200 or 250 for Forced Induction - WHAT DO YOU THINK' ?

200 or 250 for Forced Induction ? WHAT DO YOU THINK?

Gathering parts and info for a pending small block six FORCED INDUCTION build. Recently acquired a set of TRW Forged 200/250 pistons and had a lengthy discussion with my favorite machinist'. Build target is moderate street / weekend strip car with target of a@ 250 - 300 HP.

I am undecided to build another 250 for forced induction or use the 200. The advantage of 250's displacement/torque advantage is somewhat negated by the shorter stroke FI revving capabilities and of the 200 and the 200's somewhat simpler HiPo parts availability.



My current Vortech SC 250 is built for low RPM boost using conservative rev limiter to keep it intact. My built NA tri-power 250 with shot peened/worked rods, custom pistons, and custom made 250 balancer can shift @ 5500 but most stock component 200's can safely rev until they run out of breathing'.

I have two 250 blocks, and a running 200 (76 Mav') other than in cars. Broke 250 Turbo engine with blown pistons after too much boost/fun. May use new build in one of current 3 pedal 5 spd cars but this build project includes a 66 Ranchero automatic . (currently 289/C4) .

Have fun

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The larger displacement engine does give a much wider power band.
The peak power is still a matter of the cylinder head.

How much power were you making before you broke the supercharged 250?

What do you have for heads?

What is the weak link for rpm in a 250 six?

Broken 250 had a Buick draw-through turbo. AFR's were still good but increased boost (@15lbs) led to cracked off ring lands.

I have three 'virgin' heads - two mid 70's 62 cc heads and a DOxx with 54 cc closed chambers. (also three in cars with built heads)

The 250 basically is the stroked version of the 200 and the added rod length adds to the piston speed and reciprocating forces as well as increasing usable torque/powerband. The 'under-box' bore/stroke of the 7 main 200 contributes to a anvil strong bottom end.

200/250

BORE = 3.68"

STROKE:

200 = 3.126"

250 = 3.910"

250 stroke is .784 " longer than 200 and 250/200 deck is same difference.

have fun

Sounds like you really want to use the 200.
Are you going to use a turbocharger or the Vortech?

If I remember correctly the 200 connecting rods are the weak link.
Will you be using the stock rods with the TRW pistons?

thanks for the response:

... currently plan on turbo although basic build is same.

... AFAIK the (early ?) 200 rods are forged but appreciate info on suitable/available rods.

.. 250 OEM rod/deck height is odd but preserves lower CR (@ .120).

... 'have two good 250 blocks and a 200 on a run stand - interested in trend to smaller displacement motors built to handle big displacement power ...

(friend just turned in his Jeep with 3.7 V6 for new Jeep - more-power with 2.0 Turbo, )

have fun

You may have read this thread before but here is the link to the discussion on aftermarket rods for the 200 six.
viewtopic.php?f=1&t=77943#p600461
You would need custom pistons to use these rods. Autotech is the recommended supplier.

There was a time when you could still find the 1965 to 1968 Ford 300 connecting rod which worked well for the 250 six but those days are gone.
It is possible to use a Chevy LS 6.00" long rod for the 250 six if the crank journals are turned down to 2.100"
The big end is .940" wide versus .990" for the 250 rod. You can just let the rod float with the extra .050" side clearance or you can tighten up on the side clearance at the piston and let the piston control connecting rods side movement.
I believe the LS rods do not have the offset beam like the other Chevy V8 rods.
Piston pins are .927" requiring a custom piston.