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Thread: 2nd Ring Gap?
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post #63 of (permalink) Old 01-25-2006, 11:19 PM
Join Date: Jan 25,2006
Posts: 12

It took me a while to get here. I am Barry Rabotnick, and I used to be somebody. I don't have a handle or a nickname. First I'll give you a quick resume so that we can have a pissing contest on even terms - since its already underway.... This'll be kinda long so you may want to have a potty break and grab a beverage first...

I ran Speed-Pro for Federal-Mogul for 12 years untils the corporate beancounters eliminated all support for the brand a few months back. No manager (me), no sales guys, no NHRA trailer, no ads - - it just runs on autopilot. Ticks me off, but I have moved on... the Scott G. quoted in an earlier post used to report to me. I wrote some of the other stuff that was referenced.

Before Speed-Pro I worked with Holley for 8 years. I also know a little about carburetors. That might come in handy on another thread someday.

I just finished 9th in the recent Engine Masters Challenge contest - - with an FE Ford. It made 752HP on 91 octane. not a winner - - but I chose the FE for the challenge of doing it. I can build engines a little bit.

Now the ring gap deal. I don't have access to the kind of support data that I could throw at you six months ago. Its too bad - - but thats just the way it is.

Big second gaps work. We run them in most if not all OE applications no matter what the RPM. We ran them in Greg Andersen's Pro Stocker. We ran them in Moran's turbo stuff. And everything in between.

The original concept work was in math from a computer simulation series run on a Cray in Ann Arbor. This was followed up by OE dyno testing and development aimed at emissions and fuel mileage enhancement. You cannot sell an OE on a change of this magnitude without solid support. After the OE modeling showed an advantage we input the data from a then current Cup motor to see if it also applied to higher power, higher RPM applications. It did.

The reason for the testing was to gain an enhanced understanding of the ring and piston package as a dynamic sliding seal system - rather than as a bunch of parts. Old thinking was that the smaller the gap - the better. Since 2nd rings ran cooler we set the gaps smaller and thought that we were doing good things. For top rings we were right - as tight as you can without butting is the answer. But for second rings it was not true - - they function as a squeegee for oil moreso that anything else. By allowing blowby gasses to flow through the ring gap we were able to improve top ring sealing and add directional impetus to any scraped oil helping to send it back down to the sump.

The measurement that was most significant was the pressure equalization between the area above the top ring and the area between the top and second ring, as expressed in degrees of crankshaft rotation. With the traditional small gap 2nd we saw pressure equalization at 91 degrees after TDC. With a gapless second we saw pressure equalization at 79 degrees after TDC. With the wide gap 2nd we saw equalization at 181 degrees after TDC - - in other words we had the top ring seated until the piston turned around. Since positive pressure above the top ring translates into work sealing the ring and moving the piston there are clear advantages to maintaining control of that ring as far down the hole as possible.

Now - - how big a gain will you see? No hard and fast answer. If you were looking for a "you'll get a zillion horsepower, use less oil, get better mileage, pick up more girls" line you will be disappointed. I leave that kind of promotion to the other ring guys. What I can tell you is that, within a sample range of applications, the larger gap will generally outperform the old traditional setup by a measurable amount. Sometimes its a bunch, sometimes its a little, and sometimes you can't really tell the difference. I cannot recall an instance where the old school combo had a measurable advantage. Depending on the likelihood of ring lifting you can see 20+ HP - - or you can see nothing.

A vacuum pump used in concert with the large gap can allow very light tension rings for the rest of the ring pack. Remember that the ring and piston package is a combination and a system - - not just a collection of pieces. Similar system thinking has led the OE customers to using rings packs that were considered too light for even race use only a few years ago - - 1.0mm, 1.2mm, 3.0mm 8 lb tension reduced radial wall rings are pretty common in normal cars today, and they last 150,000 miles.

The drop in Speed-Pro sets haven't changed simply because it costs money to implement a change, they are price sensitive parts, and partially because nobody there really gives a damn anymore....

Feel free to say that you don't believe me. I don't really have a dog in the hunt since I don't work there anymore. This does not mean that all your old stuff don't work - - it just means that it could get even better without spending any more money. If anything I should probably be telling you to buy somebody else's stuff just to get back at them (I will have my own ring line available in a month or so...). I could probably dig up a dyno test saying I'm right and you could dig up one saying I'm wrong. We're equal that way - - its the nature of the internet. Of course Ford, GM, Mopar - - and Greg Anderson - - agree with me.....

Have fun
Barry R.
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