Smog bump
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Senior User
Joined: Apr 2000
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From: Central Pennsylvania
Looking in the exhaust ports, there is a small bump near the opening and also a larger "boss" where the exhaust gasses go into the EGR system. I'm assuming grinding off the smog bump refers to the small bump near the opening. If the smog boss is meant, then will the egr system become inactive?
Tony
Tony
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From: Central Pennsylvania
I don't like to bump topics up, but I'm sure many of you guys have ported the smog bump off your heads and this topic was just missed. Any help on this? Does grinding off the smog bump mean the EGR intake bump or just the small raised area just at the exhaust port opening. Anyone have some pictures of what this looks like?
Tony
Tony
Mountain Pass
Joined: Aug 2004
Posts: 143
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From: Tacoma, WA.
Pics of a good D0VE exhaust port
The above are pics of a 230 CFM D0VE exhaust port. This is the same exhaust port that will support 700 HP Dyno proven. You shape the thermactor boss into a vane to seperate the flow paths on the long side or roof. Leave the roof bump and the exhaust bolt hole bump behind the right side exhaust manifold bolt hole. The bump in the roof if removed requires the roof exit to be raised with no flow increase. Removal of the bump behind the bolt hole requires the right wall to be widened. Both do nothing for flow and make the port larger with the same flow. Velocity drops not to mention that you have to remove more iron for the same amount of flow...
Hope this helps a bit...
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Senior User
Joined: Apr 2000
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From: Central Pennsylvania
Yes, thanks for the pics. I didn't realize the dove heads had thermactor/egr systems. I understand from what you are saying that you can remove too much material and that shaping for flow rather than only enlarging is the goal. Correct?
Tony
Tony
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Mountain Pass
Joined: Aug 2004
Posts: 143
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From: Tacoma, WA.
Exactly...
The cross section of the stock port will support 250 CFM. the problem lies in the overall shape of the bowl and short turn.
Years ago the assumption was that all of the bumps had to be removed. Flow bench and dyno research has refuted this. Plus it is just too much extra work for no gain at all.
Remove the thermactor boss. Leave the others just smooth them. The EGR system is not related to thermactor as a system but a part of the overall emissions system. EGR feeds exhaust gasses to the intake tract to reduce combustion temps and reduce Nox emissions. It takes exhaust gasses from the cross over in the intake manifold.
Years ago the assumption was that all of the bumps had to be removed. Flow bench and dyno research has refuted this. Plus it is just too much extra work for no gain at all.
Remove the thermactor boss. Leave the others just smooth them. The EGR system is not related to thermactor as a system but a part of the overall emissions system. EGR feeds exhaust gasses to the intake tract to reduce combustion temps and reduce Nox emissions. It takes exhaust gasses from the cross over in the intake manifold.
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