SiCk PuPpY

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!
JD

rskrause

A blower application is hard on a crank for a couple of reasons. It's isn't so much power output as it is load on the snout from the SC pulley and detonation. A boosted motor with 9.4:1 will detonate on pump gas. If someone tells you different, they are just plain wrong. That's why you are putting forged pistons in it - it must be able to tolerate detonation. But detonation is also harmful to the crank, especially with a manual transmission it really will shock load the crank. Nitrous on top is going to make this worse.

OTOH, a stock crank in good condition is pretty strong. If you plan to re-use it it should be thoroughly inspected by someone who knows what to look for visually. It should be magnafluxed, checked for straitghtness and have all critical dimensions checked. The journals should be polished. All of this can cost more than some people want to put into a stock crank.

The most logical choice depends on a variety of parameters. Your budget, just how reliable the car has to be, how much hassle is it for you pull a motor and repair it, etc. One thing to consider is that most crank failures don't take out the rest of the motor. Unlike a rod failure, for example.

Rich

LameRandomName

Is that enough injector?

SiCk PuPpY

I'm on a semi-tight budget (read: already $2,200 into this so far) Would a Scat 9000 crank be better and more affordable since they are already balanced and polished? I heard of some people dumping serious money into getting these rebalanced with heavy metal even though they are supposed to be "pre-balanced". Or are there reasonably priced forged cranks out there that will require minimal/no additional balancing? I'm going with ARP main cap bolts since this is an occassionaly driven car that will rarely see any track time. Also, I will hardly ever use the nitrous, since the new set-up will be all I need for the speed fix (but it's good insurance to have).

SiCk PuPpY

Brian Herder recommended those injectors, so I hope they will.

rskrause

I am unfamiliar with the SCAT crank you refer to. No crank will be balanced" for your application unless your rods, pistons, pins, and rings have a specified bob-weight that the crank was manufactured for. Any cast crank will need to be externally balanced. If I were on a realt tight budget I'd do a good visual inspection of the stock crank and mic out all the journals as well as check for straightness. If it looks ok, use it. It will also need to be balanced (extrernally). The cheapest aftermarket crank I am familiar with is the Eagle 4340. They are Chinese, which I don't like but they work good. GM has some decent forged cranks in the $500 range.

Rich

Blownbird355

You could also try to find a GM one piece rear main truck crank for around $250 or so. I believe they are out of certain 90 model trucks.

97TA-WS6-Con

Sick Puppy: I like your choice of car