Best of all worlds: BWR Non-Adjustable Penske Shocks with Intro pricing! - Page 8 - LotusTalk - The Lotus Cars Community
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post #141 of 185 (permalink) Old 05-14-2015, 09:47 AM
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On my liners, I just taped a piece of thin aluminum sheet metal to where the tires rub. Better than worrying about the tires destroying the liner!
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post #142 of 185 (permalink) Old 05-14-2015, 09:57 AM Thread Starter
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All these cars rub the liners! We have a base suspension car with the tiny fronts and it has rub marks! By going to stiffer springs the Penskes actually help with that.

That said, I applaud LionZoo doing this to get what he wants. I would ignore it or put stiffer springs on it since it will still ride better than stock, but he is making it his own style. That's cool and that is what these cars are about!

Bump stops are super-easy to install on the NA Blackwatch Racing Penskes. Loosen the spring perch enough to remove the spring(probably 15 turns), slide the spring off. Put the lower eyelet in a vise(with something to protect the aluminum eyelet), loosen the 3/4" nut. Remove eyelet. Slide the bump stop on. Reverse process. tighten nut to 24 lb-ft.

DO NOT DO THIS ON SINGLES OR DOUBLES! It will mess up the adjusters!


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post #143 of 185 (permalink) Old 05-14-2015, 10:29 AM
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Yeah it doesn't worry me too much. I have done suspension development work before and it'll be nice to get back into the game, in a small way. If I can't get bumpstops to work properly, I can just remove them and run them as is. If I can get them to remove properly, I feel like it might be a positive contribution to community. Maybe could even be an option for the kit. This won't be an irreversible mod, so it'll only cost me the money for the bumpstops and the development time.

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post #144 of 185 (permalink) Old 05-15-2015, 01:33 PM
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Awesome to hear. +1 on the initiative to try bumpstops, please let us know how it goes.

BTW Lionzoo, I didn't realize you were in Brea. I'm right nearby in Rowland Heights!

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post #145 of 185 (permalink) Old 05-15-2015, 03:05 PM
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I just moved recently. There's apparently a few of us in Brea (Carol, Paul, and Lawrence). We all live right by each other. Should do a meet up sometime.

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post #146 of 185 (permalink) Old 05-18-2015, 01:58 PM
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Absolutely! I'd love to chat and compare cars.

So much great Asian food in the area, we should meet up. What's Paul's SN?

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post #147 of 185 (permalink) Old 05-26-2015, 06:40 AM
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We installed our set yesterday. I have to say, thanks for making it so easy. The rears were cake. The most difficult thing on the whole install was the innermost nut on the ABS Bracket. That sucker did not want to come off (corrosion on the threads). I had to grab the base of the rubber bushing with pliers and spin it 1/16th of a turn at a time. That nut took longer than the rest of the install combined.

The instructions were awesome. Though I did cringe slightly at "Torque spec is good and tight." I'm an engineer, I like real numbers.

Car feels better, can't wait to try it out in a more performance environment.
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post #148 of 185 (permalink) Old 05-26-2015, 09:50 AM
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We installed our set yesterday. I have to say, thanks for making it so easy. The rears were cake. The most difficult thing on the whole install was the innermost nut on the ABS Bracket. That sucker did not want to come off (corrosion on the threads). I had to grab the base of the rubber bushing with pliers and spin it 1/16th of a turn at a time. That nut took longer than the rest of the install combined.

The instructions were awesome. Though I did cringe slightly at "Torque spec is good and tight." I'm an engineer, I like real numbers.

Car feels better, can't wait to try it out in a more performance environment.


If my memory serves me right the torque specs I believe is 32lbft. I refreshed the nylocks while I was in there.
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post #149 of 185 (permalink) Old 07-26-2015, 08:45 PM
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Alright folks, after a long wait, bumpstops are on the front dampers.

First of all, I ordered a set of the FCM 36mm bumpstops. 36mm Bump Stops The bumpstops out of the box are about the same length or perhaps a little bit longer than the stock Bilstein stops. They're definitely thicker than the stock stops though, suggesting that the rate is higher, so I wouldn't recommend putting them on untrimmed.

Luckily, there's a notch right in the middle of the stop that allows for easy cutting.



The stop on the right is an out of the box stop. The stop in the center is my trimmed stop, and the stop on the left is the leftover piece.

Install was very straightforward, and I marked the location of my perch so I could get back to my height setting.



Now the Penskes come with rubber O-rings on the damper shaft. This allows for easy spotting of how much the dampers compress in use. Remember that the only problem I had with rubbing was at the bowl at Streets of Willow, a right hand turn the day I drove it. What's interesting, and expected is that the O-ring on the passenger side was a farther from the bottom mount of the damper than the one on the driver side. This suggested, not surprisingly, that the driver side was compressing more (due to the higher g-load from the bowl, which is a very heavily banked corner). I was hitting about 1 g of cornering force turning left, but saw about 1.3 g in the bowl. The O-rings were right at the top of where the bumpstops are on the passenger side, but were level with the lip of the bottom gold perch on the driver side. Thus, it seems that the added stops won't engage at less than 1g of corner force and so the stops should have minimal effect on the engineered behavior of these Penskes. They'll just give that little bit of extra stiffness in the bowl to prevent rubbing!
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post #150 of 185 (permalink) Old 07-26-2015, 10:40 PM
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So the reason for the new bumpstops were just to have stiffer ones than stock?

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #151 of 185 (permalink) Old 07-26-2015, 11:21 PM
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So the reason for the new bumpstops were just to have stiffer ones than stock?
In a way yes. It's to prevent rubbing in the bowl while keeping the stock tuning for most other situations.

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post #152 of 185 (permalink) Old 07-27-2015, 01:26 PM
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Is it safe to say then, that the shock was NOT bottoming out even at 1.3g in the bowl [before adding the bumpstop]?

I know it had been previously stated but please exercise caution when driving at streets again. I think that if you take the car to the same limits as before in the bowl, your shock will definitely bottom out on the bump stop (since we know that the bump stop limit is lower than the O-ring indicator) and that might introduce a new dynamic to the system. I don't know what the outcome will be.

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post #153 of 185 (permalink) Old 07-27-2015, 01:53 PM
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"Bottoming" is kind of a relative statement. I believe the dampers were definitely on the (internal) Penske bumpstops, but those stops were probably not stiff enough to prevent compression all the way to where my (one inch smaller than stock diameter) wheels were rubbing the fender liner. These stops simply add a bit more rate, and perhaps a second step, to the bump stop curve.

I'm not scared of any real changes to the dynamics of the car. If anything, it'll just understeer a bit more when it hits the second stops, but there's so much grip through the bowl that I'm confident I'll be able to keep the throttle pinned down out of it. Also, I need to change my alignment settings slightly as the car previously just had too much understeer for my tastes.

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post #154 of 185 (permalink) Old 07-27-2015, 03:41 PM
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Quote:
Originally Posted by LionZoo View Post
"Bottoming" is kind of a relative statement. I believe the dampers were definitely on the (internal) Penske bumpstops, but those stops were probably not stiff enough to prevent compression all the way to where my (one inch smaller than stock diameter) wheels were rubbing the fender liner. These stops simply add a bit more rate, and perhaps a second step, to the bump stop curve.

I'm not scared of any real changes to the dynamics of the car. If anything, it'll just understeer a bit more when it hits the second stops, but there's so much grip through the bowl that I'm confident I'll be able to keep the throttle pinned down out of it. Also, I need to change my alignment settings slightly as the car previously just had too much understeer for my tastes.
Internal bump stop?

Smaller piston than you have, but similar internal construction:

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post #155 of 185 (permalink) Old 07-27-2015, 04:43 PM
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What's that black thing? It looks like an external bump stop to me.

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post #156 of 185 (permalink) Old 07-27-2015, 08:02 PM
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I was asking what you meant by "(internal) Penske bumpstops". I use traditional bump stops on my dampers. The image I showed was meant to point out there are no bump stops internal to the damper assembly, which is how your statement read.

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post #157 of 185 (permalink) Old 07-27-2015, 10:33 PM
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Okay for some reason I remember reading somewhere that the Penskes had internal stops, but I can't find where that somewhere is and so I may be mis-remembering. Regardless, if they DON'T have internal stops, that might be an even better reason to put on some stops as internal damper components hitting each other is probably not a good thing.

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post #158 of 185 (permalink) Old 07-27-2015, 10:56 PM
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Looking at the pictures in this thread, doesn't look like they come with any.

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #159 of 185 (permalink) Old 07-28-2015, 08:14 AM Thread Starter
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Bump stops are just springs used for NVH(Noise, Vibration, and Harness). Ultimately with enough force the shock or spring will go solid, OR the A-arm will hit the frame, OR the tire will hit the liner/clam. At that point the the car will lift. This is OK. Obviously, you don't want to do it constantly but the suspension and car will not explode when it happens.

A couple of examples:
Example 1:
Base suspension has a spring rate of ~235lb/in on the front. There is 3.5" of total shock travel and bumpstop is 1.4" long, leaving 2.1" of travel before the bump stop.

When you place the car on the ground the body weight absorbs over 1" of additional travel(It should be more, but the pre-load on the springs reduces that amount)

This leaves only about 3/4"-1" of travel before the bump stops kick in. When the bump stops engage, the effective spring rate goes up. Increase in spring rate = change in handling characteristics. In the front the car starts to push, in the rear it makes it loose. Unfortunately, the spring rate ramps up very fast creating very fast handling changes at the limit: instant push(front) or instant oversteer(rear).

So when loaded up in a 1.3G corner, the 420lb front corner weight, that outside force in roll could be as high as 750lbs! It only takes an additional 176lbs(235 X 0.75") of additional spring force before it hits the stop. That additional 330lbs puts the car deep into the bump stop, rapidly raising spring rate, making the car want to push. If it hits a bump in this condition, front slide or rear snap are nearly certain outcomes. This is also why even stock cars wear holes their liners. Soft springs and bump stops allow that much travel.

Example 2.
With the Penske shocks, the spring rates on the NAs are 350lb/in Front so immediately we have less travel/in. Stroke length is the same at 3.5". No bump stop except the 1/8" thick o-ring. The car loses less stroke at rest because the springs are stiffer(also in pre-load on NAs) So the car loses at most 1" at rest in the front, leaving 2.5" of travel. This means that car has ~875lbs of spring force prior to reaching the o-ring. This travel is linear with consistent handling characteristics because the spring rate does not change. Ultimately it takes more force to get the wheel to move up into the wheel well. Add to this the superior low-speed compression force of the shocks and you can see why bump stops are a bad idea handling-wise.

Now LionZoo specifically wanted the stops to control the wheel motion to keep his liners from being touched when he tracks the car in a specific banked, high G corner. As long as one understands the handling impacts, fair play.

However, depending on usage, I would either stiffen the springs or best yet, rivet in some aluminum rub patches to the fender liner to protect it regardless of spring and shock package. That way you get the springs, travel, ride, and consistent handling you want.


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post #160 of 185 (permalink) Old 07-28-2015, 09:59 AM
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Fred, while it's true that bumpstops limit motion and in theory, if your dampers are valved for one spring rate, you get best performance without stops, what is to stop component on component contact within the damper? Is it just the rubber O-ring? That sounds like very little margin.

Keep in mind, a good dumpstop isn't just an on off component. They ramp up in force so that the jerk from relative movement of the components of the damper isn't too high. A controlled landing if you will. With the O-ring, it's basically on or off.

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