Lotus Elan and Lotus Elan Plus 2 Forums

My engine builder guru contends that a CR box wont last at 8000-9000 rpm.
There is some bearing that slings all its oil off and sh*ts the proverbial
bed spreading the gearbox oh-so-neatly all over the track and in the car.
He sez that only a dog box or equivalent will do. Are there any mods to
this bearing that will stop all this madness? Pete

Hi Pete,

What'd be the difference between the CR box and the dog box? Both would
still be running on the same bearing. Although, the dog box would most
definitely be running with s/c gears... so it's not just the issue of the
bearing but more the load that it carries?

Cheers,
Brian

----- Original Message -----
From: "Peter Steilberg" <***@***.***>

Sent: Wednesday, March 16, 2005 9:42 AM
Subject: [LotusElan.net] Prepping a tranny



My engine builder guru contends that a CR box wont last at 8000-9000 rpm.
There is some bearing that slings all its oil off and sh*ts the proverbial
bed spreading the gearbox oh-so-neatly all over the track and in the car.
He sez that only a dog box or equivalent will do. Are there any mods to
this bearing that will stop all this madness? Pete

Pete

3 basic style of box internals available for your elan

a. Orginal lotus / ford, close or semi close ratio - helical gears
syncro change , sleeve bearings on third motion shaft gears.

b. Racing conversion, various ratio sets -straight cut gears, syncro
change , needle bearings on 3rd motion shaft gears

c. As for b. but using dog change rather than syncro change.

I have run type a. and b. boxes in 8300 rpm engines that occasionally
get accidently overrevved into the 9000 rpm area. Never had a bearing
failure in lots of miles of either. I moved from orginal boxes to
straight cut boxes due to fatigue failure of the more delicate
helical gear teeth ( and the age of the avialalbe orginal internals
as they are all second hand now) compared to new and the more robust
inherent design of straight cut gear sets.

If buildng a serious 8000 to 9000 rpm engine then I would recomend
going to a racing conversion rather than orginal for reliability and
choice of ratio but this is driven more from the HP and torque your
putting though it rather than gear box speed and the use of needle
bearings in the racing conversions.

Use of a dog box versus syncro box is really a matter of personal
preference. All the true hard core racers say dog boxes are stronger
and change quicker. However the dogs wear quickly if your gear change
technique is not perfect at matching the revs. The pros whose gear
change techique is not good using dog boxs here in OZ wear out the
dogs in one race ! I think people who use dog boxes are those who
have sponsors to pay for the rebuilds.

I may be wrong with all of the above and your engine guru right. I
have never run a gear box with an engine that regularily is driven to
a 9000rpm limit and maybe all my experience breaks down at 8500rpm.
Then again if you have the time and money to do rebuilds after every
2nd raceweekend which is whats required with a 9000rpm engine then
you can also do gear box rebuilds at the same frequency.



regards
Rohan

Rohan: Actually -- I don't know how I ended up in this situation. I wanted
to build a really really reliable elan racer. Something fast in a vintage
context to play with all the illegal 356 porsche's.

So now I have a $15,000 all steel motor good to 9 grand and 170 hp -- stage
three. I want to race occasionally, drive occasionally, and just have fun,
but not worry about my engine popping a cork! So now it goes like this. If
you have elan, you need the motor, then you need the sump, then the drive
shafts, then you need the diff mountings, then you need the wheels blah blah
blah. Then at a certain point it sounds like, hey now you have a 170 hp
race elan and its gonna break the gearbox -- either because of power or
because of rpm. Then, even if I move to a dog box, I'll break that cuz I
can't shift. Yikes. I should have stuck with 7000 rpm.

Now, I hear that you can't do turn 3A at Pacific Raceways without a drysump
or it'll smoke the motor.

It's a vicious circle! I tellya!

they say that about all the fast cars



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Peter

I guess I have gone down the same route of you for much the same sort
of reasons, however I have done it progressively over 20 years and
found what breaks and what does not by experience. The internet and
this sort of group did not exist when I started unfortunately as it
would have saved me a bunch of money! At least in my historic racing
class in Australia the 356's and early 2 litre 911 are not a problem
legal or not. Its just the mid 70's 3 litre Carreras with $100,000
engines I struggle with. But my mate in his S4 7 with a little less
weight and little better handling has their measure as well !

Your engine may be good for 9000rpm but I would recommend a rev
limiter set at around 8000 to 8500 to avoid prematurely shortening
its life. It will rev to well over 9000 in a fraction of a second
with a missed gear change and at 9000rpm plus the life of bearings
and other components is getting very short and valve bounce becomes a
problem.

With a serious 170 plus hp engine and track work on reasonably sticky
tyes ( I use YOKO A032R soft 175 X 60 and Hoosier Street TD 185 X
60 ) you will start to break things in the drive train. Gear box as I
have said, diff output shafts, rear hub shafts and the original
wheels. Replacement of donuts with CV's or equivalent is a given. All
need replacing with stronger components. If you stiffen the springs
and shocks for better track handling then you wil start to bend and
crack the chassis and this will need strengthening also. The rear
hubs may also start to crack but that probably relates more to the
number of times you have them on and off the shafts. You also really
need a LSD to put the power on the ground coming out of a corner.

Oil surge is an issue and you need good sump baffling and an overfull
sump, or an accusump or a dry sump to get you through long tight RH
corners without loss of oil pressure, especially ones you accelerate
up to with little braking.

Also you need lots of detail work on the engine to actually keep a
high revving high hp twincam engine running properly and not break. I
have had issues with alternators, oil pumps and dizzies due to
vibration at high revs in the engine.

As you say a viscous circle or as I view it a never ending challenge
to build a a reliable racer at a reasonable cost. I have a new and
what I hope will be 180hp plus motor on the stand now. I am sure it
will show other weaknesses to be tackled in turn.

Staying with less than 7000rpm and say 145 to 150hp is certainly
easier but not nearly as much fun. Even at these lower power and rev
limits many of the other issues still need to be tackled. Good luck
wih your project and happy to talk about any or all of the issues you
will need to tackle

regards
Rohan

--- In ***@***.***, Peter Steilberg <psteilberg@m...>
wrote: