Rear diffuser & engine placement question

[slngsht]

 

Can't upload photo??

 

anyone else having a problem?

[WestTexasS2K]

I very seriously doubt you are just spinning tires in the just the 8-9k rpm range. You are more likely to experience this problem when Vtec kicks in. What gear are you in when it happens?. I can see spinning wheels in 1st 2nd and 3rd gear ,but 4th isnt likely unless you have very bad tires. It should be very obvious when tire spin happens. The back end will usually move sideways left or right.

 

It sounds like you steering is just getting light and unstable so it gets a little scary at highway speeds 70-90mph range. In all you alignment specs I see nothing about caster in there. Caster gives the car stability at speed. The less caster you have the lighter and more sensitive your steering is going to be. The more caster you have gives you more stabilty and will also increase steering effort at low speed and the steering effort will get easier as you pick up speed. For a street car I like 5.5-6 degress of caster. You can take your hand of the steering wheel and it will track very straight.

 

I think you can use a little more rake in the car as well. The specs you gave you have 10 mm of rake not sure if that is with you in or out of the car. If you set that up with out being in the car then you may be dropping the rear to much while you are in it giving the car a nose up attitude and this will cause some problems in stability.

 

If the car only gets very light under acceleration which is expected, but if it is to a point you feel insecure in the cars predictabilty. You might want to go to a stiffer rear spring to keep the back from squating so much under acceleration. In return this will keep more weight on the front tires and keeping the car planted.

 

Aero work isnt really going to affect your car handleing and performance until you get up to 110 mph or so. At highway speeds I dont think you will notice much of a difference.

 

I dont know what rear end you have is it a straight axle or IRS? If it is an IRS you might be getting bump steer when the suspension moves it changes the tow on the tires making a handful to drive.

 

Tires are very important on a light 7 type vehicle. The Mickey Thompson tires are more drag oriented tires. I know that it says that it is made for drag racing and street use. I think you will find the the sidewall are very flexible on that tire. They use are pressure to support the sidewalls. On a seven you run below 20 psi which can give you alot of side to side movement as the car walks over the tread when underinflated in a soft side wall tire.

 

I would stick with tires that are known performers on sevens. That has been hashed out here several times before. There are many brands and depending on the use and weather conditions you drive in. Toyo RA1 or R888 are good max performance tires. Michelin Pilotsport 2 are a very good street/ trackday and are excellent in the rain. ( Most people dont drive in the rain.) There are dozens of brands and models to choose from.

 

Hope you find a solution to the problem but I think alot of money on aero work isnt going to give you a good return on your money.

[MichaelD]

To much toe out will also cause some "darting" at highway speeds. In moderation one might describe it as lightness or a drifting effect in the front end.

[jimrankin]

The Rangers might be a bit off but WT is right on. At anything under a 100 MPH it almost always comes down to suspension/tire set up if the car isn't stable. Jack up your tire pressure well past where you are normally running and see if it's sidewall flex before you do any other suspension changes. If that didn't show that the sidewall flex is the problem move on to getting a copy of their exact set up from a "like" car on this site, not just another 7 clone, that isn't having any problems and copy it. If your still not stable at highway speeds you either have a broken weld(s)somewhere letting the frame flex or you just aren't used to driving it yet. Most new cars are set up really castered and quite a bit towed in so they feel "stable". Since the average driver isn't concerned with turn in response and power steering can overcome the caster easily you get used to that type of driving feel without noticing it till your in something fun.