Gearbox advice

[J Stewart]

I'm hoping someone can give advice to a 7 newbie.

I bought a Vauxhall engined (all steel fettled by Roger King)with 220-230bhp a few months ago and the gearbox recently let go.

I now need a complete new box and have been offered an SPC 5sp semi-helical replacement. Is this the right way to go? I was going to get a longer 1st put in but was wondering whether to put a shorter 5th in as the car will only pull 6500rpm in top (or is this down to the full screen?).

 

Thanks

 

Jon

[Alex Wong1697456877]

The SPC semi helical has a longer first and shorter top than the standard type 9 ratios. If you want to stay with Quaiffe products, you'd have to go for a straight cut box to get the ratio's you're suggesting. They're not available in semi-helical. With my 200BHP engine and with a screen, I could get 7000rpm in 5th although this was on a flat out all the way around oval. With the 240BHP engine and no screen, I can get more quite easily, but I've never hit the rev limiter in 5th (7900rpm)

 

The semi helical box is a good piece of kit and I've been very happy with mine. I'd recommend having stronger selector springs put in but this is cheap to do. I have been thinking of selling mine though but haven't decided if needle bearings are essential. The semi helical box doesn't use needle bearings, although Steve at SPC says the heavy duty version (with needle roller bearings) is now available. Having said that, I think the ratios in the semi helical are perfect for my 240 BHP engine and although the longer first used in some straight cut boxes has some uses in very tight sprint circuit corners, the shorter one is easier to live with on the road and is better for starting from standstill.

 

Edited by - Alex Wong on 29 Oct 2001 19:52:13

[Paul McKenzie]

I've got the same gearbox as Alex on a standard Vaux .carbs and it's great. Two things to look out for though, one-if you're a hooligan and want to spin the wheels in first (and second) moving off from the lights, you can't do that easily any more - in other words your 0-40 time is probably poorer, but on the circuit which is what the 'box is for the ratios are perfect, secondly 'doesn't whine like a straight-cut box' -true - but, it does whine, and the frequency is exactly right to ensure you always arrive home with your dentures cold-welded together. However, for many of us, this is part of the fun and adds to the seven experience.

Paul

[philwaters]

I know two people running with SPC Semi-cut gearbox's and having driven both and passengered in one over a 400 mile round trip to Cadwell on the 5th this month, can say it is a lot nicer than a straight cut box. I don't know how much power they can take but I'd try to get a comparison drive in both.

 

Phil Waters

1600 X/flow - soon to be 2000 Zetec wink.gif

[Alex Wong1697456877]

if you're a hooligan and want to spin the wheels in first (and second) moving off from the lights, you can't do that easily any more

 

I can. teeth.gif Powder Puff demonstrated this on the Rumble. He still owes me about 2mm of Yokohama rubber. teeth.gif

[EFA]

Richard Larkham has an 8.4mph/1000rpm 1st gear ratio (2.04gear,3.92diff,205/60/13tyres) , and has no problem tearing up tarmac. He has a 165bhp Zetec.

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

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[Paul McKenzie]

Wow, That comment brought you all out to play. Looks like I need smaller wheels and bigger power for hooligan reinstatement.

Paul

 

[R2D2]

Has anyone considered the Quaife "dog" box for competition cars. I realise that it is noisier because it uses spur gears and the gearchange is bit difficult for a road car but it should give a faster change and I think that there is more choice of ratios.

 

It should also get rid of the syncro ring problem and is quite strong.

 

I think Tran-X make one as well but don't have quite as many ratios available.

 

I use a 4-speed dog box for rallying and quite like speed of gearchange.

[EFA]

Caterham six speed and 5.5" clutch changes quicker than Quaife dog box.

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

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[R2D2]

Arnie,

Do you think that your clutch has the biggest impact due to the much lower inertia.

 

I always thought dog engagement was faster because it removed the blocker ring?

[EFA]

The lack of inertia has a lot to do with it yes.

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[andygriffiths]

 

I have fitted a Quaife 5 speed box with a long first gear but i have had a semi-helical 5th gear put in so that it is quiet in 4th and 5th because 4th is 1:1 ratio.The long first gear is easy to use as well.I was also debating for six months which option to go for but be sure because its not cheap.I was running a type 9 box before and 1st was useless,but it will also depend on BHP because the HPCs have so much torque a long first wont be a problem especially over 200HP.

 

Andy. G

[J Stewart]

Thanks for the replies.

The car came with a longer 1st and never had a problem spinning up!

I spoke to Steve at SPC yesterday and he recommended the heavy duty semi-helical box with HD lay shaft and ally casing (which saves 4-5kg). The only problem (apart from the cost) is the casing not being available until December!!!

[EFA]

Funny, but do SPC not sell 6 speeds or something??

 

Can't knock SPC's salesmanship!

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

 

Edited by - fat arnie on 31 Oct 2001 10:08:38

[Alex Wong1697456877]

The Semi Helical CR 5 speed is less than half the price of a Caterham 6 speed.

 

 

Edited by - Alex Wong on 31 Oct 2001 10:47:06

[Chelspeed]

I use a Quaife dog box bought thro SPC. It's absolutely magic.

 

If Quaife have told Steve the alloy casing will be ready in December then expect it about March.... I was waiting for a 4 speed alloy case in winter 1998/99 and a 5 speed alloy case last winter. Both took twice as long as they first said. But worth the wait, quaife and SPC do really good kit.

 

For the cost of the 6 speed box you could get a Quaife sequential dog box from SPC.

[Robert Q]

I changed to the 4 speed Quaiffe Dog Box (with newer 4 dog design) last winter and agree with Chelspeed It's Magic the way you slice through the shifts very quickly. I use my Vx powered WF for sprints and hillclimbs plus the odd local blast up to about 30 miles each.

 

I also looked at all of the semi-helical boxes but decided I may as well go the whole Hog to benefit from the wide choice of ratios and extra strength of a real competition unit.

 

Before I bought the Dog Box I was also concerned about the possible noise spoiling the driving experience. However I am pleased to say it is a lot quieter than I expected.. yes 1/2/3 gears are noisey - but I'm normally only transitioning through these rapidly and always end up in Top which is one-one and quiet of course.

 

I set the gearing to 56/60 (depends what wheels are fitted) in 1st and 140 ish in Top and have no problem getting the wheels to spin (if I want to, normally I feather this out for quick starts)

 

The ratio's are excellent and very close. Don't see the point in a 5 speed Dog Box you would soon get fed up driving round with the S/C whine in 5th.

 

For road use I just get into 4th quickly and leave it there the Vauxhall engine is plenty torquey enough. Only slight down side the box sometimes objects 3 - 4 changes when going slowly in town, a bit of concentration though and she's there.

 

Like Chris I had experienced balky rings with a heavy duty type 9.

 

You also benefit from the hooligan feature of clutchless changes on the way up the box (or you can drive as normal if preferred.

 

After fitting I took my mate out and he was stunned at the sound/speed as we drove round pulling out of bends - going hard through the box with no need for a clutch as we overtook several cars at once. As he said afterwards "It's certainly a lot quicker than my 911!".

 

You probably get the drift by now - no way would I remove the Dog Box even if I stopped doing sprints and hills, noise hardy notice it - how long are you in the lower gears for - when you are the idea is to Boot it and then there is noise from everywhere Induction/Exhaust/Gearbox - just the way I like it!

 

 

 

 

[Daniel]

I've just read all the posts and found it very interesting and have the following questions:

 

Am I right in thinking some of you have had a Type 9/Quaife 5 speed box built with S/C gears on 1,2,3 &4 and a helical gear on 5th?

 

Has anyone used the C/R helical cut gear kits from BGH/Brian Hill in either a type 9 iron casing or a Quaife?

 

Thanks

 

 

 

 

[murph7355]

Isn't a Quaife sequential over 3k?

[EFA]

One matter I will clarify which I think has been overlooked regarding tall first gears is that (for a fixed torque output from the engine) the taller the gear the narrower the band is between bogging down and colossal wheelspin when trying to make that perfect start.

 

Your max speed in first gear is also (obviously) restricted by engine RPM.

 

So perhaps we should refer to mph/1000rpm insead of actual engine speeds.

 

For example a 2.04 first in the quaife gear set should only be used with a 3.92 diff this gives 8.3mph/1000rpm on a 22.5" tyre dia.

 

The 2.69 first in the 6 speeder therefore will give a shorter 7.3mph/1000rpm ratio and hence improve acceleration.

 

It does, but in both the above cases the perfect start is a knife edge between bogging down and a cloud of tyre spoke.

 

Run the 6 speed with a 3.92 diff and the gearing drops to 6.3mph/1000rpm

 

 

I can personally vouch that the first of these setups makes for lousy acceleration times, but very relaxed cruising ( 4800rpm at the ton)

 

The latter gives 5950rpm at the 100mph mark which is tiring if you travel on roads where you wish to hold 100mph+ cruising speeds. Imagine driving through France on those fantastic smooth D roads where short bursts of 100 - 120mph are possible in a quick Seven. This is very fatiguing driving. Unbearable are motorways!

 

So the whole thing is a compromise.

 

Best all round combi IMHO has to be 6 speed and 3.62 with perhaps larger rear wheels for road use.

 

 

I'm personally going for 13" front wheels as to mainatain geometry, with a 15 or 16 inch rear. Having discovererd Kuhmo do the S700 soft compound street legal motorsport tyre in the following front sizes:

175/60/13 (191mm section width, 536mm dia)

215/50/13 (226mm section width, 541mm dia)

135/45/13 (234mm section width, 537mm dia)

 

and for the rear, same tyre available in:

 

225/45/15 (579mm dia, 3.2% overdrive compared to 8/22/13 ACB10)

225/50/15 (602mm dia, 7.5% overdrive compared to 8/22/13 ACB10)

225/50/16 (627mm dia, 11.75% overdrive compared to 8/22/13 ACB10)

 

Sadly the S700's have only 5mm of tread when new......

 

 

Gearings a big issue. The gearbox is only a small part of it.

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

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[Chelspeed]

> Isn't a Quaife sequential over 3k?

 

2.2k from SPC for a 5 speed sequential dog box. Virtually identical price to the Caterham 6 speeder. I agree it's not cheap but someone recomended the Caterham box and in my opinion the Quaife sequential is a better bet for similar money. It's a hell of a lot of box for your money.

[murph7355]

Must be the 6spd version that's more pricey then.

 

[Alex Wong1697456877]

2.2k eh...? I thought it was over 3k.

 

Hmmmmm........ wink.gif

[Rob Morris]

I run an SPC Semi Helical box in my Vauxhall folowing the failure of the std 5 speeder at a mere 3,000 miles. Initially I was pissed off with having to spend circa £1,200 on such a young car, however, It remains the best upgade i've made to date. Whilst the box whines at low speed its but a fraction of the noise from a quaffe unit and above 40mph the induction noise is far greater.

 

As per Alex's box my first is higher 55mph and top gear is down to 137mph (Oh for as much power as Alex)

[R2D2]

Bit confused about taller gearing causing more problems controlling wheelspin.

 

Wheelspin is obviously only going to occur when the engine/transmission provide more torque at the driving wheels than the tyre can transmit.

 

Take a good Vx engine 125lbsft engine torque at 2000rpm as a constant.

 

This means with a 2.04:1 first gear and a 3.92 final drive the torque at the output of the axle is 1000lbsft.

 

at 5000rpm the engine will deliver 175ftlbs equivalent to 1400 lbsft.

 

Delivery of torque between these two points is fairly linear so the actual slope of the final torque rpm curve is 133lbsft/1000rpm.

 

Now take the same engine with a 2.69 first and a 3.62 final drive.

 

Output torque at 2000 rpm is 1217ftlbs and at 5000rpm is 1704ftlbs.

 

This gives a slope of 162ftlbs/1000rpm but not only is the slope steeper but the torque level is higher as well.

 

(I have assumed that dumping the clutch at 2000rpm doesn't produce wheelspin but as my seven doesn't have this type of power I don't know if this is true.)

 

It seems to me that the steeper the torque/rpm curve and the higher the torque level the trickier it is to avoid wheelspin.

 

When we reach top gear assuming a 1:1 5th the situation changes dramatically.

 

The output torque at 2000rpm with a 3.92 diff is 490ftlbs and at 5000rpm 686ftlbs

so the slope is only 65ftlbs/1000rpm

 

With the 3.62 diff the numbers are 452ftlbs at 2000rpm, 633ftlbs at 5000rpm and a slope of 60ftlbs/rpm.

 

The car with the 3.92 diff should accelerate just a little more quickly than the car with a 3.62.

 

I would have thought that the car with the 3.62 diff would give lower revs at cruisng speed in top (assuming a 1:1) than the 3.92 as the rpm/1000 would be higher in this gear.

 

I think the issue is matching the gearing to the torque curve of the individual engine and the intended application.