Qs about 351W rings and pistons

[DanM]

I'm about to go pull the old rings off of the 351W pistons I just pulled when I disassembled the block. Is there anything I might need the old rings for in the future? Or can I just pitch them? First engine teardown/rebuild and I don't wanna throw away anything that might come in handy later.

Also, and excuse the newb question, but if my block only needs a small overbore to clean up the walls (like 0.010"), do I still need new pistons? Or can you just get slightly larger rings? I assume for larger overbores you need corresponding pistons...

[Bruce Edwards]

Rings are a one shot deal. If you bore it you need new pistons. Your machine shop should be able to tell you what size you need to go to on the bore.

[DanM]

Thanks, yeah I haven't taken the block to the shop yet. But I'm doing the min bore necessary to clean up the walls (whatever they tell me that is).

Any recommendations as to piston types I can start to research (brands, etc.?). This is going to be a streetable, moderate output engine. I want 350hp NA. I'll be using the stock crank and con rods. Don't think I need anything fancy in the piston department. Can you recommend any decent ones? Or should I just go to Ford and get 30-over OE replacements or whatever?

[Bruce Edwards]

Get a nice set of sealed power hypereutectice, may not be the correct spelling sorry, pistons. They run cooler are stronger than standard cast pistons and will perform well to the HP you want to run. Set them up with a set of moly rings, top groove only, also by Sealer Power.
Do not forget to grind the crank, resize the rods (install new rod bolts) and have the heads redone or install a set of aluminum ones.

[DanM]

Thanks for the tips. Do you think hypereutectics are necessary for the pretty modest amount of power I'm looking for? Or would cast be sufficient?

I won't cheap out on this, but at the same time, I don't want to throw away money on parts that are overkill for what I want.

Do you happen to recall what the stock compression and deck height is? My block is from a late 80s vic.

[Bruce Edwards]

Vic,

Should be in the 8.5 range. Yes I would not use stock cast pistons in any engine that gets close to 1 hp per inch. They are just not that strong and the others are that much better for not much more. I do not rember the deck height sorry.
If you want to get that kind of power from the engine you will need to raise the compression.

[DanM]

Agreed, although I haven't quite decided how I'll raise compression just yet. I won't be using the stock heads, so I can either use other heads with smaller chambers (maybe GT40s or something?), have the heads milled a bit, or raise it via different pistons.

Is something like this what you're suggesting?
http://www.fastengineparts.com/produ...ew.php?id=2065

[Bruce Edwards]

More like this;

http://www.fastengineparts.com/products_view.php?id=525

[DanM]

Cool, thanks. So the coated skirt ones versus straight hypereutectics? Or did you recommend those ones because they're flat-top instead of dished?

[Bruce Edwards]

The coated ones run tighter and cause less wear on the bore. The flat tops will give you a bump with out head work. I do not like dished pistons in performace engines. It is my feeling that a flat top has a better flame travel than a dished piston. I smooth out the valve pockets with sandpaper to remove any sharp edges, clean the piston before you install it if you do this, to help cut down on hot spots caused by carbon build up. The carbon will form on any ruff surface it can get a grip on. If the carbon gets hot it will glow and cause the engine to ping or knock. Bad for the pistons, rings and bearings.

[DanM]

Awesome. So I guess I'll look into some flat-tops, GT-40P heads, and a decent cam, and that should net me my 350hp pretty handily.

Thanks for all the help, Bruce!

[DAVID GAGNARD]

Dan;

Bruce beat me to the reply,defintely use flat top pistons with the four "eyebrows".......That's what I have in my 351-W,but mine are the el-cheapo cast pistons and I wish I had sprung for the extra bucks and had gotten better pistons... So far,they have held up,but I expect any time for one to let go at the track........

My guess is with 60cc head chambers you are looking at at least 9 to 1 or better compression depending on the piston to deck hieght in your engine.... When I put my engine together,I found my pistons were .070 down in the hole and had my block deck cut around .035 or .040,can't remember which to get my compression up where I wanted it,just over 10 to 1 ........

Install the crank and a couple of pistons and measure the piston to deck height,(it may vary a quite a lot from block to block) and then calculate your compression ratio and go from there..........

David

[DanM]

David,

Excuse my ignorance... eyebrows?? Do you mean valve reliefs? Why would I need a piston with 4-valve reliefs?

Sounds good, though. 10:1 sounds perhaps a touch high for my goals, I figured I could do it with something in the 9s, but perhaps not. Either way, that's still far off both time and money wise. I still need to have the block bored so I know what size pistons to order so I can measure the depth before I need to know what compression I need.

And thanks again for the help. This forum kicks ass!

[Bruce Edwards]

Dan,

You need to figure the compression so you can get the HP you are shooting for. It all has to balance with the rest of the parts you choose for the engine. Building engines is an art not just someone throwing a bunch of parts at something and crossing their fingers to see if it all works together.
The compression needs to work with the cam you pick. The heads need to work with the cam for flow. The valve springs need to work with the cam for lift. The pushrods need to be strong enough for the added load. The timing set need to be strong enough to hold the camand crank timing in sync. The balancer need to be able to handle the extra load and higher RPM. The oil pump needs to be able to handle the extra flow. The oil pump drive needs to handle the extra load of the pump and on and on.

[DanM]

Bruce,

Understood. The car this will eventually go into (maybe) is a V6 right now (don't laugh, it's all I could afford!). I spend some time over in a couple V6 forums as well. There's a large company out there called SuperSix that sells 'upgrade' packages for the 6-cyls. They swap heads, intakes, cams, all this crap, but it's rather poorly matched and ends up netting an extra 30-40hp. Then a fellow came along and just took a look at what would *match* well with the stock heads and intake, speced out some cams, and has people dynoing at +30hp at the wheels with JUST a $150 cam. Just goes to show you that one part chosen to match correctly is better than $1200 worth of parts that look good on paper.

Obviously I'm a beginner... I only really know two important facts about engine building. The first is that stuff has to match and work together. The second is to take whatever you *think* it's going to cost you, and triple it. Fortunately I think those are the two most important things to keep in mind....

[DAVID GAGNARD]

Dan;

Some call them "eyebrows" but they are valve reliefs.....You can get pistons with four reliefs or two reliefs or actually one big/long relief,they come in all shapes and sizes..........The four reliefs would be more suited to your build.......

Yes you will have to find out just how much your block will need to be bored before ordering your pistons.......Usually if the block does not have too much wear they will bore it .030..... Once that is determined I like to order my pistons because different pistons call for different clearances and your machine shop will need to know the final specs to hone the block to........

Usually,but not always, the two valve reliefs and the one long one will give more compression,just depends on the piston....... You can call the piston manufacter and find out the cc's of the piston before hand and that will also help you determine compression ratio......

Dish pistons will lower your compression ratio quite a bit,probably more than you would want............

David