Dual exhaust question.

[Nick88]

I want to completely get rid of the factory 2.25 Y pipe. I don’t want to spend a whole bunch to get a 2.5 inch kit, but I have a ton of left over 3 inch exhaust piping. My question is, with a 1988 TBI 350, I know 3 inch duals is massive massive overkill, but if I use some 2 1/4 inch mufflers I also have laying around to choke it up, would that create more back pressure to keep from losing low end torque by using such large pipes as duals. My plan is to run it back and put an H pipe probably around the bell housing, then put the 2 1/4 inch mufflers out to 45 degree dumps in front of the rear wheels, I believe they are 2 chamber mufflers. Just want to know if it would be wayyy too much even choked down because I have it laying around and just don’t want to dish out over $100 bucks to weld up some 2.5 or 2.25 pipe when I have some slightly larger and meaner looking pipe laying in the yard. Any help is appreciated.

 

[454C2500Longbed]

I want to completely get rid of the factory 2.25 Y pipe. I don’t want to spend a whole bunch to get a 2.5 inch kit, but I have a ton of left over 3 inch exhaust piping. My question is, with a 1988 TBI 350, I know 3 inch duals is massive massive overkill, but if I use some 2 1/4 inch mufflers I also have laying around to choke it up, would that create more back pressure to keep from losing low end torque by using such large pipes as duals. My plan is to run it back and put an H pipe probably around the bell housing, then put the 2 1/4 inch mufflers out to 45 degree dumps in front of the rear wheels, I believe they are 2 chamber mufflers. Just want to know if it would be wayyy too much even choked down because I have it laying around and just don’t want to dish out over $100 bucks to weld up some 2.5 or 2.25 pipe when I have some slightly larger and meaner looking pipe laying in the yard. Any help is appreciated.

3 inch is certainly overkill, it would slightly reduce the scavenging effectiveness, being a lower output motor. However, you're also not going to have any noticeable effects. Also, backpressure is bad and kills both horsepower and torque. The only thing that more backpressure does is kill midrange and high end power, leaving you with the illusion that it has more low end. Choking 3" down to 2 1/4" is no small potatoes though, that'd be a hell of an adapter. Choking an engine is never a good thing when you're seeking power, but if that's what you got laying around and you want to put it together, go for it.

 

[Nick88]

3 inch is certainly overkill, it would slightly reduce the scavenging effectiveness, being a lower output motor. However, you're also not going to have any noticeable effects. Also, backpressure is bad and kills both horsepower and torque. The only thing that more backpressure does is kill midrange and high end power, leaving you with the illusion that it has more low end. Choking 3" down to 2 1/4" is no small potatoes though, that'd be a hell of an adapter. Choking an engine is never a good thing when you're seeking power, but if that's what you got laying around and you want to put it together, go for it.

I get that back pressure is bad in any circumstance, I should’ve worded it better, I was more saying add them to almost simulate a 2.25 system with bigger pipe by using a smaller muffler by changing the flow rate in a way.

 

[Erik the Awful]

I'm running a 2.5" dual exhaust on my 350, and I have a pretty good sized cam in it. I wouldn't worry about a 2.25" exhaust on a 305 if you put an x-pipe on it with some decent mufflers.

And that's the rub. The mufflers are going to be your restriction. If you go with mufflers that aren't a restriction, it's going to be loud. If you can find the Engine Masters episode where they did their cheap muffler shootout, it's very eye-opening. "Turbo" mufflers killed about 60 hp on a 600 hp engine. Chambered mufflers were just a little better. The mufflers that you can see straight through did the best, killing less than 20 hp, but they do almost nothing for the noise level. I'm running Cherry Bomb Salutes, and they're loud. NOTE: The YouTube version of that video is pretty hacked up and doesn't show all the numbers. I had MotorTrendOnDemand and was able to see all the numbers to build a spreadsheet to compare performance versus noise.

Muffler​	HP​	DB @ idle​	DB @ Peak​
Summit Turbo​	546.4​	64.8​	91.1​
Summit Welded​	545.6​	63.4​	90.6​
Walker Turbo​	540.4​	64.5​	89.3​
Cherry Bomb Turbo​	538.9​	61.9​	87.4​
Hush Thrush​	530.3​	63.3​	87.6​
Thrush Turbo​	529.6​	62.3​	88.3​
Cherry Bomb Pro​	548.6​	66.3​	95.3​
Rumble Welded Chambered​	546​	65.1​	96.4​
Summit Two Chamber​	544.1​	67.3​	91.6​
Thrush Welded Chambered​	542​	67.5​	92.6​
Cherry Bomb Salute​	605.1​	​	97.8​
Open Header​	607​	​	​

 

[95burban]

Yes it’s overkill but it will work, I’ve done it a few times because I didn’t want to redo the exhaust at a later date. I always wanted to do 4in single exhaust like the mufflex system for f body cars.

 

[Nick88]

I ended up doing it today, ran an adapter off the 2.25 pipe coming out the manifolds to a 3 inch pipe on either side back to a huge h pipe behind the transfer case right before the mufflers, then after the mufflers a couple 90s on either side doing dumps right in front of the back tires, hopefully that way I wont get any pesky exhaust fumes in the cab with my back window down. Sounds super good, the random mufflers I had laying around made it much quieter, even though ive been told its still super loud, I guess I just got used to the volume of a exhaust cutout with a rotted out muffler.

 

[Schurkey]

Perhaps a moderator will move this thread to the "Exhaust" sub-forum.

 

[Nick88]

Perhaps a moderator will move this thread to the "Exhaust" sub-forum.

Sorry about that, didnt know there was an exhaust sub forum- Im still new here