Lotus Elan and Lotus Elan Plus 2 Forums

Agreed, if one particular issue. Has one particular solution.
Wiki-coming soon, if one had the time to compile the pertinent information.

Thanks again lotuselan.net

Hi Sandy

What Rohan says is correct - we'll find it easier to help if you stick to one thread for any particular issue.

There is also a matter of what is called "netiquette" or more specifically "forum etiquette". A little harder to define, but your posting habits are odd enough to annoy some people (ask me how I know! ). Not that I am an arbiter of etiquette, of course.. but just try to keep it on one thread, if it relates to one issue. I am sure that - once you get used to it - you'll find it easier to get the answers you are looking for.


Cheers
JonB

as already stated: way too much compression even though the the head has a height of 116,96 and 38cc head volume: which is standard. static "measurement" (clay) revealed more than 2mm clearance between inlet valve and piston at tdc. the current pistons have a 3mm dome which lead (twice now) to the following gasket condition. i'd like to shave as little as necessary, let's say 1 mil off of the pistons!! anxious to get some opinions - hope this "letter" achieves the target of being received where it M U S T get/be sandy

el-saturn wrote:as already stated: way too much compression even though the the head has a height of 116,96 and 38cc head volume: which is standard. static "measurement" (clay) revealed more than 2mm clearance between inlet valve and piston at tdc. the current pistons have a 3mm dome which lead (twice now) to the following gasket condition. i'd like to shave as little as necessary, let's say 1 mil off of the pistons!! anxious to get some opinions - hope this "letter" achieves the target of being received where it M U S T get/be sandy

Hi Sandy
I would question the "way to much compression". You need to do a full set of measurements and full compression ratio calculation before you can say that. Like I said before the gasket should be good for 13:1 and you will not be running that on road fuel without serious pre-ignition and knock. Using a 87mm bore gasket certainly would make the fire-ring area around No 4 cylinder to the water passage weaker and the most likely point of failure but there may be something else going on like pre-ignition or overly advance timing leading to higher than normal cylinder pressures.

I use a 85mm gasket bore in my 83.5mm bore engines and have never had a failure like yours when running 13:1 on Avgas let alone 11:1 on road fuel'

Below are the calculations for a standard sprint 1558cc specification engine and for my last 1596 cc ( 83.5mm bore) race engine build designed to run on 98 octane ( R+M/2) premium unleaded and relatively short duration cams (300 degrees seat to seat inlet and 285 exhaust) This build was deliberately conservative as not much data around on race engines using standard fuels and for the one I am building now I will aim for maybe 11.3 comp ratio.

Note the race engine has a standard thickness head with a slightly larger than standard head chamber volume due to larger valves and relieving around the valves for improved breathing. The piston is a JE piston with a 5mm intruder height and larger cut outs having been machined down from the normal 6 mm you see supplied by most race piston makers.


Compression ratio :
swept volume 389.37 cc 398.38 cc

head chamber volume 36.00 cc 41.00 cc
gasket space volume 3.29 cc 3.97 cc
deck clearance volume 2.76 cc 2.82 cc
piston head land volume 0.95 cc 0.73 cc
piston intrusion volume -1.00 cc -7.63 cc

Clearance volume 41.99 cc 40.89 cc
CR 10.27 10.74

Your engine with 38 cc combustion chamber and larger bore gasket and 3 mm intruder height I would expect to be around 11:1 at most and "not way to much" but it depends on the other measurements also such as piston deck to block top clearance and clearance down the side of the piston to the top ring ( piston head land volume)

Getting a 12 or 13:1 comp ratio in a Twin Cam takes some work with a racing valve engine as the valves have to be seated further into the head to clear each other and it generally requires substantial shaving of the head to reduce the combustion chamber size down into the 35 cc region

cheers
Rohan

Frankly speaking - and I always like to be frank - I have to confess that for me at least the whole subject of Sandy and his gasket problems is becoming completely ridiculous. Way, way more complex than it needs to be. The great gods Chapman and Duckworth with their KISS (Keep It Simple Stupid) philosophy would not be impressed. I thought I explained a perfectly simple method requiring grade 2 maths only for measuring the compression ratio Sandy has at the moment in the post about Rohan's engine build that Sandy inexplicably jumped to and yet all ears seem to be closed. I don't mind if people want to tell me it's rubbish and won't work or it's too hard - after all I enjoy a good debate!!

Maybe it's all because I don't happen to own a Lotus Elan. Not that I have anything against them or wouldn't wish to own one. There!!! I've blown my own gasket and I've had enough!!!

we do have one thing in common: the 505 which i also drove! ..........but i just didnt get the answers i wanted (the math is simple) from people who really work with engines and due to their experience SEE the problem AND even a crazy solution - as you do at (lets say) brands when there's thermal problems and NO workshop sandy

rgh0 wrote:

Compression ratio :
swept volume 389.37 cc 398.38 cc

head chamber volume 36.00 cc 41.00 cc
gasket space volume 3.29 cc 3.97 cc
deck clearance volume 2.76 cc 2.82 cc
piston head land volume 0.95 cc 0.73 cc
piston intrusion volume -1.00 cc -7.63 cc

Clearance volume 41.99 cc 40.89 cc
CR 10.27 10.74

cheers
Rohan

Rohan, can I ask about your standard and race head gasket volumes - what diameter and thickness are they based on?

You will need a good knowledge of geometry and some fancy measuring instruments in order to accurately calculate the volume of those cut outs which look as if they will contribute quite a bit to the compression space.

i once had to copy parts, so i'm pretty well equipped - BUT making things simple: we have appr. 3cc for the INLET and close to 2cc for the OUTLET cutouts - weighed in gramms using fresh water and adding some guessing due to surface tension! Sandy ps - the water stays if you position your piston properly AND ........wife still hates seeing pistons in HER kitchen!

2cams70 wrote:Frankly speaking - and I always like to be frank - I have to confess that for me at least the whole subject of Sandy and his gasket problems is becoming completely ridiculous. Way, way more complex than it needs to be. The great gods Chapman and Duckworth with their KISS (Keep It Simple Stupid) philosophy would not be impressed. I thought I explained a perfectly simple method requiring grade 2 maths only for measuring the compression ratio Sandy has at the moment in the post about Rohan's engine build that Sandy inexplicably jumped to and yet all ears seem to be closed. I don't mind if people want to tell me it's rubbish and won't work or it's too hard - after all I enjoy a good debate!!

Maybe it's all because I don't happen to own a Lotus Elan. Not that I have anything against them or wouldn't wish to own one. There!!! I've blown my own gasket and I've had enough!!!

I am happy to try to try to each some of the intricacies of engine building and even if Sandy does not want to listen initially...he will have to eventually as engineering is not really a matter of opinion.... in the meantime maybe others will benefit

I try to be accurate in what I say but it is hard to summarise it all in a paragraph or two. Hence I apologise if my posts get to long and difficult to follow at times. I find it much easier sketching on a whiteboard while I talk when teaching young graduate engineers about the real world challenges and how to solve them.

cheers
Rohan

promotor wrote:

rgh0 wrote:

Compression ratio :
swept volume 389.37 cc 398.38 cc

head chamber volume 36.00 cc 41.00 cc
gasket space volume 3.29 cc 3.97 cc
deck clearance volume 2.76 cc 2.82 cc
piston head land volume 0.95 cc 0.73 cc
piston intrusion volume -1.00 cc -7.63 cc

Clearance volume 41.99 cc 40.89 cc
CR 10.27 10.74

cheers
Rohan

Rohan, can I ask about your standard and race head gasket volumes - what diameter and thickness are they based on?

For the standard gasket I use 83.5 mm dia bore with compressed thickness of 0.6 mm. For my composite fibre gaskets I use in hte race engines its 85.0 mm bore with 0.7 mm compressed thickness. Its hard to measure the actual compressed thickness of the gaskets as they spring back a little once removed so these are my best estimates

cheers
Rohan

Guys - I don't really wish to blow my own horn here but I do happen to have graduated from university with a Bachelor of Mechanical Engineering degree with 27 years post graduate experience - 22 of which have been in the automotive industry working for two leading vehicle manufacturers (I won't say which). I've had some great times, especially in Product Planning where you get to drive and benchmark all sort of vehicles under all sorts of conditions. Even driven on the odd proving ground or two. I've enjoyed mucking around with all things mechanical and electronic for as long as I can remember.

I don't understand why we are using such a complicated method to determine compression ratio when all we are trying to do so at this stage is to get an idea of what it currently is and to establish whether or not it is reasonable. IF it turns out to be unreasonable only then I agree the combustion chambers should be cc'd, piston intruder volumes calculated to determine how much to shave off, etc. At this stage though it isn't necessary. Just fill up the cylinders and measure the volumes. No need to calculate.

el-saturn wrote:we do have one thing in common: the 505 which i also drove

At least Sandy we share some things in common. I bought a 505 wagon to haul 4 kids + friends around. It's an 8 seater with three rows of forward facing (yes forward facing!) seats. There's no other wagon like it. I bought it to avoid having to buy one of those abomination on wheels SUV's. I'm not proud. I don't need to sit up high looking down at the traffic. I get my revenge on all the SUV's when I'm driving/testing big trucks! The SUV's look like ants!

Seriously though the suspension set up in that wagon is quite remarkable. The ride versus handling balance is excellent and that long travel suspension is something special. Speed humps? What speed humps?

My point was about, quote ?perfectly simple method? a calculation, not a practical assessment.