Factory exhaust

[Rusty_S85]

On the OE exhaust layout for these trucks the 2 1/2" Y pipe to a single round muffler to a 2 1/4" tail pipe. I wanted to ask what does everyone here think the capability of this exhaust layout is power wise?

I had intended to keep the OE layout minus converters and running shorty headers but I have many telling me that this OE layout will not support over 250 hp even though I remember reading years ago it was capable of handling up to 400 hp up to 5,500 rpm for a 302 displacement. Now I am second guessing myself if I just spent a bunch of money on exhaust components that I probably shouldnt use now as it wont meet my 300 - 350 hp goals.

[Angelo Voltura]

On the OE exhaust layout for these trucks the 2 1/2" Y pipe to a single round muffler to a 2 1/4" tail pipe. I wanted to ask what does everyone here think the capability of this exhaust layout is power wise?

I had intended to keep the OE layout minus converters and running shorty headers but I have many telling me that this OE layout will not support over 250 hp even though I remember reading years ago it was capable of handling up to 400 hp up to 5,500 rpm for a 302 displacement. Now I am second guessing myself if I just spent a bunch of money on exhaust components that I probably shouldnt use now as it wont meet my 300 - 350 hp goals.

It'll be just fine. Pipe size is really relative...the effects of scavenging and velocity are far more important. Obviously you don't want to strangle a 500hp engine with a 1.5" pipe and a 3" pipe is mega overkill on a 150hp engine.

The way I look at it is this, and this comes from a friend who has 30+ years of engine building and dyno experience. 150-250hp, 2" pipe. 300-375hp, 2 1/4", 400-600hp 2 1/2". Anything past that point run a 3" and really you don't need much more than 3" pipe for almost any horsepower level after that.

[Rusty_S85]

On the OE exhaust layout for these trucks the 2 1/2" Y pipe to a single round muffler to a 2 1/4" tail pipe. I wanted to ask what does everyone here think the capability of this exhaust layout is power wise?

I had intended to keep the OE layout minus converters and running shorty headers but I have many telling me that this OE layout will not support over 250 hp even though I remember reading years ago it was capable of handling up to 400 hp up to 5,500 rpm for a 302 displacement. Now I am second guessing myself if I just spent a bunch of money on exhaust components that I probably shouldnt use now as it wont meet my 300 - 350 hp goals.

It'll be just fine. Pipe size is really relative...the effects of scavenging and velocity are far more important. Obviously you don't want to strangle a 500hp engine with a 1.5" pipe and a 3" pipe is mega overkill on a 150hp engine.

The way I look at it is this, and this comes from a friend who has 30+ years of engine building and dyno experience. 150-250hp, 2" pipe. 300-375hp, 2 1/4", 400-600hp 2 1/2". Anything past that point run a 3" and really you don't need much more than 3" pipe for almost any horsepower level after that.

Thats what I figured but I saw it mentioned and I did some reading and its like for single exhaust 2 1/2" is only good for 245hp at most and for 300hp you need 3" single and I am like I dont believe that cause single 3" is equal to dual exhaust in 2 1/2" and I know many muscle cars making 350 - 400 hp with 2 1/4" dual exhaust which is smaller than single 3" exhaust.

But with everything online it seems like its all stating I should be running 3" and it has me a little concerned I might be choking my engine down when I throw this on as Im going to be running hedman shorty street headers with OE ball flange with OE 2 1/2" Y pipe with a straight 2 1/2" pipe ending in a 2 1/2" to 2 1/4" reducer to a magnaflow XL 3 chamber 6" round muffler and then the OE mandrel bent tail pipe in 2 1/4".

If need be I could always opt out of the 2 1/4" and have someone mandrel bend me the tail pipe using what I have as a pattern in 2 1/2" and then buy a new magnaflow 6" round muffler in 2 1/2" and run it all in 2 1/2" but I didnt think the 2 1/4" tail pipe would be that big of a restriction that far after the motor in the exhaust system.

[Rembrant]

Thats what I figured but I saw it mentioned and I did some reading and its like for single exhaust 2 1/2" is only good for 245hp at most and for 300hp you need 3" single and I am like I dont believe that cause single 3" is equal to dual exhaust in 2 1/2" and I know many muscle cars making 350 - 400 hp with 2 1/4" dual exhaust which is smaller than single 3" exhaust.

But with everything online it seems like its all stating I should be running 3" and it has me a little concerned I might be choking my engine down when I throw this on as Im going to be running hedman shorty street headers with OE ball flange with OE 2 1/2" Y pipe with a straight 2 1/2" pipe ending in a 2 1/2" to 2 1/4" reducer to a magnaflow XL 3 chamber 6" round muffler and then the OE mandrel bent tail pipe in 2 1/4".

If need be I could always opt out of the 2 1/4" and have someone mandrel bend me the tail pipe using what I have as a pattern in 2 1/2" and then buy a new magnaflow 6" round muffler in 2 1/2" and run it all in 2 1/2" but I didnt think the 2 1/4" tail pipe would be that big of a restriction that far after the motor in the exhaust system.

How often do you plan to be running at 5500 RPM? That's where your 300-350HP is.

I remember going through all of these thoughts and calculations, and had originally planned on 2 1/2" duals for my 300HP 302. I ended up with BBK shorty headers, 2 1/4" full duals, with Magnflow mufflers with an "H" pipe just in front of the mufflers. When I talked to the muffler shop that built this exhaust for me, I remember him saying that 2 1/2" exhaust was overkill and that there were trucks out there more powerful than mine running 2 1/4" exhaust.

I know a lot of guys don't like shorty headers, but I really didn't want to screw around with long tubes on this truck. My exhaust is all run in the stock locations with the exception of a driver's side exit for one of the duals. The BBK's are chrome (and still look good thousands of miles later) and they have 1 5/8" primaries (I think?).

 

[Rusty_S85]

How often do you plan to be running at 5500 RPM? That's where your 300-350HP is.

I remember going through all of these thoughts and calculations, and had originally planned on 2 1/2" duals for my 300HP 302. I ended up with BBK shorty headers, 2 1/4" full duals, with Magnflow mufflers with an "H" pipe just in front of the mufflers. When I talked to the muffler shop that built this exhaust for me, I remember him saying that 2 1/2" exhaust was overkill and that there were trucks out there more powerful than mine running 2 1/4" exhaust.

I know a lot of guys don't like shorty headers, but I really didn't want to screw around with long tubes on this truck. My exhaust is all run in the stock locations with the exception of a driver's side exit for one of the duals. The BBK's are chrome (and still look good thousands of miles later) and they have 1 5/8" primaries (I think?).

Thats my thing most of my driving will be freeway driving and if I need to pass someone at 75 mph the rpm will shoot up there when I nail the throttle. Thats why I am wanting to make sure I am going the right way about this cause I am going single exhaust, I dont want the added expense of dual exhaust and then having to route exhaust from driverside to passengerside the back to driverside as I would want the tail pipes to come out behind the tires on each side if I had dual exhaust.

I will be using my hedman headers which are 89470 part number which is a 1 1/2" primary tube shorty street header with a 3" OE flange collector. From here my plan can change cause Bassani makes a offroad Y pipe that I have to get confirmation on but I believe it will fit the OE flange as this Y pipe is for 86-95 and my header is 86 - 96. But if its mandrel bent with no joints on the Y pipe except from after the Y then I can consider this as an option as from the way I understand the description it is 2 1/4" tubes before the Y then when the left and right banks merge at the Y it comes out of the Y as a 3" pipe. I also found that Magnaflow makes the same muffler I bought but slightly larger for a 3" inlet/outlet pipe. This would mean I would have to source a local shop that can do mandrel bending of exhaust that can use my 2 1/2" replacement tail pipe as a pattern to bend me a 3" pipe and remove the mount from the 2 1/2" and attach it to the 3" then I can simply assemble the exhaust myself.

From the charts I found it appears 3" single exhaust is good for 300hp. But my motor based off other similar builds and DD2000, I should be in the neighborhood of 375 - 385 hp which I am hopeful 3" single exhaust with the large 7" round muffler would flow enough to support it.

I do still need to source the Y pipe as I want a new mandrel bent Y pipe and I am still on the hunt for a Magnaflow one before they started adding precats to them. Since I havent found and bought a Y pipe yet I can easily spend $350 on the Bassani Y pipe and run 3" single exhaust all the way to the back of the truck.

[ArdWrknTrk]

Thats my thing most of my driving will be freeway driving and if I need to pass someone at 75 mph the rpm will shoot up there when I nail the throttle. Thats why I am wanting to make sure I am going the right way about this cause I am going single exhaust, I dont want the added expense of dual exhaust and then having to route exhaust from driverside to passengerside the back to driverside as I would want the tail pipes to come out behind the tires on each side if I had dual exhaust.

I will be using my hedman headers which are 89470 part number which is a 1 1/2" primary tube shorty street header with a 3" OE flange collector. From here my plan can change cause Bassani makes a offroad Y pipe that I have to get confirmation on but I believe it will fit the OE flange as this Y pipe is for 86-95 and my header is 86 - 96. But if its mandrel bent with no joints on the Y pipe except from after the Y then I can consider this as an option as from the way I understand the description it is 2 1/4" tubes before the Y then when the left and right banks merge at the Y it comes out of the Y as a 3" pipe. I also found that Magnaflow makes the same muffler I bought but slightly larger for a 3" inlet/outlet pipe. This would mean I would have to source a local shop that can do mandrel bending of exhaust that can use my 2 1/2" replacement tail pipe as a pattern to bend me a 3" pipe and remove the mount from the 2 1/2" and attach it to the 3" then I can simply assemble the exhaust myself.

From the charts I found it appears 3" single exhaust is good for 300hp. But my motor based off other similar builds and DD2000, I should be in the neighborhood of 375 - 385 hp which I am hopeful 3" single exhaust with the large 7" round muffler would flow enough to support it.

I do still need to source the Y pipe as I want a new mandrel bent Y pipe and I am still on the hunt for a Magnaflow one before they started adding precats to them. Since I havent found and bought a Y pipe yet I can easily spend $350 on the Bassani Y pipe and run 3" single exhaust all the way to the back of the truck.

Rusty, I wouldn't go crazy looking for mandrel bent tubes especially if you end up at 3".

Gary got a beautiful press bent exhaust made up at a local shop.

If you haven't seen it (and the commentary leading up to it) it's worth going back in Big Blue's thread to have a look.

And, I'm 100% with Cory.

If you don't drive it at 5,000 rpm all the time you're WAY better off to keep volume down and velocity up than to lose all that heat and scavenging under 85% of your driving.

If it was a strip car that you could drive to the track I would feel the other way.

[Jacob84]

Rusty, I wouldn't go crazy looking for mandrel bent tubes especially if you end up at 3".

Gary got a beautiful press bent exhaust made up at a local shop.

If you haven't seen it (and the commentary leading up to it) it's worth going back in Big Blue's thread to have a look.

And, I'm 100% with Cory.

If you don't drive it at 5,000 rpm all the time you're WAY better off to keep volume down and velocity up than to lose all that heat and scavenging under 85% of your driving.

If it was a strip car that you could drive to the track I would feel the other way.

If it makes you feel better about it Rusty, I went to my exhaust guy wanting a single 3 inch exhaust to make sure I wasn’t wasting any power and he told me it wouldn’t do any good. He said the only way he’d recommend that is if I had a turbo. I’d have no issue running a 400 horse motor with a single 2.5 inch exhaust. 600 horse? Sure I’d get a 3 inch

I’ve got 2 inch pipes from each manifold to a y. Then a single 2.5 to an xcelerator (magnaflow offbrand) muffler and 2.5 inch tail pipe. It’s not mandrel bent either. Got real good torque and I’m not missing out on anything up high. I get much more excited about low and midrange torque than I do about total hp. Torque is a lot more fun when you’ve got 33s and stock gears

[Rusty_S85]

Rusty, I wouldn't go crazy looking for mandrel bent tubes especially if you end up at 3".

Gary got a beautiful press bent exhaust made up at a local shop.

If you haven't seen it (and the commentary leading up to it) it's worth going back in Big Blue's thread to have a look.

And, I'm 100% with Cory.

If you don't drive it at 5,000 rpm all the time you're WAY better off to keep volume down and velocity up than to lose all that heat and scavenging under 85% of your driving.

If it was a strip car that you could drive to the track I would feel the other way.

Ill take a look at the exhaust, I dont want to have the local shops here do it cause Ive seen how they do the hangers and I just know the shop is going to attach the hanger to the bed instead of my frame. If I go with 3" I figured why not go mandrel bent but as of now I am not sure. I am on the fence and trying to figure what to do. I just dont want to choke the engine down because I will be having the truck dynotuned once I get the engine finished.

Seems like online all the charts list 3" exhaust for 300 - 400 hp but then reading forums there are posts like what was presented here about 2 1/2" being perfectly fine for single exhaust for a 302 that is stock or mildly built.

[ArdWrknTrk]

If it makes you feel better about it Rusty, I went to my exhaust guy wanting a single 3 inch exhaust to make sure I wasn’t wasting any power and he told me it wouldn’t do any good. He said the only way he’d recommend that is if I had a turbo. I’d have no issue running a 400 horse motor with a single 2.5 inch exhaust. 600 horse? Sure I’d get a 3 inch

I’ve got 2 inch pipes from each manifold to a y. Then a single 2.5 to an xcelerator (magnaflow offbrand) muffler and 2.5 inch tail pipe. It’s not mandrel bent either. Got real good torque and I’m not missing out on anything up high. I get much more excited about low and midrange torque than I do about total hp. Torque is a lot more fun when you’ve got 33s and stock gears

I've got original stock headpipes (2 1/2") going to a welded muffler 8" dia X 40" long, single 3" out behind the right hand tire.

There's no restriction in my system and the stock sizes seem to work fine.

It would be interesting to compare CFM between a 460 and a 351 or 302.

I may just do that across the rev range.

[Rusty_S85]

If it makes you feel better about it Rusty, I went to my exhaust guy wanting a single 3 inch exhaust to make sure I wasn’t wasting any power and he told me it wouldn’t do any good. He said the only way he’d recommend that is if I had a turbo. I’d have no issue running a 400 horse motor with a single 2.5 inch exhaust. 600 horse? Sure I’d get a 3 inch

I’ve got 2 inch pipes from each manifold to a y. Then a single 2.5 to an xcelerator (magnaflow offbrand) muffler and 2.5 inch tail pipe. It’s not mandrel bent either. Got real good torque and I’m not missing out on anything up high. I get much more excited about low and midrange torque than I do about total hp. Torque is a lot more fun when you’ve got 33s and stock gears

So you have 2 1/2" single all the way out back, I wonder how it would work with mine as my muffler is 2 1/4" to fit my 2 1/4" tail pipe. My plan was to do it like Ford did it with 2 1/2" to the muffler then 2 1/4" from the muffler back. I could toss the magnaflow 2 1/4" muffler and buy a 2 1/2" and find a shop that can bend me a 2 1/2" tail pipe using my 2 1/4" as a pattern and to rob the hanger off of.

For me most of my driving will be idle to 3,000 rpm. Highway driving will be a lot of my driving and I will be between 2,500 and 3,000 rpm for highway driving. The only reason I was thinking on this is cause I dont want to choke my 306 down when I nail the throttle at 2,750 rpm for example at highway speed to pass and the rpms shoot up to 4,000 and I just lack power.

Currently I have a 2 1/4" tail pipe that is not mandrel bent I thought it was but when I looked closer noticed its just a really nice traditional bent pipe without the ribs on the inside bend but a smooth radius.

Muffler I currently have is the 13645 Magnaflow XL 3chamber 6" round offset/offset in 2 1/4". I can go up to 2 1/2" or even 3" but would require going a different route with my tailpipe.