L_perm

When I look casually at my car's intake and exhaust systems, several things occur to me that I don't fully understand. Some things about the systems make sense to me, but others aren't clear. Here are a couple of things that make sense to me:

1) Less restriction on the inlet to the compressor is always good.
2) Less restriction on the outlet of the turbine is always good.

Having written #1, I wonder if the (necessary) tapering of the intake pipes creates any pressure at the compressor inlet, or does the compressor simply pull the air, end of story?

Between the compressor and the intake ports on the engine, things aren't as clear. Compressed (heated) air leaves the compressor and enters the intercooler, where it is cooled. There is some amount of pressure drop due to the cooling. The compressed air then moves through the y-pipe, throttle opening, and is split by the intake plenum before being further split by the intake manifolds. A couple more things seem intuitive:

3) A larger diameter pipe reduces pressure but will flow more air.
4) A smaller diameter pipe increases pressure--the air speeds up--but can be restrictive if too small.

Is it my imagination, or are the intercooler inlets smaller than the outlets? If so, why? It seems like it should be the opposite, given that the pressure is lower at the outlet.

The lower end of the Y-pipe seems to have an I.D. that is less than the intercooler outlet. Why? Is this the restriction that brings the pressure back up post-IC?

The Y-pipe appears to taper larger between the lower end and the merge. Why?

The stock setup connects the Y-pipe to the throttle body with a plastic pipe that has a reduced I.D. relative to the top of the Y-pipe. I assume this is to taper down to the size of the throttle opening, which is smaller than the top of the Y-pipe. Why?

Is all of this just optimizing given the restrictions of packaging space and mass production? In other words, Porsche needed to hit 480hp for marketing purposes, the stock setup was tweaked just enough to achieve that, and the sloppiness in the air flow between the compressor and intake manifold is there because it can be. It may represent a less-than-ideal air flow, but it didn't need to be better?

Part of why I'm asking these questions is because I have some hardware upgrades and a tune, and I'm wondering about a couple of further upgrades. Specifically, I have FVD 66mm upgraded turbos and ICs with the silicone hoses. I also have the GT3 TB and 82mm IPD plenum. I should be at around 650hp--not super aggressive, but not stage 1. (I also have an FVD exhaust and headers.)

Intuitively, the larger TB and plenum made sense to me because it got rid of the taper between the top of the Y-pipe and TB. I got the upgraded ICs to protect the engine as much as anything. I understand the air intake box is not restrictive at anywhere close to my power. The two pieces left are the intake pipes and the Y-pipe.

I already have the do88 intake pipes, as that seems like a good idea--reducing restriction at the compressor inlet. What I am less sure about is the Y-pipe. As I mentioned above, the lower end of the stock part looks like a restriction, but do I need that restriction at lower rpms--with my upgraded turbos?

IPD's charts show all the gains in the midrange. That's fine. User dyno plots here and elsewhere seem to show the same, though sometimes very minimal. Dyno restrictions? User reporting on trap times, for example, seem to show real gains. In reality, there are very few observations to go on. Anecdotal reporting seems to suggest that tuners (who focus on dyno plots?) don't like them below about 700hp, while others (who focus on trap times?) like the upgrade.

What I see when I look at my car--once I get the do88 intake pipes on--is an intake system that has been upgraded from air box to manifold, except for the Y-pipe, and that makes me wonder, especially given the apparent restriction at the lower end of the Y-pipe.

Sorry for such a long post. Any reply to any part of it is appreciated. I'm not just looking for advice on the Y-pipe. I would like to have a better understanding of the questions I raised above.

TIA,
Louis

Kevin

The stock throttlebody can handle power levels to break/crack your rods.. Can your fuel octane and tuned power output support 1.6 bars of boost? What are your boost levels now. Sustained not peaks.. Can you IC handle those boost pressures?

The 997GT2RS plenum is smaller than the 997TT and 997TT....

atcbi5

So are you basically saying some of those upgrades are not needed? Great feedback nonetheless. Very appreciated. If I would upgrade to the next level, I would install the champion intercooler or the GT2 units. I have exhaust and a FVD tune.

wrxman60

Thanks for this, I just installed a set of silicon inlet pipes, we'll see how much of a difference I'll feel

TTurboRoo

Another member recently posted Dyno results for his car with exhaust and UMW Tune, before and after installation of the DO88 pipes. He appeared (though any two dyno pulls will vary) to show about a 15hp and 5tq increase with the DO88s installed!

L_perm

If these are peak numbers, then they are less important to me than the effect on the low-mid range. I've never been after a higher peak really. I've always been after immediate power on demand, so to speak. Any peak hp gains, in particular, are icing on the cake.

The best peak outcome I can think of would be to simply continue my current hp curve upward along its trajectory for another 600 rpm. Maybe the current peak is where it is because the turbos can't spin faster without breaking. Perhaps there is a breathing restriction somewhere--maybe the cams/valves are the restriction, though I'm at about 650 hp, and many others here run 700+ on stock internals, so I wouldn't think the cams/valves would be an issue. For the same reason, I wouldn't think it's a fueling restriction. I just don't know.

We know the engine can spin at 7,000 rpm, but something in most tunes I've seen is keeping it from gaining more hp beyond about 6,000-6,200, or so. If anything, tunes seem to move the stock hp peak left. Maybe it's the tuning for a huge torque plateau that does it. I don't really understand why I couldn't have both--huge torque plateau and an hp curve that continues to climb to 6,800 rpm. (My redline with the FVD tune is at 7,100.)

Big fast torque needs big fast air pressure buildup. Big hp needs big air volume. Right? So, you can't have the absolute max of one without giving up some of the other. But, I don't think I'm asking for the absolute max of either. If the hardware is capable of continuing my current hp curve upward from 650hp at 6,200 to 680hp at 6,800, and it is capable of a big torque curve that peaks at 620lbft, or so, then what is keeping it from doing both. In other words, both of these peaks are under what others are getting from their tunes. If I were at 680hp at 6,800 rpm, then I would likely be below what many with 750, 775+ tunes are at with the same, stock internals, and similar breathing hardware. Or maybe not. Maybe those peaks come early and drop off sharply enough that no one is actually getting 680hp by the time they hit 6,800 rpm. Again, this leads me back to thinking the turbos are the high-rpm restriction.

I guess what I really want is a GT3 engine in my Turbo. More linear acceleration and wide power bands that go on forever--even if not as violent--are more fun. The damn GT3 didn't have back seats though, so I got a Turbo back when they could both be had for the same price.

cdk4219

Larger turbos don't typically equate to immediate throttle response, especially on a small displacement engine. Variable vane units certainly help, but smaller turbos will certainly give you a flatter curve down low. Anything you can do on the intake side of the compressor, and the outlet side of the turbine will certainly help this effort. On the pressure side of the compressor and inlet of the turbine, the extra work seems to reap less benefits.
Spooling faster for you means less restriction in the air inlet area, and a free flowing exhaust, not to mention the correct tune.

saabin

That was me, and the graphs are in my dyno thread.. But the "after" included a revised tune and a splash of 100 in addition to the do88 pipes... So it wasn't just the inlet pipes.

L_perm

I agree. I don't tend to think of my "hybrid" turbos as larger, at least not by much. Below is the description of my turbos from the FVD website. Notice that it states "750+ crank hp" achievable. I'm only running somewhere under 650 with nearly the entire intake and exhaust systems upgraded. (I'm not running the BMC filter, and don't plan to.)

FVD Brombacher 997.1 TT “700 Series” Upgraded Turbos

Facts:
- CNC re-profiled compressor housing and backing plate
- New, lightened and larger compressor wheel (12 blades)
- Reworked turbine wheel, lightened and optimized for higher flow and reduced backpressure.
- All new bearings.
- All new piston rings and seals.
- All parts cleaned, inspected and measured to motorsport specifications.
- All parts are balanced (static & dynamic) up to 120.000 rpm with balancing protocol.
- 47.55 mm inducer
- 66 mm exducer
- Flow rate = 37 lbs. / minute or 280g/s
- Remanufactured by Borg Warner certified technicians
- Shaft tolerances are strictly maintained to ensure durability

We start by re-profiling the OEM VTG turbocharger compressor housing and modifying the compressor backing plate. This is done to replace the factory compressor wheel with a larger 12 blade, modified compressor wheel. The larger wheel is also lightened allows the turbo to flow a larger volume of air (more power), and aids in quicker spool up.

In addition we increased the size of the inducer and exducer to compensate for the higher volume of air traveling through the compressor. We increase the exducer on the turbine side to 66mm (OEM is 60 mm) and the inducer to 47.55 (46.9 mm). These larger sizes were achieved with larger factory housings, which allow our turbos to be cost competitive and are done on an exchange basis.

Borg Warner certified technicians remanufacture our turbos. This ensures reliability, superior performance and cost effectiveness. They ensure that each individual part is within the specified Borg Warner tolerance.

Combined with our proprietary software, exhaust, BMC drop in filter, and other engine components you can achieve 750+ crank hp.

Kevin

Lperm. those turbocharger specs are not possible for a VNT KO4 997TT.. There is not enough metal to machine that large of a hot side turbine wheel.

For instance the larger GT2RS VNT turbine has a Inducer Major (largest diameter) of 47.66mm with exducer (exhaust outlet>blades that you see) of 43.85mm

Unless you have removed the stock VNT and installed a 993TT or 996TT K16 the Inducer Major is 54.65mm with a exducer of 48.70mm

However, your specs are larger than X50/GT2 K24's.. Which has the Inducer Major at 56.66mm and exducer 52.43mm

Your turbocharger specs are almost as large as the '94 965 3.6 turbo K27 which measure Inducer Major at 69.78mm and exducer 58.11mm

All measurement given were done this evening with a digital caliper in haste but within .50mm

I have first hand knowledge of these compressor wheels. I have CNC'd the larger 48.4 and 50mm inducer compressor wheel into these turbochargers.. Exducer Major is 66mm (in fairness it's a extended tip design>the wheel major diameter is 61.93mm)

https://rennlist.com/forums/996-turb...zc-turbos.html

My point is, while theoretical 750 HP might be obtained on race gas and low ambient temperatures. One would have to push this compressor wheel above 1.5 bars..

On my dyno I have made 672WHP >> race gas, and over 1.5 bars with this family of KKK/Borg Warner compressor wheels. This was done with a larger turbine and straight pipe exhaust..

Porting of the turbine housing cannot reach your published specs. The larger GT2RS and 997.2TT turbine housing measure 41.47mm and 41.93mm which can be enlarged "some" Again measured from the 997GT2RS turbine and 997.2 turbine hot housing this evening.

The limiting factor is fuel octane, and your target boost pressure levels. 93 octane can only support "X" amount of boost with "Y" exhaust and "Z" intercoolers.

Lperm, you have some good component/hardware in your hybrid KO4 VNT's.. To myself the specs aren't plausible..

nzskater

Interesting. Most AM suppliers of upgraded OEM turbo kits list them as being 63/65/67mm or there abouts. What are they measuring to define this number/size? Must be a different point?

L_perm

Is this part of the FVD description key to the specs they report:

"These larger sizes were achieved with larger factory housings..."

You can see the re-installed, upgraded turbo in my avatar. The compressor side of it looked new.


Yes, everyone is reporting something between 63mm and 67mm. From what I can tell, they are reporting the diameter of the compressor exducer.

L_perm

Kevin,
I think the FVD writeup wrongly refers to the turbine exducer as 66mm. That has to be the compressor exducer. Reading over the FVD info, it looks like the only change on the turbine side is a "reworked" (lightened) turbine wheel. I don't see any reference to re-profiling the turbine housing. All of the re-profiling seems to be to the compressor side, so it can accommodate a 66mm exducer with 47.55 inducer.

Louis

Kevin

It's easy to install a larger compressor wheel. It is a lot harder to re-profile the hot housing. With the VNT's you must address the hot side.. That's why Porsche re designed the hot side for the 997GT2/GT2RS/997.2 The area inside the housing must be addressed to reduce the engine exhaust port backpressure. I will post about this on another thread.

One also must address opening up the factory header port and turbine housing inlet diameters! Ala GT2RS... Putting all your cash down on black (compressor side) requires hedging your bets on red (backpressure reduction).

L_perm

Understood.

I'm fine with the power I'm getting from the "hybrid" FVDs. I just want to make sure I'm getting the most of out of them, in terms of what can easily be done to the intake system. I don't want to mess with fueling, bigger turbos, or internals at this point. If I were to go down that road, then I would probably go with an entire 3.8 - 4.1 build. That may be in the future, but for now, I'd like to make sure my modified intake/turbo/exhaust hardware are all playing nicely together.

The do88 pipes seem like a good idea. The questions I have are:

1) Does a bigger (IPD) Y-pipe make sense, given the rest of the intake is modded?
2) Should I undo the GT3 TB and plenum change (I have the stock TB)?

I received my new, dedicated laptop yesterday, so I'll be installing the Durametric software this weekend. I'll send you an email for guidance on logging. I guess it makes sense to do some logging before the do88 pipes are installed?

Louis