Is backpressure not an issue if power goals are low?
11-30-2018, 02:42 PM
#41
run a boost activated cut-out. I made 1074 wheel though a 3 foor long 3.5" dia DP with a kooks race bullet in between the turbo and the cut out. when it was closed it just sounded like a mild cammed truck. when it was open, it was glorious screaming eagles breathing fire.
11-30-2018, 03:11 PM
#42
Launching!
It seems like your pre-turbo back pressure ratio was 1:1 at lower boost settings, isn't that good? Someone mentioned that their S475 Borg was over 2:1 in back pressure to compressor pressure at high boost...I would only be at the boost pressure that's needed to make 550-600 rwhp.
The Turbonetics version of the 7875 actually just has a 3" v-band. We did a step up into a 3.5" downpipe so it'd be easier to modify if I needed to go bigger in the future, then split it into dual 3" pipes, each through a high-flow cat and a Dynomax Ultraflo muffler. Noise level is tolerable without resorting to a cut-out. I think you'd probably be fine if you just build a Y-pipe that connects up to your current exhaust. Or you could do a really quiet set of mufflers and a boost operated cut-out if you want maximum comedy.
11-30-2018, 03:15 PM
#43
I don't know what pre-turbo backpressure was. It's pretty hot on that side of things and we were only comfortable sticking a pressure transducer in the downpipe, which showed that we had a LOT of backpressure between the turbo and the muffler (which was adequate for my previous setup, a turbo V6 at ~450 whp). I'm guessing actual pressure on the "drive" side of the turbo was completely ridiculous, because it made another 100 whp at the same boost pressure after we improved the exhaust. Basically, I had a 3" SpinTech welded muffler and those are apparently a lot more restrictive than advertised.
The Turbonetics version of the 7875 actually just has a 3" v-band. We did a step up into a 3.5" downpipe so it'd be easier to modify if I needed to go bigger in the future, then split it into dual 3" pipes, each through a high-flow cat and a Dynomax Ultraflo muffler. Noise level is tolerable without resorting to a cut-out. I think you'd probably be fine if you just build a Y-pipe that connects up to your current exhaust. Or you could do a really quiet set of mufflers and a boost operated cut-out if you want maximum comedy.
The Turbonetics version of the 7875 actually just has a 3" v-band. We did a step up into a 3.5" downpipe so it'd be easier to modify if I needed to go bigger in the future, then split it into dual 3" pipes, each through a high-flow cat and a Dynomax Ultraflo muffler. Noise level is tolerable without resorting to a cut-out. I think you'd probably be fine if you just build a Y-pipe that connects up to your current exhaust. Or you could do a really quiet set of mufflers and a boost operated cut-out if you want maximum comedy.
12-05-2018, 11:54 PM
#44
Sorry been busy and havent been able to reply sooner. my setup is an On3 84mm billet turbo..which still has the 75exducer. Im using flipps and vbanded truck manifolds to 2.5 merge pipe. My boost pressure stayed the same 17psi but lowering my backpresure..post turbo dramatically changed the engine efficiency to make more power all else being the same. But for the Op..for the power level you are looking for I doubt backpressure will truly show itself.Once you start to push the limits of your setup..well,better to over build now and save the headache.Too much backpressure no matter how you slice it does more than just rob power. Im sure at my level it wouldnt matter as much which turbo i had on in the t4 size budget friendly realm would change much.they are all very similar builds/size and i dount i hit max potential of my turbo to go any bigger..yet.
12-06-2018, 12:21 AM
#45
Sorry been busy and havent been able to reply sooner. my setup is an On3 84mm billet turbo..which still has the 75exducer. Im using flipps and vbanded truck manifolds to 2.5 merge pipe. My boost pressure stayed the same 17psi but lowering my backpresure..post turbo dramatically changed the engine efficiency to make more power all else being the same. But for the Op..for the power level you are looking for I doubt backpressure will truly show itself.Once you start to push the limits of your setup..well,better to over build now and save the headache.Too much backpressure no matter how you slice it does more than just rob power. Im sure at my level it wouldnt matter as much which turbo i had on in the t4 size budget friendly realm would change much.they are all very similar builds/size and i dount i hit max potential of my turbo to go any bigger..yet.
I'll also be using a 2.5" pre turbo hot side as it's just convenient with my flipped 2.5" v-banded truck manifolds.
Thanks for the info.