This thread prompted by an idea discarded long ago and revived by a recent post from @Chris914n6 elsewhere noting his decision to add a cat to his 914. Curious to hear thoughts on upsides and downsides with this idea. Feasible? Effective? Ineffective? Stupid? Sure to cook the engine's—or the 901's—oil? Or?
Talk about threads I thought I'd never start, but my 914 is pretty smelly in 2020 in a way it wasn't when I started driving it in the 1990s…because all cars have become so much cleaner and the older cars on the road back then are long gone now. Turns out, there are such products out there—and I am surprised by the price disparity.
https://www.holley.com/products/exhaust/cat...l/parts/2000124
https://shop.redline360.com/products/g-spor...gh-output-85030
Full Version: Adding a catalyst, or two, to a 914?!
First a disclaimer... I put it on my Nissan swap. Being from a fwd I copied the under engine Y tube into a single that goes thru the cat and into an SC 1 in 1 out banana muffler.
For the T4s, apples would be a triad or similar single exit header.
Science stuff.
Heat is fine plenty of air flow under the trunk. Back pressure is practically none.
You don't need an o2 sensor but you do need a well tuned engine as too much gas or oil will burn out the cat.
Cats were first installed with TBI injection, which is really just a carb with an injector or two in it and is super rudimentary.
That being said, you really should install a wbo2 sensor & gauge to tune the engine first, specially carbs. 12point7 is likely the cheapest good setup.
We still have the sniffer test. Back when I had carbs and later the 2.0fi, it would barely pass under 250 ppm HC. The 97 Nissan setup was less than 1, which was actually a problem because the sniffer detected fresh air and wouldn't accept it. That's a big reason OBD2 cars are computer tested because the sniffer can't read that low.
That is a rear o2 in the pic. It's sole purpose is to check the function of the cat and for me keeps the CEL off until there is a real problem.
Click to view attachment
For the T4s, apples would be a triad or similar single exit header.
Science stuff.
Heat is fine plenty of air flow under the trunk. Back pressure is practically none.
You don't need an o2 sensor but you do need a well tuned engine as too much gas or oil will burn out the cat.
Cats were first installed with TBI injection, which is really just a carb with an injector or two in it and is super rudimentary.
That being said, you really should install a wbo2 sensor & gauge to tune the engine first, specially carbs. 12point7 is likely the cheapest good setup.
We still have the sniffer test. Back when I had carbs and later the 2.0fi, it would barely pass under 250 ppm HC. The 97 Nissan setup was less than 1, which was actually a problem because the sniffer detected fresh air and wouldn't accept it. That's a big reason OBD2 cars are computer tested because the sniffer can't read that low.
That is a rear o2 in the pic. It's sole purpose is to check the function of the cat and for me keeps the CEL off until there is a real problem.
Click to view attachment
^ Very cool.
I'd be hesitant to add cats to a carbureted engine, even one that's tuned well, but something to think about with EFI.
I'd be hesitant to add cats to a carbureted engine, even one that's tuned well, but something to think about with EFI.
Modern high flow cats are really good. Trying to get the exhaust plumbing is the tricky part. the 75-76 cars did it, but not in a great way.
4-1 headers make adding a cat much easier, but you loose heat. And I admit I kinda like driving a car that smells like oil and gas, because its what I remember cars you to smell like when I was a kid growing up in Texas and California.
Zach
4-1 headers make adding a cat much easier, but you loose heat. And I admit I kinda like driving a car that smells like oil and gas, because its what I remember cars you to smell like when I was a kid growing up in Texas and California.
Zach
The cat won't last long with an aircooled, you would also need to run an emissions factory air pump system, you know that thing owners ripped off and tossed in the trash in the 70's-80's.
Cats like to run 14.7-14.8:1 so stoch or a bit lean, the reason most early FI ran on a narrow band O2 sensor. Running a aircooled at stoch would kill the aircooled engine, even with modern FI and anti knock sensors. With my'67 bug EFI and wide band, using nickies I've leaned out my 2.6 type 4, at just under 14:1 my head temp skyrocketed, at say 13.75:1 I have to be very careful of pulling hills, the best I can do with a comfortable margin is 13.5:1. Many cars would still be running carbs (at least into the 2000's) if cats played well with them.
Running rich, as our cars do, using a cat would help the reduction of CO and hydrocarbons but at the expense of NOx. Then add the fact they won't last long and it's hard to get enough heat into them to make the cat work, etc....
I looked into this as well
Now if running a FI watercooled conversion installing a cat makes perfect sense.
Cats like to run 14.7-14.8:1 so stoch or a bit lean, the reason most early FI ran on a narrow band O2 sensor. Running a aircooled at stoch would kill the aircooled engine, even with modern FI and anti knock sensors. With my'67 bug EFI and wide band, using nickies I've leaned out my 2.6 type 4, at just under 14:1 my head temp skyrocketed, at say 13.75:1 I have to be very careful of pulling hills, the best I can do with a comfortable margin is 13.5:1. Many cars would still be running carbs (at least into the 2000's) if cats played well with them.
Running rich, as our cars do, using a cat would help the reduction of CO and hydrocarbons but at the expense of NOx. Then add the fact they won't last long and it's hard to get enough heat into them to make the cat work, etc....
I looked into this as well
Now if running a FI watercooled conversion installing a cat makes perfect sense.
QUOTE(Mark Henry @ Oct 1 2020, 06:15 AM) 
The cat won't last long with an aircooled, you would also need to run an emissions factory air pump system, you know that thing owners ripped off and tossed in the trash in the 70's-80's.
Cats like to run 14.7-14.8:1 so stoch or a bit lean, the reason most early FI ran on a narrow band O2 sensor. Running a aircooled at stoch would kill the aircooled engine, even with modern FI and anti knock sensors. With my'67 bug EFI and wide band, using nickies I've leaned out my 2.6 type 4, at just under 14:1 my head temp skyrocketed, at say 13.75:1 I have to be very careful of pulling hills, the best I can do with a comfortable margin is 13.5:1. Many cars would still be running carbs (at least into the 2000's) if cats played well with them.
Running rich, as our cars do, using a cat would help the reduction of CO and hydrocarbons but at the expense of NOx. Then add the fact they won't last long and it's hard to get enough heat into them to make the cat work, etc....
I looked into this as well
Now if running a FI watercooled conversion installing a cat makes perfect sense.
^ Great input. Thanks Mark!
Suspect the much more sensible move for a carbureted air-cooled engine is EFI.
QUOTE(horizontally-opposed @ Oct 1 2020, 09:21 AM)
Suspect the much more sensible move for a carbureted air-cooled engine is EFI.
EFI helps a bit with emissions, but not as much as you may think. With iron cylinders you can only run say at 13.2:1 (nickies can give you about a .5 leaner mix in my testing) compared to the 12.7:1 I'm running in my 3.0 weber six.
Most guys say the air cooled engine is air/oil cooled, when in fact the rich fuel charge is also providing some of the cooling to the head.
The 914-6 conversion I bought uses 993 heater boxes and two high flow Cats. I like it, know it leaves some power on the table, but the 914 doesn't stink.
The CIS is set a bit on the lean side, noticeable only when cold.
Looks clean though, the guy did a good job.
The CIS is set a bit on the lean side, noticeable only when cold.
Looks clean though, the guy did a good job.
I am all for clean air.. I do like to keep breathing.
But I think that the car hobby people of all types are a very small subset of the driving public. So the added emissions from not running cats on our cars is offset by the general public that buys a new car every few years. Things like catalytic coatings on radiators that clean up the air as the radiator moves through it have been in cars for years now. Plus, car hobby people in general keep their hobby cars better maintained than the regular public. Some of which don't even know how to open the hood on their cars.
I maintain the emissions components such as charcoal canisters and alike on my 914s. But trying to get a 50 year old carbureted 914-6 to work with cats is like putting a elevator in an outhouse. It just doesn't belong.
Just my $.02.
Clay
But I think that the car hobby people of all types are a very small subset of the driving public. So the added emissions from not running cats on our cars is offset by the general public that buys a new car every few years. Things like catalytic coatings on radiators that clean up the air as the radiator moves through it have been in cars for years now. Plus, car hobby people in general keep their hobby cars better maintained than the regular public. Some of which don't even know how to open the hood on their cars.
I maintain the emissions components such as charcoal canisters and alike on my 914s. But trying to get a 50 year old carbureted 914-6 to work with cats is like putting a elevator in an outhouse. It just doesn't belong.
Just my $.02.
Clay
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