Lotus Twincam - big valve
Discussion
A factory built Big Valve gets most of it's power increase from cams and compression - the valve size itself is said to be only accountable for 1 bhp, so if all you can do is see a complete engine measure from the cam cover gasket face to the bottom of the oil/air seperator box (this aways gets the bottom machined flat in a skim) - Unfortunately I'm nowhere near any refs at the moment but will be in a day or so if you can wait I'll get you a figure - unless someone is nearer their refs .......
further info: the head is mounted on a x-flow 711M block, bored out to 1739cc. lotus alloy sump.the timing cover is the short one, so there is a spacer on top. 2 x 45 carburators. non-standard camshafts. cant give any infos about conrods or crankshaft as i havent opened the engine ever.
the rocker cover says lotus twincam big-valve...but somebody told me these covers are interchangebale between standard and big-valve engines.
is the following true? (these letters should be casted nearby the sprak-plugs)
H= high compression
N= hohe kompression and big inlet valves
S= big valves
heads pre 1968 do not have any letters casted.
the rocker cover says lotus twincam big-valve...but somebody told me these covers are interchangebale between standard and big-valve engines.
is the following true? (these letters should be casted nearby the sprak-plugs)
H= high compression
N= hohe kompression and big inlet valves
S= big valves
heads pre 1968 do not have any letters casted.
Yes, the Big Valve head should be stamped with an 'N' (in front of No. 1 spark plug, from memory).
The original Sprint camshafts can be identified, if you lift the cam cover, by having two grooves in the bosses at the sprocket end.
But yes, cam covers are interchangeable.
It sounds academic, because if the engine you are looking at has 45 carbs, hot camshafts and is built on a 1739cc Crossflow bottom end, I'd be astonished if it wasn;t ported well beyond basic Big Valve spec., anyway.
The original Sprint camshafts can be identified, if you lift the cam cover, by having two grooves in the bosses at the sprocket end.
But yes, cam covers are interchangeable.
It sounds academic, because if the engine you are looking at has 45 carbs, hot camshafts and is built on a 1739cc Crossflow bottom end, I'd be astonished if it wasn;t ported well beyond basic Big Valve spec., anyway.
as i said i havent found any letters casted. so its pre-1968? since when lotus offered big-valve heads?
the rocker cover was off a view days ago...now closed again, nicely sealed to avoid any leakage....so we wont open it until we need to do.
i remember a "ford" logo on the camshaft-sprockets and was wondering what ford has to do with the lotus camshafts...
the rocker cover was off a view days ago...now closed again, nicely sealed to avoid any leakage....so we wont open it until we need to do.
i remember a "ford" logo on the camshaft-sprockets and was wondering what ford has to do with the lotus camshafts...
If the head isn't stamped, then its parentage is questionable, to say the least.
But like I said, it's academic. What does it matter... you clearly can't make any sort of claim to 'originality' if it's on an overbored Crossflow bottom end with non-standard carbs and induction, so why does it matter whether the head is a 'genuine' Big Valve or not?
You can port any Twin Cam head to better than Big Valve spec, these days, anyway...
But like I said, it's academic. What does it matter... you clearly can't make any sort of claim to 'originality' if it's on an overbored Crossflow bottom end with non-standard carbs and induction, so why does it matter whether the head is a 'genuine' Big Valve or not?
You can port any Twin Cam head to better than Big Valve spec, these days, anyway...
If you're going to heavily modify a Twin Cam engine, it doesn't much matter what head you start out with; the premium for the Big Valve head would probably match or outweigh the extra cost of porting a lower-spec head to fit bigger valves.
... but I've seen Westfields and VX220's with Lotus badges on them (
Hello, if you're the plonker with the lightning yellow VX220 with a Lotus badge on nearly every panel that I see parked in Tewkesbury occasionally!), and I know a few Elan owners who seem to think that BRM cam covers are chic. People do strange things.
... but I've seen Westfields and VX220's with Lotus badges on them (
Hello, if you're the plonker with the lightning yellow VX220 with a Lotus badge on nearly every panel that I see parked in Tewkesbury occasionally!), and I know a few Elan owners who seem to think that BRM cam covers are chic. People do strange things.Yep, 'fraid the tall-block conversion is definitely 'botched together'.
It doesn't matter in a Westfield (though to be honest, I've never figured out why anyone would want to use a Twin Cam in a Westfield, anyway - there are far better engines available, these days, so the only real reason to use a Twin Cam is for originality in a car it was fitted to 'in period'), but - like the Spyder spaceframe chassis - it has to be admitted that it is a negative feature despite being technically superior to the original form.
It doesn't matter in a Westfield (though to be honest, I've never figured out why anyone would want to use a Twin Cam in a Westfield, anyway - there are far better engines available, these days, so the only real reason to use a Twin Cam is for originality in a car it was fitted to 'in period'), but - like the Spyder spaceframe chassis - it has to be admitted that it is a negative feature despite being technically superior to the original form.
Lol back in my yoof what I wouldnt have done to have 711m cross flow twink engine.. Time and the onset of 4-valve per cylinder K-series/duratecs etc have surpassed the old 2 valve lotus engine, which considering it was last made in the very early 70's isnt too bad.
If you like retro stick with it. But the originality of the big valve badge only really applies when on the stock block in the original car IMO. This one is just modified engine in a kit car regardless of head spec.
If you like retro stick with it. But the originality of the big valve badge only really applies when on the stock block in the original car IMO. This one is just modified engine in a kit car regardless of head spec.
but its nothing unusual to use a 711M block? read lots of pages about tuning twincams like that. especially twincams used in escort and cortina´s. also burtonpower has an own section, even suplies taller timing-covers to avoid spacers.
this conversion, done well, mustn´t have a negative touch?
this conversion, done well, mustn´t have a negative touch?
also to the story: how comes this engine into a westfield:
the builder of the kit was a garage owner, used in repairing lotus-cars and driving hillclims (not with this car). the kit was built in 1987/1988, also registrated in ´88. car was one of the 1st models with independant rear suspension!!
i guess he thought using a lotus engine in his kit would "bring" some originality into this car. maybe he already had the engine or parts in stock.
also it looks as there havent been saved any costs to built a really nice and good running engine. unfortunately i do not have any contact details of the kit-builder.
the builder of the kit was a garage owner, used in repairing lotus-cars and driving hillclims (not with this car). the kit was built in 1987/1988, also registrated in ´88. car was one of the 1st models with independant rear suspension!!
i guess he thought using a lotus engine in his kit would "bring" some originality into this car. maybe he already had the engine or parts in stock.
also it looks as there havent been saved any costs to built a really nice and good running engine. unfortunately i do not have any contact details of the kit-builder.
Edited by Comadis on Monday 4th August 21:32
Comadis said:
this conversion, done well, mustn´t have a negative touch?
I'm afraid it does... at least in any car where the Twin Cam might be considered to be in any way 'authentic'.Originality is important in anything old enough to genuinely justify the use of a Twin Cam.
It's just like the Spyder spaceframe chassis, or a 5-speed gearbox conversion, or a solid driveshaft conversion in an Elan. Nobody disputes they are technically superior to the original items (I fitted a Spyder chassis to my last Elan, because I was expecting long-term ownership, so didn't worry about originality or value), but they will knock a chunk off the value of the vehicle, whether you like it or not.
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