Low rwhp on twin turbo setup
09-03-2010, 10:02 AM
#41
The more i learn about rear mounts, the more i realize why they need larger exh housings.... the exh gasses are cooler (vs. front mounts) so they take up more space, so you need larger housings to decrease backpressure. If this is correct (i'll confirm that this weekend), what housing should i get? .81 or 1.06? p.s.. when i was building this combo, i expected boost to start at 4000 rpm so i was a little surprised when it was at 3500 rpms. I'll update with backpressure numbers this weekend. Thanks!
EDIT: looks like i got this backwards.....
EDIT: looks like i got this backwards.....
Last edited by TracyRR; 09-03-2010 at 08:28 PM. Reason: fixed
09-03-2010, 12:12 PM
#43
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The more i learn about rear mounts, the more i realize why they need larger exh housings.... the exh gasses are cooler (vs. front mounts) so they take up more space, so you need larger housings to decrease backpressure. If this is correct (i'll confirm that this weekend), what housing should i get? .81 or 1.06? p.s.. when i was building this combo, i expected boost to start at 4000 rpm so i was a little surprised when it was at 3500 rpms. I'll update with backpressure numbers this weekend. Thanks!
09-03-2010, 07:56 PM
#46
The more i learn about rear mounts, the more i realize why they need larger exh housings.... the exh gasses are cooler (vs. front mounts) so they take up more space, so you need larger housings to decrease backpressure. If this is correct (i'll confirm that this weekend), what housing should i get? .81 or 1.06? p.s.. when i was building this combo, i expected boost to start at 4000 rpm so i was a little surprised when it was at 3500 rpms. I'll update with backpressure numbers this weekend. Thanks!
09-05-2010, 12:01 PM
#51
I tested backpressure and you guys were dead on....! At 10 pounds of boost i had 35 pounds of backpressure pre-turbo. My exhaust out of the turbo is nothing more than a foot of 3" pipe with a dynatech race split mufflers (straight through design). This would of course put me at 3.5:1 backpressure/boost ratio which as i understand it is WAY too high! So, should i buy the .81 or 1.06 housings (both would be T3 housings)? Thanks to everyone who have contributed so far!! I have learned a bunch with much more to learn!
09-05-2010, 02:23 PM
#53
FormerVendor
I tested backpressure and you guys were dead on....! At 10 pounds of boost i had 35 pounds of backpressure pre-turbo. My exhaust out of the turbo is nothing more than a foot of 3" pipe with a dynatech race split mufflers (straight through design). This would of course put me at 3.5:1 backpressure/boost ratio which as i understand it is WAY too high! So, should i buy the .81 or 1.06 housings (both would be T3 housings)? Thanks to everyone who have contributed so far!! I have learned a bunch with much more to learn!
For example, if you have 10psi at the intake manifold but 30psi at the outlet of the turbo than your backpressure issue is due to having to drive the turbo that hard to overcome the pressure drop across the cold side and not because the turbine housing is too small.
09-05-2010, 03:17 PM
#54
That backpressure may also be due to cold side inefficiencies. You have to measure boost right out of the turbo as well.
For example, if you have 10psi at the intake manifold but 30psi at the outlet of the turbo than your backpressure issue is due to having to drive the turbo that hard to overcome the pressure drop across the cold side and not because the turbine housing is too small.
For example, if you have 10psi at the intake manifold but 30psi at the outlet of the turbo than your backpressure issue is due to having to drive the turbo that hard to overcome the pressure drop across the cold side and not because the turbine housing is too small.
09-05-2010, 05:47 PM
#55
That backpressure may also be due to cold side inefficiencies. You have to measure boost right out of the turbo as well.
For example, if you have 10psi at the intake manifold but 30psi at the outlet of the turbo than your backpressure issue is due to having to drive the turbo that hard to overcome the pressure drop across the cold side and not because the turbine housing is too small.
For example, if you have 10psi at the intake manifold but 30psi at the outlet of the turbo than your backpressure issue is due to having to drive the turbo that hard to overcome the pressure drop across the cold side and not because the turbine housing is too small.
09-05-2010, 11:02 PM
#56
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Check for leaks on the hot and cold side. All arrow point to cold side right now. z28cobrakiler is right. You want hot expanding air. Thats why it is so critical to wrap your exhaust on a remote set up.
09-05-2010, 11:17 PM
#57
I just found two cold side leaks. i sealed up the cold side from the turbo's to the top of the I/C and ran 15 - 20 pounds from my compressor. It was two brackets that partially broke the weld and were leaking. Each leak was about 1 inch in length and the thickness of a hacksaw blade or so..... It was putting out a good bit of air but i don't know if that would be considered 10 pounds worth of leaking....? I will keep looking once i reweld the brackets. Thanks guys!
09-06-2010, 12:12 AM
#58
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good to hear ya finally finding things. everyone knows how frustrating some problems can be when there are so many variables to check. that when u finally start to pin point things its such a relief. good luck
09-06-2010, 09:08 PM
#60
Rear mount cars seem to like stock manifolds more then longtube headers because they keep the heat in.
Rear mount cars also benefit greatly from wrapping the whole exhaust with exhaust wrap to keep the heat in.
Also get rid of your cats if you still have them.
Rear mount cars also benefit greatly from wrapping the whole exhaust with exhaust wrap to keep the heat in.
Also get rid of your cats if you still have them.