Ring gaps

[iTurbo]

I'm putting together a 2.5L TIII engine with forged Venolia pistons from FWDP. These appear to use the same rings as stock. Can I follow the '91 FSM TIII specs as far as ring gaps or do I need to run a different gap than FSM?

[Pat]

What do you intend on doing with the motor? Higher the power (heat), the looser the gap.

[thedon809]

I'm not t3 but I just gapped my rings. I went with about .018-.019 top and .020-.021 middle.

[iTurbo]

What do you intend on doing with the motor? Higher the power (heat), the looser the gap.

The last TIII motor I built I set up with stock ring gaps, which were .017" to .020" if I remember right. That was with the stock TIII pistons. That engine is still rocking with a T3/T04E 50 trim turbo, big intercooler, 20 psi boost etc.. I made sure to follow the FSM exactly on that one.

This time it's a 2.5L with +.020" pistons, but will be using a smaller Buick GN turbo (Super 70) and 20 psi or less. Really looking for a crazy fun street car that spools right up rather than ultimate HP this time. I worry a little that the Venolias might like a slightly bigger gap because of the expansion of forged pistons (even though I know the stock TIII pistons were forged as well).

[Pat]

I'm running .019/.021 on a street strip motor one with no issues. Race motors, I tend to run looser. I'm comfortable giving up a bit of seal to keep the rings from butting together on a hard run. You probably could go a bit tighter, but you should check the ring manufacturer recommendations also.

Piston brand shouldn't matter in ring gap. The piston will expand and contract, but it's how the rings and sized to the bore that matters. Piston expansion will only impact piston to wall clearance.

[thedon809]

What gap do you run on the oil rings? Wiseco says minimum of .010.

[Pat]

Oil ring gap was always way wider than the min. Never messed with the further.

[thedon809]

Hmm. Mine had pretty much no gap. I set them all to .010. Should I go wider?

[Ondonti]

Hmm. Mine had pretty much no gap. I set them all to .010. Should I go wider?

Never much good advice on this but I think compression that passes the 2nd ring has to go somewhere...

[Pat]

Never much good advice on on this but I think compression that passes the 2nd ring has to go somewhere...

I would tend to agree. No idea on what an ideal gap should be.

[5DIGITS]

I'm not t3 but I just gapped my rings. I went with about .018-.019 top and .020-.021 middle.

If I recall, those numbers are the upper service limit.
Is this standard bore?

[5DIGITS]

I'm putting together a 2.5L TIII engine with forged Venolia pistons from FWDP. These appear to use the same rings as stock. Can I follow the '91 FSM TIII specs as far as ring gaps or do I need to run a different gap than FSM?

The single piece vs multi-piece oil ring is the significant factor for installation gap.
If the pistons use T-III style rings, use the T-III values.
Otherwise use the T-II values.

[thedon809]

If I recall, those numbers are the upper service limit.
Is this standard bore?.020 oversized wisecos. Plan on making 300-400whp with this bottom end.

[DoubleD]

.020 oversized wisecos. Plan on making 300-400whp with this bottom end.

That is the same gap I am doing on my TIII motor with .020 oversized Wiseco's, but my HP goals are 450 to start and upwards of 500+WHP down the road.

[Ondonti]

I would tend to agree. No idea on what an ideal gap should be.

I have been tending to do gap similar to my 2nd rings because I don't see the gap being a big deal with oil control. I don't know how well those rings even seal with the cylinder or the real theory behind how they work :P

[iTurbo]

The single piece vs multi-piece oil ring is the significant factor for installation gap.
If the pistons use T-III style rings, use the T-III values.
Otherwise use the T-II values.

The last TIII I built, I used Sealed Power E640K ring set. They use a multi piece oil control ring with upper and lower rails and an expander ring in the middle. The rings I put in an '85 TI were E453K. They also used the same type of multi piece oil control rings. I guess I've never even seen a one piece before.

In both cases I tried to follow the FSM to the best of my ability. I actually did not have to change the initial measured ring gaps at all. Right out of the box they fit right within spec. I'm not sure if I was lucky or that is normal.

[thedon809]

I have been tending to do gap similar to my 2nd rings because I don't see the gap being a big deal with oil control. I don't know how well those rings even seal with the cylinder or the real theory behind how they work :PI called wiseco and they said .015-.020.

[5DIGITS]

The 'general' charts and manufacturers will typically lean towards the conservative side.
Although, the 'general' charts specify a ring end gap with minimal (if any) consideration to upper ring land dimensions or operating RPM.
With the expected thermal exposure differences of a 1/2" vs 1/4" or a 3/16"upper ring land and the impact of engine RPM and the related thermal DC, I'd expect a resulting impact on ring end gap installation.
Considering the above, I've never assembled an engine with ring end gaps at the service limit.