One of weakness of lowering the FD is u will hit the frame rail!!! That why I think in most of case is to use 17inch slick some thing under 250
But lately is hard to find proper size
And in my case with 300/650/18 slick althought with 30kg spring I still hit frame rail time to time on hard braking !!!
So during this Offseason I decide to chop the frame rail and reweld to top !!
By doing this I gain another 1.5cm of clearance, hope this will slove my problem

 

I think you should have gone to stiffer springs . Most guys with those tires run 1100 -1300 lb springs. Your car will still dive now, just more!

 

With my rough and ready calc of divide by 2, he's more than 1500 lb already. Ride height and shock valving might have been my first port of call. Any bumpsteer correction on that thing?

Can't get over how popular it was with the Japanese to waste their time pop riveting - with what looks like aluminium rivets, rather than stitch welding back then.

 

The Japanese GT300 cars had to run this too tall for FD RX-7 tire size as well.

This is Revolution FD, but I believe is an ex-GT300 race car.
http://image.superstreetonline.com/f...ect-mu-caliper

You can see once they are back on correct diameter tires the modifications to unibody and body contour are not needed.
http://image.superstreetonline.com/f...ce-rear-bumper

 

With 30kg Spring , it equal to 1650lb rate
But swift spring tend to be on Lower frequency compare to hypercoil
I have to admit my shock Is pretty tired so before this season start I will rebuild it too !!

 

That right , I am also rebuild my shock this season , and BTw the bump steer have not thing to do on how car will react on ride height at bump
I think what u mean is roll center

I bought this car from Japan , not suprise it come with a lot of Jdm style touch.....
Personally I will use roll cage to tide every thing up

 

The taller the slick , it get mote foot print under compression

The revolution build it from ground up
Using GT300 spec
But with GT500 power ( 13B Turbo instead of 20B pp) and time attack aero

 

Yes, full slicks are going to be the fastest for a variety of reasons.

The Revolution FD is competing in Time Attack so must use full treaded street-able race tires (DOT-R in USA). So far no one is making a competitive Time Attack tire bigger (wider or taller) than 295/30-18 that I know of.

 

did this solve your problem?

i'm considering running 645 or 661mm diameter slicks, but worried about the clearance as well.

can you detail how you modified it?

and why not just raise the ride height alittle?

 

Yep
This solve my problems no more hitting frame rail at last race
As ridehigh Which is I am not plan to change any time soon
Since this ride hight work pretty good on my front aero splitter

If u plan to use slick over 640 u will have same problem like me ..... when I am using 650/640/17
I am perfectly fine but once to 680/650/18 the size and extra grip make it a night mare

Few thing u can do , like how I cut frame rail ,
Or using linner bump stop to have soft hit on frame rail

About rise up the ride hight , we need to go as low as u we can before we hit some thing , if u want rise up to fit the tire? Better switch to shorter tire, unless u get the almost for free....

 

did you notice a big benefit going from 17 to 18? worth the hassle to modify the apron?

 

Is about tire wheel selection choice
For 280 and above is easier to find in my area is 18
So if u can find 650 under tire , use that
But once u go over that u really need to cut the frame rail to get 100% of tire

 

You might want to just use some spacers on your bump stops if you just want to keep the tires off of the frame rails.

When are your tires hitting the frame rails?

 

I'm doing this right now to a friends car.

275/35/18x10.5 +15 offset I think.

Had to chop some material away from the side next to the headlight bracket behind the top mount of the stock oil cooler. Beat the wheel well back towards the firewall.

I also had to cut back a lot near the back outside frame of the wheel well. Then I had to re-weld re-enforcement plates.

I removed the shock to get full suspension travel and held the tire up with a transmission jack until it touched the top of the wheel well. Then I turned the tire left and right cutting on both front and back sides until the tire cleared the frame. Then I had to beat back the wheel well towards the firewall until it cleared. I had to move a lot since there are spacers on the tie-rods to make the wheel have more angle.

I'll post some pics when I'm done.

P.S. I did read all the comments on shocks and tire sizes and what affects what, but my friend knows what he wants and he has different goals. I would like to just stay on topic on what has to be done when you start getting into tis type of modification.

P.P.S. I'm not a pro frame guy - just your average garage monkey who knows enough to be dangerous... lol

 

Here is what I did.

 

how does the suspension hold up?