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Cataylitic convertor help

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BlazerDawg

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So I just bought a 72 k5 with the factory 350 in it. It's been a dream truck of mine for a pretty long time, and it is far from perfect. I had to petition my wife pretty hard to get it, and I need to make find some ways to "soften the edges" to make riding in it more palatable for her. She understands that a carbureted engine is going to smell different than EFI, but she's having trouble getting over the odors a 50+ year old truck is inevitably going to produce. I'm a pretty long ways away from having the funds and time to convert to EFI or do an LS swap, so I'm thinking maybe adding a catalytic convertor would be a good first step to modernize and make her more comfortable. How possible/viable would this be, has anybody on here done this on a stock first gen, and what are some of the things I should consider/look out for? Thanks and excited to join this community of weirdos lol
 
BlazerDawg said:
So I just bought a 72 k5 with the factory 350 in it. It's been a dream truck of mine for a pretty long time, and it is far from perfect. I had to petition my wife pretty hard to get it, and I need to make find some ways to "soften the edges" to make riding in it more palatable for her. She understands that a carbureted engine is going to smell different than EFI, but she's having trouble getting over the odors a 50+ year old truck is inevitably going to produce. I'm a pretty long ways away from having the funds and time to convert to EFI or do an LS swap, so I'm thinking maybe adding a catalytic convertor would be a good first step to modernize and make her more comfortable. How possible/viable would this be, has anybody on here done this on a stock first gen, and what are some of the things I should consider/look out for? Thanks and excited to join this community of weirdos lol
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It's not that hard, it's as easy as going to an exhaust shop and have them put it in.
If you have dual exhaust it will cost you double since they have to put one on each side
 
Where is your exhaust exiting the truck, and how is the tune on your carb? Both can effect the fumes, but with a proper tune it shouldn't be bad at all
 
You should get the carb tune and spark timing mostly good first. That will help some with the smell, but even EFI stinks without the cat(s). Misfires or improper mixture can damage the catalyst. There is a big difference in the performance/smell with small/cheap cats vs. large/better units.

Also make sure the exhaust isn't leaking or dumping under the truck. The proper exit for a Blazer is at the rear corner(s). Straight out the back sucks fumes in from any leaks you have around the tailgate and lift hatch (the back of the vehicle is a vacuum while in motion).
 
I'm taking it in tomorrow to get the rusted oil pan replaced, and I'm going to let them tune the carbonator for me to help me get a baseline of how the engine should feel when its properly tuned (never tuned one myself, but understand the process in theory). As far as the exhaust, its dual in front of the rear tires. So best spot would be behind rear tires on the side then?

Also, I understand with cats I'll probably need to tune the carb more often to make sure the mixture is right and I'm not destroying my exhaust system. Overall I know its not a bad habit to have anyway and I don't mind if it makes the ride and performance better. I guess I just want to make sure there aren't other factors I need to consider first.
 
The cats only work properly when they're hot. They need to go
BlazerDawg said:
So best spot would be behind rear tires on the side then?
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Yes, based on tons of user experience. The cat(s) should go as far forward as they can be packaged, to help them heat up and light quickly. Just because you have 2 tailpipes doesn't mean you have full true dual. When they came catted from the factory, it was a single unit roughly underneath the driver's seat.
 
BlazerDawg said:
I'm taking it in tomorrow to get the rusted oil pan replaced, and I'm going to let them tune the carbonator for me to help me get a baseline of how the engine should feel when its properly tuned (never tuned one myself, but understand the process in theory). As far as the exhaust, its dual in front of the rear tires. So best spot would be behind rear tires on the side then?

Also, I understand with cats I'll probably need to tune the carb more often to make sure the mixture is right and I'm not destroying my exhaust system. Overall I know its not a bad habit to have anyway and I don't mind if it makes the ride and performance better. I guess I just want to make sure there aren't other factors I need to consider first.
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A tune is a must and by not stating the obvious I jumped to the question asked.
As for the exit point, on the side is good, in the back not so good.
But when the top is off all bets are off
 
imiceman44 said:
A tune is a must and by not stating the obvious I jumped to the question asked.
As for the exit point, on the side is good, in the back not so good.
But when the top is off all bets are off
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would behind the tire and out the side be better than in front of the tire, or would it create the same vacuum issue as going straight out the back?
 
BlazerDawg said:
would behind the tire and out the side be better than in front of the tire
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Yes, that's what I'm saying. You don't want the tips near your windows or straight out of the back. I think the angle of the exit is kind of splitting hairs, the location is most important. Others can share their experience if they know more.
 
Don't know much about the cat converter advice, but the exit it very important. As has been said rear corners or behind the tire is best. I have done duals straight back, duals out the side in front of the tire, duals dumping down under the truck, and now I have duals exiting out both sides near the corners. I have done all of these carb and tbi. All on my first gen.

It is important to have it tuned properly and carb adjusted properly. Seal all leaks in the floor, also wrapping the exhaust makes a big difference in temps under the truck.
 
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