I'm looking for some info on converter placement with respect to the headers. I understand that they should be close to the collector to utilize as much exhaust heat as possible to make them work. But, the converter should also act as the theoretical "end" of the collector therefore changing scavenging properties just as different length collector extensions can alter low to midrange torque.

Application will be a 383 LT4 w/ 20+# boost using 1-3/4" long tube headers (maybe 1-7/8"), 3" collectors & dual 3" exhaust (possibly 3.5 collectors & exhaust) making approximately 900hp (hopefully more). This is all a space compromise as I would prefer larger if possible & will run the largest cats that fit depending on location.

With current PA state inspection laws requiring all cars to pass a visual check of emissions equipment (even if they do not have to pass the sniffer in rural areas), I would like to place these as accurately as possible, without too much experimentation. I only want to build 1 stainless exhaust system.

Does anyone have actual dyno results of HP differences by placing cats farther from the collectors? Hoping that some of the engine builders with a dyno can share some info.

Also does anyone have a power comparison with & w/o converters to try to justify this exercise.

Hope this is advanced enough for this site, but I doubt there are too many cars of any type at this power level trying to run cats.

Thanks for any info that you can provide.

 

That's an excellent question! I am at that power level using the Random Tech dual high-flow cats and Y-pipe. I have not tested without cats, but am going to try that this year, though I plan to keep the cats. I am interested to hear some answers from someone who has more info.

Rich Krause

 

Rich,
I guess this makes us the only ones?

I am very curious of the cat power capabilities as I hate to sacrifice a lot of power. The D-1R can push a lot of air in, so I am trying to get it back out with as little restriction as possible.

I'm surprised to see that you have a 3" y-pipe with cats. Are you running a larger exhaust (4" by chance) & did you replace the single 3" collector? If still running a single 3" exhaust, your cats may not be the biggest restriction in the system. Either way your power numbers are impressive.

 

Still a 3" exhaust. It is probably a major power loss. That's one reason I plan to experiemnt with various parts disconnected. I want to decide if it's worth the cost/time to do something else. It's too bad no one markets something decent in the way of a really high-po exhaust setup. I want the cats because I am a "green" kind of guy. Kind of unusual for a motorhead.

Rich Krause

 

Rich,
The exhaust is definitely an issue. Personally I witnessed picking up .1 sec on a '99SS Camaro by going from a SLP 3" y-pipe adapted to a 4" mufflex, by cutting off the SLP 3" collector & substituting a 4" flowmaster collector. This was on a 12 sec N/A car, so you should see major HP with some exhaust. I'm concerned that the dual 3" on my Camaro is not enough..... just not sure I can fit dual 3.5" without excessive torture.

As far as Cats, I will run them if I can find a good solution. I'm not necessarily environmentally biased, but am not opposed to it if reasonably possible.

 

Thats pretty interesting, since both of you have blowers perhaps the exhaust is hotter and you could move the cats farther away. I have seen heated cats on other non-fbody cars.