[Johnny406]

Some of you may recall that I had a bit of misfortune a few weeks ago when I started assembling my new 428 build. I was using some old Venolia supercharger pistons and I had them balanced along with my 990 forged crank and Eagle ESP rods. When assembling it, I discovered that my pistons were a good .047 in the hole. In the end, I decided it was better to order new pistons over milling the block.

With that said, I spoke with the real nice folks at Race Tec pistons and they offered to make me a custom set with a higher compression height, .990 pin and standard (not metric) ring grooves.

The pistons showed up today and they are certainly beautiful. The problem is that they are substantially lighter than the estimate as they were "supposto" be within 5 grams of the current pistons. Though I knew the pins would be lighter because they are the 2.500 length over the 3.00 of the Venolia pistons, I was told that as long as I could get the piston, pin, ring combo within 15-20 grams, I wouldn't need to get my assembly rebalanced.

The Race Tec pistons are 37 grams lighter than the Venolia 528/566
The Race Tec pins are 46 grams lighter 128/174

It's 83-84 grams lighter would be great if I hadn't already spent the $250 to get it balanced.

Though I hope I'm wrong, I really see no other choice than to re-balance it again, correct?

[Jack Gifford]

Fill the pins with lead?

[Scott Roberts]

Not being an ass but welcome to racing.... nothing ever fits.

[WDCreech]

What size and how thick are the pins? .990 x 2.93 are usually about 10 grams per .010" .150 wall 150 grams, .170 wall 170 grams etc...I wouldn't worry about lightening the assembly 30 or 40 grams but more than 50 I'd rebalance. I've got a set of .990 x 2.93 .170 wall je pins, 170 grams with less than 10 runs on them. I could possibly trade, if they where the same length and diameter.

Marty Creech

[mgarblik]

Taking that weight off is a good thing as you know. Re-balancing to the new bobweight would be the best solution. I have some BME pins and Venolia Pins. (used) that may be quite a bit heavier than what you have. I can make you a killer deal on them but that's not my first choice to correct the balance. PM me if you want me to weight what I have and go that route. I am guessing my pins will get half of the weight back in. They are very thick taper wall pins.

[taff2]

I usually get my rotating assembly overbalanced by 2 or 3 %, but you're way over that, rebalancing is no doubt the best way forward for race use. Street use, put some thick wall pins in and don't worry about it.
I've had the same problems with custom pistons from Ross, the first set had the valve relief angle cut for early heads (I have a '59 389 block but told them I'm using later '70s heads). The second set is a whopping 120 grams heavier than my target weight of 500 grams! They put a solid 5/8" thick dome instead of a hollow dome, and 120grams is a big chunk to mill out. I ended up buying another stock bore 389 and boring to 4.090" to reuse my existing pistons (had only done 40 runs, I just wanted to up the compression ratio close to 10.5-1 for a bit more power on my turbo combo, hence the dome).

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[WDCreech]

Another option is pin buttons . But , taking 80 grams off the bob weight is probably a better idea. A couple % overbalance on a pontiac or on small block wedge engines is probably a good idea too . I like BBC's a little underbalanced.

Marty

[Dragncar]

Originally Posted by Johnny406

Some of you may recall that I had a bit of misfortune a few weeks ago when I started assembling my new 428 build. I was using some old Venolia supercharger pistons and I had them balanced along with my 990 forged crank and Eagle ESP rods. When assembling it, I discovered that my pistons were a good .047 in the hole. In the end, I decided it was better to order new pistons over milling the block.

With that said, I spoke with the real nice folks at Race Tec pistons and they offered to make me a custom set with a higher compression height, .990 pin and standard (not metric) ring grooves.

The pistons showed up today and they are certainly beautiful. The problem is that they are substantially lighter than the estimate as they were "supposto" be within 5 grams of the current pistons. Though I knew the pins would be lighter because they are the 2.500 length over the 3.00 of the Venolia pistons, I was told that as long as I could get the piston, pin, ring combo within 15-20 grams, I wouldn't need to get my assembly rebalanced.

The Race Tec pistons are 37 grams lighter than the Venolia 528/566
The Race Tec pins are 46 grams lighter 128/174

It's 83-84 grams lighter would be great if I hadn't already spent the $250 to get it balanced.

Though I hope I'm wrong, I really see no other choice than to re-balance it again, correct?

I just picked up my Scat 4340 4.25 crank from getting re balanced. It was only 80$ for it. I first had it balanced for PPR/RPM billet 6.8 rods. But wised up and decided to run some Crower mid weights of the same length. They had to add a bit of weight on 2 of the holes they originally drilled but it was no big deal. The shop said the crank was VERY hard to drill so thats a good thing. But had to pay extra for it.
Note: the RPM rods came about when a guy brought in a set of Crowers and asked for them to be copied. Those folks have no qualms about doing it.

[Johnny406]

I did find some pins that came in at a 176 grams each but at a cost of $26.70 each would be no cheaper than rebalancing it anyways.

https://www.ebay.com/itm/JE-Piston-W...AAAOSwQVlcdFLq

[t money]

As Dragncar said rebalance the crank will not cost that much weight match the pistons and pins you should have all the weights of the other parts big & small end of rods, rings , bearing do the math get your new bob weight. Your just balancing the crank ( not rebalancing the rotating assembly )