Thread: 4BD1T Turbo Sizing and Performance Prediction.

Originally Posted by Dougal

... Borg Warner use a number called Phi on their turbine maps:

... Garrett use "corrected mass flow" for theirs:

... But that said, even the T25 turbine can deliver backpressure below boost for the lions share of it's full load operation and can still provide enough boost to max out a standard pump.
At 750C EGT I'm getting 32psi drive pressure to produce 25psi boost at 3,500rpm with the 0.49 A/R T25 turbine. ...

Corrected mass flow is:
Mass flow corrected = Mass flow x (Pref / Pin) x square root (Tin / Tref)

Phi = Mass flow x square root (T) / P

where temperature T and pressure P in both cases are absolute values.

So in essentially both approaches are correcting the mass flow. What we don't know for Garrett turbine maps is what reference temperature and pressure they base their turbine maps on.

Actually those curves in the turbine maps, are disguising the full picture, they are a simple fit through a larger set of data curves. See the pic below.

With the T25, or GT22 turbines, for our purposes, it appears that their waste gates are not flowing enough at the higher engine rpm's. It is a long time since I have looked at these and have to wonder if it would be practical, or possible to port them to improve the flow.

Also adding preload from the actuator to increase boost would, I suspect be counterproductive for satisfactory flow through the waste gate. A good boost controller can be better for this purpose.

I note that the EFR turbos have quite large waste gates, and the ports have been designed for good flow, this with a larger turbine.

The GT22??V with it's largish turbine housing could be a good solution, given a good control system for the vanes that doesn't cause to much restriction during cruise. Though as we know, the turbine maps don't seem to be available.

When the exhaust flow is above the curve for the turbine, the excess needs to be set out through the waste gate, as the curve depicts what the turbine can handle.

If the exhaust flow lies below the curve, the turbine is too large and it's performance will not be as good as one where the curve matches the flow.

I used their compressor reference temperature and 1 bar for reference pressure. This made the result as expected, but it could certainly be out by a few degrees or pascal's.

I am getting very little wastegate flow in my calculations. The gt22 turbine flows roughly 30lb/min in real terms at 700c.
The t25 turbine at 750c chokes out at roughly 24 lb/min. Interestingly this was a near perfect fit for where my engine would choke the exhaust and hit the wall power wise at 2500rpm and full load with the wastegate clamped.

I'm not convinced the wastegate needs to be bigger. I cannot develop any measurable boost at 700c egt with the wastegate actuator disconnected.

Lower temperatures allow higher real mass flows through the turbine. But less power is extracted too.

My understanding is that turbo manufactures, develop their turbine (and maps) using "hot gas stands".

For that reason I would expect that the reference temp and pressure, would be the inlet conditions of the hot gas stand. However they could correct them to "standard conditions", but why expect them to do that for a turbine when they don't correct compressor maps to "standard conditions".

If the high drive pressure is not down to the waste gate, then I would suspect that the turbine size may be a little small and so require such a high expansion ratio to develop the required torque/power.

To save me going back through all of your data and posts, for comparison, what drive to boost ratio results did matchbot give for the EFR turbos?

Originally Posted by Bush65

To save me going back through all of your data and posts, for comparison, what drive to boost ratio results did matchbot give for the EFR turbos?

The efr turbos were generally getting drive pressure below boost for most of the full load range. Some high rpm points were drive above boost by several psi.
The efr turbines are larger, but also more efficient which almost completely offsets the size difference. I do have in my calcs the phi number bw use to compare against the garrett turbines.

It appears the new generation garrett turbines applicable to us are the gt22 and largest of the gt28.
The gt25 and smaller gt28 are old style with poor efficiency.

I can`t even begin to understand half of what you fellas are discussing
I brought this up before but it must have got missed .Is there any advantage in being able to advance the injection timing other than at start up? Your opinions greatly appreciated but please remember you are talking to an idjit

Thanks AM

Originally Posted by Ancient Mariner

I can`t even begin to understand half of what you fellas are discussing
I brought this up before but it must have got missed .Is there any advantage in being able to advance the injection timing other than at start up? Your opinions greatly appreciated but please remember you are talking to an idjit

Thanks AM

I'm not sure where this question is leading, thus not sure how to answer.

You are no doubt aware that there is an automatic timing advance unit on the FI pump, for when the engine rpm changes.

Originally Posted by Bush65

I'm not sure where this question is leading, thus not sure how to answer.

You are no doubt aware that there is an automatic timing advance unit on the FI pump, for when the engine rpm changes.

My injection pump has a ECU controlled advanced timing interval on startup for smoke control as I wont be running a ECU I could control it with a manual switch and was curious
as to being any advantage at other revs .Sorry about the vague query

Thanks Noel

Originally Posted by Ancient Mariner

My injection pump has a ECU controlled advanced timing interval on startup for smoke control as I wont be running a ECU I could control it with a manual switch and was curious
as to being any advantage at other revs .Sorry about the vague query

Thanks Noel

OK.

Do you know, if by manually controlling the normally ECU controlled start-up timing advance, if it would affect the injection timing across the range of the auto advance curve, such that it would simulate a change to the static advance?

If so, then if you made it so the injection timing could be easily adjusted from inside the cab, it could be useful for finding the best static advance setting for the injection. You may find, there are optimum settings for torque/power and economy for different vehicle loads, different ambient conditions, such as temperature and air density changes with altitude.

Regarding your first comment in the earlier post:

Originally Posted by Ancient Mariner

I can`t even begin to understand half of what you fellas are discussing
snip ...

I'm willing to clarify/expand any technical issues. Your not the first to express those sentiments in this thread.

So I will make a start later today. I think it may be useful to start from the beginning and spread it over a number of post for each topic. It will take some time and I won't have any this Friday or Monday.

Given the title of this thread, I trust Dougal won't see this as a hijack. If so I can take it to a new thread.