928SS

on my stroker motor, the break in was on the dyno. a few short test runs and then WOT repeatedly. greg brown from precision did the work, seems to think if you are gonna run hard break it in hard. same MO on my al holley built race bikes too. a few heat cycles and bwaaaaaaaa...

Matt Sheppard

Greg Brown is the MAN!

928SS

I always compare him to al cause they are both of the same mindset. 1 wound up doing 2 stroke race bikes, the other pcars. both masters, imho.

I always wonder what would happen if they met and built a race motor. a 1200chp 3.8L NA 2 stroke V8?

RonCT

Debated at length here and elsewhere: https://rennlist.com/forums/showthre...light=break-in

Mike Murphy

Debated, sure, but never fully understood or completely explained. Even the debate that you point to says that 300-500 easy miles are required. This is different from the original post that says to run it hard very soon after initially building it.

Larry Herman

The paradox is that on new cars there are some componants that like to be broken in easy, like camshafts, transmission gears, and other high load items. There are some that need immediate load to seat properly, like rings, and there are some that shouldn't care either way as they should not ever have metal to metal contact, like bearings and seals.

Pick your poison.

928SS

good point - my context was only referring to motors, not an entire drivetrain when I do new clutches or brakes, it's entirely different.

txhokie4life

Ok I'm doing a PCA DE event this weekend.

Rebuilt the 924S motor using new (to the block) crank, piston rod from a #2 rod bearing failure.

New rings. Top end left alone (it was rebuilt last summer).

It's a race car so no street time to break in the engine.

We've had it idle off an on no more than 20minutes or so at a time.
Temps are good, oil pressure is good. Exhaust pressure feels very strong.
We have not done a compression test.

Because we had an oil pump fail shortly after turning it over -- we have run for a few
minutes at <2.5K rpms (prior to the failure). But we drained all the oil then and
it looked great. So in essence we've flushed the oil once already.

We also installed an oil cooler and accusump and replaced the oil pump despite ("those never fail" :-)

I've read a bunch of posts on break-in.
My plan is to run the weekend DE with a limit of RPMS to <=5K but I'm not sure I understand
light load vs 3/4 load vs full load. What does "load" mean in this sense?

I was planning on running the entire weekend DE at this 5K limit, then changing the oil in
preparation for our endurance race late July.

Guess I'll have to be patient and work on non-WOT high RPM driving this weekend :-(

thx,

Mike

ajcjr

the best way to make more hp is to run the engine for a little while and then rehone the cylinders. In dragracing we use to make dyno hits on the motors, rehone them, two more hits on the dyno and then bombs away!!!

More importantley when starting a new engine you should use non detergent break in oil, it grabs any metals or pieces in the engine and basically gives it a good cleaning.

My theory, beat it from the beginning.

txhokie4life

We all know the drag racers get rebuilt engines between runs -- or at least the top end -- amazing! -- but expensive.

This is a lemons/chumps racer :-)
I don't have that kind of luxury (time or money) --
Unless something breaks -- we're not opening
this puppy back up.

Mike

M758

My 944 spec motor got new rings and main/rod beraings and I broke it in on track. I idled it a little when I first built it to warm it up and make sure it did not have any leaks.

First session out I took my laps and ran part throttle for 5 mintues and increaing rev limit. After this I went 3/4 throttle to redline, but also let off the gas and allowed it to engine brake much more than a normal lap. After a few minutes of that I just went WOT and finished the session driving normal.

I drained the dino oil in the motor after that and ran my next session at the the track like normal. That motor make great hp and nearly won a national championship with it. I am still running it now, but had to redo the head due to a shift error on my part.

ajcjr

only top fuel cars get rebuilt heads everyone, im talking about a normally aspirated, it helps get a better seal.