johnbull
Expert Class
Posts: 314
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posted June 01, 2013 03:25 PM
Flatshifter ignition cut causing a spit exhaust shim
Running a supercharged ZX14 2006 engine on a race car.
On the last two race weekends the engine has suffered jumped out exhaust shims, luckily it did not drop a valve on both occasions.
The head is running KPMI valves, springs, retainers & buckets. Cams are stock.
On both occasions this has happened exiting a corner exactly on an upshift when the flatshifter cuts the ignition coils causing the bang out of the exhaust.
Anybody else suffer from this problem? The valve springs have been on the engine for 2 or 3 years now. Could it be that they have lost some strength?
Appreciate all replies.
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John Bul Racing. Malta.
  
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zx12mark
Pro
Posts: 1654
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posted June 01, 2013 03:31 PM
your at redline all the time on your dwarf car ?..........I bet your springs are sprung...........
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1badzx12r
Needs a life
Posts: 8321
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posted June 01, 2013 03:35 PM
 Edited By: 1badzx12r on 1 Jun 2013 23:36
I spit 3 shims in the pass in 5 years all 2 exhaust and 1 intake. . new springs always stop it
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http://www.youtube.com/watch?v=S06nIz4scvI
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johnbull
Expert Class
Posts: 314
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posted June 01, 2013 04:02 PM
quote:
your at redline all the time on your dwarf car ?..........I bet your springs are sprung...........
Not a case of hitting the rev limiter mate. It only happens on up shifts when shifting at wot with the ignition kill>
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John Bul Racing. Malta.
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oldkawboy
Needs a job
Posts: 2125
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posted June 01, 2013 04:36 PM
Springs do get tired, heat cycles are tough on them too.
You might get by on just shimming them but with the money you've saved by not dropping a valve I'd "spring" for a new set.
Dan
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Oz Booster
Expert Class
Posts: 230
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posted June 02, 2013 02:00 PM
may have to kill fuel too, your backfire will be unseating the valve , bent some valves on my busa on the dyno with the rpm limit kill pop and they were not light or old springs
turbos can get some nasty back pressures
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