Classic Inlines
603 W Pecos Ave
Mesa, AZ 85210


 
OZ250-2V Cylinder Head

The advantage of the OZ 250-2V head/manifold is that it relives the asthmatic conditions associated with the stock log head without major modifications or multiple carbs being adapted to the log head.  Dyno test have shown that a stock 200ci engine with only the OZ 250-2V head/manifold, a two barrel carb, and headers yielded a forty percent increase in horse power. While flow test results on a stock OZ head were 176CFM intake and 110CFM exhaust, porting and polishing, with most of the attention given to the exhaust runners/ports, will yield dramatic increases over the asthmatic log head. Possibly as much as 50%.

The only drawback is that these cylinder heads were only produced for a few years, and the production ended thirty years ago. Hence, only used heads are available, if and when they can be found. Occasionally, we come across a head for sale, but it's pretty rare. Then years ago, you could pick up a used head for $150-300 bucks, but nowadays they are selling for $650-850 bucks, or higher. And you still have to pay to have it shipped over from Australia, and have it rebuilt. For a good rebuilt head, already in the USA, expect to pay anywhere from $1200 to $1600 or more, depending on what's been done to the head. For example, a head with larger valves and a good port job is going to sell for more money, than one with a standard rebuild. Make sure it includes the intake manifold too, otherwise it's useless, unless you can fabricate one from scratch.

If and when we purchase a cylinder head for resale, we always hot tanked and magna fluxed the cylinder head to make sure the head is free of cracks and/or other defects. Since the cylinder heads are used, they usually need to be rebuilt, including fitment of unleaded valve seats and new guides. However they will bolt directly to a US 170/200/250 block without any modifications to the block or the cylinder head. While the stock non-adjustable rockers from your old head can be used, it is preferable to upgrade to a stock adjustable rocker assembly. Roller tipped or full roller rockers may also be used.
Plus you can use the stock valve cover or an aftermarket alloy valve cover, as well as the stock exhaust manifold or headers. They all bolt right up.

CAUTION: Stock or Chrome US valve covers will work, however they will require minor modifications to the gasket retainer rim, so it clears the intake runners on the OZ head. If you fail to modify the rim, the valve cover will leak and you'll wind up with oil everywhere.

There are several options for valves. First, it should be noted that the stock OZ valves differ from US valves in stem size. Therefore the valves are not interchangeable, but this is not to say that US valves can not be used.   US valves have 5/16 stems, OZ valves are 11/32, therefore you will need to replace the valve guides to use US valves. Bronze guides will need to be custom made, but steel/iron guides are readily available.

OZ250-2V Stock Valve Specs
Valve
Intake
Exhaust
Head Diameter
1.649
1.388
Stem Diameter
0.342
0.341
Stem Length
4.266
4.278
Tip Length
0.218
0.224

The removable intake manifold accepts a two barrel Stromberg carb, but a Holley carb adapter as well as gasket sets and pushrods are available from Classic Inlines for an additional cost. Modifications will be required to the carb linkage, or a throttle cable may be used instead. The stock exhaust manifold can be used but headers are suggested for optimal performance gains. The use of a port divider available from  is Auto Krafters or Clifford Performance is also suggested.

The trend seems to be to install over sized valves since they will offer the best performance.  It is possible to install 1.75 (intake) and 1.50 (exhaust) but the bowls will need to opened up a little for proper clearance. The machinist will need to use caution when installing the new seats in the number one cylinder, as it is possible to hit the water jacket during the machining process. Classic Inlines stocks 1.75 intake and 1.50 exhaust valves from SI Industries for use with OZ heads (with 5/16 stems). The retainers must also be replaced.  One option is the use of one piece retainer, either from a 260 v-8(which may be difficult to locate) or from a ford 4.0 v-6. These are not required, but are an option. Several manufactures will carry retainers for US valve sizes. Other options include using stock OZ250-2V valves or having custom valves manufactured by various US manufactures, including SI Industries and Manley Valves.  FSPP can order stock OZ valves and/or related parts from Australia upon request.

Complete heads may be available from time to time which includes all used valve train components (valves, adjustable rocker assembly, springs, retainers, locks, etc). Price of the complete head is $875.00, or whatever the current market price is, whether higher or lower.










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