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Skervey
Skervey Reader
3/17/15 10:32 a.m.

Hey guys as the title states im interested in putting manual exhaust cutout on my V8 RX7 build. I want the car to sound stock most of the time but scream with open pipes when I feel like making car alarms go off.

First- I want manual cutouts because the electric ones are just to slow. I want to be at a red light and as soon as the light turns green I want the cutouts open all the way. The electric ones I have seen on youtube take a few seconds to open witch is good for a hot rod pulling into a car show but not for me.

Second- I have seen ones for sale that are just want I need but... they are around $200 each -Cutouts that I want-

and they are in the UK (im in the USA) so then it would be just as much for shipping. I have seen the mister gasket cutouts but they are cast iron and iv heard they leak. But they are only $50 witch is much more resinible

So I did some more looking around and found that people were using throttle body's as manual cutouts witch would work well but with dual exhaust it might be hard and lets be honest its a bit redneck, at least for this build

So anyone know of another source for cutouts, or maybe where I can buy broken electric cutouts so I can modify them to be cable driven? Iv been trying to come at this issue for sometime now and I thought I would ask around for help!

GameboyRMH
GameboyRMH MegaDork
3/17/15 10:40 a.m.

I've looked into the very same thing, and I think the throttle bodies might be your best bet. It's really surprising that there's no off-the-shelf solution available for this, and that cable-type cutouts aren't more popular for their simplicity and vastly lower cost.

Apexcarver
Apexcarver PowerDork
3/17/15 11:08 a.m.

Was involved with a car that had the Mr Gasket ones.

DONT DO IT.

They leak, they clatter, they generally suck the big one.

We ended up ripping them off and throwing as far away from the car as possible.

RossD
RossD PowerDork
3/17/15 11:12 a.m.

What about an external wastegate? You'd have to figure out how to get it to actuate at low vacuum so it dumps when you have your foot into the most.

Woody
Woody MegaDork
3/17/15 11:17 a.m.

JC Whitney used to sell them.

Skervey
Skervey Reader
3/17/15 11:58 a.m.

Thanks for the response guys!

Thanks Apexcarver, I figured they were crap but its the only cheap solution around.

Iv thought about a external wastegate as well but cost and complications with it just seem like more than its worth. Also if I cam the 302 im putting in my car it may not have enough vacuum and not work properly.

What throttle bodies have been used in the past? Needs to be a big one I hope to use 2.5" pipe. I could grind all the unnecessary parts of the throttle bodies and weld on a flange so I can simply bolt it on and off.

doc_speeder
doc_speeder HalfDork
3/17/15 12:33 p.m.

In reply to Skervey: 2.5" is only like 63mm. Any GM truck from 99-2000 that has cable TB should work. They are all considerably bigger than that. Likely earlier than that too, but I'm not well versed on the pre LS-Juan trucks.

Skervey
Skervey Reader
3/17/15 2:29 p.m.

Thanks doc_speeder, I did find these from a 5.3 out of a F150 and they don't seem to bad. $60 for 2. Might order one and see if I can mock it up into something useful. -F150 throttle body-

I guess it would withstand the heat, I would have them 1/2 way down the car more than likely.

Shiftinwithoutliftin
Shiftinwithoutliftin
2/27/17 12:10 a.m.

In reply to Skervey:

Check out this new design from Cuthroat Exhaust Systems. What a simple but perfect idea! https://youtu.be/3Ch4hCTPTZw

GameboyRMH
GameboyRMH MegaDork
2/27/17 8:36 a.m.

Looks like a great idea for a "bolt-in cap" cutout, but the aim of this thread is to have something driver-controllable. I've still been looking into this as recently as last week. It seems that all of the cheap cable-operated cutouts leak and that's why they're not popular. For me personally I'd be fine with waiting a few seconds for an electric cutout, but the price is steep and can strike again if the electric motor fails.

RealMiniParker
RealMiniParker UberDork
2/27/17 9:40 a.m.

In reply to GameboyRMH:

So when the electric motor craps out, can you build a better mousetrap, and ditch the electric part to rig a cable to it?

GameboyRMH
GameboyRMH MegaDork
2/27/17 9:48 a.m.

Yeah it should be possible, either with a springload at the valve and a lever with detents to move it, or maybe something like an extra long push/pull choke cable.

curtis73
curtis73 PowerDork
2/27/17 9:54 a.m.

Someone here (I think) did some cutouts with old throttle-by-wire TBs. They open super quick.

Not sure how they would handle the heat long term though.

You could also just use some junkyard TBs with a cable. Cheap, and they wouldn't seal perfectly, but might work as a cheaper solution.

singleslammer
singleslammer PowerDork
2/27/17 10:06 a.m.

I am probably over thinking it but what about a hydraulic cut out? Should be as fast as a manual with the ease of use of an electric. I don't have any engineering to prove this but someone around here could probably tell me why I am wrong.

RealMiniParker
RealMiniParker UberDork
2/27/17 10:34 a.m.

How about solenoid operated? Repurpose some door lock actuators, they'll open it right-quick. Wire it with a switch on the throttle that hits at WBO, to operate the solenoids.

outasite
outasite HalfDork
2/27/17 12:18 p.m.

As I recall (it's been almost 50 years) GTOs had an optional manual exhaust cutout. Probably NLA but may be worth researching.

fidelity101
fidelity101 SuperDork
2/27/17 1:25 p.m.

skip that mr gasket crap, they had the same release cable for a choke kit and it was horrible.

classicJackets
classicJackets HalfDork
2/27/17 2:07 p.m.

I am also interested in doing something along these lines. Opening these up while cruising would be a blast!

Knurled
Knurled MegaDork
2/27/17 4:54 p.m.

I suggest not doing it since you have to tune the car for one way or the other.

RealMiniParker
RealMiniParker UberDork
2/27/17 5:00 p.m.

In reply to Knurled:

Can MS handle two different tunes. that can be switched by a... switch?

Streetwiseguy
Streetwiseguy UltimaDork
2/27/17 5:52 p.m.

I cannot imagine any rational reason for adding a cutout on a rotary, other than inducing an axe wielding rage any time you were within a mile of me.

Knurled
Knurled MegaDork
2/27/17 6:33 p.m.
Streetwiseguy wrote: I cannot imagine any rational reason for adding a cutout on a rotary, other than inducing an axe wielding rage any time you were within a mile of me.

Quiet exhausts that are cheap are very restrictive. So when you go to the dragstrip, you open the cutout, at which point you run dead lean, until you make a bunch of tuning changes. Then it runs really rich when you cap it back up and go home.

Granted it was a lot of fun tuning it in, but I remember one run where the ground straps of all of the spark plugs were just gone... not broken off. They melted away. Er, I think we need mo' fuel!

Streetwiseguy
Streetwiseguy UltimaDork
2/27/17 9:20 p.m.
Knurled wrote:
Streetwiseguy wrote: I cannot imagine any rational reason for adding a cutout on a rotary, other than inducing an axe wielding rage any time you were within a mile of me.
Quiet exhausts that are cheap are very restrictive. So when you go to the dragstrip, you open the cutout, at which point you run dead lean, until you make a bunch of tuning changes. Then it runs really rich when you cap it back up and go home. Granted it was a lot of fun tuning it in, but I remember one run where the ground straps of all of the spark plugs were just *gone*... not broken off. They melted away. Er, I think we need mo' fuel!

I include drag strips and all other race tracks in my axe wielding rage zone. Its all I can do to not climb out of my roadrace car and start beating RX7 drivers to death in pregrid. Everybody else is sitting there quietly, with their engines shut off, and half a dozen Rotards are sitting there going braaapbraapbraapbraapbraapbraap and drowning me in raw gasoline fumes. Shut the stinking piles off.

jstand
jstand HalfDork
2/27/17 10:53 p.m.

Maybe a bit redneck, but what about adding your own cable or pneumatic actuation to a 2.5" ball valve?

Not the cheapest option, but if you can get some to handle the temp they won't leak.

Skervey
Skervey HalfDork
2/28/17 10:58 a.m.

Wow this thread came back from the dead! I played around with the idea of using throttle body's. I started to make a flange for a 5.0 TB. But it never came to be, couldn't fond a good quiet light small cheap muffler so it wasn't worth it in the end.

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