Well if anyone should know it'll be you FI guys, so I'm asking for some help here looking for a cheap solution if possible. I tell you now I'm FI illiterate and don't pretend to know or understand the components of FI, but I'm asking for help from you who do!

The scenerio is I have a N/A 346 built top end that flows REALLY good. It's a daily driver car that I autocross. I built my exhaust using modified long tubes with a custom 3" y-pipe using a Flowmaster 3-4" merge collector. Then it reduces back to 3" where I have a manual cutout capped, then goes into a stock ws6 catback. Past the stock ws6 catback muffler I welded in silencer inserts like shown below from carchemistry.com.


This has achieved the quiet sound I'm looking for when cruising back and forth to work, but has caused too much backpressure. How much? I don't know for sure as I haven't hooked up a pressure gauge to it, however it's enough that when I get the motor to 5,500 rpms it blows the y-pipe right off the headers. I built the y-pipe and know it's not easy to pull off...so I'm guessing I'm building at least 20+ psi back there. Now I know I could get better clamps (which I will), and I could just open my cutout but I don't want to have to push a button to open the cutout everytime I wanna take the car up in the RPMs.

So here's what I'm wondering. Can I just put an exhaust wastegate or blow off valve in before the muffler as it's the first place of flow restriction? I don't want a vacuum type deal, probably something only spring pressure related. Do I need to worry about it being a high temperature unit? I figure I need it to be adjustable whether I put some washers on the spring to raise the pressure rate before release but I'm not sure exactly how much psi we're talking here either. Am I looking at a wastegate or bov? From what I see they're the same thing but the bov is a smaller diameter dump, slower release, and higher pitched whistle noise.

I've spent a TON of time fabricating my exhaust and would really like to keep it, hence why I'm here asking you now. If I can't get a cheap solution I'll probably end up doing true duals dumped with fake tips in the rear (it's a TA...can't not have tips) but I REALLY don't want to go that route.

Any ideas?

 

Just use an electric cutout.

 

Edit
what I would do is use a hobbs switch measuring exhaust back pressure and have it hooked up to a relay to your cutout and then at a desired back pressure it will automatically open your cutout
And this will be much cheaper then adding a wastegate

 

take out the baffles you welded in the tips.
either run them as intended right off the headers, where the exhaust is high speed, or just get a stock catback that doesnt have alot of miles on it.

either way, it will be quiet. very quiet.

but running header inserts in the rear of the car is not very effective from a performance or economy perspective. there are better baffling options out there.

 

ya know...I never even thought to just hook up another automated switch to my cutout...that's exactly what I'll do...thanks for the help guys!

 

that isnt a very well thought out solution.

 

well I tried making it more complicated than it needs to be apparently...

If I get QTP's cutout controller it can automatically open or close by grounding or not grounding the trigger wire...so more than likely I can hook that up to a nitrous switch and call it a day...WOT, cutout opens....let off the gas...cutout closes. Interfacing through the controller will prevent burning up the cutout motor.

I could also use the controller and tie into a AC low pressure cut off switch which I could tie into a scrader valve that I put on a small tube that I weld to the exhaust...the cutout switch with ground/not ground accordingly to pressure in the exhaust...however making this look clean might be harder than it sounds.

So I think I can make it work and work very well.

 

what you're forgetting is how fast the cutout opens.
by the time the cutout fully opens, you're going to be at the end of your WOT run before its halfway open.

 

I think it take 3 secs to fully open...and all i'm worried about here is releasing the pressure built up in the exhaust...the cutout doesn't have to be fully open to do so..so it should do the job.

If you have another idea by all means hit me with it...but I think this'll be the best method to get to work efficiently.

Remember...when I'm racing I'll open the cutouts the whole time which through the controller will bypass the wot switch...if I'm on the road cruising it'll use the wot switch and releave the pressue only when i'm getting on it.

BTW..it won't be opening only at true WOT...i'll extend the switch pin with something that'll give me flex and install on the pedal...so the switch will open when I'm closer to 50% open.

 

I like your ideas be sure and post again and let everyone know how it works out for you.

 

You seem like one of those guys that over thinks and likes to make **** as difficult and as complicated as possible.

You should work for or go drive a Volvo. Those seem like they would be right up your alley.

 

thanks...will do

 

thanks for the help bud...you're a great guy

 

you know, the guy i quoted above does make a great point. I mean, personally i think you could work for ANY european car maker, not just volvo... but thats besides the point.


you DO have everything overcomplicated.



first off.. why not fix the actual problems... such as your plugged exhaust?

theres ZERO reason to have exhaust backpressure.. nevermind backpressure so high that you're blowing the y pipe off the headers.

you can make the car dead silent without choking it like that.

 

well I've tried and seen a few different setups...the one I have now sound wise is the best but for efficiency reasons just might not be the best solution. I could get it to work with a controller on the cutout and still might do that...but for now I'll take your recommendation and go back to the drawing board for quieting down the exhaust differently than I've done it now so I don't have this problem in the first place.

Side note...you've been helpful, but no need to come off as a douchebag doing so.

 

its all in the tone you read it.. dont read it so seriously, pretend the guy is your friend smiling and joking at you as you read it, and you'll be alot closer to how I intend it.. lol.

on a 3rdgen ive seen people run a long glasspack type bullet muffler before the axle, and then into a catback... if you did that into a stock catback you wouldnt even be able to hear the car idle... if thats your goal.

 

ah...well I apologize for calling you a douche then...haha

only problem is I have no room to put something like that into my i-pipe as the cutout sits right there. that's why I put those silencers in behind the muffler..but if that's what's killing me then I'm not sure what i'm trying to accomplish can happen without putting something like what you're saying in the i-pipe

I'm really debating about just starting all over...go header, cutout, cat, muffler, turn out and be done. then put fake tips in the rear...I'm getting tired of dealing with exhaust

 

Do a 4 inch Magnaflow or Borla muffler after the merge with a turndown, problems solved

 

Weld a 60mm wastegate in right after the merge. Then mess around with the springs until you get it to open when you want. You can pickup a cheap Chinese WG from Ebay for under $150.

 

the inserts you welded in are phucking you. you should never ever have so much pressure you blow off the y pipe, thats insane. i've never even heard of a rear mount turbo guy having issues like that, let alone an N/A car. the stock cat back should be more than quiet enough. the cheap solution to your problem is taking them out...

and why do you go from the 4" FM merge back to 3"? you should be running a 4" cutout...