Building a reliable 140-150bhp TC

[jono]

Hi,

I have posted on the Plus 2 section previously about doing a Zetec conversion on my Plus 2. However having looked into it further I have decided afte rmuch deliberation to stick with the LTC and make the existing engine more powerful and useable for everyday. This is in part due to the need to junk a perfectly good Spyder TC chassis but I guess I am also drawn to the character of the Lotues twink.

140 - 150 bhp is my aim and I want to retain tractability and above all reliability. My existing engine is SE spec with standard valves and single groove inlet cam, so I think the rated output is 115bhp to 118bhp according to the original spec sheet.

What is the best way to achieve this? The engine was rebuilt 10k miles ago and looks to be in very good condition but will need a rebuild as it has stood for 14 years unused.

Do I need to go for a big valve conversion or new valves seats for that matter or can I run the engine on unleaded?

I am pretty much convinced that throttle bodies and an Emerald ECU or similar is the way to go even though I know this will not come cheap. This is mainly for reliability and economy but I guess this on it's own will get me on my way to increased power and torque.

Next up I guess it will need some porting work and a decent exhaust system but could I retain the existing cams and hope to see the sort of outputs mentioned?

Any advice appreciated especially from those who have followed this route.

Also recommendations on who to get to do the headwork and machining.

I had someone recommend a small engine builder who did good work on his twink head based just outside Newark (Notts UK) but can't recall their name.

Burton and QED come with mixed reviews and I hear they are very expensive too

Cheers

[john.p.clegg]

Jono
I was going down the same route and purchased a 2.0 Mondeo for an engine swap,after staring into the engine bays for a period-decided against it....but am still on the path to EFI the twink.....this together with its long stroke crank,1.625 i/l valves and 1.4 ex valves,QED 420 cam ported head and the home made supercharger (truck fan driven off the crank) should give some usable power and hopefully correct mixture throughout the rev range.....

John

[SimonH]

Jono,

I am doing a similar thing with my car. I was doing the Zetec thing then backed out and now am going with the twincam fitted with efi and a coilpack. Cant be bothered with carbs and distributors and points.

I am using a guy called Nick Stagg for the basic engine work. He is very good although a fair way from you as he is in Bristol. Rebuilding I will do myself.

I dont really know how much more expensive QED are for parts. But bear in mind a lot of builders appear to (willing to be proven wrong here but the ones I asked do) use QED parts anyway so they may be quite reasonable value in some ways.

They will regrind your cams to 420 spec for about ?65 each cam against ?175 per new one which didnt seem too bad.

Cheers,
Simon

[jono]

Cheers chaps,

Simon, out of interest how do they regrind your existing cams and achieve higher lift (or is it duration they are altering ).

I was given to understand that the Lotus twincam responds well to higher lifting but not increased duration - surely this would need them to add some metal to the cam lobes and then regrind them? As you can probably tell I'm not too up on the techy side

Another question what EFI system are you using?

[SimonH]

Jono,

They remove metal from the base circle, plus regrind the lobes to get the correct duration and profile.
You can now use a thicker shim to take up the clearance so that when the cam is at max lift has more opening than before.

The 420 cam is a fairly high lift cam with a reasonable duration so you wont get that lumpy idle associated with long duration cams. I have the details somewhere but not to hand.
It has been recommended to me to give a good 140hp when used with a ported head.

My spec will be a ported big valve head (big valves probably not needed but its a S130 car) 420 cams, 0.040 overbore and 40mm weber throttles.

My ecu is by EFI technology, an Italian company, they make the current Lotus ecu's. I know its not the usual one to use but I work with them so its easier for me than say an Emerald.

A supercharger is an interesting addition John. I have an M45 eaton blower at work. Wonder if I should try to fit that? Could be interesting performance in a plus 2.

Cheers,
Simon

[lotuselan2]

You will definitely need more displacement to achieve your target. More stroke and more diameter. The taller block would help get started.
Ken

[handi_andi]

Hiya
Am amused by this post having just read a great article in the Club Lotus magazine about doing an ECU conversion on a twin-cam resulting in aroudn 40-42mpg on a long run although surprisingly the guy didn't appear to get much more power which surprised me. If you are a lotus club member then the article is available in a full form with pictures from headquarters is my understanding.

Hope this helps

Andy

[SimonH]

You wont get that much more power from just bolting on throttle bodies, the carbs will already breathe reasonably well so not much gain there.

With head porting and high lift cams 15hp should be attainable, whether on TB's or carbs, maybe more but if you dont expect too much you cant be disappointed.

What you will gain is better starting, midrange torque and fuel consumption.

Simon

[rgh0]

140 to 150 hp with good road tractability achievable from a twin cam. You can do it with a normal block or a tall block. Throttle body fuel injection annd mapped electronic ignition will not help much with the max power but it will help with easy starting and cold running and better low speed torque response and smoothness.

3 Key things required are:

1. A well ported head using bigger valves
2. A high lift cam shaft of .410 lift or more and around 280 degree seat to seat duration
3. A good set of big bore headers

The above will get you over 140 hp at 6500 rpm in a 1558 twink with 10:1 comp ratio which a standard bottom end can handle. More capacity will get more power at 6500 rpm, more revs will get you more again.

When using a high lift cam you need longer valve stems and special springs to accomodate the higher lift. This in turn requires a smaller cam base circle to fit in the taller valves under the cam shaft. A lot of detail work required to build a high power twink head right and I have seen people mess this up many times so be careful who you select to do the work and ensure they have built this sort of head before and are not experimenting on yours.

cheers
Rohan

[handi_andi]

A supercharger is an interesting option although sat here at work I am trying to figure out in my minds eye where exactly in the crowded front end there would be space to fit one. A turbo is an interesting idea as well but that would have to go at the end of the tubular manifold and I think thats right by the passenger footwell so not much room there either.

I know it is slightly off topic but it is an interesting idea.

Nitrous anyone?????

[dusty]

Is it worth it?

Are you really going to notice an extra 25bhp on a road car?

This is a genuine question, I'm not trying to start an argument!

I have my engine in pieces at the moment an if its genuinely worth going to the trouble of porting the head and fitting special valves and cams I'd look at doing it.

Cheers
Jon

[carrierdave]

Hi All,
My car was equipped with the standard SE engine. I have since changed the pistons for the bigger valve cut outs. I had the crank, pistons, fly wheel rods and clutch cover all balance last year ? This made a big difference in the running of the engine. (Its surprising the difference in weight from one piston to another)

This year I have had the head off. The cam?s have been re ground by Kent Cams to a CPL2, which was ?62.50 per cam. I got them back in 7 days and they look the business!!

I have just had the head work done; this consisted of new bronze valve guides and new sprint valves plus a new set of standard exhaust valves.

I had the throat of the inlet seat increased by 1mm to allow for the increase in inlet valve diameter; as without this I can not see the purpose of fitting sprint valves in standard valve seats. The throats were then blended in, back as far as the valve guide.

I was going to have the exhaust valve seats replaced with unleaded but based upon my very low annual mileage, it did not seem worth it.

I have now got hold of some 33mm chokes along with new jets etc.. to match the S130 spec.

Hopefully I should have it back together for the end of this year ? I?m in no rush at the moment.

Not sure what it will give me ? Hopefully just a nice smooth and responsive ride.

Dave

[elancoupe]

My car has a standard height 1700 on Dell'ortos, 10.25:1, fairly mild porting, standard (big) valves, and Bean's 112 grind cams. It has been dynoed at 140 hp, 133 lb/ft of torque.

It was built 14 years ago, so that would seem to be reliable enough.

[chrishewett]

Mmmmm!
Chris

[lotuselan2]

In my mind the 1700 cc did most of the trick for 'elancoupe' and then he matched everything else to benefit from the added displacement.
Ken