Building a 331: periodic update

As some of you know, I've been around a while doing a series of upgrades to my 66FB. It has a TCP front suspension, Global west rear, TCP subframes, TCP tower bracing, new front discs to replace the original GTs, a full exhaust using Doug's Tri-ys, a custom X-pipe and Delta Flow 50s, and some other odds and ends to the interior and electrical system. I've been doing a lot of thinking and studying about the power and drive train mods, and have finally settled on what I'm going to do. Nothing exotic - which was a big part of the decision process BTW, but good performance pieces. In this thread, I'm going to share my experiences in build in the 331 stroker, which is my answer to the power question.

My basic parts list is:
FRPP 302 Sportsman block, ARP main studs, no girdle
Scat 9000 crank, Scat I-beam rods, Mahle piston kit, Clevite bearings
AFR 185 heads (upgrades: roller springs, valve upgrade, 7/16 studs, better valve seals)
Custom Ed Curtis cam (www.flowtechinduction.com)
Rollmaster timing set
Eaton roller lifters
Miller Engineering roller rockers
Crane distributor (optic trigger), Jacobs Fire Control 2000 spark box and coil
Edelbrock RPM Air-gap, Edelbrock Victor water pump
Fidanza aluminum flywheel
ATI superdamper
Carb - probably a Quickfuel; Holley mechanical fuel pump

The block has been bored and honed (w/ torque plates) to 4.0305, which was determined by the machine shop (I'm using Dougan's in Riverside, CA) to be optimum after measuring the pistons, and had the mains bore checked for straightness (which was fine).

After that, I mocked up the shortblock and began taking measurements: Piston-to-deck, rod clearance, crank runout and thrust, and basic pin fitting to rods and pistons. I haven't checked bearing clearances, yet. I wanted a minimum of 0.100" clearance between the crank counterweights and pistons, and between the rods and cylinder bottoms. A little less probably would have been fine, but that was my number. I had to just touch two cylinder bottoms to clear the rod bolts (I had about .065" clearance before hitting them with a carbide bit). All other clearances have checked out fine, except piston-to-deck, which was between 0.010-0.015". I had the deck squared and taken down to 8.195", which leaves the pistons 0.005" in the hole. Just right. I am shooting for a quench height of 0.040-0.045 for all cylinders. Decking was expected as the compression height of the pistons is a little short at 1.165". These are nice pistons, though - the wrist pin does not intersect the oil land and it uses a metric ring set (1.5, 1.5, 3mm) for less drag.

I took a die grinder and a bunch of sanding rolls to the block to remove sharp edges and the worst of the casting flash and seams. I paid attention to the oil drain-back holes and adjacent areas. I did not install oil restrictors, which are not necessary on a 302-based motor (a 351 would be a different story).

I also took sanding rolls to the rods. Scat I-beams are cheap, made in China pieces tha won't win any awards for beauty. I profiled and polished them, then re-balanced them. This might be of interest to some of you. I did not invest in a rod fixture. I installed the crank in the block and snugged down the caps. Then I rotated the block on the engine stand so that the crank was to one side (not right-side-up, or up-side-down, but sideways) and hung a rod (with bearings) on a rod journal. The rod hung to the side (not in the bore) so that I could place the small end on a triple-beam scale. This scale measures to .01 gram. Using just a little WD40 on the rod bearing, it moves quite freely on the crank pin, but not free enough that all friction is overcome. This slight friction was enough to make the weight vary. To solve that, I used a tack hammer (any small hammer would do) and tapped the crank counterweigth to set up a little vibration to break the friction on the rod bearing. Tap, tap, tap, adjust scale, tap, tap, tap, adjust scale, etc. I then removed the rod and lightly ground the small end (if needed), then repeated the weighing procedure until all of the rods weighed +/-1.5 grams. I then weight matched the rod caps, them checked the overall weight of the rods. They were all +/- 2 grams. Since I had a little variation with the pistons, I planned to mix and match rods, pins, and pistons to achieve as good a balance as possible. I would up within a gram.

When I took the rotating assembly (incl. flywheel and damper) in for balancing the crank, the shop re-balanced the rods. I had them pretty close with my "shadetree" mechanic's method, but they touched up a few of the rods. The important weights were as follows: pistons were 419g +/- 1g, pins were within .1g, rod sm. end was 147g, bob weight was 1605g using a 50% factor. They had to take a ton of metal off the crank to balance it because the piston kit was so light. All but the center counterweight had material take off. The crank came in at 41 lbs. With an alum flywheel, a expect this motor to rev quickly.

The only surprise, so far, is that the brand new, FRPP block had a freeze plug driven into a water jacket and another freeze plug installed behind it. I discovered it after hearing a tink, tinkle, rattle sound when I rotated the block on the engine stand. I looked all over for a loose washer, etc. before checking the water jackets with a flashlight. I expected to find some loose casting flash, but nooooooooo, some lazy so-and-so didn't have the time to retrieve the freeze plug he/she drove into the block. I removed the nearest freeze plug and fished it out. All is well.

I am now waiting for the heads, cam, roller lifters, front cover, gasket kits, and a bunch of other stuff, which has been on order for weeks with two suppliers. I'll update the thread when I am further along. In the meantime, if you have questions about this build, I'll try to answer them.

That's right, most 331 cranks are designed to be able to be balanced to 28oz. That means that they have to have enough material in the counterweights to handle many combos of pistons, pins, rods, etc. and still balance to 28oz. Depending on the weight of your piston kit, more or less material will need to be removed to achieve this. Such a crank can be balanced to 50oz, but more material must be removed from the crank. Considering how muuch was removed from mine to balance to 28oz, I can hardly imaging how much would be removed to achieve a 50oz balance.

Surely you know what the balance specs are on your damper? Or do you have one, yet? The damper and flywheel must use the same imbalance (neutral, 28oz or 50oz) and then the crank balanced to that, bearing in mind the weight of your piston kit. If your engine builder doesn't know the imbalance spec of the motor he built, I would remove the rotating assembly and have it balanced. When you do that, determine what imbalance you want, then take in the correct damper, flywheel, crank, pistons, rings, wrist pins, wire locks (if used), rods, and rod bearings. Have the pistons and rods weight matched. The shop will then determine the bob weight from your components and balance the assembly.

BTW, when a stroker assembly comes "balanced", my understanding is that means that the rods and pistons are weight matched to some tolerance (maybe +/- 2 g), but it does not mean that the rotating assembly is DYNAMICALLY balanced, which is what your machinist will do.

Also, your damper will likely come a bit tight with respect to its fit on the crank snout, and may need to be honed to fit. Don't be surprised if this is the case, but it's not always the case.

It looks like we have similar tastes in motors.

347Fastback: Vandenberg? Is that right? Nice area - I like central Cali. I plan to be at a few shows after the car is done. I'll post when I do. Maybe we can meet up.