Drive pressure vs boost benefits

[mike diesel]

Now that I have ventured into the built engine and big(ish) compound world, I am now trying to tweak/tune everything to work perfectly together. In this case it is drive pressure vs boost.

I have never checked drive pressure except way back when I still had a box stock 4094vvt. It was almost always a 2:1 ratio, drive pressure being higher as expected.

My valley turbo is a 72/87/1.0 and when ran as a single it was making about 45 psi boost.

But now since I've added the 88/112/1.23 atmo over it, I see about 51-55psi boost overall and 22- 24 psi from the atmo...depending if I'm street driving or going down the track.

I figured for sure the secondary charger would be driven alot harder and overall boost would be in the 65 psi range. I'll be checking back pressure here shortly and comparing the numbers. Last week I dynoed 875hp at 52psi. From what I understand, a 1:1 ratio is ideal.

I'm wondering if tightening up the secondary turbine housing to a .90ar would drive the secondary charger harder benefitting me at all? I am perfectly happy with how it performs now so if making changes won't benefit me, then I obviously will keep it how it is.

I unhooked my gate because I figured i didn't need it at this time since I can't drive the secondary very hard as it is.

What are your guys' thoughts?

 

[Hot COCOAL]

Your train of thought being that making the exhaust housing of the secondary (valley) turbo would make more drive pressure and heat and therfore more velocity and the overall effect would drive the atmo harder?

Sounds good on paper, but I would think adding restriction on the secondary turbo would just choke the potential of the entire system...?

Now if you were to make the exhaust housing on the atmo smaller, say to a 1.10A/R, wouldn't that have essentially have the same effect youre looking for?

I would think by tightening the A/R of the atmo and leaving the secondary's A/R the same as it is now would decrease spool time, increase charge air velocity and keep drive pressure in check while also allowing the system to still flow very well through the secondary...???

Just throwing my take out there, I dont know much of anything about thermal dynamic properties

 

[mike diesel]

Only issue with that is, I have no idea where I'd find a tighter housing for the f1 101/112 turbine wheel. I can only imagine what it would cost also. The kit spools surprisingly fast as it is. I see what you are saying though by tightening up the atmo turbine housing..

 

[S Phinney]

Those boost numbers are about where you want them. Drive pressure would be on the turbine side of things. That's the number you would want in the 1.3 to 1 to 1 to 1 ratios. That gets determined by several variables. Check that first. The fuel you have really isn't enough is why you only see lower 50s. The chargers are not even happy with that fuel. You need to have 100 overs to drive this system well enough. Then you can begin to tune it.

 

[Hot COCOAL]

What brand of turbo is the Atmo?

Comp turbo might have something for it?
http://compturbo.com/products/turbos/class-legal-turbos

I Saw a 1.10 and 1.08 A/R exhaust housings available there...

The fuel you have really isn't enough is why you only see lower 50s. The chargers are not even happy with that fuel. You need to have 100 overs to drive this system well enough. Then you can begin to tune it.

I thought Mike already had 100 overs?

 

[hondarider552]

I've never ran a drive pressure gauge. I determine how much is too much based on how far my up pipe bellows expand:roflmao:

 

[mike diesel]

Those boost numbers are about where you want them. Drive pressure would be on the turbine side of things. That's the number you would want in the 1.3 to 1 to 1 to 1 ratios. That gets determined by several variables. Check that first. The fuel you have really isn't enough is why you only see lower 50s. The chargers are not even happy with that fuel. You need to have 100 overs to drive this system well enough. Then you can begin to tune it.

Yea i know i need more fuel. I know drive pressure is turbine side, I just didn't know if having to low of drive pressure would hurt performance in anyway. There is a thread over on comp d about a guy supposedly having 40 psi drive pressure with 80 psi boost. That just doesn't seem possible. With the fueling i have, I figured my drive pressure is lower than boost psi but not by much.

What brand of turbo is the Atmo?

Comp turbo might have something for it?
http://compturbo.com/products/turbos/class-legal-turbos

I Saw a 1.10 and 1.08 A/R exhaust housings available there...


I thought Mike already had 100 overs?

My atmo is a turbonetics custom y2k. And no, i am still running 30% over injectors.

 

[countrycorey]

What brand of turbo is the Atmo?

Comp turbo might have something for it?
http://compturbo.com/products/turbos/class-legal-turbos

I Saw a 1.10 and 1.08 A/R exhaust housings available there...



I thought Mike already had 100 overs?

I think it's a turbonetics F1?


Corey

 

[S Phinney]

I believe the Comp D thread is about a super charger and turbo combo. I see less than 1 to 1 most if the time. That also contributes to higher smoke levels until you are up in the boost. It has to be tuned to get a compromise between total boost, drive, atmosphere boost and druvability if you drive it much. It can get complicated so it really helps to keep things as simple as possible to accomplish your goals.

 

[Burn Down]

I've never ran a drive pressure gauge. I determine how much is too much based on how far my up pipe bellows expand:roflmao:

Seems legit

 

[mike diesel]

I believe the Comp D thread is about a super charger and turbo combo. I see less than 1 to 1 most if the time. That also contributes to higher smoke levels until you are up in the boost. It has to be tuned to get a compromise between total boost, drive, atmosphere boost and druvability if you drive it much. It can get complicated so it really helps to keep things as simple as possible to accomplish your goals.

Yea i kept the turbines loose to try and not have to use gates. What is an ideal boost ratio...as in atmo boost to overall boost? I've seen a few different opinions on this.

 

[S Phinney]

Usually right there around half the total boost. Smallest tune I will see around 80 total and 42 atmosphere with 95 psi of drive pressure. I don't see any boost driving around unless I get into it. Now if I ran a different cam like I use to run my drive pressure would increase and I would see some boost driving around. Previous camshaft really was a better choice for driving the vehicle.

 

[Hot COCOAL]

Now if I ran a different cam like I use to run my drive pressure would increase and I would see some boost driving around. Previous camshaft really was a better choice for driving the vehicle.

How did the other cam's specs differ?
Can you make a comparison?

More lift/duration on intake, how different was the grind, steeper ramp rate with flatter lobes...less LSA?

Just curious:baby:

 

[S Phinney]

Cam 1 had about 500 lift on both intake and exhaust with stock ratios. Cam 2 had about .020 more intake lift and .017 less exhaust lift with a about 10 more degrees of duration. Main reasons for the drop drive was overlap from exhaust duration. I wouldn't recommend the second cam for daily driver trucks. I know some guys are running it but there are complications with smoke levels with it. Takes longer for turbos to light with it from design. Cam one would be a great can for daily use.

 

[Yellow Jacket]

Our 3.0 truck has less than 1:1 boost to drive... . My s366/s480 setup ran 32 psi atmo and 68 psi total with 90 psi drive, had a stock intercooler that leaked slightly.

 

[IdahoRob]

I data log drive pressure, boost, rpm and then review and make turbine/waste gate/fueling changes based on the data. You'd be surprised how rpm affects drive, to say I have below 1:1 drive to boost would not be lying, but the same 1/4 mile pass the drive can be 1.75:1 to boost. So IMO hearing a drive/boost ratio for a certain set-up is not explaining what is really happening.

Kind of like a HP dyno graph, I don't tune for best peak number but for the best curve where the intended purpose of the vehicle is going to be used. So in my personal case, I set-up the turbos up for the rpm I run. The graph will cross over from good to bad each shift put keep the sweet spot in the rpm range the longest.

Adjustments are made with turbine housing, waste gate(s) size/spring psi/air psi.

Boost leaks will throw the true numbers off a bunch, so I recommend making sure there are no boost leaks before fine tuning a set-up.

 

[coker6303]

My 364.5/480 setup was around 58-60 total and 23-25 atmosphere with drive being around 65-70 if I remember correctly. No waste gate and tight housings on both (forget what AR).