Turbo's, Lag and Gearboxes.

[Snowman]

Chances are I'm way off track in my thinking and that I have been hanging around Roy for too long - but I have a quick question for the experts in regards to turbo lag variances with the different skyline gearboxes.

I am looking at upgrading my turbo's next year. The car is used mainly on the track so I was also looking for response. Having said that down in Vic (not sure about other states) there is a definite advantage to having extra HP in many cases.

My initial thoughts were to go with the ever faithfull 2530's. They have been tried and tested and I know they are great. But having said that MOST of the track cars I know are 32/33's. I know recently markr34gtr has put some GT-RS on his car and he seems to think they are great. Now guys like SK have said that they are perhaps still a little too laggy.

Which got me thinking - below are the different gear ratio's for the different GTR's.

R32 / R33 5 Speed R34 Getrag 6 Speed

1st - 3.21 1st - 3.83

2nd - 1.93 2nd - 2.36

3rd - 1.30 3rd - 1.69

4th - 1.00 4th - 1.31

5th - 0.75 5th - 1.00

6th - N/A 6th - 0.79

Final - 4.11 Final - 3.55

So 3rd and 4th on the 32/33's are basically the same as 4th and 5th on the 34. Which leaves the 34 with basically an extra gear in the lower range - which is really where response becomes the issue in track racing. Would it then stand to reason that it would be easier to keep "laggier" turbo's on boost with an R34 than it would be with an R33. Or basically could you say that GT-RS lag on an R34 would be similar to an R33 with 2530's - ON A TRACK?? Im not really worried about standing start lag, or normal street driving lag here.

Or am I missing something important in my thinking?

[Abo Bob]

Are you shifting at 8000rpm?

What size tyres are you using?

Just pluggin details into a calulator.

[R31Nismoid]

you would think you'd tehre would be an advantage with the 34 as you say with the gearing where RPM drop wouldnt be as much on a change.

that said... are the diff ratios the same too?

[Abo Bob]

Early calculations show the biggest drop (ignoring 1st to 2nd cos it's the track) to be 1987 rpm so you could get some pretty laggy turbos there and keep it above 6000rpm all day.

Factor in some awkward corners where it's not worth changing back a gear and with that gearbox you still only need 2500-3000 rpm at the top to play with.

I never realised that's where the extra gear was on the 34. Gotta be happy with that.

[Snowman]

Yeah shifting at 8,000rpm.

Tyres are 265/35/18.

[Abo Bob]

Diff different but gear ratios are relative.

R33 top speed in 1st gear and R34 are 2 km different.

[Abo Bob]

Ok I stuffed something up there before.

Excluding 1st to 2nd, biggest drop in rpm is 2271.

My other comments stand, particularly the one about happiness and stuff.

[Sydneykid]

Based on my experiences the R34 GTR gearbox is not a great deal better than the R32/33 gearbox as far as rpm drop on upchanges is concerned.

This the R34 GTR;

8,000 rpm in 1st is 4,950 in 2nd

8,000 rpm in 2nd is 5,750 in 3rd

8,000 rpm in 3rd is 6,250 in 4th

8,000 rpm in 4th is 6,100 in 5th

8,000 rpm in 5th is 6,300 in 6th

This is the R32/33;

8,000 rpm in 1st is 4,600 in 2nd

8,000 rpm in 2nd is 5,500 in 3rd

8,000 rpm in 3rd is 6,100 in 4th

8,000 rpm in 4th is 6,100 in 5th

The most important gearchanges on many circuits is the 2nd to 3rd, 5,750rpm (R34) versus 5,500rpm (R32/33). Closely followed by the 3rd to 4th 6,250rpm (R34) versus 6,100rpm (R32/33).

I don't think 250 rpm (2nd to 3rd) and 150 rpm (3rd to 4th) is going to enable a much larger turbo selection. The R34 is definitely superior, but it isn't going to make say 2540's a more attractive proposition than 2530's on a 2.6 litre. The GTRS's would be still unworkable.

Following are the ratios we use in the 6 speed dog box;

8,000 rpm in 1st is 6,000 in 2nd

8,000 rpm in 2nd is 6,250 in 3rd

8,000 rpm in 3rd is 6,250 in 4th

8,000 rpm in 4th is 6,250 in 5th

8,000 rpm in 5th is 6,500 in 6th

Plus you would need to factor in the speed of the gearchange itself (milliseconds compared to tenths). I believe that would enable say GTRS's to be used, even on a 2.6 litre.

Hope that makes sense:cheers:

[Emre]

Forget the gear ratios for a moment Andrew.

By changing gears at 8000 rpm, you should never feel any lag, regardless of which one of the two you choose.

The fact that I am aware of is that, 2530s are going to build boost earlier than the GTRSs, doesn't matter what gear you are in. Don't forget, you can't always stay in between 6-8000 rpm.

An example : If you are coming out of a hairpin doing 60 kmh in second, which turbo is going to accelerate you quicker...?

Another example : If you are holding 150 kmh through a sweeper in 4th, which turbo is going to give you quicker response...?

If you have an extra cog in there, use it to your advantage.

Why would you wanna give that advantage away and get back on the same terms with an R33...?

Now you owe me $450.02

[Roy]

Ouf of interest, on an RB26 with 2530s, when do they make 1 bar of boost? At 60km/h in an R34 thats about 4250rpm in 2nd gear, are they on the boil at that rpm?

My thoughts, grab either a T66, cheap 2530s or N1s, whatever you can get your hands on cheaply, then spend the $600-900 on some 2nd hand cams. That means you may lap me every 5 laps instead of every 7 laps:(

[RedRocket]

sorry to nitpick but I think you are talking about turbos' operating ranges, not lag.

[Emre]

2530s produce 1 bar @ around 4000rpm in 3rd, on my stock engine. This can obviously differ from car to car, depending on other specs.

60 kmh was just a guesstimate I used at that moment. 4250 in second sounds about right and it would be about 7000 in first; an awkward situation to be in IMO. Imagine if it was a 70 kmh corner.

That means you may lap me every 5 laps instead of every 7 laps:(

Don't short change yourself mate.

If you are doing 1.25s, you will be right on his tail, or maybe in front.

RedRocket,

You are right.

However, if GTRS has the same response as the 2530 as it's publicised, their operating range would be similar.

And yes, you are nitpicking.

[Snowman]

Forget the gear ratios for a moment Andrew.

By changing gears at 8000 rpm, you should never feel any lag, regardless of which one of the two you choose.

The fact that I am aware of is that, 2530s are going to build boost earlier than the GTRSs, doesn't matter what gear you are in. Don't forget, you can't always stay in between 6-8000 rpm.

This fact I am obviously aware of. But the reason for my thinking here is say currently Chris and I have a basically identical set-up other than the differeneces between the 33 and 34. Corners like turn 4 at Sandown and Phillip Island I can take in 3rd whilst he takes in 2nd. This is simply because I stay on boost in 3rd for these corners and there is an advantage to having one less gear change in there for me. Now say they are 80km/hr corners (based upon the gear ratio chart Roy sent me 80km/hr for me in 3rd is 4,000rpm which is about what those corners are for me). In 2nd gear 80km/hr is at 5,500rpm. I would expect the GT-RS's to be running with decent boost at that figure?

An example : If you are coming out of a hairpin doing 60 kmh in second, which turbo is going to accelerate you quicker...?

Ok - say at Winton after the 3 hairpins you come out of the last one at 60km/hr in 2nd. That is say at 4,250rpm. There is roughly 200m to that big left hander (long track). Say as you come out of the corner the 2530's are on boost - but the GT-RS's don't come on until 5,500rpm. Given that 2nd gear has a raito of 2.36:1 - how much time really would elapse before it came on boost? And if say given an extra 30kw's of power over the 2530's - which car would reach the left-hander 200m away first?

(I really don't know the answer to this which is why Im asking the questions!).

[Amaru]

Ouf of interest, on an RB26 with 2530s, when do they make 1 bar of boost? At 60km/h in an R34 thats about 4250rpm in 2nd gear, are they on the boil at that rpm?

I put 2530's on a rebuilt engine (still 2.6L, just with some forged internals, BNR32) and 1 bar would hit like a freight train at a tad over 4000rpm, making not much before hand. When I wound them up to 1.5 bar it only took an extra few hundred rpm to build the extra boost.

Put in some Tomei 260in/ex poncams, and the power seems to be more linear and comes on alot smoother, starting to build boost a bit after 2000rpm and on full boost (which is now 1.25 bar) by 4000rpm. The main difference the camshafts made was extra low down torque, which the car didnt have before, it was a complete gutless pig before 4000rpm.

-BUT- My turbos are second hand, but were rebuilt by HKS (I have receipts) in Japan before I bought them with 0kms on them after the rebuild. Wether they were rebuilt to standard 2530 spec or not, I couldnt say. Ive been told by a few people they arnt as responsive as 2530's should be, but pack a bit more top end punch.

[Emre]

And if say given an extra 30kw's of power over the 2530's

From what I've seen so far, I really do not understand this 'an extra 30kw of power over 2530s' comment. I haven't seen GTRS produce any more power than the 2530s on an RB26, anywhere on the graph. If 2530s can provide all the air an RB26 can consume and than more, what use is the theoretical extra air GTRSs can provide (unless you have a purpose built engine to suit the GTRSs)...?

I have an extra 50kw on you on the track, but our times do not suggest this. Ben with similar power to me but with extra suspension settings, have ~2 seconds on us.

Assuming all of us have similar abilities behind the wheel, (disregarding my advantage of being able to hit walls) what does that tell you...?

[Sydneykid]

Ok - say at Winton after the 3 hairpins you come out of the last one at 60km/hr in 2nd. That is say at 4,250rpm. There is roughly 200m to that big left hander (long track). Say as you come out of the corner the 2530's are on boost - but the GT-RS's don't come on until 5,500rpm. Given that 2nd gear has a raito of 2.36:1 - how much time really would elapse before it came on boost? And if say given an extra 30kw's of power over the 2530's - which car would reach the left-hander 200m away first?

(I really don't know the answer to this which is why Im asking the questions!).

There is another question, as if it wasn't hard enough already. If you had say GTRS's you might not have the throttle response to drive the 3 hairpins and come out at 60 kph. The dulled response may cost you say 5 to 10 kph, in which case the GTRS's really then have a problem and the 2530's would easily stay in front for the whole straight.

I haven't back to back tested them, it would be possible to achieve a precise answer via the data logging though. What I can say is the Jap performance shops seem to all stick with 2530/2540/T517/N1 size turbos for their time challenge RB26's. When the capacity gets up (2.7/2.8/3.0) they start to look at larger turbos, but then singles seem to rule.

I think centre of gravity issues may be a factor in large twins which have to be high/forward mounted due to their size. There is also the issue of total weight, a 650 bhp twin set up weighs noticeably more than 650 bhp single set up. The low/rear mount single would be demonstrably superior in both of these areas.

[Snowman]

Ok - so what this comes down to is forget the gears - on a 2.6L RBDETT 2530's are as big as the engine can use and so unless there is an increase in capacity or in usable RPM (say upto 9,000rpm) Im not going to generate more power with bigger turbo's so there's no point even thinking about it.

Cause the plan was to also incorperate some JUN 87mm pistons and 260/260 poncams with the engine - but thats still really a 2.6L engine.

[Emre]

That is pretty much what I am saying, bearing in mind that we are talking about track cars.

Sure, you can bolt a T51 on an RB26 and have an awesome top end, but at what cost...? I don't mean it in $$$ value either.

[Sydneykid]

Ok - so what this comes down to is forget the gears - on a 2.6L RBDETT 2530's are as big as the engine can use and so unless there is an increase in capacity or in usable RPM (say upto 9,000rpm) Im not going to generate more power with bigger turbo's so there's no point even thinking about it.

Cause the plan was to also incorperate some JUN 87mm pistons and 260/260 poncams with the engine - but thats still really a 2.6L engine.

What I would do;

* Increase the bore to 87 mm = 2.5% increase in capacity to ~2,630 cc's

* I would also increase the static compression ratio at the same time, get it up to 9 to 1.

* I would go for 264 degree cams with about 9.7 mm lift (I prefer Jun for their lift/timing combinations)

* The increased camshaft overlap will lower the effective (dynamic) compression ratio.

* Port the cylinder head and match the combustion chamber volume (make sure to keep the standard squish).

* Stick a set of forged rods in it with ARP rod bolts and up the revs to 9,250 rpm

* ARP main studs and head studs of course

* Give GCG a call and talk through a pair of GT25 based turbos that will make say 725 bhp at 1.3 -1.5 bar.

But that's just me:cheers: