A year ago, I picked up a spare set of 243's as part of a "basket case" LS1 engine purchase. Got the whole engine for $500.00, and sold off the MS3 cam for $300.00, so I'm not into this setup much at all currently. I recently decided to use the block to build a 383, and decided that I wanted to have AI port the set of 243's that I got in the deal.

Upon closer inspection, I found that the heads had been previously CNC ported....so I was thinking that I REALLY hit the jackpot, and would be able to sell the heads, and use the funds to help buy a new set from AI. I decided to have my machinist clean up the heads (they were a bit grungy), and run them on the flow-bench....so I could know exactly what I was going to be selling. Well, after seeing the flow numbers, I would not wish these heads on ANYONE. They are pretty terrible....even WITH a larger exhaust valve than stock! So, I'm trying to find out if anyone might have any idea who/where these might have come from. I have a set of stock-valved, hand-ported 243's for comparison (only the second set of LS heads ever ported by my machinist...he did a pretty damned good job! IMHO) that I will list specs side by-side to show how weak these CNC-ported heads appear to be.

CNC 243's w/larger exhaust valve.......Stock hand-ported 243's

Intake............................................ .........Intake
Lift 0.125" 73.2 cfm.............................Lift 0.125" 83.2 cfm
0.250" 149.2 cfm.................................0.250" 169.4 cfm
0.375" 202.1 cfm.................................0.375" 226.8 cfm
0.500" 223.4 cfm.................................0.500" 273.0 cfm
0.625" 241.8 cfm.................................0.625" 287.4 cfm
0.700" 244.3 cfm.................................0.700" 282.8 cfm


Exhaust........................................... ...........Exhaust
Lift 0.125" 66.1 cfm................................Lift 0.125" 78.6 cfm
0.250" 119.6 cfm.....................................0.250" 142.6 cfm
0.375" 148.6 cfm.....................................0.375" 172.1 cfm
0.500" 166.0 cfm.....................................0.500" 194.6 cfm
0.625" 178.5 cfm.....................................0.625" 210.9 cfm
0.700" 185.0 cfm.....................................0.700" 214.8 cfm



Now here's where is get's really interesting....

I have the flow data from the "Before" of my hand-ported 243's, and it appears that this set of CNC ported heads flows worse than the stock casting in most areas!

Stock 243 castings...un-touched:

Intake @ 28"........................................Exhau st @ 28"
Lift 0.125 74.6 cfm...............................Lift 0.125 71.8 cfm
0.250 155.4 cfm..................................0.250 122.4 cfm
0.375 208.4 cfm..................................0.375 151.4 cfm
0.500 208.9 cfm..................................0.500 167.1 cfm
0.625 212.1 cfm..................................0.625 177.5 cfm
0.700 215.1 cfm..................................0.700 182.6 cfm


So, based on the flow values of the CNC'd heads, does ANYONE have a clue who might have been producing/selling these?? I'm guessing that if someone spent the time to make a CNC file for these, they must have been mass-produced. If nothing else, I hope that this serves some kind of educational benefit for others here....in the sense that bigger valves does not always mean better.


Anyway....long post, but I'm just wondering if these heads can be ID'd off the flow numbers that I posted. I'm probably just going to send these off to AI, and hope that they can do something with them.

 

we need pics to maybe ID them...interesting thing is that a stock 243 head should flow 262 cfm @ .600 lift on the intake, I had a set of 243s I ported flowed before and after...stock was 262 cfm @ .600 hand ported 292 @ .600 cfm intake, with gains in every lift area...the key is to NOT hog them out...if ported properly you will gain flow at all lifts..

You can CC the intake runners to compare how much material was removed from the cnc and hand ported heads...hoping to see some pics

 

They are un-marked...just plain-looking 243's with stainless retainers and a set of dual springs. Other than that, no markings on them. I'll try to get some pics in the AM. Just curious....how many inches were your flow numbers measured at?

 

I whipped those out in my garage on my CNC.......

How's things?

Ron

 

I'm not sure how many inches they were flowed at, I tried to find my sheet just now...maybe its at work, but me and Jim Evans flowed them here in Rolla MO...

Look in the valve cover area, If they didn't grind those numbers off they will say 243 under there as well, also its easy to tell by the shape of the combustion chamber whether its an LS1 or LS6 head, take some pics if you can

 

28in.

 

Link to stock heads flow benched .

http://www.performanceworks1.com/ls1__ls6_head_flow.htm

My heads were on a 4in bore

 

HA! Going great Ron...just got the 383 bottom end back from the machine shop, and hoping to start assembly soon.....just gotta get the heads now How are things going with you?

I'll double-check with my machinist to verify what they were flowed at. The outside of the casting is definitely 243, but again, I'll snap some pics in the next couple of hours.

 

Looking at the link, the corrected numbers shown @.600 are 257.2 for a stock ls6 head with a radiused intake port on a 3.9" bore. I'm assuming this means "not" an un-touched factory casting?

I also was able to verify from my machinist that all of the rates I've show were indeed @28" test pressure....but on a 4.0" bore....corrected numbers. I'll be back with pics of the heads in a bit.

 

Unfortunately, this should prove that it is all about the runner design (with both velocity and flow in mind), and taking out material/shaping the port in the correct places, rather than just fully cnc'ing the whole runner.

 

Exactly what I was thinking. I'm kinda surprised that someone would go through all the trouble with developing a CNC file, given the end results. They DO flow better on the intake side after .500, but appear to lose flow just about everywhere else.

Anyway, here are some pics. They've been through the ultrasonic bath, but could still use some touching up....they were pretty nasty beforehand.

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I'm wondering if they are even worth sending out to AI, considering that it's possible that they have already had too much material removed??

 

It will prob cost more money to fix them then it is really worth...

On a side note if you plan on hand porting your own heads and don't have much experience I have found it is better to just remove casting slag from the manufacturing process rather than trying to reshape or "port match" the heads. I hate when people think they can give sbc head treatment to LS heads. By the way I'm not criticizing anyone just throwing some thoughts out there.

 

Kinda what I was fearing. I was really hoping to just be able to use them as a core exchange (worst case scenario), but don't even think they'll be able to serve that purpose. OTOH, I can't sell these with good conscience to anyone, so probably just going to shelve them for now. They should at least be able to serve duty (eventually) on someone's stock rebuild or something.

 

Ive had several sets of 243s on the bench and they are all pretty much @260@600, give or take a couple cfm, @28" water, stock with a radius plate, or clay. something definitely way off with that set

 

Sounds like those might have been someone's learning stages. Hopefully they improved the program before they started selling them to people.