Reply to "Valve train, intake manifold and header questions"

> Crower enduro roller rockers with a 1.9 stamped on them.

Crower makes a 1.9:1 rocker for SBC applications that changes the pivot point
(backset 0.090" relative to their normal SBC enduro). Given that 2V heads
(Aussie or U.S.) peak at a relatively low lift, that's an odd choice of rocker.
Also, Crower sells the rockers in sets of 8 to be used on the intake side only.
On a head with decent exhaust flow (like a 351C-2V), a shorter exhaust ratio
(0.1 or 0.2 less) on the exhaust side generally works better. We tested and
verified that on the dyno mule 351C-4V.

It appears to me you have the Crane rocker arm guideplate conversion kit (p/n
52655-16 is for 351C but they also make another one for 429/460 BBF). This is
a bolt-on conversion that requires no machining of the cylinder heads. Crane
recommends the kit for open valve spring pressures of no more than 320 lbs.
To install the kit, you remove the stock valvetrain and chase the rocker arm
pedestal bolt holes with a 5/16" x 18 tap. Fel-Pro thread locking compound is
then used to hold the new studs in place. Curing time is approximately 6 to 8
hours. Crane recommends the top five head bolts be replaced with 1/2" x 4 1/4"
grade 8 Allen head cap screws since, with the rocker arm conversion in place,
it's almost impossible to put a socket on the original head bolts. You will
also need to check if your rocker arm pedestals are cut on a 90 degree or
dovetail angle. There is a different part number for each case. Since the
guideplates are plastic (Crane calls the material "Feflon", you can re-use the
stock, non-hardened pushrods, assuming they are the right length and up to the
spring pressure.

> They are in 2V heads that don't have a stamp in the corners so we think they
> could be the aussie 2v's.

They may also be 351M-400 heads. Larger cast-in raised numerals may be located
on the intake side at the top corners, near the valve cover rail. U.S. 351C-2V
and 351C-4V heads will usually have the raised letters. Boss 302 and 351M/400
heads may not. Aussie 2V heads may not have the numerals on the intake side
but the four that I owned have a smaller raised numeral on the exhaust side,
down low near a corner head bolt. The odd thing is that three of the Aussie
heads have a raised numeral 2 and the fourth has a raised numeral 4 (but it
still has 2V ports). I've heard of 3's in that location as well.

Note that most 351M-400 heads have a bad exhaust port. US 351C-2V and
Aussie closed chamber 2V heads have a nice smooth exhaust port. Most
(early 400 heads may be an exception) 351M-400 heads have a "potbelly"
port with the water jacket drooped down around the valve guide. You
can't grind the potbelly out because there's water inside it.

The closed chamber 2V's are from Australian 302C's (there are also open
chamber Aussie 2V heads from Aussie 351C-2V engines) and will carry an
ARD1AE casting code. The codes are located on the underside of one of the
middle intake ports and foundry marks (CC or CF for U.S. heads, GF for
Australia) are located in the rocker arm area. The Aussie closed chamber
heads I've inspected all have a sundial mark in the rocker arm area but
Steve Liebenow has inspected Aussie heads without the sundial mark.

> Is there a draw back to using the airgap if I don't turn up to the 6500 rpms
> it's rated for?

As George mentioned, the Air Gap doesn't have carb heat if that is important
to you. Also the Air Gap is substantially taller so won't fit under stock
engine screen. Other than that, the Air Gap will outperform the Performer
across the RPM range. If you want EGR (good for cruise MPG), a Holley Street
Dominator 2V has that feature, along with carb heat and will fit under a
stock engine screen. It's a single plane but in testing on a 393C with
ported Aussie 2V heads, it outperformed the RPM Air Gap from the lowest
RPM we tested (2500 RPM). However, I wouldn't expect that to be the case
on a mild 351C with unported 2V heads.

> Which headers would be best on these heads?

I ran Larry Stock's Hedman headers when I ran Aussie 2V heads. They had
1 3/4" primaries and a 2 1/4" collector. If the heads are really Aussie 2V,
the flange will seal against 4V heads (U.S. 2V heads may need some gasket
trickery to seal). Remember it's the ANSA mufflers that are the biggest
HP loss on the engine (50 HP loss on a 400 HP 351C dyno verified).

Dan Jones