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Learning how to build Lotus Seven replicas...together!
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PostPosted: August 20, 2016, 9:24 am 
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Like many of you I have always considered middies to be the ultimate road handler, racer, sexier sportscar. I would also consider rear engines (behind the rear wheels) a thing of the past, etc. Am I right, am I wrong?

I read this morning the following a professionally written article that may change my mind:

http://www.caranddriver.com/features/th ... est-page-3

In this piece the author and colleagues test two expensive Porsche monsters the 911 GT3 and the Cayman. The former as you recall is the rear engine traditional type, and the Cayman the modern middy. To my surprise the rear engine 911 GT3 came out winning over a series of tests involving handling and other things. I personally owned two three rear engine cars: a fiat 600, a Simca something, and of course a Porsche carrera. I remember driving the Porsche at the speed of light (200 kmh) which was allowed where I lived then, never feeling a sense of instability. Cornering displayed yes oversteering characteristics but I was factoring that in my driving.

Now my theoretical question to the forum is this. Why rear driver engines are not even part of the conversation in this forum. What I see is middies and Front engines. I think that there is a huge potential for the locost to be built like the Silva (UK) with front wheel transaxles turned rear transaxles. Even the good old air VWs and Corvairs would possibly make decent rigs. What do you think?


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PostPosted: August 20, 2016, 9:56 am 
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Because this entire forum was created to help people build a Lotus 7 type car, not necessarily to build the best-handling car ever. There are mid-engine cars here and in fact there's an entire sub-folder for them which you're in now. Keep in mind that the Porsche 911 has had about 60 years to solve their over steering issues, so it may not be fair to compare it as being better than a newcomer.

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PostPosted: August 20, 2016, 10:11 am 
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KB58 wrote:
Because this entire forum was created to help people build a Lotus 7 type car, not necessarily to build the best-handling car ever. There are mid-engine cars here and in fact there's an entire sub-folder for them which you're in now. Keep in mind that the Porsche 911 has had about 60 years to solve their over steering issues, so it may not be fair to compare it as being better than a newcomer.


Thanks,
My question was not meant to be a negative comment about this forum which I have enjoyed since 2002 or 2003.
Here I failed to acknowledge the fact that nowadays FWD transaxles moved to the rear are often called middies.
I am hoping to start a discussion of the respective merits of both technologies RRs and Middies :)


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PostPosted: August 20, 2016, 11:24 am 
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I have the molds for Dick Tatum's Crusader street car which was essentially a two-place Formula Vee.
Rear engine on a VW drive-train and suspension it still worked pretty well.
No room in font of the rear wheel center-line for a mid-engine so it's to remain rear engine.
Not being a big fan of the VW I'm looking to use a bike engine,
But it will still be rear mounted and hopefully lighter with a lot more power.

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PostPosted: August 20, 2016, 3:21 pm 
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RichardSIA wrote:
I have the molds for Dick Tatum's Crusader street car which was essentially a two-place Formula Vee.
Rear engine on a VW drive-train and suspension it still worked pretty well.
No room in font of the rear wheel center-line for a mid-engine so it's to remain rear engine.
Not being a big fan of the VW I'm looking to use a bike engine,
But it will still be rear mounted and hopefully lighter with a lot more power.



Hi Richard,
It sounds like an exciting project. I guess you would get yoursek one of these diffs with a big sproket around it and bolt on a bike screemer like the hayabusa .
I have looked up your post on the subject:
http://www.locostusa.com/forums/viewtop ... 18&t=15677

It seems to me that this machine could also live happy with a race version of the Corvair flat 6...or am I biaised?


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PostPosted: August 20, 2016, 6:20 pm 
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Finished car is very light, even a stock "40 Horse" VW is enough for most folk.
I never got to weigh the one I nearly completed several years ago.

Kind of looking for an FJR1300 engine for the next one and hope to do an even lighter build.
Should be insanely fast if I can carry off the build I have planned.

Bike engine is all I can think of that would be lighter than a VW to help with weight bias.
Corvair is heavier than VW and this car is pretty short wheelbase.
Need enough weight on the front wheels for steering input to affect the direction of the car. :wink:

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PostPosted: August 21, 2016, 4:02 am 
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phil wrote:
Why rear driver engines are not even part of the conversation in this forum?
Affordable engine/trans setups to use in a rear engine layout are not typically desirable. Desirable engine/trans setups to use in a rear engine layout are not typically affordable. Then consider that the general layout doesn't have the best reputation. But yes, for those who understand how to capitalize on it, the rear engine layout also has more overall traction potential.

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PostPosted: August 21, 2016, 8:43 am 
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My takeaway from that article was it was not exactly an apples to apples test . I don't think one can make a broad-brush conclusion that rear engine beats mid engine. It doesn't prove, or even suggest, rear enginee over mid engine. Only this car against that car. Even that article mentions this:

Attachment:
Capture.JPG
Capture.JPG [ 75.26 KiB | Viewed 3370 times ]


And don't forget, even our Locost builds of what we call Front engine are, by definition, mid engine cars. The engine is located between the front and rear wheels

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PostPosted: August 21, 2016, 10:36 am 
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rx7locost wrote:
My takeaway from that article was it was not exactly an apples to apples test . I don't think one can make a broad-brush conclusion that rear engine beats mid engine. It doesn't prove, or even suggest, rear enginee over mid engine. Only this car against that car. Even that article mentions this:

Attachment:
Capture.JPG


And don't forget, even our Locost builds of what we call Front engine are, by definition, mid engine cars. The engine is located between the front and rear wheels



I tend to share your points, or most of them, Certainly your last one about Front engine sevens. http://www.photodrop.com/galleries/ff0ccd6a shows my first seven engine bay.


YOUR OTHER POINTS.

My goal is not to argue rear engines against mid engines. This cannot been argued, not even by experts, because to many factors are at play. And I am not an expert. Just a curious hobby builder with little experience with suspensions. On this I believe that suspension is the key factor in engine location. A rear engine provides maximum traction under straight line acceleration and over steers in cornering. Porsche has spent six decades sweating the balance and the 911 is a case in point to the fact that rear engines have their merits. At my humble level, I hope to get deep into the relationship between rear engine position and suspension. When I say "humble" this is what I mean. I have a steep learning curve ahead. I will be designing my second Seven around a flat six Corvair engine with transaxle. Unless I change my mind, this engine will be left in the Chevy Corvair original position which is rear. I will have to design my own suspension and I am at ground zero.


Last edited by phil on August 21, 2016, 5:42 pm, edited 3 times in total.

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PostPosted: August 21, 2016, 10:55 am 
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"...........Chevy Corvair original position which is rear. I will have to design my own suspension and I am at ground zero."

I think you should build it! We'll help.

I have to confess I got my drivers license in the family '61 Corvair (divorce settlement) and I always dreamed of pulling the whole rear assembly and building something less "family car". Mom would't allow it.

Swing axles or the later setup?


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PostPosted: August 21, 2016, 11:10 am 
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Bobber wrote:
"...........Chevy Corvair original position which is rear. I will have to design my own suspension and I am at ground zero."

I think you should build it! We'll help.

I have to confess I got my drivers license in the family '61 Corvair (divorce settlement) and I always dreamed of pulling the whole rear assembly and building something less "family car". Mom would't allow it.

Swing axles or the later setup?


Thanks for your positive feedback. You should try again with your mother.
The rear axles were drastically modified by GM in 1965 models, This they say improved stability. I will not use the Chevy's hardware but build my own, perhaps involving a Dedion control bar and trailing arms+ watts lateral control device... (see Steve Graber and La Bala)
:cheers:


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PostPosted: August 21, 2016, 11:45 am 
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phil wrote:
Bobber wrote:
"...........Chevy Corvair original position which is rear. I will have to design my own suspension and I am at ground zero."

I think you should build it! We'll help.

I have to confess I got my drivers license in the family '61 Corvair (divorce settlement) and I always dreamed of pulling the whole rear assembly and building something less "family car". Mom would't allow it.

Swing axles or the later setup?


Thanks for your positive feedback. You should try again with your mother.
The rear axles were drastically modified by GM in 1965 models, This they say improved stability. I will not use the Chevy's hardware but build my own, perhaps involving a Dedion control bar and trailing arms+ watts lateral control device... (see Steve Graber and La Bala)
:cheers:


I think you should build it too. I think we have had few DeDion builds lately (ever?). I thought about going DeDion when building mine. I ended up going with full independent rear suspension.

It is all about the learning and sharing. If you decide to move the Corvair engine forward, it won't be the first decision change you make. I assure you of that. :mrgreen:

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PostPosted: August 21, 2016, 1:05 pm 
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I've had a few Corvairs and run them hard.
The '65 up suspension is similar to earlier 'Vette and actually works fairly well.
With a Seven type build you are going to shed a lot of weight.
So you need to consider how you will move some of the remaining weight forward to retain proper weight balance.
You may want a further forward seating position than standard since YOU are also a significant weight.

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PostPosted: August 21, 2016, 2:09 pm 
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I trust people understand the definition of a mid engined car, "A mid-engine layout describes the placement of an automobile engine between the rear and front axles". So my 7 is a mid engined car.

Graham


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PostPosted: August 21, 2016, 5:11 pm 
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RichardSIA wrote:
I've had a few Corvairs and run them hard.
The '65 up suspension is similar to earlier 'Vette and actually works fairly well.
With a Seven type build you are going to shed a lot of weight.
So you need to consider how you will move some of the remaining weight forward to retain proper weight balance.
You may want a further forward seating position than standard since YOU are also a significant weight.


Yes,
I will move the cockpit forward by about 6 to 8 ". Set a sizeable gas tank and battery close to the front wheels. There will be an oil tank (crankcase oil) piped and an oil cooler there too. And of course the spare wheel and the boot (or trunk) as well as anything else that has some weight. Tentative goal would be front 40 rear 60 wheel distribution, if I can.

The main area of research and experimentation will be (maybe) a "air spring Gs compensation system". I will talk later in detail about this subject which I brought up 10 years ago and dropped. In a nutshell: a computer sensing Gs controlling 4 air springs' pressure reacting to acceleration , deceleration, centrifugal forces to help the car in hard racing conditions. All this is only in my head , but some of my relatives with advanced computer knowledge are telling me that this is a good idea. (Not a new idea however, Citroen and BMC both had a shot at it in the 1070s).


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