Backpressure Testing With New Hot Pipes
 

A few months ago I put a backpressure gauge on my hot pipes to see what was going on...I always suspected there would be excessive backpressure, but didnt have any data on it. I got it hooked up (thread here: https://www.performancetrucks.net/fo...-gauge-498800/) and found the BP ratio to be in the 2-3 range depending on gear and boost level. This setup is with a 1.10 T4 BW s400sx3-80mm compressor and the 87/81 turbine. This is the same kit from Kyle (kbracing) that several guys here run including stock48. It works great for what it is, but I wanted to see how much of a restriction running into the back of the log was...

Heres a pic:
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Notice a couple things here...the crossover is 2.5" which is fine, and combines at the rear of the passenger side 2.5" log manifold, which the turbo sits directly on that. The wastegate also recombines with the downpipe instead of dumping to atmosphere. This obviously works very well since this is how the majority of people make their kits for these trucks. Stock48 went 140mph with a setup just like this so clearly it isnt too bad, and I pushed my truck to 109mph in the 1/8th with it.


Fast forward a few weeks and I had a local guy (Walker at MPFab in Birmingham) modify what I had and make a new crossover and replace the T4 with a T6.
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He reused my driver side manifold, cut off the flange, and put a 2.5" vband on it.

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For this side, he cut the front part of the old log off and made the crossover combine at the new T6 flange. The back side of the log is sealed up. He also put in a divider to keep the banks seperate all the way up, and put the wastegate where they merge to offer better gate control. Also notice the wastegate now dumps by the tire instead of recombining at the downpipe.

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It moved the turbo towards the engine and forward, so several things had to be modified, but not a big deal. Guy is a beast of a welder!

For the turbo I stayed with the exact same turbo, but put a 1.25 T6 housing on it to fit the new flange. Everything else remained exactly the same.

Heres the video from tonight, starting at about 70 and rolling into it to hit full boost in 3rd gear by around 80mph.

The gauge on the left and the digital one are attached to the intake manifold, and the round one in the middle is the backpressure gauge which is a 0-60psi gauge. The boost gauge on the intake is a 30inhg vacuum to 30psi gauge.

It looks like the backpressure remains close to 1.5 to 2.0 only rising in the upper rpms.


So what does this tell us, besides I need a bigger turbo :lol:
Obviously going from a BP ratio of 3 down to 2 is good and makes more power, which is noticeable, but spool is also noticeably slower. Not excessively slow, but it is noticeable considering its the exact same turbo just different hot side. I think with some boost controller tweaking I can regain most of that by using a stiffer spring and higher gate opening pressure. So I will not say spool is worse because that can be compensated for.

Power on the top end is better, which is expected due to the large turbine housing. But I think the most important thing to take away is the way it has been done in the past (first pic) isnt that bad after all, especially for a smaller engines (under 400ci). At some point, it will definitely be a restriction, however, 1000rwhp isnt it :lol: This points to the turbine being more of a restriction than the pipes or housing.

Eventually I move up to the big boy BW s500 turbo with the 100mm turbine and 88mm compressor with a 5" dp...

Great results and documentation as always man.

Does that dude weld or what??!! Solid looking stuff there.

Thanks for sharing man! I would't go swapping turbo's just yet, I'd let that one eat some more. I think the closer you get to 1-1 it's going to become pretty soft on the street. But I guess if your 90% geared toward track performance, that maybe ok with you.

Yea im not giving up on this guy yet! I think if I can keep knock out of it I can get a solid 9s pass on an 80mm, which is pretty good IMO. Street performance is really good, half a second of brake boosting and im there. I mentioned above I can get more aggressive with the wastegate settings, so I may play with that some more. I also have a cam change in mind.

Walker is an awesome welder, more of an artist really. Mines pretty ugly compared to most of his stuff. He built CurtD's turbo pipes, now Spoolin's, and is also building Mitch some new pipes.

Nice write up and explanation

Damn I remember not long ago you were building a 408 for fun if I am correct. Now you are dong more R&D then GM does for factory stuff!

As always nice set up!

Is that a divided flange turbo?

looks great:sigh:

yes, all the big BWs have a divided housing

Looks awesome man. In for 1/4 results...