View Full Version : Exhaust Pressure Results 4.8L/76mm
Foose04
09-28-2012, 02:56 AM
Figured I'd share this over here in case some new guys comes in here looking put a snail on his cheby.
Going to copy and paste my post I made on PT.Net because i'm lazy and thats what lazy guys do. :bigthumb:
Well i've had the itch to do this test so I finally stepped and knocked it out. I did the best I could so I hope it's useful to others in picking out the proper turbo for their setup.
Before I go on, I want to first say I'm very happy with what I have done performance wise with my Magnum turbo. That said, i'm just has happy to remove it for something better suited for my application.
I made a video showing the tonights testing with Go-Pro mounted on gauges. It did pretty well, but it was night time so it is what it is.
My test setup had a pressure drop of 4-5 psi at 50psi. This is likely from the 10 feet of hose required from cross-over pipe to pillar. Posted results in video did not include correction but I WILL include it in the posted numbers for those who don't watch the clip.
Test sample was from 3 runs that all had close to identical feedback. I can't confirm RPM, but all pulls was above 3500 before going to WOT and ending slighty above 6000.
From the camera on Average (corrected):
5 PSI Boost = 17 PSI Exhaust
10PSI Boost = 29 PSI Exhaust
15PSI Boost = 41 PSI Exhaust
18PSI Boost = 54 PSI Exhaust
21PSI Boost = 55 PSI Exhaust
Notice a nearly 3-1 Exh/Boost ratio from start to finish.
I then tested a 65 Wet shot, I turned boost down to counter boost spike to maintain a max of 21psi. Results showed little no gain in back pressure on the smaller nitrous shot that was triggered at 4000RPMS.
Conclusion, my truck never really picked up MPH at the track above 16-17PSI. Even at 20-21psi, MPH was nearly identical supporting the turbine wheel is past it's efficiency. I had to install a stiffer wastegate spring to make 18+psi possible, but this is a bad choice with this turbo.
While the BP seems high, i've read a lot of factory cars have BP of 2.5-3/1 for fast response and street manners. So this isn't horrible, but it is on the high side for a gear head looking for power.
In my "opinion". If your looking to make MAX power on this turbo on a 4.8L, keep it at or below 15psi with a upgraded cam engine. On a 5.3L, expect it to be a few PSI lower, 6.0 even lower.
Happy Boostin guys!! I will run the same test on my new BL475R within the next few weeks.
Video of testing, recommend watching in 720HD to see gauges:
<iframe width="1280" height="720" src="http://www.youtube.com/embed/qDE0j04_FiE" frameborder="0" allowfullscreen></iframe>
http://i152.photobucket.com/albums/s192/blackhawkawd91/IMG_2815.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/IMG_2816.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/IMG_2821.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/IMG_2827.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/IMG_2839.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/IMG_2840.jpg
1997b4c
09-28-2012, 07:16 AM
That's a lot of back pressure keeps a lot of heat trapped
GreebeanZ28
09-28-2012, 08:09 AM
Yep, time for some bullhorns.
ForceFed4g63
09-28-2012, 08:30 AM
Good tests Rob, thanks for posting it up. I want to do either a turbo 4.8 or 5.3 in the fox so this helps!
Foose04
09-28-2012, 01:47 PM
That's a lot of back pressure keeps a lot of heat trapped
Yeah I wouldn't think the exhaust valve is a big fan of opening to 55PSi of exhaust wanting back in the engine. :?
Yep, time for some bullhorns.
If has another 1000HP I'd have horns all over this truck. :razz:
Good tests Rob, thanks for posting it up. I want to do either a turbo 4.8 or 5.3 in the fox so this helps!
I bet this BW turbo is going to be about right man. We'll see though.
454rat
09-28-2012, 02:11 PM
Get a job! well done on the trouble shooting, its interesting to know how the pieces work and effect each other. some of the factors would also obviously include exhaust size and type for back pressure.
Foose04
09-28-2012, 02:23 PM
Hey it's my weekend! Yeah just wanted some before and after data. I knew it was high, but didn't expect 3 to 1 as early as 5psi. The exhaust down-stream is also getting redone. Hows the Red Dragon?
ForceFed4g63
09-28-2012, 02:43 PM
What's the diameter of your exhaust?
Foose04
09-28-2012, 04:44 PM
3" with a cutout mid truck.
ForceFed4g63
09-28-2012, 04:53 PM
I bet you would benefit hugely from making it at least 4"
RoadconeTuning
09-30-2012, 10:25 AM
thats way high...
Foose04
10-03-2012, 12:38 AM
Update shots on the swap. She sure is purrrdy... Waiting on DP/Intake/cat-back tubing. Can't wait, this rig should roll out.
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-21.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-11.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-10.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-13.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-14.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-19.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-20.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-24.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-23.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-22.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-12.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-16.jpg
bwelch
10-03-2012, 01:04 AM
6.3x here you come...
TurboWS6
10-03-2012, 01:12 AM
Sweet.
ForceFed4g63
10-03-2012, 09:03 AM
Very nice, switching to twin scroll should help a bit too!
RoadconeTuning
10-03-2012, 09:09 AM
twin scroll wont make a bit of a difference if he doesnt have the hot side setup for it...
BAD BOB
10-03-2012, 09:17 AM
twin scroll wont make a bit of a difference if he doesnt have the hot side setup for it...
but will work just fine on a open flange
RoadconeTuning
10-03-2012, 11:30 AM
yup, the 7M-GTE powered supra and 3S-GTE MR2's both have a CT26 turbo... the MR2 turbo is twin scroll and kills about 15hp up top due to restriction tho.
Darryl Buckner
10-03-2012, 11:41 AM
Bob needs to hook you up with a side exit exhaust in the front fender, that should drop a little back pressure..:bigthumb:
Foose04
10-03-2012, 04:17 PM
6.3x here you come...
I dig your style Sir!
Bob needs to hook you up with a side exit exhaust in the front fender, that should drop a little back pressure..:bigthumb:
Roberts crazy enough to do it.. I said man this 4"going to be a tight fit. "Robert, no I'd do 5" if it was mine." Lol
oldskoolstang
10-03-2012, 06:01 PM
I can watch those asses bouncing all day.....
Nice upgrade. Hope the rest of the install goes smooth for ya.
RoadconeTuning
10-03-2012, 06:58 PM
Y U NO STACKS?!
minytrker
10-03-2012, 06:59 PM
Thats some interesting results. I shouldnt have any problems with a S480 and 5in straight exhaust.
BAD BOB
10-03-2012, 08:31 PM
Thats some interesting results. I shouldnt have any problems with a S480 and 5in straight exhaust.
nope, we dont on the 73
schardbody
10-03-2012, 08:44 PM
Any questions, I'm bored?????
TurboWS6
10-11-2012, 02:15 AM
Whats the status on the turbo swap?
Foose04
10-11-2012, 09:02 AM
She's in. Robert had some work to do to make it happen, but did awesome. We're lucky to have someone like that in the local area. Truck is a different beast all together though. It sounds different going from a 3" exhaust with an open cutout, now it's sealed to the rear 4" setup. Makes it sound a lot deep and pretty quiet actually.
As far as power, it's a damn Freight Train once you get the fire cookin. It's going to take more RPMS to wake it up, as expected, but she's moving so damn air thats for sure. That compressor is actually really quiet to, so that with the quiet exhaust, all you really get is a deep note and pinned to the seats effect lol.
Next up is a wastegate change though, the 40mm doesn't have a change keep boost down. It opens at 12-13psi and by 5500rpms she ripping past 20 on the way to the moon. I'm thinking about just doing a 60mm gate so I won't have any issues and less rise during shifts as well.
I get back in town this weekend, but head back out on Tuesday for another week.
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-29.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-26.jpg
http://i152.photobucket.com/albums/s192/blackhawkawd91/file-27.jpg
ForceFed4g63
10-11-2012, 09:05 AM
Looks awesome Rob! You don't waste any time lol
RoadconeTuning
10-11-2012, 10:01 AM
id be interested in seeing what the exhaust back pressure looks like now.
TurboWS6
10-12-2012, 12:32 AM
Next up is a wastegate change though, the 40mm doesn't have a change keep boost down. It opens at 12-13psi and by 5500rpms she ripping past 20 on the way to the moon. I'm thinking about just doing a 60mm gate so I won't have any issues and less rise during shifts as well.
Try dumping that gate to atmosphere until you get the bigger one. If there is any pressure at all in the downpipe it will have effect it. Worth a try since your going to have to replace the gate pipes anyway if you run a larger gate. Just make sure its not shooting exhaust gas at something flammable. Make sure you check over the boost source to controller to gate sensing line for any leaks.
Like I said at the track the little 38mm is holding the S482 on my car down to 7 psi just fine and I dont have any exhaust leaks pre-turbo. So that 40 should do the trick.
BAD BOB
10-12-2012, 07:41 AM
Try dumping that gate to atmosphere until you get the bigger one. If there is any pressure at all in the downpipe it will have effect it. Worth a try since your going to have to replace the gate pipes anyway if you run a larger gate. Just make sure its not shooting exhaust gas at something flammable. Make sure you check over the boost source to controller to gate sensing line for any leaks.
Like I said at the track the little 38mm is holding the S482 on my car down to 7 psi just fine and I dont have any exhaust leaks pre-turbo. So that 40 should do the trick.
I feel that with the waste gate pipe going into the downpipe at such an angle that it creates a vacuum effect and helps the waste gate work a little better.
One difference with his waste gate than most is that the gate. Only pulls off one bank of the exhaust which somewhat limits the amount that it can do. I'm sure one way or another he will get it squared away
454rat
10-12-2012, 08:54 AM
We need another trip to the track!
Foose04
10-12-2012, 10:17 AM
Good tips but if it don't work going into the DP it don't work for me as I don't want a open dump. I got one last thing to try and that is to see if I get more travel of the valve itself if I remove a coil in the spring. If it doesn't increase the the valve throw then it won't flow no more and it's a done deal. A 60mm gate is almost dumping the whole left bank as its a 2.36 inch valve on a 2.5" pipe. Anther plus as I said is boost on shifts. I'm used to 1-2psi increase on every shift, be nice to control that better.
We need another trip to the track!
Just found out I'm not leaving till Thursday, you want to do Darlington Wednesday? I got 2 get me some street tunes in first.. Lookig forward to it! :mrgreen:
Foose04
10-12-2012, 10:23 AM
Looks awesome Rob! You don't waste any time lol
Thanks dude! I been stuck for a while and it was time... Hope this is the last turbo swap for a long long time.
id be interested in seeing what the exhaust back pressure looks like now.
Just by spool... I would be shocked of its 1-2, likely less.. ill hook it back up though and post up.
TurboWS6
10-12-2012, 01:33 PM
I feel that with the waste gate pipe going into the downpipe at such an angle that it creates a vacuum effect and helps the waste gate work a little better.
One difference with his waste gate than most is that the gate. Only pulls off one bank of the exhaust which somewhat limits the amount that it can do. I'm sure one way or another he will get it squared away
Didn't realize it was only coming off of one bank. You got a point on the scavenging effect didn't really think of that.
RoadconeTuning
10-12-2012, 04:28 PM
i've never liked the whole bleed off one bank thing, it stresses the engine unevenly and youll end up with different fueling bank to bank. just seems like you'd run into a lot more reversion with the bank that doesnt have the wastegate. I'd do pretty much whatever it takes to move that wastegate to the merge... you might be surprised how much it helps.
sleakwrx
10-14-2012, 01:43 PM
That is such a nasty setup.....I wish I had room under my bonnet to get something that huge but again I'm sure my lil 2.5L couldn't even come close to spooling that monster. Very nicely done. I've heard mixed reviews on piping the EWG into the exhaust, but I think I'm leaning that way on my ride based on moving to VA soon. That brings me to my question....I have a catted DP on my car would I want someone to patch the EWG pre or post cat? Also any recommendations are far as a good quality welder who wouldn't charge an arm and a leg, or look at me funny when I tell them what I want done?
LXtasy
10-14-2012, 01:54 PM
Robert @ Masterbend Muffler in Summerville, sc. He will take care of you.
TurboWS6
10-14-2012, 03:18 PM
Robert @ Masterbend Muffler in Summerville, sc. He will take care of you.
^This X2
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