cold exhaust manifold

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christinsley1
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cold exhaust manifold

Post by christinsley1 »

Hi,
1st post - please be gentle!

Living Downunder, running a TR7 v8 - Holley 390 carb, Edelbrock dual plane manifold and Mallory twin points distributor, tubular manifold, yella terra roller rockers.

Thought it was running OK before attempting to upgrade to electronic ignition - epic failure.
Back to points again, dwell angle spot on 33 degrees, points gap 18 thou against target of 22.

Always though engine bay surprisingly cool after a run - checked exhaust manifold temps with laser pyrometer - cylinders 2,4,6,8 = approx 200 celcius, 1, 3,5,7 approx 60 celcius!!!!

Spark tester shows reasonable spark getting to all plugs.
When I pull leads off 1,3,5,7 there is no change to the engine note.

Clearly left hand bank of cylinders are doing very little work...... but why?

Any ideas please.



stevieturbo
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Re: cold exhaust manifold

Post by stevieturbo »

Can you see if fuel is being drawn in both sides of the carb relative to how the inlet manifold is divided ?

Presumably with an old dizzy, sparks will be ok.

But the inlet manifold and carb will be divided in a particular way. So there could be an issue there, whether it's the carb, gaskets, install etc

Are the plugs on that side wet or dry ?
9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

christinsley1
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Re: cold exhaust manifold

Post by christinsley1 »

Thanks for the ideas - I'll check them tomorrow.

Fuelling would seem to be the issue - the cold side plugs are cleaner.

The dual plane manifold is not split left hand and right hand - so a blocked jet would logically affect cylinders on both of engine.

I'll check every possibility.

Thanks

christinsley1
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Re: cold exhaust manifold

Post by christinsley1 »

Just discovered my inlet manifold is the often criticized Offenhauser JWR 7001.

Does anyone have a schematic of the internal design - trying to trace back my engine lack of fuelling (?) on LHS to a particular barrel of the Holley 390.

Google appears devoid of such information.

Thanks

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Ian Anderson
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Re: cold exhaust manifold

Post by Ian Anderson »

Get a can of EZ start and spray around the inlet and see if revs rise as some point.

My guess is that there is a leak,on the inlet side, drawing in external air as,opposed to through the carb

Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.

stevieturbo
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Re: cold exhaust manifold

Post by stevieturbo »

I actually had one of those years ago....cant remember totally how they're split though.

https://www.woolfe.uk/product/jwr-7001- ... fold-4bbl/

I've a funny feeling the two single ports do each feed one bank, with the rear large port feeding all 8 ?

Or something like that

https://www.woolfe.uk/product/jwr-7001- ... fold-4bbl/
9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

stevieturbo
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Re: cold exhaust manifold

Post by stevieturbo »

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

christinsley1
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Re: cold exhaust manifold

Post by christinsley1 »

Solved, Thankyou.

Air leak - for some strange reason there was no cap covering the unused PCV inlet to the carb.

Finger over the inlet - harmony returned to the world.

Exhaust manifold temps now pretty consistent on both sides.

Now I can start sourcing my Holley sniper EFI kit. happy times ahead.

stevieturbo
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Re: cold exhaust manifold

Post by stevieturbo »

good stuff

Although I wonder if that manifold design might affect a Carb style injection system ? I'd be asking that question for sure.
9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

scudderfish
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Re: cold exhaust manifold

Post by scudderfish »

Time for me to learn something. Why would an air leak cause those symptoms?

stevieturbo
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Re: cold exhaust manifold

Post by stevieturbo »

scudderfish wrote:
Fri Dec 31, 2021 9:16 am
Time for me to learn something. Why would an air leak cause those symptoms?
Drawing in far more air than fuel....no chance of combustion. The air leak itself must be for runners only linked to that bank.

And a carb will only lift fuel from the venturi....if air has passed through the venturi. An air leak in the manifold...means that cannot happen
9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

scudderfish
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Re: cold exhaust manifold

Post by scudderfish »

stevieturbo wrote:
Fri Dec 31, 2021 3:06 pm
scudderfish wrote:
Fri Dec 31, 2021 9:16 am
Time for me to learn something. Why would an air leak cause those symptoms?
Drawing in far more air than fuel....no chance of combustion. The air leak itself must be for runners only linked to that bank.

And a carb will only lift fuel from the venturi....if air has passed through the venturi. An air leak in the manifold...means that cannot happen
Every day is a school day :)

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