-5's Vs Rs's On A Larger Then Stock Motor

[NickR33]

Ash what's the setup on your GTR? do you have a graph to throw up?

[R31Nismoid]

They are some hybrid, not sure on the specs. I forgot to get the graph... but I'm going out there on Sat so ill get it then

in 5th under load, there is at least 4-5psi on @ 2400rpm

4th is around 3000-3200. Steve's seen it

(im also gonna get a -9 graph of another mates car and overlap)

[Beer Baron]

piggaz, I have had some success on 2 cars of mine with the tomei manis and found they seemed to make a difference even with GTSS turbos as they spooled up very hard with the tomei mani's. the aim is to get that exhaust gas hitting the turbine wheel hard by giving it the most direct path possible, but given how much pressure there is between head and turbine in the manifolds design is probably not so crucial but the tomeis do have much bigger runners. having said that the stock manifolds should not really hold it back at all. they have their good points too. being thick cast mani's they keep much more heat (energy) in the pipe which is desirable too. there is no doubt they are good enough. on my two cars that I used tomei mani's on they held up fine while I had them and I know one car that has been running now about 3 years with them still good. BUT on the flip side I have heard of a few tails of cracked ones too. there are a few factors in that. a lot of people done have a bracket to hold up the front pipes which means all the weight of the turbos, dumps and front pipes are hanging on the mani's. EGTs is another big factor as is engines that get shut down hot without a "warm down" period to let temps normalise slowly. that can and will crack the manifolds.

Have you considered switching to a set of GTS4 diff gears? they are a great match with the OS gearset you have and will shift your power graph in the right direction speed wise.

The key thing I've found to get the best out of the twins (be it GTSS, 2530, or GTRS) is getting the gas in and out of turbos as well as you can. I would reccomend a set of stock ported or tomei mani's, a set of tomei big bell mouth dumps (or other comparable ones but I've never seen others as big as the tomeis), matched to the BIG HKS front pipes (there are small ones and big ones, you need the big twin 70mm into single 90mm ones), with a free flowing cat or pipe and a free flowing exhaust.

same goes for the intake. you want a nice smooth passage for that compressed air from the turbos to the inlet. you can keep the stock inlet piping and twin turbo pipe but replace the other intercooler pipes for a hard pipe kit (not expensive). nismo plenums are good too but I've never seen much top end power increase from them, but they definitely help with response which is not easily measured on a dyno(on/off/on throttle and a bit of midrange gain too). you can also got a full suction kit if you like, I'm a fan of them but they are a bit expensive from HKS or trust so on a dollar to improvement basis they are not a necessity. A good intercooler is important too. These days I don't see a reason to use anything much other than ARC. they are amazing. Their 70mm cores are easily good enough for a 350+kw circuit car and are lighter than a standard core, and allow plenty of air through to the radiator too (something not many people conider when they jam a massive 180mm thick core in there). the 100mm ARC cores are good too if you need something with a bit more volume.

Obviously tune is key too but again it's a bit hard to quntify. you just have to hope that the tuner you choose is doing the right stuff. from memory you have a fairly reputable one.

to sumarise, my suggestions to get twins working hard on a GTR:

mani's are not crucial but ported stock is good and I've had good results with tomei too

BIG dumps are important, I do not like the small split dumps, even the genuine HKS ones

BIG front pipes are important too. I don't like the everyday china twin 60mm ones, try for something bigger

the rest of the exhaust is important too. you want that gas to have a nice free path out.

inlet piping is less important but still some thought should be given to it.

intercooler is important. get a good one.

the tune, and tune some more.

but if the turbos are just not suitable for the package then it will never be right. a set of -5s or 2530s would probably wake your car up. Look at the change in Gav's car.

don't stress though, you'll get there.

[R31Nismoid]

GTR cooler cores do not have a major drop at all though... I believe its around 1-1.5psi which @ 20-24psi which is acceptable and comparable to most cores around that marker.

Intake temps though I'm not 100% sure on, someone else might have such data - if they do so it'd be very interesting to see it.

Arguable point i guess, depends on ones budget and if there is data to backup the expense other than placebo.

Also the hard piping kit... Whats the reasoning?

If you are keeping the intake and TT pipe - then a hard pipe kit is only then replacing a few pieces which are already internally the same diameter and not that much different. Add to the fact you do need some hose in places to absorb movement.

It's also known that going to a full hard kit tends to induce comp surge on larger twins as the rubber piping does flex a bit and this absorbs the reverb.

It'll be interesting to see comparative stuff when Paul get back down to Uni with the different manifolds on there.

Any difference in that area should show itself on a dyno.

[NickR33]

They are some hybrid, not sure on the specs. I forgot to get the graph... but I'm going out there on Sat so ill get it then

in 5th under load, there is at least 4-5psi on @ 2400rpm

4th is around 3000-3200. Steve's seen it

(im also gonna get a -9 graph of another mates car and overlap)

what psi is it making the 340 at? much more in it?

sounds a good 500+rpm more responsive than my car and only makes a little less power up top

I'd really like to try some GTS4 diff ratios and E85... maybe I can sneak them in before my other half spends all our money on a mortgage...

[Piggaz]

BB,

Cheers mate. When the car was on the dyno getting tuned in Nov Yavuz did say that there was a restriction somewhere in the exhuast. I never thought it would have been the dumps. Guess who will be buying a set of tomei dumps now. I wish I knew this when I had the turbo's off less than 3 weeks ago to rip off those rubbish Tomei manifolds! Looks like the huffers will be coming off again!

I would say that going back to a set of -5's I will come pretty damn close to the power im making now..... if not more with a whole lot more response. Having your cake and eat it aswell?

[bodge]

Beer baron do you think changing dump pipes makes a big difference. I have standard ones on mine. I am running -5 turbos making a very optimistic claimed 380 rwkw. The reason l ask is l am pondering on the thought of replacing them with either tomei ones or Greddy ones with the separte outlet divider pipe for the waste gate. P.S my car was built by race pace and thinks it won't make that much difference and not worth the trouble.

[Piggaz]

I was having a think today. My last tune on pump 98 was 370 rwkw. The previous owner of my car (Mik) also made 370 rwkw on bels dyno. Now my new tune on E85 is 402 rwkw @ 25 psi. Ok sure I made a big more grunt BUT I would dare say that power was made up by the extra timing thrown at it. So there is an obvious restriction somewhere.

[Super_Dude]

What size is your downpipe? Most of the downpipes people use have a 70mm flange to meet the factory cat. If youre using one of these downpipes I bet that's your restriction. I would try modifying your exhaust and downpipe up to the size of your exhaust system (80mm+)

[Piggaz]

Ill go from the start

Nismo AFM's

ARC Duel entry 105 mm cooler

Nismo plenum

Ported factory manifolds

GT RS's

HKS split dumps

HKS Front pipes (twin 70 mm into 85 mm)

3.5 'cat'

Kakimoto Full mega N1 catback.

[JAGR33]

Interesting conversation here so thought I'd throw in my 2c for what it's worth...

- Peak power and average power serve two different purposes, I'd take higher average power over greater peak power any day.....

- Gav's graph is a perfect example, look at the hump in the mid range after installing -5's, truely amazing..

- What do you want to use the car for? If dyno and drag, stick with the GT-RS's, if streetability/response/circuit then go -5's....

- In regards to the OS gearset I had the same problem, due to the gearing I found my car 'doughy' and sluggish around 3rd gear corners (and too fast for taking it in 2nd), due to the revs sitting lower at the same given speed, but this was on a 2.6 with -5's, so extra cc's might improve it a bit. Either way went back to the standard box and gearing and sold the OS gearset box...

- Sounds like you have an amazing setup and my opinion is the -5's will compliment it even more.

- Look at tangomatt's setup, I've driven the car and it's something I'd most probably will not experience again (in a pre-R35 GT-R) although he does have V-CAM....

Good luck with it all......

[NickR33]

Jack logic has no place on the internet!

I reckon if your going to rip the turbos off again you'd be mad not to go a set of -5... you can pretty much cover the cost when you sell the RS

Also a 90mm exhaust is probably the way to go at your power level IMO

I've got the HKS dumps and they don't seem to be a restriction... but I'm only making 360rwkw so not sure that's relevant to you

[Beer Baron]

yeah opinion is divided on the HKS dumps (haha great pun). personally I hate them and I have a set on my new GTR. funnily enough it's also not making the power it should at the moment either and apart from the dumps the rest of the exhaust is how I want it (3.5inch decat, 90mm titanium cat back with just a single muffler which is 90mm through, and decent front pipes). But other people, experienced people, tell me the HKS dumps work fine and even though they are small they work. it's a lot of money to waste based on my 'theory' though.

I will say in the cars of my own that I fitted tomei dumps to they run very nicely, particularly noticeably as they transition onto boost very hard and certainly had no restriction.

Mik and his dad are pretty switched on so if you've got Mik's old car I'd wager there is not much wrong with it. if he made 370kw through those dumps then they may well not need replacing. having said that what worked at 370 may be becoming a bit of a restriction at 400+. Anyway, give it some thought and talk to a few people before you spend the dough. but yeah if it were my car I'd be trying a set of 2530s and some tomei or similar dumps, and see if it won't make 400kw on E85 with 25psi.

Also remember there are not as many 'genuine' 400kw cars out there as it seems. it actually takes a fair bit to get a genuine 400kw+ at the wheels on a GTR (or any car).

as for the dude above, if you car really is making 380kw then why change anything? racepace no what they are doing, so if they are your builder/tuner then I would listen to them. they have built enough quick cars to earn that respect.

[Moodles2]

What's involved with port matching a stock exhaust manifold? Is it something that can be done in your backyard with an angle grinder or do a workshop/machine shop need to do the work (matching port to -9s)

[Piggaz]

yeah opinion is divided on the HKS dumps (haha great pun). personally I hate them and I have a set on my new GTR. funnily enough it's also not making the power it should at the moment either and apart from the dumps the rest of the exhaust is how I want it (3.5inch decat, 90mm titanium cat back with just a single muffler which is 90mm through, and decent front pipes). But other people, experienced people, tell me the HKS dumps work fine and even though they are small they work. it's a lot of money to waste based on my 'theory' though.

I will say in the cars of my own that I fitted tomei dumps to they run very nicely, particularly noticeably as they transition onto boost very hard and certainly had no restriction.

Mik and his dad are pretty switched on so if you've got Mik's old car I'd wager there is not much wrong with it. if he made 370kw through those dumps then they may well not need replacing. having said that what worked at 370 may be becoming a bit of a restriction at 400+. Anyway, give it some thought and talk to a few people before you spend the dough. but yeah if it were my car I'd be trying a set of 2530s and some tomei or similar dumps, and see if it won't make 400kw on E85 with 25psi.

Also remember there are not as many 'genuine' 400kw cars out there as it seems. it actually takes a fair bit to get a genuine 400kw+ at the wheels on a GTR (or any car).

as for the dude above, if you car really is making 380kw then why change anything? racepace no what they are doing, so if they are your builder/tuner then I would listen to them. they have built enough quick cars to earn that respect.

A mate of mine who is also on here mentioned the other day that his car also has HKS dumps. Now he has built a few cars in his time and is experiencing something similar to what I am... doughy off boost and doesnt make what it should when it is it on song. Seems very funny.

[Rolls]

What's involved with port matching a stock exhaust manifold? Is it something that can be done in your backyard with an angle grinder or do a workshop/machine shop need to do the work (matching port to -9s)

Just draw on the mating surface with a black texture and go to work on them, they will be 'matched' however you could still completely stuff it up. You want the flow to be maximised and there are various things you need to take into account, I would speak to someone who does it and see what they say first.

[bodge]

yeah opinion is divided on the HKS dumps (haha great pun). personally I hate them and I have a set on my new GTR. funnily enough it's also not making the power it should at the moment either and apart from the dumps the rest of the exhaust is how I want it (3.5inch decat, 90mm titanium cat back with just a single muffler which is 90mm through, and decent front pipes). But other people, experienced people, tell me the HKS dumps work fine and even though they are small they work. it's a lot of money to waste based on my 'theory' though.

I will say in the cars of my own that I fitted tomei dumps to they run very nicely, particularly noticeably as they transition onto boost very hard and certainly had no restriction.

Mik and his dad are pretty switched on so if you've got Mik's old car I'd wager there is not much wrong with it. if he made 370kw through those dumps then they may well not need replacing. having said that what worked at 370 may be becoming a bit of a restriction at 400+. Anyway, give it some thought and talk to a few people before you spend the dough. but yeah if it were my car I'd be trying a set of 2530s and some tomei or similar dumps, and see if it won't make 400kw on E85 with 25psi.

Also remember there are not as many 'genuine' 400kw cars out there as it seems. it actually takes a fair bit to get a genuine 400kw+ at the wheels on a GTR (or any car).

as for the dude above, if you car really is making 380kw then why change anything? racepace no what they are doing, so if they are your builder/tuner then I would listen to them. they have built enough quick cars to earn that respect.

Race Pace say it makes 380RWKW, l don't. Taking into account the amount of stock components the car still retains, makes the claimed power figure seem like hocas pocas, and driving it indicates that it is a highly inflated power figure. The reason l asked about dump pipes is l would like to hear someone elses point of veiw if they would make a difference as l think having standard dump pipes from what l have read may be a key factor in holding the car back. As for them buliding quick cars? maybe going around a circuit this holds true, as for a qiuck street car with the odd trip to the drag strip, going by my example l am not so sure if the above statment holds true.

[Piggaz]

After having a look around at dumps the Midori Seibi items look like a goer. Internal Diameter of 76.3 mm which is 3 inches. Bigger then the new Tomei items which are 68, the Mines which are 70 (split type) and I would assume the Nismo's. From what I can gather the Series one Tomei's were 2 and 3/4 inch internal diameter.

[JAGR33]

Race Pace say it makes 380RWKW, l don't. Taking into account the amount of stock components the car still retains, makes the claimed power figure seem like hocas pocas, and driving it indicates that it is a highly inflated power figure. The reason l asked about dump pipes is l would like to hear someone elses point of veiw if they would make a difference as l think having standard dump pipes from what l have read may be a key factor in holding the car back. As for them buliding quick cars? maybe going around a circuit this holds true, as for a qiuck street car with the odd trip to the drag strip, going by my example l am not so sure if the above statment holds true.

Did you buy the car from a previous Racepace customer or did you have the mods done yourself? Seems like you're not convinced with the power claims so why not take it back there and get another dyno run? Maybe something is not right, maybe there's a boost leak there could be something holding it back hence not feeling the claimed 380rwkws. The Racepace dyno is not known to be a 'happy' dyno....

A quick track car would be an equally quick street car unless your racing over 200km/h. However a quick track car does not make a quick drag car as peak power is the emphasis.

Hope that helps.....

[bodge]

Did you buy the car from a previous Racepace customer or did you have the mods done yourself? Seems like you're not convinced with the power claims so why not take it back there and get another dyno run? Maybe something is not right, maybe there's a boost leak there could be something holding it back hence not feeling the claimed 380rwkws. The Racepace dyno is not known to be a 'happy' dyno....

A quick track car would be an equally quick street car unless your racing over 200km/h. However a quick track car does not make a quick drag car as peak power is the emphasis.

Hope that helps.....

JAGR33

No l did not buy the car from a previous Racepace customer and all the mods that have been done to the car were done by Racepace. As for taking it back there for another dyno run l am have not done that as yet but, l have placed it on another dyno just for a comparsion and result l got has really pissed me off and confirms my suspicion that the figure l have been given and using the amount of standard components on the car is misleading and from a over inflated dyno. As for your comment as something may not be right, everything has been double checked and turns out to be O.K. I understand your point that peak power is what is required for a quick drag car, but given the claimed power figure l got from the Racepace dyno the car should if everything else is perfect dispatch a high 10 second pass. Going from other cars as an indcation some having less power than my car it is far from it. I will take it back to Racepace after l have claimed down to see if they can find a problem.