What cams for the twink?

[PSJ]

So since I'm having have the engine rebuilt I'm going to upgrade the camshafts to give it some more poke. It's already the big bore twink with the crossflow bottom end etc. But I'm sure the cams are just standard TC cams.

 

What camshafts do I get? Are the sprint one's the best to go for? Or are there better ones which give better power gains?

 

Thanks, piers.

[Klunk]

Hi Piers ,

 

First question I would ask yourself is 'what do I primarily use/want to use the car for?'.

 

If it's mainly for road then you'd be better off with a milder profile which gives some performance increase at the top but mainly gives a good spread of power/torque low down where the engine will spend most of its time.

 

If it's going to be mainly for track then more power up the top end will be more useful as, again, that's where the engine will spend most of its time. However bear in mind what the maximum revs is your crank will take; also what your gear ratios are. You can work it all out on spreadsheet and quickly identify where you will have problems.

 

Somebody once told me that you should choose the cam you would like and then order the next one down. I have to say, from experience, that this is definitely the option I would recommend if it's primarily for the road.

 

Regards,

 

Giles

 

 

 

Edited by - Klunk on 23 May 2011 14:43:22

[PSJ]

Thanks Giles.

 

I wouldn't be using it on the track, but it is going to be used for fast road use :)

 

Piers.

[Sheds Moderator]

Klunk has it right, what he's talling you is that you don't get owt for nowt. If you fit a hotter cam then you will get more power at the top end, say between 5000 and 7000 rpm. The snag is that you will pay for this with an engine that has LESS power between (say) 2000 and 4000 rpm than before. The whole thing is a compromise, racers don't care because they drive in such a way that they are always in the power band. Road cars are trickier.

 

A classic case in point was my 1.4 kss - beyond 4000 and certainly 5000rpm it went like bloody hell, but pulling away in traffic at 2000 rpm it was shocking, with less performanvce than a 1.4 metro. This was a snag round town - picture the scene: I'm tootling about in 2nd gear, first being too low, doing 10-15mph. The traffic clears and I want to pull away crisply so I put my foot down. The car accelerates with all the elan of an invalid carriage with a flat battery, spluttering away unil it hits about 30. It then wakes up and starts breathing as it should, but by that time there's a Corsa breathing down my neck and a 19 yr old who's convinced "Caterhams? Naah, had one in town the other day, I had him for breakfast".

[PSJ]

Well I was looking at the QED420 camshafts. Iv read they give better low down torque over the sprintcams and are capable for 140-150bhp.

 

Anyone have Exp of these cams?

 

Piers.

[George C]

Just a thought. It used to be that hotter cams more or less allways created drivability problems. These days with 3D ignition systems you can go further with the cam and still have excellent torque low down. Its still best to be conservative with the cam but you can push it a bit further than before.

[MarkyMarc]

Who is rebuilding the engine? If they can't answer question for you, perhaps you should consider an alternative. The twink is one of the most developed 4 cylinder engines on the planet and the depth of experience in engine-builder land is staggering. Racing Fabrications or Connaught Engines have probably built engines to your ideal spec - why not give them a call.

 

Marc

[PSJ]

It's not being rebuilt just yet, but will be in the next couple weeks. I was just gathering info so I could spec the engine up once it's been stripped down and diagnosed. :)

 

Thanks for the contacts mark. Will check them out :)

 

Piers.

[bstark]

I'd echo George's comment about 3D ignition, regardless of the cams you end up with.

 

The difference in low-mid range torque, particularly on part-throttle was astonishing on a xflow with a 234 cam (by no means the hottest) when switching from a dizzy to a Megajolt.

[skeetsy]

Hi again Piers,

 

I'm not sure if this will help you to identify the cams in your engine, but when you take the head off and the cam sprockets off the cam's you will find numbers stamped into the end of the camshsfts.

 

As I said the engine I played with had L1 race cams, but it was a bit peaky!

 

I would seriously speak to someone who knows how to build and tune twincams, since when you move to hotter cams there are a number of issues around machining engine components, spring seats, etc. and also uprating other components to ensure things don't go belly up!

 

I sourced a lot of components from QED back in the late 80's and I always found them very helpful on the phone.

 

Good luck with the rebuild

 

All the best

 

Richard

[Klunk]

Thanks BOSS ( ) for clarifying my ramblings.

 

The QED420 appears to be the cam giving good "driveability" and a healthy increase in power. However, whilst good, the low down torque will still be worse than the QED360 (with no other changes made) - why sell it if the QED420 is better in all respects? I found a few posts saying that you have to pocket the pistons more to make the most of a QED420.

 

However, power and torque are a combination of many factors and I believe some heads had bigger valves and higher compression. Ignition timing, as the guys have said, makes a huge difference. Choke size in carbs is another - most people think bigger is better. Too large a choke means slower air speed, poorer atomisation, less power. The list goes on.

 

As Marc says, you really need to talk to people who have worked on this engine. Just be wary of people selling you a headline BHP. At the end of the day, that's what sells engines to most people. Make sure you get what you want.

 

All the best,

 

Giles

[Darryn R]

Hi Piers

I have the qed420s in my engine very pleased with them in 1600 form they gave me 150bhp at 6800 134lb torque at 5500 pulled very strong from 1500rpm straight to 7000, I now have a 1700 with the 420 and have 161bhp 142lb torque, Yes if you dont use forged pistons the normal lotus pistons will need deeper pockets, also the valve spring seats may need to be made deeper for the increased valve lift, would send you a picture but having trouble loading

 

regards Darryn

[skeetsy]

Quoting Klunk: 

Choke size in carbs is another - most people think bigger is better. Too large a choke means slower air speed, poorer atomisation, less power.

 

In my experience choke size is usually determined by the volumetric capacity of the engine and the rpm that it will run at.

 

hence you will need larger chokes if you increase the capacity of the engine, or if you increase the rpm that it develops peak power at (or indeed if you do both).

 

But the larger chokes that you need to develop power on a high revving engine will have a negative impact on the driveability of the engine at the lower revs, just as Klunk alludes to

[PSJ]

Oh god.. I don't fancy needing to replace all sorts of other internals to suit the cams. Forged pistons are £400 Alone or something arnt they? Would the forged pistons be a cheaper option to getting the pistons and seats modified to suit? I suppose getting my current cams "re-profiled" to the Q420's will keep costs down quite abit so the forged pistons may be an affordable option :)

 

Would I just be better getting the 'sprint' cams or do they need other mods to suit them too!?

 

Thanks for the link to identify the cams Richard, hopefully that will come in use :)

 

 

I'm all abit confused by the 3D ignition? Can anyone explain this more? Is this a huge and costly change?

 

Piers.

[Sheds Moderator]

The thing is that you have to consider the engine as a whole, it's a machine. Carbs, manifolds, cams, ignition, they all form part of the machine. If you just drop in a hot cam without considering everything else it will run like a three legged dog. Carbs are a crude device at the best of times, so are mechanical points. It's harder to get a carbs/points engine to run well throughout the rev range with a hot cam then an injection engine.

 

3D ignition means an electronic ignition sysyem (basically) like a Megajolt, or an Emerald, or an ECU based system like you get on a modern car. It isn't a pushover to install and make work, but you know and I know that a decent elec ign/injection system on say a 1600 engine will deliver about 120bhp and 40mpg - more power at the expense of economy if you want - try getting anything like that from carbs and points.

 

 

[George C]

Your chosen engine builder will be able to supply you with a 3D ignition. If the engine is run in on the dyno you can also get a bespoke 'map' created for your engine and the carbs set up to suit - no need for rolling road sessions later and you have a nicely run in and set up engine from day one.

 

The 3D will enable the ignition timing to be infinatly variable as the timing of the spark can be completely different depending on revs, throttle opening and possibly temperature. The variables on a distributer are much less and tend to be optimised for higher revs.

 

Fitting is really easy (I hate electrics and managed it). The engine builder I use (Scholar) sold me an MBE system which works well and the software they use can be accessed easily (unlike the Webber system).

[Klunk]

not having a good 'plain speaking' day yesterday - thanks Skeetsy, that's what I meant.

 

I would go for George's option. Both engines I have had built I have had done this way and they been superb 'out of the box'.

 

Regards,

 

Giles

 

Edited by - Klunk on 24 May 2011 09:59:13

[Sheds Moderator]

Do bear in mind though that an Emerald/MBE/Weber Alpha system will be £500ish though. Is an Emerald new about £600, dunno whether this includes the rolling road session to make the map work properly.

 

I know you want to keep the Lotus running and that's a very creditable aim, it's a great engine but it isn't going to be cheap. Especially not if you want to take the opportunity to get power gains. This is why people fit Zetecs and the like! Like you say though, you want to keep the Lotus engine, it's the engine for the car. In your shoes I'd be staying with the standard 126 bhp and the existing carbs and ign system. Otherwise you are into a world of expense, maybe a £2k bill, and (say) 10 bhp over the original engine. I've driven 130 bhp and 140bhp 7s, and I can't tell the difference. It's not the way I'd spend my money.

[PSJ]

^^ this is very true. Originally I only wanted the twink running strong (120-130bhp). I only thought on cams as i thought it would only cost sub £300 for the upgrade. But if it means spending over an additional £1k for ~10bhp I'd rather not. I'd want to put that extra money into new suspension and bushes etc, things that NEED replacing rather than things I just want. Although, my dad has said the ignition has been upgraded to electronic years back but don't have info on which system :D

 

So yea if there isn't a better cam that isn't too much hassle to fit then I won't bother just stick with what it's got.

 

Changing engine for me makes the car pointless. Id be better off selling it and saving and buying a R300 or similar :D lol. But I like the rare and special retro feel, soul, sound, passion and sentimental value this car/engine has :D.

 

Piers.

 

Edited by - PSJ on 24 May 2011 10:19:24

[Sheds Moderator]

I think that's decent logic. This particular car is special to you and the engine is a big part of that, so it's worth hanging on to. As you say if you just wanted a driving machine then you'd be better trading it in for a K. Even in its current tired state a Vegantune Lotus Caterham 7 will fetch a good price, and you'll be most of the way to if not an R300 then a Supersport, maybe with a few tweaks.

 

Your electronic ignition system from years ago won't be anything clever, it will either be a simple TAC system which offers no gains over points other than longer life/freedom from adjustment, or a simple pointless system which will have a basic map. These were around in the 80s, they worked OK but an Emerald it's not.

 

I don't think you necessarily have to get a 3D ignit system to run a hotter cam, it's just that the car will run so much better with one than without, and the more tuning you do the more difficult it will be IMO to get a carbs/points engine to run throughout the rev range. I suspect that what you have now is a sweet spot, possibly even/probably leaning towards the peaky end of what you'd want to live with in a road car.

[PSJ]

Exactly. When I get home tonight I will see if I can see any indication to what ignition system it is, but as you say it's prob not brilliant.

 

I suppose at the end of the day iv been driving it with only 60-70bhp (that's really embarrassing lol). So 120-130bhp is going to feel pretty quick as it is 😬. Should feel like a different car!

 

Maby in a few years when the cars back to scratch and I'm bored of the power I may invest ££££ into getting some interesting gains we will see.

[myothercarsa2cv]

I never get bored of 'only' 120bhp, because my daily driver has 31.8bhp...

 

Get it working sweetly then worry about upgrades 😶‍🌫️

[Sheds Moderator]

Hey, 31.8 brake, you must have the roadburning "carbu double corps" version, you speed freak you.

[myothercarsa2cv]

That's me! Double choke carb, electric ignition, Harley D coil, lightened flywheel, higher compression pistons, fan blown induction 😶‍🌫️ All worth precisely 2.5bhp *eek*

 

So really, a grand for 10bhp is pretty good value, Piers 😬

[PSJ]

only thing i can see regarding which ignition is it using is a little grey box type thing called - lumenition !? was upgraded in 1996..

 

 

 

Edited by - PSJ on 24 May 2011 20:29:51