Exhaust question/opinion

[sleazy rider]

i bought my 91 zr-1 from the original owner in jan 2020. during his ownership of this car he had taken it to lingenfelter for the 475 hp package and then later shipped the engine to him for lingenfelter's 368 cid 530 hp package. now that i own the car, #1299, i procured a set of stainless works 2" headers with 3" collectors thru the zr-1 registry. also included were 3" cats and 3" mid pipes and had everything jet hot coated. i also bought a 3" internal 'x' resonator which leads me to this question. coming out of the resonator should i:
1. finish out with 3" exhaust to the mufflers which are 2 1/2" borlas
2. finish out with necking down from the 3" to 2 1/2" from the resonators to the mufflers
the muffler shop can get either size tubing to do the job but had no input on which size tubing i should go with for an efficient exhaust.
what is your experience or opinion?
thanks

[HAWAIIZR-1]

I would go with option 1 and replace the Borlas with a 3? inlet mufflers of your choice. If you really like the sound and look of the Borlas then keep them. JMHO.


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[Corvette95]

You need to consider drone, can you live with it or not...then go from there. Your X-pipe and mufflers will determine this. I also added heat shielding under the driver and passenger footwells and tunnel. It will be hotter with the new exhaust. I also fabbed an extra set of factory heat shield to work with the new headers. I also wrapped all the wiring near the exhaust with DEI thermal shielding. Also, I used OBX headers, with custom extensions to customer dual straight resonator and then to Borla mufflers (which are the best flowing muffler (per Marc H website - Gen1 Borla not full Borla which is restrictive) and I am very happy with sound and no drone. You will need an oil dipstick relocater bracket. All this is assuming it has stock headers on it now. Also, you may need to dimple front header on the drivers side to clear steering shaft, you have the best shot at now having to do this with the works headers. Post some more pics of your project, looks interesting.

[XfireZ51]

Depends on what your preference is. If u are looking to maximize power, then first make sure ur resonator maintains a ?true dual? configuration. Resonators w internal Xpipes sometimes are actually a Y, ala MagnaFlow. Then make sure ur 3? pipe enters a muffler w a 3? inlet rather than necking down to 2 1/2?.
Some of us have incorporated the C6 NPP valves and tips on mufflers for exhaust note control rather than use a resonator.

[Karl]

I would go 3" all the way to the muffler. If you must then option 1 for now.

I believe the 530hp was with the factory manifolds on.

There is a lot left in that 368 as this person found out.

http://zr1.net/forum/showthread.php?t=32002

[Paul Workman]

REVERSION is the issue when the 3" hits the 2-1/2 Borlas (or Magnaflow mufflers too). Ask Dominic what those true 3" mufflers are (I don't recall), but they sound very good, and a few ponies (10-25?) more might be had with them. I would definately want to delete those Borlas tho!

If DRONE is an issue, then the Corsa route is the way to go. And, (IIRC) Marc Haibeck reported some HP boost compared to the 3" system with the 2-7/8"(?) dual resonator/muffler Corsa system. (You'd wanna verify spec w/ Mark tho!)