3" vs 4" exhaust size
04-23-05, 05:34 PM
#27
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Originally Posted by Zero R
With that said I'm real stupid and run a 5" DP that transitions into a 4" rear section. If I could run a full 5" I would but at the moment it just isn't happening.
04-23-05, 05:37 PM
#28
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lol....my brother runs open dp on his protege5 - T. We definately noted an increase in power/ spool up speeds. While sounding like a UPS truck of course. Not recommended on internally wastegated turbos;p
04-23-05, 06:06 PM
#29
Originally Posted by Carl Byck
Who said Back pressure helped spool? I see statements about small amounts of BP helping torque, but certainlly not spool, as you say, just the opposite.
Originally Posted by the_glass_man
A little back pressure can be a good thing. It can help with spool. A 3" exhaust is more than enough.
As for back pressure being good, nope.
"Relieving too much backpressure can't be good because a certain amount of backpressure is needed for optimum performance."
Actually that's bassackwards. A good exhaust/manifold/header will not only relieve backpressure, but goes one further and creates a vacuum in the header/manifold. When the next cylinder's/exhaust valve opens, the vacuum in the system pulls the exhaust out of the cylinder. This is what the term "Scavenging" means, also why and where the "tuned" comes from. Things may work a little differently on our rotaries but the principles are still the same.
Last edited by Zero R; 04-23-05 at 06:13 PM.
04-23-05, 06:53 PM
#30
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MY opinion I have run a 3.5" DP and complete 3.5 system for 5yrs. but I got the idea from caterpillar who had done R$D in 1958 , which is a 7 degree expansion rate starting from the exducer dia. out to a 100% increase in conduit dia. it was in some old text book i read, but im not sure caterpillar knows what there talking about etheir? RON
04-24-05, 12:41 PM
#32
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a guy I know who works at yaw power said that 3.5 will outflow a 4" because of the scavenging and some other stuff, I don't remember exactly what he said. I was thinking of running 5" off the turbo for ~ a foot then down to 4" for the rest of the dp and have the rest of the exhaust be 3.5. I need to find some v-bands tho... Hey Carl, I thought I saw you say you can get v-bands from NAPA truck division or something??? I asked about it once at a regular NAPA and they acted like I was on crack..
04-25-05, 02:46 PM
#36
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awesome, thanks carl, I think there's one just a few miles from me, but was hoping they weren't going to act like I had no idea what I was talking about like the regular store. ronbros3, the reason I was going w/ 5" off the turbo is due to a 5" v-band turbine exit, otherwise I would just go with 4", but that seems like more work cutting the existing flange off and welding on a smaller 4"...
-Aaron
-Aaron
05-03-05, 05:12 AM
#37
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Originally Posted by 2a+RoN
awesome, thanks carl, I think there's one just a few miles from me, but was hoping they weren't going to act like I had no idea what I was talking about like the regular store. ronbros3, the reason I was going w/ 5" off the turbo is due to a 5" v-band turbine exit, otherwise I would just go with 4", but that seems like more work cutting the existing flange off and welding on a smaller 4"...
-Aaron
-Aaron
Its for the gT40 with the 5inch cast flange.Ready to go.
05-03-05, 09:21 PM
#39
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Originally Posted by 2a+RoN
ooh... that bolts up to the 5" v-band outlet? how much and where did you get it from?
Maybe I got ripped by the band cost but to buy a blank of SS and have it mic-ed and machined with two sizes......
Uh want to buy?PM me.
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