I'm adding a twin turbo to my 87IROC with intention to run 5-8psi now and more later. Should I be concerned with EGR and should I block it off? And whY?

Thanks

 

I have mine installed and working fine with 6-7psi of boost. The EGR improves efficiency under cruise conditions, and has no detrimental effects that I know of. Leave it be.

 

“improves efficiency?” how’s that?

Is this like one of those “exhaust back pressure makes more power” trick answers?

 

If you do remove the EGR or the AIR you should do everything in your power to modify the PROM to reflect these changes. Both the EGR and AIR systems are not monitored by the ECM in the sense that the ECM will know its unplugged and act differently. So if the PROM is tuned to account for EGR and AIR and they are not connected, the PROM will continue to work as if they were connected. I think this affects your spark tables and A/F ratio to some extent, not sure on specifics. But if you want specifics you can find them by searching. Do it. Dooo it.

 

Of course you tune for what is actually on the car at the time, but basically all the EGR is doing is introducing a part throttle inefficiency that makes the a/f mixture not burn as well cutting down combustion temps and lowering NOx.

Not that lowering power at that point is that big an issue, but the argument that it improves efficiency is stretching it.

 

When the EGR valve opens, the pumping losses are lowered because the pistons don't need to draw through a closed throttle plate (extra flow is coming through the EGR ports). Intake vacuum is lowered, and ignition timing is advanced. Does that mean efficiency is improved?

I guess what I really meant was that there really is no reason to ditch the EGR IMO, especially for a street application. Do you agree with that much?

 

I was always curious why people wanted to ditch the EGR anyhow . Does it make more power ?

 

No, EGR will not effect max power because the EGR is closed at WOT anyway. Even with the added exhuast manifold pressure of a turbo, the EGR will stay closed, because exhuast back-pressure actually forces the EGR valve pintle into it's seat.

 

Huh, interesting idea. Prove it… it would actually be an interesting experiment. I suspect that you’ll find that the flow through the valve is too low (what, is the seat something like a ¼ “ in diameter) to effect pumping losses at part throttle and the timing advance is not enough to make a difference WRT to the efficiency.

As long as it’s not causing other issues, sure. The problem is that is almost never the case.

In almost all cases it gets it’s exhaust gas by directing flow through the exhaust crossover which heats up the intake. Even if that was not the case, I would be shocked to find that the hole that they use to feed that passage doesn’t significantly hurt exhaust flow, taking a big chunk like that out off the bowl.

On the LT1’s they avoided that whole problem and caused another. They ran the exhaust straight to the back of the intake manifold using external tubing to the actual exhaust. The big problem there was packaging… that tube got sandwiched under the cowl, between the firewall and back of the intake. The heat from it tended to melt the RTV sealing the back china wall under the intake, causing an oil leak that tended to get into the bellhoushing (fowling the clutch…).

On the LO5 truck engines they are well known to cause a part throttle cruise surge. I didn’t believe it and resisted messing with it for a long time (couldn’t imagine what it was actually hurting, and figured that since the truck sees some towing duty I could use the detonation resistance. I finally gave in and tried it (just plugged the vacuum line) and guess what? It fixed the surging problem right away. In that case the standard valve appears to flow too much on that setup.

So yea, if everything is working right, matched right, tuned right and well designed then sure, it wouldn’t hurt anything, may even help control detonation on a hot day with the thing heavily loaded.