sliced 2261 early L36 castings...4781 castings next
 

figured ya'll would be interested...mods feel free to move if warranted

Attachment 52328

i sliced down the middle of the guides on the center chamber and aliced the end cylinder a little more selectively to check out coolant passage wall thickness. i have yet to drill the many holes for measuring the wall thickness's in different locations so that i can compare the 2261 casting to the 4781.

2261 being the early 95-97 L36 only heads, and 4781 being the late 98+ L36/67 casting that has the meat for injector boss machining for the L67 in head injectors


i am looking for the casting number (and preferably a junk head) for the 96-97 L67 heads as well as i would like to know the same of the SIII L26/32 castings (and slice one of those up too...)


dont worry i will be using the high res digicam for the good pics after drilling

Attachment 52329

also:

http://i131.photobucket.com/albums/p...61casting1.jpg



the valve inserted will be for checking the throat angles to balance mid/high lift flow...i sure hope the L36 4781 has thicker port walls.... (the casting number of our 98 and 99 L67 heads is the same 4781)

Attachment 52330

next up is one of my 4781 castings (with undrilled inj bosses aka L36 app)
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Nice! I have pics of an L67 head cut up somewhere.
With the L36 and the undrilled injector boss, you'll be able to see where the real casting imperfections comes in. GM left a nice little pocket in there.

Edit. Ya know it took me a minute, but after looking at those pics agian It seems like the earlier castings are hands down the way to go for porting L36 heads. As I stated above, there is a nasty little pocket left under the injector boss in the later L36 heads..
I know what I'm getting next trip to the j-yard..
Looks like yet another advantage to add to the list for the factory freak 95 L36.

I would like to see a good picture of the intake side if you have one available, please. Thanks :D

y do you say late 98 are they any 98 whit the 2261 head thank you nice work

here was a Part Number change sometime in the 98 model year. the 97 heads were prone to cracking

i sliced up my 4781 casting today...i'll try to post up pics and get good shots of the intake and exhaust ports with valves inserted on both chopped heads

Heres the pics I was talking about:
L67 heads:
Attachment 52292
Attachment 52293
Attachment 52294
Attachment 52295
Attachment 52296
Attachment 52297
Attachment 52298

OK, short of pulling off the valve covers, is there any way for me to tell which casting number of heads are on my 1998 LeSabre L36?

Yep. Look for the injector boss:
Left is the early right is the later
Attachment 52286

So, for an L36 at least, which casting is better, and why?

(or is that what this thread is investigating...)

The earlier casting would be better from a intake port flow standpoint.
Look at the Intake ports in this pic:
Attachment 52284
Now look at this one.
Attachment 52285
Although the second does have an injector hole, on a L36, that little pocket you see there is still present.
There is some talk about the earlier casting having cracking issues though..

Got it. I've got the older casting apparently, since I see no injector bosses.

http://www.bonnevilleclub.com/forum/viewtopic.php?t=73973&am
 

Since you're all slicin' and dicin' could you PLEASE take the time and measure the intake ports for me( with a dial or vernier caliper) L x W? Your help is greatly appreciated.

95naSTA wrote Yep. Look for the injector boss:
Left is the early right is the later
did they change the valve covers on the L36 whit the later style head because my 98 valve cover don t have the injector boss

the best is of course to pull a valve cover...in these pics the pen is pointing to it's location on top of the water passage
2261
Attachment 52265
4781
Attachment 52266

i agree with you there but after drilling the port walls both are nearly equal there are differences but not many, the 2261 casting has thicker exhaust port walls...however the port has a smaller crossectional area than the 4781...the exhaust port needs work to equal the OE 4781 btw in some area's the heads deck is only 1/4 inch thick...both castings have 5/16ths deck thickness except in the area's i found (this is the same between the two)

unless you pull the Valve cover you cant be sure...if you look in the above pic of the 4781 casting you can see how that boss is unmachined for the injector, with the valvecover on it looks identical to the 2261 in those area's...

put it this way, you cant put L67 valvecovers with the injector cutouts on the 2261 casting, but you can put the L67 VC's on the 4781 with unmachined or machined bosses (aka L36 or L67 style)

i will try, do you want the 2261 or 4781 dimentions? also be aware the ports arent quite "square" and may vary a small amount from head to head...(because of core shift etc when it's cast)

i have 95 2261 L36 covers and 98 4781 L36 VC's and they are identical

OK, so does anyone know why and where the 2261 casting is more prone to cracking? (or is this the reason for the investigation...)

Is there some kind of statistical data showing the older head being more prone to cracking? Is it possible that more have been reported simply because they've been around longer and/or there might be more of them?

What would be the symptoms of a cracked L36 head, anyway?

Those are great questions, Agra.

It seems the older heads are better for making power, while the new ones are rumored to be more reliable. Data to support either of these conclusions would be great.

It does appear that the '95 models are generally quicker than other years, from what we've seen on these forums.

The general quickness of the 95's is known to be due in part to the lesser torque-managment in the PCM and the fact that the 95 is the lightest chassis of all years.

While it may be due in part to the head design, does anyone have any data to show that the newer heads crack? I've not heard anything on this relating to the L36.

here is the thread about the heads cracking

http://www.3800pro.com/forum/showthread.php?t=11

Those are L67 heads, Pat. Not L36. They're quite different. Let's compare apples to apples here instead of apples to oranges.

In spite of what that topic says, it's impossible for the L36 to have the same casting as the L67. They are two different part numbers and are not interchangable. They are different parts in particular with regards to injector bosses.

Back on topic, who's had a FWD GM L36 head crack?

When I sent my heads in for a core, which weren't the earlier casting because I replaced the heads before, they were cracked in between the valves. Thats what milzy told me.

Sounds possible if there was alot of detonation in the cylinder for some reason. But I don't see any other reason that it would crack.

It's not very uncommon to have cracking between the valves..
I could probably find examples if clubgp's search was better.

Still sounds like some overheating issues. Cast iron heads are very difficult to crack, even between the valves. The last several heads I've pulled that were cast iron were not cracked at all, even between the valves. And that includes many different sizes. Even on my '71 with 150k miles on it, no cracks. My '93 Bonneville with 220k miles on it, no cracks.

Now, don't get me wrong, in a general sense, it may be easy to crack the heads between the valves. Just one mistake as far as cooling is concerned (low coolant, driving on a dead water pump, plugged radiator) or running for a while with KR (most likely to cause cracking around the valve), and you have cracked your heads between the valves.