250 XFlow Rockers

[aussie7mains]

Matt does not build anything...

If Jeff does as many small sixes as people say then id imagine he would have or his machinist will have a torque plate. For a Small six it is necessary to torque plate hone engines as the bore distortion can be up to .001 at the top of the block, granted its less on a crossflow block than a pre crossflow.

Your cam is on the small side for 450fwhp unless you are jamming in some boost.

Best Ive heard for a crossflow NA was 365bhp, and that cam would not do it, you need more like 250degrees @0.050. With some manifold pressure can be done, still going to need a fair bit of boost to do it, id guess 30psi? I did see an alloy billet block for a barra, but the cost!!!!!! The really hot barras all seem to be destroked to around square dimension, (Errol Quartermaine)

 

[Cox Custom Mechanical]

Best Ive heard for a crossflow NA was 365bhp, and that cam would not do it, you need more like 250degrees @0.050. With some manifold pressure can be done, still going to need a fair bit of boost to do it, id guess 30psi? I did see an alloy billet block for a barra, but the cost!!!!!! The really hot barras all seem to be destroked to around square dimension, (Errol Quartermaine)

Apparently there is a drag racing guy that has got over 400hp N/A but it would be an absolute pig on the street. 350ish at the flywheel with the right combo should be able to do it with about 10-12psi with a turbo, but with a blower it would need to have a bit more motor to account for the pumping loss and more than likely 15psi.

 

[boingk]

Hi mate I did a very much budget attempt at a build on the good old 250. My info may help you.

Stock 250 block / crank / rods
200 pistons to suit a '66 Stang - cheap casties giving about 11:1 overall
Set ring gap conservatively for NA use
Crow 14872 but I'd recommend the 14626. The 872 has 231@50 and 550 lift, the 626 is a step up
Yellaterra rockers, decent Cleveland damped springs to handle the lift and Crow superduty pushrods - you'll bend stockers instantly
Intake was the Aussiespeed unit with a 650cfm Holley Brawler Mech-sec. Great carb, should've been smaller though. 465 to 570 max
Exhaust was Pacemaker headers into a 3" straight pipe with a 24" long, large-bore truck muffler and diff dump. Sounded great, went well
Ignition was via the TFI distributor feeding an MSD 6AL-2 box and Blaster SS coil

She was never dynoed but I ran her on the street and she was very good fun with an Excedy sprung ceramic button clutch. Very nice with a four speed floor shift.

The unit was an XF ute, about 1400kg / 3100lb or so with a 3.45 rear diff ratio. It went quite well and I estimate had around 250hp at the tyres.

The problems I ran into were cooling and ignition timing - she liked about a max of 32 degrees from 2500rpm after a ramp of 15 degrees from idle. Cooling needed a high-flow thermostat and alloy radiator, the stock units weren't up to task.

This won't get you 400hp - not even close and especially not at the wheels, but for maybe 250ish hp you're into the game cheaply and it'll be fun, fast and reliable on the street on pump fuel.