986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Experiment: Installing 986 Coilovers on a 987

steved0x · 03-28-2019, 05:25 AM

I've got a set of 986 PSS9 installed on my Boxster, and now I need some suspension for my 2009 Cayman as I transition the Boxster back to stock format to sell it. (Ha, I am probably going to end up keeping both of them)

My plan was to remove and sell the PSS9 to a spec boxster person (as I didn't realize there was a shortage of PSS9) and use that money to fund some coilovers for the Cayman, but now that a new coilover is approved for spec boxster, I figure folks are going to want to move to that:

PCA Announces New Spec Boxster Shock Package

So, I need to find some coilovers for the Cayman. I have liked the PSS9 on the Boxster, and have shaved time on every track I have been to with them, and I have been thinking about moving them over to the Cayman.

There are a few issues to work out:

Struts tops - these are the same across 986/987
Strut bottoms - these are bigger on the 987
Height/positioning - in addition to the strut bottom being bigger, are there any other differences in height or mounting?

Strut tops

The strut top mounts are the same between 986/987 so no issue there. I have Tarett camber plates on the front and a stock rear strut top mount retrofitted with a monoball cartridge from Elephant racing so I am covered there.

Strut bottoms

I understand that the strut bottom diameter is larger on the 987 than the 986. I have heard that the backs are the same, and I have also heard that the backs are also larger on the 987.

Several vendors sell the same sku for 986/987 and include adapter sleeves so that the same kit can be used for either car, with the adapter sleeves not being used when installing into a 986. Ohlin's Road & Track is one. I reached out to them and they would sell the sleeves to me at $90 each, yikes

I reached out to several other vendors and MCS has the sleeves for $50 each and was able to set me up with a set. In the process of doing this, I learned more about their company and talked with some folks and I came away pretty impressed with their company and offerings. It is some serious $$$ though (relatively speaking

)

Height/positioning

Here's where I have some unknowns. I am hoping that the 986/987 struts are about the same between the 986/987 versions of the PSS9 (and between 986/987 struts in general, but this is unknown to me right now until I get a chance to take some measurements), this is the tricky one. Since the PSS9 does not have an independent height adjustment, the trick is getting the car to sit at the right height while keeping the piston in the sweet spot so that it has a good range of travel and doesn't bottom or top out too early.

Since the only set of 987 struts I have access to are installed in the Cayman, I don't have easy access to make those measurements. When I get a chance I am going to put it on jack stands and take the wheels off and see if I can get some measurements that way.

I am not too worried about the fronts, as the allowable range for the spring collars, as measured from the sway bar upper pinch bolt, has overlap between the 986/987 front PSS9 strut. Fro looking at pictures I can see that the fronts are very similar so I'm not too worried here.

In the backs, that range does not overlap between the 986/987:

I am hoping this is because the 987 rear PSS9 spring is a single larger progressive spring, vs the liner spring/helper spring combo in the front of the 987, and on both front and back for the 986.

I am hoping that the rear wheel carrier is substantially the same between the 986/987, with regard to the relation of the sway bar pinch bolt and the travel of the shaft, and I should be OK.

Stiffer springs

At the same time as I do this, I am thinking about going to some stiffer springs. Tarett sells the spec boxster springs which fall within the damping range that the stock PSS9 damper can handle. Right now my understanding is that the stock PSS9 springs for 986 are:

260 lbs/in front, 41.8% front (ratio front to back spring rate)
362 lbs/in back, 58.2% back

spec boxster is
447 in/lb front, 47.1%
503 in/lb back, 52.9%

That's a fairly big jump in rates and a moderate change in front/back ratio (unsure how important that ratio is, I just know I don't want to deviate too much from these "tested" ratios.

If I go spec boxster springs and don't like it, I figure I can easily resell them to someone doing a fresh SPB build.

Another choice would be to move that 362 spring to the front (they are the same size) and get the front SPB spring (447 in/lb) and put it on the back, giving me:

362 lb/in front, 44.7%
448 lb/in back, 55.3%

That wouldn't be as big of a jump in spring rate all at once, and has a ratio that splits the difference between spec box and stock PSS9.

If I were to do this but put the SPB 503 lb/in spring in the back, that gets me:

362 lb/in front, 41.8%
503 lb/in back, 58.2%

Which is exactly the same ratio as the original PSS9 rates.

I have noticed on the PSS9 stock rates that I can run my Tarett bars in the front, 2nd hole to softest, and rear bar 2nd hole from softest, and the car feels great. (Previously I had the front bar set to the middle hole with the M030 springs, too much understeer and when I moved the back bar up one hole in hardness, I didn't like the way it felt)

This is the area that scares me the most, playing with these spring rates, I feel like I could easily get into a bad situation, and while the fronts are pretty easy to get to, the backs are a big hassle. If I have to tweak I would rather do it by swapping front springs.

That's where I am right now. I am probably a weekend or two away from being able to actually get started on this work, but if anyone has been down this road before I would love to hear your feedback

03-28-2019, 05:25 AM	#1
steved0x Registered User Join Date: Dec 2012 Location: FL Posts: 4,143	Experiment: Installing 986 Coilovers on a 987 I've got a set of 986 PSS9 installed on my Boxster, and now I need some suspension for my 2009 Cayman as I transition the Boxster back to stock format to sell it. (Ha, I am probably going to end up keeping both of them) My plan was to remove and sell the PSS9 to a spec boxster person (as I didn't realize there was a shortage of PSS9) and use that money to fund some coilovers for the Cayman, but now that a new coilover is approved for spec boxster, I figure folks are going to want to move to that: PCA Announces New Spec Boxster Shock Package So, I need to find some coilovers for the Cayman. I have liked the PSS9 on the Boxster, and have shaved time on every track I have been to with them, and I have been thinking about moving them over to the Cayman. There are a few issues to work out: Struts tops - these are the same across 986/987 Strut bottoms - these are bigger on the 987 Height/positioning - in addition to the strut bottom being bigger, are there any other differences in height or mounting? Strut tops The strut top mounts are the same between 986/987 so no issue there. I have Tarett camber plates on the front and a stock rear strut top mount retrofitted with a monoball cartridge from Elephant racing so I am covered there. Strut bottoms I understand that the strut bottom diameter is larger on the 987 than the 986. I have heard that the backs are the same, and I have also heard that the backs are also larger on the 987. Several vendors sell the same sku for 986/987 and include adapter sleeves so that the same kit can be used for either car, with the adapter sleeves not being used when installing into a 986. Ohlin's Road & Track is one. I reached out to them and they would sell the sleeves to me at $90 each, yikes I reached out to several other vendors and MCS has the sleeves for $50 each and was able to set me up with a set. In the process of doing this, I learned more about their company and talked with some folks and I came away pretty impressed with their company and offerings. It is some serious $$$ though (relatively speaking ) Height/positioning Here's where I have some unknowns. I am hoping that the 986/987 struts are about the same between the 986/987 versions of the PSS9 (and between 986/987 struts in general, but this is unknown to me right now until I get a chance to take some measurements), this is the tricky one. Since the PSS9 does not have an independent height adjustment, the trick is getting the car to sit at the right height while keeping the piston in the sweet spot so that it has a good range of travel and doesn't bottom or top out too early. Since the only set of 987 struts I have access to are installed in the Cayman, I don't have easy access to make those measurements. When I get a chance I am going to put it on jack stands and take the wheels off and see if I can get some measurements that way. I am not too worried about the fronts, as the allowable range for the spring collars, as measured from the sway bar upper pinch bolt, has overlap between the 986/987 front PSS9 strut. Fro looking at pictures I can see that the fronts are very similar so I'm not too worried here. In the backs, that range does not overlap between the 986/987: I am hoping this is because the 987 rear PSS9 spring is a single larger progressive spring, vs the liner spring/helper spring combo in the front of the 987, and on both front and back for the 986. I am hoping that the rear wheel carrier is substantially the same between the 986/987, with regard to the relation of the sway bar pinch bolt and the travel of the shaft, and I should be OK. Stiffer springs At the same time as I do this, I am thinking about going to some stiffer springs. Tarett sells the spec boxster springs which fall within the damping range that the stock PSS9 damper can handle. Right now my understanding is that the stock PSS9 springs for 986 are: 260 lbs/in front, 41.8% front (ratio front to back spring rate) 362 lbs/in back, 58.2% back spec boxster is 447 in/lb front, 47.1% 503 in/lb back, 52.9% That's a fairly big jump in rates and a moderate change in front/back ratio (unsure how important that ratio is, I just know I don't want to deviate too much from these "tested" ratios. If I go spec boxster springs and don't like it, I figure I can easily resell them to someone doing a fresh SPB build. Another choice would be to move that 362 spring to the front (they are the same size) and get the front SPB spring (447 in/lb) and put it on the back, giving me: 362 lb/in front, 44.7% 448 lb/in back, 55.3% That wouldn't be as big of a jump in spring rate all at once, and has a ratio that splits the difference between spec box and stock PSS9. If I were to do this but put the SPB 503 lb/in spring in the back, that gets me: 362 lb/in front, 41.8% 503 lb/in back, 58.2% Which is exactly the same ratio as the original PSS9 rates. I have noticed on the PSS9 stock rates that I can run my Tarett bars in the front, 2nd hole to softest, and rear bar 2nd hole from softest, and the car feels great. (Previously I had the front bar set to the middle hole with the M030 springs, too much understeer and when I moved the back bar up one hole in hardness, I didn't like the way it felt) This is the area that scares me the most, playing with these spring rates, I feel like I could easily get into a bad situation, and while the fronts are pretty easy to get to, the backs are a big hassle. If I have to tweak I would rather do it by swapping front springs. That's where I am right now. I am probably a weekend or two away from being able to actually get started on this work, but if anyone has been down this road before I would love to hear your feedback Last edited by steved0x; 03-28-2019 at 05:29 AM.