First, some background info. This all started when one forum member (who isn't extremely mechanically experienced) asked for tips about changing his intake manifold in-car. He mentioned in his original post that he will be swapping to an RPM Air Gap. Numerous people gave him lots of helpful tips, and things were going quite well... until halfway through page 3, where a more experienced guy said this:
Be advised, expect some cold weather, light throttle, hesitation issues with that Air Gap intake.
On page 4, I quoted that line and asked for further clarification. I pointed out that I do experience regular light-throttle hesitation at step-off, and that I have so far simply attributed it to running a carburetor. Somebody else was first to chime in, and told me this:
The Air Gap intake is not equipped with the water/ coolant crossover to help pre-heat the carb., thus taking longer for warm up.
Now
this does not really concern me in the slightest. I don't mind giving the car a couple of minutes at fast idle before I set off in the morning. Furthermore, once I swap over to EFI I presume this won't be an issue at all. But then the guy who first warned about the Air Gap finally checked back in and said the following:
A way to tell if this occurring is to get the car up to operating temp then let it sit for 5-10 minutes with the engine off. If you take off after letting it sit and the problem is gone for a short period it is because your intake got heat soaked. The problem will redevelop once enough cold air has been sucked into the carb to cool the intake back off. This is a real issue when the ambient temps are below freezing, but can also develop when the temps are only just below 60-65 degrees.
The cold intake at low air speeds will pull the fuel out of the fuel/air mix and make it puddle on the intake walls. Once the air speed picks up in the intake the fuel will evaporate and then get pulled into the cylinders. If you had an AFR gauge it would show up as a lean to rich condition at 'tip in' when cruising. It's hell to try to tune around. You end up having to live with it or give up on the intake and swap to a conventional one.
Later, he went on to explain how he always avoids Air Gap manifolds because he "only builds streetable cars" and if that's what you want, you must avoid these manifolds like the plague. I thought that sounded pretty harsh.
So, back to the issue at hand: a slight hesitation when trying to gently** pull away from a stop. It is definitely worse when the engine isn't up to full operating temp, though it does seem to still be there even once it is fully warmed up. Like I say, I've just lived with it because (a) I figured it was a carburetor thing and (b) I don't know nuthin' about tuning no carburetor. I just borrowed this from my co-worker Mike who had been running it on his similar 454 (before he went to EFI). I figured if it worked for him then it ought to work for me, so I plopped it on my intake and called it good.
To you who run an Air Gap with a carburetor, have you seen behavior like this?
**: gentle acceleration from a stop. Yes, that's how I've been driving the car. Unlike Mike's peg leg El Camino, my Grand Prix has a functional limited slip differential. If I get on the throttle too aggressively, the tail end has a propensity to ignore the steering wheel and instead head off in whichever direction it thinks looks most fun. While this might be entertaining when I'm alone in the middle of nowhere, it usually causes concern when I am close to other motorists.
For the curious (
mbryson, I'm looking at you), I don't even need to be stopped. On my way home from work tonight, I was on Pioneer Crossing just west of I-15 where the road crosses over the railroad tracks. I was in the center lane, doing between 40-45 MPH. As I began climbing the hill, the car in front of me began to slow because the car in front of him was doing the same... even though the light on top of the hill was green. I could see our light was going to change soon, and if the first bozo kept slowing down we'd all have to stop. The right lane was empty and nobody was coming up from behind, so I hit my signal and started to change lanes. Just as I crossed into the right lane, I gave the throttle a light prod--at least I thought it was light--in order to coax the TCU to drop down out of fourth gear and into third. The computer was perhaps a bit too eager, because it went past third and instead dropped into second gear. By now I was steering a bit to the left so as to follow the curve of the road, and the sudden onset of torque caused the tires to break loose and the tail end began sliding out to the right. It completely surprised me, but I quickly lifted off the throttle to kill the wheelspin, then got back on it much more gently in order to remain in my lane and safely crest the hill.
I've realized this car commands complete respect from its driver.
