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Exhaust leak-- car slows down

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Exhaust leak-- car slows down

Postby bigjoe1 » Mon Mar 03, 2014 5:40 pm

Has anyone ever seen this-- The gasket between the header and the head was blown out ( over half way around the port was GONE ) the car slowed down about one tenth , and about three miles per hour at the drag strip. I remember many years ago, on street driven cars that we drove to the drag strip. If the gasket between the header and the head sounded like if was leaking, the car would run slower than normal until you replaced the leaking gasket,, Does this ring a bell for any one out there ??


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Re: Exhaust leak-- car slows down

Postby 1989TransAm » Mon Mar 03, 2014 5:51 pm

Could it be that particular exhaust pipe is not doing its far share of tugging on the intake track during the overlap period. That would cut down on the cylinder filling a tad.
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Re: Exhaust leak-- car slows down

Postby groberts101 » Mon Mar 03, 2014 5:56 pm

Sure have. I think the effect is amplified on bigger CID and/or RPM capability setups too. Seems like it dampens the negative pressure waves.. thus creating a "softer pull" in the primaries. I can only assume that it would affect a merge style collector to some degree as well.

Also consider the possibility on huge overlap cams to momentarily pull fresh air into the pipe which may.. or may not.. add exhaust volume and cool it down too early in blowdown. Double whammy.

PS. I've also seen it so bad that it screws with idle/transition circuits and causes fueling issues too. So, the affect seems to do something negative even when the engine isn't under load.
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Re: Exhaust leak-- car slows down

Postby bigjoe1 » Mon Mar 03, 2014 6:15 pm

This is on our 900 Hp 434 SB Chevy turning 8500 RPM-- I hope this is the problem


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Re: Exhaust leak-- car slows down

Postby groberts101 » Mon Mar 03, 2014 6:36 pm

bigjoe1 wrote:This is on our 900 Hp 434 SB Chevy turning 8500 RPM-- I hope this is the problem


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Can't say if that would be the problem attributed to the slowdown.. but I sure couldn't see it helping the situation any.

Have you logged the A/F ratios or maybe EGT's to see what affect the leak may be imposing?
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Re: Exhaust leak-- car slows down

Postby Dan Timberlake » Mon Mar 03, 2014 6:37 pm

Any exhaust gas temp, plug temp, or (meaningless now) A/F info for that cylinder ?
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Re: Exhaust leak-- car slows down

Postby jacksoni » Tue Mar 04, 2014 8:09 am

Look at Maxracesoftware's (larry Meaux) post in this thread:

viewtopic.php?f=1&t=39088
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Re: Exhaust leak-- car slows down

Postby BOOT » Tue Mar 04, 2014 11:48 am

jacksoni wrote:Look at Maxracesoftware's (larry Meaux) post in this thread:

viewtopic.php?f=1&t=39088



Makes me wonder about the effect of multiple small header leaks.
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Re: Exhaust leak-- car slows down

Postby JoePorting » Tue Mar 04, 2014 12:44 pm

Interesting. Wouldn't think something so small would have such a major effect. Was the gasket only blown out on a few ports or all the exhaust ports? If it's only a few ports, then the negative effect is even more amazing.
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Re: Exhaust leak-- car slows down

Postby SonnyJames » Tue Mar 04, 2014 1:02 pm

Happened to me repeatedly. Bolts in my 3 piece headers kept coming out on 7 and 8. Car would slow down a tenth Joe.
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Re: Exhaust leak-- car slows down

Postby groberts101 » Tue Mar 04, 2014 3:20 pm

jacksoni wrote:Look at Maxracesoftware's (larry Meaux) post in this thread:

viewtopic.php?f=1&t=39088


Good link. The trend seems to be fairly consistent and becomes more pronounced at higher power/airflow levels.
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Re: Exhaust leak-- car slows down

Postby bigjoe1 » Tue Mar 04, 2014 4:10 pm

In my case , only one port was leaking. The car is so loud, no one noticed it untill we pulled the engine out for a look see.



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Re: Exhaust leak-- car slows down

Postby donc » Tue Mar 04, 2014 6:00 pm

I broke a headergasket in the burnout box on a heads up run car slowed a tenth, glad Im not the only one.
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Re: Exhaust leak-- car slows down

Postby 340king » Tue Mar 04, 2014 7:03 pm

That most certainly is an issue. I lost a gasket where I lost the two center ports. I slowed down so much it was embarrassing. So yes, the flange gasket leaking does make a huge difference.

If you are going to continue to use gaskets, I would recommend a look at the SCE or other soft metal gaskets as a way to reduce that possibility.
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Re: Exhaust leak-- car slows down

Postby 6sally6 » Tue Mar 04, 2014 7:08 pm

Big Joe...do you do ALL the wrenching on your race car or is your son just as sharp?
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