Fabricating And Installing An H-Pipe

[toobroketoretire]

A couple of weeks ago I decided to fabricate and install an h-pipe on my big block '71 to quiet the exhaust noise down a bit. Dual exhaust is certainly better than a single exhaust for larger engines operating at higher rpm's but the uneven firing impulses of our American V8's still present a problem. You see, our V8 engines have their troublesome 8/4 and 5/7 cylinders firing only 90 degrees apart and the slug of exhaust gas from the first cylinder to fire interferes with the slug of exhaust gas from the cylinder after it. By installing an h-pipe some of the pressure from the first cylinder is bled off into the other exhaust pipe so the next cylinder's exhaust blows out a bit easier. Because the pressures are highest AT the engine the best place to install an h-pipe is as close to the engine as possible. As I'm not running the noise reduction cover under my torque converter (aka dust cover) I chose to install my h-pipe right behind my torque converter where it would do the most good. After the installation my exhaust was about 25% quieter and it appears I gained a tiny bit of power and fuel mileage. To be able to clear the bottom of my torque converter I designed my h-pipe using 5 angle-cut pieces to achieve a 3/4" dropped center which gave it about 3/8" of clearance.

 

[Tom Bryant]

That sounds about right. There was an article in either Hot Rod or Car Craft around a year ago comparing an H pipe to a X pipe. Both were mounted in the most common location, just to the rear of the transmission, and everything else was the same. If I remember correctly the H pipe produced around 3-5 pounds of torque more than the X pipe. I'm not totally sure why that would be unless blowing both sides into a X would briefly cause a restriction where a H would just allow excess pressure to move from side to side as needed.

Your theory of moving the pipe forward is similar to what Chevy did with the C1 high performance engines, as well as the higher performance V8 passenger car engines in the '50s. That was to place a crossover pipe between the 2 banks just a few inches below the exhaust manifold flange which definitely produced a smoother sound. Guys would cap off or use pipes from a standard 283 with duals to make their glass packs louder, never knowing they were giving up low to mid range torque.

Tom

 

[toobroketoretire]

That sounds about right. There was an article in either Hot Rod or Car Craft around a year ago comparing an H pipe to a X pipe. Both were mounted in the most common location, just to the rear of the transmission, and everything else was the same. If I remember correctly the H pipe produced around 3-5 pounds of torque more than the X pipe. I'm not totally sure why that would be unless blowing both sides into a X would briefly cause a restriction where a H would just allow excess pressure to move from side to side as needed.

Your theory of moving the pipe forward is similar to what Chevy did with the C1 high performance engines, as well as the higher performance V8 passenger car engines in the '50s. That was to place a crossover pipe between the 2 banks just a few inches below the exhaust manifold flange which definitely produced a smoother sound. Guys would cap off or use pipes from a standard 283 with duals to make their glass packs louder, never knowing they were giving up low to mid range torque.

Tom

The 1950's Ford 272" V8's used a cross over pipe at the front of the engine (over the thermostat) but many people got severely burned by that HOT pipe (including me). The idea is to bleed off the pressure pulse of cylinders #8 and #5 (Chevrolet V8's) so the Cylinders #4 and #7 could blow out a bit easier. An h-pipe does make the exhaust note more mellow and that's why I did it. The Ferrari V8's use a 180 degree "flat" crankshaft that gives a left right left right left right left right firing order and that's why their exhaust note is so smooth. But flat crankshafts have to be fully counter weighted which means they weigh a lot more and cost more to produce than our American "twist" crankshafts that are twisted 180 degrees after the forging process.

 

[Tom Bryant]

Oh yes, I remember those 272 Fords. Exhaust would exit the front of the left manifold, go over the top of the engine at the front and into the front of the right manifold. All 8 cylinders passed through the right manifold before exiting out the pipe. It was hard to believe, even back then, that they would do that. Duals really helped those cars.

Tom

 

[toobroketoretire]

Oh yes, I remember those 272 Fords. Exhaust would exit the front of the left manifold, go over the top of the engine at the front and into the front of the right manifold. All 8 cylinders passed through the right manifold before exiting out the pipe. It was hard to believe, even back then, that they would do that. Duals really helped those cars.

Tom

My ex brother-in-law showed up at my house many years ago with his mid 50's Ford pickup and had some kind of problem with his 272" engine. I popped the hood open and without thinking leaned my whole forearm against the top of that pipe and my skin literally melted off in a 2" X 6" sheet. I'm sure others have done the same thing and I'm sure that is why Ford quit doing that.

 

[kpic]

Although, it can be "calculated" using CFD (Computational Fluid Dynamics CFD Software - Creating Computational Fluid Dynamics Simulations ) software. However, from what I've gathered as close as you can get it to the exhaust ports is best and also use the same diameter pipe as the exhaust or it's a waste of time.

 

[Mac]

My ex brother-in-law showed up at my house many years ago with his mid 50's Ford pickup and had some kind of problem with his 272" engine. I popped the hood open and without thinking leaned my whole forearm against the top of that pipe and my skin literally melted off in a 2" X 6" sheet. I'm sure others have done the same thing and I'm sure that is why Ford quit doing that.

Not completely… I had a 1988 Ford F150 with the 5.0l engine. It had a small EGR pipe which got plenty hot but it wasn't big enough to act as an H-pipe.

Mac

 

[toobroketoretire]

Not completely… I had a 1988 Ford F150 with the 5.0l engine. It had a small EGR pipe which got plenty hot but it wasn't big enough to act as an H-pipe.

Mac

The exhaust crossover under the intake manifold also acts like a small h-pipe. I installed my h-pipe as an experiment to see if it would reduce my exhaust noise (it did) and see if it would add some power and maybe increase the fuel mileage a little bit. I keep super accurate records on my fuel mileage so if the h-pipe increased my fuel mileage I'll soon know. I was shocked when my ram air increased my fuel mileage by 3-1/2 mpg; from 10-1/2 to 14 mpg. Thinking it was a fluke I ran another 10 tanks thru it and each one showed the same 3-1/2 mpg increase. As my air cleaner is sealed to my hollow L-88 hood every bit of the air is coming from the front of the car so it is a true RAM air as well as being COLD air. So rather than sucking in 200 degree underhood air it's sucking in 100 degree frontal air on 100 degree summer days.

 

[Mac]

The exhaust crossover under the intake manifold also acts like a small h-pipe. I installed my h-pipe as an experiment to see if it would reduce my exhaust noise (it did) and see if it would add some power and maybe increase the fuel mileage a little bit. I keep super accurate records on my fuel mileage so if the h-pipe increased my fuel mileage I'll soon know. I was shocked when my ram air increased my fuel mileage by 3-1/2 mpg; from 10-1/2 to 14 mpg. Thinking it was a fluke I ran another 10 tanks thru it and each one showed the same 3-1/2 mpg increase. As my air cleaner is sealed to my hollow L-88 hood every bit of the air is coming from the front of the car so it is a true RAM air as well as being COLD air. So rather than sucking in 200 degree underhood air it's sucking in 100 degree frontal air on 100 degree summer days.

My 73 has the actuated flaps on the hood but, since the system wasn't sealed, no difference in atmosphere and only a small difference in temperature (if any) but more engine noise. I believe this is referred to as 'perceived horsepower' for some reason.

Mac

 

[toobroketoretire]

My 73 has the actuated flaps on the hood but, since the system wasn't sealed, no difference in atmosphere and only a small difference in temperature (if any) but more engine noise. I believe this is referred to as 'perceived horsepower' for some reason.

Mac

With my ram air I'm getting 1" Wc of pressure at 60 mph and 1-1/2" Wc at 80 mph. I have a feeling it's the slight pressure that is responsible for the fuel mileage increase.