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Breaking in built motor- Advice


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I'll finally be starting my 76' Z tonight (hopefully).  It's been down for about 9 months since I lost oil pressure and found some metal bits in the oil pan.  I decided to rebuild it (N/A L28) with some goodies- balanced bottom end, flat top +1mm pistons, had the head ported/polished and got a 270/280 .464 cam from Delta.  Topped that off with some 265cc turbo injectors.  After machining, the machinist calculated 9.9:1CR.

 

I'm going to follow the break in theory of a warmup followed by 3rd gear pull/ coast down for 15-20 miles- then an oil change. 

 

My concern is that the new motor will be a little more prone to detonation and the Volumetric Efficiency (is that the correct term?) has changed.  I have SDS fuel and coil pack ignition system, and had this running pretty well before the swap.  My plan is to take the fuel values down to 70% of their current values due to the injectors, and take the timing back a couple of degrees across the board until I can get it dialed in. 

 

My question revolves around airflow- at different manifold pressures, I should be flowing ~20+% more air.  I don't want to create a lean condition as I'm trying to break in the motor.  I do have the mixture knob so I can make fairly instant changes if I see a lean condition.

 

Does anyone have words of wisdom for tuning while trying to break in a motor with a new set of dynamics? 

 

Thanks!

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I would extend the first oil change to 100 miles.   Do more then just a series of 3rd gear pulls and coast downs.  Idle, light throttle cruise, pulls through all the gears, etc.  Run the motor cold, get the motor hot.  Run on the freeway at a steady rpm for five  minutes, changing the rpm by 500 every 5 minutes.  Do it in the range of 3,000 to 5,000 rpm.

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Engine started.  Took me a while to get it to idle correctly, it's not pulling much vacuum (~10") and I had to pull a lot more out of the RPM fuel than I thought.  Didn't get a chance to drive it because the slave cylinder was blown.  Must have not put it back together correctly... :wacko:  Picking up a new slave after work and going to adjust the valves and maybe try again. 

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Took it out for a test drive last night and it's running pretty good.  I think I ended up around 60% of the original fuel values, but I'm still running pretty rich.  I adjusted the fuel in the driveway working through the rev range to about 4k, and slowly increased (guessing at) the values above that.  Took it out on the road and did some 2nd gear accel/decel pulls, a couple in 3rd too, didn't make it to the freeway though.  I am getting what I think is detonation around ~3500 with my foot in it, and also spinning the clutch :o .  I'm going to try to get the timing dialed in better after work today- this is difficult because my hall sensor took the place of my timing indicator...

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I've done the first oil change on mine after 10 minutes of running. I let the engine for a minute or two idling and then put the engine at 3000rpm. Once it was warm, I stopped the engine and did an oil change. I also removed the oil pan to find a lot of debris (metal chips) and pieces of paper towel that were somehow clogging partially the oil sender. I was very careful during the build but it happened.

 

I've cleaned everything, change the oil and oil filter. I then proceeded with breaking in procedure, I was going at WOT but I was making sure to never go above some rpm limits that went up over time (started with 3500rpm). I've got after 2000mi no oil consumption and a very healthy engine.

 

Check also carefully valve clearance over time. Mine were moving constantly for the first 500mi. Now everything is steady, I can enjoy my engine with no back feelings ;)

 

Regarding your tune, if you've got knock, just back up a little timing to get safe.

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Good info Clarkspeed!  That seems to be where I'm hearing some noises, so I'll bump the values in that range and work my way back out of it. 

Lazeum- I checked the valve clearances after the initial warm up, but thanks for the reminder to check them again.

Then I'll go finish up my JohnC style break in.

 

New clutch is on it's way!

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