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Discussion Starter #1
When I bought my ‘66 it came with a tired 302. Upgraded the 302 to a roller 5.0L. Meanwhile, I have been randomly looking for a correct-for-the-car 289. Found a "core" short block with date codes that match my car’s build date. In its 50+ years it has, at least once, visited the machine shop. It’s been bored and had some head work.

My question has to do with the heads. They are C6OE with 1.84” intake valves. Exhaust remains stock at 1.45". The runners have not been ported. The chambers look unmodified. Assuming the only mods are larger intake valves, will there be any noticeable performance increase over the stock 1.67” valves?
 

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I have C8-4V heads with 1.54" and 1.84" valves and the heads are ported . My engine is not stock.
I would get an estimate from a machine shop before ruling out any options . Bigger exhaust valves
would not be a bad idea depending what the rest of your engine plans are .
 

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My original 289 has some C5AE professionally ported heads with 1.94 1.60 valves that don't hold a candle to the TW 170 heads on my 331. Bigger valves mean nothing without the proper porting to take advantage of the larger area. If your goal is originality I understand. If you want to go fast....
 
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Zuki, the short answer is that yes, the heads will be better for the bigger valves. If there was any supporting work (like bowl cleanup, port matching, etc) then even more so.


The early 289 heads can be really good, if they're worked over by a professional. I wouldn't put in anything bigger than what you've got though. Going with the biggest valves you can run just means more shrouding from the cylinder walls, and decreased velocity. The runners don't lend themselves well to being hogged out to large dimensions, but for a small displacement, fun little 289, they work great. If you have to do a valve job, like @c6fastback says, the bigger exhaust size would be a good idea too.
 

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Discussion Starter #5
Thank you All. Your input is helpful and appreciated. My goal is a fun cruiser that looks stock with a touch of higher performance. Knowing these are good heads helps me to keep the stock look alive in the engine compartment (when the 5.0L is swapped out). A 289 with cast iron heads rather than performance aluminum heads will meet my needs.
 

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Do what ya gotta do but no way would I give up a 5.0 roller for a stockfish 289 on the street. Now if say you had the racing bug and had to stay vintage legal that would be a different $tory
 

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My thoughts are run the heads if they are in good shape, however, if they need any work I would put that money towards aftermarket heads or even a set of GT40P heads from an explorer. Even with larger valves they will fall far short of aftermarket aluminum heads.

Another thought is you could dress your existing 5.0 as a 289 with early timing cover, water pump, valve covers, early style distributor, etc. The good thing about those heads on a 302/5.0 is they will bump the compression up. Just remember if you were to run the old style distributor with the 5.0 you will need to change the gear to mate with the roller cam.
 
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