Lotus Elan

711M - how would you build it?

PostPost by: Tahoe » Fri Aug 05, 2011 4:42 pm

I was just given a really nice 711M short block with a bell housing, and would like to build it into a nice road engine. It shows no signs of any hard wear and has never been rebuilt, and it was stored properly. My friend has 3 711M's, all in the same condition and he needed a little extra room so he said take one of them. I probably won't start on it until next year sometime, but my goal is to build something that is extremely friendly on the street. Max HP isn't a concern here, but drivability is. Any words of wisdom on how you would build one and what power you would recommend? I haven't rule out fuel injection either. I've also located a spare weber head, but haven't had the time to see it yet since it's 500 miles from home. If it's a good head, I'll keep my engine as is, and use that head with the new block. Not in a panic since my engine runs great, but would like more power than what I have now, which appears to be stock HP.
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PostPost by: twincamman » Fri Aug 05, 2011 5:45 pm

Good question ----I have 711 cortina /pinto engine I considered converting to twin-cam ,but on further thinking I have decided to keep it push rod . the intent was to put it in the europa to replace the Renault or use it as a spare for the Super 7 or Elan in the event of a catastrophic twin-cam detonation as a stop gap so the car could be used while repairs were being done . The Renault is a delightful piece and I will keep it in the car .There is a set of twin carbs and manifold for the push rod and so the HP out put should be comparative and the thought of fooling around with spacers and longer chains and pistons etc etc is just foolish in my opinion -----so I recommend a good push rod with twin dcoe s is as good a twin cam any day and a lot simpler to keep running and in tune AND WHO USES 8000 RPM ON THE STREET ANY HOW -------ed
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PostPost by: pauljones » Fri Aug 05, 2011 6:59 pm

Russ,

Sounds like a good spread of torque is what your after,me too,and im in the same position.My 711m block will have a longer stroke 82 or 84mm,84mm pistons and rods to suit,with a flywheel,all in steel.Around 3.5k worth.With the head CNC milled and one off cams made to suit,add another 2k.Front cover for a tall block and better water pump with chain,spacer ect,add yet another 1k,Most of the bits coming from Burton power.

This is the quote I got back from Burtons early last year when I asked the same question,hence why it can wait.I wont bore you with the rest of the answer except for the mention of power.This lot should be good for 170 to 180 horse with 160 to 170 torque.With the rest of the bill making near the 10k mark,my pockets not that big.

To be honest,as I have the bare block and the Emerald EFI.I would consider using an alloy crossflow head.Alot cheaper to build,And consider it as an EFI 1700cc crosser,Perhaps a small amount off the power and torque,but a hell of a lot cheaper.

Paul
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PostPost by: bcmc33 » Fri Aug 05, 2011 9:53 pm

Hi Russ,

I now have a 711M engine in my Sprint based on a new block from Ford. It was bored to Twink standard size (3.250") and decked to suit a QED420 head. This gives 1661cc with hopefully more torque with 10.5:1 CR.
I currently have it running on EFI settings tuned to my old Twink QED420 engine with 83.25mm bores - and it goes very well (for English speakers - it goes like "stink"). I have still to complete another 20 running-in cycles this coming weekend in order to have it ready for the rolling-road set-up on Monday afternoon at Aldon.
Brian Clarke
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PostPost by: Tahoe » Sat Aug 06, 2011 3:22 am

I guess I need to do more research. I would be very happy to be around the 150 HP range with excellent torque. I'd like to stay twincam, and I'd really like to do EFI. I need to start thinking about the overall cost and the other changes I'll want to do as well. I'd love to find a close ratio box to go with this engine or the gears to convert mine. I admit I haven't looked for close ratio gears. Are they available aftermarket or will I need to source original ones? I've decided not to go 5 speed at any point and will stick with the 4 speed. I feel good about taking my time doing this and keeping my current set up as long as possible so I can stay on the road.
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PostPost by: garyeanderson » Sat Aug 06, 2011 6:44 am

http://www.lotuselan.net/cgi-bin/search ... oom_sort=0

elan-archive-f16/1700cc-stock-twin-cam-block-t11169.html

145 to 160 hp with 130ish lb/ft in a 1700 are good numbers for a street engine. 1600 crossflow crank in 711 blocks with .100 to yield 1700 is an economical way to start. Keep the cam duration as short as possible with as much lift a you can on the intake, I don't think that any twin cam has much of a problem exhausting the spent gases and I would tend to keep this near to stock as possible for street use.

some old Dyno sheets at
elan-racing-f12/bsfc-for-racing-twincam-t21422.html
The pink dyno sheet is the engine in my S2 Elan that is running now, It does not like to be dragged trough town at 25 mph (it wants to either slow down or speed up but a constant speed below 35 is a bit of a pain). It is very willing to put a smile on your face at the drop of the pedal once it' on the cam.

It doesn't hurt any that the my Elan is a stripped out rat and weighs in at under 1300 lbs.
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PostPost by: cabc26b » Sun Aug 07, 2011 7:20 pm

+1 on P-A's advice -

Not a lot to do on the bottom end work if you keep to a 77mm crank . I would look into having a discussion with John up at omnitech on head, carbs, cams exhaust ( if you have the budget, send the head up to him) John has a handle on the balance between drivable and power

G
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PostPost by: pauljones » Sun Aug 07, 2011 7:43 pm

Don't forget the likes of Ric Wood, CNC'd head with larger valves, the sizes of which caused a bit of a debate, and cams ground to suit. Total of around 2k. Big money I know. Not had this done myself, but a friend has a full engine from him in a cobra replica that fly's.
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PostPost by: rgh0 » Mon Aug 08, 2011 4:32 am

i agree keep the bottom end standard except for twin cam pistons with big cutouts for the bigger valves and cam and bored out for 1700cc.

With a road ported head with 1.625 /1.4 inch valves set up for 10.5 comp ratio and high lift short duration cams ( eg QED 420 or John McCoys .440 lift 280 degree or the equivalent .410 lift cam from Dave Bean) you should generate above 150 hp in a 1700 block at 6500 to 7000 rpm

cheers
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PostPost by: bcmc33 » Tue Aug 09, 2011 7:43 pm

Just to let you know that the rolling-road results for my new tall-block 1661cc engine gave me 125.6bhp @ 5884rpm and 118 lbs ft of torque at the wheels.
The bhp is what I expected, but the torque is a little more than expected.

I know it's not sufficiently accurate, but assuming 20% transmission losses, the flywheel power would be 157bhp and the torque 147 lbs ft.

As it happens, I'm only interested in what I have at the rear wheels. :)

All I have to do now is cure an oil leak before Saturday.
Brian Clarke
(1972 Sprint 5 EFI)

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PostPost by: pauljones » Tue Aug 09, 2011 7:51 pm

Brian,

That's a good set of numbers, can you post your specs please?
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PostPost by: bcmc33 » Tue Aug 09, 2011 8:50 pm

pauljones915 wrote:Brian,

That's a good set of numbers, can you post your specs please?

Paul,

The engine was based on a brand new 1600 block from Ford US. I had built up all the parts to make a tall block engine with an old 711M block, crank and con-rods etc to be mated to my old Twink head modified to 420 level.
My engine man (Paul Exon) doubted that the block was good enough to bore out for the planned 83.25 pistons for a reliable full 1700cc - so, in a mad moment, I bit the bullet and ordered a new block on the basis that it would have the potential of a 40 year life.
We then decided to bore the block to the standard Twink size of 82.55 and decked to suit the 420 head for a CR of 10.5:1.

I'm impressed with the performance of the flat torque curve from 2500 to 5500 rpm, and the car drove perfectly in rush hour traffic yesterday.
Brian Clarke
(1972 Sprint 5 EFI)

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PostPost by: Tahoe » Wed Aug 10, 2011 3:13 pm

Thanks for the excellent advise and resources! I've been computerless for several days and haven't had a chance to catch up. You guys are getting me excited about doing this build, can't wait to get started. Getting ready to leave Monday morning for Laguna Seca fo a week so won't have a computer for another week. I'll take pics af all the Elans and 26R's I see there.
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