OK... searched 'till my fingers are bleeding... stroking my '89 Renix and considering upgrading to '91 head and TB.
2 questions...
1. Is the HO head worth the trouble now that there are bored Renix TB's? Seems I read Dr. Dyno said 5 HP gain? Is the swap worth it for the header choices?
The header choices are primarily extant because the 1991-2007 242ci doesn't have the EGR sytem. More on that in a moment.
However, the primary restriction isn't in the throttle body, and it isn't in the intake. It's in the intake port in the head. The problem is that the incoming air charge has to make a sharper turn in the 2686 head than it does in any of the later heads - which slows it down (recall how inertia works.) By reducing the angle (which is why later heads have higher intake ports,) you reduce the resistance in the airflow - because you lessen the effect of inertia somewhat.
2. Will there be smog test or performance issues with not running the EGR system?
Performance? Not that I've noted. I haven't done with/without dyno runs to objectively evaluate the mod, tho.
Smog Test? Yea. If you have a "visual" as part of your test, the monkey hooks up a hand vacuum pump to your EGR valve and pulls a mild vacuum. If the engine stumbles and dies, you pass that test (since you're diverting enough exhaust gas into the intake to take your AFR below the "lean burn limit.") However, the engine actually runs
cleaner without the thing working - it's just that the regulatory bodies suffer from HICS (Head-In-Cement-Syndrome,) and can't understand that something can be removed to make an engine run cleaner (or replaced outright with a better system. I'd love to ditch my EGR in favour of a water/MeOH fog setup - it would not only have a beneficial effect on emissions, but it wouldn't crap everything up in the intake stream with carbon, like the EGR does. And it would give cleaner chambers.)
Result? I keep the EGR system working to make the Air Police happy. I disconnect it when I'm not getting smogged (illegal? Technically. However, I've seen back-to-back smog tests that show that the engine runs cleaner
without the thing - I can't get CARB to wake up to that little factoid, but I figure I'm complying with the
spirit of the law, if not the
letter. Most laws are written around some logical disconnect anyhow...
("I'm sorry sir - that just fails the common sense test.")
But, when HC and CO get dropped to nearly nothing with no real net effect on NOx emissions by not having a functioning EGR valve (and replacing the EGR forces the HC and CO to near-failing levels,) I'll stick to what I'm doing. Again, the spirit of the law vice the letter of the law - sometimes good people do bad things for good reasons. I just have to remember to hook the thing back up when I have to go see the Air Police...
(Come to think on it, my having been at loggerheads with CARB for the last several years is probably why I keep getting sent to Test Only stations - which triples the cost of the test. Bastids...)
