The Best 907 Engine Modifications
An overview
It
is a great myth that rebuilding the Lotus 907 engine found in the Jensen
Healey is unduly and excessively expensive. In the U.S. a home mechanic
can do a reasonable, stock rebuild for around $2,500. Aftermarket, forged
pistons will save you a lot of money- in my opinion, the only way to go.
If you live in England then you'll pay more, everything in England costs
more, but it's still not that bad. The Lotus power plant is the heart
and soul of the Jensen Healey and in my opinion well suited for some minor
performance enhancements. But keep in mind that these improvements are,
for the most part, recommended for engines that are being rebuilt or that
are in good condition. You'll see little benefit from strapping on new
parts to that old, tired lump if a complete rebuild is due.
The original 140 horse power Lotus 907 engine provided some exciting motoring
when the Jensen Healey was introduced. It was a huge improvement over
other British cars of the time and it's 16 valve engine was years ahead
of other production cars. However, you would be amazed at what an additional
40 to 50 HP provides as it completely transforms the car. If you have
the inclination, the time and the resources, it's an upgrade that's well
worth the investment.
Reusable camshaft cover
gaskets
Ease your
pain, end the burning-oil-on-the-exhaust-manifold syndrome. These handy
gaskets are relatively easy to install and fix a major design flaw. You
do need to clean out the threaded bolt housings thoroughly before installing
or they will not work. Only US $26 from the Club
Store.
Oversized stainless steel
exhaust valves
Don't
ever burn another exhaust valve. The 907 is famous for trashing them.
Get out of the victim cycle with a set of eight. Originally built for
motorcycles, our favorite Jensen Healey cylinder head shop (West Coast
Racing Head Services in Reseda, California) sources these out of Florida
and modifies the stem lengths. Not cheap at US$25 each, but a sound investment
and much better than the original Lotus part which is constructed from
a less durable stainless alloy.
Higher compression pistons
Sure, you can help support Lotus Development and spend US$650 a hole for
new Hepolite piston & liner assemblies, but why? In the U.S., and around
the world, JE
Pistons are the hot tip. Get them .035 oversized and have the worn
liners bored to match. Expect to pay $30-$70 per liner for boring. These
are forged, not cast like the Hepolites, expansion is almost the same.
Check with manufacturer's specs about bore size. I use 9.5:1 compression
for my everyday Jensen Healey. The finest money can buy, a set of four
runs about US$570 including wrist pins from the Club Store.
Camshafts
Unlike
many other engines, by virtue of its design, you can run fairly high-lift
cams in the 907 engine before it becomes undrivable. I advise prudence
with camshafts unless you only plan on driving your car on weekends or
to the races. Hot cams turn fuel economy into a dream and make hydrocarbons
go up as well. The
Lotus 107 camshafts are good, peppy camshafts for street use and won't
pound your stock valve train into oblivion prematurely. Great for under
5,500 RPM. If you are looking for a high horsepower, streetable 907 engine,
then the "104" cams are the way to go. New springs required.
JH Guru, Garry
Kemps comments on the 104 cams: "Personally I think the 104 is quite
a good cam: not particularly in a 2 litre and especially a low compression
engine but if they are in a 2.2 with decent compression (10+) they are
perfectly easy to get along with. I have seen in the states a bit of confusion
about what a 104 exactly is: it should be 272 degrees (at 10thou lash)
and 0.415" lift. I think there may be a few reprofiles around purporting
to be a 104 but really are just something "close enough". The
107 is a good all rounder but it does tend to run out of breath around
5500rpm : It'll pull up to 7000rpm OK but really its starting to lose
its edge after 5500 (in a 2.2 anyway). The 104 however will pull clean
and strong to 7000 rpm, it comes alive at about 3-4000 rpm but that's
not to say there's nothing below that, It'll tick over just fine at 900rpm
and is totally docile to use in traffic."
2.2 Litre Crankshaft
If you
want the fast street motor to keep up with modern iron on the road, a
stoker crank is a must. More torque means more power and we all like that.
Upgrading the 907 engine to the later 2.2 configuration in congunction
with a complete upgrade (higher
profile cams, higher compression pistons and 45mm Dellortos)
will result in a very pleasant, streetable, 200 plus horse
power engine. We recommend the reworked 2.2 cast, Vauxhall / Bedford crankshafts.
They're good up to 7000 rpm and are manufactured to the same standards
as the original crank found in the 907 engine. A 2.2 crank in your Lotus
907 engine can make your Jensen Healey or Jensen GT the smooth, fast road
car it was meant to be.
Lotus / Jensen Healey Engine
Main and Rod Bearings
Vandervell,
the original supplier to Lotus for their engine bearings is no longer
producing for the 907 engine. What's left in stock is crazy expensive-
+.20 rods are running about $250 and +.10 mains $360 per set! It's totally
out of control. The answer? Engine bearings made for a Holden 2 or 2.2
liter motor. We've sourced high quality trimetal copper-lead (the same
or better than original), main and rod bearings from the manufacturer
in Tasmaina, Australia. Technical notes: The new bearings do not drop
in and do need minor modification (this is how they avoid Lotus infringement
lawsuits in the UK). The 1, 2, 4, 5, main bearings have nips that are
slightly wider than the old Vandervell's and your block will need some
minor filing. The center #3 main bearing has the nip on the opposite side
so a small intent will need to filed on the other side, but both these
things should be quite easy to do yourself. I've done it in 30 minutes.
Adjustable Camshaft Gears
The newer
style half moon tooth belt is a must have for any big time performance
engine. A belt/gear set will set you back about US$900 (these have gotten
real expensive the last few years) but the piece of mind you get from
that heavy duty belt makes it something to consider. Positive grip prevents
belt jumping and improves torque off the crankshaft (dyno tests indicate
an extra two bhp). An added bonus, the belts last much longer (I change
mine at 40,000 mile intervals) and replacements now run about US$50 for
the quality US made version.
Multiple Spark Discharge
The MSD (Multiple Spark Discharge)
ignition control unit installs easily. Its' wires just plug onto extended
coil adaptors provided and the power lead. Takes only seconds to convert
back to stock configuration. Unit provides instant starts and better fuel
burning characteristics for better power and cleaner running throughout
the rpm range. Save your engine, over 80% of engine wear is attributable
to cold start cranking. I run mine with the stock distributor and points.
Points last about 40,000 miles and no reliability problems that many people
have with electronic ignition systems. I originally used this on a engine
that was only running on 2 1/2 cylinders for a few months and it actually
make the car drivable (it did get bad gas milage). For my money, the best
single improvement you can make on your engine. Smog legal in California.
Usually available from "performance" type auto-parts stores. The MSD Model
6a runs about$140, check around for best pricing.
Here are possible fixes-
1. Switch out your stock ballast resistor for a generic Chysler/Dodge
(part no. 3874767) ballast resistor or aftermarket Borg Warner (part no.
RUE 1) ballast resistor, also refered to as a coil resistor, about $5
at your local auto parts store, (as recommended in the MSD Manual). This
doesn't always work well and has different effects on each Jensen Healey.
In my case it works fine.
2. Purchase the MSD Tach Adapter for about $80.
NOTE:
The addition of the MSD will likely render your electric Smiths tach nonfunctional.
MSD offers a tach adaptor, which seems to work on some cars but not others.
Before purchasing an MSD Tach Adapter I recommend you contact the MSD
Tech Department and inquire about your car.
3. A permanent fix- send your tach to a place like North
Hollywood Speedometer and have the Smiths tach updated with an internal
circuit board that works with the MSD. A great fix that looks stock, about
$150, and a possible way to go if your speedo is tired and needs rebuilding
anyway.
Pertronix Ignitor
Favored
by many racers, the Pertronix Ignitor (formerly Per-Lux) is robust and
well constructed (quality made in the USA) with a model built specifically
for the 25D Lucas distributor used in the Jensen Healey (Model LU142).
It replaces the old-fashioned points and condensor for a reliable magnetic
"trigger". Never change those damn points again! Everything fits cleanly
and neatly inside the distributor housing, no unsightly external electric
box is needed as with the Crane-Allison brand electronic ignition- not
my favorite set-up (most of these seem to be improperly installed). If
you have an MSD, you don't need another electronic box on the car anyway.
The Pertronix Ignitor is a "stand alone" component and you'll notice improvement
over stock points even without the addition of an MSD unit. The Ignitor
is immune to dirt, oil, heat and moisture and switches twice the energy
of conventional systems.
Dellorto Carburetors
The U.S.
spec Strombergs are hard working, reliable units. They last for ages,
are resonably easy to rebuild and return great fuel economy. But the true
believers go with Dellortos. Looks alone should convert you. Not only
that, they run cleaner than the Strombergs and offer a performance edge
over the Federal fuel system. We all know that port on port carburetion
is superior. The 40mm pair that came on the non-Federal Jensen Healeys
works nicely, but the 45mm's offer an even greater performance edge. Dealers
like Richard Appleyard in the UK can make you a deal on a used set that's
rejetted properly with a second-hand manifold in the $1,000 range or check
the Club Store to see what's in stock. Dave Bean Engineering is selling
Weber kits at about US$1,800, the webers will always produce a mid-range
flat spot on the 907 engine that's almost impossible to eliminate, so
I prefer the improved Dellortos anyday and would skip the Webers on the
Lotus 907.
Lightened flywheel
Lighten
the original boat anchor? The really cool Tilton aluminum 7 pounder is
long gone these days. Other possible models can be had. The aluminum flywheel
Improves acceleration, especially from a dead stop. Consider this with
an overall engine upgrade package. A less costly alternative is a lightened
steel (stock) flywheel. Talk to your local machine shop and see what they
can do- realistically you won't be able to get this below 19 pounds without
some risk that it may blow apart during use. The aluminum flywheel will
make your pedal a little touchy, but well within most owners level of
tolerance for weekend and around town use. The stock flywheel is heavy
for a reason- it makes the engine run smoother at high RPM. If you're
building a go-fast engine and must have an light flywheel you will need
to take care and get a precision balance of the bottom end (which I recommend
on any kind of rebuild anyway).
Oil Pressure
Not normally
a problem for street Jensen Healeys, but a real issue for track racers
is the 907 engine oil pressure problem. More commonly seen during long,
hard, sweeping turns when a slight drop in pressure will be noticed. Severe
and extended high RPM use can turn this unnoticable problem into a oil
starvation issue with unexpected and expensive results. Track use will
create another set of problems as the 907 engine does not have the beefed
up bottom end seen on the 912 engine. There are several inexpensive fixes;
restrict oil flow to the head is the most effective and hinging the restrictor
baffles in the sump also can help. A strenghening plate will be the most
effective item you can install to make the 907 engine bullet proof on
the track. See an excellent
in-depth article about 907 oil circulation problems and cures for performance
engines here.
