Carolina Horsepower - Exhaust Pressure Results 4.8L/76mm

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Exhaust Pressure Results 4.8L/76mm

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/s...1/IMG_2815.jpg

http://i152.photobucket.com/albums/s...1/IMG_2816.jpg

http://i152.photobucket.com/albums/s...1/IMG_2821.jpg

http://i152.photobucket.com/albums/s...1/IMG_2827.jpg

http://i152.photobucket.com/albums/s...1/IMG_2839.jpg

http://i152.photobucket.com/albums/s...1/IMG_2840.jpg

That's a lot of back pressure keeps a lot of heat trapped

Yep, time for some bullhorns.

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!

Quote:

Originally Posted by 1997b4c (Post 191689)

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. :?

Quote:

Originally Posted by GreebeanZ28 (Post 191696)

Yep, time for some bullhorns.

If has another 1000HP I'd have horns all over this truck. :razz:

Quote:

Originally Posted by ForceFed4g63 (Post 191699)

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.

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.

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?

What's the diameter of your exhaust?

3" with a cutout mid truck.

I bet you would benefit hugely from making it at least 4"

6.3x here you come...

Very nice, switching to twin scroll should help a bit too!

twin scroll wont make a bit of a difference if he doesnt have the hot side setup for it...

Quote:

Originally Posted by RoadconeTuning (Post 192209)

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

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.

Bob needs to hook you up with a side exit exhaust in the front fender, that should drop a little back pressure..:bigthumb:

Quote:

Originally Posted by bwelch (Post 192195)

6.3x here you come...

I dig your style Sir!

Quote:

Originally Posted by Darryl Buckner (Post 192222)

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