-5s or -7s - Page 6 - GT-R Register - Official Nissan Skyline and GTR Owners Club forum

frostmotorsport · 26th July 2008, 05:42 AM

your sig is appropriate!!

what you have said is true, I don't argue that. And yes, I know how turbochargers work...

The point I was making was general rule of thumb, not feckin NASA calculated numbers.... Glenn puts it well, saying regardless of how you achieve it x HP = x stress on the engine.

Obviously, all rule of thumb - as you say, different turbos = diff temps etc etc

*yawn* - too much science!!

Moelders · 27th July 2008, 10:37 PM

Thanks for the replies

Sam: Although a lot of the theory that you talked about is far to technical for a non-mechanically minded person sch as myself, your overall explanation seems to agree with what I was suspecting, that being, for engine life expectancy, it would be better to get say, 330kw from a 2530 or equivalent Garret running at ~1.2bar than it would be getting 330kw from GT-SS turbos running at say, ~1.5Bar.
As surely the hotter the air going in, the harder the engine is working and more detonation prone it would be (I know it depends on the tune, but surely that would mean it would be an easier "Safe Tune" on the larger turbo equipped car?)??

Anyway, thanks for the reply, because for me, that would definitely sway my answer to this poll towards the 2860-5 (or 2530s). I would happily take the 500rpm or so loss of response for the ability to make the same power at less boost, causing less stresses on engine and turbos, and the further benefit of then being able to push more power later once the engine internals are strengthened etc.

SamuraiSam · 28th July 2008, 02:50 AM

Moelders: Your interpretation of my overly technical post is absolutely correct on every point and includes a few of the reasons why I recommend the -5's/2530's as the smallest turbo that should be put on an RB26, and will suggest it EVERY TIME over a smaller turbocharger.

Moelders · 28th July 2008, 05:17 AM

Good stuff

P.S. These forums are evil... Only just shelved out the $$ for an R34 V-Spec and already thinking of getting 2530s etc.! Will try to resist the temptation, and enjoy the car as it is... for a while anyhow!
So damned tempting though!!!

Lith · 28th July 2008, 05:36 AM

Quote:

Originally Posted by SamuraiSam

According to the chart at 75% efficiency you would be heating the air about 305 degrees. And at 58% efficiency you'd heat it about 365 degrees. So that's 60°F hotter air at the same pressure! Your intercooler is going to work to bring that charge temp down, but it makes sense that if you start with colder charge air in the first place, the intercooler will be able to bring the charge air temp that much more.

Can I be difficult and query why GT2560R-9s aren't more popular?

GT-R Glenn · 28th July 2008, 07:41 AM

No, this poll / discussion is about -5 or -7 ...
lol

Lith · 28th July 2008, 07:46 AM

'scuse me while I slither back to my cave :P

For what its worth, if I had a GTR and was looking for the same area of power with twins I'd be seriously considering them. I know a chap running the "smaller" -4s on a VQ35DE+TT and they made 520whp on 1bar, because they couldn't run any less boost than that lol. No lag at all though, its effectively NA in behaviour.

GT-R Glenn · 28th July 2008, 09:48 PM

Quote:

'scuse me while I slither back to my cave :P

So you are a student in Palmy ....

Lith · 28th July 2008, 09:53 PM

Quote:

Originally Posted by GT-R Glenn

So you are a student in Palmy ....

Haha if only. I was last a student 10 years ago

SteveN · 28th July 2008, 10:03 PM

Quote:

Originally Posted by plkettle

extra boost can stress the head causing the head to lift (usually fixed by uprated head bolts), blowing out headgaskets, cracking heads at real high boost etc

No, DETONATION does that as the fuel cant cope with the current situation, not boost pressure itself.

You think an extra 15psi or even 30psi of pressure makes any difference when the cyl pressures are hundreds and hundreds of psi anyhow?

People are scared of boost without even knowing what they are scared about. No need.

Lith · 28th July 2008, 10:38 PM

Quote:

Originally Posted by SteveN

No, DETONATION does that as the fuel cant cope with the current situation, not boost pressure itself.

You think an extra 15psi or even 30psi of pressure makes any difference when the cyl pressures are hundreds and hundreds of psi anyhow?

People are scared of boost without even knowing what they are scared about. No need.

I agree with a lot of what you say there, though bear in mind that whatever pressure in the intake manifold is gets compressed afterwards! Its not going to end up being cylinderpressure + manifold pressure, I'd say given whatever is forced into the valves it would be closer to say normal dynamic cylinder pressure x PressureRatio.

frostmotorsport · 28th July 2008, 11:33 PM

Quote:

Originally Posted by SteveN

No, DETONATION does that as the fuel cant cope with the current situation, not boost pressure itself.

not sure I agree with that.... must mention it to my engine builder who slapped me about the ears when he rebuilt my 4G63 - as we'd been running 23PSI on a standard motor and stretched not only the head bolts but the threads in the block!!

if I understand simple physics correctly - and I think this is what Lith is getting at.... - cylinder pressure is dictated by the amount of air stuffed into the cylinder (in this case by boost) x the compression ratio - so a small increase in boost pressure = a relative (and large!) increase in cylinder pressure ergo more stress against the head bolts/gasket etc.

I know det killed my valves and pistons over time, and will certainly contribute to cylinder pressure - but it was the excessive boost we ran that caused the head to lift and kill everything....

now awaiting correction....

frostmotorsport · 28th July 2008, 11:43 PM

Quote:

Originally Posted by GT-R Glenn

No, this poll / discussion is about -5 or -7 ...
lol

agreed - though if there is a better turbo for the application - why not investigate it?? funny that the majority of people have voted for -5's - which surprises me, as the RB26 is quite laggy with stock tubs. Guess it's all personal preference though!

Interestingly enough, I've been driving a MY98 WRX of late

and even as a non-STi - it would EAT a GTR point to point. any GTR.

they are just so much more chuck-able and the turbo spools almost from idle..... quite impressive.

Lith · 28th July 2008, 11:56 PM

Thats a funny impression, they really do feel like that. One of my mates had one of those and I would have agreed with him - it had GAB suspension and a few boltons and one night back in ~1999/2000 he was hooning up Mt Vic (you'll know the road) when there was nothing else around then he heard a noise. Then got the odd flash of head lights.... then suddenly a pair of headlights were on his cars tail - and somewhere along the line he got a flash of licence plate "F1RACR".

GTRs don't have as much dramatic, but to make a real comparison you have to have another car there to do so

And I just put that other turbo comment there as sometimes thinking outside the square is a good way to go. If we always stuck with the same thing, everyone here going for >500hp would have T04Rs

Moelders · 28th July 2008, 11:58 PM

Sorry to bring up the Garrett 707160-9 again since this is about -7's and -5s, but I have an on topic point, honest!

The link GT-R Turbos seems to show that the -9 Garrett is the same as the HKS GT-SS, whilst the -7 is the equivalent of one of the R34 N1 Turbos??
Is the table incorrect? As I thought from reading many other posts, everyone seems to see the -7 as the GT-SS equivalent??
If the -9 is the GT-SS equivalent then I am definitely confused as to why it wouldn't be more popular??
Or am I misreading the table?!?! (pretty sure not

)

View Poll Results: -7 or -5 turbos?
-5 for power - gimme gimme gimme!	61	63.54%
-7 for spool-up - it's a street car after all!	35	36.46%
Voters: 96. You may not vote on this poll

28th July 2008, 07:46 AM	#82 (permalink)
Lith GTR Register Member Join Date: Oct 2006 Location: Palmy, NZ Posts: 789	'scuse me while I slither back to my cave :P For what its worth, if I had a GTR and was looking for the same area of power with twins I'd be seriously considering them. I know a chap running the "smaller" -4s on a VQ35DE+TT and they made 520whp on 1bar, because they couldn't run any less boost than that lol. No lag at all though, its effectively NA in behaviour. Last edited by Lith; 28th July 2008 at 07:52 AM.

Thread Tools
Show Printable Version Email this Page
Display Modes	Rate This Thread
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode	Rate This Thread:

26th July 2008, 05:42 AM	#76 (permalink)
frostmotorsport GTR Register Member Join Date: Aug 2007 Location: Wellington, NZ Posts: 765	your sig is appropriate!! what you have said is true, I don't argue that. And yes, I know how turbochargers work... The point I was making was general rule of thumb, not feckin NASA calculated numbers.... Glenn puts it well, saying regardless of how you achieve it x HP = x stress on the engine. Obviously, all rule of thumb - as you say, different turbos = diff temps etc etc yawn - too much science!!

27th July 2008, 10:37 PM	#77 (permalink)
Moelders GTR Register Member Join Date: Jul 2006 Location: Sydney Posts: 23	Thanks for the replies Sam: Although a lot of the theory that you talked about is far to technical for a non-mechanically minded person sch as myself, your overall explanation seems to agree with what I was suspecting, that being, for engine life expectancy, it would be better to get say, 330kw from a 2530 or equivalent Garret running at ~1.2bar than it would be getting 330kw from GT-SS turbos running at say, ~1.5Bar. As surely the hotter the air going in, the harder the engine is working and more detonation prone it would be (I know it depends on the tune, but surely that would mean it would be an easier "Safe Tune" on the larger turbo equipped car?)?? Anyway, thanks for the reply, because for me, that would definitely sway my answer to this poll towards the 2860-5 (or 2530s). I would happily take the 500rpm or so loss of response for the ability to make the same power at less boost, causing less stresses on engine and turbos, and the further benefit of then being able to push more power later once the engine internals are strengthened etc.

28th July 2008, 02:50 AM	#78 (permalink)
SamuraiSam GTR Register Member Join Date: Oct 2007 Posts: 390	Moelders: Your interpretation of my overly technical post is absolutely correct on every point and includes a few of the reasons why I recommend the -5's/2530's as the smallest turbo that should be put on an RB26, and will suggest it EVERY TIME over a smaller turbocharger.

28th July 2008, 05:17 AM	#79 (permalink)
Moelders GTR Register Member Join Date: Jul 2006 Location: Sydney Posts: 23	Good stuff P.S. These forums are evil... Only just shelved out the $$ for an R34 V-Spec and already thinking of getting 2530s etc.! Will try to resist the temptation, and enjoy the car as it is... for a while anyhow! So damned tempting though!!!

28th July 2008, 07:41 AM	#81 (permalink)
GT-R Glenn GTR Register Member Join Date: Nov 2002 Location: Waiuku NZ Posts: 1,221	No, this poll / discussion is about -5 or -7 ... lol

28th July 2008, 11:56 PM	#89 (permalink)
Lith GTR Register Member Join Date: Oct 2006 Location: Palmy, NZ Posts: 789	Thats a funny impression, they really do feel like that. One of my mates had one of those and I would have agreed with him - it had GAB suspension and a few boltons and one night back in ~1999/2000 he was hooning up Mt Vic (you'll know the road) when there was nothing else around then he heard a noise. Then got the odd flash of head lights.... then suddenly a pair of headlights were on his cars tail - and somewhere along the line he got a flash of licence plate "F1RACR". GTRs don't have as much dramatic, but to make a real comparison you have to have another car there to do so And I just put that other turbo comment there as sometimes thinking outside the square is a good way to go. If we always stuck with the same thing, everyone here going for >500hp would have T04Rs

28th July 2008, 11:58 PM	#90 (permalink)
Moelders GTR Register Member Join Date: Jul 2006 Location: Sydney Posts: 23	Sorry to bring up the Garrett 707160-9 again since this is about -7's and -5s, but I have an on topic point, honest! The link GT-R Turbos seems to show that the -9 Garrett is the same as the HKS GT-SS, whilst the -7 is the equivalent of one of the R34 N1 Turbos?? Is the table incorrect? As I thought from reading many other posts, everyone seems to see the -7 as the GT-SS equivalent?? If the -9 is the GT-SS equivalent then I am definitely confused as to why it wouldn't be more popular?? Or am I misreading the table?!?! (pretty sure not )