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Old 08-25-2009, 01:36 AM   #1
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Headers vs. Manifolds and EFI vs. Carb

Ok, I only know a little. But a car man friend of mine (works for Nissan/Infinity International) suggested that I go with straight headers instead of manifolds and that I should consider a single exhaust with one muffler instead of two mufflers and two exhaust pipes (for cost).

Also, he said I should do an EFI conversion, instead of using the current engine set up. He believes that electronic fuel injection will be much better for gas mileage. But what really are the benefits/cons, costs, and effort to do such?

Any suggestions? 78 Argosy 28' MH 454 gas.

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Old 08-25-2009, 06:22 AM   #2
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I don't know about the exhaust issue other than a dual system usually breaths better and is more efficient.

On the fuel issue, modern fuel injection systems are more efficient and less troublesome than carburetors. That being said, the cost of converting may be high enough that you will never amortize the financial benefit.

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Old 08-25-2009, 06:46 AM   #3
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I have toyed around with a bit of this stuff on my Jeeps.
From my little bit of knowledge your friend is correct on most of what he has said. The key to a good exhaust system for a gas engine is it free up the exhaust so the engine breaths better but it also must have the proper amount of back pressure in the system which helps the combustion chamber to be more efficient.
Headers flow more freely than most stock manifolds for reasons such as the restrictive bends in the manifolds, to much intermixing of the exhaust gasses (not a smooth flow) and often times there is still cast left on various parts of the manifold left over from the molds. The down side to headers is that you must have a quality gasket and fasteners or they will leak.
Single exhaust - Single exhaust are good for low end torque but the size should be 3" diameter for such a big motor. A 3" diameter will flow at high speeds almost as well as a dual system.
Dual exhaust - Duals are better for highway cruising.

Carb vs Throttle Body vs EFI - Both have their pros/cons. I have converted my old Jeep 360 engine from a carburetor to a GM Throttle body system.
For the most part a carburetor is simple and reliable depending on which on you have. The aftermarket carbs such as Holly or Edelbrock can be tuned and work pretty well.
TBI - Throttle body injection - Best bang for the buck. Only has a few sensors and very reliable. I have a GM tbi system converted to work on my Jeep 360 engine and I love it. The system is from the 1990 era GM vehicles with a chip burned for the cam and spark curve on my engine. Parts are available in any home town auto parts store. It runs darn near perfect in all weather and elevations. I gained about 2 miles per gallon and has great drivabillity. Aftermarket tbi systems such as Howell are great. These have been great people to deal with.

Howell Engine Developments Inc. - Home

EFI - These systems are the most expensive. They require a change to the intake manifold of course. Other than that I don't have much other information.
With a tbi or efi you may gain a few horse power and a bit of mileage if you spend the time tuning the system properly. Once it is tuned your done versus a carb that may need tweeking from time to time.
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Old 08-25-2009, 07:17 AM   #4
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Headers are the most cost effective performance / economy upgrade you can do.

You'll also dissipate heat much better with headers.

I used Headman's and Flowmaster 70 mufflers. Got all my stuff from Summitt Racing.

Going with fuel injection on these big motors is not reputed to make all the difference one would think. The relative gains are wiped out by the expense.

Lift the carb with a spacer and keep an eye on the vacuum gauge for economy.

If you go with a dual setup use the reducers that will come with the headers to go back from the headers with 2.5 pipes. A little back pressure is a good thing.
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Old 08-25-2009, 07:17 AM   #5
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Electronic Fuel Injection for the GMC Motorhome.
Don,

Finish your research and as mentioned above you must take into consideration the initial cost and how long it will take to break even.
(it took over 120k for me on our 95 454 Burb, sold at 170k).
The first mod I did was stainless headers and a 4" single exhaust from Banks Engineering, it made the most significant improvement in mpg and towing ability.

IMHO..... ck out the engine (how many mi on it?), get it running as effienciently as possible do the exhaust first and work from there.

Don't forget about the Gear Venders option....
Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.
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Old 08-25-2009, 09:19 AM   #6
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Y'ure gonna have to drive a million miles to break even. The gas savings will not be enough to justify the expen$e. Unless U fabricate and install your own stuff and utilize junk yard parts as well.

Keep it simple. The headers and open exhaust does help. You will notice more gain in power than mileage. Will cool the engine compartment down alot too. Those cast iron headers retain alot of heat. Headers move it lower and the flow under the chasis moves it away. I'd stick with dual exhaust.

Ditto on: Headman's and Flowmaster 70 mufflers. Got all my stuff from Summitt Racing as well. Best value. I stuck with the stock rochester quadrajet and oem ignition but made sure it's not defective. I did put the more agressive ignition advance weights in the distributor. I might have gained 1 to 2 mpg overall.

Drive and accelerate slow will get you more savings. I drive 55 mph or slower. Still lucky to break much over 10mpg.

A family member has a newer airstream motorhomewith fuel injection, fancy exhaust, overdrive transmission and does have much more power. But still only gets 12 mpg with similar gentle driving.

good luck.
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Old 08-25-2009, 10:19 PM   #7
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Thanks for the tech advice. It looks like throttle body injection and Headers - Headman's with Flowmaster 70 with 2.5 pipes. Yes?

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Old 08-25-2009, 10:32 PM   #8
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Wow. It looks like doing EFI would be illegal on my rig given that it's a 78' and I want to license it in California.
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Old 08-26-2009, 02:43 PM   #9
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Quote:
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The gas savings will not be enough to justify the expen$e. .
Hopefully you will post changes to mpg when all mods are in.

My 454 1999 std configuration except for K&N air filter, with new plugs, wires, coil, distributor cap and rotor got 9.5 mpg on last trip of 2,500 miles, all types of terrain driving mostly 60 with dash a/c.
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Old 08-28-2009, 04:45 PM   #10
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i installed this from retrotechspeed.com
now i can plug in my laptop and tune the engine!
i dont even have to bother looking @ the dash, my laptop tells me everything accurately.

my 310 went from about 4mpg to 8 going 75mph
i bet i might hover around 9 going 55 tho

the engine went from very rough and no power to humming after new fuel lines, pump, filters and EFI
i am very happy with it's performance. but lets hope the software wont be compleatly out of date in another 25 years...cause i know gasoline engines might.
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Old 08-28-2009, 05:16 PM   #11
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WOW...they must be raking in the $'s.

Interesting that they don't highlight any mpg gains.
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Old 08-30-2009, 02:51 PM   #12
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Quote:
Originally Posted by mary quite c View Post
i installed this from retrotechspeed.com
now i can plug in my laptop and tune the engine!
i dont even have to bother looking @ the dash, my laptop tells me everything accurately.

my 310 went from about 4mpg to 8 going 75mph
i bet i might hover around 9 going 55 tho

the engine went from very rough and no power to humming after new fuel lines, pump, filters and EFI
i am very happy with it's performance. but lets hope the software wont be compleatly out of date in another 25 years...cause i know gasoline engines might.
Wow! That's quite impressive. Now you can tune your fuel delivery but have you considered an MSD ignition with an adjustable timing setup?

Are you running the self learned setup on the EFI or have you changed any of the parameters??

The nerd in me would want to have it plugged into my laptop all the time so I could monitor alongside my GPS.
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Old 08-30-2009, 06:50 PM   #13
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What does MSD stand for?
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Old 08-31-2009, 05:15 AM   #14
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MSD Ignition

MSD is a brand name.

I believe it comes from the fact that it is a multi-strike,(MS), ignition system, if the computer senses a mis-fire it will strike that cylinder again in a nano-second.
Had a MS ignition on our 454 Burb, noted for their lumpy idle, smoooothed it right out.
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