Fat roadster

[robo]

Is a fat roadster that is built with a slightly heavier engine and associated parts really that much different to a lightweight car? Seems to me that betwwen the heaviest and the lightest there is only 170kg, surely that can be compensated for with brakes, springs and rubber.

Bob

[TSM Locost]

Luego Viento big enough ? 6 4 4 i think. some with large V8's

[wylliezx9r]

Is a fat roadster that is built with a slightly heavier engine and associated parts really that much different to a lightweight car? Seems to me that betwwen the heaviest and the lightest there is only 170kg, surely that can be compensated for with brakes, springs and rubber.

Bob

What is your projected weight then Robbo ?
I wouldnt be worried about springs and brakes so much but the loads the chassis has been designed to handle ? Nothing a bit of extra triangulation cant sort though I suppose.
There was a thread on LCB showing an Roadrunner with a LS7 V8 in it, most of the people on there shunned it saying it would snap in half etc etc, I thought it looked really cool but I'm no structual engineer.

[robo]

What is your projected weight then Robbo ?
I wouldnt be worried about springs and brakes so much but the loads the chassis has been designed to handle ? Nothing a bit of extra triangulation cant sort though I suppose.
There was a thread on LCB showing an Roadrunner with a LS7 V8 in it, most of the people on there shunned it saying it would snap in half etc etc, I thought it looked really cool but I'm no structual engineer.

I was going to target for under 700kg:o with a 302 ford. I have put every aspect of the build on a diet but with a 2mm chassis and some strengthening plates its not going to be a lightweight. The engine weight with ali waterpump,lightweight flywheel and clutch, gear reduction lightweight starter is under that of a pinto but then it holds more water and oil so its a futile battle.

Bob

[spud69]

I was going to target for under 700kg:o with a 302 ford. I have put every aspect of the build on a diet but with a 2mm chassis and some strengthening plates its not going to be a lightweight. The engine weight with ali waterpump,lightweight flywheel and clutch, gear reduction lightweight starter is under that of a pinto but then it holds more water and oil so its a futile battle.

Bob

Hi dont think you need to worry about putting the power through the chassis Bob, especially 2mm wall tube, Caterham have announced the R600:

http://www.egmcartech.com/2012/10/05/new-275-hp-r600-superlight-is-the-fastest-caterham-seven-ever/

275hp through the superlight chassis, going to be a track day only car and will be quite awesome but then it should be at £45k. You also see lots of big V8's going through similar chassis so the weight shouldn't be an issue. 350lb springs on the front are quite stiff, I've found the roadster tends to feel better with upgraded springs on the rear but it ain't too expensive to try a few spring rates.

Andy

Andy

[Davey]

I'm aiming for 750KG kerb weight with a Cosorth V6 motor. My chassis is a hybrid of sorts, originlly a Locust (spit) but spaceframed with guidance from the bible and here. Original chassis is still in there at 3"x2" box section but very basic design. Space frame additions are mainly in 25x25x3.2mm box with the rear diff cage being 60x40x3.2mm. Aticipating around 225BHP max but significant torque throughout the rev range. Mine is intended to be a quick andcomfortable road car but it might get chucked at Loton Park hill climb occasionally.

D.

[Not Anumber]

Sounds good retaining the original Locust chassis and extending it into a spaceframe - it wont be one of the liohtest chassis but it should be very strong. If the car is regstered as a Locust on the V5 I can see the advantage straight away.

[baz-r]

i dont think weight is a issue more engine/drive torque trying to twisting things up

say we took a std book chassis with sierra diff etc then put a big cc torquey v8
the actual engine weight is not a great deal more to deal with but the stress twisting the diff area and chassis will be in the lower gears (gearbox is multiplying torque in all gears below 4th)

pinto engine 98-160NM x 3.58 (t9 1st) = 350-572.8NM
302 v8 5.6 engine 500NM x 3.35 (t5 1st) = 1675NM :eek:

other kits have had trouble with cracks and breaks in the rear diff areas so i think some extra bracing will be needed to prevent flex. as the movement will work harden things and crack.
it would not take alot of work to make and fit gusset plates and add extra diagnals in the seatback and diff box areas etc