Piston Ring End Gap....?

[2003 Venomous]

I am in the process of building a Teksid for my 03. I have a question in regards to the piston ring end gap. I have called Diamond and Total Seal and they say .025-.026 on both top and second ring. That seems very loose for a street and occasional strip motor; dont like the idea of a lot of blowby and crankcase pressure. What are your thoughts? Had a friend who builds mod motors frequently say about .018. I know this is a very controversial topic, but wanted to get some insight form others who have built and are are running them now.

Motor specs:
.020 Teksid
Diamond Pistons 9.5 CR with CC of heads
Total Seal rings
Stock rod length and stroke
3.3 Lysholm running 20# at Denver altitude....should hit 25# with the current pulley combo at sea level
Will run both E-85 and Premium fuel tunes

Let me know what your opinions are and if you need any other info.

Thanks,
Chris

 

[encasedmetal]

.025 is too loose in my opinion. You'll find the majority go with .022 on the top usually. I like your buddy prefer tighter gaps on my rings. Since I've been building mod motors with tighter than usual gaps I've had zero blowby and my catch cans are always clean besides a drop, maybe two of condensate after warming up. The key to running a tighter gap though is making sure you've finished the cylinder for it- I prefer a 400 grit finish before installing rings.

 

[Quick Strike]

Mine are Total Seal with the SS top ring. They are at .025" top and .027" second ring. There is no blow-by or oil burning, but plenty of power and they are that much further away from butting under heavy load.

 

[2003 Venomous]

Gents, Thanks for the input.

encasedmetal - I dont have a catch can, but I do not want to recirculate lots of blowby through my motor. I assume your recommendation is what you have been using with success....

Quick Strike - You went with the loose gap. Do you have the PCV still hooked up or a catch can? Also, what is your car primarily used for?

It appears the best choice is in the mid 20's or so. Any more suggestions/recommendations from other members with experience......

 

[MalcolmV8]

.025 is too loose in my opinion. You'll find the majority go with .022 on the top usually. I like your buddy prefer tighter gaps on my rings. Since I've been building mod motors with tighter than usual gaps I've had zero blowby and my catch cans are always clean besides a drop, maybe two of condensate after warming up. The key to running a tighter gap though is making sure you've finished the cylinder for it- I prefer a 400 grit finish before installing rings.

At what point is the gap to tight that you risk the ring ends touching and having no room to expand and ruining the engine?
I wish I could remember what gap I went with in 09 when I built my motor but it was to the specs supplied by total seal. I'm sure it was on the looser side as I notice a very fair amount of blow by into the intake although I'm also running 27.5 lbs of boost.

I'm in the process of doing another setup and trying to decide what I want to do with ring gap. To big means blow by. To tight means building a new motor. It's why people always go on the looser side.

 

[broke7]

Just had my builder set mine up at .025 and .026


Street/strip. Have a catch can setup...would rather have it a tad loose vs running into issues later running it tighter.

 

[Quick Strike]

Quick Strike - You went with the loose gap. Do you have the PCV still hooked up or a catch can? Also, what is your car primarily used for?

The PCV and all original emissions equipment is hooked up. I use it as a weekend toy and may take it to the track once or twice a year. It only has about 5k miles since the rebuild in 09. The blower was off for gasket issue somewhat recently and there was no oil in the intake or intercooler. A few thousands of an inch will have no significant impact on blow-by, but may be the difference between butting or not.

 

[encasedmetal]

At what point is the gap to tight that you risk the ring ends touching and having no room to expand and ruining the engine?
I wish I could remember what gap I went with in 09 when I built my motor but it was to the specs supplied by total seal. I'm sure it was on the looser side as I notice a very fair amount of blow by into the intake although I'm also running 27.5 lbs of boost.

I'm in the process of doing another setup and trying to decide what I want to do with ring gap. To big means blow by. To tight means building a new motor. It's why people always go on the looser side.

you also have to consider the design of the piston (which brings in consideration of low rpm side load, and higher rpm capability), and how you finish the cylinder. It's not just a blanket one ring gap ends all discussion.

 

[MalcolmV8]

you also have to consider the design of the piston (which brings in consideration of low rpm side load, and higher rpm capability), and how you finish the cylinder. It's not just a blanket one ring gap ends all discussion.

OK. I won't be finishing the cylinder myself, a machine shop will. I've never known to ask for anything specific. They request the pistons up front (or buy them for me) based on what they measure in the block. I tell them what piston to wall clearance I want to go with, they bore (if needed) and then hone and return to me. Should I be asking for something special on the hone finish?

In what way does the low RPM side load and higher RPMs of our motors affect ring gap?

 

[Quick Strike]

Your ring manufacturer will specify a finish. Just relate that to the machine shop along with the spec sheet for the pistons. It is not rocket science. Just be sure to check clearance and sizes yourself upon return from the shop. In other words check their work yourself. You can usually rent or borrow the tools needed.

 

[MalcolmV8]

Your ring manufacturer will specify a finish. Just relate that to the machine shop along with the spec sheet for the pistons. It is not rocket science. Just be sure to check clearance and sizes yourself upon return from the shop. In other words check their work yourself. You can usually rent or borrow the tools needed.

Yup invested in those tools a while ago. I double check every clearance myself. Nothing gets assumed.

 

[Quick Strike]

I have them on permanent loan from my Dad. At least until he remembers he loaned them out to me.

 

[MalcolmV8]

I have them on permanent loan from my Dad. At least until he remembers he loaned them out to me.

LOL one way to do it

 

[encasedmetal]

OK. I won't be finishing the cylinder myself, a machine shop will. I've never known to ask for anything specific. They request the pistons up front (or buy them for me) based on what they measure in the block. I tell them what piston to wall clearance I want to go with, they bore (if needed) and then hone and return to me. Should I be asking for something special on the hone finish?

In what way does the low RPM side load and higher RPMs of our motors affect ring gap?

When you use a slipper skirt design (full skirt) you need to shoot for a more robust skirt thickness, as they spread the cylinder wall load over the greatest area possible on the cylinder wall. While it will not prevent cylinder distortions it will take you farther down the road before you get them. The difficulty with the slipper skirt design is as that load is distributed across the piston skirt you need to use a thicker skirt to add the strength necessary to prevent the skirt from collapsing. When you use an abbreviated skirt like strut style f1 pistons the load is not decreased but the skirt support, because of the reinforcing rib placement at the edge of the abbreviated skirt, provides the required additional strength. Additionally the portion of the skirt between the two supports is more resistant to deformation than it would otherwise be if it were spanning a wider space. It is sort of like trying to bend a short bar or a long bar of the same diameter. Narrow skirt vs wider skirt, the narrow skirt (properly supported) flexes less. When you take a piston with a heavy skirt the piston skirt is near indestructible at low speeds but the rotating assembly has an upper rpm limit you don't want to continuously test. That doesn't mean you can run one of these pistons on a high banked oval continuously flirting with 8000 rpm. It does mean that for the short period of time you are at 8000 rpm in a drag application you should easily live to fight another day, again and again. With a strutted piston skirt you will experience similar reliability at low speed because of the geometry and will have a much higher rpm that they are capable of operating at without being pulled apart by their own weight - because they will be lighter. At lower speeds these pistons will more heavily load the block's cylinder walls. The increased cylinder wall loading would shorten the time between engine rebuilds due to cylinder wall load and subsequent distortion. rings gaps as a result should be set based upon piston design, desired application, and results- not just a blanket material score. different pistons expand in different ways so a generic ptw clearance figure ain't worth a dogs ass.

Your ring manufacturer will specify a finish. Just relate that to the machine shop along with the spec sheet for the pistons. It is not rocket science. Just be sure to check clearance and sizes yourself upon return from the shop. In other words check their work yourself. You can usually rent or borrow the tools needed.

Total seal recommends with stainless top rings that you finish with 280 grit, but in mine only the last .0003 are finished with a 400. If you finish it with a aluminum oxide 280 it wears half the ring before it breaks in. And takes way longer to seat. A 400 is use to break off the high peaks left by the aggressive stones.

 

[stuntstere]

I would go with the ring or piston manufacture recommendations. If it was my motor I would put the top ring around .022" to .024" and the second ring .003" to .005" larger than the top ring. So the second ring would be anywhere from .025" to .029" depending on the top ring gap. Oil ring gaps should be .015"

 

[Brutal Metal]

.022