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Is my exhaust too restrictive now?

n8in8or

n8in8or

I never met a project I didn’t like
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I'm starting to wonder if my exhaust is too restrictive now that I'm making more power. I've been driving around with my windows open, and of course when I'm next to a wall or something I just have to lay into it. Well when I've done this all I hear is the turbo whistle and more of a "whooshing" sound from the exhaust rather than the V8 growl. I recently passed my brother on the highway and I asked him what he heard - he also said he just heard whistle. This is making me think that perhaps the exhaust is too restrictive. Does this sound right? I know this could be confirmed with some pressure taps, but before I went through that trouble or started doing additional exhaust upgrades I wanted to hear what you guys thought on that. Now when I'm hearing this whoosh, I'm at about 25psi of boost, so maybe that's just a normal sound once I'm running that much pressure? My main motivation for making sure that the exhaust flows as much as possible is that I now have plenty of fuel and the exhaust cleans up overall, but it's still sometimes a bit smokier than I'd like. Also if I could reduce some exhaust restriction this would help reduce EGTs a little.

In case you aren't able to see my signature, here's my exhaust: The base of it is a Diamond Eye exhaust for a Sub modified to fit the Tahoe, so that means I have a 3" downpipe and then a 4" system after that. The first mod is a 4" x 30" FTE Diesel Resonator/Muffler, this is mounted immediately after the downpipe per their instructions (basically where the factory catalytic convertor was). The second mod is the addition of a Dynomax Ultra Flo 21172 muffler in front of the axle, this is a straight through, perforated-core muffler.

I had already been thinking that I wanted to make a full 4" downpipe. Now I'm thinking that if I do have an exhaust restriction that is my first culprit. The second would be the Dynomax muffler. I tried looking up the cfm specs on the muffler, but I can't find them yet.

As far as testing goes, does anyone know if a standard boost gauge would stand up to the heat and soot of exhaust if I used my old boost gauge to test back pressure? The first thing that would be easiest to test would be to remove the muffler.....it isn't as simple as a straight pipe because I had to weld an elbow to the muffler in order to make it fit, but still easier than making a new downpipe.

So what do you think? Am I worried about nothing? Should I start investigating? Any tests or test methods I haven't thought of or that you've done in the past that I haven't thought of?
 
The full sized HX40 18 cm2 requires a 4" down-pipe, a straight 3" id pipe will flow around 747 +- cfm in a normally aspired application then deduct for loss in pipe turns unless going with cobra head turns throughout.

The FTE has very little restriction, IMO a muffler will restrict cfm flow up top unless over sized for application.

25 lbs of boost on gauge would be 2.7 pressure ratio or about 60 +- lbs of air.

Measure drive pressure and back pressure @ different rpm's with & without the 3" down pipe. There are a few 4" down-pipes for the 1st gen Ram Cummins that will fit tightly or cut down some for testing. Consider, when gate pops open that will cause some back pressure too.

Copper tubing from exhaust to gauge should be OK, if worried get a cheap gauge for that side...

Other things like how much air can you cram through 400 motor so rpm to cfm and VE (boost increases ve) also must be considered see: http://www.thetruckstop.us/forum/threads/rpm-to-ve-cfm-flow-through-the-6-5td.45002/

Lastly, intake and head flow could be improved via porting, however, no engine dyno data exists that I know of and it is the subject of much debate and arguments..as it relates to the 6.2/6.5 platform.
 
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Just another thought, I forgot your running a water to air CAC, the CAC and/or its plumbing "to many turns and/or pipes too small" could cause problems too.
 
So, there are a few places to measure your boost to better determine what is going on 1st is at compressor outlet, 2nd is just before CAC to see how much loss if any is there, 3rd is after CAC again to see how much loss if any is between 1st and this point, 4th would be at intake to see overall loss if any.

CAC temp plays a role up top as EGT's climb so measuring before and after CAC will tell you how efficient the CAC is.

Keep in mind feeding a low rpm diesel is much different that feeding say a small ricer motor that can scream 2,3 even 4 times the rpm's a 400 cid idi diesel can "more rpm's the more cfm that can flow through any given cid." Remember the idi is 15% +- less efficient than a di to begin with.
 
FellowTraveler said:
The full sized HX40 18 cm2 requires a 4" down-pipe, a straight 3" id pipe will flow around 747 +- cfm in a normally aspired application then deduct for loss in pipe turns unless going with cobra head turns throughout.

The FTE has very little restriction, IMO a muffler will restrict cfm flow up top unless over sized for application.

25 lbs of boost on gauge would be 2.7 pressure ratio or about 60 +- lbs of air.

Measure drive pressure and back pressure @ different rpm's with & without the 3" down pipe. There are a few 4" down-pipes for the 1st gen Ram Cummins that will fit tightly or cut down some for testing. Consider, when gate pops open that will cause some back pressure too.

Copper tubing from exhaust to gauge should be OK, if worried get a cheap gauge for that side...

Other things like how much air can you cram through 400 motor so rpm to cfm and VE (boost increases ve) also must be considered see: http://www.thetruckstop.us/forum/threads/rpm-to-ve-cfm-flow-through-the-6-5td.45002/

Lastly, intake and head flow could be improved via porting, however, no engine dyno data exists that I know of and it is the subject of much debate and arguments..as it relates to the 6.2/6.5 platform.
Click to expand...

Ok, so depending on my VE, I could definitely be getting restricted by the 3" downpipe. I don't think I'd get a Ram downpipe and modify it, I'd likely start from scratch. I would probably attempt to fabricate my best approximation of a cobra head too. Then, as I think about this more, it makes me think about redoing my header to move the turbo forward in the engine bay to give me more downpipe room. If I do that, then it makes me think about doing a front crossover like Burning Oil and 6.5L. So that's why the 4" downpipe scares me...SCOPE CREEP!! I think I can make a 4" fit as-is though so if I can keep my dreams under control then I may be ok.

I ported my heads when I built the engine and port-matched the intake to the heads, but didn't port the intake itself.

FellowTraveler said:
Just another thought, I forgot your running a water to air CAC, the CAC and/or its plumbing "to many turns and/or pipes too small" could cause problems too.
Click to expand...

I have just 2 bends, the first being a 2.25"-3" adapter without about a 30* angle. The second is a 3" 90* bend. The CAC is oversized for the application to reduce restriction.

FellowTraveler said:
So, there are a few places to measure your boost to better determine what is going on 1st is at compressor outlet, 2nd is just before CAC to see how much loss if any is there, 3rd is after CAC again to see how much loss if any is between 1st and this point, 4th would be at intake to see overall loss if any.

CAC temp plays a role up top as EGT's climb so measuring before and after CAC will tell you how efficient the CAC is.

Keep in mind feeding a low rpm diesel is much different that feeding say a small ricer motor that can scream 2,3 even 4 times the rpm's a 400 cid idi diesel can "more rpm's the more cfm that can flow through any given cid." Remember the idi is 15% +- less efficient than a di to begin with.
Click to expand...

I'm not too worried about measuring boost pressure/CAC efficiency at this time. When I first installed the CAC I noticed no discernable change on the gauge at 15psi of boost pressure measured at the intake manifold plenum before and after installation. This tells me that it is very unrestrictive though it would be interesting to read some actual numbers. Right now the radiator portion of my CAC is mounted under the truck, I have a plan in the works to create a custom front bumper that will house the radiator. This should make the CAC do a better job of cooling the boosted air.

FellowTraveler said:
Turbine blade count matters and the more blades the quicker the spool at the expense of more back pressure, less blades less back pressure at the expense of spool time.

Then there is the t-3 issue built into the GM 6.5td platform which limits upper flow numbers but is great for a DD.
http://turbolabofamerica.com/turbine-housings/
Click to expand...

When I upgraded the wheels on my turbo I went with a 10-blade turbine instead of 12 blade to give me less restriction.

Yeah, I wish I had done a T4 flange when I built my header....
 
Put it on the dyno then decide if you need to mess with it. Does the Sun go out from the exhaust smoke? Seriously what conditions RPM/Throttle does it smoke that you don't like and how long and bad?

The V8 growl gets old on long trips as a "drone" on Patch. You can hear it 2-3 blocks away especially due to a steep grade in a residential area and a high stall converter unlocked while on said grade. No sneaking home as friends call 'I know your truck went by...' It's the 4" with 3" downpipe and large crossover. ATT of course. Yeah when I start it you know I started something vs. a boring box on wheels! Factory no cat and straight through round muffler as found on common 4" 6.5 aftermarket exhaust - literally a step up from a glasspack IMO. Compare it to the 1995 burb I had with the HX40II or ATT with BD Spool Valve and the sound is way different. The ATT sounds like a jet engine spooling up without the whistle. The Spool Valve ATT combo as @6.5L put is "is Hell trying to escape from the exhaust". The HX40II had more turbo whistle and whooshing than the ATT alone.

If you really want to mess with it then you are going to need to measure backpressure too see if you are helping or hurting. IMO I would start with a larger turbo just from the sound angle and what I know from others on drive pressure ratio of the ATT being lower than the 2.7 number thrown out above. IMO the turbo is more of a restriction than the 3" short down pipe section. You trade other things off with a larger turbo so I wouldn't change much on your setup if it's running well and mostly smoke free.
 
All data I've read relating to the HX40w 16, 18 or 19 cm2 T-3 turbine housing makes note of a 4" down-pipe requirement, after measuring back pressure decide on 4" & T-4 configuration. The later model HX SUPER 40 uses a T-3 turbine housing and an 'up angled gate actuator', early model HX super 40 uses a T-3 housing and low mounted gate actuator that interferes w/most air filter boxes, one step up from here is the HX40w w/T-4 housing and 'up angled gate actuator' which clears most filter housings on GMT400 & Dodge Ram shock towers on newer RAMS.
 
Just throwing this out here, but if a good hopped up DI motor can make 500hp with a 4inch exhaust, I don't really see why a 3 inch downpipe on a 6.5L would start to restrict things. I did find a good middle ground through. I found a 14cm T3 mount turbine housing that fits the HX40 76/64 turbine wheel. So I am currently in the process of upgrading my 35/40 to a HX40 with a 60x86 compressor wheel, billet, and a 76x64 turbine wheel. I opted for the 12 blade over the 10 to decrease spool time. The larger turbine wheel should keep flow up enough to negate the 10 blade flow. At least on a 6.5L. Will post back with results. With my 3 inch downpipe though, even when I had it set to 4500rpm max governor, the exhaust was the least of my concerns.
 
6.5L: The 4.5k rpm will allow for more flow than 3.5k as the charts I put together show (see: post 2), I suspect that is the FACTOR.

What will help any turbo spool faster is a smaller diameter x-over pipe, I consider what cfm flow a straight length of any given ID exhaust pipe can flow N/A then consider that flow is increased under boost always.....
 
6.5L said:
Just throwing this out here, but if a good hopped up DI motor can make 500hp with a 4inch exhaust, I don't really see why a 3 inch downpipe on a 6.5L would start to restrict things. I did find a good middle ground through. I found a 14cm T3 mount turbine housing that fits the HX40 76/64 turbine wheel. So I am currently in the process of upgrading my 35/40 to a HX40 with a 60x86 compressor wheel, billet, and a 76x64 turbine wheel. I opted for the 12 blade over the 10 to decrease spool time. The larger turbine wheel should keep flow up enough to negate the 10 blade flow. At least on a 6.5L. Will post back with results. With my 3 inch downpipe though, even when I had it set to 4500rpm max governor, the exhaust was the least of my concerns.
Click to expand...
Great input....
 
If you want loud . . . Take away the Dynomax muffler and I have the same thing. With the windows down, a conversation is not easy - with our without a wall next to the truck.

So, if loud is what you want, pull out that muffler and see what happens :D

I am with WW about the exhaust drone and whether the neighbors know when you come and go. Once you get a nice 'growl' from the tailpipe, the next mod is a louder stereo ;)
 
WarWagon said:
Put it on the dyno then decide if you need to mess with it. Does the Sun go out from the exhaust smoke? Seriously what conditions RPM/Throttle does it smoke that you don't like and how long and bad?

The V8 growl gets old on long trips as a "drone" on Patch. You can hear it 2-3 blocks away especially due to a steep grade in a residential area and a high stall converter unlocked while on said grade. No sneaking home as friends call 'I know your truck went by...' It's the 4" with 3" downpipe and large crossover. ATT of course. Yeah when I start it you know I started something vs. a boring box on wheels! Factory no cat and straight through round muffler as found on common 4" 6.5 aftermarket exhaust - literally a step up from a glasspack IMO. Compare it to the 1995 burb I had with the HX40II or ATT with BD Spool Valve and the sound is way different. The ATT sounds like a jet engine spooling up without the whistle. The Spool Valve ATT combo as @6.5L put is "is Hell trying to escape from the exhaust". The HX40II had more turbo whistle and whooshing than the ATT alone.

If you really want to mess with it then you are going to need to measure backpressure too see if you are helping or hurting. IMO I would start with a larger turbo just from the sound angle and what I know from others on drive pressure ratio of the ATT being lower than the 2.7 number thrown out above. IMO the turbo is more of a restriction than the 3" short down pipe section. You trade other things off with a larger turbo so I wouldn't change much on your setup if it's running well and mostly smoke free.
Click to expand...

The normal exhaust note the truck makes is just fine with me....a nice growl and plenty loud. I was just wondering if the way it changed at full boost was an indication of restriction. It sounds like not necessarily. Maybe I'll try pullin the muffler and see what it acts like.

6.5L said:
Just throwing this out here, but if a good hopped up DI motor can make 500hp with a 4inch exhaust, I don't really see why a 3 inch downpipe on a 6.5L would start to restrict things. I did find a good middle ground through. I found a 14cm T3 mount turbine housing that fits the HX40 76/64 turbine wheel. So I am currently in the process of upgrading my 35/40 to a HX40 with a 60x86 compressor wheel, billet, and a 76x64 turbine wheel. I opted for the 12 blade over the 10 to decrease spool time. The larger turbine wheel should keep flow up enough to negate the 10 blade flow. At least on a 6.5L. Will post back with results. With my 3 inch downpipe though, even when I had it set to 4500rpm max governor, the exhaust was the least of my concerns.
Click to expand...

I look forward to seeigg your results, you always do a nice job documenting your work.

JayTheCPA said:
If you want loud . . . Take away the Dynomax muffler and I have the same thing. With the windows down, a conversation is not easy - with our without a wall next to the truck.

So, if loud is what you want, pull out that muffler and see what happens :D

I am with WW about the exhaust drone and whether the neighbors know when you come and go. Once you get a nice 'growl' from the tailpipe, the next mod is a louder stereo ;)
Click to expand...

I don't necessarily want loud....in fact if I could have nearly stock quiet and no flow restriction that would be my preference. But then again there are those times.....:D

I put the Dynomax on a couple years ago before a road trip and it made a nice difference for interior sound on the highway. After I installed my intercooler I got more noise, but it's very location-specific: if I move my head to the front passenger area it's pretty much all gone! Unfortunately I can't tell which direction the noise is coming from, but since it showed up after IC install I have to assume it's from there. I still need to do sound interior deadening and I'm hoping it takes care of that problem.
 
Yeah Fellowtraveler, I guess it's sort of hard to judge since my downpipe I full 3 inch straight back with no bends and my crossover is like 2inch ID with the custom manifolds and crossover, So I'd be a totally different setup. Still, I'd say the biggest hurdle pressure wise is the turbine, not the piping
 
6.5L said:
Yeah Fellowtraveler, I guess it's sort of hard to judge since my downpipe I full 3 inch straight back with no bends and my crossover is like 2inch ID with the custom manifolds and crossover, So I'd be a totally different setup. Still, I'd say the biggest hurdle pressure wise is the turbine, not the piping
Click to expand...
I have an 18cm turbine housing right now. Do you think that is a restriction?
 
WarWagon said:
Put it on the dyno then decide if you need to mess with it. Does the Sun go out from the exhaust smoke? Seriously what conditions RPM/Throttle does it smoke that you don't like and how long and bad?
Click to expand...

I just realized I hadn't answered your question. It isn't so bad that it's blocking out the sun, no. When it's cooler out it isn't bad, but when warmer it's definitely more than a haze. I'll try to get some drive-by videos made to show both thw sound and smoke.
 
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