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Old 07-12-2010, 09:09 AM
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engine swap

OK I have a 1990 K1500 HD 4x4 w/ 305 ho TBI 5-Speed ..... I blew up and I have a 1979 305 2Barrel Carb 3 speed Auto.... I want to put in my Truck but I want to keep My TBI so is there Any thing I need to know about swapping the intake's on them ? also I am keeping the manual Tran never have done anything like this so any help is good help.......

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Old 07-12-2010, 09:47 AM
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Quote:
Originally Posted by teamropers2002
OK I have a 1990 K1500 HD 4x4 w/ 305 ho TBI 5-Speed ..... I blew up and I have a 1979 305 2Barrel Carb 3 speed Auto.... I want to put in my Truck but I want to keep My TBI so is there Any thing I need to know about swapping the intake's on them ? also I am keeping the manual Tran never have done anything like this so any help is good help.......
As you've indicated, the heads have a difference in the center bolt angles. I've heard of guys elongating the manifold's bolt holes and using special washers to match the difference. A page HERE shows some details on this.

There are also adapters for mounting a TBI onto a standard intake manifold, if you didn't want to reuse the stock TBI intake. Unfortunately, the 2-barrel adapter shown on the page linked above has a Holley 2-barrel pattern, not a Rochester DuoJet pattern, which I believe is what you have on the '79 engine. But if you have a good dual plane 4-bbl. intake to fit the '79, there are adapters that'll work.

Cams are critical for the ability of the computer to keep up w/the functioning of the engine. I have no actual experience w/how much cam you can "get away with", but this is what I've read (credited to oldbogie, IIRC):

"The factory TBI can learn to adapt itself to a cam of around 200 degrees of duration measured at .050 lift, with 110 degrees LSA or more and about .45 inch lift. Beyond that for sure a new chip and sometimes even this requires a new chip."

So, if your cam is stock in the 1979 replacement 305, and the engine is in good condition so as to make good vacuum, you might just be OK. Or, you can get a new cam and lifters (along w/a fresh timing set) and be assured of a successful swap, AFA the computer goes.

Obviously, ALL the sensors, etc. from the original engine have to be installed and connected up to the "new" '79 engine.

If there is an inspection for emissions in your area, this opens up another can of worms, so you should check into this as well. Last I knew, FL didn't do inspections, though.

To use the manual trans, you will need to install a pilot bushing into the rear center of the crankshaft, if the '79 engine was an automatic. Super easy, and the bushing is like $5.00. You'll see the old one when you pull the engine. Just don't hammer directly on the bushing- use a bushing installer or a socket sized to match the bushing and drive it gently into position.

Good luck.

Last edited by cobalt327; 07-12-2010 at 10:04 AM.
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Old 07-12-2010, 01:03 PM
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Quote:
Originally Posted by teamropers2002
OK I have a 1990 K1500 HD 4x4 w/ 305 ho TBI 5-Speed ..... I blew up and I have a 1979 305 2Barrel Carb 3 speed Auto.... I want to put in my Truck but I want to keep My TBI so is there Any thing I need to know about swapping the intake's on them ? also I am keeping the manual Tran never have done anything like this so any help is good help.......
Two problems:

- The top end is different for mounting of the TBI, emissions, and the center 4 mounting bolt angle is changed.

- The 79 has the two piece rear seal crank with the larger flywheel bolt pattern which will not match the one piece rear seal crank you have.


There are many solutions to getting the TBI on the earlier engine, but the simplest would be to bring the 90 top end, heads, intake and attached systems to the 79 bottom end. The 90 intake can be adapted to the older heads by egging the center 4 bolt holes till the bolts align to the head, a 90 to 75 degree change. But the bolt heads need to register flat to the intake; this requires either a 15 degree wedge adapter be made or the intake bolt registers be milled the 15 degrees. If you have to pass emissions using the older heads with perimeter rocker cover bolts will be a give-away to the technician that he isn't looking at a post 1986 engine.

Bogie
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Old 07-13-2010, 11:31 PM
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Thank you for the info I was thinking something like that so I guess it would be better to just keep the 79 the way it is and for get about the computer in the truck and it it run just leave it that way so thank you all so much............
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