A Little Dissapointed With My Number On -5S, Please Help :)

[kitto]

Double post

[kitto]

First of all:

Air temp and humidity are ALWAYS relevant. They effect HP so they are very important to consider.

Yeah, gotta agree. Air temp and humidity must be accounted for.

If not, false high readings will occurr. On a dynapak the

difference can be quite a lot, and therefore you will be flammed for having false readings.

[frankiman]

First of all:

Air temp and humidity are ALWAYS relevant. They effect HP so they are very important to consider.

Secondly:

HP is HP, it doesn't matter where in the world you are, only how accurately you measure it and if you don't calculate HP with air temp and humidity involved, your readings are inaccurate. We measure in HP also. We also measure using the metric system of KW but it doesn't matter which reading you take, they are both accurate.

Your buddy actually has 400-420hp at the wheels if its still standard weight

dynos recalculate the Absolute HP values measured with the air temp and humidity, then shows the SAE standardazided info on the screen

thats why i say that the air temp and humidity are irrelevant, since the dyno always compensates for them

on a colder day, yes you'll actually have more HP (measure wheel HP) but the dyno is still going to show the same number, since its SAE standardized

and his car is far from 3100lbs

i weighted mine this summer (corner balanced the car) and it was 1590kg (i have alot of stuff on the car, chassis reinforcement, roll bar, aero parts, etc..) so his would weigh pretty much the same, given hes got a sound system and i don't

[Birds]

Before we start getting confused about cross cultural octane ratings for petrol too, I'd like to point out that your 87, 91 and 94 octanes are equivalent to our 91, 95 and 98 respectively.

[The Dan]

and his car is far from 3100lbs

By 'his' I assume you mean Cobra?

That's why I calculated his HP from 3500lbs which suggests he makes 500hp at the wheels.

This is bang on the figure you would expect from -5's.

[MrStabby]

we use stock BNR32 MAFs which are mofified by our tuner (Almasi tuning, who tunes most nissans in our area),

its a trick he started doing a couple years ago, the ECU is tuned to read the new values of the MAF accordindly

stock MAF can now be used up to 600whp and more i know since i got 445whp (330rwkw) with them

To me "stock" implies standard, so I would call these MAFs "modified" rather than "stock". Also, just because a MAF runs out of resolution doesn't mean you cant make power above that level, it just means you're doing so with a great deal more risk as the ECU is only basing the maps on RPM, rather than load and RPM.

[cobrAA]

I'll go back to the original post:

1 - Yes, probably (to both parts of the question). You will lose a little bit of response but the total volume of the intake tubing and intercooler is what matters. the stock intercooler does flow well up to a point but you are probably at the point where the stock intercooler is a bit foa restriction. At 4 degree temps it doesn't sound like you need any help with cooling efficiency though.

2 - This is the contentious point about your power levels. What are the voltage readings from the AFMs? In any case they've been modified to have a lower slope (right??). I imagine you'd know if they were out of effective resolution (almost peaked out) - so you must be asking if they are a restriction? There might be some SLIGHT gain in dropping vacuum restriction to the compressor intake by swapping to 80mm Z32 AFMs but I wouldn't bet my house on a significant gain. Plus you've then got potential issues caused by low readings from the dual Z32 at low loads.

3 - I'd swap out the exhaust then do a dyno run. A 3" varex is likely to be noticeably less efficient at those boost and power levels than a 3.5" job. For smallish turbos running big boost the exhaust can make a big difference to their efficiency. Any drop in back pressure is multiplied by the turbine housing. So start here first, it's the easiest swap with the biggest potential gains.

Full disclosure - I've NEVER worked on a GTR but go get a 3.5" exhaust. Like for like, they flow 35% more than 3".

One thing I was wondering with 3.5 inch exhaust is the fact that the dump pipe is propably 3 inch or maybe even 2.5 inch. so even if I do get a 3.5. I don't see how they could flow more than the smallest piping ( the dump pipe). (I.E: you can have a 3.5 inch exhaust but if your running stock cat, your line is actually only 2.5 inch)

[GTSBoy]

It doesn't matter that you don't remove all the restriction. If you only remove some of the restriction, you will still flow more. Of course it is much more useful to change the MOST restrictive part. And if the front of your exhaust is small, then it makes sense to improve that first.

FWIW, if you are above 400rwkW, then you should be seriously looking at a 3.5" system with as little restriction as you can handle (read that as as much noise as you can handle).

You should also be putting pressure tapping points into your cooler piping either side of the cooler, and into your exhaust manifold so that you can measure the pressures at these locations so you can see exactly what is restricting flow and decide on any modifications accordingly. This makes much more sense than semi-randomly choosing mods to do.

[frankiman]

by the way, you have 2 dump pipes

2*pi*2,5^2=39.27 in^2

whereas a 3,5 exhaust is

pi*3.5^2=38.48 in^2

so pretty much the same flow

right now with a 3'' you have pi*3^2=28.27 in^2

so 1-28.27/39.27=0.28 your exhaust is 28% more restrictive than your dump pipes

[GTScotT]

CobrAA the we need to point out the difference in numbers is simple.

you came and said hi I have over 400kw from my -5s and I'm disappointed, how do I get more?

well here's the thing. Most aus -5 owners make 330-350 and 400 would almost be an absolute maximum. So to us we are wondering why you think this is bad and what more you think you should have.

acknowledging that you are in the US helps us determine what number you should be aiming for and how we can help you get there.

I certainly don't mean to step on your toes but your trap speed which is not effected by traction certainly does indicate you have the aud.equivalent of 450whp.

So now the question is where can you pick up another 50auhp. That is a fair expectation for those turbos.

I hope this helps you feel less bashed.

[SS8_Gohan]

^ he's in Canada.... ey

[XKLABA]

now don't give too much attention to the 11,8s @121mph run hes the worst driver i know

with better tires and a good driver, the car is def capable of mid to low 11s

but a buddy of ours, with stock turbos (hes been planing to swap them for a year now) does about 300 1/4mile passes on a good summer

with stock turbos, bigger injectors, intake / exhaust, boosting at 14,5-15psi, he made about 350whp (260rkw) on his last tune 2 years ago

the car has a 1-2-3 OS Giken gearset, and the driver is an expert at drag racing (puts ur all to shame really),

on cold october nights, he does passes in 12,0X ~@118mph with a 0-60feet of 1,7s (i do 1,85 with the exact same tires (tyres?))

so there ya go..

11.8 @ 121mph would suggest only minimal wheel spin, my 300rwkw R34 GTR ran 11.8 @ 118mph, so add the extra weight that car is still only a realistic 330-350rwkw

yeah ok, I'm no "expert at drag racing" but my full weight R32 GTR with 3 V12 alpine amps, a Type R Alpine 12" sub and box , Focal Utopia 6.5" splits ( each woofer weighs 5.5kgs plus the tweeter and cross over) and Boston acoustic 6.5" two ways in the parcel shelf, stock turbos, injectors, cams. intercooler blah blah blah, on 16psi made 261rwkw and with that it ran 11.49 @ 121mph then the boost got turned up to 19psi with 290.1rwkw it ran 11.36@ 125mph and 11.38@ 125mph on 18" rims and what ever tyres I was running on the street at the time, so your expert drag racer needs to get back to the track and learn to drive, so who exactly is getting put to shame

To the OP, -5s on a 2.8 making 565rwhp @ 23psi is pretty good, higher lift cams, 4" intercooler and 3.5-4" exhaust would help release a few more hp, the bigger diameter AFMs would most likely help to, but I wouldn't be to disappointing with that result given the setup

[GTR_JOEY]

I was going to mention your times XKLABA as a reply to that post, didn't wanna put his "awesome" times to shame

[fatz]

Ya mph doesn't lie

Your car doesn't make the hp you think I'd does

[SimonR32]

thats a 9,74 @141,95 pass, with stock MAFs, with 643rWhp (478 rw kw)

and what kind of fuel do you guys run on?

we 94 or 91 octane gas

i made 445whp (330wkw) with 91 octane on -7s and stock engine

Did anyone miss the -5's runing 142mph on 23psi!

Now there is something that doesn't add up ?!?

[cobrAA]

by the way, you have 2 dump pipes

2*pi*2,5^2=39.27 in^2

whereas a 3,5 exhaust is

pi*3.5^2=38.48 in^2

so pretty much the same flow

right now with a 3'' you have pi*3^2=28.27 in^2

so 1-28.27/39.27=0.28 your exhaust is 28% more restrictive than your dump pipes

another ingenier post lol! but thanks frank for the clarification. but this information also prove that going 4 inch make no sens because the dump pipe will now be the restrictive point in the exhaust and by having -5 turbos you can't just change the air exit of the turbos. To my knowledge, the R34 dump pipe are as big as the ''hole'' of the turbos.

CobrAA the we need to point out the difference in numbers is simple.

you came and said hi I have over 400kw from my -5s and I'm disappointed, how do I get more?

well here's the thing. Most aus -5 owners make 330-350 and 400 would almost be an absolute maximum. So to us we are wondering why you think this is bad and what more you think you should have.

acknowledging that you are in the US helps us determine what number you should be aiming for and how we can help you get there.

I certainly don't mean to step on your toes but your trap speed which is not effected by traction certainly does indicate you have the aud.equivalent of 450whp.

So now the question is where can you pick up another 50auhp. That is a fair expectation for those turbos.

I hope this helps you feel less bashed.

Thanks for the information. My exhaust with an utra-quiet vibrant resonator, 1 straight magnaflow exhaust and the varex valve ( closed when needed) is enought quiet and I'm curious if a 3.5 with the same component would be that much more loud.

Another thing, if I go 3.5. I doubt my sway bar will pass under the exhaust. could this be fixed by having shorter exhaust hanger ?

Edited October 14, 2012 by cobrAA

[The Dan]

another ingenier post lol! but thanks frank for the clarification. but this information also prove that going 4 inch make no sens because the dump pipe will now be the restrictive point in the exhaust and by having -5 turbos you can't just change the air exit of the turbos. To my knowledge, the R34 dump pipe are as big as the ''hole'' of the turbos.

Thanks for the information. My exhaust with an utra-quiet vibrant resonator, 1 straight magnaflow exhaust and the varex valve ( closed when needed) is enought quiet and I'm curious if a 3.5 with the same component would be that much more loud.

Another thing, if I go 3.5. I doubt my sway bar will pass under the exhaust. could this be fixed by having shorter exhaust hanger ?

Not sure about your swaybar but our swaybar goes OVER the exhaust at the rear

[GTScotT]

If you are concerned about the catback you could ask your tuner to do a few test runs with no exhaust post front pipe.

unbolt from before the cat/test pipe and see if power will start to climb with more boost or timing.

if its night and day you know that the exhaust is an issue.

As a rule of thumb I think 350kw+ warrants a 3.5" exhaust. 450 would warrant a 4". 400 odd has been seen from a 3" in the past but that is on E85, which is not on parity to PULP either when it comes to numbers.

[sydking]

One thing I was wondering with 3.5 inch exhaust is the fact that the dump pipe is propably 3 inch or maybe even 2.5 inch. so even if I do get a 3.5. I don't see how they could flow more than the smallest piping ( the dump pipe). (I.E: you can have a 3.5 inch exhaust but if your running stock cat, your line is actually only 2.5 inch)

Grab a pair of R34 GTR dumps? not 100% on the size but been proven to flow more then you currently have.

[GTR_JOEY]

If it was me just get some big F off 3 inch dumps!!

And "high" flow that cat!