1976 Riviera S/R Dual Exhaust

[24seven]

Hello All,

I have this stock Riviera running now and I would like to update it to dual exhaust. I believe this is one of the reasons for it's low horsepower rating.

A couple of observations; the crossmember only seems to support splitting the exhaust joint on one side. I still have to keep the catalytic(California) and have seen the -two in,two out type.

Would this be better or should I try to find a cross-member from another year(doublehump?) that will allow me to dump down and back. Can I expand my searches to include LeSabre's and Electra's for this crossmember.

Any and all suggestions are appreciated as I wish my 455 to breath better.

Thanks, HenryJ SoCal 1976 S/R ROA11572

[NTX5467]

In the middle 1980s, there were some Camaro IROC-Z cars which had an optional "dual converter" exhaust. In this case, both pipes ran under the same hump in the passenger side crossmember, but were staggered so they were not side-by-side in locaton. From there, each pipe went to it's respective side of the exhaust system. These were the later ceramic honeycomb converters rather than the "bead" converter you have, so it was easier to package them under the car (in basically the same space as one bead converter). If you want a true dual exhaust, you might look at how that Camaro system was configured and THEN see if a muffler shop can build something similar to it for the Riv. I believe that option was good for about 10-15 horsepower, so it's not going to be a huge increase.

What it can help with is throttle response in normal driving conditions (not just WOT, which is where max horsepower is measured).

For the first year of catalytic convertes in GM vehicles, 1975, the engines were generally retuned for better power and driveability--compared to the 1974 vehicles. The improvement was more evident in some vehicles/engines than others, though.

Therefore, you might be able to retrofit a '74 trans crossmember--key word "Might". Another key thing would be the wording of the CA emissions laws as far as exhaust systems go. If it states "factory configuration", that could rule out a dual system but if it only considers what's under the car (not how it's put configured), then a dual converter dual exhaust might be "legal" to do. If not, then you might need to do a Camaro-type dual converter arrangement with the pipes running on one side of the car, at least up front. Check with the applicable state operatives before you spend any money, though.

Remember, too, that it'll be subject so emissions checks from now on, so working to keep things "in compliance" while still tuning it for a little more throttle response might take some additional efforts.

The OTHER thing is that catalytic converters are rated for particular engine sizes. In using a dual converter system, you'd want converters rated for 1/2 of the V-8 displacment. What happens is that the smaller converters fire off quicker from a cold start, when used in a dual set-up, than two converters each rated for a 455cid V-8. So, when you take it in for an emissions check make sure the engine is fully to operating temperature and the cats are at operting temp, too.

Just some thoughts,

NTX5467

[24seven]

To NTX5467,

Thanks for all the time you took to reply!

You have given me much to consider and I appreciate

it. Thanks, HenryJ SoCal