sliced 2261 early L36 castings...4781 castings next - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-15-2007, 12:06 PM   #1
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Default sliced 2261 early L36 castings...4781 castings next

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

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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'* 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

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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)

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next up is one of my 4781 castings (with undrilled inj bosses aka L36 app)
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Old 03-15-2007, 01:28 PM   #2
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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.
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Old 03-15-2007, 02:02 PM   #3
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I would like to see a good picture of the intake side if you have one available, please. Thanks
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Old 03-15-2007, 05:00 PM   #4
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y do you say late 98 are they any 98 whit the 2261 head thank you nice work
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Old 03-15-2007, 06:12 PM   #5
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Quote:
Originally Posted by firebuick
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
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Old 03-15-2007, 07:52 PM   #6
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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
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Old 03-15-2007, 08:39 PM   #7
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Heres the pics I was talking about:
L67 heads:
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Old 03-15-2007, 09:01 PM   #8
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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?
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Old 03-15-2007, 09:13 PM   #9
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Quote:
Originally Posted by agrazela
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
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Old 03-15-2007, 09:31 PM   #10
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So, for an L36 at least, which casting is better, and why?

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