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Learning how to build Lotus Seven replicas...together!
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PostPosted: August 25, 2016, 4:02 pm 
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mainlandboy wrote:
TRX wrote:
I think the whole "front-mid" expression is more for marketing than anything else. For example, if the furthest forward point on your Locost engine are the heads of the water pump pulley bolts, and the front face of these bolts stick past the front axle centerline by 1mm, do you really think that you can say you've converted your car to a mid engine car (or "front-mid" if you prefer) just by shaving 2mm off the end faces of the bolt heads? I don't think so.


Agreed 100 percent. The term muddies the waters.


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PostPosted: August 25, 2016, 7:16 pm 
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[quote="DeanD3W"]Hi Phil,
Won't the axle tube need to go either above or below the transaxle, since to reach around the front will be too great a distance?


Yes, I will have to figure it out. Probably arching above the transmission. I will mull over your point about the effect of a tilting suspension. I still have to to a good deal of reading. :)


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PostPosted: August 26, 2016, 11:46 am 
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carguy123 wrote:
It took Porsche 60 years to tame the rear engine configuration so how long will it take you?
So it took them 60 years to figure out that things like toe control, camber control, tire width stagger, and track width all actually matter...Of course, it also took competition/enthusiast drivers considerably less time to simply figure out the handling dynamics, and subsequently how to drive around all of that...With great success, I might add. Already knowing as much as we do today, learned largely from others' past mistakes, gives the astute and studious observer a significant leg up on Ferdinand and Ferry Porsche for development and tuning a rear engine car. Which should also makes it easier for the driver to get 'up to speed' as well.


phil wrote:
I will mull over your point about the effect of a tilting suspension. I still have to to a good deal of reading. :)
Leaning the car can't really change how much total weight gets transferred to any significant degree, but can adjust how much gets transferred to/from the front tires vs the rear tires during cornering. This gives you the ability to actively adjust the handling balance. The other main benefit of better contact patch control wouldn't apply to the DeDion rear suspension.

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Last edited by Driven5 on August 30, 2016, 1:39 pm, edited 1 time in total.

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PostPosted: August 28, 2016, 1:45 am 
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Spent the day watching every configuration run at the Ferrari Club Hill-Climb today.

Every car there was quite capable as all were fully engineered to be the best possible for their configuration.
So it seems to matter less where the engine is placed than how the rest of the car is set up to work with that.

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Last edited by RichardSIA on August 28, 2016, 12:36 pm, edited 1 time in total.

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PostPosted: August 28, 2016, 3:32 am 
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RichardSIA wrote:
Spent the day watching every configuration run at the Ferrari Club Hill-Climb today.

Every car there was quite capable as all were fully engineered to be the best possible for their configuration.
So it seems top matter less where the engine is placed than how the rest of the car is set up to work with that.


To a point, high hp rwd with middy/rear puts engine over driven wheels (traction) and allows lower frontal area which in turn makes aero better. Thats quite a lot of plus points over a high hp engine dumped over the front axle with virtually no weight over the driven wheels and high frontal area. Its going to be a lot easier to engineer a quick race car with mid engine than front unless of course you are racing around cones in a car park. :)

Bob

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PostPosted: August 29, 2016, 2:06 pm 
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I agree that rearward engine placement can be made to work well as long as the design is optimized for the layout, but if we're discussing aerodynamic drag we need to keep in mind that the frontal area used in aerodynamics is the projected frontal area. This means the entire area, as viewed from the front of the vehicle (same as if viewed from the back though).

Frontal area is often spoken of incorrectly. It's not the cross-sectional area at the front of the car. No matter where the engine is placed, various layouts might have the same frontal area, but their Coefficient of Drag (Cd) will probably differ. To get a low Cd, a bunch of things matter, and I believe it is more important to smoothly close the airflow at the aft end of the vehicle than it is to split the air at the front. A rounded front, tapered rear teardrop shape is good. Even better might be a teardrop shape that is modified to make the nose a bit pointy.

I think the people-space is often the widest part of the shape as viewed from the top. If a side-by-side driver and passenger are placed toward the rear of the vehicle, as it is in a Lotus 7 layout, I love the looks of the car, with its long hood and short tail, but that is tending to create the highest drag, since the body will be forced to be wide towards the back.

Dean


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PostPosted: August 29, 2016, 4:32 pm 
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bob wrote:
I think we should take the 911 or vw aircooled out of the equation because the engines are so light...Now if we were to hang some mericun iron out the back we would have a unhealthy wieght bias...
The reports I've seen on LS1 swaps into air-cooled 911's indicate that the so-called 'murican iron (more often aluminium these days) in question is enough lighter than an complete air-cooled 911 engine that, when all is said and done, the completed swap still yields a net weight reduction...In addition to being significantly more powerful.



bob wrote:
...a high hp engine dumped over the front axle with virtually no weight over the driven wheels and high frontal area...
As stated, those are some pretty 'bold' assumptions.

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PostPosted: August 29, 2016, 4:41 pm 
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The reports I've seen on LS1 swaps into air-cooled 911's indicate that the so-called 'murican iron (more often aluminium these days) in question is enough lighter than an complete air-cooled 911 engine that, when all is said and done, the completed swap still yields a net weight reduction...In addition to being significantly more powerful.


I think that you're mistaken IRT air-cooled motors. Perhaps that's correct IRT water-cooled Porsche H-6 motors though. Any sources to back that up?

edit: It's hard to get exact numbers on these things but it appears that the 3.0 - 3.2 liter air-cooled engines were in fact in the same league as an all -aluminum LSX weight-wise. I guess that with air being so much less efficient than water as a heat-transfer medium, they had to use a lot of it to get the surface areas and strength that they needed.


Last edited by kreb on August 29, 2016, 4:53 pm, edited 1 time in total.

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PostPosted: August 29, 2016, 4:50 pm 
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kreb wrote:
I think that you're mistaken IRT air-cooled motors. Perhaps that's correct IRT water-cooled Porsche H-6 motors though. Any sources to back that up?
I'm pretty sure I've seen others, but here's one for starters: http://toy-jet.com/index2

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PostPosted: August 29, 2016, 4:54 pm 
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Driven5 wrote:
kreb wrote:
I think that you're mistaken IRT air-cooled motors. Perhaps that's correct IRT water-cooled Porsche H-6 motors though. Any sources to back that up?
I'm pretty sure I've seen others, but here's one for starters: http://toy-jet.com/index2


I'd seen that, but they aren't an unbiased source. Porsche sources do indeed back it up, however.


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PostPosted: August 29, 2016, 5:08 pm 
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kreb wrote:
I'd seen that, but they aren't an unbiased source. Porsche sources do indeed back it up, however.
Very true...Thanks for helping validate my (not always accurate) recollection. :cheers:

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PostPosted: August 29, 2016, 5:18 pm 
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Driven5 wrote:
kreb wrote:
I'd seen that, but they aren't an unbiased source. Porsche sources do indeed back it up, however.
Very true...Thanks for helping validate my (not always accurate) recollection. :cheers:


Sadly, in the internet era, AKA: the misinformation era, I constantly have to backsource claims. If my best friend said that he's known me for 46 years, I might ask for school records to substantiate it!


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PostPosted: August 29, 2016, 5:28 pm 
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Per the 75-76 spec book a 2.7 ready for install less oil is 385.8 lbs. 175 kg and thats with all the dustbins,exhausts/silencer, flywheel,clutch and alternator. Strip all the junk off and I can lift that onto a bench on my own, I have done it. No way could I wrestle an LS1 onto a bench. Some figures must be awry here

Bob

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PostPosted: August 29, 2016, 5:34 pm 
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In 1978 they introduced an all-new 3.0 motor. That one, and the subsequent 3.2 are what we're talking about. I think that the 2.7 you refer to was the magnesium-cased one and was pretty light.


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PostPosted: August 30, 2016, 2:17 pm 
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I have nothing against an LS engine, they really are a brilliant piece of kit. What I fail to see is the attraction to butcher a 911 to mash one of these v8 units in the back, the later porsche engines over here are being tweeked to produce a streetable 600+ hp so why bother? A v8 perched up so high must make it handle like a pig, that 911 engine is nestled down on the axle centerline, the V8/911 may score a few more points on a drag strip but I have never heard of or seen one winning any track races.




bob wrote:
...a high hp engine dumped over the front axle with virtually no weight over the driven wheels and high frontal area...
As stated, those are some pretty 'bold' assumptions.[/quote]

I just think of all the 200mph plus road cars about, the vast majority are rear engined low frontal cars. The rear engined 24hour le mans cars are lapping the front engined Astons and Vets some thirty odd times in the race. They are also the best part of 50kph faster down the straight. All these cars run similar HP but the mid engine stuff just runs off into the distance. In my tiny mind its down to traction out of the corners and aero down the straights . I could be wrong :)

Bob

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