KA Ring gap

[Tacomaboy]

In reguards to ring gap,I read that the top ring gap for a turbo version KA shoulp be about .019 and second ring @.017. assuming this is accurate info how will this affect my engine if I dont put the turbo on at time of build. I was thinking of the following winter for that project?

[datzenmike]

I found:

 

'89-'90 240sx KA24E .... 0.011" to 0.017" (top)

'91-'92 240sx KA24E .... 0.011" to 0.020" (top)

 

'89-'92 240sx KA24E..... bottom rings marked R or T .... 0.017"-0.023"

'89-'92 240sx KA24E..... bottom rings marked N ........... 0.017"-0.027"

 

All oil control rings are 0.008"- 0.023"

 

I should imagine the top most ring will get the hottest and expand the most and so will need the largest clearance. The second ring will be much cooler and need less.

[Tacomaboy]

I found:

 

'89-'90 240sx KA24E .... 0.011" to 0.017" (top)

'91-'92 240sx KA24E .... 0.011" to 0.020" (top)

 

'89-'92 240sx KA24E..... bottom rings marked R or T .... 0.017"-0.023"

'89-'92 240sx KA24E..... bottom rings marked N ........... 0.017"-0.027"

 

All oil control rings are 0.008"- 0.023"

 

I should imagine the top most ring will get the hottest and expand the most and so will need the largest clearance. The second ring will be much cooler and need less.

[Tacomaboy]

So I was'nt to far off then.But as far as how the engine will run with the expanded gap. Again,I dont plan on adding the turbo till the following winter. Any runnability issues till the addition of a turbo?

[datzenmike]

Turbo will add huge amounts of HEAT!!! So (IMHO) would run the ring gap at the high end of the scale as you have it. You do NOT want the ring to expand and the end gap close and jam. It will score the cylinder or break the ring and or the ring lands and then score the cylinder.

 

When you install the turbo there are a few things that will help keep it together. Remember HEAT is an engine killer. If you are making more heat you need to be able to get rid of it.... fast. Heat causes pre ignition or ping. Rather than dealing with ping when it happens, be pro active and prevent it in the first place:

 

Get an oil cooler. A good one. Oil goes to hotter places than the water. Cooler oil will remove heat faster. Turbos run hot and will coke the oil if it gets too hot.

 

Get a larger rad and cooling fans.

 

Get a cool air intake for the MAF. Why compress hot air from behind the rad??? Start with ambient air to begin with.

 

If possible use an inter cooler to remove heat in the air.

 

For extreme turbo conditions of boost look at water or alcohol/water injection to cool the intake charge by evaporation.

[Tacomaboy]

All excelent information that I will incorporate. I purchased a set of 370 injectors as per the STIG recomends and further checking showes a good choice. Again this turbo/ injection thing is a bit of new science to me,just want it as right as possible to begin with. How about fuel delivery? I will have it regulated of coarse,but how about volume? any thoughts? Thanks Mike.

[datzenmike]

I think the stock ECU can handle a light 4-6 lb of boost. For more boost you will need to replace the stock ecu or add a piggy back system to handle the extra fuel delivery.

[Tacomaboy]

Great news to here, I dont want to beat up to bad on my stock bottom end KA. Would you say Cometic head gasket a requirement or recomendation for my application?

[Icehouse]

Piston's will die with stock ring gap at 10psi, they sure rip way up there :). I know this from first hand experience. Even with the fuel at 11 to 1 they still die. Ring lands crack. I'm not sure if a bigger gap will help, almost seems like it's from detonation even though the piston tops, spark plugs or anything else in the combustion chamber look fine.... We may try gapping them bigger and see how they run.

[datzenmike]

Maybe pressure gets trapped between the top and second ring. Try increasing the second ring gap larger than the top. With stock it's fine but with a turbo............ it's different.

 

 

With a stock motor the compression is reasonable. Anything that gets past the top ring can easily get past the second compression ring. But with a turbo the compression and 'blow by' (and there will always be more leakage) are at levels where it can't get past the second ring fast enough and pressure backs up. The top ring relies on combustion pressure from above to press it down tightly against the bottom of the ring groove. When the trapped pressure below is high enough it looses contact with the ring groove and cannot conduct piston heat to the cylinder wall.

[Icehouse]

It would be fun to try all kinds of different stuff but damn it's not easy to change a piston. Easy day project. I will report back any info I learn on our future attempts.

[datzenmike]

Well it might work in boost but fail for every day driving. I'd love a job testing pistons and rings to see what works and what does not.

[Tacomaboy]

Just a quick up date, All machine work on block ,rod re-size and crank are now complete. Yesterday ordered a set of Crower stage 2 cams. Havent done anything to head yet. Digging up info and or input in that area. Wow the fog is thick here today.Good day to spend in garage chasing threads and final clean on block.