Bonnet lift specs

Jacques

Lift Support Technologies Gas Springs - Custom to Spring Lift

He built a pair for me about 5 years ago from dimensions and a picture of my wife holding the hood up. They work fine; get hood up about half way and it lifts it the rest of the way. He is quite an interesting guy from Australia with business in Saskatoon. Tell him my name, Ken Battle, to track my order. He believes strut is common with a Lambo or Maz rear lid.

Be sure you install them with the seal side down to keep oil on the seal; I think Ferrari installed them wrong way around as I see most cars with them seal side up which dries out the seal in time.
Ken

 

I just finished reverse engineering the original struts. I can post the details if anyone is interested. The basic item that had to be reverse engineered was the gas charge pressure -- turns out about 25 pounds for each of two gas springs is optimal.

McMaster-Carr has these in stock. You will need two springs (McMaster-Carr 9416K22) and four ends (McMaster-Carr 6465K27) -- total about $50 plus shipping. Installed these today and they work well. The hood opens by itself from about the 2/3 point and will latch properly when dropped.

 

Nice work!

 

Please post the details. I am interested. (If you live in Berkeley CA I am also your neighbor.) One question I've never seen answered is, how to remove the struts. The pivots holding the struts to my car look like they require drilling out, but that can't be right, can it?

 

If I understand your question correctly mine are bolted in - drilled out rivets & removed part of the hood pad adjacent to the "pivot" to get to the nuts. Replaced w/ new rivets post install.
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Finally got around to scanning the papers that had my notes on dimensions. To make the actual force measurements, I removed both struts and made an adjustable-length force gauge to use on one side of the hood. Thus, all numbers are for a 2-D model of the hood and should be divided by two when using two struts.

In choosing a strut, one needs to make sure the minimum (compressed length) is less than the binding length. It appears that the hood does not have a positive stop when open and instead relies on the extended length of the strut to limit travel. This means that one can choose a strut length that will over extend the hood. The one I chose from McMaster-Carr is a little longer than stock and the hood works without any problems.

There is some room to pick the gas spring force. I picked 25 lbs (112 N) for each side and it works well. If you choose a higher force the hood will open by itself from a lower height. If the gas spring force is lower, then the hood may blow closed from wind too easily. I found 25 lbs to be a good compromise -- the hood can be drop closed from about 18" up and stays open in a breeze.

The question about fastening struts: I suspect my car is not stock in this regard. The left side hood pin is just like the lower hood pins but longer to go through three holes in the hood. it was missing the circlip so I was able to remove it by pushing the hood pad away from the hole. The right side on my car had a conrod bolt and nut pinning the strut to the hood. It can be accessed by removing the ignition module. I dont know if it is a Ferrari conrod bolt but I left it in there.

Devinder
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Yes, in Berkeley -- PM me and we can meet up.

 

Good day Devinder,

I am curious if the struts you found had a constant force throughout its travel and/or has a deceleration stage near the end of travel? I ask, as my BB's struts had maximum "lift" when one would be just opening the clamshell, but would decelerate nearing the full extension. I found this important as it minimizes the "snap" when the clam goes to is fully open state. When I looked for some after market struts I could not find any that had this deceleration effect and opted to work with LS Technologies in order to get something that was like factory. Thus, I was curious if you found the same issue with the ones on the 400?

Cheers,

Sam

 

I don't get a snap with these at the end, however I think that is because they are properly sized. I don't think it has anything to do with a deceleration stage. I took apart one of the original struts and it is as simple as any on the market now. It just has orifices to control the gas flow from one side of the piston to the other. Gas struts work by exerting a constant pressure difference on one side of the piston versus the other. The force should be constant through the entire range of travel. The force can be adjusted by varying the gas pressure inside. The rate at which it moves can be controlled by the size of the orifice.

I suspect the "snapping" at the end of travel was due to too high a gas pressure or to much flow through the orifices making it faster than needed. On mine, the hood travel is fairly slow once I lift it about 18" up and it maintains roughly the same speed all the way to the end of travel.

Another reason for the apparent deceleration at the end could be the different linkage geometry on a BB. On the 400i, the mechanical advantage of the struts gets better as they increase in length and the force exerted by the hood is also less as it opens. It is possible that on a BB, the mechanical advantage of the strut or the effective weight of the cover increases as it is opened.


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