Volvo K24 turbo in audi application.

[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:

[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

[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 .

[prj]

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

[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".

[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]

Thats a new one

I might be wrong, just going off the top of my head.
Need to sit down with the measurements.

[terrybullwon]

then the cross-section is similar to a single 3".

Thats a new one

[prj]

I've proven differently on a dyno also with separate cars re the exhaust, have to agree to disagree

This was done on the same car. Only exhaust swapped.
If you actually look at the stock exhaust (catless!), then the cross-section is similar to a single 3".

[Jamo]

I've proven differently on a dyno also with separate cars re the exhaust, have to agree to disagree

[prj]

Back pressure and egt will be high stock exhaust I'd a restriction approaching 280 bhp, spool would be affected also 2.75 would be ok over 300
Are you lot also planning on running stock exhaust manifold as runners 1 and 5 are high on manifold and will also be affected at this power level

Stock exhaust with the cats removed is not a restriction until ~380bhp. This has been verified on a dyno. No gains at 300whp from a single 3" exhaust over the stock one with cats removed. Gains are only there if using a 3" DP as well, and even then, not that much (read: you won't feel it) until you start going higher than 380 bhp.
I suggest measuring backpressure in the catless stock exhaust...
Exhaust manifold should be RS2 replica or better, this is obvious, due to the horrid design of the stock one.

[Jamo]

Back pressure and egt will be high stock exhaust I'd a restriction approaching 280 bhp, spool would be affected also 2.75 would be ok over 300
Are you lot also planning on running stock exhaust manifold as runners 1 and 5 are high on manifold and will also be affected at this power level

[prj]

Stock exhaust and DP are good enough for this power level as long as the cats are removed... there will be very little, if any gains by fitting a larger DP/exhaust.
The main gain will be saving weight.

[Rocco]

is your dyno draw similar to my current one??

here 2 diferent lines/launchs with 2 diferent ecus,very similar anyway

[Ruffiano]

Sorry posting from my phone so excuse mistakes. I should also mention I am using a stock 3b downpipe and 2.5" exhast