Full exhaust on a 800hp street car

[thatdarncat]

...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.

[Stangman]

Thanks you guys have a good time.

[shady]

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.

[plovett]

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?

[shady]

yep. I took the gasket out and stashed it so it wouldn't get damaged.

[cammerfe]

You could build a rear-engine car.

KS

[338Raptor]

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?

[Russ67Scode]

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

[RustyCrankshaft]

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?

[338Raptor]

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.

[Barry_R]

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.

[CV355]

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. 

[machoneman]

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!

[427LX]

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.

[338Raptor]

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?