Do I really need a smog pump?
04-08-2019, 01:20 AM
#31
Rennlist Member
I will freely admit to not doing dyno tests, if everyone else will. Along with that, we know that Porsche did do smog pump and non smog pump tests. The results are: Euro rated 10HP higher without the pump. I believe Ferrari also did similar tests, and found similar results.
Interesting side minutia. In 1972, Lamborghini was forced to put smog pumps on it's 4L V12 engine for US market. The engine was rated at 350HP in 68-71. It was rated at 350 in 72 and later. Lamborghini chose an interesting route. They used the same ole smog pump as everyone else, but - they put a AC clutch drive on the snout. At 2600RPM, the tach sensor had a cutout that would de-clutch the smog pump, and produce rated HP up to redline. Apparently, Lambo felt it robbed enough HP at high RPM to stop turning it.
More minutia you say? Well alrighty then. Ferrari uses the same smog pump as all those little Fiats that were imported back in the 70s and early 80s. Ferrari, always looking for that last horse of power swapped out the vanes used on a 2L Fiat engine, and went with half-size vanes, for less power draw. It did the job, just barely but anyone with a 79-86 V8 Ferrari knows, if it's in CA, and won't blow clean, to replace it with the Fiat pump for more air(even though it does nothing once warmed up).
BTW, turning a pump with no front or back pressure is NOTHING like turning it with the vacuum draw through a filter, and pushing the air pressure down 8 small tubes(or in some cases 2, 4, or 6, or even 12 depending).
Interesting side minutia. In 1972, Lamborghini was forced to put smog pumps on it's 4L V12 engine for US market. The engine was rated at 350HP in 68-71. It was rated at 350 in 72 and later. Lamborghini chose an interesting route. They used the same ole smog pump as everyone else, but - they put a AC clutch drive on the snout. At 2600RPM, the tach sensor had a cutout that would de-clutch the smog pump, and produce rated HP up to redline. Apparently, Lambo felt it robbed enough HP at high RPM to stop turning it.
More minutia you say? Well alrighty then. Ferrari uses the same smog pump as all those little Fiats that were imported back in the 70s and early 80s. Ferrari, always looking for that last horse of power swapped out the vanes used on a 2L Fiat engine, and went with half-size vanes, for less power draw. It did the job, just barely but anyone with a 79-86 V8 Ferrari knows, if it's in CA, and won't blow clean, to replace it with the Fiat pump for more air(even though it does nothing once warmed up).
BTW, turning a pump with no front or back pressure is NOTHING like turning it with the vacuum draw through a filter, and pushing the air pressure down 8 small tubes(or in some cases 2, 4, or 6, or even 12 depending).
04-08-2019, 08:08 AM
#34
Rennlist Member
Wow, I hadn't heard that happen before. Its very little consolation, but at least it didn't happen in the middle of absolutely nowhere...and you covered ALOT of that in your trip!
I removed my entire smog pump system for a few reasons, but your incident would be another reason.
My reasons:
1. It is not necessary for the performance or operation of the vehicle. It may be necessary for governmental regulation in some locations, but not mine. (I have kept the entire system, in case it does.)
2. Removal does not detract from the performance of the vehicle.
3. It is unnecessary weight. Minimal yes, but everything adds up.
4. It is unnecessary energy drag on the powerplant. I'm not going to debate how much, but unless you show me your credible thesis refuting Newton's Third Law, I'm going with Newton. (Also, I think the OP just proved this in its worst incarnation.)
5. It seemed to be unnecessarily "in my way" when working on the vehicle.
6. As much as possible, I prefer a clean engine bay, both visually and physically.
7. **new** Possible unanticipated seizure and associated damage.
Finally, I also do not worry about the impact upon the crankshaft from removal of the associated pulley and its tension. I am comfortable with a personal conclusion that if the absence of that belt impacts the crankshaft that much, there are other problems. I sleep better at night knowing at least one other person who has seen a few 928 engines agrees:
- GregBBRD: "If the air pump belt load has any affect on the main bearings, you've got other problems."
Thanks, Jason
I removed my entire smog pump system for a few reasons, but your incident would be another reason.
My reasons:
1. It is not necessary for the performance or operation of the vehicle. It may be necessary for governmental regulation in some locations, but not mine. (I have kept the entire system, in case it does.)
2. Removal does not detract from the performance of the vehicle.
3. It is unnecessary weight. Minimal yes, but everything adds up.
4. It is unnecessary energy drag on the powerplant. I'm not going to debate how much, but unless you show me your credible thesis refuting Newton's Third Law, I'm going with Newton. (Also, I think the OP just proved this in its worst incarnation.)
5. It seemed to be unnecessarily "in my way" when working on the vehicle.
6. As much as possible, I prefer a clean engine bay, both visually and physically.
7. **new** Possible unanticipated seizure and associated damage.
Finally, I also do not worry about the impact upon the crankshaft from removal of the associated pulley and its tension. I am comfortable with a personal conclusion that if the absence of that belt impacts the crankshaft that much, there are other problems. I sleep better at night knowing at least one other person who has seen a few 928 engines agrees:
- GregBBRD: "If the air pump belt load has any affect on the main bearings, you've got other problems."
Thanks, Jason
04-08-2019, 01:21 PM
#35
Inventor
Rennlist Member
Rennlist Member
Non-cat cars, the air pump forces air into the exhaust ports to reduce HC.
With-cat cars, the air pump forces air into a tube with small holes (facing forward) in the rear third of the cat(s) over a separate honeycomb.
At higher loads (low manifold vacuum) pumped air is redirected into the airbox so as to not overheat the exhaust system.
'80 USA squeaked in before higher emissions standards in '81 with a cat and O2 sensor only.
No air pump, a unique L-Jet ECU (later ones will plug in and work), and a different vacuum advance curve.
With-cat cars, the air pump forces air into a tube with small holes (facing forward) in the rear third of the cat(s) over a separate honeycomb.
At higher loads (low manifold vacuum) pumped air is redirected into the airbox so as to not overheat the exhaust system.
'80 USA squeaked in before higher emissions standards in '81 with a cat and O2 sensor only.
No air pump, a unique L-Jet ECU (later ones will plug in and work), and a different vacuum advance curve.
Last edited by PorKen; 04-08-2019 at 01:46 PM.
04-08-2019, 05:01 PM
#36
Inventor
Rennlist Member
Rennlist Member
I have it on my list to add a relay to dis-engage the air conditioning compressor at full throttle (on both my '88 S4 and '85 GMC
).
04-08-2019, 05:20 PM
#37
Rennlist Member
Whats your fav charity.
$10/HP.
I'll dyno Saturday this weekend on a Dynojet 224. It may have eddy current, depends which one our vendor brings.
I'm willing to bet there are MORE than just the pump changes in the document that says any meaningful HP change.
$10/HP.
I'll dyno Saturday this weekend on a Dynojet 224. It may have eddy current, depends which one our vendor brings.
I'm willing to bet there are MORE than just the pump changes in the document that says any meaningful HP change.
04-08-2019, 10:12 PM
#38
I eliminated my air pump and used a belt directly from the crank pulley to the fan pulley. I figure my crank bearing will last longer due to this belt offsetting the downward pressure of the rods during the power stoke.
Last edited by Billu; 04-08-2019 at 10:12 PM. Reason: Change