Lotus Elan

New Race engine build

PostPost by: rgh0 » Thu May 16, 2019 11:12 am

The engine I swapped out a year ago has finally made it onto the engine stand for a rebuild. I always love pulling the sump off a race engine - nice steel caps, Carrillo rods and Datsun crank :D

img_6317.jpg and


Bottom end will be a bearing check and replacement if needed and replacement of the front timing chain cover which has a crack in it plus routine replacement of seals and check of other components

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Need to decide whether I clean up the current head or swap the head for the spare McCoy conversion race head shown sitting on my bench . I will be rebuilding for using 98 Octane premium unleaded the same as the current race engine in the car versus Avgas that this engine was previously built for. i will use the head which gives me the needed 11 to 11.5 comp ratio the easiest, current head and pistons in this engine give me around 12.5 to 1

End result will be like the current engine in the Elan at around !80 hp at 7500 to 8500 rpm. Always nice to have a spare ready to swap in if needed. Hopefully I will not need it for a few years yet as I aim for 4+ years from a race engine and current engine has only been in the car for 1 1/2 years

cheers
Rohan
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PostPost by: Frogelan » Thu May 16, 2019 5:48 pm

Rohan

It is always very wholesome to have your views.

Race engines are quite fragile...have you any bright ideas as to how their life can be extended ?

Andrew
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PostPost by: seniorchristo » Thu May 16, 2019 6:50 pm

Rohan
What is head your thickness for 11 to 1 compression? I have access to a head with 4.59 thickness and I’m wondering if this is milled too far for street use with standard Lotus pistons. Are the optional head gaskets available suitable for use with 91 octane fuel?
Thanks!
Chris :)
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PostPost by: rgh0 » Fri May 17, 2019 12:21 am

Frogelan wrote:Rohan

It is always very wholesome to have your views.

Race engines are quite fragile...have you any bright ideas as to how their life can be extended ?

Andrew


Three general principles govern race engine life for a twin cam that I have found. Following these principles i have not had a race engine failure for over 20 years and I have just had to swap out engines for a refresh or rebuild to an upgraded specification about every 5 years.

1. Use the best quality components you can get and check them very very carefully to ensure no defects. In particular pay attention to the crank, rods and lubrication system and valve train components. Understand the failure modes of components and ensure you select and inspect to avoid these modes
2. Assembly the components very very carefully to get the right clearances and bolt torques
3. Be careful how you tune and run in the engine and how you use it in races and in particular limit the revs to around 8500 rpm maximum as beyond that the high vibration leads to a dramatically shorter life span.

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Rohan
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PostPost by: rgh0 » Fri May 17, 2019 12:39 am

seniorchristo wrote:Rohan
What is head your thickness for 11 to 1 compression? I have access to a head with 4.59 thickness and I’m wondering if this is milled too far for street use with standard Lotus pistons. Are the optional head gaskets available suitable for use with 91 octane fuel?
Thanks!
Chris :)


The head thickness is only part of the equation, its the starting point but so no simple answer as a number of other factors follow on.

e.g. In my 11 to 1 current race engine head thickness is 4.60 but more important is the actual chamber size and intruder size on the piston. The chambers are a little bigger than standard due to the bigger valves and the machining to un-shroud the inlet valve. The pistons have a 6 mm intruder to compensate for the bigger chambers and bigger cut outs in the piston to accommodate the higher lift cam and bigger valve.

I normally build based on a 1.2mm thick fibre composite head gasket that compresses to around 0.8 mm when assembled. I have built engines that have used 2 mm thick gaskets but my small local head gasket guy no longer has the material to make these. I know Cometic will make gaskets to whatever thickness you want but in general I would not use Cometic head gaskets on a twin cam as I know a number of people who have struggled to get them to seal. i think the twink head is just to flexible. I dont know if companies like Ajusa or Payen make fibre composite gaskets for a twin in different thicknesses but its worth enquiring

11 to 1 works on my race engine on Australia 98 octane ( R+M /2 method) premium unleaded in part due to the longer duration cam of seat to seat 300 degrees inlet and 285 exhaust. Potentially it could go a little higher and I may target the new build to around 11.3 to 1. On a road engine with standard 272 seat to east duration sprint cams you should limit to around 10.5 to 1 I believe for Australian 98 octane premium unleaded unless you have a full electronic ignition with knock sensors and retard based on that. A road engine with the maximum duration thats best on the road of around 285 degree seat to seat set of cams you may be able to push towards 11 to 1 with the standard ignition on Australian 98 octane fuel.

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