I have a 1988 IROC with a 350 TPI L98 and T700. The engine is stock now, but I'll upgrade the cam and heads later this year.

The exhaust needs to be replaced.

I'll install a set of Flowtech headers, which are the easiest fit for a Right Hand Drive car.

The plan is to fit a 3" cat-back stainless steel exhaust, possibly a MagnaFlow.

I'm tossing up whether to get Dual 2.5" (like an N10) or single 3" catalytic converter - any suggestions on the best option?

 

The N10 is dual 2 1/4 not 2.5". Second of all, The N10 is just the Ypipe. The N10 is quieter also. Duals are always very hard to install vs. single. 3" single is fine.

 

Thanks for the tips.

The standard Flowtech Y-pipe has a 2.5" outlet, would you know if I need to get a custom Y-pipe with a 3" outlet made or whether I can get one of these off the shelf?

 

They are not harder to install. Also its about 10 more HP to go Duals. Just make the Y-Pipe after the cats into the 3in catback. Use 2.5 pipes going into the cats.

 

It makes sense that going from a single 2.5" cat to gual cats would give me an extra 10hp, but I thought a single 3" cat would do the same?

 

That's another reason why the 90-92 L98's made 245hp over the 87-89 except the G92 89. It made 240hp. The torque was up to 345 also. This was with the stock exhaust system. 2 1/4 pipes.

 

The question for me is which exhaust option will give me best bang for my buck.

Seems reasonable to expect that Flowtech headers and a full 3" system should give me more than 10hp?

I've got to replace the exhaust anyway so it seems sense to pay a bit more and pick up a few ponies.

 

I would at least buy a set of hedman headers. I think they are only like $40-50 more. ANyway, if you want to use the Flowtech,then they do make a Flowtech ypipe you can purchase also. Whenever you buy headers, make sure you buy the Matching ypipe made for them,but yes, you can expect at least 10 hp by installing the headers and a decent ypipe/exhaust. Maybe a tad bit more.

 

Depends on what you want to spend also. Do you wanna have to buy 2 catalytic converters? Are you willing to pay a shop to weld up your exhaust if needed? or do you want a plug and play system,you can put together yourself? http://www.summitracing.com/search/p...verter-y-pipes You may want to post the part numbers of your particular Flowtech headers and maybe you can get lucky and match up a ypipe that is made to bolt up to it.

 

The car is Right Hand Drive and Flowtech short headers fit with the least hassle.

Yes, I know they are not great, but they are the only practical option.

Thanks for the y-pipe link, I'm reading thru the options from Flowtech now but suspect I'll need a custom pip fabricated.

 

Who told you that? You should read some of the post on this site concerning Flowtech headers. Some people have had issues where things like bolt holes didn't line up properly with the heads,etc. The easiest headers to install IMO are the Edelbrock TES shorty headers. I did everything from the top! Didn't even have to remove the starter

 

The car is Right Hand Drive - so the steering box, shaft and column are on the right hand side.

The Flowtech headers sit a bit higher, clearing these components better.

 

There is almost always custom fabrication required when installing headers on these cars. Get your part number ready for your headers and look for a matching ypipe made for that part number.

 

Are there any published flow numbers comparing dual 2.25" cats to a single 3" cat?

 

Either way, it all turns into a single exhaust anyway when you get back toward the driveshaft.