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TOPIC: Turbo GpZ550 Ignition misfires starting above 10 lbs boost

Turbo GpZ550 Ignition misfires starting above 10 lbs boost 12 Mar 2020 07:17 #820795

  • garylbishop
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Not sure I mentioned but I stopped using the CVK32 after installing the Turbo.
Using the oem TK carbs. They have better pilot and choke circuits. Better fuel metering and atomization.

See links for first start on TK carbs and for a special choke lock I had to make to prevent boost from blowing the choke plungers open.

First start. photos.app.goo.gl/h8Ryx8JCkkLFA2Ut9

Choke lock bracket. photos.app.goo.gl/RqinuQfQacNBtQf56
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Turbo GpZ550 Ignition misfires starting above 10 lbs boost 14 Mar 2020 09:19 #820890

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Nice choke hold!

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Turbo GpZ550 Ignition misfires starting above 10 lbs boost 22 Mar 2020 08:30 #821395

  • garylbishop
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Update.
Head gasket leak developed under high boost.
Once warm and idling #4 cylinder was missing and backfiring and I could see leaking through the head gasket.
Oil was also spraying from the head gasket at the oil passage O ring.

While re-torquing the head nuts I discovered they were below where they should be so I pulled the head.
I'm using a copper head gasket which is good for up to 16:1 compression on a normally aspirated engine.
Higher pressures require Stainless O rings to help seal each cylinder.
I had the grooves cut for the O rings but never needed to install them. I just used copper wire to fill the grooves.

I really should have installed Stainless wire before running high boost.
Here's what happened to the copper gasket without them. It's subtle but visible and it is definitely NOT acceptable
I've ordered a new copper gasket and will use Stainless wire rings.

A few shots of the gasket and one of the O ring grooves cut into the cylinder block.
Gasket has permanent deformation
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Turbo GpZ550 Ignition misfires starting above 10 lbs boost 26 Mar 2020 09:14 #821813

  • loudhvx
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Wow, sorry to hear. Hope there wasn't any other damage... warpage etc.

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Turbo GpZ550 Ignition misfires starting above 10 lbs boost 26 Mar 2020 11:19 #821826

  • garylbishop
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loudhvx wrote: Wow, sorry to hear. Hope there wasn't any other damage... warpage etc.


Other than the head gasket all is good.
No overheating so the head is still flat.

You just can't run high cylinder pressure without a copper gasket AND the head or block O-ringed.
Copper alone can handle up to 16:1 compression but with the 12-13 lbs boost, pressure was higher than a Naturally aspirated 16:1.engine would see.

It was handling 10 lbs without a problem but after I fixed the ignition miss, it made more boost.
I have a replacement Cometic copper gasket being made and delivered in a week or so.
Between now and then I need to cut and fit stainless wire O-rings to the cylinder block. They have to fit with perfect filed ends butted together.
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