Lotus Elan

Ford Crossflow bottom end question

PostPost by: nwbaxter66 » Fri Aug 25, 2017 4:15 am

I have been looking for a plus 2 to export to the US and have received a bunch of good advice from those on the forum - thank you.

I have found a good candidate for my project and during the due diligence process identified that the car doesn't have the original motor (nor chassis) which isn't a major issue for me, but that it does have a Ford Crossflow block rather than a Lotus block and that the resulting capacity of the engine is 1660 rather than the original Lotus one.

Absent the issue of originality, which frankly isn't a major issue to me, is there anything that I should be concerned in respect to this topic - is it a consideration in the pricing equation?

My inclination is that while it might have some consideration at the higher end of market prices, in the mid teens pricing of cars with Spyder chassis already, it probably doesn't have much impact.

Any thoughts or guidance on the topic?

Thx

Nick
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PostPost by: holywood3645 » Fri Aug 25, 2017 4:37 am

I don't think it make much difference. The 711M bottom end usually selected for a larger cc twin-cam rebuild.

I built a QED SS spec motor using 420S cams and, 711M crank and rods, to bring it to 1700cc its ` 145bhp and good torque. I think anything that raises torque in Plus 2 is a good thing. A friend recently installed an Zetec in his Plus 2 with very good results.

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PostPost by: rgh0 » Fri Aug 25, 2017 7:21 am

In general a bigger capacity engine for a Plus 2 is good and should not greatly affect the value if at all, while significantly improving the driving pleasure. I would want to check how the1600 block has been fitted and the differences allowed for.

i.e
What rods and pistons fitted and how much if any has the block has been decked
what front cover and / or spacer has been fitted
has a longer chain tensioner arm been fitted
what compression ratio
how have the wider engine mount bosses been allowed for
How has the taller engine been lowered to clear the bonnet

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PostPost by: holywood3645 » Wed Mar 23, 2022 12:47 am

I built the QED 1700cc 420S spec engine. Love the power and torque it provides in my S4.
The one thing I do not like is using the 122 link chain, while it worked fine, the acute angles look pretty drastic. The block is 4mm taller than the standard block.
Would a shorter chain work?
Motor is apart, water pump failure. (Yeah I know) I have new cassette Tyler ready to go.
Thanks
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PostPost by: 2cams70 » Wed Mar 23, 2022 4:16 am

A long stroke 711M block Twin Cam will generally not be as sweet, smooth or as free revving as pre-crossflow 1500cc block one. Depends on what you like. Note the counterweight weights on the standard 711M crank were originally determined based on being used with the heavier crossflow pistons and rods.

Lotus themselves never used the 1600cc block despite the fact that it would have been available to them from 1968.
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PostPost by: rgh0 » Wed Mar 23, 2022 6:39 am

2cams70 wrote:A long stroke 711M block Twin Cam will generally not be as sweet, smooth or as free revving as pre-crossflow 1500cc block one. Depends on what you like. Note the counterweight weights on the standard 711M crank were originally determined based on being used with the heavier crossflow pistons and rods.

Lotus themselves never used the 1600cc block despite the fact that it would have been available to them from 1968.


In a conventional inline 4 the crank counterweights are just balancing the crank big end journals. The pistons and rods are in opposing pairs and are in primary balance themselves so changing pistons and rods does not need a change in crank counter weights.

I agree the 1600cc will not be quite as smooth but this is mainly due to the secondary imbalance in an inline four which is produced by the slightly difference geometry of the rods at the top of the stroke from the bottom and the different stroke and rods lengths and weights will produce a different result compared to a 1500 engine and different again if you use the 125E rods with a 1600 crank. If you use light rods ( e.g. Carrillo's) and pistons ( e.g. JE forged) the difference is not noticeable

Why Lotus did not change to the 1600 block is not clear but my guess is Lotus was already working on the 9xx series engine in 1968 for the Lotus 62 which came out in 1969 and did not want to be bothered re-engineering the engine and cars to fit the taller 1600 block when it became available as they were already planning on replacing the twin cam with the 907 engine in a few years

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PostPost by: rgh0 » Wed Mar 23, 2022 6:50 am

holywood3645 wrote:I built the QED 1700cc 420S spec engine. Love the power and torque it provides in my S4.
The one thing I do not like is using the 122 link chain, while it worked fine, the acute angles look pretty drastic. The block is 4mm taller than the standard block.
Would a shorter chain work?
Motor is apart, water pump failure. (Yeah I know) I have new cassette Tyler ready to go.
Thanks
James


The standard 1600 block is 11 mm taller than a 1500 block hence the need for the longer chain when using this block at full height. There are multiple ways to set up a 1600 block depending on rods and piston deck height used and some of these require decking the block by significant amounts hence your only 4mm taller block and more extreme chain angles using the 122 link chain.

Taking 7 mm of the 1600 block significantly reduces the top deck strength and overall block rigidity and may give problems also.

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PostPost by: 512BB » Wed Mar 23, 2022 7:33 am

I realise that the original post was 5 years ago, but what the op asked about was hardly touched on, ie value with a different engine than an original twin cam, and in my opinion, those that did comment on those specifics, were plain wrong.

I have written so many times, that you alter these cars away from their original spec at detriment to your wallet. Further, to many, with an engine swap as described, you are making the car virtually unsaleable, unless it was cheap.

Imagine this senario, a fellow is looking to buy a +2, or indeed, an Elan, but only wants such a car with a crossflow engine!!! That fellow does not exist. Who on earth would want such a car, no one. If they wanted a modified car, they would buy a zetec monstrocity.

So move the thread into 2022 and my arguements are even more on point :lol: with most folk wanting as close to factory spec as is possible, and willing to pay a premium for it.

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PostPost by: holywood3645 » Wed Mar 23, 2022 7:37 am

Decked 711M Engine ran well for 8 years with no issues. Water pump failure has forced rebuild. I’m trying to figure out if the 120 link chain will work.
It’s an excellent build design plan from QED.
Any feedback on 120 link chain possibly is appreciated.

James

These ‘told you so and’ and “I know better’ remarks are self serving pointless and referring to ‘you Yanks’ is derogatory.
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PostPost by: 2cams70 » Wed Mar 23, 2022 8:16 am

Firstly giving due attention to the OP. A 711M Lotus Twin Cam will be fine. Many people have done it before. My only issue is if in the case you already have a 1500 block based Twin Cam whether it really is worth your while converting it to a 711M tall block twin Cam.

512BB wrote:I have written so many times, that you alter these cars away from their original spec at detriment to your wallet, full stop, or for you Yanks, period. Further, to many, with an engine swap as described, you are making the car virtually unsaleable, unless it was cheap.


Guess what - I agree with you on this Leslie. (I hope you've now forgiven me regarding the previous diff pinion preload discussion!!)

rgh0 wrote:In a conventional inline 4 the crank counterweights are just balancing the crank big end journals. The pistons and rods are in opposing pairs and are in primary balance themselves so changing pistons and rods does not need a change in crank counter weights.


I don't agree that the level of counterweighting is of no importance. If that was the case the OEM's would be making in line 4 cylinder crankshafts with no counterweights. They did originally (eg. Model T Ford engine has no crankshaft counterweights) but through development came to realize that there were benefits to be had in counterweighting the crankshaft. Whilst I agree that it is not necessary to change the level of counterweighting when changing pistons and rods I'd question whether or not the design is still optimized having not given it due consideration.

The Ford 1500 pushrod engine for example has less counterweighting than the Lotus Twin Cam. That's even with the stroke being the same between the two. The 1100, 1300 and 1600cc crossflow engines all have different counterweighting. Its clearly something that the OEM's consider carefully during the design stage but the aftermarket does not.
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PostPost by: rgh0 » Wed Mar 23, 2022 9:15 am

A good description of engine balance issues that's not very mathematical is here.

https://www.youtube.com/watch?v=82rxavW0A3c

There are a number of other videos in the series.

The counter weights on an inline 4 are about reducing bending stress in the crank by balancing the crank pins weight not about balancing out piston and rod weights in an inline 4, which is why the Model T could get away with none. This is also why a 8 counterweight crank as used by some designers for high performance 4 cylinder engines as it enable a lighter crank with less bending stress at high revs,

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PostPost by: 2cams70 » Wed Mar 23, 2022 9:33 am

rgh0 wrote:A good description of engine balance issues that's not very mathematical is here.

https://www.youtube.com/watch?v=82rxavW0A3c


What a waffler that guy is!!

I do know that the Lotus Twin cam engine has different counterweighting than the 1500 pushrod engine. They have different pistons and rods.

When Ford changed the design of the 1600cc crossflow engine and it went from a semi chambered head to a flat head and the combustion chamber went from being only partially in the piston to fully in the piston (i.e the piston became heavier as a result) they also increased the counterweighting of the crankshaft at the same time.
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PostPost by: rgh0 » Wed Mar 23, 2022 10:37 am

2cams70 wrote:
rgh0 wrote:A good description of engine balance issues that's not very mathematical is here.

https://www.youtube.com/watch?v=82rxavW0A3c


What a waffler that guy is!!

I do know that the Lotus Twin cam engine has different counterweighting than the 1500 pushrod engine. They have different pistons and rods.

When Ford changed the design of the 1600cc crossflow engine and it went from a semi chambered head to a flat head and the combustion chamber went from being only partially in the piston to fully in the piston (i.e the piston became heavier as a result) they also increased the counterweighting of the crankshaft at the same time.



Think about it as you appear to not understand the machine dynamics involved. If you think he is a waffler I can take you through the detailed maths if you want :lol:

Ford probably increased the counterweight size as they increased the crank journal weight which they had to balance. They probably increased the journal weights to accept the heavier piston weight without excess stresses on their accountant driven cast iron crank.

I will say it just one more time .... the crank counter weights on an inline 4 cylinder DO NOT balance the piston and rod weights

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PostPost by: 2cams70 » Wed Mar 23, 2022 11:34 am

rgh0 wrote: If you think he is a waffler I can take you through the detailed maths if you want


Sure Rohan. Take me through the maths. It's been a long time since I've been to uni but I'm sure I could understand at least some of the concepts even now! My partner (the whingeing Pom) has a degree in mathematics. I can give it to her to nut out if I don't understand!!!

rgh0 wrote:Ford probably increased the counterweight size as they increased the crank journal weight which they had to balance.


???? No they didn't!!!

This link i think may be a bit more enlightening

https://askingthelot.com/what-is-the-fu ... rankshaft/
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PostPost by: snowyelan » Wed Mar 23, 2022 5:30 pm

Back to the original question.
My thoughts on it are that is does slightly de-value the car, but not by much. My reasoning is that elans are becoming more of a collectors car than they were a few years ago, and if this trend continues then originality will matter more.
Personally I'd pick displacement over originality, but I think I'd be placed in the minority compared to the average buyer.
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