Bump stop mod for rear Bilstein shocks - recommended?
 

Is this mod recommended? (ie. choppping off the top 1" of the bump stop to prevent bottoming out)

I have seen recommended by a few places (can't find any of the links...)

I ask because I have just had my shocks rebuilt and they are about to go back into my 2.7RS replica race car. With a full cage and 30mm rear torsion bars the car is pretty stiff. I am wondering whether bottoming out is likely to be a problem. However, I also do tarmac rallies in the car and these are hard on everything.

Cheers - Ryan

2.7RS replica (race car)
79 930 Porsche/KREMER (street car - very sensible choice...)

You need some of the bump stop. IMHO, the originals were designed as a damper/stop. You got a little cushion if you bottomed. If you're not worried about the cushion, cut 'em. But if the shock bottoms out metal to metal, there is likely to be damage to the shock or the mount.

Thanks Milt - the mod I have seen does not entail removing all of the bump stop just cutting off about the top 1" (there is an existing groove around the bump stop where the cut is made) I don't think this would allow the shock to bottom out completely.

I am more concerned as to whether you actually gain anything from this mod - ie. what is the advantge of the little extra shock travel or, to put it another way, later bump stop activation?

Ryan

The info is on the smart-racing.com site;

http://www.smart-racing.com/ProdCat/Suspensions 911/Susp911.htm

Scroll down the page, it's an SRP TechTip near the bottom.

You basically cut off 2 of the 3 rubber pieces. I did it and it works great, especially for a lowered car.

You have to wonder as to why the grooves would be in the bump stops if they were not intended to be modified. If you are racing in tarmac rallies which require softer springs to obtain maximum grip then extended suspension travel would allow the car to absorb deeper bumps than would otherwise be possible.....and we all know what happens when the car is on its bump stops and hits yet another bump in the road. As you have said, modifying the bump stop will not allow the shock to compress completely and as such you will not damage it. So, in my definately non-expert opinion, I would go for it.

Is there a certain amount of lowering where this mod is suggested/required? I'm about to install new Bilsteins front and rear on my daily driver (stock torsion bars) and plan on lowering around Euro height. The Smartracing sight doesn't give any specific information on this.

yeah, that's my question, when should you perform this mod??

My SC is at Euro ride height and I noticed a difference right away, especially in hard turns. One caveat, though, if you run wider wheels/tires up front, you may experience slight rubbing after the mod since the shock travels further. I run 225's on my SC and it did rub a bit where as it didn't before. 22mm torsion bars cured all problems. I think this mod is intended for a more aggressive setup anyway, though.