Thread: Exhaust question

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I got a '78 chevy pickup 4x4 350 headers, the exhaust I have on the truck now it 2.25 pipe from the headers back to glasspacks then turned out in front of the wheels, somebody told me that if I put a x pipe in it and maybe a different muffler that it would improve my horsepower and low end torque, if so how much would it help

Originally Posted by 1978chevy

I got a '78 chevy pickup 4x4 350 headers, the exhaust I have on the truck now it 2.25 pipe from the headers back to glasspacks then turned out in front of the wheels, somebody told me that if I put a x pipe in it and maybe a different muffler that it would improve my horsepower and low end torque, if so how much would it help

Not nearly as much as you will by dropping in a BBC!! From what I see in a quick Google search (X-pipe torque increase) you might get seven to ten HP, and two to three ftlbs of torque - not enough to feel the difference, likely.

I'd like to put a big block in it but from what I heard your lucky if they get 10 mpg, and I drive this truck on a daily basis so it would break me up in gas

if you build sbc with a lot of torque you'll be getting maybe 10 mpg nothing is free

Originally Posted by 1978chevy

I got a '78 chevy pickup 4x4 350 headers, the exhaust I have on the truck now it 2.25 pipe from the headers back to glasspacks then turned out in front of the wheels, somebody told me that if I put a x pipe in it and maybe a different muffler that it would improve my horsepower and low end torque, if so how much would it help

It might help, but nothing you would even notice unless you did a before and after pull on a chassis dyno.......

I'm not talking bout making alot of torque I was wanting to help it alittle

I've had heard/seen charts showing up to 25HP/25 Ft Lbs Torque increase. That being said those claims came from the manufacture of the different system and the comparison was usually against a restrictive stock exhaust system, other tuning was done, or additional components (headers) were added to the vehicle.

I’ve done H and X pipe installs over the years and my experience is pretty much like Roger indicated, while there might have been an improvement it was not enough to feel.

I understand you wanting fuel mileage and power for towing but at some point it’s going to be a compromise of one for the other, it will depend on what is more important to you.

Staying with the small block or going to a big block I would suggest you start by throw your notions about 400-450 HP away and start your figuring from a different viewpoint. Horsepower is just a number derived from torque and RPM. The higher you can wind an engine the more the HP it will have, but what good is 400HP at 6500 RPM if you’re trying to tow something at 2800 RPM where you’re only making 150HP. Torque is the measurement of force applied and is where you need to place you’re emphasis at (in the RPM range you will be operating).

As towing is an important consideration, first look at the RPM that most of your towing is taking place. That is where the engine will be working and you want it to be the most efficient at. Start looking at the combination of components make that make most torque in that RPM range.

on the exhaust there is alot of claims on how much Hp and Tq you will see after building some your not going to see alot less your stock exhaust is way off on size and very bad mufflers . many of claims have to do with selling you some thing new . from sbc to bbc you could build a 400 small block that could make good Tq but hard to beat a BBC .the 400sbc can work good for you if your looking for a EZ swap i have a new SHP 400 dart short block that would work out as a very nice start to a 400 sbc but for about the same price i can build a long block bbc and get 68 to 96 CID EZ over the 400 sbc

Holy crow guys!!.I am almost embarrass to have built a 383.Is this BBC month??.

Pat,Richard and me did a on line dyno build sheet on what is a peanut 383 to come up with 480 lbs of torque at only 3500 RPM.And Pat commented that could reach alittle over 500 lbs if I wanted to really get after it.Certainly well over 400 lbs off idle.Those are respectable numbers guys without the gas penalty of a BBC.

Once done,I fully intend to put a tune on it to get high teens-lower twenties in gas mileage.

In terms of headers-I totally agree with what you guys posted.

Yep thats correct but the added MPG and smoothness is welcome too, I like to fit them where possible. To determine where they fit spray some aerosol paint on the header and where it burns off is where the crossover should be.

Good advice there

Originally Posted by 1gary

Once done,I fully intend to put a tune on it to get high teens-lower twenties in gas mileage.

I hope you get there, Gary, but the best I've seen on my 347 stroker cranking about 475ftlbs of torque is 17mpg, and that's in a nominal 2400 pound fiberglass highboy coupe just tooling around the countryside. I'm hoping for more with a newly revised spark map, but if you're planning low twenties in an AstroVan I should be getting thirty or better!!

Roger-friend of mine with a 355 and a very early Edelbrock EFI soft peddling threw the mountains in Calli towing his sand rail and trailer in a Astro gets 22 mpg.No B.S.

I think,no I know for me,it is tons harder to keep that hot rodder in me in check using that knowledge combined with intended use and build a engine for that.Sure anyone knows a BBC puts out more.Would I ever use that much more??.Nope don't think so.Coming from a 4.3 to the 383 will put tears of joy on this old hot rodders face and a seriously doubt it will let me down for what I want it to do.

My point here is if a O/P comes on the forum and says he wants help with a SBC,we should help him with that because he make the decision he wants a SBC.Really not tell him to throw out what he has and start over so he leaves not getting the answer he wanted.I am just saying..........