Hey Guys just found these forums and am really impressed. Tons of uselful information .
I have an '81 Bronco with a 302, 2 barrel carb. I am in the middle of swapping it out with a 351w, 4 barrel carb and intake. My questions concern the Thermactor and EGR systems.
Emissons testing aside, how important are these to the peformance/wellbeing of the engine? I have heard different things; like the thermactor system is to help with cooling the engine, not just an excuse to drop emissons etc.
I am curious because I would like to only put on the stuff that is needed for the good of the engine. My emissons regs are not very strict anyway.
Also is the PVC system work by the carb sucking the vapor out or is it just positive pressure? I cringe to think of what it would put back into my nice new carb . Is the PCV system actually good for the engine not just emissons as well? Any help in this will be appreciated.

 

Emissions systems are a very tricky issue. On a stock engine, there is an equilibrium of all of the parts of the engine working together. This includes all of the emissions control systems. So yes, most of the emissions stuff does help the general well-being of the engine from the standpoint of it being tuned to operate with the systems intact. If you tune everything to compensate for the changes you're making, that's a different story. Now, with what you're talking about doing, that whole "equilibrium" is out the window, and you are going to have to set up the carb and timing and such on your own anyway, so there is no real advantage or disadvantage to keeping the emissions systems, just keep in mind that you might need to tweak the carb and get inside your distributor to change the advance curve some.

As far as the PCV, I would keep it. You could just replace it with another breather, but the PCV valve really is a great thing to have. It usually keeps the pressure in the crankcase at or below atmospheric pressure (which is to say, creates a vacuum), which helps prevent oil leaks and also promotes a better ring seal, which can create more power. If your valve covers are baffled well, the amount of oily crap the PCV system dumps into your carb should pale in comparison to its benefits.

 

Ditto... -Keep the PCV system it helps keep your engine and oil clean. If you re-calibrate your distributor you can run efficiently without EGR. It is sometimes difficult to get the EGR system to work properly when things are changed. The thermactor system does not cool the engine.

I have moved this thread to the 302/351W engine forum also.

 

For what it's worth, I just bought a 1990 F150 a couple of weeks ago and had a major revelation concerning all this emissions stuff. The first few tanks of gas after getting the truck yielded 11MPG. I knew something was wrong and the engine needed some work. It was sluggish off the start and seemed like it needed a lead foot to keep it going.

Last weekend I did a lot of maintenance, changed oil, air filter, new PCV hose (the old one was pretty gunked up), new PCV valve and a new oxygen sensor. I read in another forum that low gas millage may be caused by a faulty oxygen sensor. The computer didn't report it on diagnotic mode but I figured I'd give it a try. I filled up after the work I did and again today. I GOT 16MPG!!!

I used to think all this emissions related stuff was power sapping and reduced mileage. I sure don't believe it any more.

 

Emissions stuff is not a scheme at all. I had to do the same thing with my pickup when I bought it. You should change the PCV every year, whether or not it 'rattles' that doesn't mean its working. The EGR can be crucial to engines but is not always necessary, I would still keep it if you can. The thermactor can go either way. Its not real serious, but it does help. Maintenance is the key with this thing. It has a non-serviceable pump but the little filter is important, so is the charcoal box. It's non-serviceable as well but I just cut up a cheap air fiter and used that. I can't figure out how to get into the valve without wrecking it, mine stay open all the time and it should close and higher revs but its a pain.

 

Thanks guys for the replies. So then if I was to not use those systems (except PCV) I dont have to worry about burnt valves or anything. I Appreciate the help.