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914World.com _ 914World Garage _ strut & shock question for the racers ...

Posted by: SirAndy Feb 19 2006, 04:21 PM

i got a mid '80s carrera frontend with the black struts, so i'm assuming i've got the stock 911 boge shocks.

the car is lowered quite a bit and i was hitting the 3-piece rubber stops frequently.
i was told i could safely cut the rubber stop down to 2 pieces, which i did and it helped quite a bit, adding more shock travel.

but i still bottom out occasionally on a larger bump etc.

so, my question is, for the boge shocks, can i safely remove a second piece from the rubber stop and run a one piece stop only ???
Andy

Posted by: Aaron Cox Feb 19 2006, 04:22 PM

get shorter shocks....

there is a mod to the struthousing so you can rin a shorter koni insert....

not sure if you can go any shorter on the bumpstops.....

since your getting sponsored etc... go for JFZ's or FOX shocks...

Posted by: ChicagoChris Feb 19 2006, 04:24 PM

I frequent a nother BBS filled with the 911 crowd. Several of the guys own race shops and the like. If the answer doesn't come quick try them. They also offer monthly free stuff for 911's.

www.gruppeb.org

Posted by: ArtechnikA Feb 19 2006, 04:25 PM

raise the upper mounts.

yes, that is why lots of cars from "back in the day" had hood boobs...

Posted by: Headrage Feb 19 2006, 04:35 PM

How are you having bottoming problems when your car is suppose to be undergoing a /6 conversion?

Splain yerself mister...

Posted by: SirAndy Feb 19 2006, 04:37 PM

QUOTE (Headrage @ Feb 19 2006, 02:35 PM)
Splain yerself mister...

cause i drive it every day ????

Andy

PS: so, anyone have some experience with the boge shocks and rubber stops ?

Posted by: Racer Chris Feb 19 2006, 04:41 PM

QUOTE (SirAndy @ Feb 19 2006, 05:21 PM)
so, my question is, for the boge shocks, can i safely remove a second piece from the rubber stop and run a one piece stop only ???
Andy

You can run without any rubber at all ... as long as you have something on the shaft that is thick enough to prevent the shock from bottoming out internally. Race parts suppliers like Pegasus sell plastic disks with a slot and a hole in the center that you can stack on the shock for this purpose. If you actually collapse the shock to the point that the disks are engaged the spring rate will rise suddenly instead of gradually like with the stock bump rubbers.

Posted by: Van914 Feb 19 2006, 07:09 PM

Andy,
Why not have the spindles raised?
Gives Lower ride height and saves the shock travel.
Van914

Posted by: Van914 Feb 19 2006, 07:11 PM

Forgot the link
http://www.tangerineracing.com/suspension.htm

Posted by: Van914 Feb 19 2006, 07:12 PM

Front Strut Raised Spindle Modification ( $280/pair)
(stock unit on left shown for comparison)

Can be raised from 17 to 30 mm, depending on usage and wheel size

Steering arm is recurved to eliminate bump steer

Suitable for all 914 and early 911 Boge struts

Posted by: McMark Feb 19 2006, 07:42 PM

with Van and Chris. Can you call a BOGE tech and ask them?

Posted by: SirAndy Feb 19 2006, 11:31 PM

damm, i had hoped for a quick & dirty (and cheap) solution ...

oh well ...
Andy

Posted by: anthony Feb 19 2006, 11:55 PM

Raise the car higher.

Posted by: groot Feb 20 2006, 09:38 AM

QUOTE (Racer Chris @ Feb 19 2006, 02:41 PM)
You can run without any rubber at all ... as long as you have something on the shaft that is thick enough to prevent the shock from bottoming out internally. Race parts suppliers like Pegasus sell plastic disks with a slot and a hole in the center that you can stack on the shock for this purpose. If you actually collapse the shock to the point that the disks are engaged the spring rate will rise suddenly instead of gradually like with the stock bump rubbers.

I respectfully disagree, Chris.

Some dampers have internal bump stops (very few actually) and then you can run without external bump stops ... and the plastic disk does not count as far as I'm concerned, because it's too thin.

Here's why.... Go look at a cut-away view of a twin-tube damper (which is what your front strut is) on the Koni website. Wihtout a bump stop you will crash the piston (located on the rod) into the base cage, ruining the damper. You can easily screw up a mono-tube, too (which some of you may run in the rear). But the piston crashes into the floating piston.

Another reason to use bump stops... and long ones... is to raise the spring rate more gradually, which helps the tires do their job. For an example of why this is required, check out that picture of Sir Andy's car on 2 wheels.

Posted by: groot Feb 20 2006, 09:46 AM

To answer Andy's question directly:

Raise the car, raise the spring rate or move the knuckles up the strut housing. 914s don't have a lot of room to move the upper strut mount higher in vehicle. These are better solutions than reducing your bump stop, unless it's longer than 1" or so.

How much travel from static ride height to you start to get into your jounce bumper? Post a pic if you can. What is the shape and material of your bumper?

Posted by: SirAndy Feb 20 2006, 02:06 PM

QUOTE (groot @ Feb 20 2006, 07:38 AM)
For an example of why this is required, check out that picture of Sir Andy's car on 2 wheels.

that was actually the main reason why i cut off one of the 3 sections of the rubber stop in the first place!

the picture with my car on two wheels was taken when i still had the complete rubber stops, and i effectively ran out of shock travel in that pic.
getting more shock travel should, at least theoretically, help preventing another 2-wheel adventure ...

i *know* that the stop is there to protect the piston(s), but i was told that the boge shocks have a larger "safety" margin than the konis and that you can cut the rubber down more without having the piston bottom out.

i was hoping someone here knew for sure ...
Andy

Posted by: groot Feb 20 2006, 02:29 PM

I hear ya'... reasonable approach.

It's certainly possible that a Boge has a shorter piston rod and therefore may not slam the piston into the base cage. Konis (and many other dampers) are not designed this way for sure...

I still recommend trying to keep your spring rate as linear as possible. A jounce bumper can help you at the end of your damper travel to flatten your spring rate curve. A non-effective (or missing) jounce bumper has a very sharp corner to the spring rate curve... right as it bottoms out.... and that leads to ugly things.

Posted by: SirAndy Feb 20 2006, 02:38 PM

QUOTE (groot @ Feb 20 2006, 12:29 PM)
A non-effective (or missing) jounce bumper has a very sharp corner to the spring rate curve... right as it bottoms out.... and that leads to ugly things.

so, what if i:

- jack up the car, unload the suspension completely, move the rubber spacer all the way up on the rod, then measure the distance from the top of the shock to the bottom of the rubber.
that'll be my current effective shock travel.

- then, i remove the shock, i push the rod all the way down, mark it, then extend it all the way out.
that will give me the largest "possible" shock travel.

- the difference between the two should tell me how much of the rubber spacer i can cut off, if any ...

anyone see any flaws in this?
Andy

Posted by: Sideways Feb 20 2006, 03:02 PM

QUOTE (SirAndy @ Feb 20 2006, 01:38 PM)

QUOTE (groot @ Feb 20 2006, 12:29 PM)
A non-effective (or missing) jounce bumper has a very sharp corner to the spring rate curve... right as it bottoms out.... and that leads to ugly things.

so, what if i:

- jack up the car, unload the suspension completely, move the rubber spacer all the way up on the rod, then measure the distance from the top of the shock to the bottom of the rubber.
that'll be my current effective shock travel.

- then, i remove the shock, i push the rod all the way down, mark it, then extend it all the way out.
that will give me the largest "possible" shock travel.

- the difference between the two should tell me how much of the rubber spacer i can cut off, if any ...

anyone see any flaws in this?
Andy

Sounds ok for measuring the total travel of the shock, just dont forget you still need the bump rubbers to do some compressing at the top of the stroke. If not you will still bottom out the piston.

Best case you will destroy a shock, worst case it could lead to very strange handling and punt you off the road (bent teener).

Best solution is raising the spindles and allowing the shock and rubbers to do the job they are intended to do for your ride height.

Posted by: Van914 Feb 20 2006, 03:46 PM

Andy,
I went through a simular problem. I raised my car and used the Koni Race Snubbers. Automotion has them in their new calalog. You don't want to feel the shock bottom out. Been there and its can be scary.
Here is the link.

http://www.automotion.com/productpage.aspx?pid=103692&name=Koni+Race+Snubbers

Van914

Posted by: Racer Chris Feb 20 2006, 04:18 PM

QUOTE (groot @ Feb 20 2006, 10:38 AM)
I respectfully disagree, Chris.

Some dampers have internal bump stops (very few actually) and then you can run without external bump stops ... and the plastic disk does not count as far as I'm concerned, because it's too thin.

Kevin,
The disks are intended to be used in a stack, not just one at a time. If you stack enough of them it will certainly stop the shock from bottoming internally. I also understand that it is desirable to have a rising rate by using a rubber snubber instead of a sudden increase by hitting the limit all at once.

(btw, my front shocks are monotube )

Posted by: groot Feb 21 2006, 06:27 AM

Strut monotubes are not as common... because they're not so good at taking side loads. That's cool you have some. Bilsteins?

Koni sends 1 plastic disk with their strut inserts, but they also include a jounce bumper. The plastic piece on the Koni is intended to give the jounce bumper a nice flat surface to hit instead of hitting the strut can nut. It also acts a a bearing surface if you happen to be turning while you're riding on your bumpers to avoid chewing up the bumper.

Andy, you need to know how much travel you have when the car it loaded. That will tell you how much room you have before you hit the bumper. If you can see the strut rod with the wheels on, you could take the front wheels off and set the front spindles on jackstands. Bounce the car a bit and that should give you a close measurement.