Why Is My Skyline So Slow

[PM-R33]

You guys are going into very complex thermodynamics and the "perfect" size of an exhaust for the given job. Yes to small not good, to big not good. However lets save that for another discussion. You guys are both right in a way, however that aint the topic of this thread.

[Tony de Wonderful]

I know hardly anything more complex than changing my oil but I got a 52% in year 10 physics and I dont understand this. The volume of exhaust gas would be inversely proportional to pressure so you are saying that a larger exhaust volume=lower pressure in exhaust system=???=more backpressure. And lets say in the 30 minutes it takes for the exhaust gases to pass through the giant exhaust they cool down. Lower temperature means the molecules in the exhaust fumes are moving at a lower speed thus providing a lower pressure for the same concentration of particles and this somehow increases backpressure as well?

OP: Car is slow because its a 1.5tonne 4wd being powered by a 15 year old naturally aspirated 2.5L engine

It's fluid dynamics. He has a point that cooler air (denser) is more resistant to flow so will create more pressure loss through the exhaust (all things being equal).

You are confusing this with absolute pressure/density which something like Boyle's law describes for a given volume.

The 'zaust outlet on the engine 'sees' the sum total of the pressure losses through the exhaust system plus one atmosphere, not the pressure of an idealised gas where volume is held constant as temperature is increased. Pressure loss is government by viscosity, temperature, compressibility and density of air plus the friction factors and internal diameters and profile of the 'zaust system.

All things being equal:

Fat 'zausts = less pressure loss.

Thin 'zausts = more pressure loss.

How temperature loss of the 'zaust gases through the system (and the corrosponding increase in density) feeds into the equation I am not sure. It is certainly possible for a very cold, dense 'zaust gas, passing through a fat tube, to create more pressure loss than a hot, less dense 'zaust gas, passing through a skinny tube. Of course more pressure loss actual heats the 'zaust gas back up through friction, equals less density, so this is very complicated full of non-linearities and feedbacks.

If you were a geek you could mount a pressure transducer in the 'zaust manifold and measure the pressure losses through the system.

[Tony de Wonderful]

Yes to small not good, to big not good.

Top Fuel cars have open headers.

If you like this means their 'zaust system is as big as the whole atmosphere.

That is quite big.

But they go quick.

[adis]

Thats the thing, it IS the driving. Shit driving = shit times no question about it, people need to see that they need to improve their driving skills and not bitch and moan about a car with 100kw less almost matching their times.

Happy to prove you wrong. Too many 15 yo on here talk shit.

-So, here is the deal. We take my car (same set up) and you sit with me, we drive up to Heathcote, and we both run my car. And lets see if its SHIT driving. Unless something is wrong with my set up, which i doubt, (apart from boost dropping from 15 to 12-13 psi). SO you let me know if you want to take me up on my offer, pm me.

Because i was embarrassed because i was expecting so much after i heard what 'stokish' skylines get, but after a while i realized, too many shit talkers on here, not all, not saying that, just too many ppl think their car is a machine and quickest so they blow up figures to suit their ego. Im realistic, 14 is best i could get.

[adis]

Mind you i was pushing the car so hard, that wen shifting from second to third, i was getting churp from 245 tires, brand new. Now i know loosing traction doesnt make you fast, but it does mean that i tried everything and was pushing the car to limit.

I tried riding the clutch.

Burnout/no burnout.

10 runs.

3000 rpm launch

3 500

4000

5000

4500 is when i got the best result.

[PM-R33]

It's fluid dynamics.

Its actually both. Thermodynamics and fluid dynamics.

Top Fuel cars have open headers.

If you like this means their 'zaust system is as big as the whole atmosphere.

That is quite big.

But they go quick.

Don't twist my words. I can tell you know a decent amount of engineering principles, as do I. Your example is completely different to what we are talking about and im not going to waste pages of typing explaining it when i know you know the difference between open extractors on a race built engine and the examples we are talking about here referring to the diameter of an exhaust over a long length where the gasses have to travel a long distance.

Edited February 24, 2010 by PM-R33

[adis]

For your claimed power, you should be running mid/high 12s...

190 - 200RWKW is seeing consistent 12.9s from people.

Here is info from my run:

35C

60f: 2.3s (19 inch wheels down to 19psi)

mph 104.02

time 14.0034 sec

Even Tried taking the exhaust off just before cat to see if my punched out cat was restricting the flow, no difference.

Exhaust is 3inch otherwise, straight through.

Full boost 3500 rpm hi flow turbo, set to 15 psi but by 7000rpm goes down to 12-13 psi.

245 tires, brand new, on 19 inch wheels (not ideal i know).

Mines ecu

Split fire coil pack

R34 cooler (not idea i know but i dont want front mount).

Pod.

[Touge Kyousou]

+1 on n/a needing some form of backpressure in the exhaust system.

Not such a big consideration on a FI car as having backpressure will generally affect the exhaust flow/velocity of your turbo thus impacting boost delivery, turbo heat/heatsoak etc.

With the n/a, having a bit of backpressure helps exhaust scavenging like said before. I think it also helps with the combustion process itself though not totally sure. The trick is to find the optimum/balanced point for YOU. Too little backpressure will have a low rpm slug but good top end, too much backpressure will feel like a nice low end but choking top end. I remember swapping a high flow metal cat and high flow muffler plus some mandrel piping on an fto (n/a 2l v6) and instantly noticed the loss of low end but increased top end. You WILL feel it if you're in tune enough with your car. Temperature also helps with scavenging as well, hence people getting headers/extractors ceramic heat coated to keep more heat inside the pipes and less heat emanating through the engine bay.

17-18s quarter does sound kinda slow for a r33 gts4...but i wouldn't know because i have never owned one.

Like said before, best bet is to get it dyno'd, check the afrs, get them to do the runs with some kind of knock detection installed, check heat before and after runs etc etc. Try to run your line on 98octane fuel as well if you're not already. Might be an idea to flush out the radiator, check for blocks then use some decent coolant...could be something as simple as a heat issue..My v35 initially had a heat issue and only ran 131rwkw...after i addressed the heat issue and added just a few simple breathing mods, it was at 170rwkw on ISMR's conservative dyno. Oh, check all consumables too, how are the spark plugs ?

Magnas FTW =P my mate just bought an 02 maga sports...i gotta admit it has alot of poke, especially considering it's a fwd n/a. Looking at getting a magna myself for a daily haha.

[Tony de Wonderful]

Its actually both. Thermodynamics and fluid dynamics.

It is not thermodynamics directly, it is the fluid properties of the air which directly effects pressure losses through the 'zaust.

But thermodynamics effect the fluid properties (a bit).

[Super Drager]

Here is info from my run:

35C

60f: 2.3s (19 inch wheels down to 19psi)

mph 104.02

time 14.0034 sec

Even Tried taking the exhaust off just before cat to see if my punched out cat was restricting the flow, no difference.

Exhaust is 3inch otherwise, straight through.

Full boost 3500 rpm hi flow turbo, set to 15 psi but by 7000rpm goes down to 12-13 psi.

245 tires, brand new, on 19 inch wheels (not ideal i know).

Mines ecu

Split fire coil pack

R34 cooler (not idea i know but i dont want front mount).

Pod.

You do realise the R34 cooler will heatsoak VERY quickly and your "225rwkw" could end up around ~190rwkw. As for your offer before, i'd love to....but unless your paying for my plane ticket from sydney, it'll have to be another time.

[PM-R33]

It is not thermodynamics directly, it is the fluid properties of the air which directly effects pressure losses through the 'zaust.

But thermodynamics effect the fluid properties (a bit).

The temperature of the gasses inside the exhaust are important. The more heat you can trap in the exhaust the better. The hotter the gases, the faster they travel. Since thermodynamics is a study of energy conversion between heat and mechanical work it is relevant. Why do you think keeping as much heat inside of an exhaust manifold and exhaust housing is an important part of spooling a turbo. The hotter you can make it, the better. So while i agree on this discussion on NA cars it is mainly fluid dynamics, thermodynamics are just as important considering most of us on here drive turbocharged vehicles.

Any back on topic.

[Mooney]

a mod should close this thread,

wtf does a vn have to do with this guy asking about his gts4?

[adis]

You do realise the R34 cooler will heatsoak VERY quickly and your "225rwkw" could end up around ~190rwkw. As for your offer before, i'd love to....but unless your paying for my plane ticket from sydney, it'll have to be another time.

Heatsoak from one run after cooling down? doubt it. after each run car was cooled down. did 10 runs all day.

-if i was driving it hard around the track yes, but if its cool and i run it once, i doubt it.

I will not be paying any plane tickets, offer is generous enough already, just to prove my point.

[Touge Kyousou]

Heatsoak from one run after cooling down? doubt it. after each run car was cooled down. did 10 runs all day.

-if i was driving it hard around the track yes, but if its cool and i run it once, i doubt it.

I will not be paying any plane tickets, offer is generous enough already, just to prove my point.

35 degree day is pretty unfriendly to times though, especially on FI cars..

Perhaps the people getting lower times with similar power are using drag radials, gutted interiors, 90/10 sussy (drag setup sussy), low psi on rears etc etc.

Weird how your tires chirped 1 to 2 with 245s...i would've expected the car to melt the 245s on a hard shift with 225rwkws lol. My car can spin the uhp 275s on the rear momentarily on a hard 1-2 shift before they grip and it's only 180rwkw.

[bozodos]

he's right about the SMIC, and lol @ the usual N/A thread derailment.

Mooney, VN's have everything to do with it

[PM-R33]

The halarious thing is there are three distinct discussions going on in here now. Not one of them to do with the original post lol.

[UNR33L]

lol im not talking shit mate, i provided evidence.. and as for chirping third gear thats nothing special if i can do it, maybe its the 19s and the 34 cooler who knows 14.0 is not a bad time but if you really are getting "225 rwkw" maybe the dyno is reading a little high if your driving style is so "epic"

have a look around at times mate, people pulling 200rwkw can manage around 13.6 fairly easy, maybe try some 17s and another dyno?

i guess thats the only downside to a turbo car more things can effect the performance majorly.. small boost leaks etc who knows, good old n/as are just simple and u can spank em all day long hehe.. dont get me wrong as soon as i turn 21 in a few months im getting rid of this car although i could not have been happier with a P plate car.

also im running 255s on the rear and 235 on front kumo ftw altho they are getting a little bald lately need to replace them before i sell the car.

edit:

[adis]

Weird how your tires chirped 1 to 2 with 245s...i would've expected the car to melt the 245s on a hard shift with 225rwkws lol. My car can spin the uhp 275s on the rear momentarily on a hard 1-2 shift before they grip and it's only 180rwkw.

NO, you misunderstood me. I said when i went from 2 to 3 they chirped. In saying that, when i had 280 at wheels, traction wasnt that much of an issue on same tires.

[adis]

The halarious thing is there are three distinct discussions going on in here now. Not one of them to do with the original post lol.

haha made me laugh

[mad082]

Top Fuel cars have open headers.

If you like this means their 'zaust system is as big as the whole atmosphere.

That is quite big.

But they go quick.

actually they have tuned length headers. they have made the length of those pipes to the exact length that they need to make maximum power. they haven't just slapped on a few lengths of pipe to simple have the flames clear the engine block.

Here is info from my run:

35C

60f: 2.3s (19 inch wheels down to 19psi)

mph 104.02

time 14.0034 sec

Even Tried taking the exhaust off just before cat to see if my punched out cat was restricting the flow, no difference.

Exhaust is 3inch otherwise, straight through.

Full boost 3500 rpm hi flow turbo, set to 15 psi but by 7000rpm goes down to 12-13 psi.

245 tires, brand new, on 19 inch wheels (not ideal i know).

Mines ecu

Split fire coil pack

R34 cooler (not idea i know but i dont want front mount).

Pod.

ok, the 35 degree day certainly wouldn't have helped things, but other than that it is slow for the mods. also width of tyres doesnt mean much. a cheap set of 245 tyres will spin easily, while a set of decent 225 tyres will grip better than the cheaper wider tyres. my mate had a 33 making about 175kw (stock turbo, turbo back exhaust, crappy remapped ecu and the engine was tired) and was able to run 13.8. another mate of mine (a member on here) was able to run 13.6 with 200kw (mods were stock turbo at 13psi, pfc, fmic and turbo back exhaust on street tyres). as for talking about heatsoak, the stock side mount cooler will be suffering a bit from heatsoak by the time you have finished your burnout. then will be suffering from heatsoak badly by the time you have changed into 3rd gear on your run, especially on a 32 degree day.