Lotus Elan

Fast Road Twink: Two Engine Builders, Two Recommendations

PostPost by: Stevie-Heathie » Thu Feb 02, 2017 9:49 pm

Hi folks, I'm after some advice please. My Elan drives, handles and stops beautifully, but I think it would be enhanced by a sensible engine upgrade. I've spoken two well known Lotus mechanics in SE England and received two recommendations - please help me choose between them!

WHAT I'VE GOT:
- 1967 SE doc
- I suspect the engine may not be original, but it has been in the car since at least 1977:
- Engine block is a desirable 701M6015 casting, with the mysterious engine number "65M615"
- Head is stamped with something like "LPxx36",
- I have a receipt from 1977 saying the engine was "converted to big valve spec" - attached for nostalgia purposes - handwritten. Say ahhhh you old romantics.
- Not sure what cams are fitted
- Not sure if it has been converted to unleaded, (but if not then no problems have arisen in over a decade of running on unleaded)
- Cylinder head and bottom end gone through two years ago by PO, and the crank bearings were refreshed
- Weber 40s
- Recently tuned and dyno'd. Runs well, no smoke when warm. Dyno reading max power as c.100bhp
- Does not leak oil (!)
- Car ready to handle some more power - c/v joints, good brakes, sound chassis, roll cage, etc, etc.

WHAT I WOULD LIKE
- A reliable engine optimised for fast road use
- Perhaps 130-140 bhp
- Power and torque preferred lower in rev range if possible

And here are the two recommended approaches, as I said both from well known Lotus specialists:

RECOMMENDATION A
- Head off, block stays in car,
- Clean up manifolds (but no need to do a full-on porting job)
- L14 Cams
- Vernier gears to help with more accurate timing
- There will be some valve work required, the extent depends on what is currently fitted, condition, etc.
- Set up timing, carbs (maybe new jets)
- Then see how we go, perhaps think about a TTR fast road exhaust headers after living with new engine for a few months.

RECOMMENDATION B
- No need to remove head
- L2 Cams
- Valves should be compatible with L2 cams, but stand by to changeout / do whatever as necessary in case of surprises.
- Set up timing, carbs (maybe new jets)

So gents - what do you think?

Thanks in advance
Steve
Attachments
img_3780.jpg and
Receipt from 1977 - For You Old Romantics
1967 S3 SE DHC
1970 +2S (RIP - went out in a blaze of glory in 2001)
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PostPost by: Chrisis » Fri Feb 03, 2017 6:32 am

Hey Steve,

I'm building a lotus twin cam using a 701m L block and at the moment i choose to use a 1600 crank and a custom 83.5mm piston with either twin cam 125 rods or crossflow 1600 rods with a nice intruder on the piston giving me a higher compression.

generaly twin cams rev very well, but the 1600 crank should add a lot of torque and bring it lower in the rev range.

based on that i will have to use bigger valves, higher lift cams and a nice head porting.

my personal opinion for an engine upgrade do it right. check compression in each cylinder,but you really need to take everything apart and check everything crank, conrods and pistons. replace all shells and piston rings. if cylinders are ok do a honing on the block to run in the piston rings properly. then work your way up with the head. you need to check and probably replace worn valves. with a nice head porting and a higher lift- short duration cams will get you there,
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PostPost by: rgh0 » Fri Feb 03, 2017 9:48 am

Hi Steve
You have got the two classic responses to engine development in a twin cam for a road engine.
Is the 100 hp on the dyno a measured rear wheel HP or a calculated engine HP at the flywheel?> 100hp at the back wheels says you have a healthy Sprint spec engine in line with the invoice.

Builder Recommendation B
"The cheap hot up" bolting in a new cam or not so cheap depending on the margin the builder takes from you.
i.e.
Longer duration cam - L2 = 302 degrees more power but all top end and loss of mid range torque
but no increase in lift L2= .350 inches so cheap as no need to change valve and springs etc

In general this is a waste of time and money and a standard sprint or S/E spec engine is better for road use.

Builder Recommendation A
The well thought out but more expensive development step.
i.e.
Slight increase in cam duration L14= 280 degrees versus 272 degrees for a Sprint cam
Significant increase in valve lift L14= .415 versus .350 for S/E and L2 or '360 for Sprint cam requires replacement of valves, springs and followers to fit the higher lift in so more expensive

Combine this with adjustable cam sprockets for accurate cam timing, a TTR road exhaust, 33 mm or 34mm carb chokes and jetting, port clean up and slightly more aggressive advance curve on the dizzy and you will get your desired 130 to 140 hp at the flywheel from a 1558 twin cam at 6500 rpm with improved mid range torque.


All this assumes you don't touch the bottom end and its still at standard 82.55 mm and in good condition. Taking the bottom end out to 83.5 gives more, putting in a 1600 stroke crank give more again. Increasing the compression ratio gives more again, doing a more comprehensive porting job gives more again, a higher lift cam to say .440 and bigger valves gives more again, a steel bottom end for a reliable 7500 rpm top end gives more again. Lots of options and its a slippery slope but a 170 to 180 hp Elan on the road is truly a thing of joy and beauty.

I would work with builder A as that company sounds knowledgeable and trustworthy with their response to your inquiry

cheers
Rohan
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PostPost by: Stevie-Heathie » Fri Feb 03, 2017 10:53 am

Thanks so much for your thoughts gents.

Rohan - unfortunately it was 100bhp at the flywheel :-(

I agree - Option A sounds like the way to go. More ??? yes, but hopefully the "quality will be remembered long after the expense is forgotten" as they say.

Best
Steve
PS if you're interested in where the recommendations came from, feel free to PM me.
1967 S3 SE DHC
1970 +2S (RIP - went out in a blaze of glory in 2001)
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PostPost by: rgh0 » Fri Feb 03, 2017 11:11 am

Actual end cost will not be much more if any extra as the valve train probably needs rebuilding if 100hp is true engine hp and builder B would probably tell you that once the engine is pulled down and charge you more for it than builder A (who could have been more specific about the need for a non standard valve train to handle the higher lift)

cheers
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PostPost by: LorraineLH » Fri Feb 03, 2017 12:20 pm

Definitely go for recommendation A, you'd only be disappointed with B and wish you'd done it properly the first time. Head porting is all important to get that air flowing fast and smooth and make sure the cams aren't going to be too much of a pain in traffic. As well as the carb jets and chokes, ensure that your air filters aren't restrictive.
Go for it.....I'm sure your pockets are deep enough! :D
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PostPost by: ecamiel » Sat Feb 04, 2017 3:39 am

I found the TTR big bore competition headers gave a big mid range torque boost even on a relatively mild motor.
And 34 chokes didn't seem to hurt either. This was on a roughly 135 to 140 hp motor.
It doesn't make sense particularly but it was definitely true.
Also fooling with cam timing, 105 centers rather than 102 centers for example, calmed some wilder cams
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PostPost by: seniorchristo » Sat Feb 04, 2017 9:24 pm

Question
Would there be a significant increase in wear and tear on the L14 cams, followers etc. resulting from the higher lift and faster ramping of the cams?
Thanks,
Chris :)
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PostPost by: rgh0 » Sat Feb 04, 2017 10:01 pm

Higher lift short duration cams are certainly more critical to get right to avoid any wear problems.

Key things to watch.

Use cast iron cams with the thinner steel followers that are needed. Steel cams on steel followers can create galling problems
Phosphate or DLC coat the followers.
Keep spring pressure at maximum lift under 200 lbs
Use a good assembly lube and running in oil and running in procedure
Use a good synthetic oil after running in

Do it right and you will get a similar life to the normal setup. When you go to some of the extreme high ramp acceleration racing cams up around .510 lift things get tougher and valve train life drops significantly.

cheers
Rohan
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PostPost by: Stevie-Heathie » Sun Feb 05, 2017 10:20 am

So - Builder A it is then by a unanimous decision! I'll let you know how I get on, thanks for the responses!

Rohan:

Interesting point you raise about oils. I've always used Millers Classic 20-50 non-synthetic but with this hotter cam and the more precise timing / valve set up etc, would you say that would "promote" my engine to necessitate the super-duper synthetic version?

https://issuu.com/davidmccann3/docs/cla ... 0/13990480

Best
Steve
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PostPost by: Craven » Sun Feb 05, 2017 11:42 am

Hi Steve,
I don?t think this has been covered and you may be fully informed BUT, the L14 cam is best suited to a high compression ratio and this then introduces the possibility of valve piston contact with standard cut-out pistons etc etc. When I used these cams ( back in the 80?s ) it was necessary to deepen the valve spring pockets.
It was a lot of work and on the road the performance was of little different to a sprint spec engine car in the limited rev range of standard bottom end.
My advice, for what it?s worth, go for a BLUE PRINT rebuild to sprint spec.
Ron.
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PostPost by: Stevie-Heathie » Sun Feb 05, 2017 2:51 pm

Hi Ron,

You've got me thinking. If my 1977 receipt is correct then the valve gear should be all set for a couple of Sprint cams. Only forty years have passed after all :-)

Once we've stripped the head down and assessed the baseline, we'll take it from there.

Thanks for pointing out what is actually a very sensible approach.

Best
Steve
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PostPost by: Craven » Sun Feb 05, 2017 3:47 pm

Hi Steve,
You say ? For you old Romantics ? some would say just old.
Ron.
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PostPost by: jono » Mon Feb 06, 2017 9:30 am

...have you considered QED360 cams?

here is a link to my post following a rolling road session on my engine, based around those cams, which sounds like a very similar spec to what you have in mind, also the dyno result is posted as an attachment. You will see it gives very good torque. I should add that I have distributorless ignition which makes starting, running and idling great.

lotus-twincam-f39/rolling-road-session-report-t32563.html

I must say I am very pleased with my engine which is a delight to use and feels decently quick even in a lardy +2.

I'm just about to change over to a 3.77 diff (from 3.54) and a close ratio box which should make it even more fun.

Cheers

Jon
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PostPost by: rgh0 » Mon Feb 06, 2017 10:33 am

jono wrote:...have you considered QED360 cams?


Jon


The QED 360 cam is their Sprint cam equivalent. In an otherwise standard engine you will get around 125hp with it as Lotus did. If you play with a few things that Lotus could not do in a production engine such as, vernier cams for precise timing, better exhaust headers rather than the skinny cheap ones used by Lotus , more aggressive ignition timing, better intake air box on the carbs and bore the engine out to 1600cc and a bit higher compression ratio with a couple of head shaves and dyno carb set up then you will get around 130 hp and maybe a bit more.

If your after a 130+ hp road engine then that is not a bad way to go as it will certainly have great mid range torque.

cheers
Rohan
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