I'm posting this for my friend. He has an 89 RS with a 305 TBI in it. Is it possible to only change the block to a 350 block; with out changing anything else: keep the heads intake, TBI, maifolds everything. Sort of a low cost swap. I want to know because thats what I suggested to him.

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THAT'S RIGHT!
http://www.geocities.com/my1986transam
86' Pontiac Trans Am
305 LG4, 3.73 richmond rear

 

i think u can.. gotta check with some of the big timers around here though.. they would know more about what would need to be changed for the bigger motor...
Steve

 

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Why cant I see my friggin replies?????????????????

 

TA86,

If the block is the same family ('87-'92) it should be a relatively simple exchange. The blocks are essentially the same casting. But then, why would he want to keep the 305's restrictive heads? The valves on a 305 are necessarily small to fit in the smaller bore, and the head castings have relatively small ports. The tendency would be for the 350 to be constantly starved. The intake and TBI could be retained and modified to feed the 350 properly, but I would lean toward using the 350 heads with some modifications.

Since the car apparently now has a 305, and a 350 would have to be acquired to make the exchange, why not put the 350 in a stand and "freshen" it a bit at least. Check the bearings, rods, rings. Maybe remove the heads and valves, then clean up the ports for a little better flow and machine for taller springs, then screw in some studs. If you want to get goofy, install some larger valves. Clean up the sludge, possibly install a decent camshaft and new timing set, and Re-gasket everything. Install you TBI and stock exhaust.

For under $1,000.00 in parts and some of your own time, you should be able to get a fairly reliable 350 with a little better output than stock. If you planned the work well, anything you do in the future could be external, like increased ratio roller rockers, a different fuel system, a better exhaust system.

The hard part would be complete, and the final touches can be added as time/budget allow.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

vader did a good job of covering the hardware side of the swap (excpet he didn't point out that not only are the TBI heads small, they are swirl port, hence super restrictive), but making the computer run it is a completely different issue. To make it truly run right you'll need a custom chip, but if you were good and had some luck, you could band aid it together and get it tuned half decently.
...ed

 

I got my IROC with a 350 that had been swapped in. Turns out I had mis-matched 305 heads on it and everything else was stock including the computer. Yes it can be done but the gains of going to a 350 wont be realized until better heads are put on and a custom chip is made to take advantage of the increased power.