john hennessy wrote:
thanks for the information,
it rases some other questions you may wish to answer,
first, is the front and rear roll center below ground level? Yes
second, is the reason for narrowing the car that it is just too wide for the course? I'm at 72" outside to outside. Narrower is better without sacrificing much.
the change to a ledgends upright, would this enable you to shorten the steering arm length to speed up the inputs whilst retaining the rack? Yes. I want to quicken up the turning but also want to keep steering effort low. I want to avoid adding power steering to get the beefy tires we run to turn easier. Quicker ratios can impact turning effort. These cars are so light it might not be such a problem.
looking at the rack location, it is behind the steering arms, so where is the ackaman point? I do not have the exact point calculated. I do have ackerman as you observed with adjustments for the rack to move forward or back. I think this is a bigger issue on the slower tighter turns as opposed to the high speed wider turns. It turns well on high grip surfaces in tight low speed turns so I have not messed with it yet. I think I have bigger issues with scrub.
the ground clearance, you have a low ground clearance but the motor is placed quite high in the car, high enough to have to modify the tube at the front of the tunnel to clear the trans/bell housing, do you think these two things are in conflict, could you raise the chassis and lower the engine in the chassis? i am aware that this may require changes to the control arm inner points but if you were to do it over would the low ground clearance still be the same?I will be raising the chassis about 1" and modifying the lower cross brace to clear. The old rotary engine had a very high crank center as compared to a piston engine car. I also had the motor set further back in the car pushing the bellhousing in the chassis cross brace area. I took advantage of this in the engine/chassis layout to keep the chassis and bodywork low and smooth on the bottom. This might not be a big issue on the lower speed events I run but I would like to track the car and do hillclimbs someday were undercar aero is more of an issue. The new engine will also be set back in to the cross brace area and there will be significant modifications to the chassis to come. I don't think raising the chassis 1" will hurt much if I keep the bottom fairly smooth.
and lastly, the springs seem quite soft, what is the compressed spring rate at ride height, is there preload on them? the open length compared to the ride height length.Yes there is preload. I did a suspension frequency calculation on one of the on-line calculators when I changed the springs and went softer in the front. I was originally at #350 in front and it pushed really bad. My suspension frequencies were way off. To get the frequencies where they should be front and back I had to go this soft. The car does not bottom and handles really a LOT better. I subscribe to the theory: Run the softest springs and implement swaybars and shocks for tuning. I like the directions I'm going with this. Others may have a different opinion and approach
sorry to pick your brains here but it is clear that because you need to change various things, that you can see improvements that were not there in the original build and needed a redo, these refinements are what make a car quicker and for you to see the need is a good reflection on you as a driver/builder.
_________________
Building a whole car from scratch is a 1,000 little tasks, done 1 task at a time, while thinking 10 tasks ahead, then redoing it anyway.
South Bend Region SCCA D-Modifed Class Autocross & Track-Day/TT. Chevrolet 1.4 L Turbo Ecotec PowerLink to my build log:
http://www.locostusa.com/forums/viewtopic.php?f=35&t=3356
Login
Register
FAQ
Members
