Jump to content
Moses Ludel

Should You Scrap the Emission Controls on a Smog Era Carbureted Jeep?

Recommended Posts

I would like to cast some light on the EGR valve.  EGR is primarily passive and has a minimal impact on performance either way.  Its role is to dilute incoming A/F and reduce NOx.  NOx occurs at high temperatures, and the role of EGR is to lower upper cylinder heat to below 2,500-degrees F.  Otherwise, upper cylinder temps can reach as high as 4,800 degrees F, approaching the heat in familiar metal welding processes (6000-degrees F or so for full liquifying and fusion).

I traditionally have left EGR in place to keep upper cylinders cooler.  Did you notice any improvement in performance from the EGR removal and block-off?  Or did this increase detonation (ping)?  Not sure whether you made all of these engine changes at the same time and can isolate the impact, either positive or negative, of removing the EGR system.

On another note, air injection systems often get tossed.  This can lead to havoc if the air injection tubes still enter the exhaust ports yet no longer offer cooling ambient air flow.  Stainless steel tubes have been known to melt in the exhaust ports when AIR type systems get modified or "gutted" and there is no longer cooling ambient air flowing through the tubes.  The only way to properly remove AIR or air injection is to eliminate the tubes and fit the cylinder heads with suitable plugs.  As for what kind of gains might result, the AIR or injection smog pump draws a whopping 1/4-horsepower or so.  Arguably, and notable on collectible muscle cars, the AIR or pump injection system should simply be restored and left alone.

As for Pulse Air, this is also passive.  It uses existing exhaust pulses to create a low pressure "vacuum" and pumps that air into the catalytic converter to create a more complete burn in the cat.  Power robbing?  Doubtful...We do remove Pulse Air with the installation of a 50-State legal EFI conversion, the emissions drop enough to justify eliminating the Pulse Air system.  Both Mopar and Howell kits allow removal of Pulse Air but not the catalytic converter.  This requires pinching off and welding the end of the Pulse Air inlet tube at the cat.


Since the early 'sixties era of closed crankcase devices and the later carbureted engine emission controls era, owners have wondered whether to restore or eliminate devices.  Aside from the legality issues, there are times when these devices have either little negative effect or may even provide some benefits.  

For those unaware, my answer to a Jeep CJ-7 owner's emissions modifications may help.  I'd also add that Jeep pioneered the closed crankcase on the MB WWII model, and this equivalent to a PCV system eliminated the common road draft tube.  An open road draft tube would have swamped these 134 L-head crankcases during stream crossings and beach landings.  

Often, emissions devices are neither bad nor detrimental to performance.  In fact, they can even have positive effects as noted in my comments above...


Edited by Moses Ludel

Share this post

Link to post
Share on other sites

  • Create New...