I may have High Exhaust Back Pressure Issues...
10-13-2011, 08:41 AM
#1
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I may have High Exhaust Back Pressure Issues... Hey guys, pretty much getting started on my LS1 Miata Mid-Mount Turbo...
It's Pretty much a 10.9:1 346 LS1, with TSP PRC Stage 2.5 Heads, LS6 Intake.
Anyway, Since the Motor is in a Miata I have VERY limited choices on Headers. The only Bolt on Solution... Which is what I have been running for the past year are my Sanderson 1.5" Primary > 2.5" Collector Block Hugger Headers.
We are cutting off the 3-Bolt Flanges at the Collector's and welding 2.5" V-Band Flange's... Then it will go to 2.5" Mandrel Downpipes leading to a 3.00" Y-Pipe and finally to a T4 Flange near the middle of the car...
Though on my Nitrous Set-Up the car did end up making 500rwhp on these headers... But the new goal is about 600-650whp...
I have NO CHOICE but to run these headers, so please don't recommend custom sets made on the car, as budget is tight.
The real question is, will my exhaust backpressure be much higher than a typical set-up with much larger primaries?
Will I be able to make my 650rwhp goal?
The Turbo set-up consists of:
Walbro 255lph
-8 AN Line going to a stock Corvette regulator (NOT rising rate)
-Comp Turbo OIL-LESS 76mm, T4 Flange, 0.96 A/R, Billet Wheel, Triple Ball Bearing, 3.5" V-Band Outlet, Turbo.
-Precision 46mm External
-Siemens 80lb Injectors
-Stock LS1/LS6 Fuel Rails
-Large FMIC
-2.5" Intercooler Piping Mandrel
I may be Dreaming, but the goal is 550whp at 8-9psi... Possible?
I believe thats pretty much it...
Give me insight please!
It's Pretty much a 10.9:1 346 LS1, with TSP PRC Stage 2.5 Heads, LS6 Intake.
Anyway, Since the Motor is in a Miata I have VERY limited choices on Headers. The only Bolt on Solution... Which is what I have been running for the past year are my Sanderson 1.5" Primary > 2.5" Collector Block Hugger Headers.
We are cutting off the 3-Bolt Flanges at the Collector's and welding 2.5" V-Band Flange's... Then it will go to 2.5" Mandrel Downpipes leading to a 3.00" Y-Pipe and finally to a T4 Flange near the middle of the car...
Though on my Nitrous Set-Up the car did end up making 500rwhp on these headers... But the new goal is about 600-650whp...
I have NO CHOICE but to run these headers, so please don't recommend custom sets made on the car, as budget is tight.
The real question is, will my exhaust backpressure be much higher than a typical set-up with much larger primaries?
Will I be able to make my 650rwhp goal?
The Turbo set-up consists of:
Walbro 255lph
-8 AN Line going to a stock Corvette regulator (NOT rising rate)
-Comp Turbo OIL-LESS 76mm, T4 Flange, 0.96 A/R, Billet Wheel, Triple Ball Bearing, 3.5" V-Band Outlet, Turbo.
-Precision 46mm External
-Siemens 80lb Injectors
-Stock LS1/LS6 Fuel Rails
-Large FMIC
-2.5" Intercooler Piping Mandrel
I may be Dreaming, but the goal is 550whp at 8-9psi... Possible?
I believe thats pretty much it...
Give me insight please!
10-13-2011, 11:41 AM
#5
Turbo's don't follow the N/A rule of thought relating to primary, collector and y-pipe diameter. You want the opposite of a N/A motor, the smallest size primary etc. that you can get away with without killing volume off completely. You want velocity of the exhaust gas to be at very speeds and temperatures to spool the turbo properly and quickly. Then after the turbo(downpipe) you want the biggest most unrestricted route you can get the exhaust gasses out.
In your case 3" will be way to big killing spool with a t4, heck 3" is too big for most T6 set-ups. Your headers will be perfectly fine at 2.5 collectors and 2.5" y-pipe.
You have nothing to worry about here, the hard part will be getting a big enough downpipe out the turbo and out of the engine bay.
Love the thought of a turbo in a miata, especially a ls turbo miata.
In your case 3" will be way to big killing spool with a t4, heck 3" is too big for most T6 set-ups. Your headers will be perfectly fine at 2.5 collectors and 2.5" y-pipe.
You have nothing to worry about here, the hard part will be getting a big enough downpipe out the turbo and out of the engine bay.
Love the thought of a turbo in a miata, especially a ls turbo miata.
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10-14-2011, 01:01 AM
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Intercooler in/out is 2.5"...
Also, very little room to play with, can't do 3.00" charge pipe.
Downpipe will be about 1 foot long, 3.5" downpipe, dumped.
What are my losses if I stuck to the factory corvette regulator and didn't do a 1:1 rising rate?
Also, very little room to play with, can't do 3.00" charge pipe.
Downpipe will be about 1 foot long, 3.5" downpipe, dumped.
What are my losses if I stuck to the factory corvette regulator and didn't do a 1:1 rising rate?
10-14-2011, 02:39 AM
#9
the 1:1 regulator will increase fuel pressure 1 psi for every 1 psi increase in boost, compensating for what i described above.
What it boils down to is that you dont want to be diminishing your fuel pressure, as this can make it more difficult to tune the car, as well as you might run out of fuel capacity at a certain point. You may be okay with low boost pressures, but it would be better to add a 1:1 regulator.
10-14-2011, 11:48 AM
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you will be counteracting the fuel pressure with your boost pressure. For example: If you have 50psi of fuel pressure, and you are running 10psi boost, that 10psi will be in the intake manifold runners (where the injectors are) and putting pressure on the face of the injector. that means you will only get approximately 40psi of fuel pressure.
the 1:1 regulator will increase fuel pressure 1 psi for every 1 psi increase in boost, compensating for what i described above.
What it boils down to is that you dont want to be diminishing your fuel pressure, as this can make it more difficult to tune the car, as well as you might run out of fuel capacity at a certain point. You may be okay with low boost pressures, but it would be better to add a 1:1 regulator.
the 1:1 regulator will increase fuel pressure 1 psi for every 1 psi increase in boost, compensating for what i described above.
What it boils down to is that you dont want to be diminishing your fuel pressure, as this can make it more difficult to tune the car, as well as you might run out of fuel capacity at a certain point. You may be okay with low boost pressures, but it would be better to add a 1:1 regulator.
My tuner said that I should fine for now with the Vette Regulator, if we run in to any issues on the dyno (lean) then we will change regulators accordingly...
10-14-2011, 02:17 PM
#13
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Dont worry about the boost referenced regulator.
As long as you size injectors accordingly then it is not a problem. It isnt ideal, but it is not a problem.
1000cc injectors run at 60psi base pressure will easily provide far more fuel than you will ever need. Even at 20psi boost you will still have 40psi of fuel pressure, which is pretty close what most injectors are flow rated at anyway
As long as you size injectors accordingly then it is not a problem. It isnt ideal, but it is not a problem.
1000cc injectors run at 60psi base pressure will easily provide far more fuel than you will ever need. Even at 20psi boost you will still have 40psi of fuel pressure, which is pretty close what most injectors are flow rated at anyway
