Swapping in a 460 into my truck, I'm trying to decide on the exhaust size I need.

I'm guessing I'm around 400hp with the parts that I know are on it, could hit 500hp with a 750cfm carb.

Internally balanced
Roller rockers
Mild RV cam
D0VE heads
Performer intake
Fluidamper
Dura Spark ignition
iridium spark plugs
600 Edelbrock (had a 750 that was swapped to a 600 for mpg.)
Hedman headers


Truck is a 1956 F600, so this is all custom. No real room issues, pretty much a straight shot. Previous owner had 2.25" duals and an H pipe. Sounds absolutely beautiful. I thought they were too small but after researching them they seem to be spot on.

EDIT:

Now debating between 2.5" and 3" duals. Removed somethings to not add to all the exhaust misinformation out there.

 

Your a little optimistic to think a 600 CFM Edelbrock will give you 500HP.

Dual 2.5" or single 3". The dual 2.25" that was there previously would work fine too.

 

I should correct that, I did my math with switching back in a 750. Thanks for the catch.

Seems to be a lot around what's usable power, vs getting top end numbers.

After finding a few helpful formulas it would seem dual 3" is massive overkill, and overkill results in loosing torque where it's usable.
Dual 2.5"s works up to a little over 500hp, 2.25 duals work a little over 400hp.

What's interesting is peak torque seems to be better found from the dual 2.25", but still researching this out. Thanks for the help.

I did edit the first post, seems I should have spent another hour researching it before posting.

Couple things to help anyone researching it:
http://www.exhaustvideos.com/faq/how...pipe-diameter/
http://victorylibrary.com/mopar/header-tech-c.htm

 

After some more research the whole exhaust world has got to be half mis-information, or at least riddled with myths.


I've talked a bit with the gentleman who worked on my particular engine, it seems the timing was changed and the 600cfm was put on to be able to run it on standard gas. He said it really woke up and ran better before that change. Which I think with a 750cfm carb back on it I can expect to need a larger exhaust system.


For the record I'm not claiming any expertise on any of this, I don't have any direct experience and am just trying to work it out. This 460 is a whole lot more engine than anything else I've had before.

These guys ran some dyno tests that were pretty interesting. To sum them up, on a sub 400hp engine 2.5 and 3" full exhaust had no difference in power that was made or the power curve. On an engine that made 600 hp, 3" exhaust made more power than a 2.5".


So, based off that information it would seem that 2.5" might be ok for my build or it might leave a little on the table if I change things up down the line. I'm not really looking to use this truck as a race car, but it's always nice to know you have it. I recon it will be a long while though till I would put in a 750 carb though.


2.5" duals max out around 460hp according to the chart's and formulas I've found, so if I do upgrade down the line I may need to change up to a 3". Course how much validity there is to that I don't know, seeing as those guys just got 600 hp out of a set of 2.5". It might be worth while to go with 2.5" just to not be annoyingly loud.


I'll need to rethink my muffler choice. I'd like it to be fairly quite at idle and cruising, but loud at WOT. The mufflers that were on it look like they might have been Allied mufflers, they were 6" round with a 26.5" shell. I'm guessing worn fiberglass on the inside too to make them louder today than they were 10 years ago when they were installed.



Sorry for the back and forth, it's a bit of a process and a lot to bite off with the addition of the amount I'm doing to this build. Just rather get it correct the first time and not have to rebuy all of this stuff later.

Update:
Probably go with 2.5". I think 3" will be too loud and I won't benefit from them with the way I drive, also probably keep the 600 carb right now. The PO's truck was supposed to have 2.5" pipes as well, not sure why it had 2.25" in it.

 

All I can tell you is that with 2.25" exhaust on my pickup at about 4,000 rpm the vacuum gauge started rising from zero at wide open throttle so I went with 2.5" duals to the back and it stays at zero now until I lift off the throttle..

 

So, I'm in the process of making a shopping list to do this. Doesn't seem to be much of a price difference between 2.5" and 3", maybe like $100.

My truck has the room to fit anything. If it wasn't for a cross member about 3/4" in the way I could have a perfectly straight shot from the header to the tail pipe. My frame is about 9" tall as well.

Right now I'm planning on Magnaflow 12640 mufflers. They are straight through, center to center, 6X27" shell. The noise level I'm looking at is loud enough but not annoying. I'd like to be able to talk in the cab but I have a big block and I don't mind having to talk just a little bit over it, just don't want to yell. Maybe loud enough you can tell if I've turned onto the street from about a half mile if you're listening for it, but not so loud as you have no choice but to listen to it.


From what I've read 3" duals are a lot louder than 2.5" duals. However I have no experience with this.


Stick with 2.5" or go 3 duals?

 

If you are looking for a hp limiting size, forget about it unless you have aftermarket heads. For the sound you are looking for, the muffler will have as much influence as the pipe size will.

 

Single 3" with proper merge collector.

 

Internet fiction. A single 3" would be great for everything you need but you won't kill any torque by running 3" dual pipes (but it'll sound horrible).

 

Yeah I've recently discovered that, whole lot of misinformation out there. Let me edit that post so I'm not adding to it too, thanks for the catch.


At this point it's a matter of sound. I'm thinking 3" duals will not be ideal, no one seems to run them. I'd like to keep duals and use an H pipe, it's an older truck and I like the sound it makes.

Right now I'm trying to figure out what mufflers to use. The PO had 6x26.5" rounds on it, best I've been able to find out is they were welded ends and not a big name brand. They sounded pretty good, wouldn't mind slightly louder but not a lot, course they had been on their for 10 years and I don't want this truck to be too quite for several years.

It's between the Magnaflow 6x27" rounds (straight through) and maybe like a Cherry Bomb Vortex (but I don't know about the construction, not to be confused with Cherry Bomb glasspacks). Course open to anything. If it had the old Y-block in it I'd probably just get glasspacks.

 

No need to worry about killing off a little torque. There is plenty to spare. 3" duals will sound like every high school dumb*** just trying to be loud. I have single 3" which has a great rumble. Again, muffler choice makes a big difference

 

Yeah, high school dumb*** is exactly what I'm trying to avoid. I want a truck that is only talking when it has something to say.

It reminds me of the Ford GT when it had just come out. I was at a car show waiting for a Lamborghini Countach to take off since I loved that car growning up but never heard one in person. About that time a GT strolled by, it had a sound that made you wonder about it but not be annoyed, like you could simply sense it was a proper car. Then he floored it and it sounded like angry T-Rex charging into battle. Was probably the best sounding car I've ever heard, least it struck me as such at the time.

I'm trying to find something that's more fresh than muffled or held back, but not overly loud. Some character to it, it's a '56 pickup after all.

This video somewhat gets that across, but its with a 283 and thus sounds different than a Ford 460. Pretty sure he was using Mellowtone glasspacks.



I remember an old Jeep with a 350 and glasspacks, you could hear him 3 streets down. Think he was running Cherry Bombs, and recon different manufacturers might be a little less loud.


It's why I was thinking dual Magnaflows might be a good way to go, similar sound that I'm looking for but not too loud. I'll email them and see what they suggest, I'm sure I'll be the first person to ask them what exhaust I should buy, lol.

 

Tonight, I’m finding all kinds of stuff to read and ask questions about
I am currently cramming a 429 4v with a C6 into an asphalt full perimeter stock car chassis

 

Check your state laws on where you're dumping that exhaust.

Pickups with a single cab can get away with it being infront of the rear tire in most states, but dumping it behind the front tire might be illegal. The idea is the exhaust can get into the cab. Not to mention you'll go deaf.



Backpressure is important for motorcycle engines, not V8s. Not sure if I posted the video but the same guys who did the ones I posted above tested the backpressure issue out. They found there was nothing there but did notice that if you where straight piping if you had at least 18" of collector after the header it made a difference.

From what I've seen you can effect things by when and where you change pipe size. Basic rule seems to be when in doubt just keep it the same size as your header (dual).


Might have more luck in a fresh topic with pictures. This topic has gone pretty dead so not many people are reading through it anymore.

 

I went with dual 2.5 and an H-pipe. As well as two magnaflow #12640 mufflers. They're 6" round by 27". Very close to what the PO had but with no offset exit, and it was a perfect sound to me... but I wouldn't have minded things just a *pinch* louder, so I'm happy with the center exit.

Whole setup should be basically completely straight with no bends in the tubing. Got an amazing amount of clearance. Guess we'll see how that works out when I go to do it.


Thanks for the help.