As you mentioned, this spring I had a custom piston made up for me by Diamond racing. I have to thank Mike Phillips at AMP for getting me in contact with Diamond, as well as his input on the development of these new parts. It was something he had wanted to do for a while now, and luckily I had the projects in the hopper to order 5 sets of these, so they assigned a part number to them, and could sell them to me for the same price as a "shelf stock" piston. This allows me to retail them for the same price as other high quality Buick 455 pistons.
The dilemma we have faced for many years is excessive decking to run a zero deck clearance, with the readily available pistons. It was not at all uncommon to have to cut .050 off the deck, to get that zero deck. And zero deck is very important, for engine efficiency and power, as well as detonation control.
And when you do that, you have to cut the intake side of the heads to align the intake again.. it all adds up, as milling is not inexpensive. It ends up being lot of wasted motion, and although I will confess it might not be a big deal, but taking more material off an already weak block, simply can't be advantageous.
The next thing to deal with is rods.. While stock rods are fine for up to about 500 HP in a street application, the advent and widespread use of Aluminum heads these days has made that once rather elusive mark, for a street engine, to be a rather easy goal. So we are now really working the stock rods, and after ARP bolts, re-size and an often tough balance job, you end up with around $300 in a set of stockers.. That's if you have a set of 8 that can be re-done and balanced.. That not being the case was so common, I typically bring in 10 stock rods to get 8 good ones, and that's after I have picked thru my cores to throw out the obviously poorly machined or cast ones.
I would be remiss not to mention the TA Sportsman rod here.. That's really a great quality rod, no doubt, I have used many, many sets. It's certainly the easy rod for a "drop in" replacement, for you guys having machine work done at maybe a less than "savvy" machine shop. I will get to that later.
But being a drop in replacement, it has to work with available Buick pistons, in both the pin diameter and compression distance, so we are now back to the massive decking issues.
Recently, Wiseco came out with a new Buick piston. Several builders were going to Pontiac Rods from Cat, and modifying them for Buick use. Some were going to the H Beam BBC rod from Eagle Specialty products down in Miss.. That Eagle rod is a great value, plenty strong up to 700 HP, and it's a good quality piece.
These builders were using a 6.635 long Cat Pont or Eagle BBC rod and turning the crank down to fit it, and/or narrowing the rods. Also on both rods, the pin end had to be opened up for the 1" Buick pin, that the Wiseco pistons have.
The drawback here is twofold.. Extra machine work on the rods to fit the Buick crank for the pont stuff, or on the crank for the BBC stuff. As well as the pin end machining on both rods. More of a problem is that you really do have to surface the block at least .020 to clean it up completely. Most of the Wiseco/Cat/Eagle combos require a 10.560 deck height, which only gives you maybe .010 to clean up the decks. I have seen a few cases where that's not enough.
Beyond that, that Wiseco piston is not a quite piece during cold engine operation. Trust me, if you put them in at the recommended .005 clearance, you will swear the thing has a rod knock when it's cold. Especially on the milder cam/iron exhaust manifold stuff. Been there, done that. One we did this last fall was so bad, I wouldn't let it leave the shop, and ended up replacing the shortblock, as it turned out, with the TA/SRP pistoned shortblock that we originally built for you John..
I thought a better option was to have a new piston created.
We use the Eagle rod, but having the ability to do it now with the custom piston, we went with a 6.800 length. The longer rod is easier on the cylinder walls, which is a big plus when your working with the rather thin wall thicknesses that most of our Buick blocks have.
In addition to that, we had the piston designed for a 10.550 deck height, a .050 offset grind on the crank, and offset the pins for quiet cold operation, even with the superior 2618 material. And we specified them to be built with the .990 pin dia, so that eliminates any work required to the rods, beyond the normal pin fit.
The key to the combo is having access to a good crank man, and I am blessed with having one of the best in the business at my disposal. The rod pins are offset ground .050 to fit the stock size BBC big end, and use the infinitely available BBC rod bearing. Want .001 under bearings.. no problem.. hard bearings, soft bearings, dowel end bearings.. you name it. Easy and cheap.. I chuckled at my cost for a set of ACL BBC rod bearings.. it was about $25 less than the Buick bearings..
But back to the crank.. To fit the rods, beyond the offset grind down the the 2.200 inch size, the rod pin on the crank has to be widened to 1.995 to accommodate the wider BBC rod bearing, and allow for a nice .015 side clearance, and you can just get there with the stock Buick crank. But the key here in widening is having a good crank man that dresses his grinding wheel properly, to not burn the crap out of the cheeks, and produce a nice finish. Not every grinder is capable of this, or maybe more correctly stated that they will not take the time and effort to do it right.
The advantages of this combo are:
More cubes from the longer stroke
Better rod ratio with the longer rods
Easier on the cylinder walls
Lighter pistons and pins
Offset pins for quiet cold operation, even with the better 2618 piston alloy.
Drop in fit for a $450 set of 700+HP H-beam rods
No excessive decking or intake fit problems, but enough room for complete deck cleanup.
Wider rod bearings to better handle the loads
A huge choice of rod bearing types. Along with easy availabity and lower cost.
And of course they have the performance oriented 1/16 compression rings.
All this adds up to a stronger engine, for a very attractive price.
I use a P bearing with a smaller rod journal radius on motors up to 650HP, as they work fine, and don't require surface hardening of the crankshaft. This keeps the costs down.
On motors beyond 650 HP, we go to the H series bearings, which allow a bigger radius on the rod journals, and then we nitride the crank to harden it for the H type bearing.
This is all done in preparation for the future. We are going to need a strong rod with wider bearings to handle the loads. Our BBB street/race motor future lies directly with that TA Tomahawk block. Power output on these street motors will be impressive, and I already have a development block on order, to build multiple combinations for killer street strip motors..
I truly believe that 650-700+ Street friendly Naturally aspirated HP is on our near future.. and with forced induction.. well then your pocketbook is the limit, not the parts..