1700 Lotus Twincam

[jono]

Hi,

My SE spec engine for my Plus 2 is currently with an engine builder and waiting in the queue for his attention. The proposed rebuild spec is to fit bigger valves, fast road cams and a rebore with big valve pistons. I am intending to run the engine on throttle bodies and ECU with the aim of creating a mildly tuned reliable and tractable road car which I can use everyday if I wish (considered Zetec but have ditched it as I didn't want to rip the heart out of the car).

I am now thinking of going down the 1700 route and retaining the L block bottom end so that the car could be returned to original spec in future if desired.

A couple of questions - how easy is this to achieve and could any parts from the L bottom end be used in order to create the 1700 capacity?

Also, will this alone make much difference to the driving characteristics of the finsihed engine or is it only really worth considering if I was going for a higher state of tune?


Cheers

Jono

[SADLOTUS]

I did this and I'm very pleased with the result.
77mm crank, 83.5mm pistons = 1685cc
My L block, mexico crank and custom 83.5pistons.

150bhp@6800, 134lbs torque@5500 (107lbs@3000)

http://www.lotuselan.net/forums/viewtop ... c&start=15

Dynos should really only be used to compare before and after, I was unable to do it before but the engine builder has built many different kinds of TC and said he was very happy with the combination and the results.

regards
Paul

[RotoFlexible]

I was convinced to go to 1700cc on my recent rebuild. In my case, the choice was simplified by the fact that I was going to need custom pistons because the block was already .040 over and worn (my engine builder wanted nothing to do with sleeving the block).

I don't know if you can find in-stock pistons that will accommodate the longer crank throw using the stock TC rods. Dave Bean used to list them but I don't know if they still exist. If not, you are in for custom pistons at least.

If you are going for custom pistons, then you can choose a longer rod. My engine builder insisted on this, muttering about stroke-to-rod ratios, and in fact the Formula Ford rods (stock Ford crossflow rods??) we used get the ratio into a better range. (Bill actually would have preferred Cosworth rods, longer yet, but that runs into big money.)

The crank was an issue. After an expensive side trip, we ended up with a SCAT Formula Ford crank, prepared by a US FF engine builder. This may not be such a problem in the UK.

Since we were upgrading an old engine, Bill also insisted on new main caps. So it was a clean sweep: not one part of the bottom end was retained.

With "fast road" type cams, mild porting, and 10.5:1 CR the result is an engine that feels just like a regular Twin Cam, but stronger across the power band. It did 145+ BHP on the dyno (engine, not chassis) with the broad power curve typical of a Twin Cam. On the road, it is very well behaved, but driven in anger, it gets to the red line significantly faster than before.

[jono]

Paul,

Those are very impressive figures

Presumably the mex crank is a longer throw than the Lotus one - is that how it works?

Jono

[john.p.clegg]

Jono

What ECU are you going for?

John
(Halfway there with Megasquirt)

[jono]

John,

I will turn the question around if I may

...not decided yet and I am open to suggestions. My engine builder works closely with an ex QED chap who is an injection expert so I will take his advice on it. I guess it is not going to be cheap though

Jono

[john.p.clegg]

Jono

I am halfway there doing a Megasquirt,am running the ignition on it at the moment and am verrrry impressed,have never had a steady tickover before and starts first time,what more can I say...

John

[SADLOTUS]

Jono

I am no engineer (caveat over with!)

The 1558cc twincam has dimensions:
3.250 inches (82.55 mm) bore
2.900 inches (72.746 mm) stroke

The Mexico's is 77mm

Mine is still on 40's with an old 2" Geoff Howe manifold, TTR/Lucas distributor, Gustafson starter and K&N.
Good dyno figures may also have been due to octane booster

Paul

[europatek]

Hi Jon,

I'm running a 1700cc twin cam in my Mk1 Cortina. The engine started life as a standard Escort motor to which I have done the following:

1600GT crank
125E rods
84.0mm Datsun L16 pistons, flycut to suit the valves
Capacity is 1720 for memory
Bigvalve spec head
Wade 205 cams (Australian camshaft grinder) 30,70/70,30.
42DCOE Webers
Standard escort extractors

I've found this combination to work very well. The engine is very responsive, very torque and very easy to drive. I'm running it in the car with a 2000E style gearbox (2.9:1 first) and a 3.7:1 final drive and car keeps up with modern traffic with no problem at all, even with a load on board. I'm thinking of this combination for my Elan.
With respect to the use of Datsun parts, this has become reasonably common place in Australia, with cranks, rods and pistons being used. The component quality is good and generally cheaper than Ford/Lotus/Cosworth. The crankshafts are forged steel and can be modified to fit the Ford block (a custom flywheel is needed), 240Z or 240K 6cyl rods work well if using a 1600 block and pistons are available in sizes from 83.0 to 86.0mm, some have a slight dish and some are flat top. I once had an engine with a Datsun L18 crank, 240k rods and 85.0mm pistons in a 1600 block which gave a capacity of 1760cc and it went very well.
Hope this gives you some help and ideas.
Regards,
Matt.