Its my understanding that the EGR is an intake heater, for putting hotter exhaust gasses into the intake to heat the engine quickly.

Is this correct?

I've read many statements that blocking the EGR improves performance or gas mileage. Is this true? What are the down sides of blocking it?

 

Not correct. The EGR valve allows exhaust gasses back into the intake for the primary purpose of lowering combustion temperatures. I know, at first it doesn't make sense (I've been corrected a while back about this)...the supplied charge of exhaust in the cylinder is basically inactive. The burn is not as explosive, less heat is generated. The lowered combustion temp lowers amount of NOx generated as a byproduct. Unfortunately, the EGR effectively reduces "meaningful" displacement. Many folks have been defeating their EGR's for better performance and smoother low RPM operation. The "heat riser" is responsible for heating the stock, carbed intake. There's a temperature controlled valve (more like a flapper) that helps redirect fresh, hot exhaust gasses into the underbody of the intake. If you ever have looked at an exhaust manifold (carbed log) you'll notice that in the center where it comes in contact with the intake it's open, open to allow these hot gasses into the passages of the intake's underbelly. This is why the Clifford intakes will not work with the old carb log because of the heat riser opening...the OFFY intakes have this provision built in to accept the opening, but I don't beleive there's actual passages in the Offy for heating - hence the use of heated carb spacers. Sorry for going overboard.

 

[updated:LAST EDITED ON 15-Dec-02 AT 11:32 PM (EST)]I have heard that blocking the EGR only work for manual trannies. It's supposed to help a lot if your truck jumps and bucks. I am making a plate to completely block it off here next week. I have heard that restrictor plates and automatic trannies do not get along well. Hope this helps.

 

Thanks for the thorough description!

So basically if i'm not having any problems (I have a manual tranny) I shouldn't really bother blocking it?

I don't really like the idea of exhaust going into my boom boom chambers tho.

 

Well, rhetor, the chief complaint it was meant to 'fix' was troubles some of us had when starting off from dead stops. When doing so with a manial tranny, many of us noticed the truck would attempt to stall (or, at very least, the intitial hitting of the gas pedal caused the RPM's to lower instead of rise to counter the application of the clutch).

You can try this out while stopped - leaving it idling, just slowly start to apply the gas - if it sounds (or, if you have a tachometer, looks) like it goes down at first, you may have the problem.

I used to hold that it was meant for manual trannies only, but after reading the reports coming back of Inline SIx owners with auto transmissions who blocked their EGR's off with good results, I'd recommend it to just about any 4.9L owner now. (save for Mass Air vehicles - there doesn't seem to be any evidence that mass air 4.9's have any such problems to fix)

But I agree - if you don't have any complaints, why even play with it?