Engine parts swapping?? Help an engine newbie

[majicwrench]

Have a head off of a 1438 with the fun dual carbs. Will it function on a 1756?? Is there any reference material out there that shows what will work with what?? I also have a head that came with, but not on, the 1756. How can I identify the head, or does it matter?? The 1438 has got some serious domes on what seem to be roughly .030" oversize pistons, the 1756 pistons are very much flattop, am a bit worried about the 1438 compression ratio.
Please teach me,
Keith

[So Cal Mark]

i believe you will find a mismatch with the front water jackets in the two cylinder heads

[narfire]

A long long time ago a fellow told me the 1438 heads are different in that as Mark said the water passage at the front is different as is the bore, but center to center(bore) they are the same.
Evidently a compression increase.
Hope someone can chime in as well.

[mdrburchette]

I believe the 1438 is of the 125 family so you can swap it with 1608 parts. A 1756 is of the 132 family so you'll have to find a 1592 head to swap with it or use the 1756 head on a 1995.

[racydave]

The 1438 sounds like a screamer! Hope it is a healthy engine!

[htchevyii]

The 1438 head has much smaller ports. The front water passage is also too large to seal on a later engine, (1438 &1608 interchange. The 1438 also lacks the coolant passage at the rear of the intake manifold. With welding, (to the front coolant passage), a 1438/1608 head can be used on a later engine and with grinding , (per Pete Angel) he's used a 2.0 head on a 1438.

Pete Angel wrote: (from Mira)

From a visual inspection of original, un-ported 1438 & 1608
heads, here are the measurements of two examples:

Port Opening Size(mm)
Appl. Casting Nos. Intake (area) Exhaust(area)
---- ------------- ------------- -------------
1438 124AC 4166393 32x41 (1312) 32x38 (1216)
1608 124AC 4239436 38x46 (1748) 35x40 (1400)
--------------------------------------------------
Difference 436 mm2 184 mm2

The area of the intake port opening is significantly larger on
the 1608(25%). The exhaust port opening is slightly larger(13%).
Through visual inspection, the port runners are comparably
larger in volume on the 1608 than the 1438.

Other detected differences:
The 1608 head has an additional H2O port at rear of intake
manifold mounting face. Cannot use 1438 manifold on 1608(or
higher)because of this (and vice versa). Haven't cc'd yet, but
the combustion chambers on both heads appear the same, except
the 1438 has less material at the piston relief notches on
forward and rearward edges of each chamber(possibly done by PO
to accomodate high comp pistons). The other dimensions of the
chambers appear identical between the heads. Based on these two
samples, the 1608 would have a slightly higher CR than the 1438.

Head gaskets are interchangeable(if not the same). All mounting
locations are identical(head bolts, cambox mtg, intake & exhaust
bolt patterns, H2O inlet hsg, hi & lo temp sendors). Oil
pressure feed and drainback holes are identical. Any other
differences aren't apparent. Input by the parts experts may
suggest differently concerning valves, springs, guides,
retainers, etc.

BTW: the combustion chamber center-to-center spacing on all 124
DOHC heads is the same. Fiat did not stretch the spacing of the
chambers to accommodate the greater piston-to-piston spacing of
the larger blocks. If they had, the valve locations, cam boxes &
cams would've had to change as well. You will find that the
center of the combustion chambers do not align with the piston
centers on the larger blocks, making the 1438 & 1608 head/block
configurations more symmetrical (& efficient?). A 2.0L head will
bolt directly to a 1438 block and work(fact)with only slight
mods to a single water passage ahead of #1 cyl. The 1800 head
should be able to do the same.

[majicwrench]

Hey great info thanks!!!
How do I identify the head that came with, but not on, the 1756?? Is there a casting number that means something on it somewhere??
FYI the 1438 is a 124 AC and the 1756 is a 132
Sounds like the thing to do is just get the 1438 running, tho I was wondering if I wouldn't be happier with the bigger engine and lower compression. Might have to cc the 1438 and see what it is.
Keith

[ventura ace]

Trey, good info. Here are a few pics showing the water port differences on the bottom sufaces of the heads:

1438 head


1756 head


And a picture of both heads with 1438 head gaskets laid on top of them. The two 1438 gaskets are slightly different. You can see that the gasket on the right (on the 1438 head) has slightly elongated holes for the 4 small water ports at both ends of the head (2 at each end). The gasket on the left (holes not elongated) partially covers these water ports on the 1756 head, due to the more outboard location of these ports on the 1756 head. I'm not sure, but the gasket with elongated holes may have been made to allow using a 1756 head on the earlier 1.4L or 1.6L blocks. Even so, I believe those 4 water ports would be somewhat restricted by the misalignment. BTW, the 1438 head appears larger, only because it has cam towers in this picture, and the 1756 head does not.


Take a look through the rest of these pictures to see more pictures of both heads with a 1756 head gasket laid in place, showing basically the same story . . . and a few more pictures showing the same kind of difference between Hal's 1608 head (for 80mm pistons) and his 1592 head (for 84mm pistons). (Sorry, Hal, for taking so long to post these pictures!) I tried to put a few notes with each picture for explanation -- but I'm sure it can be quite confusing. I have a list of Fiat twin cam head castings and their applications. If you let me know the casting numbers for each head, I may be able to find them on the list.
http://smg.photobucket.com/albums/v26/v ... l%20heads/

Alvon