[Amc-list] performance six

[Tom Jennings <tomj@xxxxxxx>]

Since I just hot-tanked and cleaned up an original '64 232 (or 199, who 
knows) head, I pulled out the two Navarro heads and lined all three of 
'em up on the bench.

The two Navarro heads are different.

One is a 3170717, identical in every way including numbers to my 64 
stock head. It's had some work done; combustion chamber polished, and 
the deck has an O-ring groove cut. Minor porting, and there's scribe 
marks on the manifold face where the ports were squared and matched. 
There's extra tapped holes, and the location dowels were removed and 
tapped. These holes all match the turbo manifold. The center two exhuast 
ports are de-siamesed (milled for an insert plug, missing on this head). 
The ports are as rough as stock otherwise, and valves are stock diameter 
(quick check with the calipers across the seats, so I could be off .010) 
but one oddity -- the exhaust valve guide holes are about .43" diameter 
instead of the .3something of stock. QUITE large.

The other head is very special; an AMC casting with "RD" and digits 
where the part number goes. It's got extreme porting, and has the same 
decking, polish, O-ring groove and extra manifold bolt/stud holes. The 
de-siamese plug is in place. Exhaust is the same as the other, 1.4" but 
huge stem, but the intake is about 1.9". It's definitely a different 
casting than stock, but it's very hard to figure out. The only 
differences I can find are all cosmetic, the relatively rough stuff 
around the outside of the thermostat housing is smooth-cast, not ground 
or milled, but cast that way. Similarly around the rear welch plug. I 
inspected the water jacketing as far as I could, seems identical. Same 
length and height. Don't have a scale accurate enough to check weight.


I re-bought an old copy of Smokey Yunick's POWER SECRETs, even though 
some of it may be dated it's still very smart. I think it makes clear a 
lot of the stuff in this Navarro motor -- it's built to survive detonation!

In places, the cylinder walls are .4" thick. Double O-ringed, head and 
block. THe pistons are TRUE FORGED brand, and very heavy overall. I 
don't know race motors for sh** but these pistons are thick and heavy!

The two different Navarro motors ran at (I'm fairly sure) 550 hp and 750 
hp, both from 181 cubic inches. That's 3 and 4 hp/cuin! 45 - 100 PSI of 
turbo boost, and no intercooler. I still don't understand how this thing 
ran -- inlet temperatures must have been extreme.

The pistons are flat-topped with a shallow dish, and the combustion 
chambers are about .1" deeper than the stock 64 head. So it's not hugely 
lower than stock compression (but definitely not higher).

Sadly, the pistons I have don't match the bores. I'd never actually 
checked before! The block bore is 3.690" and the pistons (below top ring 
parallel to pin) 3.723". With Starrett dial caliper, I could be off a 
few thou. Pins are full floating, .928" diameter. Compression height is 
2.084". This was a 199, but I have no rods, don't know stock rod length 
or compression height stock, so these pistons could be from any motor at 
all, maybe not even AMC. ANyone have piston data?


So I have no real idea what this pile of parts was from, other than some 
  combination of Navarro Rambler. It's certainly a mishmash of first gen 
and later-gen motors, plus who knows what. It's somewhat of a relief, in 
that I don't have to worry about ruining some museum piece.

Basically I have a hopefully good stock block with nice expensive work 
done, plus sleeved and O-ringed (which could be a liability). Plus I 
have an exotic head with thousands of dollars worth of work in it, and a 
custom cast stainless steel turbo manifold. Since the block is sleeved 
SMALLER, and the walls are crazy thick, I may be able to bore it for 
these pistons, if they indeed are compatible. So until I do a complete 
inventory it looks like it would make a nice 300+ hp, 6000 rpm turbo 
street motor. Pretty good for $300.
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