Duratec Gearbox/Diff Choice

[Ferrino]

I recently bought a used “rolling chassis” project: it’s a 2002 Arch/imperial De Dion chassis with a bunch of parts (LHD, as I’m in the US). There is no powertrain at all (it used to have a 2.0 Zetec with Type 9) and despite running a bike-engined 7 previously, I’ve decided to go with a 2.0 Duratec this time around. I’m planning to run it with throttle bodies (eg. Jenvey) and am told it should make 180-185 BHP, which is my goal for a road-focused car which will make occasional trips to the track.

What I’m less clear about (coming from a bike-engined live-axled 7), is the best gearbox and diff to pair with the Duratec.

It seems that everyone who has fitted the SPC/Tracsport semi-helical gearkit in their Type 9 5-speed loves it to bits and this is currently my first choice. I’ve spoken to a couple of shops who will build a Type 9 with this kit (First Motion & Road & Race) and ship it out to the US, since Steve no longer builds gearboxes with his kit.

For diff, I was planning to go with a 7” Sierra diff with a 3.92 CWP and the Quaife ATB. This seems to be the “LSD” of choice for road-going cars that periodically go on track. There is also the Tracsport plate-type LSD, but I’m not sure how well suited it is for road use.

I’d love to get some feedback on these choices, please. Is there anything I’m missing? I must admit, when I heard Caterham was now using MX-5 gearboxes, I thought this would be a natural choice over the older Type 9 setup. But it sounds like it would take some work to fit to my imperial chassis and the custom ratios are not as available as the Type 9. I think I’ll miss the sequential from the bike engine, but the Quaife/SADEV offerings are at least double the cost of a freshly-built Tracsport-based Type 9.

Thanks!

[Golf Juliet Tango]

You are right that the MX5 box will not fit older chassis. All the details are in the LF archive. Jan 2015, tagged as Mazda.

Sadly there are only two articles tagged Differential.  I don't think anyone has yet written an article comparing LSDs (or other devices aiming for  ea similar effect) from the driving seat.

 

[Jonathan Kay]

I don't think anyone has yet written an article comparing LSDs (or other devices aiming for  ea similar effect) from the driving seat.

But there are some strongly held (o)pinions. What's the feasibility of some back to back testing, preferably blinded?

Jonathan

[AdamQ]

I rebuilt my 1999 De Dion Duratec a couple of years ago and decided to pay some attention to the gearbox and diff.  My usage is similar to yours.

I did my research and arrived at exactly the same configuration as you have.  I went to see Phil at Road and Race with my gearbox and left with just one part of the configuration changed: I went for a plate type LSD (Titan I think (definitely not the Tracsport one)) as opposed to the ATB based on a discussion with Phil.  I've never driven a car with an ATB so can't make any comparison.  All I can say is that I'm extremely happy with the LSD I have got.  The plate LSD vs ATB question seems to evoke strong passions in people (especially Steve at Tracsport!).

You're right about the Tracsport gearkit - it's heavenly (and I went from modified BGH ratios, not from a standard Type 9 and the difference is still a quantum leap).

I'm sure you're already aware of this, but, given that you've already got the TBs/Jenveys, with a change of cams, some uprated springs and some ARP bolts on the bottom end, you've got an easy jump to about 210 BHP - it's documented here somewhere, but I'm pretty sure that's all Caterham do to go from standard to 420 spec for the Duratec cars. 

Good luck with is all!

Adam

[Wrightpayne]

I’m sure I read an essential mod on increased power duratec was to keyway the front crank pulley - the cam sprocket only being clamped in place?

[ECR]

I drive a 2.0 VX which is inherently an understeering car. I drove with a quaiffe torque bias dff for 20 plus years and was very satisfied both on the road and on many trackdays/sprints. A few years back I fitted a ZF plate type diff and the reduction in understeer on track was noticeable. I also seem more able to drive the car on the throttle now ....I will have to keep on top of adjustments to the diff now which was not a required job on the quaiffe unit. For my use I much prefer a plate diff.

[AdamQ]

In standard form the cam sprocket is indeed only clamped in place - between two diamond-studded (bling bling!) friction washers.  I don't know at what level of tune it's considered essential to key the crank - I might be wrong, but I'm pretty sure the factory 420 crank isn't keyed - I'd be interested to know whether or not the CSR crank is.

In my case I did get the crank keyed retrospectively, not because it slipped or because I was even worried about it slipping, but rather for convenience because without a key you lose all the timing if you take things apart (during an oil pump change for example) and it's difficult to reassemble accurately given the massive torques involved (perhaps I should say that I found it difficult ...).

FWIW ...

[Jonathan Kay]

I'd be interested to know whether or not the CSR crank is.

"Caterham CSR260 Build Manual": that's for the engine, not a Seven Assembly Guide.

Jonathan

[John Vine]

AFAIK, none of the CC-supplied Duratecs (2.0, 2.3) comes with a keyed crank.

JV

[Garth]

AdamQ - interested you went for the Titan LSD and not the Tracsport one. I have not looked into the Tracsport myself, but '7 Wonders of the World' who posts on here thinks it is the much better engineered unit! Worth another look Ferrino?

[AdamQ]

Garth, from memory, my decision was based on cost and usage - regarding the latter mainly road with the odd track day and regarding the former, and I might very well be wrong here in which case I apologise to those concerned, the Titan wasn't a huge number of pennies more than the ATB whereas the Tracsport LSD was - not massively maybe, but significantly (from memory).  I'm not really sufficiently well-informed to offer opinions on these things, but I agree with '7 Wonders of the World' - I believe that the Tracsport unit is extremely well engineered.  I also believe, based on various conversations and what I've read (and my experience so far), that if the Titan is properly set up and maintained well it does its job excellently. 

Decisions, decisions ...!

[Garth]

I have not looked at the Tracsport, but might have when I had my Titan installed (it did not come up as an option!) - better look at what maintenance is required on my Titan then - have generally thought one just needs to make sure the oil is good and then diffs are pretty maintenance free!

[Ferrino]

Thanks all. I was leaning towards the ATB because the consensus seemed to be it was better suited to road use, quieter, and maintenance-free (compared to plate LSD). Might chat to Steve about

Re. the Tracsport semi-helical ratios, which 1st gear ratio do people like? There is a choice between 2.29 and 2.48. The 2.29 seems very long to me, but it would probably bring 1st into use on slow corners. I would plan to use a 3.92 final-drive, so I guess I should crunch the numbers with the different ratios...

Another choice on the Tracsport is whether to upgrade to needle-bearing on all mainshaft gears (I think standard is just 1st and 2nd). Apparently this is designed for high-RPM setups that spin 8 KRPM+.

I was aware of the non-keyed crank pulley, but wasn't sure if it was of concern to a stock Duratec. If I'm tearing down the engine anyway, it might make sense to upgrade. Is there a kit to convert to a keyed setup?

[Jonathan Kay]

... which 1st gear ratio do people like? There is a choice between 2.29 and 2.48. The 2.29 seems very long to me, but it would probably bring 1st into use on slow corners. I would plan to use a 3.92 final-drive, so I guess I should crunch the numbers with the different ratios...

I don't think that I've seen anyone recommend the stock first in the five speed box over something longer.

I'd change it if the gearbox ever had any work done.

Jonathan

[p.mole1]

I would go with 2.29 these cars are very light and do not require a low first gear. If you are not going to do track days a LSD is probably not necessary however if you must have one an ATB  is what you want it will be quiet if properly built and require no maintenance  or oil additives.. Plate style LSD are better for the track if you are bouncing over kerbs or lifting a rear wheel. 

[AdamQ]

I went for 2.29 for first gear and don't regret it at all (my diff is 3.92).  I didn't do the needle-bearing upgrade.

I'm not aware of a kit to key the crank.  I don't think there's any concern whatsoever for a stock Duratec (or even a moderately highly tuned one - as mentioned above, as far as is known, Caterham don't key any of their Duratec models) - I only had mine done for convenience.  A decent machine shop should be able to do it fairly easily and cheaply - just to give an idea (I know it's not a geographically viable option for you) Dunnell offer the service for £85 + £8 for the key ...

[7 wonders of the world]

2.29 with a 3.92 ZF LSD in mine

Re Keying the crank, Cosworth said when the engine hit te market the diamond washers were more than man enough for the job on both crank and cam, most builders shyed away from this opting to key the crank 'just in case'

However as is the norm Cosworth were correct and I couldnt find any of the regular big builders who now keyed then as saying it wasnt necessary.

Mine sees 8500 regularly - I have faith in Cosworth.

Guessing Dunnell charge more for the pulley and sprocket as these need to be jigged up and spark eroded otherwise the crank sensor gets a little upset.

[7 wonders of the world]

The Quaffe is not an LSD merely a torque biasing device, it can never offer 100% lock up under any circumstances.

The best plate LSD currently out there is the Tracsport, it builds on the key features of the proven ZF.

The Titan simply isnt up to the job, burnt plates broken bellevilles etc all prove this.

If you find a ZF with the wrong ramps (45 degree) BM me and I will put you in touch with a guy wgo can regrind them to 30 degrees. The origianl ZF's CC used also need the preload dropping as they came with 65lb/ft !!

 

[Molecular--Bob]

I have an original ZF in mine, so interested in the preload question. What is the effect of high preload in the way the diff works? Would the Caterham supplied ZF have the right ramp angles or is there still a chance that they would be the 45 degree ones.

[7 wonders of the world]

the high preload in a light car will have the effect of inducing understeer on turn in as the rear wheels are restricted in their ability to rotate at different speeds.

Some CC supplied ZF's were supplied with the correct 30 degree ramps others with the stock ones from ZF which were 45 degree, the shallower the ramp angle to more clamping force is applied to the clutch pack under drive.

 

 

[rgrigsby]

I had an original ZF LSD in my Seven for years, Road & Race modified the ramp angles and set the correct pre-load and it made a significant difference on track.

I switched to a Titan LSD 8 years ago and it felt like another step up in drivability, I've not had any reliability issues with the diff so it's interesting to hear about some of the problems. 

FWIW I'm running it with a 250bhp Duratec and a BGH modified type 9 gearbox.

Thanks

Robert

 

[Ferrino]

Thanks for all the feedback! I am currently looking to pair the Duratec with the following:

• Tracsport semi-helical gearset (in rebuilt Type 9) with ratios: 2.29/1.61/1.225/1.0/0.82 (so the long 1st and 5th choices)
• Quaife ATB (in rebuilt 3.92 Sierra diff)

The ATB-vs-Plate LSD has been the toughest decision, but I think the ATB is the best choice for me as this car will spend most of it's life on the road and I don't want to worry about servicing the Titan/Tracsport. The main criticism of the ATB seems to come from those who have become more serious about trackdays/racing and don't want to spin away an airborne wheel when they encounter kerbs or off-camber tight turns. It seems that the action of the ATB is also a bit less abrupt.

Comments?

 

[7 wonders of the world]

Please don't put the Titan and Tracsport in the same box, the former does need frequent maintainence due to its design, the tracsport is a different kettle of fish all together though, quiet, reliable and a proven design. and when built correctly subtle yet capable of transmitting significant torque

The Tracsport is the perfect partner for the gearbox

The Quaife can never transmit the torque the Tracsprt can and therefore traction, handling is compromised..... 

[Jonathan Kay]

... so the long 1st and 5th choices...

The taller first sounds very sensible, as discussed above.

I'd imagine that with that amount of power that you won't have any shortage with the higher top... but have you checked the engine speed at some relevant cruising speeds, and the gap between 4th and 5th?

Jonathan 

[7 wonders of the world]

Based on 13" rims shod with 205/60 tyres driving via a 3.92 final drive

RPM drop 4th - 5th = 1530 rpm

70mph = 3338

80-mph = 3811