Building a daily driver 1974 C10 SWB with a 76/65 turbo on a 4.8

Down pipe is a 3" and I was thinking of a single 3" exhaust exiting behind the rear wheel. I want the exhaust to be pretty quite and I was wondering how restrictive I can go with my muffler before I start to create excessive back pressure. I was thinking about a typical Walker turbo muffler a little over 2' long would quite it down enough but am I gonna add too much back pressure?

 

 

It will be fine. Just build a full 3" system.

Such a setup has already been proven to make over 700hp easily.

 

You can still make big power but your going to be pushing the turbo harder and going to need much higher gate pressure to make the boost you want. Backpressure post turbo is going to be way up and thats going to affect a few different things like spool, pressure ratio etc.

 

It's a C10. Should be basically straight pipe to the muffler. Run your 3" exhaust to and through the muffler (no tail pipe yet), log backpressure in the exhaust and go from there. If it's good finish it. If not, start over at the turbo and step it up to 4". That should be overkill at your power level.

 

Are you guys logging pressure before or after the turbo.

 

Normally before, but after will let you know if your full exhaust is a restriction. Easy enough to place a bung in both and swap the sensor around to log each one if your short on inputs.

 

Most of them who rant about too much backpressure have never logged either.

But ideally you would log both.

 

 

A 1974 c10 would look better with dual exits anyway, so why not put two huge mufflers in play? You have the room to have low backpressure and low noise. Use that extra real estate to get the best of both worlds with only a modest penalty in weight and piping complexity.

 

A guy here called redbull was on the dyno with his 3rd gen TA which had either a 5.7 or 6.0 LS and a 84mm on3 turbo with a 75mm exhaust wheel. He ran a 3" down pipe out to the back of the car into a 3" magnaflow catback. The 3rd gen and 4th gen have the same exhaust and right before going over the rear axle he put in a 3" cutout so the exhaust could flow out before making the bend. On the dyno even with the cutout open (basically at the back of the car) he was seeing 9psi back-pressure in the exhaust in the down pipe in boost and you could watch the gauge he was holding as it was making a pull. He has since added a 2.5" cutout and that dumps it right out the fender about 3ft after the turbo. Hes picked up alot of power without even opening the other cutout and has dyno results to prove. I don't remember his back-pressure now but I can tell you that opening my cutout changes the entire demeanor of the car... like 50rwhp different with sooner, faster and harder hitting spool. I have to even compensate my EBC settings for closed vs open cutout otherwise it would be easy to overshoot my intended boost. I also have logs back to back pulls showing that with the cutout open that my spool is like 400rpms sooner and all in sooner as well, plus my INJ DC% is way up so its making more power. Ive never logged backpressure bc I dont have room to make a shorter dump but opening the cutout and feeling/hearing the difference is all the proof I need.

The good news is you have alot of options. A 3" full exhaust will make the power you want but your leaving a bit on the table that is easily obtainable. I like the idea of gametechs if you got the room to run dual exhaust with large mufflers that wont affect flow (but can quiet it down) then do it. Most of us never have "too much room" so thats never really an option. The added weight is nothing.

 

I do plan on a cutout when I hit the track or play hard but I really want this to be a stupid quick daily that just has a quite rumble.

I do have an *** load of room so maybe I split after the downpipe and run dual, that would give me some room to grow as I expect I'll do what the majority of us do when we get bored and toss a bigger windmill on it. If I go dual is a single dump at the split enough?

I still wonder about the muffler type, I love my dynamax ultra flow's on my Nova (SBC/Nitrous) but thought a straight thru would be too loud for what I want to do with the C10. I know a turbo kills much of the exhaust note but wasn't sure by how much. Is the consensus a straight thru muffler enough?

 

As long as the dump is the same size as the pipe it would be fine. So use a 3" cutout on the 3" DP. Remember when the cutout is open a good bit of the flow is bypassed (exhaust will flow with least resistance) but even if thats the case the exhaust will still flow through the rest of the exhaust at the same time. So think of the cutout as "added flow" to your current exhaust.

You ONLY want a straight through muffler on a turbo car.

I run a single in 3" dual 2.5" out dynomax ultraflow firebird specific muffler and its pretty quiet. Opening the cutout is a huge difference in noise.

here is a recent video of my car, its in a enclosed tent (it was also 20*F outside). you can hear my valve train in the beginning and the last 5s or so is my over by the exhaust. Its got a little bit of a deep rumble but its very quiet. I even thought about putting in a shorter muffler for a little more loudness but then I think I like the stealth and the ability to make it loud and faster when I want.

I also have a video on my phone of the car idling with the cutout open and then closed so I could record the difference, I just haven't put it on youtube.

 

Heres the video of it with the cutout open and closed. This is a dash cam so its not even close to good audio but its a HUGE difference in sound. With the cutout closed you mostly hear my tranny pump or PS pump.

The video shows the exhaust cutout open in the beginning and its idling/free reving, then I close it about 1/2 through and you can hear it get dead silent. You can also hear a bit of the turbo whine when I let off the gas on the free Rev with the cutout open on the decel (high pitched whine), but you can't hear it with the cutout closed.

 

I propose two Warlock mufflers. They have a mellow tone with the cutout blocked, and are straight through with it open. You just replace the bolt on cutout with an electric one, and have on the fly adjustability.

 

CBB, thanks for the vid, the open/close sound helped a ton. I have a duramax with 4" exhaust and a diamond eye "quite" muffler that is a straight thru muffler and it is what I would consider quite enough. I wasn't sure if an oil burner would be different than a gas job but your vid tells the story. Looking like a turbo/straight thru combo with a cutout for the C10 is a good option for me, especially if I go with a single pipe out the back which is the economical option. I know duals belong on the truck but I like the idea of a 3" single as a "conversation piece"

GT: Thanks for the Warlock suggestion, I didn't know those existed. If I drop the extra cash and go dual that is for sure a consideration. I have actually been looking to quite down my Nova a bit as I plan to run it on the street more. I was going to install a muffler with more restriction and vband them in place so I could drop them at the track. This might be a better option especially if I go with electric cutouts so I don't need to crawl under the car as much.
https://www.jegs.com/i/Flowtech/387/50560/10002/-1