2.25" exhaust limitations?

GoldOlds · May 30th, 2007, 02:29 PM

My '69 Cutlass has dual 2.25" exhaust that was installed less than a year ago. It was nicely done, all mandrel bending, no compression bends, with 40 series Flowmasters. I'd like more grunt under the hood than my mostly stock 350 rocket has. How much cam, compression, carb, hp, torque, etc. can an engine have and still breathe effectively through 2.25" exhaust? The factory manifolds will be replaced by headers, although I haven't picked any specific make/series yet. I'm still toying with the idea of plopping in a 455, but I'm not sure an engine that big can breathe through 2.25" with hardly any mods.
Thanks,

- GoldOlds

Huron · May 31st, 2007, 02:49 AM

Quote:

Originally Posted by GoldOlds

How much cam, compression, carb, hp, torque, etc. can an engine have and still breathe effectively through 2.25" exhaust? Thanks,

- GoldOlds

Hello GoldOlds,

I'd say that you could run a pretty healthy small block with 2.25" exhaust. It should be able to support an engine putting out 350+ horsepower. Most street small blocks are somewhat below that. If you have headers, 3.55:1 or more rear gear, 10:1 compression ratio, reworked heads, and a cam with more than 216 degrees duration @ .050" lift, then that is where I would start looking into backpressure issues. In summary though, 2.25" exhaust is probably more than enough for most street small blocks.

Huron

Pinner · May 31st, 2007, 09:35 AM

Your 2.25" exhaust will be just fine. Even for a big block motor. I'm finishing up a build on a 350 in my 85 Cutlass, 10.25:1,cam, head work, headers, 2.25" dual exhaust. If your interested I'll let you know how it runs.

GoldOlds · May 31st, 2007, 11:57 AM

Thanks, guys! That's just the sort of info I'm looking for. If I stick with the 350 route, I'll probably go with the Performer RPM, a cam similar to the .050" duration numbers Huron mentioned and some mild head work (porting to accomodate the 1.995/1.6?? valves). Compression won't likely exceed 9.5:1. My gear ratio is 3.73:1. I'm not sure exactly what I'll do for a carb; maybe have the Q-jet rebuilt. Maybe get the 670 Street Avenger I've been considering. The bottom line is I'd like to get the Cutlass into the 13s and at the same time have a VERY street friendly car. Pinner - yes, I'd DEFINITELY like to know how your combo turns out.

- GoldOlds

May 30th, 2007, 02:29 PM	#1 (permalink)
GoldOlds Senior Member Join Date: May 2007 Location: Chatham-Kent, Ontario Posts: 117	2.25" exhaust limitations? My '69 Cutlass has dual 2.25" exhaust that was installed less than a year ago. It was nicely done, all mandrel bending, no compression bends, with 40 series Flowmasters. I'd like more grunt under the hood than my mostly stock 350 rocket has. How much cam, compression, carb, hp, torque, etc. can an engine have and still breathe effectively through 2.25" exhaust? The factory manifolds will be replaced by headers, although I haven't picked any specific make/series yet. I'm still toying with the idea of plopping in a 455, but I'm not sure an engine that big can breathe through 2.25" with hardly any mods. Thanks, - GoldOlds

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May 31st, 2007, 09:35 AM	#3 (permalink)
Pinner Junior Member Join Date: Mar 2007 Posts: 13	Your 2.25" exhaust will be just fine. Even for a big block motor. I'm finishing up a build on a 350 in my 85 Cutlass, 10.25:1,cam, head work, headers, 2.25" dual exhaust. If your interested I'll let you know how it runs.

May 31st, 2007, 11:57 AM	#4 (permalink)
GoldOlds Senior Member Join Date: May 2007 Location: Chatham-Kent, Ontario Posts: 117	Thanks, guys! That's just the sort of info I'm looking for. If I stick with the 350 route, I'll probably go with the Performer RPM, a cam similar to the .050" duration numbers Huron mentioned and some mild head work (porting to accomodate the 1.995/1.6?? valves). Compression won't likely exceed 9.5:1. My gear ratio is 3.73:1. I'm not sure exactly what I'll do for a carb; maybe have the Q-jet rebuilt. Maybe get the 670 Street Avenger I've been considering. The bottom line is I'd like to get the Cutlass into the 13s and at the same time have a VERY street friendly car. Pinner - yes, I'd DEFINITELY like to know how your combo turns out. - GoldOlds