Risks of running 3.5 inch exhaust
11-15-09, 05:46 PM
#1
Risks of running 3.5 inch exhaust
I'm planning on picking up a complete 3.5 inch exhaust (downpipe to muffler) soon, just wanted to know if there are any complications I should need to be prepared for in doing so. I'll have BNR's stage 1 turbo so that 34mm wastegate should be more than enough to handle boost creep and I have 550cc primaries with 720cc secondaries. I'm sure this exhaust system will increase the amount of power i'll be making so with the injectors i have would you think I could even run over stock boost?
Thanks guys,
~Ant
Thanks guys,
~Ant
11-15-09, 07:02 PM
#2
I predict you will still have boost creep even with the BNR's ported wastegate, but I hope I am wrong.
If you do still have boost creep you can make a restrictor plate to fit on the furthest back flange in the system (like a gasket w/ smaller hole in it). This will provide the great spool up of the large exhaust, while limiting flow on the top end to prevent boost creep. It will still be much better than the 3" system.
I have used 3.5" JIC Magic Spec 90 turbo back exhaust and Racing Beat 3" turbo back exhaust. The 3.5" system provided better turbo spool and much better low to mid range power. Top end power is very close between the two.
I finally ended up using the JIC 3 1/3" front pipe and the Racing Beat 3" rear section to lower noise levels while retaining the better low end.
I found the 3" Racing Beat downpipe and presilencer are quite restricive and really impact turbo spool.
If you do still have boost creep you can make a restrictor plate to fit on the furthest back flange in the system (like a gasket w/ smaller hole in it). This will provide the great spool up of the large exhaust, while limiting flow on the top end to prevent boost creep. It will still be much better than the 3" system.
I have used 3.5" JIC Magic Spec 90 turbo back exhaust and Racing Beat 3" turbo back exhaust. The 3.5" system provided better turbo spool and much better low to mid range power. Top end power is very close between the two.
I finally ended up using the JIC 3 1/3" front pipe and the Racing Beat 3" rear section to lower noise levels while retaining the better low end.
I found the 3" Racing Beat downpipe and presilencer are quite restricive and really impact turbo spool.
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11-16-09, 12:12 AM
#8
Thanks for the quick advice man. Did you experience any boost creep with the 3.5 exhaust? If so what setup were u running?
Yes, I had major boost creep if I took the tip silencer out!
Set up is a S5 based BNR Stage 4 hybrid turbo.
Started with clipped "O" trim exhaust and standard ported wastegates- insane boost creep.
Went to larger clipped "P" trim exhaust wheel and externally vented stock wastegates ported out as large as possible- still had boost creep.
Went to 60mm external wastegate and wastegate passages ported out to the limit of the turbo housing casting- still had boost creep.
Finally ported the turbo manifold and runners huge to favor wastegate flow over turbine flow, back welded the turbo housing so WG runners could be ported more and no more boost creep. Went back to unclipped "P" trim exhaust wheel.
Yes, I had major boost creep if I took the tip silencer out!
Set up is a S5 based BNR Stage 4 hybrid turbo.
Started with clipped "O" trim exhaust and standard ported wastegates- insane boost creep.
Went to larger clipped "P" trim exhaust wheel and externally vented stock wastegates ported out as large as possible- still had boost creep.
Went to 60mm external wastegate and wastegate passages ported out to the limit of the turbo housing casting- still had boost creep.
Finally ported the turbo manifold and runners huge to favor wastegate flow over turbine flow, back welded the turbo housing so WG runners could be ported more and no more boost creep. Went back to unclipped "P" trim exhaust wheel.
11-16-09, 09:21 AM
#10
sorry I missed your comment, it's an s4 turbo. Are you running a 3 1/2" exhaust as well and not creeping? I ran my stock s4 turbo with a RB 3" downpipe, test pipe, and 3" Apexi N1 and it only creeped occasionally when it was cool outside with the stock 11mm wastegate (did not know it was stock until I pulled the turbo). Like arghx stated, maybe there are some other factors
11-16-09, 01:21 PM
#11
well in my stage 2 car with an s5 turbo i have a moderatly street ported motor with an apexi 3" exhaust and get no creeep at all will stay at 5 psi all day.
on my s4 stock turbo with the 3" racing beat exhaust i ported the wg, and was finding boost creep on both my ported turbo motor and a stock port motor.
note: i dindt do any of the extreme porting like replacing the flapper with a larger one, that might help considerably, i only ported it to the edge of the stock door on both my turbos.
so no i havnt tried 3.5" but i am reporting my findings with 3" id imagine larger would amplify the problem. note both my cars have a very free flowing 3" intake which can creat even more creep.
on my s4 stock turbo with the 3" racing beat exhaust i ported the wg, and was finding boost creep on both my ported turbo motor and a stock port motor.
note: i dindt do any of the extreme porting like replacing the flapper with a larger one, that might help considerably, i only ported it to the edge of the stock door on both my turbos.
so no i havnt tried 3.5" but i am reporting my findings with 3" id imagine larger would amplify the problem. note both my cars have a very free flowing 3" intake which can creat even more creep.
11-16-09, 02:03 PM
#12
Thanks for the info, I'm gonna give it a shot anyways, if it creeps i'll experiment with different sized restrictor plates until I find one that will keep it from creeping. I'll try & keep u guys informed if anyone is interested in doing the same upgrade, cheers.
11-16-09, 02:23 PM
#14
tru that arghx,
I mean, I understand if you are building an exhaust for a bigger system, but if this is your long term turbo kit, build an exhaust to match it. Throwing restrictors and mufflers in the way will choke the motor. Why pull in all that air, then plug up the exhaust?
The other thing you have to consider with a 3.5" is the noise. You will have a very loud exhaust with 3.5". Ask me how I know....
I mean, I understand if you are building an exhaust for a bigger system, but if this is your long term turbo kit, build an exhaust to match it. Throwing restrictors and mufflers in the way will choke the motor. Why pull in all that air, then plug up the exhaust?
The other thing you have to consider with a 3.5" is the noise. You will have a very loud exhaust with 3.5". Ask me how I know....
11-16-09, 03:47 PM
#15
I know, a 3.5" is overkill for a bnr stage 1 or any bnr probably but a friend of mine is selling this to me for a very generous price and for the quality of this exhaust (compared to mine) I would be kinda stupid to pass it up. The gasket would only be temporary. I'm a big fan of quick spooling, which is why I still have my top mount, going with the bnr stage 1, and keeping the twin scroll actuators, throw in a 3.5" exhaust and I'm predicting full boost almost instantaneously.
11-16-09, 03:48 PM
#16
tru that arghx,
I mean, I understand if you are building an exhaust for a bigger system, but if this is your long term turbo kit, build an exhaust to match it. Throwing restrictors and mufflers in the way will choke the motor. Why pull in all that air, then plug up the exhaust?
The other thing you have to consider with a 3.5" is the noise. You will have a very loud exhaust with 3.5". Ask me how I know....
I mean, I understand if you are building an exhaust for a bigger system, but if this is your long term turbo kit, build an exhaust to match it. Throwing restrictors and mufflers in the way will choke the motor. Why pull in all that air, then plug up the exhaust?
The other thing you have to consider with a 3.5" is the noise. You will have a very loud exhaust with 3.5". Ask me how I know....
11-16-09, 05:26 PM
#19
wtf is the point of a big exhaust with a huge restriction in it? Why don't you engineer a complete system instead of throwing parts together?
Because on a turbo car the large piping (low backpressure) allows the turbo to spool much more easily so you GAIN low and midrange power.
The restriction at the very end of the exhaust limits total flow of the system which only impacts the power at the top end where you would have the boost creep. The key is to restrict it enough to limit boost creep and no more.
For instance I found the 3 1/2" JIC Magic w/ its tip silencer in (about 2" exhaust outlet) spools much faster than the full 3" Racing Beat turbo back. Both could limit top end flow to the point where I didn't have boost creep.
Because on a turbo car the large piping (low backpressure) allows the turbo to spool much more easily so you GAIN low and midrange power.
The restriction at the very end of the exhaust limits total flow of the system which only impacts the power at the top end where you would have the boost creep. The key is to restrict it enough to limit boost creep and no more.
For instance I found the 3 1/2" JIC Magic w/ its tip silencer in (about 2" exhaust outlet) spools much faster than the full 3" Racing Beat turbo back. Both could limit top end flow to the point where I didn't have boost creep.
11-17-09, 11:05 AM
#23
Thanks for the quick advice man. Did you experience any boost creep with the 3.5 exhaust? If so what setup were u running?
Yes, I had major boost creep if I took the tip silencer out!
Set up is a S5 based BNR Stage 4 hybrid turbo.
Started with clipped "O" trim exhaust and standard ported wastegates- insane boost creep.
Went to larger clipped "P" trim exhaust wheel and externally vented stock wastegates ported out as large as possible- still had boost creep.
Went to 60mm external wastegate and wastegate passages ported out to the limit of the turbo housing casting- still had boost creep.
Finally ported the turbo manifold and runners huge to favor wastegate flow over turbine flow, back welded the turbo housing so WG runners could be ported more and no more boost creep. Went back to unclipped "P" trim exhaust wheel.
Yes, I had major boost creep if I took the tip silencer out!
Set up is a S5 based BNR Stage 4 hybrid turbo.
Started with clipped "O" trim exhaust and standard ported wastegates- insane boost creep.
Went to larger clipped "P" trim exhaust wheel and externally vented stock wastegates ported out as large as possible- still had boost creep.
Went to 60mm external wastegate and wastegate passages ported out to the limit of the turbo housing casting- still had boost creep.
Finally ported the turbo manifold and runners huge to favor wastegate flow over turbine flow, back welded the turbo housing so WG runners could be ported more and no more boost creep. Went back to unclipped "P" trim exhaust wheel.
11-17-09, 12:17 PM
#24
BLUE TII, when were you reaching full boost with your bnr stage 4 setup with the bullit 90 system?
3,400rpm in 4th or 5th gear for 14psi full boost.
Very nice setup as always. I do admit, you make me want a rotary again. Very nice car with a great attention to detail.
Nah, they really do blow up all the time w/ a turbo- lol. Na is sounding pretty good to me- especially if you can still have power!
3,400rpm in 4th or 5th gear for 14psi full boost.
Very nice setup as always. I do admit, you make me want a rotary again. Very nice car with a great attention to detail.
Nah, they really do blow up all the time w/ a turbo- lol. Na is sounding pretty good to me- especially if you can still have power!
11-17-09, 12:44 PM
#25
I switched powerplants more for aftermarket support, simplicity, and reliability. I actually still love the rotary, just wasn't in the cards for what I wanted and needed.
Just live vicariously through my car (same color!) and I live through yours.
Either way, very nice car.