Exhaust leak-- car slows down

General engine tech -- Drag Racing to Circle Track

Moderator: Team

bigjoe1
Show Guest
Show Guest
Posts: 6104
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703
Contact:

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 ??


JOE SHERMAN RACING

1989TransAm
Guru
Guru
Posts: 5928
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

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.

groberts101
Guru
Guru
Posts: 1300
Joined: Sat Mar 08, 2008 3:08 pm
Location: Minneapolis

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.

bigjoe1
Show Guest
Show Guest
Posts: 6104
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703
Contact:

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


JOE SHERMAN RACING

groberts101
Guru
Guru
Posts: 1300
Joined: Sat Mar 08, 2008 3:08 pm
Location: Minneapolis

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


JOE SHERMAN RACING


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?

Dan Timberlake
Guru
Guru
Posts: 1338
Joined: Tue Jan 15, 2013 8:10 pm

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 ?

jacksoni
Expert
Expert
Posts: 979
Joined: Sat Dec 18, 2004 2:54 pm
Location: Maryland

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

User avatar
BOOT
Guru
Guru
Posts: 1279
Joined: Fri Apr 09, 2010 5:23 pm
Location: Michigan

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.
I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

JoePorting
Guru
Guru
Posts: 2489
Joined: Mon Jun 14, 2010 2:16 pm
Location: Lake Elizabeth, CA

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.
Joe Facciano

SonnyJames
Member
Member
Posts: 147
Joined: Tue Dec 06, 2005 3:12 pm
Location: Beautiful NJ!

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.

groberts101
Guru
Guru
Posts: 1300
Joined: Sat Mar 08, 2008 3:08 pm
Location: Minneapolis

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.

bigjoe1
Show Guest
Show Guest
Posts: 6104
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703
Contact:

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.



JOE SHERMAN RACING

donc
Guru
Guru
Posts: 1197
Joined: Sat Dec 04, 2010 9:10 am

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.

340king
Expert
Expert
Posts: 561
Joined: Tue Mar 11, 2008 7:43 pm
Location: Fort Pierre, SD

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.

6sally6
Expert
Expert
Posts: 607
Joined: Sat Jan 30, 2010 12:01 am

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?
6sally6
Sorry to be a LITTLE off topic! :oops:


Return to “Engine Tech”

Who is online

Users browsing this forum: 406shark, Bing [Bot], bone6145, Carnut1, ijames, joedyna98, lefty o, MadBill, VMC and 30 guests