Boring Block, piston selection?

[JoshT]

Just heard back from machine shop and I've got to bore 0.030 over. I need some quick help on piston selection. I'll say up front I'm hoping to use pistons in stock for pickup at Summit Racing.


The engine is 2000 Explorer 5.0L. it's getting ported GT-40P heads and a camshaft from Bigdogs Porting through Facebook. I hate to share their "secrets", but cam card is attached for specifications. I have sent this to them as well, but I'm off work tomorrow.and hoping I can go and get pistons and get to shop before the weekend.

I'd go with an oversized stock piston, but it isn't available without special order or waiting a week plus for RockAuto to ship them (if actually in stock and not drop shipped). I can be at summit racing tomorrow morning picking up pistons if I can select from what they have in stock.


Most in stock pistons have a higher compression height, so PTV clearance becomes a concern, but they also appear to have larger valve reliefs. Stock compression height appears to be 1.595 inches on a flat top piston with 4 valve reliefs. The following are what is available in stock at local Summit.


These shorter 1.585 compression height:
SUM-17303C-30


These with 1.605 compression height:
Sealed Power H273CP30
Summit SUM-17302C-30
DSS Racing 8720-4030


These with 1.608 compression height:
KB KB115K.30


The first would definitely work, but looses some compression, and I doubt I want that. The others I'm unsure about. Price wise I like the sealed power and summit options, and for my build they should be more than adequate strength wise. The KB set is the most expensive at over $500, but it includes rings, which seems like a plus, a is probably the best quality piston on the list. I'm just concerned about PTV clearance. Don't want to get the bottom end assembled and find out that the valve hit the pistons.

 

[Mechrick]

I used the Sealed Power set in my Bronco. No complaints and the price was right. Also, the .030" Sealed Power pistons are the stock weight which simplifies balancing.

It's a good idea to have the pistons on hand before the final cylinder hone so the clearance can be checked and set.

 

[19Walt93]

Stock replacement/ hypereutectic pistons would be fine and shouldn't break the budget. I would check piston to valve clearance but I'd bet it'll be good. If you use pistons with a lower compression height you'll lose compression and kill power so I'd avoid it.

 

[JoshT]

I used the Sealed Power set in my Bronco. No complaints and the price was right. Also, the .030" Sealed Power pistons are the stock weight which simplifies balancing.

It's a good idea to have the pistons on hand before the final cylinder hone so the clearance can be checked and set.

Which sealed power set? The ones I posted are not oversized stock replacements.

The go ahead was for the boring, the final hone will wait for pistons.

The sets mentioned above are all in stock at my closest Summit Racing. I can have them bought and delivered to machine shop tomorrow to keep the ball rolling. Otherwise I'm waiting for pistons to be delivered with no real idea as to when that will be. A lot of what I'm seeing, if it isn't in stock, it is custom order or several weeks lead time to shipping them out.

Stock replacement/ hypereutectic pistons would be fine and shouldn't break the budget. I would check piston to valve clearance but I'd bet it'll be good. If you use pistons with a lower compression height you'll lose compression and kill power so I'd avoid it.

I also posted in a couple of experienced SBF engine builder groups on Facebook. Sounds like I've got no concerns with PTV on any piston I'd consider using.

I've definitely been thinking about the compression, and have been playing with the math. I did not get a chamber size, but was told that a the it changes enough to drop a few points. The particular example they gave was the piston they normally use for builds which is the DSS Racing 8720-4030 in OP. Math puts that piston at 9.91:1 CR with the stock chambers. They said their port drops it to about a 9.7:1 CR. Reversing the math puts the chamber at about a 59.5cc, so redoing the math with that number. (actually cheating with Summit's CR calculator)

If I apply that to all the pistons I'm considering I get the following list:

P/N	Corrected C/R	Price
Silv-O-Lite 30 over stock repalcement (per RA listing)	9.37:1	unavailable in time
Summit SUM-17302C-30	9.73:1	192.99
Summit SUM-17303C-30	9.25:1	171.99
Sealed Power H273CP30	9.15:1	160.99
DSS Racing 8720-4030 (forged)	9.73:1	409.95
KB KB115KMT.30 (rings included)	9.38:1	554.99
Wiseco Pro Tru PTS500A3 (forged)	9.15:1	629.99

Interestingly this endeavor also showed that stock engine should be 9.5:1 instead of 9.0:1 like I believed, looks like that is due to the smaller combustion chambers on the GT-40Ps. With that in mind, I'm currently leaning towards the Summit (cast/hyper) or DSS (forged) 9.73:1 CR pistons. The Summit ones at the front of the line for price. Won't lose CR, and the stock tuning should be able to compensate for that small gain.

 

[rubydist]

I would definitely go with one of the sets that gives you 9.73:1. Your cam is not aggressive enough to worry about valves and pistons meeting.

 

[Mechrick]

Sealed Power H273CP30

Those are .030" over and the same ones I used.