Measuring Turbo Exhaust Back Pressure

[M5-]

Just curious if anyone has ever actually measured the exhaust back pressure on any of these turbo systems. I was at a turbo repair/system builders yesterday talking turbo sizing etc and that was the first question he asked me. In a perfect world you would like to see 1:1 so 18 lbs boost 18 lbs back pressure but I guess that is somewhat un-realistic. 2:1 he claims creates unreal heat so......Thats Bad

M5

 

[sledhead162]

I have not messed with it on sleds yet but I have messed with drive pressure on my cummins. On this new kit im building for my sled im going to put a drive pressure gauge on it to see where I am at. Yes 1:1 is perfect with the diesels that is the biggest reason for blowing head gaskets is drive pressure. when your pushing 70lbs of boost you want drive pressures close.You wants to use copper tubing about a foot or two coming right off you r manifold or turbine housing and coil it up. Then adapt it to normal plastic tubing to your gauge this Works the best the copper will get rid of the heat. I also put a needle valve inline to fine tune the gauge cause it will jump with the exhaust pulses. Hope this helps

 

[gunnerthesnowman]

Just curious if anyone has ever actually measured the exhaust back pressure on any of these turbo systems. I was at a turbo repair/system builders yesterday talking turbo sizing etc and that was the first question he asked me. In a perfect world you would like to see 1:1 so 18 lbs boost 18 lbs back pressure but I guess that is somewhat un-realistic. 2:1 he claims creates unreal heat so......Thats Bad

M5

You mean like this !!!
I have a back pressure senser on my OSP kit , and yes the heat build up from this is unreal ,
On a G2871 with a .86 A/R on a apex , the back pressure is 3:1 higher if your running a .64A/R , but this is what you have to do to get your low end response back after going 9:1 OR 10:1 compression .

On my OSP kit , i run stock compression , G3076 .84 A/R and my low end response is like stock ,my back pressure is 1:1 or alittle lower , no heat issues here ,
But to do this i am running his complete standalone ECU.

 

[M5-]

Gunner

What are you doing with timing?

M5

 

[sledfvr]

interesting

 

[sledfvr]

So a 2860 with a .86 a/r should have less back pressure than a 2871? So a bigger cold side would cause the compressor to shove more air through than the exhaust turbine can keep up with, causing more heat back pressure? Am I thinking about this right? I was wanting to go to a 2871 with a .64 housing, but now I don't know.

 

[Wheel House Motorsports]

definately a wise thing to monitor when really trying to take things to the next level of tuning.. shows you how efficient things really are..

like gunner said, you can get your low end boost, but at the sacrifice of insane exhaust pressure/heat to force it up quickly.

 

[sledfvr]

more heat backpressure=more cracked headers=not good

 

[M5-]

So a 2860 with a .86 a/r should have less back pressure than a 2871? So a bigger cold side would cause the compressor to shove more air through than the exhaust turbine can keep up with, causing more heat back pressure? Am I thinking about this right? I was wanting to go to a 2871 with a .64 housing, but now I don't know.

I don't think you are thinking about this quite right. A 2860 and a 2871 use the same hot side so in theory should have close to the same back pressure if they are the same A/R. The difference is the 2871 won't need to work as hard to supply a fixed cfm or lbs of air depending on how you want to think of it so in theory the 2871 can actually operate at a slightly lower rpm and maybe be closer to the optimum point/island on the compressor map hence less back pressure. All this can only work so far and ultimately needs to be matched to the desired performance criteria engine size etc etc bigger is not always better too big and you are off the map on the opposite side, the key is finding the balance between low end performance, all out top end power and back pressure, at least thats my take on it.

When I asked the question I was hoping someone had some actual data to support buying a 2860 over a 2871 or vise versa all in relation to the Apex rather than the "My buddy has a 2871 and it rocks" selection system. I know the map numbers for the Gt2860, 2871, 2554, 16T, 19T, HKS2530 and a few others but it really is of no real use without back pressure numbers to match. Once you know the back pressure in your system you can figure out which way you need to go when selecting the perfect turbo.

M5

 

[BigFish BC]

yes there is so much the snowmobile turbo kits are still lacking in knowledge they get better every year but still short on some things like this.of coarse it depends on max boost you are running too, 16-17lbs makes less back pressure than 20lbs.