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Old 08-19-2010, 07:32 PM
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will throttle body work on GM performance intake

I have a 350 w/vortec heads and a GM 12486570 intake. Can put this motor in a 1987 suburban and use the throttle body set up it has or will I need to tear out all the TBI stuff.

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Old 08-19-2010, 07:38 PM
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You can but then you need to make sure you keep all the other components of the tbi system such as cats, o2 sensors, computers, etc... It also depends on what kind of cam you cam in there. If it's too radical the tbi system will not like it and it will run terrible.
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Old 08-19-2010, 08:09 PM
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OK, Thanks. I just acquired this motor from a friend, and I know the machinist so I can get that info tomorrow. I know these Guys know what they are doing and set it up with the right pistons for vortec heads that will allow you to still run pump gas. all I know about the cam at the moment is what I was told about it being a nice cam that really opens up at higher rpm still making it streetable; what ever that means. Their guess was it should be pushing close to 400 HP.
Maybe I'm asking to much.

Thanks again. I been having a hard time finding a good mechanic in my area and really enjoy this forum
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Old 08-20-2010, 09:27 AM
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With a Vortec engine even without mods with a TBI system it`s going to run deadly lean, the fuel system will need to be modified and it will need a custom chip to work correctly. TBI engines had horrible swirl port heads that choked the engine to death, the Vortec is just the opposite. The cam has to have a wide LSA and be within working limits of the TBI system. If the injectors have never been replaced this will make the lean issue even worse as while TBI injectors will work forever, they flow less as time goes by creating a lean condition on the stock engine so on a vortec it`ll be severly lean, possibly so severe you could burn the valves or cook the pistons. If the vortec is what I had then I`d convert over to a carb and play it safe before I risked cooking a good engine.
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Old 08-20-2010, 10:50 AM
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Quote:
Originally Posted by acarpenter
I have a 350 w/vortec heads and a GM 12486570 intake. Can put this motor in a 1987 suburban and use the throttle body set up it has or will I need to tear out all the TBI stuff.

You'll need an adapter one of the below will fit.

http://cgi.ebay.com/ebaymotors/Holle..._Vehicle_Parts

http://cgi.ebay.com/ebaymotors/Holle..._Vehicle_Parts

The Vortec heads on the 87 bottom end will not make any difference in fueling. The power limit will be set by the wimpy cam in these engines. It will not let the engine rev to a point where the heads will become effective add to that your computer has a 99.9 mph speed limiter in it so just bolting the Vortec heads is a moot point as far as the rest of the system is concerned.

To get some action out of the heads will take a better cam, the Edelbrock 3702 will wake this engine up and let it use the potential in the Vortec heads. http://www.edelbrock.com/automotive_...chevy_sb.shtml
This cam is about as far as you can go without a chip and that sometimes gets iffy. TBI is very sensitive to manifold vacuum in relation to throttle position and RPM. These relationships are extremely valve motion dependent. Changing the cam and or rocker ratio affects/effects these relationships big time. The computer is mapped to these specific relationships with the OEM cam, it does NOT take input and compute solutions, it takes input and looks on a map for the solution. If the input does not match the map, oh well! If you change any of the relationships the computer looks to the wrong place on the map. A new chip can be programmed with new relationships and to eliminate the speed restriction see these guys http://www.tbichips.com/
The computer has a little learning capability, damn little, it is there to trim the fuel delivery to stay within legally specified limits for the required period of time from new. It provides automatic adjustment for normal production part variation and to adjust for engine aging. An 87 has probably used all that up.

While you're in it, I'd recommend replacing the timing set, gears and chain, to put the cam back into synch with the crank. Do this whether you're replacing the cam or not.

The Vortec heads will pick up a little compression against the swirl ports but probably not enough to notice any performance change. This is another place where there are gains to be had, but you've got to talk about different pistons with less crown volume and a D shaped dish to optimize the combustion chamber shape of the Vortec head. So that's a down stream activity with a bottom end rebuild.

Keep in mind that restoring compression on top of a worn bottom end usually increases oil consumption and blow by. This will reduce the engine's detonation tolerance and will probably force you to up the fuel octane used.


Bogie
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Old 08-20-2010, 02:20 PM
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Sorry, I guess I forgot to mention the bottom end has been machined as well.
Block boiled, magna fluxed, inspected, bored, cam bearings installed, mains done line hone etc...

Hey DoubleVision I'm with you, why risk cooking a good engine. Can you tell me how much trouble it would be to convert this tbi system to carb in the 87 1/2 ton 4x4 chevy burb.

Thanks.
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Old 08-20-2010, 07:56 PM
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Quote:
Originally Posted by acarpenter
I have a 350 w/vortec heads and a GM 12486570 intake. Can put this motor in a 1987 suburban and use the throttle body set up it has or will I need to tear out all the TBI stuff.
This is just a brief overview.

To try to use the TBI system as-is will require you to change the cam from the performance cam in it now to a very near stock vacuum producing cam.

The performance cam that's in it now will very likely not make the vacuum required for the TBI to meter fuel correctly. You can use a custom chip to compensate for this- there are several chip sources that will work w/you on your specific combination.

Should you want to do away with the PCM and the TBI, etc. and run a carb, you will first need to be sure the smog police won't flunk you for emissions or visual compliance in your jurisdiction.

The trans shouldn't be a problem, so you will need an HEI distributor from a pre- '86 truck or pre '81 car w/a 4-prong module and a vacuum advance. They are available cheap from the aftermarket as well.
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