I'm considering putting in a gauge to monitor drive pressure but not sure the best way to install with an ATS manifold and HTT 64/65/13ss. What is the best method (copper tubing, etc.), where should I drill and tap? Thanks for the help. Tac

 

I have been hearing quite a bit about drive pressure lately. Can someone explain exactly what it is?

 

It is a lot like being constipated.

Seriously, it is basically the resistance to exhaust flow. As your rpms increase, you increase your EF (exhaust flow). As your EF increases, it hits resistance from your turbo EH (exhaust housing) and the diameter of your exhaust pipe and then the muffler/kitty.

The turbo EH can effectively process only so much EF dependent on the size of the EH. (12cm flows more than 9cm; 14cm flows more than 12cm and etc.) Once the EH reaches a saturation point (also the turbo starts to get to the end of its compressor map and a lot of resistance is being made to compressing any more air) it holds back the EF thus creating back pressure in the exhaust manifold and the cylinders... this pressure is your drive pressure... esentially the amount of pressure that exhaust gasses are creating to get out of the cylinders and down the tail pipe.

 

Drive pressure, to the best of knowledge is the pressure driving the turbo, coming out of the motor. Too much can blow gaskets and turbos. I hear copper wiring is the best for the boost senor but I dunno. I am curious to see other responses. I think when I do twins....in about 19203890128 years but when I do them I will get a boost gauge to watch drive pressure.

 

I going to twins in 2-3 weeks, as soon as Rip gets his work load to a dull roar and he is going to install a gauge on one of the turbo's bottom one I think.

 

When I checked my drive pressure I just pulled out my pyro and put a fitting in the hole. I ran about 1 foot of copper tubing in a coil to cool the exhaust some so it didnt melt the plastic air line. You can calculate the ratio then of boost compared to drive pressure. I noticed on my application that as soon as I got much over 42 PSI the drive pressure ratio went through the roof. Once I found that sweet spot I set my wastegate to start to open around 40 but it fully opens at 42. Now I am fueling enough that the wastegate fully open still does not flow enough. I need to get that SPS62 on before too long

 

You can also use your "drive pressure" gauge to monitor "braking pressure" of an exhaust brake. I used this method to tune my Jacob's to the max recommended 60 psi backpressure.

It's a good idea to use metal line (copper or stainless) for the first foot or so coming out of the manifold; however, there won't be any real flow through this line, so the only heat the line will see will be from conduction.

--Eric

 

Thanks for the info. It looks like I will being drilling and tapping the manifold for it. Thanks Tac

 

XLR8R has a kit for measuring drive pressure. Checkout his website.

MikeyB