US 250 w/xflow head & deep dish pistons?

[Anonymous]

Ok so I have my heart set on building a xflow head/us block engine for my stang. According to Jack the main reason you would not want to use a US250 with a xflow head is because the chambers on the xflow head are pretty small and you would end up with a CR that is way too high. I kinda like the idea of starting out with the 50 extra inches and extra HP. SO..... :idea:

If I deck the block to zero and get lucky enough to find a larger chamber (56cc) xflow head, I would still need some deep dish pistons ( like 21cc) to keep the CR around 9.3:1.

What do you think about this? Will I be even be able to find pistons? Ideas? How would it work? Is it worth it? I know it would be easier to use a 250 xflow block, but then I have the trans problems etc. Plus this is supposed to be about us being able to use our us blocks and not have to have alot of parts shipped around the world.

 

[xctasy]

Great point, Spyke. Any engine with "Little Orphan Annie" parts is a liability. At least with a 250 or 200 US block you will get some common parts. The alloy head uses 3.8/351C/400/429-460 valve gear, so you should be ok for most things.

The alloy head would handle some extra compression...you could go to 9.5 :1 if you had a conservative ignition curve.

The x-flow to US 200/250 block thing is it's all new territory. The block face needs work, and there are steam holes to tap and close. I think, and always have thought, that a steel spacer plate that intergrates the US block to the Aussie cross-flow head is the best option. If you could use an 80 thou steel plate, and some drill vertical holes in the block near the lifter gallery to gain outboard space, you could perhaps fit a sealable steel plate which dovetails into the block like a window gasket, it would sure make life easier. Then you could run a head decked 50 thou on a finish machined block. Problem is the head has to clamp down on the outer part of the gallery. On balance, Jacks method is the most practical.

I think we need to cut him a little slack, and wait for the genius to see how it all pans out . We're all fans of what he's doing. If the thing can cope the termal stress then he'll have a winner.

As for the Aussie block, the salvage cost, block adaptor and small differences in engine mounts between 250's, and the greater height over the US 200 will rule it out as an easy swap for really early Falcons. And the ignition isn't just a Duraspark II, and other US versions are not straight swop-overs. But its got the following eight plus points:-

* US 73 (1976 to 1985) or US75 emissions compliance (86 to 92), std EGR valve,
* plentiful unleaded versions,
* the avaliability of the Toploader/T5 bellhousing form CRS in Australia,
* the factory C4 automatic bellhousing adaptor,
* the factory EFI option (83 to 88),
* great aftermarket headers,
* power steering and low mounted and compact a/c brackets
* and over half a million to choose from means a cheery pie original will wake up any US car fitted with an I6.

And the US dollar buys a few Aussie sheckles right now!

But the Argie Special Performance and Maxi Eccono 2-barrel head bolts right on. Make amigos with South Americans, is all I can say!

 

[Anlushac11]

8)

Some things to pint out with the crossflow head.

If your worried about compression dont get the block decked to zero deck height.

Also you can polish the combustion chambers to pick up a few cc's there.

And keep in mind that aluminum dissipates heat more effeciently than cast iron. Therefore you can usually run a wee bit higher compression with an aluminum head than you can with a cast iron head. In the 302 heads, aluminum meant you could safetly run a 10.5:1CR instead of a 9.5:1CR.

Of course that will depoen on so many differnt factors like air temperature, fuel octane, combustion chamber shape, etc.

I am finishing up the porting of my Oz 250 head so I can have it ready to sell. BUT

I am going to wait for a report back from Jack before I jump on the Xflow head. And I looked into the EFI setups and it looks like I will be going carb. Its a $ thing.

 

[addo]

Check with Alloydave, but there are low crown pistons (made for the long rod 250s) and also a deep dish (24.7?) units from memory. As the shape of the dish should mimic the chamber to a feasible extent, don't be afraid if it suits the prescription.

Cheers, Adam.

 

[MustangSix]

It makes no sense to me. I still think that considering all the work that has to be done, it's easier to just use the Oz block for a 250. The only transmission choice you lose is the AOD/AODE.

Look at all the custom work you've just listed just to adjust CR - custom pistons, machining, plus custom pushrods, two sets of gaskets (Oz upper, US lower). Here's another good reason - there are no adjustable/indexable timing sets for the US250 and neither the 200 or the Oz stuff interchanges.

The deck height on the Oz block is not the same as the US 250. Oz pistons in a US block still end up down in the hole by .080", so you'll need cu$tom pi$ton$ to get a good deck height and still not go overboard on compression. And despite the great thermal properties of alloy heads, I think 10.5:1 on pump gas is stretching it.

Crossflow on a US200 makes some sense - short deck, light weight engine, with a head capability matched well to the capacity of the block.

But Crossflow on a 250 doesn't make sense. All you gain for all that extra work is the bellhousing pattern. It would be far easier to make a tranny adapter for an Oz block if you want an AOD. T-5 and C4 are already available.

I guess the bottom line is, if you want a Crossflow 200, you need to build a custom engine. If you want a Crossflow 250, there's no need to go thru all the gyrations. The real thing is available and easily done.

 

[alloydave]

we got pistons.......we got 15.3cc......22cc.......27.9cc.....8.6cc all to suit
long rod 250 motors..

cheers dave