Backpressure-what can I do?
Backpressure-what can I do? I have a 408 and a TTI Street kit with a T-76, AFR 225s, FAST 90 intake ported by Tony Mamo with AFR, 90 MM FAST throttle body, custom comp cam, dual welbros, built 4L80E, Moser 12 bolt w/ 3.42s, wideband commander, boost guage. Here are the engine specs:
Combination Motorsports Outlaw Iron block:
LS1 6.0L iron block
Callies Racemaster 4340 Forged Crankshaft 4.000" Stroke
Callies Compstar Connecting Rods 6.125"
Mahle Forged Pistons 4.030" Bore, -12cc Dish
Mahle Plasma-Moly Piston Rings
PolyDyn Coated Clevite H series Cam, Rod, Main Bearings
ARP Main Studs
Fully Balanced
Assembled short block complete with build sheets
IS BACKPRESSURE GONNA HURT ME? IF SO, WHAT CAN I DO TO MINIMIZE WITH THE PARTS I HAVE???? PLEASE HELP!!!!!!!!!!!!!
THANKS!!!!!!!!!!!!!
Sorry I didn't include this: 10 # of boost maximum!
Combination Motorsports Outlaw Iron block:
LS1 6.0L iron block
Callies Racemaster 4340 Forged Crankshaft 4.000" Stroke
Callies Compstar Connecting Rods 6.125"
Mahle Forged Pistons 4.030" Bore, -12cc Dish
Mahle Plasma-Moly Piston Rings
PolyDyn Coated Clevite H series Cam, Rod, Main Bearings
ARP Main Studs
Fully Balanced
Assembled short block complete with build sheets
IS BACKPRESSURE GONNA HURT ME? IF SO, WHAT CAN I DO TO MINIMIZE WITH THE PARTS I HAVE???? PLEASE HELP!!!!!!!!!!!!!
THANKS!!!!!!!!!!!!!
Sorry I didn't include this: 10 # of boost maximum!
Last edited by kcfan; Apr 27, 2006 at 10:39 AM.
Precision Turbo and others have told me that over 1.5:1 backpressure at the turbo can be problematic.
But it will depend on how much boost you run. You'll need to measure it.
But it will depend on how much boost you run. You'll need to measure it.
TECH Senior Member
Joined: Nov 2001
Posts: 10,341
Likes: 1
I would put a T88 on there if possible.
Also I have heard the street kit intercoolers aren't ideal. I have no direct experience with them however. An intercooler upgrade might help your power delivery (but will not affect your backpressure)
Also I have heard the street kit intercoolers aren't ideal. I have no direct experience with them however. An intercooler upgrade might help your power delivery (but will not affect your backpressure)
Originally Posted by CHRISPY
I would put a T88 on there if possible.
I’d make sure you had the biggest of everything that kit has to offer (ie Dp, wastegate, log ect). I don't know where the wastegate on your kit is located, but the newer kits have the wg closer to the passanger manifold, which is better and would definatly help reduce bp. I'd also run a cutout right off the DP, that would atleast let you get a lot of air out of the turbine as soon as possible (also give you a bunch of power). Then there's maybe looking to get a tangental housing on the turbo, but that would also take a little modifaction. That's about all you can do.
The main problem is that your motor could make 500+rwhp WITH OUT a turbo kit. And really, the street kit is made for 500-650 rwhp, so in reality, that turbo kit could be a restriction (I had a similar problem with the T-60 turbo on a street kit). If it were me, I'd sell that kit and get a better on (ie TTi race kit, PTK, Hi/flow, GRM race ect)
Later,
Dave
TECH Senior Member
Joined: Nov 2001
Posts: 10,341
Likes: 1
Backpressure that he is referring too is between the uppipe(s) and the turbo(s).
You might see pressure drop on the cold side between the turbo and the intercoolers but that is not the same thing he is talking about.
You could increase the AR on the exhaust side to mitigate it or go bigger turbo.
Cheers,
Chris
You might see pressure drop on the cold side between the turbo and the intercoolers but that is not the same thing he is talking about.
You could increase the AR on the exhaust side to mitigate it or go bigger turbo.
Cheers,
Chris
Originally Posted by SUPER DAVES Z
Yeah an 88 won't fit without serious modifaction (would not be worth the trouble).
I’d make sure you had the biggest of everything that kit has to offer (ie Dp, wastegate, log ect). I don't know where the wastegate on your kit is located, but the newer kits have the wg closer to the passanger manifold, which is better and would definatly help reduce bp. I'd also run a cutout right off the DP, that would atleast let you get a lot of air out of the turbine as soon as possible (also give you a bunch of power). Then there's maybe looking to get a tangental housing on the turbo, but that would also take a little modifaction. That's about all you can do.
The main problem is that your motor could make 500+rwhp WITH OUT a turbo kit. And really, the street kit is made for 500-650 rwhp, so in reality, that turbo kit could be a restriction (I had a similar problem with the T-60 turbo on a street kit). If it were me, I'd sell that kit and get a better on (ie TTi race kit, PTK, Hi/flow, GRM race ect)
Later,
Dave
I’d make sure you had the biggest of everything that kit has to offer (ie Dp, wastegate, log ect). I don't know where the wastegate on your kit is located, but the newer kits have the wg closer to the passanger manifold, which is better and would definatly help reduce bp. I'd also run a cutout right off the DP, that would atleast let you get a lot of air out of the turbine as soon as possible (also give you a bunch of power). Then there's maybe looking to get a tangental housing on the turbo, but that would also take a little modifaction. That's about all you can do.
The main problem is that your motor could make 500+rwhp WITH OUT a turbo kit. And really, the street kit is made for 500-650 rwhp, so in reality, that turbo kit could be a restriction (I had a similar problem with the T-60 turbo on a street kit). If it were me, I'd sell that kit and get a better on (ie TTi race kit, PTK, Hi/flow, GRM race ect)
Later,
Dave
Any of these kits allow you to keep AC?
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SSU Moderator
Joined: Nov 2001
Posts: 4,857
Likes: 0
From: Austin, TX
you're gonna move serious air with that motor. Too much for the log and too much for the on-center small t76. PTK (shhhhhhh!) keeps A/C and can fit a T4 PT88 I think, and hiflo said they could too. I'd wait for HiFlo and get a custom turbo or just PT88.
Originally Posted by RyanJ
you're gonna move serious air with that motor. Too much for the log and too much for the on-center small t76. PTK (shhhhhhh!) keeps A/C and can fit a T4 PT88 I think, and hiflo said they could too. I'd wait for HiFlo and get a custom turbo or just PT88.
What are my best options to reduce backpressure while keeping what I have?
Thanks to all!!
SSU Moderator
Joined: Nov 2001
Posts: 4,857
Likes: 0
From: Austin, TX
well, if you've already got the kit...then I think it sounds fine. 
I think you can only go so big on a TTi street kit. Its like an on-center T76 with a smaller comp. cover? Can't remember. I think the max is .96 A/R. Unless you can find a larger on-center A/R, or talk you're builder into trying to fit an on-center PT88 (which I think PTE makes now), just stick with what you have and don't put any exhaust on it. There are probably some other things you can do with the tune to keep heat out of the log I think...to advanced for me.
I think you can only go so big on a TTi street kit. Its like an on-center T76 with a smaller comp. cover? Can't remember. I think the max is .96 A/R. Unless you can find a larger on-center A/R, or talk you're builder into trying to fit an on-center PT88 (which I think PTE makes now), just stick with what you have and don't put any exhaust on it. There are probably some other things you can do with the tune to keep heat out of the log I think...to advanced for me.
..... An Idea which im sure has been stated before is a durations which favors the intake with a smaller exhaust duration on the cam. Thats what I run at least. Yeah the other thing is definitely a larger housing.
Originally Posted by kcfan
Ryan, Thanks for the advice. This build has been going on for 13 months now and I really don't want to think about asking my builder to disassemble the turbo kit already mounted on the car, sell the kit, buy another kit, sell the turbo itself, buy another turbo, etc.
What are my best options to reduce backpressure while keeping what I have?
Thanks to all!!
What are my best options to reduce backpressure while keeping what I have?
Thanks to all!!
Last edited by ESR; Apr 27, 2006 at 01:00 PM.
My advice is to not worry at 10psi. You've worked on it for 13 months and it's ready to go. Get a GREAT TUNE on a dyno with a wideband and you'll be fine...even if you have to drop the boost down to 8psi while tuning (probably will not), you'll make killer torque and be safe.
Enjoy the ride the rest of the year and if you get bored over winter, add a different kit....8 to 10 psi may make you very happy.
Enjoy the ride the rest of the year and if you get bored over winter, add a different kit....8 to 10 psi may make you very happy.