Toolbelt0

A 300whp very fun and reliable setup can be had for cheap. Evergreen K27/6 turbo, cat bypass pipe, "I prefer the Fabspeed". Tial 38mm Wastegate, Rogue A tune chip, 3 bar FPR, A good street/race cam, Maxes out the fuel system at around 15lb boost. And is a hoot to drive.

SirLapsalot

Ah my bad missed the crank hp reference, in that case I think that 400 number is not too far off.

It depends on your goals, but the OP referenced street car... A back pressure ratio of 1:1 will not be an enjoyable street car for most people.

Speaking of, there’s been references to “high” back pressure recently but I think it would be more valuable if we could actually quantify that for these cars before making blanket statements, which can end up being slightly misleading.

Of course, generally speaking, as back pressure increases there will be a point where power output will suffer, and knock propensity will increase. However where the balance point lies between those things and spool is what should be determined instead of just assuming less back pressure is always better.

I’ve demonstrated in another thread that, what I consider to be reasonable, back pressure ratios can be achieved with OE parts. I can pull that data back up and post another screen shot when I’m at my PC but I see 1.4:1 - 1.7:1 depending on boost target. That is with an Evergreen modified #6 hot side and stock crossover…EGTs are never excessive at those levels. I don’t think I’ve ever seen higher than 800C, with an average in the 700s. Most turbos are rated to 950-1000C. Would I rather see less than 1.7:1? Yea probably, but at the sacrifice of spool? Considering I have seen no adverse effects at 1.7:1, no not really. Would it be wise to run a more modern turbo capable of similar spool but lower back pressure, yes of course but like everything it’s a compromise of cost/convenience/ease of install etc.

Anyway, in my case I’m seeing 1.22bar of boost by 3100 rpm and 337whp. Again, personal preference, but I’d much rather have that over a car with 400+ that doesn’t come in until +4krpm on the street.

Personally I think more important than getting bogged down in EBR numbers is focusing on implementing proper tuning using a qualify stand alone. I’ve found that carefully calibrating the fuel/IG/boost control with audio knock detection followed by carefully calibrating the CL knock control allows safely operating at 17-18psi on pump gas with the power levels most here have said is a good street reliable number. That being said, I think the more people that provide empirical data on EBR, spool, power output, etc. with various build specs, the better off everyone will be when planning their builds. Considering your focus on EBR hopefully you will be able to provide that data from your build…

944 timbo

Sounds like engine delta pressure (intake manifold pressure – exhaust manifold pressure) should be examined. The line 4th from bottom in the calculated values section https://www.borgwarner.com/go/1DWDPI
This example is Borg Warner EFR 7670 with either a 74mm 83a/r or a 70mm 80a/r.
And the percentage of wastegating line is interesting, still trying to figure out how best to use that info.

I am certainly not an expert but I have been playing with this tool for a while now and its been very helpful.

944 timbo

If its not to much bother, I would be interested in having a look if you have a link?

SirLapsalot

This is an on-road 1.22bar 3rd/4th gear pull screen shot I had posted previously:

blade7

I wonder what differences there are in the oil and water cooling on the latest GT2 and GT3, I think there's over 200 bhp difference in the power outputs.

Eldavo

Blade - Sounds to me like you want to buy my 8V engine and the turbo I have on my 16v one as a package

sherry66

No , he’s buying the 968 head I have to go with the 16v turbo pistons that are cluttering up his garage !

944 timbo

Thanks for this.
I was doing some research last night and found this article. In there it says
"The turbine wheel acts like an exhaust backpressure multiplier; hence the term pressure RATIO. If the turbine is operating at a pressure ratio of 3.0, then 2psi of pressure in the exhaust after the turbine wheel turns into 6psi before the turbine wheel. If you have 4psi after the turbine, it turns into 12psi before the turbine when the turbine is operating a pressure ratio of 3.0."

So for your chart would that be (MGP- Exhaust pressure) x EBR?

blade7

After paying comp insurance, for it to just sit in my garage for over 2 years, I just want to drive the flippin thing. Changed the oil and filter last week, have to take it for an MOT next. Then fit the VEMS in time for your trip to Cadwell...

blade7

Nah, I'm waiting until you finish that Hartech engine, and sell it off for buttons . Either that or Penguins car, when it only maps up to 399 rwhp and he throws in the towel.

SirLapsalot

If I understand your question correctly then, no not quite. The terminology may get a bit confusing as some of it is used interchangeably or differently by different people, but I am only measuring pre-turbine pressure. Here's a translation of the terminology you see in the screen shot above:
MGP = Manifold Gauge Pressure (I'm measuring this via a TMAP sensor in the intake manifold, it is converted from an absolute pressure to a gauge pressure in this channel)
Exhaust Pressure = Pre-turbine exhaust pressure (I'm measuring this in the cross over pipe via a gauge pressure sensor)
EBR = Exhaust Back Pressure Ratio (This is a math channel I created that simply takes the ratio of the Exhaust Pressure and MGP)
EGT = Exhaust Gas Temperature (I'm measuring this via a thermocouple directly at the inlet of the turbo, so pre-turbine)

The section of the article you quoted is referring to a pressure ratio of the turbine. In the example I showed we only have one variable from that equation. I am not measuring post turbine pressure and we do not have advertised data on the turbo to know what the turbine pressure ratio is supposed to be. Most of our cars are street cars so we're a bit limited on what we can reasonably do to completely optimize post turbine back pressure. Larger down pipe, cat delete, larger diameter exhaust back to a straight through muffler or straight pipe, etc. are about all we can do. In my case I do have a 3.0" cat-less exhaust with a borla muffler, but OE downpipe.

Anyway, as always it's a slippery slope once you start trying to optimize everything. Also nothing is free, compromise exist with every mod...

sherry66

All buttoned up Blade , but that’s a keeper . Onto the 924 .
Nice turbo on piston heads that was owned by Lee noble that’s had a few mods . Gives an idea how much it affects value playing around with these cars even with decent history .

Eldavo

I’ll see if I can get down August - October unless you fancy a trip to Croft in August?

Penguinracer

The entire exhaust back pressure discussion is an important one in terms of optimising these engines for whatever use scenario you are targeting.

The other area where I think we could perhaps look at things a little differently is not to talk about boost pressure- which is nothing more than a measure of restriction - an important practical limitation though it is.
I think we should be talking about an engine's VE in terms of the air mass it can flow in lb/min.
You can apply a rule of thumb to convert that air flow to crank bhp - approximately 10 crank hp per lb/min airflow.
Two engines with different VE's will flow different amounts of air at any given boost pressure - and as an engine is essentially a pump - we need to be thinking of the engine system in terms of pumping efficiencies rather than pumping restrictions.
Basically no two tuned 951 engines are the same - we all have various combinations of parts, whether they be factory, aftermarket or own build - so we all have slightly different "systems" - so let's look at the air flow mass of our systems to identify which are being most efficient before they encounter unacceptable levels of restriction.
That said, we tailor our build to our intended use - so some might choose to sacrifice top-end efficiency for enhanced low-end or mid-range transient response - all valid - it's horses for courses.