Backpressure - Can big wastegates help?
something similar to this may be helpful for the rear-mount guys. basically what phil said earlier, its dumping before the "bottle neck"
i have almost zero back pressure, instant spool, no boost creep, and can spin +7,000 rpm, with a 76mm rear mount, .96 exh
Yes, i will hopefully complete the new exhaust by next weekend.
I have this cover already.
Yes, i will be changing my exhaust around and will also move my wastegates up front. Thanks
I have this cover already.
Yes, i will be changing my exhaust around and will also move my wastegates up front. Thanks
What are you using to measure backpressure and is that 2.5" tubing? there is probably a good bit of turbulence at your merge.
Last edited by Phil99vette; Dec 27, 2010 at 09:44 AM.
Just a quick clip from 40mph to ?mph....i was trying to lug it in 2nd gear only for a backpressure test. the 335 r888's broke loose around 18 pounds of boost. Backpressure was 39 pounds at 18 pounds of boost...little over 2.1:1 b/p ratio. I have larger exh housings coming so i will followup with another test next week. Not sure if i attached the link properly but it is in my photobucket. Tracyrr-corvette. p.s... excuse the quality... my buddy must have been drunk.
http://s1008.photobucket.com/albums/...t=M4H00068.mp4
http://s1008.photobucket.com/albums/...t=M4H00068.mp4
I finished the new hot side.... Coming out of the manifolds is 2.5" diameter pipe for less than one foot, then it steps down to 2.25" for approx six feet and then steps down to 2" diameter pipe for approx two feet..... I also relocated the tial 38mm wastegates up front just after the exhaust manifolds and positioned well for good flow. Everything is wrapped from front to back. My original hot side consisted of 2.5" all the way with some pretty restrictive bends. My butt dyno says it spools quite a bit quicker with the new exhaust AND the larger exhaust housing T3 .82 versus my old exhaust and the smaller T3 .63 exh housing. In addition to the smaller diameter hot side, i also relocated the turbo's higher and closer to the center of the car so as to give a straight shot for the hot side to reach the turbo's and also for better ground clearence. I will run a backpressure test this weekend to see how much better the backpressure ratio is and will update then with another short clip. In the next couple weeks, i will fab the cold side.... The current charge pipe is dual 1.75" pipe and seems to be wrapped around every inch of the car..... the new cold side i will fab will be dual 2" pipe and approx four to five feet shorter per side. I am hoping to make my rear mounted twins more efficient with less backpressure and quicker spool..... So far the hot side is a success, i'll update soon. Thanks for all of the help!
I finished the new hot side.... Coming out of the manifolds is 2.5" diameter pipe for less than one foot, then it steps down to 2.25" for approx six feet and then steps down to 2" diameter pipe for approx two feet..... I also relocated the tial 38mm wastegates up front just after the exhaust manifolds and positioned well for good flow. Everything is wrapped from front to back. My original hot side consisted of 2.5" all the way with some pretty restrictive bends. My butt dyno says it spools quite a bit quicker with the new exhaust AND the larger exhaust housing T3 .82 versus my old exhaust and the smaller T3 .63 exh housing. In addition to the smaller diameter hot side, i also relocated the turbo's higher and closer to the center of the car so as to give a straight shot for the hot side to reach the turbo's and also for better ground clearence. I will run a backpressure test this weekend to see how much better the backpressure ratio is and will update then with another short clip. In the next couple weeks, i will fab the cold side.... The current charge pipe is dual 1.75" pipe and seems to be wrapped around every inch of the car..... the new cold side i will fab will be dual 2" pipe and approx four to five feet shorter per side. I am hoping to make my rear mounted twins more efficient with less backpressure and quicker spool..... So far the hot side is a success, i'll update soon. Thanks for all of the help!
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo Thanks for the help phil! I would have never thought smaller hot side pipe would improve my combo until i started reading your threads on crossover pipe size.... You got me thinking and i appreciate all the help!
hey kyle, what size hot and cold pipes do you run?
hey kyle, what size hot and cold pipes do you run?
Currently as a front mount, i run dual 2.5" into a 3" merge, kind of typical i suppose, lol.
and the cold side is a 3" from the compressor to the intake.
I considering doing some smaller ones, like 2" etc. but was told for fabrication purposes as i am def. a novice, it would be easier to to this route.
That and im not making near the power you gents are. lol. But, i will continue to pay attention to yours and phils ideas and testing. Keep up the great work.
When i was rear mount, i ran a dual 2.5" into a single 3" that ran about 6' long to the turbo.
Currently as a front mount, i run dual 2.5" into a 3" merge, kind of typical i suppose, lol.
and the cold side is a 3" from the compressor to the intake.
I considering doing some smaller ones, like 2" etc. but was told for fabrication purposes as i am def. a novice, it would be easier to to this route.
That and im not making near the power you gents are. lol. But, i will continue to pay attention to yours and phils ideas and testing. Keep up the great work.
Currently as a front mount, i run dual 2.5" into a 3" merge, kind of typical i suppose, lol.
and the cold side is a 3" from the compressor to the intake.
I considering doing some smaller ones, like 2" etc. but was told for fabrication purposes as i am def. a novice, it would be easier to to this route.
That and im not making near the power you gents are. lol. But, i will continue to pay attention to yours and phils ideas and testing. Keep up the great work.
The car is definitely making more power!! I measured backpressure today and it went from 2.1:1 b/p ratio with the .63 housings and old exhaust to 1.75:1 with the .82 housings and the new smaller exhaust..... Instead of killing the tires at 18 pounds of boost, it now does it at 16 pounds. The spool up is better and it makes more power, i'm pumped!! I'll update when i fab the cold side..... Thanks guys
The car is definitely making more power!! I measured backpressure today and it went from 2.1:1 b/p ratio with the .63 housings and old exhaust to 1.75:1 with the .82 housings and the new smaller exhaust..... Instead of killing the tires at 18 pounds of boost, it now does it at 16 pounds. The spool up is better and it makes more power, i'm pumped!! I'll update when i fab the cold side..... Thanks guys
I finished the new hot side.... Coming out of the manifolds is 2.5" diameter pipe for less than one foot, then it steps down to 2.25" for approx six feet and then steps down to 2" diameter pipe for approx two feet..... I also relocated the tial 38mm wastegates up front just after the exhaust manifolds and positioned well for good flow. Everything is wrapped from front to back. My original hot side consisted of 2.5" all the way with some pretty restrictive bends. My butt dyno says it spools quite a bit quicker with the new exhaust AND the larger exhaust housing T3 .82 versus my old exhaust and the smaller T3 .63 exh housing. In addition to the smaller diameter hot side, i also relocated the turbo's higher and closer to the center of the car so as to give a straight shot for the hot side to reach the turbo's and also for better ground clearence. I will run a backpressure test this weekend to see how much better the backpressure ratio is and will update then with another short clip. In the next couple weeks, i will fab the cold side.... The current charge pipe is dual 1.75" pipe and seems to be wrapped around every inch of the car..... the new cold side i will fab will be dual 2" pipe and approx four to five feet shorter per side. I am hoping to make my rear mounted twins more efficient with less backpressure and quicker spool..... So far the hot side is a success, i'll update soon. Thanks for all of the help!
I thought we were talking about a 1 5/8th stepped to a 1 1/2 and then into a 2.5" collector. The 4 1 1/2's would have exactly the same area as a 3" collector. But most turbular headerd single T4 systems use a 1 5/8th-1 3/4 primary and choke that straight down to a 2.5" collector/merge and then choke it again into a single T4 flange.
Just something to think about. Suppose in a particular turbo setup, the turbine wheel/housing is the restriction of the hot side. Suppose you've reached a plateau where adding more boost is no longer making any more power due to back pressure. Now also suppose this setup has excessively large waste gates for boost control, and now you want to spray a 200 shot on top of this combo. Would it make the power you would expect from a 200 shot, or would the restrictive turbine/wheel combo still limit power?
Just curious to see what everyone thinks.
Just curious to see what everyone thinks.
Reducing surface area of the hot side piping retains more heat which allows more exhaust to be bypassed through the waste gate and around the turbine with a bigger turbine housing while retaining the same spool characteristics. All that = reduction in back pressure, more power and faster spool.