[TheBac]

Thanks Idahofox and Rick for the info on the LB7 turbo on the LLY.

LB7 on LLY This is the kind of thing we should be talking about.

 

[fingers]

The IHI <> VVT swap should be interesting. Rick and I both expect a performance drop since the VVT does generate more/better boost across the rev range.

FWIW the VVT generates huge amounts of drive pressure compared to the IHI. For instance, at 20 PSI of boost, the IHI drive pressure is about 25 PSI and the VVT is over 40 PSI. At 30 PSI of boost, the IHI is around 40 PSI but the VVT is close to 70 PSI.

On the 6.6 Dmax, each PSI of backpressure costs about 2 HP in strictly mechanical terms. So by reducing the VVT's drive pressure to be 1/2 way closer to the IHI you could easily find 30 HP. That 30 HP, BTW, is equiv to about 1200 BTU/min.

That's all the theory. I'm looking forward to the results from the swap. It will give me confidence to push forward with the vane redesign if it works.

 

[killerbee]

Jon

What is your estimation then of parasitic HP loss to the VV turbo?

 

[TxChristopher]

The IHI <> VVT swap should be interesting. Rick and I both expect a performance drop since the VVT does generate more/better boost across the rev range.

FWIW the VVT generates huge amounts of drive pressure compared to the IHI. For instance, at 20 PSI of boost, the IHI drive pressure is about 25 PSI and the VVT is over 40 PSI. At 30 PSI of boost, the IHI is around 40 PSI but the VVT is close to 70 PSI.

On the 6.6 Dmax, each PSI of backpressure costs about 2 HP in strictly mechanical terms. So by reducing the VVT's drive pressure to be 1/2 way closer to the IHI you could easily find 30 HP. That 30 HP, BTW, is equiv to about 1200 BTU/min.

Hmmmmmm.........

Jon

What is your estimation then of parasitic HP loss to the VV turbo?

:damnit

That's all the theory. I'm looking forward to the results from the swap. It will give me confidence to push forward with the vane redesign if it works.

Whats the timeframe looking like? opcorn:

.

 

[Turbotug]

originally posted by TxC..
GM releases say that they increased the flow of coolant through the heads looking for more cooling, going off that we have long thought they didn't open them up enough to deal with the new heat they knew they had coming. The LBZ has new heads yet again. Be aware too that the heads also determine compression, and that the exhaust ports are the largest source of heat in any engine, and are always completely water jacketed. They are the easiest place to screw up. Its happened before. Many a cylinder head has been ruined by removing too much material when porting or casting and resulting in either cracked seats are a chronic overheat problem.

I was under the impression that the bowl in the piston, piston protrusion, and headgasket thickness determined compression ratio. The head surface/valve area looks to be flat and does not have a compression chamber like a gasser. DMAX head in cnc lathe

 

[TxChristopher]

originally posted by TxC..
GM releases say that they increased the flow of coolant through the heads looking for more cooling, going off that we have long thought they didn't open them up enough to deal with the new heat they knew they had coming. The LBZ has new heads yet again. Be aware too that the heads also determine compression, and that the exhaust ports are the largest source of heat in any engine, and are always completely water jacketed. They are the easiest place to screw up. Its happened before. Many a cylinder head has been ruined by removing too much material when porting or casting and resulting in either cracked seats are a chronic overheat problem.

I was under the impression that the bowl in the piston, piston protrusion, and headgasket thickness determined compression ratio. The head surface/valve area looks to be flat and does not have a compression chamber like a gasser. DMAX head in cnc lathe

All true, except the design of the head still comes into play as you must take into account the cylinder firing pressure.

.

 

[fingers]

Engineering is as much as art as it is a science. You can exhaustively go over a problem and "engineer" a solution that fails because of unaccounted for variances in the application. Happens all the time. Knowing what to ignore and what to pay special attention to is the mark of a "good" engineer. Experience helps, but a humble attitude goes further.

Having said that, there is no substitute for engineering when it comes to Cheaper, Faster, Better improvements. You have to have a grasp of the numbers to see which way a design is going, or can go. Otherwise, you are left stumbling in the dark. But as the saying goes: "Even a blind squirrel stumbles across a nut once in a while" and some people get lucky in their attempts.

ME? I'm not an engineer. I just like to make my truck run better.

 

[fingers]

All true, except the design of the head still comes into play as you must take into account the cylinder firing pressure.

.

 

[idahofox]

All true, except the design of the head still comes into play as you must take into account the cylinder firing pressure.

.

What is this Please ? :shrug:

 

[stevebos]

All true, except the design of the head still comes into play as you must take into account the cylinder firing pressure.

.

Hi Chris:

Does this relate to effective (vs. static) compression ratio?

 

[TheBac]

GM releases say that they increased the flow of coolant through the heads looking for more cooling, going off that we have long thought they didn't open them up enough to deal with the new heat they knew they had coming. The LBZ has new heads yet again. Be aware too that the heads also determine compression, and that the exhaust ports are the largest source of heat in any engine, and are always completely water jacketed. They are the easiest place to screw up. Its happened before. Many a cylinder head has been ruined by removing too much material when porting or casting and resulting in either cracked seats are a chronic overheat problem.

I was under the impression that the bowl in the piston, piston protrusion, and headgasket thickness determined compression ratio. The head surface/valve area looks to be flat and does not have a compression chamber like a gasser. DMAX head in cnc lathe

You, sir, would be correct. The cylinder area on the Dmax head is flat, save for the valves. The bowl in the piston is the chamber.

 

[TheBac]

The IHI <> VVT swap should be interesting. Rick and I both expect a performance drop since the VVT does generate more/better boost across the rev range.

FWIW the VVT generates huge amounts of drive pressure compared to the IHI. For instance, at 20 PSI of boost, the IHI drive pressure is about 25 PSI and the VVT is over 40 PSI. At 30 PSI of boost, the IHI is around 40 PSI but the VVT is close to 70 PSI.

On the 6.6 Dmax, each PSI of backpressure costs about 2 HP in strictly mechanical terms. So by reducing the VVT's drive pressure to be 1/2 way closer to the IHI you could easily find 30 HP. That 30 HP, BTW, is equiv to about 1200 BTU/min.

That's all the theory. I'm looking forward to the results from the swap. It will give me confidence to push forward with the vane redesign if it works.

Jon, you have my apologies if I spoke out of turn on your experiment. I think its the best idea I've heard in a long time, and couldn't wait to tell the membership.

 

[killerbee]

On the 6.6 Dmax, each PSI of backpressure costs about 2 HP in strictly mechanical terms. So by reducing the VVT's drive pressure to be 1/2 way closer to the IHI you could easily find 30 HP.

I am still fumbling over this statement. It implies that that over 60 HP must be dedicated to the VVT to spin it.

Am I missing or misunderstanding something? I mean, I understand that it is preliminary, and you will test it, I just don't get the remote possibilty of 60 HP. What criteria does this come from? You've peaked my interest.

 

[fingers]

Work out the mechanical HP to pump 3.3 liters of gas per revolution against a given pressure. THAT is the minimum HP the backpressure is costing in purely mechanical terms. That does not account for all the other things like scavanging of the chamber or the fact that the pressure in the chamber is alway higher than in the manifold. I used 2800 RPM as a base RPM.

 

[Diesel Tech]

Jon

How about the internal EGR affect?

 

[fingers]

Jon, you have my apologies if I spoke out of turn on your experiment. I think its the best idea I've heard in a long time, and couldn't wait to tell the membership.

No problem Tom. I don't do it for the fame anyway.

This wasn't possible prior to tools like EFI Live, even though I thought of it long ago.

 

[fingers]

Jon

How about the internal EGR affect?

I called it scavanging, but the same thing.

Also, I would like to correct the pure mechanical HP loss at 2800 is 1.4239 HP/PSI of drive pressure. I rounded WAY up. My fault. Still significant.

 

[killerbee]

open mind

I called it scavanging, but the same thing.

Also, I would like to correct the pure mechanical HP loss at 2800 is 1.4239 HP/PSI of drive pressure. I rounded WAY up. My fault. Still significant.

The turbo, in it's "free lunch" aspect, is driven by exhaust, a waste product (expanding exhaust gases that have left the cylinder), so it is not tapping power from the motor, at least not like a parasitic device, alternator for example.

This is where I am not seeing a benefit, but I am trying.:Thumbup: My limited forced induction knowledge is showing.

Are you saying that excessive turbo backpressure is causing less expansion (thus less work performed) in the cylinder? For that to be the case, drive pressure would have to be significant (vs negligible) compared to cylinder pressures.

 

[Diesel Tech]

Anything that plugs the exhaust causes internal EGR. Internal EGR is what happens during valve overlap in the cylinder. When the exhaust pressure is greater than the incoming pressure the exhaust will flow backwards into the intake port. Once the exhaust valve closes it will now draw that same burnt air back into the cylinder. So you have used energy to put burn air into the intake and then more energy to pull it back into the cylinder where it does not good. This affects fuel economy as well as power output. Basic engine operation and the turbo is the plug in the exhaust. This is the same reason a free flow exhaust lowers EGT's, increases power and fuel economy.

 

[fingers]

The turbo, in it's "free lunch" aspect, is driven by exhaust, a waste product (expanding exhaust gases that have left the cylinder), so it is not tapping power from the motor, at least not like a parasitic device, alternator for example.

This is where I am not seeing a benefit, but I am trying.:Thumbup: My limited forced induction knowledge is showing.

Are you saying that excessive turbo backpressure is causing less expansion (thus less work performed) in the cylinder? For that to be the case, drive pressure would have to be significant (vs negligible) compared to cylinder pressures.

A turbocharger is not a free lunch. Never was. The engine has to fight the backpressure to get the exhaust through the turbo, That takes WORK. Work over time is POWER. The nice thing about turbos has been they only consume power in pace with the work they do. Very one for one as apposed to the constant drag of a direct drive supercharger. The "better" the turbo, the better the ratio between the drive pressure and the boost.