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Learning how to build Lotus Seven replicas...together!
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PostPosted: January 15, 2008, 1:53 pm 
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Joined: March 31, 2006, 1:55 am
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Location: Pittsburgh, PA
hi,
i know that the lotus 7, caterham 7 and all of the locosts people are building to replicate the originals are made to be great handlers.. but i am curious to see how "quick" they are... i want to build a locost but at the end of the day i don't want to be bummed out about it because my WRX or the neighbors camero are faster..

so, if you could please post any performance figures you have for your car or the original lotus 7 that would be great. caterham posts all of their figures on their website but i don't think that i will be building a 260HP CSR replica any time soon..

also, maybe someone with more knowledge on the subject could even tell me, if i build my car with specs close to one of the caterham models, say the Caterham Seven Superlight with 150 HP weighing 1100lbs, could i expect numbers similar to the superlights 0-60 of 4.7 seconds?

i would think, but, i am still asking

thanks

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PostPosted: January 15, 2008, 3:29 pm 
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Joined: April 23, 2006, 8:26 pm
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Yes to your last question. The car's are all roughly the same size so it comes down to a power vs. weight thing.

I'm not sure you're going to get helpful data to your main question though. So much depends on driver technique, tire compound, engine torque, and shift points.

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PostPosted: January 15, 2008, 6:36 pm 
I've had cars tested by a couple of magazines. My own car comes in pretty close to a Superlight both in numbers and in the real world on the track. The skidpad numbers for the first three came from a dusty parking lot. All the Car and Driver cars were driven by the same driver for testing.

Car and Driver, my car:
Power (C/D est): 175 bhp @ 7000 rpm
Torque (C/D est): 145 lb-ft @ 5900 rpm
Toyo RA-1 tires, 205/55-14

Transmission: 5-speed manual
Wheelbase: 92.0 in
Length/width/height: 128.0/65.5/42.5 in
Curb weight: 1279 lb

Zero to 60 mph: 4.7 sec
Zero to 100 mph: 14.8 sec
Street start, 5–60 mph: 5.5 sec
Standing ¼-mile: 13.8 sec @ 97 mph
Braking, 70–0 mph: 141 ft
Roadholding, 300-ft-dia skidpad: 0.98 g

Car and Driver, Mark Rivera's turbocharged car:
Power (C/D est): 260 bhp @ 6500 rpm
Torque (C/D est): 215 lb-ft @ 4500 rpm
Toyo RA-1 tires, 205/50-15

Transmission: 5-speed manual
Wheelbase: 99.5 in
Length/width/height: 136.0/66.9/50.0 in
Curb weight: 1497 lb

Zero to 60 mph: 4.1 sec
Zero to 100 mph: 11.1 sec
Street start, 5–60 mph: 5.2 sec
Standing ¼-mile: 13.0 sec @ 107 mph
Braking, 70–0 mph: 171 ft
Roadholding, 300-ft-dia skidpad: 0.86 g (control arms were bent by this point, whoops)

Car and Driver, Jon W's BMW-based car:
Power (SAE net): 101 bhp @ 5800 rpm
Torque (SAE net): 100 lb-ft @ 4500 rpm
Yokohama R compound tires, not sure of size.

Transmission: 5-speed manual
Wheelbase: 100.0 in
Length/width/height: 133.0/62.0/44.0 in
Curb weight: 1460 lb

Zero to 60 mph: 7.8 sec
Zero to 80 mph: 15.0 sec
Street start, 5–60 mph: 8.5 sec
Standing ¼-mile: 16.1 sec @ 82 mph
Braking, 70–0 mph: 233 ft
Roadholding, 300-ft-dia skidpad: 1.00 g

Car and Driver, Caterham SV:
Power (SAE net) 147 bhp @ 5800 rpm
Torque (SAE net) 140 lb-ft @ 4000 rpm

Transmission 5-speed manual
Wheelbase 90.7 in
Length/width/height 136.2/66.3/44.0 in
Curb weight 1438 lb

Zero to 60 mph 4.6 sec
Zero to 100 mph .15.8 sec
Street start, 5-60 mph 5.5 sec
Standing 1/4-mile 13.7 sec @ 95 mph
Braking, 70-0 mph 174 ft
Roadholding, 300-ft-dia skidpad 0.96 g

Automobile magazine tested a Miata-based Westfield. They do 0-60 tests a bit differently and don't subtract the rollout. This means the times are about 0.3 seconds longer than a R&T or C+D numbers.
Power: about 150 hp at the crank
Toyo RA-1 tires, 205/50-15

0-60: 5.5 seconds
30-70 mph passing: 6.4 seconds
1/4 mile: 14.5 seconds at 94 mph
70-0 braking: 156', 1.16g peak deceleration
Lateral acceleration: 1.15g (measured on a real skidpad)

But that's not all you get. A friend of mine runs a modified WRX and can certainly outdrag me on the straights on the track. But I'm dramatically faster around the rest. When I autox with the Corvette club, I'll often take FTD by a 5 second margin.


Last edited by Keith Tanner on January 15, 2008, 6:53 pm, edited 1 time in total.

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PostPosted: January 15, 2008, 6:44 pm 
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KB58 wrote:
I'm not sure you're going to get helpful data to your main question though. So much depends on driver technique, tire compound, engine torque, and shift points.



..... and possibly even more critical is how much "development' work the builder puts into the car after its built. Read thru Keith's build/development log at " http://www.cheapsportscar.net/ "


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PostPosted: January 15, 2008, 7:18 pm 
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Joined: April 23, 2006, 8:26 pm
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Location: SoCal
True, and I see I forgot tire width as a huge contributor to a faster time.

And you're right, if the suspension's set up for zero camber change with bump, it'll hook up even better, versus a car that's set up for camber control around corners with static camber.

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PostPosted: January 15, 2008, 8:32 pm 
There's an argument there for live or deDion rear ends, as seen in the Caterham SV. All the other cars on the list had IRS.


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PostPosted: January 15, 2008, 9:50 pm 
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The voice of reason
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Joined: January 10, 2008, 4:47 pm
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I'm impressed with the braking on Keith's car. Serious mistake for those
other cars to try and follow you into a corner... :shock:

Except maybe the Westfield... It's hard to compare numbers from different
pavements ( and weather ) though.

Certainly the light weight helps.

I advocate for deDion and even live axles on street cars, because so many
street cars have bad IRS - often with a lot of bump steer. But with these cars
there should be the possibility to have well designed IRS. The Westfiled had
good numbers...

If you can just up the traction a bit more, the inside wheel will be pretty
irrelevant...

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PostPosted: January 15, 2008, 10:00 pm 
I can tell you from experience chasing that Westfield around that I do have a bit more braking - it's due to the fact that you can adjust the bias from the cockpit so it's always set up just right. I think the other numbers came out pretty well for my car. The biggest difference was the skidpad, the dusty parking lot was definitely not in the same league as the Bosch skidpad used for the Westfield test. I would have loved to pull the windshield and see how much of a difference it would have made in the quarter mile.

Jon's car has the IRS right out of the donor, IIRC. I know Mark Rivera's had a complete Miata rear subframe so it had the Miata geometry, although the car had absolutely no setup time (or even bodywork) when the testing was done. The Westfield and my car have custom IRS setups.

I'm not sure what this means, can you elaborate? Are you talking about cornering, straight line acceleration or what?
"If you can just up the traction a bit more, the inside wheel will be pretty
irrelevant..."


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PostPosted: January 16, 2008, 12:00 am 
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My car had Yokohama A032, 175/60-13, hard compound tires on the donor wheels that are 6" wide.

The rear suspension is the donor semi-trailing arm IRS with too-stiff springs and open differential. The front suspension has poor geometry, converted struts with very little, if any, Ackerman and a 1990 Miata anti-roll bar. It does like to turn in.

The front right brake was locking so Larry took it easy to save the tire. Even with perfect brake function the rear drums would probably not provide the best brake feel or very short stops.

That's what you get for $2500 on a car built by amateurs who ran out of patience and talent.


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PostPosted: January 16, 2008, 11:14 am 
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The voice of reason
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Yes, I meant cornering. I wasn't very clear. Was trying to do a quick mental
calculation of the weight transfer - 1.n g's, cg height of ~20 inches?, and 62" wide / 2... Um, it's a big number :?

Someone else recently mentioned 1.7 g's on slicks. At that point the
inside wheel geometry would not matter much at steady state cornering.

I think lowering the car would be a big help for handling on the track. Is
the issue of using different size wheels/tires for track and street mostly a
problem for the front suspension geometry, like scrub radius? Or is the
story worse... I see your on 14" already so not sure how much you could
get with 13" slicks.

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PostPosted: January 16, 2008, 11:23 am 
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The voice of reason
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Jon W:

Considering you got to useable vehicle for that cost, I don't think anyone
can beat you! And certainly no lack of talent or patience.

Folks on the British forums are firm believers in drum setups for even
competition use in many sevens. For less then "mumble" horsepower and
severe track use, you should be able to get that to work as well as anything.

I suspect that if the tester was being easy on the brakes, that's what made
the long stopping distance. Ackerman is probably not an issue, except
maybe at slow speed in parking lots or driveways. Just tell people you try
to keep the front wheels straight ahead when cornering - issue solved!

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Car9 Roadster information - models, drawings, resources etc.


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