Big Valve conversion

[steveww]

Hi,

I have just bought a 1970 Elan S4 SE dhc. This is my first Lotus so I
know I have a lot to learn so here is my first question of many....

It is possible to convert a standard valve head in to a big valve
head? If it is possible I was thinking of having the machine shop do
this when I get the head converted for unleaded fuel.


Thanks.

[s2lola]

One of the great marketing spoofs of alll time was the "Big Valve" Lotus
engine. Can't remember the dimensions off hand, but the difference relative
to standard is really quite small.

cheers,
Bill Tebbutt

-----Original Message-----
From: stevew_w [mailto:***@***.***
Sent: Monday, June 02, 2003 7:36 AM
To: ***@***.***
Subject: [LotusElan.net] Big Valve conversion


Hi,

I have just bought a 1970 Elan S4 SE dhc. This is my first Lotus so I
know I have a lot to learn so here is my first question of many....

It is possible to convert a standard valve head in to a big valve
head? If it is possible I was thinking of having the machine shop do
this when I get the head converted for unleaded fuel.


Thanks.












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[types26/36]

Steve,
The answer is yes, the inlet valves are 40 thou larger(1mm) But that
alone will not give the reputed 126BHP. It was a package deal,the
C.R. ratio was raised to 10.3 by skimming 40thou (1mm off the head)
the cams changed,the carbs rechoked & rejeted and the inlet ports
reworked(according to some) a nice new Tappet Cover and we have the
"BIG VALVE" engine.
Regards Brian.
64Elan/72Sprint/J.P.S.Europa



In ***@***.***, "stevew_w" <stevew@s...> wrote:

[nigelrbfurness]

Steve
In my opinion the big valves are not worth it. Change
the cam, get the tappet clearances all the same within
a thou, carb jetting correct and get the distributor
replaced/overhauled and that will bring you very close
to the pretend 126 BHP. The big valves give no more
than 1 BHP (according to most commentators) and make
it more difficult to get a good idle and low-speed
pickup. I think most people will admit that on a
modern dyno the 1558cc big valve with sprint cams will
produce no more than a genuine 117-120 BHP. For more
BHP you need capacity, 1760cc will get you closer to
130 genuine horses. The magic figure for a 140 MPH
Elan is 105 BHP genuine, corrected for air
pressure/temp at the wheels. All the foregoing is
just _my_ opinion (fire extinguisher for
flame-throwers!). For the genuine info talk to QED at
Loughborough or Miles Wilkins at Fibregalss Services.

Good luck
Nigel Furness


Nigel Furness



--- Brian Goodison <***@***.***>
wrote: > Steve,

[sprinterdave]

In message <bbfcrc+***@***.***>, stevew_w <***@***.***>
writes

-- QED will do a very god job in converting your head. You only need to decide
how much you can afford.
Dave Shiers

[steveww]

Thanks for the info. So when I get the unleaded work done I will have
them do some porting, polishing and a skim while they are at it. I was
thinking about new cams as well so no problem.

You say to get real power increase the capacity but can you bore out the
block to 1760cc with out any problems?

Nigel Furness wrote:

[types26/36]

Steve,
Its not that simple,the 1500/T.C. block will not bore out to make
1760cc The normal way is to use the 1600 block,bored to 85mm with the
longer 1600 stroke gives 1760. there are some other things also need
doing ie.longer t/chain,spacer to change front cover height(or tall
front cover)and some other minor mods.
The best you can get from a 1500 block is 1650cc but it becomes very
weak and may need sleeving.
Regards Brian.
64Elan/72Sprint/J.P.S.Europa





In ***@***.***, Steve Waterworth <stevew@s...> wrote:

[lotuselan2]

The "big valve" head is really a small change, check the difference in valve
size.

If you want a real upgrade and increase the reliability at the same time,
find a used BDR and get it rebuilt. You can even throw away the drip pan.

Ken
'69 +2 with Cosworth BDR

[gobw2]

Well, Nigel, I always respect your opinions. No flame here.

Questions - I know a fair bit about MY car (ought to after spending over
1/2 my life with her) but little about what I have not owned or worked
on. There were many variations of the TC engine by people other than
Lotus. To name a few, Vegantune, Cosworth, BDR, etc. Did the factory
install any in the Elan? What did these folks do to the TC, and how much
power did they get out of it? Low end torque? Is the BDR 1600 block
based?
Thanks for whatever knowledge you can share.

George 67 S3

[nigelrbfurness]

Steve
For a reliable 1760cc overbore (85mm) you need either
a very good 711M block (check the cylinder wall
thickness) or a SA 1600 block which you may have to
import from South Africa but there are some in the UK.
You should definitely talk to Andrew at QED if you
want to do this as it is very important ot collect the
right set of components. I have seen some real crap
assembled from bits of old Transit engines and other
sources. Might be all right in a boy-reacer's MK1
Escort (no offence intended) but not in an Elan where
an engine blow up might have real consequences for
safety. I have seen 1760cc engines self destruct in a
spectacular way! You should be aware also that
1760cc engines based around the standard crossflow
crank will not rev safely to 8000 rpm where the 125E
crank will (mostly!). You should also investigate a
lighter flywheel for this engine than the standard
1600 X-flow one.

Just my opinion, not an authoritative statement.
Good luck
Nigel Furness



--- Steve Waterworth <***@***.***> wrote:

[Elan45]

Don't bother doing either. As Bill T has just mentioned, the "big valve" was only .031 [.8mm] larger intake valve. No increase on exhaust. Hardly worth the bother, except that if you are doing valve work, the small intake valve is actually harder to find, so it is easy to convert. But also, the TC combustion chamber shape and alloy head make unleaded conversion even more UNnecessary than it would normally be considered. Just drive the car and enjoy!

Roger



I have just bought a 1970 Elan S4 SE dhc. This is my first Lotus so I
know I have a lot to learn so here is my first question of many....

It is possible to convert a standard valve head in to a big valve
head? If it is possible I was thinking of having the machine shop do
this when I get the head converted for unleaded fuel.


Thanks.












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[steveww]

I also hear that the Ford BDA has been used in the Elan and Spyder are
putting the new Ford Zetec in as well. Not really looking for masses of
power, the engine will need a rebuild anyway so I thought I would tweek
a little while I was at it.

***@***.***e:

[steveww]

That is what I thought. I am happy to sick with the 1558 TC and the low
100s bhp. Getting the Elan was not about having the fastest car but
about having fun. I had a Porsche 911 for 3 years but you are very
limited where you can really use it and keep your license not to mention
stay out of jail. Once you have done 165mph a few times the novelty
wears off, with the Elan you can do 70 be feel like 130

Brian Goodison wrote:

[lotuselan2]

BDR is based on the 1600 "Kent" block. I have a 1700 cc version in my +2. I
do not believe Lotus ever used this motor or any variants there of.

BDR is capable of 225HP at 1600cc with 500 mile rebuilds! This is the BDA
Formula Atlantic spec. At 1700 cc and with "road" cams and 45 mm Delortos it
has assume torque and can produce 190HP at 9000 RPM. I have this spec carbs and
cams but I have stock / blueprinted crank and rods so I can run it up to 7500
RPM now and then. I have all of the torque but less than the hirgh PRM
power.

BDR's are reliable and easy to maintain. Cosworth is a great company to deal
with for parts and advice (in US).

Ken
'69 +2 with BDR

[lotuselan2]

Besides Zetec the new Duratec (200+HP) is an great looking option. I do not
know anyone has fitted one yet. I friend is considering for a Europa
conversion.