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01-29-2011, 08:46 PM #1
- Join Date
- Apr 2006
Has anyone done a carb to TBI swap on a 454, long backround story.
Here's the deal, I am working on a friend's truck he just bought recently. An almost showroom looking 1984, that's right a 27 year old Chevy, K30 one ton 2WD camper special, pick-up with a 454 engine. Brought it to me and it was running like crap. I did the basic tune up to it. Plugs, cap, rotor, and fuel filter, set timing. It was extremely lean. Idle mixture screws were out 7 full turns, almost to the point of falling out of the carb. Oh, did I mention it has a rebuilt carb on it? Number traces out to a 1980 454 truck. Ordered a rebuild kit for the carb and he had to make a trip with the truck. He Calls me from Maryland a few days later he's heading back to PA and the truck will not go over 45 mph with out backfiring. He does in fact make it back. Truck is missing bad, backfires if you try to accelerate and has no power. We (I have another friend helping me) think he might have burned a valve or melted a piston. Compression test shows 70 in #6 and 150-170 in the rest. I put air into #6 and no air comes out the exhaust or out the intake???? I pull the valve cover off of that side and I find no push rod on #6 intake valve. A fishing expedition with a magnet gets me a bent pushrod missing 2". Order pushrod, install, crank over engine, see valve barely move, also notice #2 intake is barely opening. Tell owner he needs a new camshaft.
I call around for parts and hear alot of stories on how the new engine oil ( API spec SM) kills flat tappet cams due to its lower zinc and phosphorous levels. Cannot talk him into a roller cam. Install new Summit cam with bottle of break in additive and tell him to use offroad oil or always add a bottle of additive to it at every oil change.
Start truck break in cam at 2500 RPM for 30 minutes and tackle carb. End up drilling main jets from 74 to 78, drill idle dip tubes from 40 to 46 drill idle ports (when screws go) from 78 to 95 and epoxy air bleeds and re-drill to 50, they were 70. all sizes in thousands. Mixture screws are now out 2 turns truck idles nice and smooth, runs great with no bogs.
I am still not sure carb is setup as well as it can be. Not sure if my epoxy job will last.
I am trying to get him to convert the truck to fuel injection. I think gas mileage will improve and so might power. Even the best carb tune-up is really only good for one day a year when the temperature, humidity and barometric pressure is just right. If I do a factory TBI swap from a newer truck closed loop should take care of all that.
SO.... Will it get better mileage? What will I need? IF I can find a 454 TBI truck in the junk yard and pull the whole setup off, what else will it take, this truck has dual gas tanks so I'm thinking an inline fuel pump after the switch valve. There is already a fuel return line from the mechanical pump, so that's covered. Do I need a speedometer connection? I can weld in a bung and add the O2 sensor to one exhaust, truck has duals. Should I use the 4BBL manifold and put an adapter on it or swap to the the TBI manifold?
If it will get 1 or 2 MPG better it should pay for itself in a short time. comments. All I can find searching the forums is TBI to carb swap posts, I prefer to do my tuning with a laptop and EPROM burner.
01-30-2011, 08:27 PM #2
Holy crap that was a lot !!! kinda skimmed it over first off idle kills older 454 motors they dont sling enough oil at idle to keep the cam wet and yes go find a tbi truck and get every thing o2 plugs also and convert it to FI if i missed any point or you have any ??? let me know. roller motors dont mind idle
99 tahoe 2 dr. 4x4 7.4 4L80-e NP246, SAS, dana 60 hp, sterling 10.5 rear, gibson headers, and alot of tricks of the trade !!!!!!IF YOU'RE NOT CHEATING YOUR NOT TRYING!!!!!!!!
03-21-2011, 08:16 AM #3
- Join Date
- Apr 2006
Bump. So has anyone actually done this? What kind of MPG increase might I get? Truck is now running great but MPG sucks........
03-22-2011, 05:45 PM #4
Ask holley they have sold thousands of the tbi setups and for cold starts and all around daily driving as a bonus to added mpg. and power its a no brainer if you have the extra money
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