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 Post subject: Blown head gasket
PostPosted: Sun Oct 06, 2019 4:52 pm 
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Joined: Tue Oct 30, 2012 8:32 pm
Posts: 105
I have a 408 with less than 1k miles and it 11 to 1 comp aluminum B351 heads with a stout cam and it blew a head gasket street driving, motor always runs at 200* stick trans and shifts at 6500 I don't remember this being a problem with Clevelands could changing from pump gas with lead added to 100LL AV fuel contribute to this ?


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 Post subject: Re: Blown head gasket
PostPosted: Sun Oct 06, 2019 9:09 pm 
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Joined: Thu Jul 25, 2019 9:05 pm
Posts: 35
preaction wrote:
I have a 408 with less than 1k miles and it 11 to 1 comp aluminum B351 heads with a stout cam and it blew a head gasket street driving, motor always runs at 200* stick trans and shifts at 6500 I don't remember this being a problem with Clevelands could changing from pump gas with lead added to 100LL AV fuel contribute to this ?



I have never had a problem with more rpm, compression and lots of nitrous, 200^ seems like the cooling system is not happy, are the head gaskets on correctly? Did you re-torque the heads after the first run in period. The higher octane fuel might be wasted on the compression but I don't see that causing the head gasket failure. Does the tune seem happy as a bad tune can kill engines, never mind gaskets.

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 Post subject: Re: Blown head gasket
PostPosted: Mon Oct 07, 2019 1:53 am 
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Joined: Wed Oct 31, 2012 4:57 am
Posts: 200
Gday,
200 is too high for me if thats what it runs all the time?
Retorque headgaskets? Except for mls they will compress.
Correct torque specs for head bolts or studs
Tune up is the biggest issue, make sure you have no detonation at all.
To answer your question but.
Not sure about your fuel over there, but between pump fuel and avgas here the density is a fair bit different.
If you are spot on with pump fuel and dont jet up you will be lean on avgas
Cheers


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 Post subject: Re: Blown head gasket
PostPosted: Mon Oct 07, 2019 6:16 am 
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Joined: Mon Oct 29, 2012 9:05 am
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What gaskets were they and where did it blow?

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 Post subject: Re: Blown head gasket
PostPosted: Mon Oct 07, 2019 9:30 am 
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Joined: Mon Oct 29, 2012 2:39 pm
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I run my street/strip Cs at 195~200 so IMHO 200 is fine. Especially with an aluminum radiator in the car, you need that water hot to carry heat out of the engine. I get the dragster engine to 185 on alcohol before I roll into the water box.

That said, any head gasket issues I have experienced with a 351C has been an install issue. Decks not cleaned or other debris that managed to compromise the sealing surfaces. Even when "unseen" on tear down. I'm running 11.8 CR with methanol which makes big cylinder pressure and no issues with regular Felpro Blue 1013s.

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 Post subject: Re: Blown head gasket
PostPosted: Mon Oct 07, 2019 10:51 am 
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Joined: Tue Oct 30, 2012 8:32 pm
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The engine usually runs 190* thought I would post what it gets at the top of its range it seems to run cool after checking with a IR temp tool no part of the engine ever gets over 200. The head gaskets used are unknown to me but were never retorqued the timing is set at 16* and 34* I will get it apart this week and get a closer look thanks.


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 Post subject: Re: Blown head gasket
PostPosted: Tue Oct 08, 2019 8:14 am 
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Joined: Mon Nov 05, 2012 3:54 pm
Posts: 62
preaction wrote:
The engine usually runs 190* thought I would post what it gets at the top of its range it seems to run cool after checking with a IR temp tool no part of the engine ever gets over 200. The head gaskets used are unknown to me but were never retorqued the timing is set at 16* and 34* I will get it apart this week and get a closer look thanks.


The machined finish on both the block decks and heads is quite important too. Perhaps a few good pics of them and the gasket that blew would be of diagnosis help here.


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 Post subject: Re: Blown head gasket
PostPosted: Tue Oct 08, 2019 5:27 pm 
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Joined: Wed Oct 31, 2012 4:57 am
Posts: 200
Most of the headgasket failures i see on these are caused by tuneup issues, too much timing or too lean.
The engine detonates , only 4 headstuds, head lifts slightly and so begins the end of the gasket.
The spark plugs usually tell the story in this case.
What gaskets? Retorqed or not?
Bolts or studs, what lube? What torque?
Cheers


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 Post subject: Re: Blown head gasket
PostPosted: Tue Oct 08, 2019 8:45 pm 
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Joined: Tue Oct 30, 2012 8:32 pm
Posts: 105
I got it apart today and was stopped by the rocker arm mounting base screws which needed a torx size I up from the 5 I have I should have the heads off tomorrow and post some pics. There was antifreeze piled up behind intake valves on both sides of the engine though.


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 Post subject: Re: Blown head gasket
PostPosted: Fri Oct 11, 2019 1:09 pm 
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Joined: Tue Oct 30, 2012 8:32 pm
Posts: 105
I took some pics and got hung up trying to compress them Ill try and work on that got down to the head bolts and the top row is so close to the rocker bosses that it takes a turned down 3/4" socket so Im on that.


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