Swapping from 241's to 853's
 

I have a 2000 SS that has 350k miles. The drivers side head has now thrown 2 spark plugs in the past 6 weeks. They are stock 241's. I'm pretty sure they are just worn out from the mileage on the motor, it is 100% stock. Instead of putting another helicoil in I am just gonna swap the heads out with replacement lower mileage ones. I can't seem to find that many low mileage replacement 241's but have found a few 853's. If I switch, do I need to change or look at anything else? The car is staying stock, so don't suggest looking at anything else. Thank you.

If going through all that work, I'd pop some new lifters in there and a set of stock unmolested 243/799 heads

Exactly!

I do not have the mileage Josh has but am curious as well. I have a stock 2004 GTO LS 1 with the stock/factory 241 cylinder heads on it, will the 243's be a direct bolt on, I mean will everything else fit, align and perform as intended. (just do a head swap) Engine is factory stock. Thank You.


Tim john---

as long as the heads haven't been cut on the decks you're good to go. if they have been cut in the past might need shorter pushrods

If you put the 243 on you can use MLS head gaskets. If not, use the composite gaskets. There's a notch on the 853/241 heads that won't deal with MLS

I posted the same thing then deleted it because of the snarky last sentence. "don't suggest looking at anything else"

I thought the casting notch was only on 97-99 perimeter bolt v/c styles ??

Kings tend to be a bit snarky cuz; well......they're kings. :cheers:

nope. I have center bolt style. It's on them too. And into some 2000 models. That's why I mentioned it. OP should look for the notch and purchase gaskets accordingly

What kind of performance gain could one expect with the swap from 241 heads to the 243's, all else being factory stock on a 2004 GTO LS 1 engine sans Hooker/Holley Blackheart mid length stainless steel headers. Being the compression would go up a tad would that be an issue w/ fuel, computer tune as is ? Would the 2004 LS1 GTO fuel rail covers still fit (2004 is different than 2005/6). Thank You.


Tim john---

You'd gain 10-15 hp and about 1 mpg from the compression. Tune will be ok, but you'd gain from tuning ass swell

Thank You very much Darth, appreciate you taking the time.


Tim

1998 was the last year for perimeter bolts (806). '99+ (853/241) are center bolt.