3in to twin 2.25in exhaust- (GT35) How much power/spool are we leaving on the table?
#1
Senior Member
Thread Starter
3in to twin 2.25in exhaust- (GT35) How much power/spool are we leaving on the table?
As title really.
I have a car here with a GT35 single turbo setup running a 3in turbo back system that splits to twin 2.25in near the rear diff.
I have seen many people saying even on a small turbo like a 35 there are gains to be had going bigger than 3in, but really, how much is to be gained?
Enough to warrent making a bigger system?
I'd be maybe more interested in spool/response/torque (or even lower EGTs) improvments than bhp, but of course that's nice too
Would just a bigger downpipe and keep the current rest of system be a big help?
Needs to stay fairly quiet for track use, so the split to twin silencers is useful, and I don't want to spend a fortune making a complete new system for only small gains.
Thanks
I have a car here with a GT35 single turbo setup running a 3in turbo back system that splits to twin 2.25in near the rear diff.
I have seen many people saying even on a small turbo like a 35 there are gains to be had going bigger than 3in, but really, how much is to be gained?
Enough to warrent making a bigger system?
I'd be maybe more interested in spool/response/torque (or even lower EGTs) improvments than bhp, but of course that's nice too
Would just a bigger downpipe and keep the current rest of system be a big help?
Needs to stay fairly quiet for track use, so the split to twin silencers is useful, and I don't want to spend a fortune making a complete new system for only small gains.
Thanks
#4
Too Many Projects
iTrader: (10)
Assuming 0.063" wall thicknesses, dual 2.25" actually has more cross-sectional area than a single 3" does (7.08 sq. in vs. 6.49 sq. in.), however with the extra wall area there will be significantly more drag near the outside of the tubing with the dual 2.25" setup than with the 3". I think performance wise, dual 2.25" and single 3" would be similar, with the 3" edging it out.
More to the topic....is the motor ported? I believe with a ported motor you will see gains in response and horsepower potential if you were to move to a 3.5" downpipe and 3" downpipe-back. With the stock ports, you probably won't notice any real difference in response, but maybe in power potential.
Personally I run a straight 4" exhaust (modified A-Spec exhaust with a RandomTech cat) and I noticed great improvements in terms of response with my T04Z and street port over the previous 3" setup.
More to the topic....is the motor ported? I believe with a ported motor you will see gains in response and horsepower potential if you were to move to a 3.5" downpipe and 3" downpipe-back. With the stock ports, you probably won't notice any real difference in response, but maybe in power potential.
Personally I run a straight 4" exhaust (modified A-Spec exhaust with a RandomTech cat) and I noticed great improvements in terms of response with my T04Z and street port over the previous 3" setup.
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#8
Senior Member
Thread Starter
Yes, street ports, nothing too crazy.
Sounds like we not losing out too much, but as the downpipe needs modifying a little, if we can make it bigger too, than sounds a good plan.
The engine is mostly about response and big midrange power, so that was my main concern, extra power up top would be a bonus though.
Because if you already have dual 3in but less than about 700bhp, why'd you want to change it?! Unless it starts as a single 3in, which makes a twin 3in later pointless.
Sounds like we not losing out too much, but as the downpipe needs modifying a little, if we can make it bigger too, than sounds a good plan.
The engine is mostly about response and big midrange power, so that was my main concern, extra power up top would be a bonus though.
Because if you already have dual 3in but less than about 700bhp, why'd you want to change it?! Unless it starts as a single 3in, which makes a twin 3in later pointless.
#9
Rotary Freak
iTrader: (10)
I was thinking of changing it because someone offered me $1500 for my system???!!!??! Daym??? But I changed my mind.
So from what you're saying these are the steps I should do to make my dual 3" system worthwhile:
1. Cut my y-pipe in half
2. Buy more 3" piping and weld it to each section of y pipe to make "true duals"
3. Buy 2 60 trims
4. Buy 2 wastegates
5. Make a twin turbo manifold(s)
6. Bolt on twin turbos
7. Attach each 3" exhaust pipe to each turbo.
8. Dyno at 700+whp
And yes I was actually thinking of doing this too.
#10
Trunk Ornament
iTrader: (11)
I've found that when working with dual exhausts, it becomes tricky to calculate out just how large to go with each of the "daughter" pipes. See, the headloss equation states:
where:
hf is the head loss due to friction (SI units: m);
L is the length of the pipe (m);
D is the hydraulic diameter of the pipe (for a pipe of circular section, this equals the internal diameter of the pipe) (m);
V is the average velocity of the fluid flow, equal to the volumetric flow rate per unit cross-sectional wetted area (m/s);
g is the local acceleration due to gravity (m/s2);
f is a dimensionless coefficient called the Darcy friction factor.
As the cross-sectional surface area of the pipe increases, the speed of the exhaust exiting the pipe will inherently decrease. You want to try to match as closely as possible the size of pipe for amount of flow coming out. Otherwise, you'll get more "headloss" and end up actually restricting the flow with a huge pipe. It's a common misconception with many people that the bigger pipe, the better.
where:
hf is the head loss due to friction (SI units: m);
L is the length of the pipe (m);
D is the hydraulic diameter of the pipe (for a pipe of circular section, this equals the internal diameter of the pipe) (m);
V is the average velocity of the fluid flow, equal to the volumetric flow rate per unit cross-sectional wetted area (m/s);
g is the local acceleration due to gravity (m/s2);
f is a dimensionless coefficient called the Darcy friction factor.
As the cross-sectional surface area of the pipe increases, the speed of the exhaust exiting the pipe will inherently decrease. You want to try to match as closely as possible the size of pipe for amount of flow coming out. Otherwise, you'll get more "headloss" and end up actually restricting the flow with a huge pipe. It's a common misconception with many people that the bigger pipe, the better.
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