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914World.com _ 914World Garage _ Break in Compression 2 Liter

Posted by: newdeal2 Dec 20 2004, 05:13 PM

OK, here's the scoop. I have the car running [the infamous 2 liter D jet re build] reasonably well. I re did the compression test [all plugs out/Throttle open]and it ranges from 120 -140.

I have been told that the WebCam [by Raby] having a longer duration and better lift will throw numbers off since it is intended to improve the mid range. I have also noted from various sources that it could be a simple valve adjustment that will bring the numbers closer.

Am I getting too anal here? IPB Image

Posted by: Jake Raby Dec 20 2004, 05:39 PM

Did you have the throttle open when taking the numbers??

What cam are you running?

Posted by: newdeal2 Dec 20 2004, 06:49 PM

Yes, throttle open and it is your WebCam 73 grind

Posted by: Jake Raby Dec 20 2004, 07:17 PM

Have the rings had time to seat yet??

If not that could make a big difference. What static CR did you set it at??

Posted by: newdeal2 Dec 20 2004, 08:05 PM

I ran in the motor for 20 min's @ 2000 rpm. and have put about 10-15 miles on it with periodic 75% throttle and engine breaking to load the pistons.

Since this is my first re build what is static CR?

Posted by: Jake Raby Dec 20 2004, 08:32 PM

The calculated compression ratio...

Sounds liek the rings are not seated yet.. Unless the engine is dynoed it takes atleast 250 miles to get them to seat well.

Posted by: newdeal2 Dec 20 2004, 09:08 PM

Makes sense. I need to relax and drive, get the timing right, etc.

I didn't do any caculations since all I changed was the piston type [stock to euro] and purchused them with the cylinders as a set. I checked the deck height and moved on.

The car is running a little choppy at 3-4000 rpm. No excessive noise so I think it's a tuning issue. Should I hold off on valve adjustment or do it now since I didn't do it after the run in?

Posted by: Jake Raby Dec 20 2004, 09:41 PM

Oh no........

The first step to engine building is NEVER ASSUME ANYTHING!

Every engine has to be built like all the tolerances are unknown..

How many ccs were in those heads??

Posted by: newdeal2 Dec 21 2004, 06:29 AM

Everything was kept stock, only changes as noted [cam and euro pistons] in my earlier reply. Crank and heads as well as align bore was done by a Porsche mechanic locally.