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Discussion Starter · #1 ·
The car is a 30,000 mile 1997 M6 T/A. I was in the middle of a heads/ cam upgrade when I discovered the cam bearings were toast. I was going to leave the bottom end alone. But now that the motor is out of the car, i've decided to upgrade with forged pistons and rods.

Here are some of the current mods:

-Vortech V-1 Supercharger (currently 6lbs)
-Crane Fireball ignition w/ retard control
-NX Express kit (50-150 wet shot)
-Custom Ground Comp Cams Xtreme lobes 224/236 dur 502/520 lift (1.5
ratio) 115 LSA +3 degrees of adv. ground in
-Jet-Hot long tubes (coated)
-Random tech Y-pipe w/ dual cats
-Ported heads/ Intake (flowed 251 and 194 @ .500 lift without a pipe)
-Manley valves and Combination Motorsports spring kit
-SVO 42 lb "green top" injectors
-Racetronix 255lph PnP Walboro pump kit
-SPEC Stage III clutch

*I will be most likely be using PCMforLess for the tuning*

My questions are listed below. I am purchaing the Probe -13.8cc 9.4 to 1 forged pistons and Probe 5.7 full floating forged rods. I going with these pieces because I can get them through a local dealer for $550:

-How much can the stock crank take? Has anyone ever broken one?
-Should I overbore the block to a 355? Would the gains be worthwhile and what are the drawbacks? (harmonics, crank stress?)
-How much additional boost can I run on the S-trim before I exceed the capabilities of my fuel system, valvetrain, and stock crank? (The car must be able to pass emmissions). The blower is currently spinning at 35,000 when the motor is @ 6,000 rpms. The unit is good to 55,000 but stops making boost around 50,000.
-Should I do a partial fill with hard-block to stabilize the block (would this
cause overheating in a F.I. motor)?

Sorry about the long post, but I ned to get my plan of attck in order before I take another step forward. The car has been down for over a year; I've been deployed to Iraq and am just now working on getting it back together. I really miss rowing the gears!

Thanks in advance and cheers!

· Registered
1,248 Posts
Stock crank wont take much more than what your throwing at it. FYI callies cranks on sale from one of our sponsors Victory. Id get a callies it dont get too much better. The 355 wont hurt you too bad, i dont no ANYTHING abotu turboes or s/c's but if im not mistaken you can take 9psi before really messing anytihng up.
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