pipe sizing for a twin rear mount?
pipe sizing for a twin rear mount? I'm going to be running a twin GT35 turbo setup. I'm running the stock 2.75" exhaust y"d to the turbos (t3) housing. My question is should run a 2.5" or a 2 1/4 cold side pipe back to the front? or would it even matter? they will be y'd back to one pipe. I haven't found any real great info on this.
Conventional wisdom always says go bigger, but it really isn't going to matter - so whatever fits best. I would select it based on what fits best and what arrangement you can get a nicest "Y" for when they join.
I wouldn’t call it conventional wisdom. I’d call it a typical misconception. Which is pretty much wrong with remote mount turbos… and even conventional turbo systems. Most DIY guys go way overboard on the exhaust hot side and cold side diameters. It not only hurts response, but you can actually slow the velocity’s down so much that it requires the use of a smaller than ideal turbo to have “normal” spool/response times. When you could have run a much larger turbo with less overall system back pressure using a smaller diameter hot side.
How is your “Stock 2.75 exhaust” plumbed into twins? Sounds like you may be are going larger than needed on the hotside already. What kind of power are you wanting?
.25” change in cold side diameter won’t add all that much total volume to the system. But every little bit helps, esp with a manual trans. You also want velocity up going through a heat exchanger as well. It makes it more efficient. Slowing the air down to a crawl through the IC does the opposite of what you want.
How is your “Stock 2.75 exhaust” plumbed into twins? Sounds like you may be are going larger than needed on the hotside already. What kind of power are you wanting?
.25” change in cold side diameter won’t add all that much total volume to the system. But every little bit helps, esp with a manual trans. You also want velocity up going through a heat exchanger as well. It makes it more efficient. Slowing the air down to a crawl through the IC does the opposite of what you want.
Agreed - many street builds would be better served with smaller hotside piping before the turbo
You want the optimal sized piping... always. Especially with max effort racing setups. What people think is optimal is usually the problem. The only real way to know is to test. Or to have a significantly greater understanding of ideal gas laws and mathematics than 99.9% of us have! lol
2" OD from each factory manifold to a 2.25" single pipe and split back into 2" feeding each g35 works really well on small bore LS stuff to about 600 whp. Use the shortest runs as possible and wrap them. 2.25" is plenty for the charge pipe returning.
As an example I ran 2" from factory manifolds to each side of a dual scroll T6 S480 on a little 4.8. 2" 16G mild steel (which is really like 1.8" id) worked really well and it allowed me to spool a relatively large T6 S480 easily and maintain lower overall system back pressure than most small bore LS setups with t4 single setups. Yet I could spool just as quickly (or better than) many T4 setups with similar cubes. Run a larger cam, and make more power per pound because I used smaller piping and a larger turbo. Also ran a 370" motor and a 5.3" on the same 2" hotside combo to the same mid 8 sec ET's and trap speeds. 2" hotside piping is all most street/strip mild setups need. Yet we still see guys throwing 2.5" and 3" hot sides on mild setups. It just added weight, cost, and more difficult to plumb. Remote setups are even more sensitive to exh diameters.
IMO for most sub 900whp setups... 2" is the way to go. I've yet to see any data to prove otherwise.
2" OD from each factory manifold to a 2.25" single pipe and split back into 2" feeding each g35 works really well on small bore LS stuff to about 600 whp. Use the shortest runs as possible and wrap them. 2.25" is plenty for the charge pipe returning.
As an example I ran 2" from factory manifolds to each side of a dual scroll T6 S480 on a little 4.8. 2" 16G mild steel (which is really like 1.8" id) worked really well and it allowed me to spool a relatively large T6 S480 easily and maintain lower overall system back pressure than most small bore LS setups with t4 single setups. Yet I could spool just as quickly (or better than) many T4 setups with similar cubes. Run a larger cam, and make more power per pound because I used smaller piping and a larger turbo. Also ran a 370" motor and a 5.3" on the same 2" hotside combo to the same mid 8 sec ET's and trap speeds. 2" hotside piping is all most street/strip mild setups need. Yet we still see guys throwing 2.5" and 3" hot sides on mild setups. It just added weight, cost, and more difficult to plumb. Remote setups are even more sensitive to exh diameters.
IMO for most sub 900whp setups... 2" is the way to go. I've yet to see any data to prove otherwise.
Last edited by Forcefed86; Apr 26, 2024 at 11:08 AM.
You want the optimal sized piping... always. Especially with max effort racing setups. What people think is optimal is usually the problem. The only real way to know is to test. Or to have a significantly greater understanding of ideal gas laws and mathematics than 99.9% of us have! lol
2" OD from each factory manifold to a 2.25" single pipe and split back into 2" feeding each g35 works really well on small bore LS stuff to about 600 whp. Use the shortest runs as possible and wrap them. 2.25" is plenty for the charge pipe returning.
As an example I ran 2" from factory manifolds to each side of a dual scroll T6 S480 on a little 4.8. 2" 16G mild steel (which is really like 1.8" id) worked really well and it allowed me to spool a relatively large T6 S480 easily and maintain lower overall system back pressure than most small bore LS setups with t4 single setups. Yet I could spool just as quickly at the T4. Run a larger cam, and make more power per pound because I used smaller piping and a larger turbo. Also ran a 370" motor and a 5.3" on the same 2" hotside combo to the same mid 8 sec ET's and trap speeds. 2" hotside piping is all most street/strip mild setups need. Yet we still see guys throwing 2.5" and 3" hot sides on mild setups. It just added weight, cost, and more difficult to plumb. Remote setups are even more sensitive to exh diameters.
IMO for most sub 900whp setups... 2" is the way to go. I've yet to see any data to prove otherwise.
2" OD from each factory manifold to a 2.25" single pipe and split back into 2" feeding each g35 works really well on small bore LS stuff to about 600 whp. Use the shortest runs as possible and wrap them. 2.25" is plenty for the charge pipe returning.
As an example I ran 2" from factory manifolds to each side of a dual scroll T6 S480 on a little 4.8. 2" 16G mild steel (which is really like 1.8" id) worked really well and it allowed me to spool a relatively large T6 S480 easily and maintain lower overall system back pressure than most small bore LS setups with t4 single setups. Yet I could spool just as quickly at the T4. Run a larger cam, and make more power per pound because I used smaller piping and a larger turbo. Also ran a 370" motor and a 5.3" on the same 2" hotside combo to the same mid 8 sec ET's and trap speeds. 2" hotside piping is all most street/strip mild setups need. Yet we still see guys throwing 2.5" and 3" hot sides on mild setups. It just added weight, cost, and more difficult to plumb. Remote setups are even more sensitive to exh diameters.
IMO for most sub 900whp setups... 2" is the way to go. I've yet to see any data to prove otherwise.
