-5s or -7s

[frostmotorsport]

hi all,

am planning to buy some new Garrett 2860 turbos in a day or two - but question is whether to go for the -7s for response or -5s and risk it being a bit more laggy.

Remember that this is a currently standard R33 GTR with factory turbos and will always remain a road driven car - so a big single is completely out of the question (have drive canmans one and while it makes fantastic power, you have time to make a cup of tea waiting for the boost to arrive!!)

so - popular consensus on -7s for response or -5s for power?

[Monster GT-R]

Do you have a boost controller ?

[Lith]

Don't use Canmans as an example of a single turbo setup - he has a filthy old T66 on his, you'd be foolish to use that as a representation of single turbos.

In terms of -7s and -5s, I'm a little split on that.... I quite like the way -7s drive - they will make enough power to scare most non hardened speed demons etc, definitely the option for a primarily road car. -5s definitely make the move into something a bit more competitive.

I think if you think of your car as a road car that you like using quite a bit, and want to have fun with it - go -7s. A lot of people I know who have gone to the -5/GT2530/equivalent type size start finding their car less fun for anything other than on the track, unless you are a bit more like the KismetCapitans of the world and happy enough doing frequent high speed street races as the -5s only show their advantage over -7s when you get them wound up in my opinion. Before high revs, -7s and -5s on 1.5bar both give a very similar whack in the back in my opinion - the -5s just keep whacking when the -7s are starting to settle down.

[frostmotorsport]

cheers Lith - good info & advice. to answer the above question, yes I do have a boost controller - currently pushing the standard tubs to .96bar or thereabouts. prob is you can feel the car starting to come alive @ approx. 1bar but I don't want the twin grenades to go off!!

[Lith]

Its just my take on what they felt like btw, there could be others with other opinions... hopefully other people will come in and add their 2c.

[Monster GT-R]

Originally Posted by Lith

In terms of -7s and -5s, I'm a little split on that.... I quite like the way -7s drive - they will make enough power to scare most non hardened speed demons etc, definitely the option for a primarily road car. -5s definitely make the move into something a bit more competitive.

I agree the -7's on a stock engine would make more sense. On the technical side, for the engine to respond quickly to the -5's it has to be modified to breath more or those turbos will lag alot, ( alot is relative). That means alot of money , parts and more money.

[Monster GT-R]

Also, by increasing the fuel air ratio in the lower RPM band, that will get the turbo to spool up faster (sooner). If you have the capacity to do that then it can make for more fun.

[GarethK]

Originally Posted by Monster GT-R

Also, by increasing the fuel air ratio in the lower RPM band, that will get the turbo to spool up faster (sooner). If you have the capacity to do that then it can make for more fun.

Making the car richer at lower rpm = cooler EGT = slower spool. If that's what you meant be 'increasing fuel air ratio' then I disagree it will makethe turbo spool quicker.

[Lith]

I was about to make a comment on that too - I know I have heard that in theory, however when road tuning cars so far just tuning for power seems to work best. You can get higher EGT by retarding timing, and therefore spooling the turbo maybe a bit quicker - though on the flip side you are using the air you are pumping in worse.

[plkettle]

i have had -5's for the last 2 years and i think they are great, dont think the spool up is slow at all and the power is great for a road car

1.5 bar is giving me 600hp at the fly with 480 lb/ft,
i never tried to wind it up to 1.9bar like kismetcaptain but i expect its pretty mad as the difference between 1.1 and 1.5 is HUGE in the way it feels when it takes off

however now im used to it i want more...

[UKPAISLEY]

Well I am doing the same, trying to decide on 7 or 5, I do have stage 1 cams as well.

However, what is needed to wave bye to the latest generation of WRX and Evo, can the smallar turbo do this, or to I have to wait for the kick to come in ???


Thats what I am getting at !,, I drive slow, but when I go for it I go, so the revs are high !, but we all like drivability what the verdict!

[plkettle]

the -5's cant spool much slower than -7's surely as mine honestly feel like stock in the response

I get full boost 1.5 bar by 4000rpm easy
get to 0.8 bar (like stock) by around 3400rpm

I never drive about at less than 3k rpm in any gear so i never really expirience turbo lag ?

If you dont want much more than 500-530hp then get the smaller ones, but if you want some scope for the future to get 600-650hp then get the -5's.

honestly, you will be surprised how quickly you will get used to 500hp and want more.

[frostmotorsport]

Originally Posted by plkettle

i have had -5's for the last 2 years and i think they are great, dont think the spool up is slow at all and the power is great for a road car

SO what mods do you have done to your car to support -5s? I only have std computer and a/m boost controller.... a Fcon ProV is on the cards in the future for complete fuelling control and tuning, but I suspect it could be at least a year before I can afford that so plan to run these turbos on std computer and boost controller till then, but don't want to turn it into a complete dog of a thing to drive.

I'm leaning towards the -7s - but curious to know if the diff is say a little more hesitation prior to boosting, or if it's like the diff between standard twins and a giant, mack truck single on a 2.6????

[kismetcapitan]

I think the difference is slight. I was about to get the -7s...but then I realized that I'm me and not a normal human, and that I was going to push these turbos to the absolute limit, so I went -5s.

Given a stock ECU, I would definitely NOT touch the -5s. I knew a guy who did, thinking he'd run them at 1 bar until he could afford to upgrade the ECU and fuel system and god knows what else (I've lost count of mods needed to support over 600bhp!), and then blew out his pistons within three months.

Get the -7s (I voted -5s but in your situation its very risky), keep the boost down until you get the FCon and some huge injectors, and then when you remap, get that high boost kick - there's plenty of it at 1.5bar for either turbo. I'm just a madman, that's why I need more

[Monster GT-R]

Originally Posted by GarethK

Making the car richer at lower rpm = cooler EGT = slower spool. If that's what you meant be 'increasing fuel air ratio' then I disagree it will makethe turbo spool quicker.

I was meaning , going from 11:1 up to 13.5:1 or more. Leaning it out, increases the EGT temperature and you through putting more gas sooner as there is more air. This spools it faster (sooner). BUT the trade off is your acceleration in that RPM band could be slower and this tends to make the boost come at you all at once. There is a RPM point and this varies with each engine as to when to bring the fuel air ratio back down and control knock and to produce your HP. This has to be done by a talented tuner of which there are a few here on this form.