FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: 338Raptor on December 08, 2019, 01:24:32 AM
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Is anyone running a full exhaust system on a street car with more than 800 flywheel horsepower?
I’ve used a couple online exhaust size calculators. They say I need 3.25” dual exhaust to support 800 horsepower. Since exhaust pipe doesn’t come in 3.25” diameter I’ll need to step up to 3.5” or settle for 3” and lose some power. Routing dual 3.5” to the back of the car is going to be a challenge. Routing 3” will be a little less of a challenge. But not restricting power is my main objective.
Does anyone have direct experience with this? Do I really need 3.5”?
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Electronic cut outs.
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Use four pipes that give you the same area as two 3,25" pipes
it is easier to route them and they give you more ground clearance
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I have 3.5" from the collectors to the back bumper. It's not particularly easy but it can be done. This is with ladder bars and coil overs, stock gas tank.
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I used 3.5" reducer at header to oval tubing with a X pipe fabricated from two 90* oval tubing bends. Spin tech mufflers and oval tubing out the back. Sounded like a high compression small block @ 9k rpm.
385 engine, 565ci, 818 @ flywheel. No data to confirm any HP loss, but ran well.
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For what it's worth, Barry's car sounds like no other and I like it. A lot.
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I'd go 3.5 oval, with X pipe, all cruves mandrel bent and fit to minimuze flow disruption and use an absorption (not Flowmaster style) mufflers as far back as you can.
Be very careful on muffler choice, some cores are pretty small from Borla, although in general I love their mufflers
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I like the suggestion of 3.5” oval with mandrel bends.
Which 3.5” in/out mufflers flow well and are relatively quiet?
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I run Jones Full-Boar perforated tube stainless on my truck and it's pretty quiet, although even with a 3 inch mandrel bent it barks with your foot in it. That's a real good option and the price is better than others for a stainless body
Magnaflow and Dynomax Ultraflo both should be OK when your foot is out of it too. Perforated tube with packing is pretty gentle until you get in it. The X or H will calm it down when you want it to as well.
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Where can you get 3.5" oval tubing with mandrel bends? I didn't even know it was possible to mandrel bend oval tubing,
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I found these sources online.
http://mandrelbendingsolutions.com/oval-tubing/
https://www.racemufflers.com/Oval-Exhaust-Tubing-s/1832.htm
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I run 2x3.5" pipes on a 550 hp street car. Could I get by with 2x3"? Yeah, I suppose so. I have run 2x3" over the axle and out the back. I now use 3.5" pipes because my collectors are 3.5" and I don't like to neck down the exhaust right after the collector. At least not until after my crossover pipe. And since I am dumping the exhaust in front of the rear axle, it is only another couple of feet. So 3.5" all the way for me.
But 800hp needs some serious exhaust, in my opinion. I say do what you have to do. Dump it before the axle or out the side or use 4 pipes, but don't choke an 800 hp engine.
I think you need at least 3.5". More is better, until you are just adding weight with pipes that are bigger than you need them to be.
JMO,
paulie
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I have a full length 3 1/2" with X-pipe system on my 68' Mustang fb. I used all stainless mandrel bends except the turn-ups after the mufflers, could only find inconel mandrel bends with a tight enough bend radius. My pipes are hooked to REF header with merge collectors.
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Here's a setup we built for the '65 Galaxie Tunnelport. 3" Piping, not 3-1/2". Figured that if we wanted all the power, it could be loud. For normal street driving, it'll only be kind of loud. The cut out pipes dump right after the mufflers (did this so it hopefully won't beat your ear drums inside the car), the muffler pipes will continue on to the back of the car. Once the rear axle goes back in the car the exhaust system can be finished, weld it all out, and send off to get coated.
I would think that a 3" system like this would suffice for 800hp? But maybe it won't.
(https://i.postimg.cc/SxfBdCNb/IMG-0779.jpg) (https://postimages.org/)
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I found these sources online.
http://mandrelbendingsolutions.com/oval-tubing/
https://www.racemufflers.com/Oval-Exhaust-Tubing-s/1832.htm
Interesting, thanks for the links.
But I'd have to say, I don't see any way to get curves while going over the rear axle, using those bends. Not to mention the 'flat' part of the oval is on the 'side' of the tubing (as it would be used to go over an axle), which means it's taking up valuable space. Space that just isn't there on many cars. I just don't see how oval tubing could be used in a full system, unless it was dumped out the side, and I'm really not a fan of that. One problem going down a track, or even a highway, and you'll be spraying your tires with oil. My instinct tells me that that would not be a good thing.
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I think I'd mix flat and oval to wherever it was an advantage, to include standing it on it's side along the gas tank.
A lot of fab time, but could be slick
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Following up on My427stang's comment, couldn't you swage the ends of the pipe to make them round and fit onto each other, then rotate the pipe into whatever orientation that you wanted? That might make fitting it into different parts of the car a bit easier. I especially like the idea of running the flat side along the floor of the car, then rotating it 90* to go over the axle and along the frame and gas tank.
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I'd just like to add...….Good Problem to Have!!
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Do any of you really think twin 3.5" exhaust will not cost some horsepower on an 800 hp engine?
paulie
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Well what is Ford using on the 700+ HP 2020 Mustang??
Just use 3.5 to the muffler and 3.0 tailpipe. Even 2.5 tailpipe won't hurt a thing.
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This made me curious, so I looked up an online calculator.....
http://www.mk5cortinaestate.co.uk/calculator5.php
Claims 3.00" pipe is good for 739bhp. 3.50" is good for 1006bhp.
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Well, there is a difference between maximum supportable horsepower, and whether a pipe size costs power. Is it conceivable that two 3" pipes COULD support 739 hp and whether two 3" pipes would not cost any hp?
JMO,
paulie
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Do any of you really think twin 3.5" exhaust will not cost some horsepower on an 800 hp engine?
paulie
What's the alternative? I think it's all in execution, if done nice it'll work well, cobbled together, not as much
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Well, that was not my question. But your question is certainly valid. And your question is more to the point of the OP's question.
800 hp is A LOT! I guess I figure that when you are at that point everything is out the window and you can do what you want, even if your exhaust system costs you 50-100hp it is still going to be a crazy ride.
JMO,
paulie
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I found these sources online.
http://mandrelbendingsolutions.com/oval-tubing/
https://www.racemufflers.com/Oval-Exhaust-Tubing-s/1832.htm
Interesting, thanks for the links.
But I'd have to say, I don't see any way to get curves while going over the rear axle, using those bends. Not to mention the 'flat' part of the oval is on the 'side' of the tubing (as it would be used to go over an axle), which means it's taking up valuable space. Space that just isn't there on many cars. I just don't see how oval tubing could be used in a full system, unless it was dumped out the side, and I'm really not a fan of that. One problem going down a track, or even a highway, and you'll be spraying your tires with oil. My instinct tells me that that would not be a good thing.
You can, it just takes a LOT of effort. You can get several styles of "twist" so that you can transition from vertical to horizontal, or the other way around. You can also make pie cuts, or buy them and make whatever angle you need. It's certainly a lot more work than dealing with common full round tube, but it can be done if you really want to.
Use a twist to lay the oval on the side, go over the axle, and another twist back to vertical if you so desire or require.
Here are some pre-made pie cuts in oval tubing.
https://www.racemufflers.com/Oval-Exhaust-Pie-Cut-s/2181.htm
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The new 760hp Shelby GT500 seems to be 3" but at the X pipe it necks down, looks to be 2 1/2" at the smallest point. I bet there will soon be aftermarket X pipes claiming an extra 40hp. They used 2 3/4" pipe on the last 662hp 5.8L GT500's.
A local ProStreet car had oval exhaust before that was available aftermarket. It was made by slitting the 3" round pipes in half and adding 2" strips. It was 3 x 5" oval, probably similar to 4 1/4" round. The pipes had the flats at the top and bottom to fit under the floor and then turned upright to fit past the gas tank and springs. Round tips. I wouldn't have known until I saw the exhaust for sale at a swap meet.
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My experiences with high horsepower street engines have led me to use a smaller exhaust pipe over the years, coupled with some electric cutouts. Actually being able to use something like 800 HP on the street is not possible, in my experience. You'll just spin the tires. I've done burnouts while going 65 or 70 MPH; what's the point if you can't hook the tires?
If you do decide to go with a big exhaust, think about how much weight you will be adding to the car, compared to a smaller exhaust. On the street, the big exhaust won't help you, and the extra weight will slow you down.
Put a good 2-1/2" exhaust system on the car, with either electric cutouts or caps that can be removed at the track. With the electric cutouts you can open them on the street if you want to get full flow through the headers, and if you go cheap with the caps, you can pull them off easily at the track to get your open headers that way. My advice is not to waste a bunch of time and money on some huge exhaust system, because it won't do you any good. Just my opinion, of course...
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I mentioned that, too. That is, once you have reached the ideal pipe size, going bigger just adds weight. And of course it makes packaging more difficult.
I would still tend to err on the larger side. The weight gain from 3 to 3-1/2" can't be too much? And choking an engine even a little bit makes me feel bad.
What do you run on your high hp engines, Jay? Small pipes, but with cutouts?
paulie
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2-1/2" pipes with decent mufflers, and electric cutouts. My Mach 1 (supercharged, about 900 HP), used a 3" pipe system (pictured below) and I always regretted doing that. I put the electric cutouts right in line with the collector extensions, and took the exhaust off the side of the extension. That exhaust system was a pain to build and get it to fit; if I ever redo it, I'll go back to 2-1/2". My Drag Week car uses 2-1/2" pipes, and I just drop the whole exhaust system when running at the track.
(http://fepower.net/Photos/Posts/exh06.JPG)
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Hey Jay do you think your cool with that exhaust ;). That looks to good to start the motor.!!. How do you drop the exhaust when you go to the track. I have the over the rearend pipes then no tailpipes which is easy to drop the exhaust how do you do it with the tailpipes on it. They dont look like they come off.
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...How do you drop the exhaust when you go to the track. I have the over the rearend pipes then no tailpipes which is easy to drop the exhaust how do you do it with the tailpipes on it. They dont look like they come off.
Jay is driving right now, we’re on the way to PRI, I’ll take a stab at answering - the exhaust pictured with the cut-outs, used on his ‘69 Mach 1, doesn’t get dropped, he just opens the cut-outs while on the track. The exhaust his most recent Drag Week car, the ‘69 Shelby clone has, does get removed at the track, but it doesn’t go all the way to the back, it ends at the rear tires.
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Thanks you guys have a good time.
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I used to unbolt the pipe from the header flange and rebolt it along side the flange to the flange, if that makes sense. That way it was quick and easy.
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I used to unbolt the pipe from the header flange and rebolt it along side the flange to the flange, if that makes sense. That way it was quick and easy.
Yeah, that makes perfect sense. You just moved the back of the exhaust over to one side and put a couple of bolts back in. So that it was not centered? You just have to swing it a couple of inches. Right?
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yep. I took the gasket out and stashed it so it wouldn't get damaged.
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You could build a rear-engine car. ;)
KS
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For my situation I really don’t need to drop the entire exhaust system (65-70 lbs) for my time at the track. When I want to go fast at the track I’ll take my Top Sportsman car. My goal for the 800 hp Fastback is to have an insanely fast street legal car. I’m more interested in a full exhaust that doesn’t restrict power output. I think a 3.5” oval/round combination would best fit my needs.
Also, how much weight would I really save by going with a full 2.5” with cutouts vs a full 3.5” system. 10-15 lbs?
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Not 800 hp in this video but mid 600’s (pre turbos)
This is 3 inch pipe and spin tech muffler’s
https://youtu.be/FhGcccBG3Fc
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Also, how much weight would I really save by going with a full 2.5” with cutouts vs a full 3.5” system. 10-15 lbs?
For mild steel 2.5" round tube with a .065 wall it weighs 1.69 lbs per foot.
For mild steel 2.5" round tube with a .120 wall it weighs 3.05 lbs per foot.
For mild steel 3.5" round tube with a .120 wall it weighs 4.33 lbs per foot.
I'd have to look up the weights for other alloys/stainless, but thats off my cheatsheet on my desk. So potentially quite a bit of weight savings depending on how much exhaust you're going to run. But it weight isn't a concern and you have room for 3.5" or are willing to spend the time fabbing the oval bends to make the room then why not go bigger?
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These are the weights I found for 16 gauge 304 stainless exhaust pipe.
2.5” 1.706 lbs/ft
3” 2.057 lbs/ft
3.5” 2.407 lbs/ft
I’m estimating dual exhaust will take approximately 20 feet (10’ per side) plus two mufflers.
The weight difference between 20 feet of 2.5’ and 3.5” would be 14.02 lbs plus the difference in muffler weight. Additionally the difference in muffler weights may be negated by the weight of the cutout valve. I can’t see the weight difference for the entire exhaust system making a noticeable performance difference.
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As I mentioned earlier - my 3.5 inch system is welded up from mandrel bends and straight sections. Mufflers are Magnaflow 3.5 in/out. Engine is 433cid and makes just over 700 on my dyno, shifting at 7500 RPM. I have no idea whether it hurts power at all since I have not run open headers for over a decade - maybe two decades. The car runs into the tens with the system in place. when I go to the track (rare these days) my prep includes lowering the tire pressure (runs on M/T ET Streets) and putting on my helmet and jacket. I am cetain that the system weighs a bunch, but in a 3600+ pound car I kinda don't really care.
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I have run 1196rwhp through 2x2.5, but I also had a 5" electric cutout from the turbo downpipe that dumped out the front bumper. You could feel a major difference in how fast the turbo spooled, but this also helped retain street manners. That, and my '14 GT500 had a 2x2.75", necked to 2.25" on the H-pipe, pushing 800hp- full exhaust including mufflers, resonators, cats, H-pipe, and longtubes, plus the engine had a set of moderate blower cams.
I chased exhaust diameter in the past and found diminishing returns rather quick, though I'm not one to try to squeak every last hp out of the high end rpm range. If it's a street car, how often are you going to be up around redline to realize the benefit of slightly less exhaust restriction?
As others pointed out, electric cutouts are the way to go if you want a full exhaust but retain the ability to open it up when needed. I've run multiple cars with cutouts on the street and it always stinks the car out with exhaust fumes no matter where you position them. You can consider running a muffler bypass pipe from the cutouts, around the muffler, back to the outlets but at that point it's more of a sound change than any tangible power gain. '18+ GTs have the active exhaust option, which is mainly in the muffler- the mufflers have a bypass tube with an in-line butterfly valve- that also might be something to consider (and something I plan on doing when my '69 build is underway). I wish my '18 GT had active exhaust, but I'd rather spend the money on the '69...
Plus, there's something to be said for rolling around quietly when needed... There were many times that I picked up the keys to a loud car, thought about what time it was, put them back and drove the DD so I wouldn't make the neighbors mad.
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I mentioned that, too. That is, once you have reached the ideal pipe size, going bigger just adds weight. And of course it makes packaging more difficult.
I would still tend to err on the larger side. The weight gain from 3 to 3-1/2" can't be too much? And choking an engine even a little bit makes me feel bad.
What do you run on your high hp engines, Jay? Small pipes, but with cutouts?
paulie
I have run 1196rwhp through 2x2.5, but I also had a 5" electric cutout from the turbo downpipe that dumped out the front bumper. You could feel a major difference in how fast the turbo spooled, but this also helped retain street manners. That, and my '14 GT500 had a 2x2.75", necked to 2.25" on the H-pipe, pushing 800hp- full exhaust including mufflers, resonators, cats, H-pipe, and longtubes, plus the engine had a set of moderate blower cams.
I chased exhaust diameter in the past and found diminishing returns rather quick, though I'm not one to try to squeak every last hp out of the high end rpm range. If it's a street car, how often are you going to be up around redline to realize the benefit of slightly less exhaust restriction?
As others pointed out, electric cutouts are the way to go if you want a full exhaust but retain the ability to open it up when needed. I've run multiple cars with cutouts on the street and it always stinks the car out with exhaust fumes no matter where you position them. You can consider running a muffler bypass pipe from the cutouts, around the muffler, back to the outlets but at that point it's more of a sound change than any tangible power gain. '18+ GTs have the active exhaust option, which is mainly in the muffler- the mufflers have a bypass tube with an in-line butterfly valve- that also might be something to consider (and something I plan on doing when my '69 build is underway). I wish my '18 GT had active exhaust, but I'd rather spend the money on the '69...
Plus, there's something to be said for rolling around quietly when needed... There were many times that I picked up the keys to a loud car, thought about what time it was, put them back and drove the DD so I wouldn't make the neighbors mad.
Good points overall. I agree that with your big hp, the cutouts, electric or manual, are the way to go with say 2.5" readily available mandrel bent SS pipes OR coated plain steel out the back for tooling around town AND at less that WOT you'd lose not many hp's.
Gotta figure too: just how often would the engine be anywhere near WOT? 10% of the time? 5%? JMO!
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On my 85 LX I run 3 inch pipe with Flowmaster merge/X pipe into Flowmaster series 10 3 inch mufflers and then
custom made resonator 3 inch diameter, 9 inch long tailpipes that have a 2 1/2 ID louvered core.
I have since added a 2 inch diameter angled disc just at the pipe exit that reflects unwanted frequencies back into the muffler to quiet drone.
Works really well and has a unique sound.
This pictured was before I added the resonator tips.
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Do you have any pics of the angled disc you are using to reduce drone? I haven’t heard of that method. Is it really that effective? Doesn’t it restrict exhaust flow?
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...My Mach 1 (supercharged, about 900 HP), used a 3" pipe system (pictured below)...
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(http://fepower.net/Photos/Posts/exh06.JPG)
Where was that gorgeous exhaust system when I was you trunk monkey? Back then, the cockpit was the muffler, and the window was the tailpipe. ;)