Strength of stock bottom end?

CobraSix

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Just curious what the stock 4.1 Xflow can handle for boost? It's an EFI (think a 84DA, but will have to double check). I'd like to run around 7-10 psi with minimal bottom end modifications. Anyone see any problems with this?
 
None at all. 260 kW (350 net hp at the flywheel) is the limit for the rod bolts on a regular un prepped basis. 1983-1985 AIT Turbos used 9 psi boost, and gave 270 hp net (200KW). Stock 4.1 Pistons are okay as long as the rev range is not raised above 4500 rpm for a post 1985 engine. Short stroke Falcon 3.3's reved to 5500 rpm, so that fixes the maximum design piston speed to 4800 rpm for a 4.1 x-flow.

Main issue is compression ratio. EFI engines ran 8.8:1 right through every year, but carb engines varied from 9.35 until Jan 1986 to 8.7:1 for post 1986. After 1986, the trough in the pistons for X-flows was increased to lower compression.

Mike Vine and AIT and Garret Air Research Australia Prty had good results with 7:1 compression via machining head or via one 1.5 mm spacer and two head gaskets. So C/r is reduced via 59 thou of steel and then an extra stock 41 thou of stock MonoTorque head gasket for a deck drop of 100 thou. Similar to the stock US 250 arrangment.
 
So,

Put a rev limiter on the car to limit to around 4500. In my experience (limited as it is) there seems little reason to rev a turbo engine since the torque can come in so low. But that limit is good to know for when sizing a turbo.

Any simple upgrades for the pistons and rod bolts? I have to pull the engine apart anyway since the condition is somewhat unknown. Supposedly it ran in 2005.

but 9 psi should get me to my goal of around 225 RWHP.
 
I think 9psi will put you closer to 300rwhp....

In looking to build my 250 there is no off the shelf piston for them (forged) so it will need to be a custom set. The same pretty much goes for rods (granted preped stockers with ARP bolts would go a long way) I am going to bit the bullet and just go to a longer custom steel rod with a shorted forged piston. Between that and main studs I should be good for about any kind of power I am going to make. I am a big fan of building stout short blocks that are worry free.

someone correct me if I am worng but isn't the other weak spot on the crossflow the push rods? an upgrade on those will prob be needed for higher RPM useage and for stiffer valve springs.

mine was a runner too....crossing my fingers it still is and once I get the car finished I am pulling the 250 out for a build up for makign some big power.
 
Just for comparison's sake, there are several guys with 250 Chebby engines making close to 750 HP with forced induction with only main studs and main girdles, and also cast cranks. Several 292 guys are making over 800 HP with the same mods. I dont know what the peak power levels for the small Ford are, but probably now even close to what the Chebby are at. So you'll probably be fine with doing similar mods to yours. They are using good aftermarket rods and pistons though.....
 
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