Absolute Shower

Anyone noticed the difference between the JDM 6 speed (different ratios) to the UK 6 speed? Is the JDM box worth more?

David_Wallis

in what sense noticed the difference??

You mean tried both or seen the difference between the 5th gears and drop gears etc?

T-uk

john banks has the uk box and it suits his highish daily motorway use.

personally I would prefer a JDM for a nicer spread of gears as I hate the short/tall mix of the UK, for fast back road use.

I think much is to do with how the car is set up. I am yet to drive a UK with more than about 350bhp that feels flexible with the 7k redline. IMO they just peak too close to the limiter to remain flexible. a 400bhp sti is a very nice set-up as although it will usually peak slightly higher in the revs than a UK with similar mods , it still has a far taller rev range to remain flexible.

if I was starting again or had the cash to mod my UK to this level I would use a P1/STI engine , 20g turbo with supporting mods and a JDM 6 speed box. this should peak about 6800rpm and still remain flexible due to the rest of the rev range to decide where to shift in.

David_Wallis

stevens is going to be a fooking animal then..

it will make jb's look tame

Absolute Shower

Sounds good to me...JDM it is.

Do you guys know if the JDM's come with suretrack diff as the 'norm'. If not, how can you tell if it is a suretrack item without taking it apart...part number kinda thing.

T-uk

glad to hear it

I still think john's car will never show it's true potential with the six speed. with the classic 5 speed ratios I was sure he could have been in with a chance of taking andy's 1/4 time but not now. if he bumps up the rev limit to stretch the first 4 gears , it might help but then we might get another snapped rod thread

Adam M

I think the jdm is too short even with 3.9s for a car with 400 plus bhp.

Forester sti 6mt is in my opinion the best option.

anyone know if it is real yet?

john banks

Living with the car daily I am delighted with the UK box and the odd jump from 4th to 5th is not noticeable or relevant. I certainly would not want it any shorter. I would actually say that 5th and 6th are right and the first four are too short. This is where the higher rev limit would come in I suppose.

My car is always going to be a compromise as it is a road car and nothing more. I always take the moderate option of the mad ones available. It is more than enough to entertain me still

For daily use a JDM box with even a quietish 3" exhaust would do my nut in.

Apart from standing starts (which I probably do a few of a year ) in real world use I don't think it is any slower than with the 5MT, if anything quicker since the change is so much quicker and sweeter. I have something very close to all the old 5MT ratios, the only relevance of the superiority of the 5MT would be drag racing IMHO. Other than that, 3rd, 4th, 5th and 6th are so close to the 5MT 2nd, 3rd, 4th, 5th it is fine.

Nice thing with UK parts and gearing is the availability of spares through Subaru. Not to be underestimated for convenience when running a daily driver that could pop anything at any time.

David_Wallis

what revlimit do you think will show the potential 9k or 9.5k?

or 10k + as rigoli and other mad uk car(s)

David

T-uk

on a 2litre or bigger david?

sti9 block with it's treated crank and some decent rods and pistons could be a decent screamer. bigger cc's would be how brave you get with what you think the crank can take.

T-uk

don't listen to him , john's a straight line god that goes out harassing motorbikes so only needs 5th and 6th his mid-range torque does help to hide the jump from 4th to 5th. his lower gears are useless for anyone not waiting until the front wheels are straight to get back on the power , it simply runs out of revs. 5th and 6th are ideal but any thing that is 3rd/4th gear , like round-a-bouts you find it going for the limiter all too quick.

see above

the only reason a 6speed is better is that the 5speed would have been eaten by now. how many miles are you at with it now anyway?

john banks

If it goes for the limiter too quickly then there is too much torque at the wheels... solution, use the next higher gear. If it hits the rev limiter mid bend you are in too low a gear. If it has enough torque low down (don't see how you would ever get better and you certainly wouldn't even with short gearing on a 2.0) then you can't say it will bog down in the next higher gear, the spacing isn't that bad.

A 2.0 with an 8000 RPM limit will still have a narrower power band than a 2.5 with a 7000 RPM limit using the same turbo.

2.5/2.0 * 7000 = 8750 RPM limit on a 2.0 to give as flexible power band plus of course the cylinder heads to breath properly at those revs rather than just exist. I suspect a nice breathing nigh 9000 RPM limit Scooby without variable valve timing would be a bitch for fuel economy (yes it is an issue on a daily driver), low down torque (but gearing could offset), refined idle, emissions compliance should you need to fit a cat. For a hi-po flexible daily driver I don't think the 2.0 cuts it. I would never go back.

Think diesel Think V6/V8 style torque delivery

I know I won't convince you T-uk, but I love it anyway

Limiter in 3rd is 73 mph and 4th is 96 mph... just how quick do you want to go around a roundabout? 3rd from 40mph will have virtually no lag (4000 RPM). What is wrong with a gear that can pull nicely from 40-73 mph? When you at 4000 RPM you already have a lag free (even in 3rd gear) 300+ BHP. It is better with progressive boost control and the P1 suspension - you'll need to try it.

john banks

Just to say that a similar power 2.0 with the same turbo and 8000 RPM limit would have equivalent turbo response at 5000 RPM but could rev to 8000 RPM. So if you were at 5000 RPM at 40 mph you'd get to the limiter at only 64 mph.

A 24% increase in capacity should be nicer than a 14% increase in rev limit

M3 virtually matches M5 in gear with only about 70% of the torque and 14% higher rev limiter.. the other deficit is made up from weight. With the Scooby the 2.5 weighs no more than the 2.0 and goes in the same car.

Andy.F

What gearbox are these "mad" cars going to run David ? I believe a recent 'performer' has just blown his Lateral PAR box

Andy

David_Wallis

I dont know.. why dont you ask your friend ron?

The only performer you may be refering to hasnt blown a PAR part.. as you know!

it also increased in size apparently between the phase 1 and phase 2 boxes..

David

T-uk

but if you have a low entry speed due to say a blind bend that then opens out your goosed.

faster than it lets me

I do agree it is the best option for you though.

nice to see you still theory everything but you won't convince me that a "strong" 5speed is best

john banks

My argument is that a 2.5 with a 7000 limit will still be easily more flexible than a 2.0 with an 8000 limit using the same turbo making the same power. To keep the 2.0 on the boil to give the lack of lag of the 2.5 you will have even less road speed increase before you hit the limiter.

So for your low entry speed due to a blind bend that opens out you have the same choice on the 2.0/8000 and the 2.5/7000. If you are revving the 2.0 25% higher to get the same response as the 2.5 from the turbo, you are in more danger of hitting the limiter mid bend in the 2.0 than the 2.5.... if you go in at 40mph at 4000 RPM in the 2.5 and 40mph at 5000RPM in the 2.0 (or the nearest gearing to that for comparion's sake) you can only increase your speed by 24 rather than 30 mph! That is a far less flexible and usable power band. Consider the torque at the wheels and where the power band is - you just use taller gearing on the 2.5 and the torque still more than compensates for a redline on a 2.0 below 8750 RPM. There is no contest IMHO.

For drag racing I agree on the 5 speed, for anything else there can be no disadvantage to having the 6 speed. Some changes will be across the gate, some won't, can't see it making a difference? Some roads you will use 3rd and 4th, some 4th and 5th. On the roads where you use 3rd and 4th you would be 2nd and 3rd on the 5 speed and have across the gate changes. When you would use 4th and 5th on the 6 speed the situation is reversed. Other than that, once rolling there is always an equivalent ratio available on the 6 speed that the old 5 speed had.

I also don't agree that you should necessarily tune the car deliberately to make power well before the red line. The red line is piston speed and conrod limited. Whilst you will get more acceleration by having the red line higher than the peak power, if your red line is limited by engine internals you will still get more acceleration (more average power) by having as much area under the curve as possible. You won't have a mechanical shift light warning you to change gear by a drop of torque but the car will still be faster than if you drop the power deliberately. By using high compression you may be boost and therefore torque limited by octane, so why peak power at 6000 RPM if you can hold the boost (assuming efficiency) to 7000 RPM, the power will keep increasing to the red line and you'll have more area under the curve. Yes it would benefit from a higher still rev limit, but there is no point detuning the top end just because your internals won't allow you to rev beyond peak power.

john banks

The pink plot is about what my car is running at Star, the blue plot would be what I might get using a larger turbo and keeping the boost up at the top (I think the flowed large port heads and STi cams are up to this - the reason it drops presently is the turbo before the cams run out). It peaks at the rev limiter. It will still be faster than the old one (the little triangle between the curves shows this), power delivery will be more linear towards the red line. It would be better still if I could then rev it out to 8000 RPM as when I changed gear I would then drop back in at higher power, but just because I can't is no reason to detune it. If it slams into the rev limiter and I can't cope I need to practice and get a shift light

john banks

A 2.2 revving to 8000 RPM (still on the short stroke) would be of similar flexibility to a 2.5 revving to 7000 RPM if you really want a screamer? Suppose the bore walls would allow you to run more boost, but otherwise it would just be all noise from higher revving and shorter gearing?

Bob Rawle

Personally speaking you should go with what suits you, we all have differing preferences, I like the JDM ratios, 6th is a tadge longer than I'm used to with the STi5 and the rest nicely spaced, so I'm in "heaven" when John would be in "hell", to be honest I don't see what s bad about cruising at 3600 rpm, a 2.5 does generate more torque at low revs (mapping dependant) however I would defy a 2.5 car to pull away dramatically from a well set up 2 litre, all the 2.5's I have come across have yet to match the STi5 for sheer adreniline rush, I will probably change that view in the next couple of months though (no not mine yet).

bob

RB5_245

So the moral of the story is to build yourself a helical cut sequential box

Dave

john banks

I think the only gain from the 2.5 is real world flexibility, out and out performance is limited by other factors - turbo, breathing etc, so since the 2.5s presumably haven't had c.500 BHP they would be boring compared with the 5 Bob?

Comparing back to back a 2.0 and a 2.5 both with c.400 BHP, when driven flat out there was little in it, but even with the 2.0 doing left foot braking to spool the turbo before the "go" signal, the 2.5 could pull up to a few car lengths unless it was only top end stuff.

To be a really nice ride I like to be able to have full boost in any gear except first by half of red line RPM. Then you are virtually never caught out by lag.

Even something as small as a TD05 on a 2.0 doesn't spool up with a yee-hah bang in the back until 4000 RPM if you are in 2nd gear (UK 5MT gearing). It can catch you with lag out of slow roundabouts.

T-uk

before this turns into a 2.5 v 2 litre thread , it is about gearboxes.

point is , short gearing needs high revs. there is no point shifting the peak points , to far up the rev range and losing the bottom end on a 7k red line of any cc unless your building a dyno queen .

the tall 5 speed gearing on jb's 2.5 was perfect imo for the set-up , he even agrees if you read , that now out of his 6gears , only 5th and 6th are right and the rest are too short. there is certainly no lazy drive in the first four gears.

I personally would prefer a 400bhp 2litre sti with JDM box because if your doing the 2.5 right you need high revs and a dog box imo. john's is a compromise but I am sure I could put this round a twisty track faster than jb's 2.5 the way it is now.

anyway jb will be buying an m5 in a few months when the ion turbo kills his 6speed. he is buying it to reduce egt's but that will only last a month tops. then he will smoke his compromised "clutch" before eating the box

Bob Rawle

Its about gearboxes woith a 2.5 slant though, John you are, I think, comparing your UK 2 litre, there is a difference, back to ratios, still down to individual choise, driving style, I wouldn't have a UK six speed in a car as I hate the badly spaced higher ratios.

bob

john banks

Of course the engine design is relevant to the gearing.

RCMS advised the clutch is good for its rating plus a third which would make it good for up to about 440 lbft. If I am going to eat the 6MT then there will be a heck of a lot of others who will be stranded without a streetable gearbox and high power 2.5 tuning for road cars will die in the water.

I can afford to have the turbo come in a little later T-uk, some have commented it comes in "too" early?

I don't think the 5MT was right for the 2.5, that was too short as well.

Bob, comparison was 2 400 BHP cars one with Type R gearing and 8000 RPM limit on 2.0 and one with UK 5MT gearing 7000 RPM limit on 2.5.

Interesting about the lap times... the T25 with lower rev limit, same gearing, same PWR as the lighter Spec C with more track orientated suspension does virtually the same lap time and murders it for flexibility, reaching higher speeds at the braking points on the telemetry at Bedford.

T-uk

I would probably agree with that as long as you do not use it as an excuse to find another 75bhp and peak at 6999rpm

Andy.F

To a degree I'd agree You must be aware that it's a 2.5 you are driving and don't just 'boot it' out of a bend like a 2.0 A bit of throttle finesse is all that's required really, I'd love a bit time to get to grips with the different response of the 2.5, I'm sure it would be quicker on track once mastered. Perhaps a stronger centre diff would help keep the back end in line too ?

Andy

john banks

Back end is nicely planted now with revised geometry and P1 suspension. Have a shot with it some time

T-uk

dumping the dawes would probably help , the back ends fine

it is probably just subarus bothched spacings I don't like

T-uk

just read the article. I think litimports have the T25 set up well as an allrounder , anymore would just make it frantic through the gears IMO,(comparing it with jb's lighter 430/400) ? given that it runs coilovers it could probably have been tweaked to take the spec c on track comfortably. there is not really that much between the two , with them both running similar PWR so the 1/2 litre will be more flexible and feel balanced due to the sensible sized turbo for the revlimit.

however , I still think with the same larger 400+bhp turbo shifting the peaks closer to 7k , the spec c would feel more rewarding and balanced but not necessarily faster until someone did a 2.5 with say a 7500rpm to make up for moving the power higher up.