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Old 08-30-2007, 12:51 PM   #1
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Added headers, improved efficiency

1987 GMC S15 2WD auto ext cab truck

I just installed a set of Pace Setter headers on my 87 S15 2.8L auto truck. No other changes. Mileage increased from an average of 18MPG to 22.5MPG, and this is just off the first tank. I'm very consistent on how I fill my tank, been calculating the per-tank average for years. Won't call it a definite improvement until I've gotten 3-4 tanks through it.

All this was was a change in pipe diameter and where the exhaust comes together from the engine to the cat. I'm expecting it to slowly get better as the computer gets used to the new operating parameters, with any luck I might start seeing 24-25MPG out of it.

The engine also has a lot more power across the entire powerband with the most improvement on top of the RPM range, so it doesn't take as much gas to maintain a specific speed. Passing is also less of a chore.

Headers are made for almost every engine out there, and is a cheap way to boost both power and economy. With a fuel cost difference (based on 3.00/gallon) of 3.3 cents per mile, the headers will have paid for themselves once I've gone a little over 9900 miles. Total cost of the headers plus the install was about 325 bucks, all said and done.

Next, and final, exhaust change while it has a 2.8L is a quieter, better flowing muffler. I'm thinking either a Walker Quiet Flow or a 30 inch 2.5 in diameter glasspack, the rest of the system is 2.25 inch diameter. A long, slightly oversized glasspack should give me a nice, quiet tone without affecting velocity too much.

Calculations -
Cost per gallon divided by miles before equals M1
Cost per gallon divided by miles after equals M2.
M1 minus M2 equals cost difference per mile
Header cost divided by cost difference per mile equals number of miles that must be traveled to recoup cost.
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Old 08-30-2007, 12:54 PM   #2
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Did you reset the ECU?
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Old 08-30-2007, 02:29 PM   #3
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I installed headers on my 1993 HOnda Accord. I don't think I gained any FE, maybe a little under 1mpg. We'll see. In the future though, you can install headers yourself.
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Old 08-30-2007, 04:55 PM   #4
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Hmm, I went through all this on my 94 f150 5.8
Summit shorty torque headers, high flow y pipe with high flow cat. flowmaster 3 inch cat back system. NO GAIN in FE.
Yes it makes more power but seems to be limited to 2500 rpm and up.
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Old 08-30-2007, 05:58 PM   #5
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You need something extremely accurate like a scan gauge, and a certain amount of runs, in the same conditions, depending on how much you suspect economy will change, to figure out if they've actually done anything. I think a SG and a dyno could conclusively say whether or not something helped, but aside from that it's pretty hard to show. Even most of Metro's stuff isn't enough AFAIK.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 08-30-2007, 06:05 PM   #6
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omgwtfbyobbq, re SG - he said it's an '87
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Old 08-30-2007, 06:08 PM   #7
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Oh yeah, or eq. Like a SuperMid IIRC. Whatever works with TBI. I imagine BSFC could be measured on the dyno as well, but that would probably be prohibitively pricey.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 08-30-2007, 06:47 PM   #8
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Quote:
Originally Posted by omgwtfbyobbq View Post
You need something extremely accurate like a scan gauge, and a certain amount of runs, in the same conditions, depending on how much you suspect economy will change, to figure out if they've actually done anything. I think a SG and a dyno could conclusively say whether or not something helped, but aside from that it's pretty hard to show. Even most of Metro's stuff isn't enough AFAIK.
What he said.

Also, I agree that most of my stuff isn't up to snuff. To begin with, I think most of it isn't even A-B-A.
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Old 08-31-2007, 08:36 AM   #9
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Originally Posted by Telco View Post
The engine also has a lot more power across the entire powerband with the most improvement on top of the RPM range, so it doesn't take as much gas to maintain a specific speed. Passing is also less of a chore.
Opening up the exhaust does this, especially if your stock manifold is very restrictive. YMMV, some vehicles have pretty good manifolds from the factory, my '96 Ford 2.3 came with factory tube shorty headers. Aftermarket headers are reportedly only worthwhile on near race and race tuned applications. Glad you found a choke point. F150s may not have this issue until used at WOT.

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Next, and final, exhaust change while it has a 2.8L is a quieter, better flowing muffler. I'm thinking either a Walker Quiet Flow or a 30 inch 2.5 in diameter glasspack, the rest of the system is 2.25 inch diameter. A long, slightly oversized glasspack should give me a nice, quiet tone without affecting velocity too much.
The Walker dynomax is a GREAT flowing muffler, and pretty quiet too. Can't comment on the quietflow. If you use a glasspack be sure it is a perforated core, not a louvered core. The louvers KILL flow at high flows and don't help down low. In any case use stock ID on the muffler to maintain velocity.

Lastly, if you're up for the experimentation and replacing the entire exhaust system anyway, use a low restriction muffler (like above) and go down one size on the entire system after the cat. Low RPM exhaust velocities will be higher contributing to good exhaust scavenging and torque, and high RPM/ max flow will be the same or better for passing horsepower. I can't find my exhaust length calculator but if you can find your exhaust cam duration, it is possible to tune your exhaust to the RPM you use most like freeway speeds, etc. by placing the muffler the correct distance from the exhaust valves.

Congratulations on the gain. Don't let the increased power suck you mpg back down.
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