Straight 6 mods?
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Junior User
Joined: Jan 2012
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Straight 6 mods?
Hello, I've posted on here for advice on repairing my truck before. Now I've decided to ask about a more positive topic; makin' it better! 
I have looked around online and found tons of mods for the motor in my truck which is a 1982 300ci inline six with a 78 intake to remove EPA's pathetic attempt to "better" the motor. I would like some input as to what mods would be useful to the motor. I'm not looking to give it hundreds of hp, and I also don't want to work with internal mods (cams and such). I have and am, however, considering purchasing a set of headers for the i6. I don't want to spend tons of money, but id like to do some stuff to make it have some more power, and if possible, improve the mileage. I've heard before that headers will improve mileage as well as horsepower. Were those words a crock of chit, or are they true? Any other useful mods? Stock 78 carter carb on the intake, stock air filter, stock everything else. The motor only has about 9k on a rebuild so i've got plenty to work with.
I have looked around online and found tons of mods for the motor in my truck which is a 1982 300ci inline six with a 78 intake to remove EPA's pathetic attempt to "better" the motor. I would like some input as to what mods would be useful to the motor. I'm not looking to give it hundreds of hp, and I also don't want to work with internal mods (cams and such). I have and am, however, considering purchasing a set of headers for the i6. I don't want to spend tons of money, but id like to do some stuff to make it have some more power, and if possible, improve the mileage. I've heard before that headers will improve mileage as well as horsepower. Were those words a crock of chit, or are they true? Any other useful mods? Stock 78 carter carb on the intake, stock air filter, stock everything else. The motor only has about 9k on a rebuild so i've got plenty to work with.
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Junior User
Joined: Jan 2012
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Yeah I considered that except I literally just put a freshly rebuilt carb on it about 2 weeks ago. Aside from that, I'm assuming that four barrels would probably drop my fuel economy. The truck is a short bed step-side. I'm only going to use so much power and then i'm wasting my wallet.
Senior User
Joined: Dec 2009
Posts: 176
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From: Spring Hill
Well offenhauser says in the intake description from Jegs "Provides increases of 50 HP over stock, or with headers and cam up to 115HP overstock! Holley 510-0-8007 390 CFM 4-bbl carburetor recommended" so with just headers im sure you could run a 350 CFM 2-barrel with a 2 to 4-barrel adapter plate. Honestly though if you dont wana tear into the motor or lose the intake because you just rebuilt the carb, i dont know what your looking to do besides headers and exhaust.
Logistics Pro
Joined: Aug 2003
Posts: 4,701
Likes: 6
I had a holley and an offy c series, and never could get it tuned right. I got a heated carb spacer, 2 to 4 adapter and ran a motorcraft 2150 and was much happier.
That being said, I think the best mods for these would be somewhere between full modified and stock. I have a new carter carb, and I think chevy rockers, efi manifolds and a good air filter would be the way to go on a daily driver.
That being said, I think the best mods for these would be somewhere between full modified and stock. I have a new carter carb, and I think chevy rockers, efi manifolds and a good air filter would be the way to go on a daily driver.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
I echo many of the comments already made.
Without tearing into the engine - a carb, intake, and headers is the way to go. I recommend first starting with upgrading the exhaust since it will be the foundation for potential future mods.. Depending on the header, get a single 3-inch exhaust or dual 2.25-inch system coupled with muffler(s) of your choice.
Stock air cleaners tend to be very restrictive. A open-element air cleaner and filter is an easy mod and is cheap to boot. You'll be rewarded with snappier throttle response and some extra horsepower.
Next up is to upgrade the intake. Switch to the Offy and even with a 2-barrel (use a 2 to 4 bbl adapter) the driveability can be improved while maintaining or even improving the MPG.
Without tearing into the engine - a carb, intake, and headers is the way to go. I recommend first starting with upgrading the exhaust since it will be the foundation for potential future mods.. Depending on the header, get a single 3-inch exhaust or dual 2.25-inch system coupled with muffler(s) of your choice.
Stock air cleaners tend to be very restrictive. A open-element air cleaner and filter is an easy mod and is cheap to boot. You'll be rewarded with snappier throttle response and some extra horsepower.
Next up is to upgrade the intake. Switch to the Offy and even with a 2-barrel (use a 2 to 4 bbl adapter) the driveability can be improved while maintaining or even improving the MPG.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I have a Hedman header, Offy 4-barrel intake and Edelbrock 500 CFM on mine. I'm happy with it. The header was a pain (had to switch to a mini-starter, re-route transmission lines and a brake line) and it's a pain to install the throttle linkage on a straight six with a 4-barrel because the carb sits 90 degrees. But I enjoy the added power. Mileage isn't all that great because I haven't spent much time tweaking the rods and jets; so far just one set of rods and adjusted the accelerator pump stroke. Don't waste your time with a 2-barrel carb if you've got a 4-barrel intake; otherwise there is no point. 4-barrels can actually be more efficient because the primaries are typically smaller.
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Fleet Mechanic
Joined: Feb 2007
Posts: 1,326
Likes: 48
From: Middle TN
+2 on the fuel injection header!!!!
They flow good and are cheep....I think I paid 50 bucks for mine
They are easier to keep sealed and tight than headers
No clearance problems
You do have to buy the front exhaust pipe the go with it
You have to make an adapter for carb heat if you live in cold country (Same with headers)
Adapt the choke heater if your carb is equipped with an exhaust heated choke
They flow good and are cheep....I think I paid 50 bucks for mine
They are easier to keep sealed and tight than headers
No clearance problems
You do have to buy the front exhaust pipe the go with it
You have to make an adapter for carb heat if you live in cold country (Same with headers)
Adapt the choke heater if your carb is equipped with an exhaust heated choke
Fleet Mechanic
Joined: Feb 2007
Posts: 1,326
Likes: 48
From: Middle TN
If you are running a 78 YFA carter carb. This would be a lean emissions carb and you need to keep your EGR working or you will have very high cylinder temps.....not good for valves or pistons.
You need to consider this before modifications.
You need to consider this before modifications.
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Junior User
Joined: Jan 2012
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Alright thanks to everyone for the good advice and heads ups. I'll probably start with upgrading the exhaust as recommended and I'll look into the fuel injected manifold. The intake and exhaust mannys I just put on are off of an old motor, so i'm not losing money in that area. Still have reservations about the 4 barrel but I'll keep considering. Also the open air filter may happen. I feel like she doesn't have as much snap as she should so that sounds like an easy way to help with that some. Thank you all.
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Junior User
Joined: Jan 2012
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Also to Bart - the carburetor that is on the truck is the same one that came off of the intake and exhaust that is on the motor now. It has no EGR. There is a spacer plate instead. It never did for as long as my grandpa had the motor. The 82 motor that is in it did have that plate, but i put the current intake/exhaust/carb on it to eliminate that aspect. I do have more power now that I did before, but still not as much as it should have which is why I asked. The EGR setup was entirely plugged off as the truck has no hookups for it, so I figured it was nothing but wasted space. I'm also inexperienced so perhaps I'm making a fool of myself.
Senior User
Joined: Nov 2007
Posts: 215
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I have a Hedman header, Offy 4-barrel intake and Edelbrock 500 CFM on mine. I'm happy with it. The header was a pain (had to switch to a mini-starter, re-route transmission lines and a brake line) and it's a pain to install the throttle linkage on a straight six with a 4-barrel because the carb sits 90 degrees. But I enjoy the added power. Mileage isn't all that great because I haven't spent much time tweaking the rods and jets; so far just one set of rods and adjusted the accelerator pump stroke. Don't waste your time with a 2-barrel carb if you've got a 4-barrel intake; otherwise there is no point. 4-barrels can actually be more efficient because the primaries are typically smaller.
