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

I can watch those asses bouncing all day.....

Nice upgrade. Hope the rest of the install goes smooth for ya.

Thats some interesting results. I shouldnt have any problems with a S480 and 5in straight exhaust.

Quote:

Originally Posted by minytrker (Post 192251)

Thats some interesting results. I shouldnt have any problems with a S480 and 5in straight exhaust.

nope, we dont on the 73

Any questions, I'm bored?????

Whats the status on the turbo swap?

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/s...91/file-29.jpg

http://i152.photobucket.com/albums/s...91/file-26.jpg

http://i152.photobucket.com/albums/s...91/file-27.jpg

Looks awesome Rob! You don't waste any time lol

id be interested in seeing what the exhaust back pressure looks like now.

Quote:

Originally Posted by Foose04 (Post 193303)

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.

Quote:

Originally Posted by TurboWS6 (Post 193480)

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

We need another trip to the track!

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.

Quote:

Originally Posted by 454rat (Post 193499)

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:

Quote:

Originally Posted by ForceFed4g63 (Post 193304)

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.

Quote:

Originally Posted by RoadconeTuning (Post 193312)

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.

Quote:

Originally Posted by BAD BOB (Post 193493)

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.

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.

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?

Robert @ Masterbend Muffler in Summerville, sc. He will take care of you.

Quote:

Originally Posted by LXtasy (Post 193747)

Robert @ Masterbend Muffler in Summerville, sc. He will take care of you.

^This X2