High Flow cats on a Blueprint 383

[Don-T]

I have a Blueprint 383 in my 73 K10. I have a dual exhaust on it with no cats. It likes to run rich at idle, about 12.5 to 1 and about 14 to 1 cruising. The fumes when idling are pretty bad. I am wondering if a pair of cats would help any with fumes and would they cause any problems?

 

[Ricko1966]

I have a Blueprint 383 in my 73 K10. I have a dual exhaust on it with no cats. It likes to run rich at idle, about 12.5 to 1 and about 14 to 1 cruising. The fumes when idling are pretty bad. I am wondering if a pair of cats would help any with fumes and would they cause any problems?

The cats will help with fumes and would be a worthy addition. No they won't cause any problems. The cats turn nox into nitrogen and oxygen. They turn carbon monoxide into carbon dioxide and they turn Hydro carbons into carbon dioxide and water. I've seen claims as high as 98 percent. But even at half that a 49 percent reduction in carbon monoxide is a big deal IMO.

 

[Don-T]

Thanks Rick. I do think that would be a big help, especially when starting and warming it up in the garage in cold weather. I do wonder if the converters can get plugged up or burned out from the engine running a bit rich? I also wonder how they might increase back pressure and cause power and mileage loss. I have a state safety inspection coming up in May and I am thinking about getting the cat converters put on at the same time.

 

[Ricko1966]

Thanks Rick. I do think that would be a big help, especially when starting and warming it up in the garage in cold weather. I do wonder if the converters can get plugged up or burned out from the engine running a bit rich? I also wonder how they might increase back pressure and cause power and mileage loss. I have a state safety inspection coming up in May and I am thinking about getting the cat converters put on at the same time.

They aren't going to hurt milage or performance,and as long as they get hot they will clean themselves up. I'd be worried about running a bit rich if maximum power and mpg are in your thoughts.

 

[Don-T]

I am working on the AFR when I can, mostly waiting for warmer weather. Right now I have 12.5 at idle, it won’t idle less than 1k in gear if I lean it much more. The cruise mixture is about 14 and wide open mix is about 12.5. When it warms up a bit more I will work on the tune again.

 

[Ricko1966]

I am working on the AFR when I can, mostly waiting for warmer weather. Right now I have 12.5 at idle, it won’t idle less than 1k in gear if I lean it much more. The cruise mixture is about 14 and wide open mix is about 12.5. When it warms up a bit more I will work on the tune again.

Are you running manifold vacuum to distributor. And do you have the right vacuum advance can?

 

[Frankenchevy]

Seems like something is up. Shouldn’t need to be 12.5:1 at idle. Is it their 450hp 383?

 

[Don-T]

Are you running manifold vacuum to distributor. And do you have the right vacuum advance can?

The engine is the 405 HP version 383 and it came with the vacuum can hooked up to the ported vacuum on the carb. I called them about it and was told that is where it needs to be. Do you believe otherwise? Wouldn’t that advance the timing at idle? Maybe that is what it needs to idle proper?

 

[Don-T]

Seems like something is up. Shouldn’t need to be 12.5:1 at idle. Is it their 450hp 383?

It is the 405 HP version. 9.5 compression.

 

[Ricko1966]

The engine is the 405 HP version 383 and it came with the vacuum can hooked up to the ported vacuum on the carb. I called them about it and was told that is where it needs to be. Do you believe otherwise? Wouldn’t that advance the timing at idle? Maybe that is what it needs to idle proper?

Yes move the vacuum advance to manifold vacuum,and readjust the carbureator. You need the extra advance at idle.

 

[Don-T]

I will do that as soon as I can start and run it again. My fan came apart and took out the water pump, radiator, a couple of pulleys, and belts. I am waiting for some parts to come in. Maybe by the weekend. Thanks for the help.

 

[Ricko1966]

I will do that as soon as I can start and run it again. My fan came apart and took out the water pump, radiator, a couple of pulleys, and belts. I am waiting for some parts to come in. Maybe by the weekend. Thanks for the help.

Go electric fan free a few more hp.

 

[Don-T]

Go electric fan free a few more hp.

That is what I am doing.

 

[Bextreme04]

I agree you won't hurt anything by putting on high flow cats. I just put a pair of 3" stainless flowmasters on with a set of long tubes to replace some worn out ones on my 2011 Suburban. It immediately jumped my fuel trims up 20%, so they definitely aren't taking anything away flow wise. I still need to get the wideband bung welded into the new y-pipe so I can go fix the tune for the new exhaust, but I highly recommend the flowmaster heavy duty high flow cats. I'm going to put the same ones on my Square with the new 454 when it goes in.

 

[Don-T]

I imagine the cats should be as close to the headers as I can get them. The issue is the transmission and transfer case don’t leave much room. Would the casts be able to do their jobs if they are behind the transfer case? The cat inlets at 32” behind the flanges on the header collectors. I suspect that wont work.