Exhaust Reversion

BFives · 04-25-2012, 07:24 AM

I did a little searching and have not found any info on this. Has anyone ever had any experience with this on their 12V?

I'm currently building my 12V and looking to get some ideas. I have been doing quite a bit of work to the heads, intake manifold, and exhuast manifolds to improve flow, but was concerned with "gasket matching" the exhuast ports as it may cause some exhuast reversion.

Has anyone gasket matched the exhuast maniolds to the heads and what were the effects- positive, negative?

Thanks

Prospeeder · 04-25-2012, 05:30 PM

well you wouldnt want the gasket sticking into the ports. Thats turbulence and restriction. Defeating all what you did. just match the gasket to the ported head. Let me know if doing that stuff helps. Im going to rip into my 12v soon for a refresh.

BFives · 04-26-2012, 04:26 AM

The concern here would be if both ports were exactly matched -(the head to the exhaust manifold)the exhaust gases may momentarily flow backwards during the overlap phase of the camshaft at low cycling rates, i.e. reversion, simply stated. However, a preventative method to overcome this problem is to match the exhuast manifold to the exact size of the gasket and leave the exhuast ports on the heads slightly smaller, 1/16" all the way around. This step makes it difficult for the exhuast gasses to move backwards. I've read through the head workshop and saw no mention of this. I wasn't sure if it was something to consider or if everyone has just been gasket matching with no issues. There seems to be quite a few here who have done work to the intake side, but no mention of the exhuast side.

04-25-2012, 05:30 PM	#2
Prospeeder AudiWorld Senior Member Garage is empty, add now Join Date: Aug 2011 Posts: 837	well you wouldnt want the gasket sticking into the ports. Thats turbulence and restriction. Defeating all what you did. just match the gasket to the ported head. Let me know if doing that stuff helps. Im going to rip into my 12v soon for a refresh. __________________ 1992 Audi 100 CS Quattro 1990 Audi 200 Avant Turbo Quattro 1991 Audi 200 Turbo 1999 Audi A6 Avant

04-26-2012, 04:26 AM	#3
BFives Audiworld Junior Member Garage is empty, add now Join Date: Jan 2011 Posts: 24	The concern here would be if both ports were exactly matched -(the head to the exhaust manifold)the exhaust gases may momentarily flow backwards during the overlap phase of the camshaft at low cycling rates, i.e. reversion, simply stated. However, a preventative method to overcome this problem is to match the exhuast manifold to the exact size of the gasket and leave the exhuast ports on the heads slightly smaller, 1/16" all the way around. This step makes it difficult for the exhuast gasses to move backwards. I've read through the head workshop and saw no mention of this. I wasn't sure if it was something to consider or if everyone has just been gasket matching with no issues. There seems to be quite a few here who have done work to the intake side, but no mention of the exhuast side. __________________ 96 Audi A4 2.8L 12v - 5spd(Bored MAF with velocity stack,Custom intake piping,cobra head connector,Audi 5k TB,ported intake, ported heads,ported exhuast manifolds,full gasket match,AAH Cams,A/C delete,Mechanical Fan Delete,External Oil cooler,"EGR Mod",Short Throw Shifter,H&R Coilovers,Poly Front Suspension,APR Snub Mount,Custom Exhaust,Rieger kit,16" BBS Mahle's,Carbon Fiber Hood,face lift headlights,facelift taillights,Custom front passengers wheel well and modified radiator support for more fresh air) 98 Audi A4 2.8L 30v 02 Audi A4 3.0L 30v 80 Mercedes 450sl 4.5L 74 Mercedes 450sl 4.5L 01 Dodge 2500 5.9L 72 Dodge Dart 5.9L 85 Plymouth Police Pkg. 5.2L 79 Lincoln Mark V 6.6L 48 Plymouth Coupe- No motor (Yet)

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