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post #1 of (permalink) Old 10-09-2002, 11:38 PM
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need some guidance on engine swap

hey all,
I'm new around here....looking for some advice concerning an engine swap.
the details:

I have a 79 k5 blazer with a nice solid motor...and not much else worthwhile. Trans is bad, body's quite rusty, right rear brake is giving me trouble and the left rear spring has three broken leaves.

I have a friend with an 89 1/2 ton Suburban with a bad motor, a rebuilt th700r4 trans and is generally pretty solid looking. It needs some glass but I have sourced that already.

I want to swap my motor for the bad one in the 'burb and save some of the other parts. Doing some research, I discovered I might need a different flexplate as the newer motor has a different bolt pattern for the torque converter or some such thing....can anyone verify this for me? Are there any other details I might need to look out for? Both vehicles have 350s. Will the flexplate from the 'burb work with my motor or will the difference in years be a problem?

The k5 is mostly stock (exhaust manifolds, hei, a/c) but does have some mods (Edelbrock manifold, carb, rv cam). The 'burb is completely stock.

Any help you could provide would be greatly appreciated! I couldn't find a whole lot of help on the web for this type of swap...Thanks!

racingboy
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post #2 of (permalink) Old 10-10-2002, 08:25 AM
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Re: need some guidance on engine swap

what kind of transmission was in the 79?
post #3 of (permalink) Old 10-10-2002, 08:28 AM
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Re: need some guidance on engine swap

In my experience the flex plate from a 305sbc is the same as a 400sbc and work and both worked going fomr a 700R4 to a th400.
...Remembered. My 400sbc flex plate was different than the 305 if I remember right since the 400 is ext balanced.
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post #4 of (permalink) Old 10-10-2002, 08:50 AM
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Re: need some guidance on engine swap

the K5 Blazer has a Turbo 350 that is going south, making some awful noises but all the gears are still working ....so far!
post #5 of (permalink) Old 10-10-2002, 09:09 AM
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Re: need some guidance on engine swap

Thanks for the reply!

my situation is like this...

79 K5 Blazer has 350sbc with TH350

89 Suburban has 350sbc with Th700R4

I would assume the 305/350 uses the same flexplate but I'm not sure...I thought I read somewhere that the newer 350's use a different bolt pattern on the flexplate for the torque converter. I think it had something to do with the newer blocks that use the one-piece rear main seal or some such thing....


post #6 of (permalink) Old 10-10-2002, 09:40 AM
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Re: need some guidance on engine swap

There is a difference in flex-plates and flywheels between the newer blocks with one-piece rear main seal and the older ones with two piece rear main. The difference is the diameter and bolt pattern of the flex-plate to the crank. I'm not aware of any changes in the flex-plate to torque converter bolt pattern.
post #7 of (permalink) Old 10-10-2002, 11:00 AM
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Re: need some guidance on engine swap

The difference is in the bolt pattern from the flex plate to the crank. You can use the '79 motor in the '89, just keep the flex plate on the '79 motor that is on there now. Are you going to keep the carb on the '79 motor? That is OK as long as you do not have any emissions inspection. Actually, there will be one problem with that scenario. Torque converter lockup in the '89 is controlled by the ECM, which you will no longer have if you use the old engine. You would have to use one of the aftermarket set-ups to control the TCC, or just wire in a toggle switch and control it manually.
post #8 of (permalink) Old 10-10-2002, 12:37 PM
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Re: need some guidance on engine swap

I see just a few issues with using a 79 motor in an 89 vehicle. The 700R4 torque converter bolt pattern should not be a problem on the 79 turbo 350 flexplate. It's possible to use an adapter plate (quadrajet carburetor to TBI) on the 79 motor. The 89 exhaust manifold might have a problem with the left hand (drivers side) oil pan dipstick on the 79 motor. There is also a very good chance the 89 right hand (passenger side) exhaust manifold has the seven bolt exhaust manifold bolt pattern and the 79 motor only has the six bolt exhaust manifold bolting pattern, causing a problem with an oxygen sensor. The 89 has a 15 psi fuel pump in the gas tank, the quadrajet carburetor only needs 6 psi of fuel pressure. All in all, I'd sell the 79 as is, take the cash, then add some more cash to fix the 89 with a new GM Goodwrench engine that fits the 89. [img]images/graemlins/cool.gif[/img]
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post #9 of (permalink) Old 10-10-2002, 02:45 PM
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Re: need some guidance on engine swap

thanks for all the good info everybody!

I have two complete vehicles to work with. I was hoping to use my flexplate on the TH700R4 trans btu wasn't sure it would bolt up.
Good call on the lock up converter...I have seen that done before but wasn't sure if I would have to worry about that. Thanks.
I am pretty sure my old exhaust manifolds on the 79 will work with the Y-pipe that is already on the 89 'burb. The flanges looked exactly the same on a cursory examination. I have been thinking about the fuel problem too. Will I be able to simply bypass the in-tank pump and use the lines to feed my mechanical pump on the 79 350? On the other hand, would it be too difficult to try to control the electric pump's pressure with a regulator of some sort?

BTW, I don't have to worry about any emissions regulations
so the older engine in the newer truck is not an issue.

Thanks again everyone for your help! I am planning on tackling this project this weekend!
post #10 of (permalink) Old 10-11-2002, 12:07 PM
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Re: need some guidance on engine swap

Ca't you use the TBI setup on the 89 on the older one? Just swap intake manifolds. drill a hole in the y-pipe for an oxygen sensor adn tack weld a bung and your good to go.
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