How much HP

[Certified Lotus]

How much HP can a stock S1 Gearbox, differential and the donuts handle? I'm rebuilding my engine and I always think about the downstream gear and what it is designed to handle.

[Maulden7]

Gearbox & diff unit itself are not the weak links, but the donuts & the diff output shafts are the items from your list that are most at risk imo (plus the rear wheel bearings)

Personally I wouldn't go above a "sprint spec" engine with stock items.

[Certified Lotus]

As I understand it, a sprint engine produces 126HP at the crank. I'm looking at building an engine with about 175HP at the crank. I was anticipating replacing the donuts and shafts with the CV rear axle conversion kit. Anything else I should be thinking about?

[rgh0]

What breaks with 175hp depends to some degree on use but I would do the following

1. Standard clutch components OK but a solid bonded clutch plate advised if doing lots of aggressive starts.
2. Standard gear box OK but if regularly using all the power in second and third gear you will eventually have fatigue failures in the gear teeth. You can replace with Quaiffe straight cut internals but they are noisy in the intermediate gears for road use.
3. Driveshaft to diff no problem
4. Diff itself no problem but a quaiffe LSD centre useful for getting the power down on the road
5. High strength diff output shafts required and CV drive shafts
6. If putting sticky tyres on the car then high strength wheel hub shafts required.to handle the tyre cornering loads
7. Make sure all the rubber mounts are in good condition to handle the extra loads and the standard engine mounts will have a short life. There are various reinforced mounts and racing mounts available.

cheers
Rohan

[el-saturn]

.............lets say cvs were never part of the concept and lets say only aggresive accelerations from ZERO to where-ever create individual component failure THEN and only for 30sec events you will need to switch to 100% race. ............ PLUS all of the loads leading to all kinds of fatigue-stricken parts are reduced to the design concept. you never win a race within the first 500meters (yards) and owning a street going racer (170hp) I don?t have to prove (at an intersection who?s faster) nothing. --- BUT two weeks ago a lamborghini aventador (white) came up the beginning of a 1st gear uphill straight (700m) behind me (about 200m) and thought he could gain a position (i started at 4000 rpms) ------------------------------------ that wide piece of "enginuity" had to back off: he looked like a big truck on an elan (or kart) circuit ----------- public road ----------- OUR MAGICAL ELANS (170hp all steel and forged: STREETLEGAL and TTR suspension) just my simple opinion sandy

[elancoupe]

http://shop.tonythompsonracing.co.uk/mo ... n-19-w.asp

[Grizzly]

Many years ago we fitted a (Dare i say it) ford zetec engine putting out 200hp at the fly in a engine-less +2 we got of Ebay for ?500, got some CV joints rigged up some shafts and the first thing it did when it was driven was snapped the Mounting lug off the diff

I have to say i've reformed my ways since then and that car has now got a Twincam engine back in it (and some seats/trim).

[rgh0]

Many years ago we fitted a (Dare i say it) ford zetec engine putting out 200hp at the fly in a engine-less +2 we got of Ebay for ?500, got some CV joints rigged up some shafts and the first thing it did when it was driven was snapped the Mounting lug off the diff

I have to say i've reformed my ways since then and that car has now got a Twincam engine back in it (and some seats/trim).

Yes I forgot the top angle steel diff brace bolted between the lugs that was introduced for the Sprints

cheers
Rohan

[Certified Lotus]

All great info, thanks. For the record, I'm not doing track days nor am I interested in street racing. Just like having great mid range torque available for spirited driving without having to get anywhere close to the red line.

I particularly liked TTR "list" of modifications. Puts things in perspective.

[Grizzly]

All great info, thanks. For the record, I'm not doing track days nor am I interested in street racing. Just like having great mid range torque available for spirited driving without having to get anywhere close to the red line.

I particularly liked TTR "list" of modifications. Puts things in perspective.

I'm not the most experienced when it comes to tuning Twincams but the ones i've driven have all started to get very peaky past the 160hp mark for the road. IMHO a real 130hp Elan is enough for the street but unless they have had work there usually more like 100hp elans which isn't so hot.

[JohnDanbyRacing]

Agree above with Chris. A full race 175hp TC needs to be kept above 4300rpm, for torque and driveability keep to around 160-5bhp and it will be brilliant for the road. I would go for TTR's latest output shafts and a Quaife/Tran-x LSD with a 4.1 diff ratio.

[elansprint71]

You will certainly need to use tougher diff mounts, both top and bottom. I trashed new standard mounts in six months on my Sprint, in normal road driving. Modern rubber components are useless. The Tony Thompson mounts I replaced them with seem bomb-proof, well worth the extra cost..

If you are going not on track, I can't agree with the recommendation of a 4.1 diff; in fact, that is probably the last ratio you would want on the road, it would be just too tiresome. I run a 3.54 with about 135 BHP and it is rapid enough to see off most traffic and cruises reasonably quietly at semi-legal speeds
I worked my way up thro' the diff ratios, over the years, before I reached this conclusion. They are still all lined up on the shelf.
My project car has a 4.1 and Quaife straight-cut box; it was built as a (stalled-project) sprint/hill-climb car by the DPO; when I get around to sorting it out, those items will be on e-bay. I have a close-ratio box and 3.55 diff ready. The Quaife has 20 miles on the clock; form an orderly queue but don't hold your breath.

One of the best ways of making your road car go faster is to join a good breakdown service like the RAC; then you can remove all that crap you normally carry around in the Elan- spare wheel, jack, huge toolbox, spare distributor, extra cylinder head, emergency alternator and 20 litres of oil.

[JohnDanbyRacing]

I do agree Pete 4.1 would certainly not be that suitable for long journeys but for back road blasts and shorter journeys it will make you believe you have 200bhp! from memory 4.1 diff at 8200rpm will do about 130mph.

[elansprint71]

.......... from memory 4.1 diff at 8200rpm will do about 130mph.

For how long?

Getting back to the original poster...
"....For the record, I'm not doing track days nor am I interested in street racing. Just like having great mid range torque available for spirited driving without having to get anywhere close to the red line."

Off topic, again... I think we put together a 1.8 steel TC, at Bob Howling's place (under the railway arches in Manchester) which showed 220 on the dyno; dropped it into a 47 and took it for testing at Oulton, where it promptly melted approaching Knicker Brook on the second lap and burnt-out the engine cover. Thank goodness we did not take it to a faster circuit.

EDIT: somewhere I have the photographs.

[rgh0]

All great info, thanks. For the record, I'm not doing track days nor am I interested in street racing. Just like having great mid range torque available for spirited driving without having to get anywhere close to the red line.

I particularly liked TTR "list" of modifications. Puts things in perspective.

I'm not the most experienced when it comes to tuning Twincams but the ones i've driven have all started to get very peaky past the 160hp mark for the road. IMHO a real 130hp Elan is enough for the street but unless they have had work there usually more like 100hp elans which isn't so hot.

While generally true there are ways to get more than 160 hp without ending up with a peaky engine that's unsuitable for the roads

This specification will give you in the better than 170hp region and be road tractable but its not cheap. Limit yourself to below 7000rpm and you will save a lot of money on the expensive bottom end but around 170 hp will be the limit

1760 cc tall block
Forged pistons, steel crank and rods advisable as you will want to use more than 6500 rpm as it will pull to 8000 but have good torque across the whole rev range.
McCoy conversion or new SAS Head to get the porting you need. !.625 and 1.4 inch valves and springs and followers suitable for the high lift cam set up.
McCoy .440 lift cam or maybe his.460 lift cam or equivalent from others - highest possible lift and short enough duration ideally below 290 degrees seat to seat. Maximum power around 7000 to 7500 rpm
around 10.5 to 11:1 to run on normal premium unleaded
45 DCOE with 36 or 38 mm chokes
TTR exhaust
Baffled sump to keep oil up to it in rh corners

cheers
Rohan