Need to order some forged slugs for the DeSoto hemi project but am not sure which ring thicknesses I should order when I get the pistons made. Not even sure what the stock sizes are ? Id prefer a slightly thinner ring for less friction but not too thin such that it may affect street reliability/longevity. Any recommendations for a mostly street/some strip blown application ? Standing by.... Rat
Yah I know ..... I need this info pronto - did a search, no dice. What nasty things have you been doing to that engine in your roadster? Rat
Email diamond pistons in the US. I just got my custom blower pistons for my 390 fe back from them and they are a super quality piece. Im sure they will help you in the right direction....Craig
I would call ( Venolia ) and see what they suggest. Also when you order custom pistons order 10 of them not 8 because other piston companies wont sale you one piston if you happened to **** one up, they make you buy 4 and their goes $450 for four ****in pistons. I like (1.5,1.5,3mm) (.043,.043,3/16) (1/16,1/16,3/16)
Funny you should ask it blew the rings out of one cylinder and pumps oil out from every oriface, so now I gotta get a job to build a new mill. Good luck on the search.
Thanx for the heads up on ordering an extra pair of slugs - sound logic. Compact, hard luck on that mill - heard things didnt pan out at Holdens.....good luck with a new gig !! Hey Loco, why that particular choice? Is it because its the best compromise b/w friction & longevity? Rat
Frank, you might first look through a numerical listing in one of the many ring catalogues and, depending on your chosen bore size, see what is commonly available. If it happens that you are at 3.75" then there are many choices, but not so many at, say, 3.73. In the relatively small bore engines you also get some metric choices which may be helpful. As for buying extra pistons, if you are good at your ***embly and keep the detonation under control then not much else will destroy them. FWIW, we like to stay with the 1/16-1/16-3/16 package if we can. No magic, just good service from the sizes. Gary
Thanx Gary - I hear ya on the tune. Looks like 1/16" is the go. Most guys recommend a CR of 8:1 on a blown Hemi with 6-8 lbs boost. Any takers/input ? Rat
Rat, There are a number of things to consider when choosing ring sizes. Probably the first is the intended rpm range of the engine. Wider rings, due to their greater m***, have been known to flutter & lose seal at higher rpm. The 1/16" top & second & 3/16" oil ring are a good compromise for the street (mostly) with some moderate strip use. There are thinner rings available; as to whether you are going to see any benefit for your application is debatable. Your local machine shop may- or may not- be able to provide the bore finish required for some of the thinner rings. Also, you will have to check to see what is available in your bore size. A lot of the thinner stuff is not available in uncommon sizes. A couple of suggestions for you: 1) A recent article that lays ring technology out fairly well: http://hotrod.automotive.com/116556/hrdp-0910-piston-ring-tech/index.html 2) As someone suggested above, talk to your piston maker & see what they suggest, and buy the rings from them. Dunno if you are getting them made in Oz or in the USA, but I can say that both Diamond & Venolia are good people to talk with. 3) One of the guys here on the H.A.M.B. is the former piston ring guru at Sealed Power & might be able to steer you. His name is Barry Rabotnick; he runs Survival Motorsports now http://www.survivalmotorsports.com/ & is a Diamond dealer. Might be worth an email or PM; he goes by Barry_R (with the underline) here.
Homespun, Ill be dealing with Venolia for the pistons, rings, pins. This engine wont see past 6200 rpm or so - so the 1/16" top and secons + the 3/16" oil rings will be fine. i just didnt see the need for the extra friction the stock sized 5/16" rings would provide. As mentioned it will be a predominantly street ride with the odd strip blast. If using a plasma moly 1/16" - 3/16" ring pack, what would the normal bore finish be in Ra ? Thanx Rat
Read through this: http://www.enginebuildermag.com/Article/2520/_piston_rings_and_surface_finish.aspx
Yes, I've always had good results with that size. Sometimes these latest tricks of the week aren't all they're cracked up to be. Just make sure and get a good quality set and don't get the end gaps too tight.
I like a fine to very fine finish on the bore myself. Tends to have less blow-by and makes more power.
Here you go Cracker.... http://www.enginebuildermag.com/Article/2046/cylinder_bore_refinishing.aspx Rat
What about "Rvk"?? What about the hardness of the block??? because that also requires different stones to get the "Ra" you desire.. If you are worried about the "Ra" ask the machine shop if they have a Profolometer and actually know how to use it... Also with a blower it should seat the rings pretty fast.
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