Volvo K24 turbo in audi application.

[Rusty]

Stock DP is the main area that's the issue for higher power as 2.5" is a little too small to cram all the hot exhaust gases through. 3" is loads better and enables a 100cpi sports cat to be fitted and the twin section to be ditched.

If you're referring to the twin cat section being equivalent to 3" then the maths is fairly simple (as Pi and the /4 for diameter can be omitted) -

3" diameter gives 9" ^2

9/2 = 4.5"^2 per pipe

sqrt(4.5)=2.12" diameter.

However, as surface area is related circumference and not XSA -

per unit length Pi x D means that a single 3" pipe has 25% less surface area than 2 x 2" pipes and there's also the effective restriction of twisting and turning the gas and splitting it in 2 directions...

[prj]

Nice.

What I was referring to earlier, is that the DP was not changed for a 3" on the dyno.
I meant that the DP remained stock (2.5") and after DP a 3" exhaust was welded on.

That made no measurable difference at 380 hp.
Maybe Jamo tested with a 3" DP as well?

And yes Rusty, I was referring to the 2x2" (or are they 2.25"?) vs. a single 3".

[prj]

Illustration of what I meant... and what gave no measurable change, except making the car loud and taking some weight off:

[driftin jo]

I have posted this before but always good for reference .


It's also worth noting that when people have 3 inch / 76.2 mm exhausts made the size is the OD of the tube so given a 1.5 mm wall section a 76.2 OD the bore is only 73.2 for ref to the figures below , these are bore size so 3 inch is a little bigger than our 3 inch etc.

I used the word tube above for a reason , generally thin walled is referred to as tube (what we use for exhausts ) and the dimensions are nearly always given for OD not bore size. Heavy gauge (thick wall section) is referred to as pipe and the size is given for bore .

This chart is one I made years ago and was taken from S.E.A testing on an engine dyno not theory.

Pipe bore size. --------- BHP obtainable without
inch / mm ------------- pipe causing restriction / reduction in HP

2 / 50.8 ---------------- 185

2.25 /57.15 ------------- 235

2.5 / 63.5 --------------- 285

2.75 / 69.85 ------------ 350

3 / 76.2 ---------------- 415

3.25 / 82.55 ------------- 490

3.5 / 88.9 ---------------- 565

3.75 / 95.25 -------------- 650

The above figures are based on petrol engines running a full length exhaust system 4 metres / 13 feet in length with free flowing silencers . More HP is obviously attainable from each size of pipe but beyond these figures the exhaust is increasingly restrictive .

[Ruffiano]

So here was my best run of the day, it was actually my first run, heat soak got me quick, i don't know if it is poor cooling on my part, or craptastic fans on theirs...



I had them do the 3rd pull in 4th gear (instead of third), it boots higher and it did infact put down the most torque, and was the second highest on hp, i think if it was my first run in 4th gear, it would have been the most powerful of the day.
So here are all three of the day:



and here is my favorite, my best run of saturday vs my best run of the last dyno day in feb

[Ruffiano]

For reference here is plot from the same day, same car (cabfab9s) same basic engine (all stock internals like mine), however he does have a 3" downpipe and 3" exhaust, LWFW, And is running a stock k24 7000 but other then that we are pretty much the same, both have aby intakes and aby intercoolers:

[URQguy]

This dyno is a heart breaker, and we are at 4500' of elevation. Dave mentioned it in his post a few pages back, but the benchmark of what kind of power he is making is the 3 b7 rs4s that ran the same day. he was clumped in the middle of a 10whp spread with them, and 2 of them were fresh off carbon cleanups from the dealer. They are rated at 440hp from the factory, and that is what I believe Dave is making with this volvo turbo.

Stock STIs make 220whp here(rated 300hp) and Stock EVOs make slightly less. If you go by these three vehicles, 25% is even a tad low for drivetrain loss on this dyno.

I have seen several guys bash on the dyno for reading very low on local forums, but it is what it is. If you have benchmark stock vehicles running on the same day with the same basic drivetrain, it is easy to compare them to derive the drivetrain loss. I would put this dyno at 26-27% based on those vehicles.

BTW, as for the 3" debate, I made 612whp on the same dyno as the above on the same day with a 3" exhaust. On road trips, I slip in a 2.5" restrictor in the exhaust to keep the exhaust manageable for 400+ mile trips. I want to dyno the results, but my butt dyno says I am atleast 300whp down. At some point I will probably make a 3.5" exhaust or probably dual 2.5s.

[prj]

You need to tune your boost control a bit it seems...
Seems to take a sharp dip there.

Thanks for the graphs.

[Wheeljack]

From what I can tell, your torque curve rise is pretty much on the same line as mine...meaning no torque lag from mine to yours, which is pretty amazing considering the capacity of the volvo k24...that sounds like a nice next step for me...so, where's that motronic chipset for this thing? ;-)

And regarding the dyno, it seemed pretty inline with my expectations...maybe I'm making more power than I think?...And these are all corrected (to STP) numbers, so the elevation is largely irrelevant, unless you are considering the potential secondary effects of air density?

[prj]

so, where's that motronic chipset for this thing? ;-)

Coming this summer (tm)

[UrS4boy]

You need to tune your boost control a bit it seems...
Seems to take a sharp dip there.

I find the peak hp to be great but the curve is surprizingly peaky. I went looking for a factory RS2 (K24-7200) hp and torque graph but all I could find is this (below) which mentions the peak RS2 hp is at 6500 RPM. So what can you do to extend this K24-7400 power peak, prj?

[prj]

I find the peak hp to be great but the curve is surprizingly peaky. I went looking for a factory RS2 (K24-7200) hp and torque graph but all I could find is this (below) which mentions the peak RS2 hp is at 6500 RPM. So what can you do to extend this power peak, prj?

Can't do anything. You need a turbo that flows up top. The reason that the power peak on the stock RS2 is so high, is because the Stock RS2 doesn't run that much boost (~1.4 bar). It runs fairly flat boost almost to redline, whereas tuned cars run high boost midrange for crazy torque, and then the turbo runs out of steam...

[UrS4boy]

Can't do anything. You need a turbo that flows up top. The reason that the power peak on the stock RS2 is so high, is because the Stock RS2 doesn't run that much boost (~1.4 bar). It runs fairly flat boost almost to redline, whereas tuned cars run high boost midrange for crazy torque, and then the turbo runs out of steam...

Here is a dyno plot for an AAN with RS2 turbo, EM, MAF and injectors (but no exhaust cam) with MTM/Dahlback s/w (at sea level), much less peaky:

[prj]

Yep, and that's why it makes much less torque as well....
I don't think you are running anywhere close to 28psi on that chart.

[Billman]

@Ruffiano

How does your boost profile looks like?