What has your experience with very minimal side seal clearance been with a turbo 13B Engine?

Is there a limit to how small of a clearance you can have on a side seal inside a turbo 13B?

I know NA users run very little clearance, but generally speaking turbo guys run larger clearance do to higher hear expansion.

Any input would be awesome!

 

Why would you deviate from what the factory service manual says?

 

Because the FSM tolerances were designed for mass production (as cheap as possible while maintaining a high standard of QC) and longevity and not necessarily maximum performance?

Mazda made a great product but they most certainly didn't make a perfect one.

 

Is there an actual benefit that you can describe or quantify or just a vague idea that difference clearances will yield "maximum performance"?

They have the clearance tied up within 4 thou (.002-.006)... that's not a sloppy tolerance in most fields.

Do seals with smaller clearances bind up in some applications? A quick plug on my calculator reveals that a 5 inch seal would expand about 6 thou due to a 200 deg F delta T. The rotor face would grow as well, but maybe at a different rate?

 

I run .001 to no clearance at all (at my own risk of course) on my high HP turbo 13B. The are threads on here about running zero side seal clearance.

 

I can say this: I've had a Mazda REW reman with a 52 Berg (no turbos) versus an S5 using all new housings and 9:1 rotors on an engine dyno for break-in and I noticed ~5 PSI difference on all faces using a close to zero side seal clearance as well as other race clearances (some pulled from Mazda's own comp manuals, others from very knowledgable builders).

Now, I understand these aren't crazy gains and I deviated from standard clearances on more than just the side seals however I think it pretty accurately illustrates my point.

 

Higher compression (my experience may be due to changing rotors though..) and SIGNIFICANTLY reduced (eliminated) blow-by which should be noticeable by all...


Granted, the break-in procedures are a bit more strict as you reduce the clearances... So if you lack self-control than I wouldn't advise running less than factory specs!!

 

I built a number of turbo engines with "zero clearance" side seals.

That is, just enough clearance that side seals and corner seals move freely, but no measurable gap unless you tweek the side seal around in its groove with the spring pushing it most the way out of the groove.

What I found is that these engines required a longer break in because as the engine gets really hot in racing the side seal clearances can get even tighter. A long break in wears the side seals in gradually.

On those "zero clearance" turbo engines that I did not break in before racing the side seals were actually distorted on the ends from trapped between corner seals and trying to expand and there was more side housing wear than there should be.

Since then I build them to around just under the specified minimum (0.01 to 0.02" with both side and corner seals pushed all the way down in their grooves) so I can put the engine in and race.

If I was building NA race engines, I would probably go back to "zero clearance" side seals as there is less heat concentrated into the rotor (less exhaust back pressure).

 

I've always built engines to .003 thousandths. As in EVERY side seal has that exact same clearance. I think when you let them fall within a stock range then you can have a sloppy engine.

Going low or no clearance is not something I would experiment with on a general use street car.

Dale

 

I went with the Mazda recommended .05 MM clearance. Do you think I should follow this break in:

0 to 500 miles, shift at 4k and minimal boost. Change oil.
500 to 1500 miles, shift at 5 to 6k, minimal boost. Change oil. Tune.


And after my break-in switch to synthetic.


I would much rather play it safe than run the risk of binding and damaging anything.

What would the break in look like if I had even less clearance?

 

Oh and to add to my question above is it safe to pre mix when im breaking in? (I did not delete the OMP)

 

yes. for the tuning part, you should be tuning the idle/low RPM areas right away, too rich is bad for break in.

 

The FSM range is way too generous IMO..... 0.05 to 0.15mm, max of 0.40mm on side seal to corner seal clearance. No thanks. I've always went on the absolute tightest side of the clearance, to 0.05--- no looser and occasionally a bit tighter.

As mentioned above, it aids in compression and minimizes blowby and fuel contamination in your oil, and IMO is one of the things that separates a good build from a simply 'ok' build.

Speaking of, don't forget to check the side seal to groove clearance

 

Thanks! Im pretty sure my clearance is honestly less than .05MM, my feeler gauge would drag against the seals and actually would push the seal side to side making one side have no clearance while the other side had .05MM.

Do you think its safe to run water injection (no meth) during break in?

 

why are you boosting high enough to need water injection during break in?

 

This. Even if you had it enabled you shouldn't be hitting the load sites that trigger it.

 

Hmmm... all that actually makes a lot of sense. I guess you wouldn't want to rely on your oil control rings to contain everything. I hope this current engine lasts forever and I probably won't build another for a customer, but I'm making a mental note to set those clearances as low as possible in the future. I'd probably stick with the low end of the factory manual rather than zero though.

 

Yeah, you can even get away with going below Mazda's minimum, but if you do than you MUST strictly adhere to an uptight break-in routine.

I want to say the last motor I built (had built in my garage for me) ran a 2,000 mile break-in (partially due to clearances, partially due to all brand new seals/bearings) with zero boost (as much as possible) and super low rpms for the first 600mi, LOTS of full heat cycles (at least 10 hours shut down between cycles) and a lot of gradual/gentle acceleration with engine braking through different rpm ranges. When we finally did the power tune it was a BEAST (for it's power)!! I don't think I even filled a single catch can part way over 3k-4k miles..

Too bad an oil fitting worked loose like a week afterwards resulting in a total loss of oil, spun bearings, and trashed internals on the way home from DGRR...

 

NNNNNNOOOOOOOOOOOOOOOOO!!!! That sucks.

What does your catch can normally fill up with? I get a bunch of stinky water condensate in mine but I have to empty it a couple times every oil change at least.

 

Prior to that build out had been filing with fuel diluted oil. The engine built by PFS would fill an entire can in under 30 miles if I was getting on it.

Life took priority after that ($10k or so) engine build. I rebuilt it like a year or so later, but it's still sitting on the stand in my garage... enjoying an Aprilia and a Miata for the time being...

 

My last motor for my FC I built with the "looser" side seal clearances (just a tad tighter than minimum Mazda spec).

Running 26psi boost and barely any venting to the catch can. Probably 1/16" to 1/4" between oil 3,000mile changes.

FC on 255 DOT-Rs didn't have the lateral grip to push the oil all the way up the side of the motor and into the catch can like the FD does though- that really exacerbates the problem.

 

I was planning on setting my water injection to start at 2 PSI, should I even get near 2 PSI of boost?

 

Proper trigger point will be based on IATs under full load, not an arbitrary pressure point. You should be staying out of boost and most certainly shouldn't be under full load during break-in.

 

oh, I for some reason thought it was based on boost pressure.

Guys what the consensus on ECU for break in? Should I stick with stock ECU?
-Mods for this build are BNR stage 3 Twins. Adaptronic ECU. Catless downpipe. Catless midpipe. Thermal Engineering catback. AEM water injection.

Everything else is left stock for now.

 

What I'm saying is that your water injection set point should be dictated by the intake temps. If at 12 PSI you're seeing danger zone temps then set water injection to 9 psi (or something to that effect). If you're just throwing water at the situation before you need to all you're doing is wasting power.