My piston manufacturer says about braking in:
Put the pistons in, and then drive the car to pole.
Means: Reckless driving from the first second.
Cheers
Chris
Von: Fot <fot-bounces at autox.team.net> Im Auftrag von van.mulders.marcel---
via Fot
Gesendet: Sonntag, 26. August 2018 10:20
An: fubog1 <fubog1 at aol.com>
Cc: fot <fot at autox.team.net>
Betreff: Re: [Fot] TR4 Race Engine Break-in Questions
Probably much more horsepower is lost by being too kind on a fresh engine than
by running it at full throttle too soon;
Marcel
_____
Verzonden: Zaterdag 25 augustus 2018 23:33:25
Onderwerp: Re: [Fot] TR4 Race Engine Break-in Questions
The short version, rings flex.
Piston pushes ring up, it's flat and against the lower face of the groove. Gas
pressure charge travels through the side gap on top past the upper face of the
ring and gets behind it right before TDC @ ignition point.
At that point the ring flexes and seals the top and lower faces of the ring
against the groove faces, and the charge is trapped behind the ring; this is
for pressure retention & max ring expansion. When the piston starts to go down,
the ring flexes back flat against the upper groove face and loses the charge
behind it and relaxes a bit.
Repeat this every combustion stroke.
The above is with power on.
On closed throttle (decell), there's a vacuum on top of the piston so there is
not a pressure charge to fully expand the ring, so it doesn't flex the same.
This flexing of the ring will give it a very very slightly ) face as a result,
it's not perfectly flat.
So ring seating isn't just to to get the initial "burnishing" of ring/cylinder
wall, it also establishes the profile of the ring face for the best seal under
both full open and full closed throttle.
It's all in the ring FLEX!
This is also why ring side clearance is so critical, I scrap more pistons for
this being out of spec than for any other reason, especially if the engine was
running rich.
My break-in routine is-
Initial start, run to temp, 1 maybe 2 heat cycles, retorque & check all.
(If new cam, 15-20 minute @ 2k rpm)
No excessive running beyond cam break-in and basic tuning with no load!
On track, 2-3 warm-up laps @ part throttle, vary RPM 4-5k, use some engine
braking.
2-3 more laps with more throttle and engine braking, same rpm.
2-3 more laps using full throttle, maybe 85-90% revs, and intentional repeated
HEAVY engine braking from WOT in top gear.
After that I usually do a retorque and follow-up; next time out should be good
to go.
This open/closed throttle running subjects the rings to the loads that it will
have under normal operation.
HTH
Glen
-----Original Message-----
Sent: Sat, Aug 25, 2018 1:30 pm
Subject: [Fot] TR4 Race Engine Break-in Questions
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