Don Terrill’s Speed-Talk

Im freshening an 11 to 1 street sbc with 4.200 bore diamond pistons. 1/16 1/16 3/16 . If i was starting over i would go with a thinner ring pack. This engine has a moroso 3 vane vacuum pump. Im thinking std moly filled top napier 2nd and std tension oil rings. Thought I would get some expert opinions on what rings I should use in this application

I guess what i would like to know is what tension oil rings would you run with a vacuum pump on the street. This is not a daily driver but will be driven a fair amount and i would like to keep oil consumption to a minimum. Also is a napier 2nd ring a good idea on a street car . I would say this thing will see 1 to 2k a year.

Why not call a couple of the piston companies or total seal see what they have to say,but for me if it not a race only and trying to get max hp I would just go with the standard tension ring pack I would even get rid of the vacuum pump.

Probably a bit biased here, but I like the medium tension stuff(sometimes grouped into the "low tension" catagory) for vac assisted street/strip type deals. Yeah you give up some extra power to parasitic losses but a clean combustion space still counts for something too.

I also like gapless rings since you end up with less blowby and may potentially find even more power by reducing pump requirements/drag. The total seal AP top rings are pricy but will worth it over the long haul.

However, with your much lower % street type deal I'd probably lean towards file fitting a medium tension set to end up with something in between a low and medium tension. Then adjust vac if needed from there. Little extra margin would be prudent, IMHO.

EDIT: sorry.. crossed some wires when commenting on street use%.

I run 8-11lb oil rings, Napier 2nd and AP steel or Moly faced with no issues on street cars, none with vacuum pumps though.
Not a fan of gapless rings.

Go with ductile plasma moly (sprayed) top ring, Napier second and standard tension oil ring assembly for your application. "Moly filled" top ring typically uses a grey cast iron ring material which is very inferior compared to the ductile iron high performance top ring. Even better would be a nitrided or PVD steel top ring, but these are harder to find for 1/16" thickness rings. There is no benefit/advantage to using low tension oil ring assembly in a street-driven application.

engineguyBill wrote: ↑Sun Mar 11, 2018 11:25 pm Go with ductile plasma moly (sprayed) top ring, Napier second and standard tension oil ring assembly for your application. "Moly filled" top ring typically uses a grey cast iron ring material which is very inferior compared to the ductile iron high performance top ring. Even better would be a nitrided or PVD steel top ring, but these are harder to find for 1/16" thickness rings. There is no benefit/advantage to using low tension oil ring assembly in a street-driven application.

Totally agree with ya Bill, I was just asked to look at a broken(not completely, just hurt) combo and the first thing I saw was moly FILLED ring and not plasma, it did have a tapered second, I'd still use a napier second any day I could find one within reason.

I mean seriously, you have a LSX block NA making 600 fwhp and you're hurting stuff in 2000 miles? All I could say was, bad parts and bad tune(was that extra 10 hp worth the bad tune)?

When you don't have control over the entire engine, and you never do, you have to watch the breathers and that little thing in the front called a belt tensioner. When things are good, nothing comes out of the breather for that split second and the tensioner is steady. That tensioner is rattling for a reason.

Good oil control in regards to the combustion chamber is a huge thing.

Thanks for the replys. Thinner rings arent enough improvement to justify buying new pistons are they?

No.
Here's a typical test. Going from 5/64" to 1.2 mm was worth ~ 8 HP @ 6,000 on a 450 HP 350. Worth considering only if you're already buying new pistons. https://www.youtube.com/watch?v=-29IWc-zrv8

On a street type build why would one look to give up durability for just a few hp.

Andy

Okay I called total seal and ordered a steel top ring Napier second ring and a 15 pound Oil ring. The bore size on this is 4.185 thanks for all the help

It all depends on how round and straight the bores are. You could run TS Gold rings on the street.

gnicholson wrote: ↑Mon Mar 12, 2018 7:58 pm Okay I called total seal and ordered a steel top ring Napier second ring and a 15 pound Oil ring. The bore size on this is 4.185 thanks for all the help

Excellent choice.

gnicholson wrote: ↑Mon Mar 12, 2018 7:58 pm Okay I called total seal and ordered a steel top ring Napier second ring and a 15 pound Oil ring. The bore size on this is 4.185 thanks for all the help

In your first post you said the pistons were 4.200 Diamonds, do you mean just the oil ring expanders are for 4.185?

Its actually 4.185 not 4.2. I was going from memory and my memory aint what it used to be.