EBP/BOOST ratio observations

[HeavyAssault]

I recently had some Y-pipe work done by Strokers Unlimited. This work entailed adding the HD bellows and creating a one piece y-pipe. Everything went together great and lined up easily with all attachment points.

For my setup I have the following: SPD tuning, Atlas 80 (currently), GOGO Stage 1 manifold, 3.5" DP, straight piped, stock intake, stock exhaust manifolds, Spearco inter-cooler, OEM IC piping (2003 cold side), Accufab intake elbow, and a Pmax. I used an Edge Insight CTS as my gauges.

My ratio seems to run within a 1.8:1 thru 1.5:1 ratio while in OD @ 70-75 MPH. Pressure readings for example run 7 EBP with 5 PSI boost. This was fairly level HWY roads with some big hills. Even at lower sppeds of 60-65 this seemed to give the same result. I would conclude that the trans locked in OD will give this result at lower speeds say 50-55ish.

On the hills and curvy back roads the ratio does swing between 2:1 to 1.5:1 depending on the pedal input. Under hard acceleration the ratio goes WAY out as expected. As much as 15+ PSI difference was noted. Once boost is coming on that difference closes to 4-5PSI if not less. I need to try a data log so I can show a graph of the way this setup responds.

In the end it just flat out flows, the turbo responds, fuel mileage is to be determined, and I can't see any reason not to share my findings.

[TexasA&M]

Pardon my ignorance, but what is the relationship supposed to be between EBP and boost? I'm going to update my insight this week to show EBP but don't know what the numbers should be, so I won't know if I have a problem or not.

[TooMuch03]

First off, great thread. Thanks for posting your findings, and keep up updated if you can datalog some.

Originally Posted by TexasA&M

Pardon my ignorance, but what is the relationship supposed to be between EBP and boost? I'm going to update my insight this week to show EBP but don't know what the numbers should be, so I won't know if I have a problem or not.

Well, ideally you want bp to boost to be as close to 1:1 as possible, but that is impossible. 1.1:1 and 1.2:1 are very good numbers to see. Now, since we are looking at VGTs in this case, the odds of seeing a ratio like that are pretty low. VGTs naturally operate at higher backpressure to boost ratios than their nonVGT counterparts. I would think with a stock turbo, you will likely see a better ratio than say the powermax or Stage 1 because they have the same turbine but larger compressors than stock. Obviously, under acceleration your ratio will increase because the vanes are closing to help the turbo spool up.

[nordstrom]

When i was trying to figure out my turbo surge (which hasent happend yet i was watching these numbers really close. Under heavy throttle with the TC locked i would see numbers like 22EBP and 21# boost as i let off they would seperate more. On my latest trip to Oregon last weekend i would see 10# EBP and 4-5# Boost while running at 70 on the freeway. I did not monitor it on the way home after having the Atlas 40 installed on my FICM

[strokin6L]

When i was runnin my 64/71/70 non vgt turbo...EBP and boost would stay 1:1 all the way up to 40psi. Then after that EBP would start to go higher than boost. At 54psi of EBP boost was 45psi...which is like 1.2:1 at WOT. I was really happy with that.

[HeavyAssault]

Originally Posted by TexasA&M

Pardon my ignorance, but what is the relationship supposed to be between EBP and boost? I'm going to update my insight this week to show EBP but don't know what the numbers should be, so I won't know if I have a problem or not.

In a perfect world 1:1 is the best one could see. I wanted to post up my configuration and findings to show others how my setup performs. Often times we try to compare setups, understand why things happen, or try to figure out what works. Surging seems to be ever present and problematic if this info guides someone to a solution then my work is done.

[freecanadian]

What sort of EBP / boost highs did others observe?

I just got my CTS upgraded to show the EBP, and ran it hard up a few hills in town.

I can't seem to get more than 32 psi of EBP, and 23 psi boost... wondering if I have a leak since those numbers seem a bit low to me and the engine was just put back together recently.

[windrunner408]

I personally have never fully understood why guys cared so much about this made up relationship of back pressure to boost ratio. The relationship or "ratio" as folks refer to it, is a parameter I'm sure that someone somewhere thought would be cool to look at and gradually people started getting more wrapped around the axle of their "EBP:Boost Ratio". Now, I'm not saying that back pressure isn't important, I'm just saying that EBP/Boost ratio really isn't important. Either your head gaskets hold at whatever the peak back pressure is or they don't.
The reason why a non-VGT turbo doesn't exhit the high amounts of back pressure until it runs out of air, is because the housing is basically acting a giant hole that the exhaust gas just flows on out without actually spinning the turbo enough to start building boost. Where a VGT turbo, on the other hand (through vane manipulation), restricts exhaust gas flow at low boost levels so it can increase the velocity of the exhaust gas to give it more energy to transfer to the turbine wheel to get it spinning sooner.
I have always maintained the stance that I have never really cared what back pressure did as long as it never got too high both before the turbo was at full boost and while at full boost. For example, it doesn't bother me if I were to have 15psi of back pressure for 5 psi of boost while cruising down the hwy at 70mph (EBP/Boost ration of 3:1) as long as my back pressure stays less than say 65psi at 50+psi of boost (1.3:1) because the 65psi of back pressure is going to be more limiting with respect to the head gaskets holding than the 15psi of back pressure for 5 psi of boost while cruising down the hwy. I hope this makes sense and provides some perspective on this topic.

[HeavyAssault]

In relation to efficiency of airflow thru the motor and the energy created it's something. The output is the same as the input relates to a more efficient use of the energy created by the motor.

Maybe I'm thinking too deep......

[windrunner408]

This MAY be true but I don't buy into the fact that since a non-VGT turbo is 1:1 as it builds boost that it is more efficient than a VGT turbo (for the reasons previously mentioned) at harnessing gas flow through the motor. Not saying you were saying that directly, just saying that this sort of data leads to this sort of conclusion is all.