241 Heads vs. 243 Heads
 

What is the difference between 241 casting heads and 243 casting heads?

241 heads were used on '99 and up LS1's. The 243's were used on LS6's and had sodium filled exhaust valves. I think the valves were larger as well.

Not all 243's have the sodium filled valves. In the early LS2's, they used the 243 with a standard valve.

243's(LS6) flow better than the 241's(LS1)

I see on ebay 243 heads that say that came off of a 5.3 that say they are casting 799 but just need the valves and springs to be the same as a LS6. What is up with those?

241, 243 and 799 castings all have the same size valves.
243/799 have slightly small combustion chambers than 241. 64cc vs 66cc iirc.

....I'm going with.....2...:lol:

'01zo6 cars got solid valves like the LS2, 02-04 Zo6 got sodium filled exhaust valves, same solid intake valves.

Wait,were the only sodium filled valves, exhaust side only?

Yes, exhaust side only
241 heads were on the C5 ('01 thru '04 and some late '00)
243 heads were on the Z06 ('01 thru '04)

Combustion chambers - 66.67 (241) / 64.45cc (243)
Intake port volume - 200cc (241) / 210cc (243)
Exhaust port volume - 70cc (241) / 75cc (243)
Intake flow at .600" - 227 (241) / 257 (243)
Exhaust flow at .600" - 180 (241) / 183 (243)

The 243 heads have a D-shape exhaust port that improves flow and came with higher lift valves springs
Both heads came with 2.00" intake valves and 1.55" exhaust valves

To my understanding, this is all the difference.

If I remember correctly the LS6 (243) stronger spings than the LS1 (241) -

Hands down the LS6 head flows better than the LS1 due to the runner volumes and the smaller combustion chambers!

LS6 heads are refined and improved LS1 heads, basically:

- Intake runner volume increased to 210cc vs. 200
- Exhaust runner volume increased to 75cc. vs 70
- Combustion chamber is smaller at 64.45 cc vs 66.67
- Compression ratio is higher at 10.5:1 vs. 10.1:1
- "D" shaped exhaust ports vs round

If you mill the deck on the LS6 head 0.030" you will get 11.1:1 compression.

Flow #'s (Stock heads @ 28") Head vs Lift

Head/.200/.300/.350/.400/.450/.500/.550/.600

LS1 / 137/ 187/ 207/ 223/ 228/ 237/ 242/ 243

LS6 / 156/ 204/ 225/ 243/ 257/ 268/ 275/ 278

In short smaller and more efficient combustion chamber allows quicker burn times, requires less ignition timing resulting in higher torque.

Thanks,Matt

Honestly though are the sodium valves even worth bragging about? I feel so dumb now, I had a so-called buddy sell me hand ported Ls1 heads, milled,and lS6 springs( I use to think daaammn)...now all I think about is...what a waste of money, same as this damn GM ASA cam with it:cuss

well, IIRC, the sodium valves weigh 74 grams and the standard valves weigh 97 grams. You might not think this is much, but, it's about 31% more weight. Might not seem like much, but at 7000 rpm, it's a lot...

What does less valve weight do though? less chance of valve float??

No, that would be spring pressure.

lighter weight valves require less spring pressure and require less force to open and close them. So, the engine makes more power.

The reality of this is that most of us will never build an engine to the point that this will make any difference at all in what we are trying to accomplish. Really, how many people actually build engines and car combos to extract the absolute most they can no matter the cost?

Nascar, NHRA, F1, IRL, ALMS, they do it.

The only person I know of that even thinks in this relm is RobZ.

02-04 243 heads had the hollow intake valve and sodium filled exhaust valve. This was for better valve-train geometry and stability since the ZO6 was reeving to 6500 rpm.

He's not the one footing the bill though, isnt that what "AMR" is for?

thanks for the info though...:thumbs:

I think Rob would argue that point with you...

I wasnt trying to state it as a fact, I just thought that was for the sponsors, or at least mostly. Either way its an expensive build no matter who's paying..:yesnod:

that is a lot of good info :thumbs: hope fully I can use it some day.