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Exhaust Modification



Stan. I am taking my 88 Callaway twin turbo to my speed shop next week and I am having the 2 small cats removed and straight pipes installed. I am also removing the factory cat and replacing it with a walker dynamax free flow cat.The mufflers will also be replaced with dynamax polished stainless steel mufflers to increase the overall flow and add some horsepower. I imagine the horsepower should be at around 405 after the modifications instead of the current 382. Also thanks for some of the tips you gave me over the phhone last night.
Best regards,
Lou Bellera
how many cats did an 88 have?

By the sound of your post, you are sayin your Callaway has 3 Cats??? how many should each (year) have from Callaway? Including the Callaway (recalled) 88 exhaust...
Thanks In advance! *89x2*
Don't know about the '88 but the '87 comes with a pre-cat in each side of the y-pipe coming off the exhaust manifold. I know they were discontinued in later years but am not sure which year. I didn't realize, though, that they started adding mufflers to the exhuast. Were mufflers stock on TT's in '88 and after?

I did the same mods...replaced the y with no precat model and replaced the cat with a Random Tech high flow cat. Mine does not have any mufflers. I can tell you the bark will become deeper...I can still remember hearing it start the first time and wondering "is that my car?" At low rpms it sounds even more like a boat motor but from 2200 and up it sounds too cool. I believe I gained more low end torque but lost high end HP. I didn't have before #s but after mods I hit 284.5 hp at the wheels and 436 ft lb torque. GM uses 16% loss for 4+3 I believe so that puts crank #s at 339hp and 519 ft lb torque.

It would be interesting to see before and after #s for your car!
88 exhaust mufflers

I was talking about removing the small cats located near the front of the car, and replacing the main cat with a flow through type. As far as exhausts goes my car is an early production model that had to be recalled because the exhaust system callaway installed was deemed street illegal because callawy didn't register the system with the EPA. However the replacement system included the standard factory exhausts system that the regular Vettes had including the stock mufflers.
Lou Bellera
My '90 has a 3 piece 2.5" OD Y-Pipe up front with no pre-cats. There is one large central 3" cat that happens to bolt in and out very quickly and easily.

By freeing up back pressure I would expect horsepower to rise but torque to possible drop... not the other way around.

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