LB7: Drive pressure vs boost

dirtydmax

dirtydmax

<---up shit creek
Sep 1, 2013
1,107
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38
47
muskoka,Ont Canada
With my triple 475's I couldn't understand why I was only seeing 45-50 #s boost on kill tune and Forced Induction said something not right so I swapped out my old gauges and installed my isspro ev2 0-100# boost and drive pressure gauges and was shocked what I saw,on tune 2 I hit 70 lbs boost and 50 psi drive pressure not even trying.Everyone I have spoken with says 1-1 is optimal but what do you guys think?Truck is running strong and am happy with the results so far but always looking for opinions.Thanks to the members that helped me get this truck to where it is.
 
hondarider552

hondarider552

Getting faster
May 28, 2008
10,627
2
36
35
Arizona
Drive pressure would drop quite a bit if you have the valley turbo as a 87mm .90 or 1.0 AR. Just for future thought.
 
andy-stevenson

andy-stevenson

New member
Jul 7, 2013
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Can someone tell me what are "normal" drive pressure to boost pressures. I understand there is no standard number and it will vary depending on tuning, turbos and other hard parts. I have a drive pressure gauge, just need to know how to use it.

What are the general trends I should see when watching drive pressure? I'm assuming it's normal to see higher drive pressures ratios when accelerating and spooling the turbo? What drive pressure ratio would be considered excessive?
 
S

S Phinney

Active member
Aug 15, 2008
4,008
18
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Quncy, Fl
andy-stevenson said:
Can someone tell me what are "normal" drive pressure to boost pressures. I understand there is no standard number and it will vary depending on tuning, turbos and other hard parts. I have a drive pressure gauge, just need to know how to use it.

What are the general trends I should see when watching drive pressure? I'm assuming it's normal to see higher drive pressures ratios when accelerating and spooling the turbo? What drive pressure ratio would be considered excessive?
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Drive pressure does vary with set up and tuning some. Excessive would be getting 1.7 to 1 to 2 to1 areas. Drive at wot is the ratio that you are concerned about. I personally feel a 1.2 to 1 area is ideal. You can get those ratios in a good place and the drivability won't be in the best place. It is a balancing act to get the most usable power and drivability.

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andy-stevenson

andy-stevenson

New member
Jul 7, 2013
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S Phinney said:
Drive pressure does vary with set up and tuning some. Excessive would be getting 1.7 to 1 to 2 to1 areas. Drive at wot is the ratio that you are concerned about. I personally feel a 1.2 to 1 area is ideal. You can get those ratios in a good place and the drivability won't be in the best place. It is a balancing act to get the most usable power and drivability.

Sent from my SM-G920V using Tapatalk
Click to expand...

OK. So I don't need to worry about high drive pressures to get the truck moving? My driveway has a slope up to the road so I see like 4:1 ratios when the trucks in first gear just trying to overcome gravity.
 
S

S Phinney

Active member
Aug 15, 2008
4,008
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Quncy, Fl
How much drive vs boost are you talking about. If you talking 5 psi drive and 1 psi boost that's not a problem. If your talking 20 psi boost and 100 psi drive that is a problem. The numbers are relative to the situation when determining if you have a issues or not. .

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IdahoRob

IdahoRob

New member
Jun 5, 2007
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Basically drive pressure is the exhaust that is trying to get out of the cylinders and backing up against the turbine. So a lot of drive pressure compared to boost (back pressure on the intake side) doesn't allow the clean air to get into the cylinders. This is the basic idea on why you want your ratios inline. Get them inline and you will make more HP.

As stated we really only worry about WOT as drive will spike a bunch on getting the charger moving and unless something is terribly wrong, everyday cruising shouldn't be a worry.

I've seen RPM play the biggest role in drive pressure changes. Now waste gating, turbine housings and VVT vane position come into play. Setting the turbo(s) up for the rpm range the truck will run at is critical. It never is perfect at all rpms so I set-up the turbos to run lowest drive in the curve that I run the rpm in.

My race set-up will run below 1:1 at 3500-3700 rpms but will start climbing as rpm goes up and will end up 1:1.4 (boost to drive) up in the mid 4k rpm. So I set my waste gates up for the rpms I run on the track.
 
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