoist every time somebody needs a visual clarification?

2x2.5 would sure slow the gas velocity some. Maybe investigate exhaust pipe wrap to keep the heat in and the velocity up.

 

[Greg_DonWindsor]

2000streetrod, I would never question your knowledge and experience with the 4.0 SOHC, as you have more experience working on it, and more detailed posts than most members on this board. Regrettably I've never had access to a 4wd dyno to provide quantitative data, though I'm sure I gained more than 2hp after the header and cat install. The 2+ mpg increase in efficiency I attained, and 0.5s faster 0-60 time would seem to suggest a greater effect of this mod, though of course it is difficult for me to determine whether the majority of this performance improvement is attributable to the headers or cats, due to the fact that I had installed both at once. Regardless, I feel that the header install is a worthwhile mod for anyone looking to extract the maximum performance possible from the 4.0 SOHC motor. I would welcome any and all criticism and dialogue to the contrary in order to help fellow board members find the best direction for their respective projects.

 

[2000StreetRod]

photos & 2x2.5"

Rod, do you keep a photo log of everything or do you throw your car up on a hoist every time somebody needs a visual clarification?

I take photos during all of my modifications so I can remember what I did and to help others who might perform a similar mod. The photos also help me plan future mods.

2x2.5 would sure slow the gas velocity some. Maybe investigate exhaust pipe wrap to keep the heat in and the velocity up.

I designed the exhaust system to accommodate the higher flow with the M90. I decided that the area of a single 3" dia. pipe (7.07 sq. in.) would be adequate. The area of two 2.5" dia. pipes is 9.82 sq. in. but that only occurs at the Y inlet. The area of two 2.25" dia. pipes is 7.95 sq. in. which is comparable to the 3" dia. pipe.

Many people paint their headers black. I painted my stock manifolds silver to reduce heat radiation. I thought about wrapping my manifolds and pipes with insulation to retain heat but I think that would promote rust and significantly reduce the life of the pipes.

 

[2000StreetRod]

headers

From an aesthetics standpoint I prefer cast iron manifolds to headers because they are quieter with a deeper sound. From a cost standpoint I prefer stock exhaust manifolds because they have no additional cost, they last longer and they are less apt to warp. From a performance standpoint I prefer headers but high performance (tuned) headers are very difficult to implement on a V6 engine compared to an inline 6 cylinder.

In my opinion the stock manifolds flow fairly well but are not tuned and could benefit from porting. Tuning for scavenging has a limited rpm range and is normally done for the upper engine speed range where max hp occurs. I added my M90 to increase low to midrange torque to improve driving pleasure. I performed dyno testing before and after the exhaust system change before adding the M90. All of the 10 rwhp increase was due to reducing flow restriction since I retained the stock manifolds. The reason I think headers would only increase performance about 2 rwhp is because they can't really be tuned due to the engine configuration. They mainly just reduce flow restriction. 2 rwhp is not insignificant since the stock rwhp is only 150 to 160 depending on the condition of the engine. For estimating purposes I use $100 per rwhp increase.

 

[Sedition]

Seems interesting, Subscribed!

StreetRod, Have you ran the quarter mile with that rig of yours yet?

 

[2000StreetRod]

header performance improvement

Many header manufacturers advertise up to a 10 to 15% increase in max hp but they do not publish any actual dyno results supporting their claim. The worse the stock manifold flow compared to other engine components the more chance of performance increase with headers. Vehicle manufacturers typically design the engine system with comparable performance components. When Cologne started manufacturing the SOHC V6 for better performance than the OHV V6 they increased the compression ratio and the flow of the intake system, heads and exhaust system. Just improving the flow of one component (such as the exhaust manifold) will not be that effective if other components (i.e. heads) still restrict the max flow of the system.

The only type of equal primary tube headers that will fit in my Explorer are short which may improve max engine rpm flow but will decrease low to mid engine speed torque. There just isn't room for long tube equal length primaries that would improve the engine range I'm interested in.

. . StreetRod, Have you ran the quarter mile with that rig of yours yet?

No, and I don't ever plan to. I'm not really interested in competing with others. I'm mainly interested in making improvements to what I have and measuring those improvements on a dyno under more controlled conditions.

 

[Flash]

Many people paint their headers black. I painted my stock manifolds silver to reduce heat radiation. I thought about wrapping my manifolds and pipes with insulation to retain heat but I think that would promote rust and significantly reduce the life of the pipes.

The best option is an internal coat of ceramic to for that, if you can justify the cost and bother.

I keep forgetting you guys have a corrosion problem there.

 

[Flash]

The only type of equal primary tube headers that will fit in my Explorer are short which may improve max engine rpm flow but will decrease low to mid engine speed torque. There just isn't room for long tube equal length primaries that would improve the engine range I'm interested in.

That is a very good point and is the crux of my enquiry.
Of the headers I've seen I've wondered if they'd do any good.

I'm not interested in top end power.

I have an M90 but it's earmarked for my BMW, it suffers from low end blah until the cam kicks in at around 2300.

As you say, the standard manifold appear ok. But i was shocked when I saw the 5.0 manifolds!