more power
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Junior User
Joined: Nov 2007
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From: Helena, MT
more power
ok so i have a strait 6 4.9l 5 speed 1989 bronco and just got back from pulling my trailer and I need a little more power I don’t want to do an engine swap I just want to increase the power of the engine I have any ideas?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com
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Lead Driver
Joined: Oct 2005
Posts: 6,129
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From: Ponca City, OK
I would like this to be added to the tips, tricks sticky.
For pre EFI 300 engines:
About the easiest way to get a few more hp out of one of these engines is to replace your oem rocker arms with the those from a Chevy inline six. They cost about $50 from any auto parts store, and are a bolt in change.
What is the difference, you ask: They are 1.73 ratio, as opposed you to your 1.6, and will give your valves a bit more lift, thereby allowing more fuel/air mix into your engine, giving a bit more hp. Simply ask for a set of rockers from a 75 C-10 with a 250 (4.1) inline six.
For pre EFI 300 engines:
About the easiest way to get a few more hp out of one of these engines is to replace your oem rocker arms with the those from a Chevy inline six. They cost about $50 from any auto parts store, and are a bolt in change.
What is the difference, you ask: They are 1.73 ratio, as opposed you to your 1.6, and will give your valves a bit more lift, thereby allowing more fuel/air mix into your engine, giving a bit more hp. Simply ask for a set of rockers from a 75 C-10 with a 250 (4.1) inline six.
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Joined: Dec 2007
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From: Boise, Idaho
Hrmm.... Upping the power of an EFI 4.9 is a bit more difficult than the carb'd motor. The computers are rather finicky to changes.
Some things you can do:
Higher flowing exhaust. (If you go with headers, you need to figure your O2 sensors out).
Computer friendly cam. Ask the manufacturer which ones are EFI/computer friendly.
A port and polish on the head.
Also, before any of that, make sure that the engine has a fresh tuneup with all fresh ignition, etc.
Some things you can do:
Higher flowing exhaust. (If you go with headers, you need to figure your O2 sensors out).
Computer friendly cam. Ask the manufacturer which ones are EFI/computer friendly.
A port and polish on the head.
Also, before any of that, make sure that the engine has a fresh tuneup with all fresh ignition, etc.
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Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
A port and polish is a process where you remove the head from the vehicle and then smooth out the intake and exhaust ports, removing sharp edges, casting flaws, rough casting, etc. to create a smoother path for the air/fuel, and exhaust to flow.
Before:
After:
It reduces the amount of power your engine has to put into moving air/fuel into and out of the engine. It's free power.
But, obviously, a job for a skilled professional, or someone with a knowledge of what they're doing and a steady hand.
Before:
After:
It reduces the amount of power your engine has to put into moving air/fuel into and out of the engine. It's free power.
But, obviously, a job for a skilled professional, or someone with a knowledge of what they're doing and a steady hand.
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Junior User
Joined: Nov 2007
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From: Helena, MT
so I would remove the head and have it taken to a macheine shope? what the cost like for somthing like that and has any one heard of replacing the rocker arms like udsuth78 said? do you need to replace the rods also is there any thing else that need to be modified?
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Moderator
Joined: Dec 2007
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From: Boise, Idaho
Changing the rocker arms for Chevy rockers is something that you can only do on a carb'd motor. It simulates putting in a more aggressive cam. However, since yours is EFI, you MUST get a cam that is specified to be okay with your computer.
A good machine shop will normally charge around $200 - $300 for a quality port and polish.
A good machine shop will normally charge around $200 - $300 for a quality port and polish.
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Joined: Dec 2007
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From: Boise, Idaho
That's difficult to say outright, but probably around 10 - 20hp. The head on the 4.9 is very restrictive, and opening it up helps all the other systems work together better. It's not a power adder, necessarily, it's a potential opener. It lets the engine have more of the power it naturally has.
It's also why it's such a great mod. It makes all other performance mods more effective, and since it adds power simply by making the engine not work as hard, there's generally a gas mileage gain out of it.
It's also why it's such a great mod. It makes all other performance mods more effective, and since it adds power simply by making the engine not work as hard, there's generally a gas mileage gain out of it.
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
what size tires are you running and what gears in currently in the bronco.
a gear swap will give you the best bang for your buck. tearing into a reliable motor may cause issues.
exhaust, good tune up, gears would be my choices unless the 300-6 is needing a rebuild.
a gear swap will give you the best bang for your buck. tearing into a reliable motor may cause issues.
exhaust, good tune up, gears would be my choices unless the 300-6 is needing a rebuild.
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Junior User
Joined: Nov 2007
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From: Helena, MT
I not shure of the tranny number but it is a 4 speed with overdrive (5 speed) and I really do miss the tranny I had in my 74 f100 that was granny geared is there a tranny that would be a plug and play that would give me that kind of gear rato for more pull? I an runing stock tires 235 75 r 15
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Joined: Dec 2007
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From: Boise, Idaho
You most likely have the M5OD transmission.
The other option is swapping in a ZF5 transmission, which does have a granny gear like the one your 74 had. However, a granny gear is only going to help get you moving from a stop. Other than that, the M5OD has better spaced gears for daily driving.
The other option is swapping in a ZF5 transmission, which does have a granny gear like the one your 74 had. However, a granny gear is only going to help get you moving from a stop. Other than that, the M5OD has better spaced gears for daily driving.