sliced 2261 early L36 castings...4781 castings next - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-15-2007, 09:36 PM   #11
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The earlier casting would be better from a intake port flow standpoint.
Look at the Intake ports in this pic:
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Now look at this one.
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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..
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Old 03-15-2007, 09:53 PM   #12
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Got it. I've got the older casting apparently, since I see no injector bosses.
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Old 03-15-2007, 10:00 PM   #13
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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.
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Old 03-16-2007, 12:16 AM   #14
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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
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Old 03-16-2007, 03:41 AM   #15
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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?
the best is of course to pull a valve cover...in these pics the pen is pointing to it'* location on top of the water passage
2261
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4781
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Quote:
Originally Posted by 95naSTA
The earlier casting would be better from a intake port flow standpoint.
Look at the Intake ports in this pic:
.................
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..
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'* the heads deck is only 1/4 inch thick...both castings have 5/16ths deck thickness except in the area'* i found (this is the same between the two)

Quote:
Originally Posted by agrazela
Got it. I've got the older casting apparently, since I see no injector bosses.
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'*...

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

Quote:
Originally Posted by karldergrosse
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.
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'* cast)

Quote:
Originally Posted by firebuick
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
i have 95 2261 L36 covers and 98 4781 L36 VC'* and they are identical
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Old 03-16-2007, 05:14 PM   #16
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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?
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Old 03-17-2007, 01:40 PM   #17
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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.
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Old 03-17-2007, 01:52 PM   #18
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The general quickness of the 95'* 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.
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Old 03-17-2007, 04:09 PM   #19
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here is the thread about the heads cracking

http://www.3800pro.com/forum/showthread.php?t=11
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Old 03-17-2007, 04:14 PM   #20
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Those are L67 heads, Pat. Not L36. They're quite different. Let'* compare apples to apples here instead of apples to oranges.

In spite of what that topic says, it'* 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'* had a FWD GM L36 head crack?
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