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Is my exhaust too restrictive now?

WarWagon said:
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?
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n8in8or said:
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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Sounds like it is time for deciding whether to keep going after hardware or tune for the hardware you have. Put another way, the software is getting out of sync with the hardware.
 
HX40 has a turbine exhaust outlet of 8.95 in2 then squeezing it into a 6.49 in2 (aka: 3") downpipe is an issue. Holset going with the 4" on the HX40 is very clear about needing it so there would be no back pressure..

HX35 has a turbine exhaust outlet of 6.49 in2 and flowing into a 6.49 in2 (aka 3").....
 
JayTheCPA said:
Sounds like it is time for deciding whether to keep going after hardware or tune for the hardware you have. Put another way, the software is getting out of sync with the hardware.
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Right on. I'm probably somewhere in the middle as my IP and the fuel it puts out is the pacing item and I'm just getting the rest of the combo to keep up with that which may take a little bit more hardware. I'm close though....
 
FellowTraveler said:
HX40 has a turbine exhaust outlet of 8.95 in2 then squeezing it into a 6.49 in2 (aka: 3") downpipe is an issue. Holset going with the 4" on the HX40 is very clear about needing it so there would be no back pressure..

HX35 has a turbine exhaust outlet of 6.49 in2 and flowing into a 6.49 in2 (aka 3").....
Click to expand...
Where is that 8.95in^2 measured at? I thought when I built my downpipe adapter I had measured the diameter being around 3" but I could be remembering that wrong.
 
That MYHolset site says a required 4 inch downpipe probably because it's a 4in flange. I've seen a lot of HX40's with 3in flange outlet from factory. So why make them if it's a restriction. A lot of the HX40 applications too are on larger engines which flow a lot more exhaust gas than a 6.5L would. I ain't buying into the turbine housing being a restriction because of a 3in downpipe.
 
JayTheCPA said:
Once you get a nice 'growl' from the tailpipe, the next mod is a louder stereo ;)
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The very first mod I did was replace all the blown and or rotted out speakers in the first 6.5 we got with some of the best aftermarket that would fit the holes. I kept the factory look and head unit. Then I shoved an Sirius radio in the aftermarket radio hole mainly so one doesn't have to change stations 50 times on a single 550 mile trip as they go out of range. I still need to find the extended cab plastic headliner part that hasn't turned to dust from the AZ heat and sun...

You see when things go "Boom!" leaving said hot oily parts embedded in the pavement (or murdered Elk all over the place) it's a requirement to listen to the calming radio while waiting for the tow truck. Cell phones may not work, fuses for the flashers may have popped from shorted in the crash wires, one battery may be missing it's blown off top, but, the Sirius XM radio is working. (Shorted flashers is why you carry the triangle and flare kit at all times. Replace flares yearly.) As my dad says: "It Ain't No Good Unless You Can Feel It!" Yeah, the factory radio operates with almost all the volume indicators lit and, no, it doesn't go to 11.

Again short in town trips are ok, but, the long trip truck has a quiet exhaust. Patch when used on long trips has me thinking of adding the second resonator that's close to the downpipe like Diamond eye offers for Duramax exhausts.
 
6.5L said:
That MYHolset site says a required 4 inch downpipe probably because it's a 4in flange. I've seen a lot of HX40's with 3in flange outlet from factory. So why make them if it's a restriction. A lot of the HX40 applications too are on larger engines which flow a lot more exhaust gas than a 6.5L would. I ain't buying into the turbine housing being a restriction because of a 3in downpipe.
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However we are talking super 40 on his application so that's why my comments..I suspect the 3" pipe is the restriction on the bigger turbine size..
 
WarWagon said:
The very first mod I did was replace all the blown and or rotted out speakers in the first 6.5 we got with some of the best aftermarket that would fit the holes. I kept the factory look and head unit. Then I shoved an Sirius radio in the aftermarket radio hole mainly so one doesn't have to change stations 50 times on a single 550 mile trip as they go out of range. I still need to find the extended cab plastic headliner part that hasn't turned to dust from the AZ heat and sun...

You see when things go "Boom!" leaving said hot oily parts embedded in the pavement (or murdered Elk all over the place) it's a requirement to listen to the calming radio while waiting for the tow truck. Cell phones may not work, fuses for the flashers may have popped from shorted in the crash wires, one battery may be missing it's blown off top, but, the Sirius XM radio is working. (Shorted flashers is why you carry the triangle and flare kit at all times. Replace flares yearly.) As my dad says: "It Ain't No Good Unless You Can Feel It!" Yeah, the factory radio operates with almost all the volume indicators lit and, no, it doesn't go to 11.

Again short in town trips are ok, but, the long trip truck has a quiet exhaust. Patch when used on long trips has me thinking of adding the second resonator that's close to the downpipe like Diamond eye offers for Duramax exhausts.
Click to expand...
I know a revving video doesn't necessarily equate to what an exhaust sounds like going down the road, but here is what my exhaust install sounded like after I first did it. This is the Diamond Eye modified to fit a Tahoe and the 4"x30" FTE Resonator/Muffler. Of course this is also with the GM8 too so I'm not sure how much this will help you.

 
I can't see the bigger turbine being a restriction either. With a bigger turbine, the volume of exhaust gases doesn't change. The bigger turbine just redirects the exhaust gasses to impact the turbine wheel at a degree less than 90*, which allows for better flow but slower spool ability. If anybody remembers physics, general torque is a force applied at angle; theta, multiplied by the Sin theta. The Sin of 90* is 1, meaning all the torque is multiplied by 1, theoretically losing nothing. At angles less than 90*, the sin of theta starts to drop to less than one, meaning only partial torque is transferred to turning the wheel. However, the flow becomes greater through the turbine. Regardless of turbine size, the amount of exhaust gases traveling through the turbine remains the same. If it's enough for the 3inch pipe to handle, then the turbine size shouldn't matter.
 
I'm hoping to hit the dyno next week. Then I'll make a 4" downpipe and we'll see if it makes a difference or not. I was just searching for a 4" exhaust ball&socket flange for the downpipe to exhaust connection and so far haven't had any luck. I tried Summit first, then a general Google search. Any suggestions? I like the idea of the ball and socket and not a V-band in that location because it allows a lot of adjustment for clearance.
 
Actually now that I'm thinking about it, I think it would be easy to take the exhaust apart just before my Dynomax muffler and see what difference taking that off has. I was planning to use my 3 pulls to try various Puff Limiter settings, but I could do 1 Puff Limiter adjustment, see what difference that makes (if any) and then drop the muffler. If the Puff Limiter does make a difference then I'll probably make an additional Puff Limiter adjustment just to see. Maybe I'll see what a 4th pull will cost.
 
I have the stock DURAMAX downpipe on mine which isn't even a full 3" with several spots where it's reduced down some, then I have the 3.5" front stock section in it back past the torsion bar crossmember, and 4" from there out the back with a straight through CORSA muffler(You can drop a 4" diameter ball straight through it if you wanted to). I know I'm currently in the 400HP range at the wheels, and have gone well beyond 500 at one time playing with a hot tune, and the exhaust never seemed restrictive to me. I know SEVERAL guys have went BEYOND 600HP on 4" mandrel bent systems, even seen one guy do over 800HP on just a 4" system. Even seen where one guy who is using a STOCK LB7 exhaust on his truck with nothing more than a muffler delete(they're 3.5" press bent), did 638HP out of his. So I HIGHLY doubt a 4" system even with that short section of 3" downpipe is ANY sort of significant restriction.
 
n8in8or said:
I'm hoping to hit the dyno next week. Then I'll make a 4" downpipe and we'll see if it makes a difference or not.
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If you do decide to try this, keep notes on how you do it as others might have an interest if the dyno results are supportive ;)

One thing to watch is the transition from firewall to floorboard is typically tight as IIRC the tranny cross-member and rear heater hoses make for congestion. So a 4" downpipe will eat into that already tight space.

And . . . a 4" downpipe will likely need heat treating right away as it will get even closer to the A/C elements than the 3" pipe.
 
JayTheCPA said:
If you do decide to try this, keep notes on how you do it as others might have an interest if the dyno results are supportive ;)

One thing to watch is the transition from firewall to floorboard is typically tight as IIRC the tranny cross-member and rear heater hoses make for congestion. So a 4" downpipe will eat into that already tight space.

And . . . a 4" downpipe will likely need heat treating right away as it will get even closer to the A/C elements than the 3" pipe.
Click to expand...
Round to oval then back to round.....
 
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