318is Roll Cage Weld in- For Chasis Stiffness Chassis Brace/Strut Bars Needed?!

[zhp43867]

I have not picked up yet but will soon pick up a 318is. This will be a DD and track car. I am going to get a roll cage and pull the back seats, but I don't want the cage to protrude in to the front passenger door area. If I get a custom for this purpose what should I make sure the welder does, design wise? My main question however is with the weld in cage, are braces needed. I am talking about things like the Mason Engineering pieces. Front strut bar, rear strut bar, chassis brace and rear differential brace. From what I have heard the front brace may still be beneficial but not the back? Also, is there a particular thread I couldn't find about DD's with a roll cage, for example a sound deadening coating replacing the carpet or some thin carpet to cover the metal?

Thanks everyone! :D

[SkinnyVT]

Just to clarify you are going to have a rollbar installed, not a cage. The rollbar will do nothing in terms of rigidity of the front of your car. There is debate whether a rear strut bar does anything on these cars stock. Whether you need/want one in the rear depends on how you have the rear braces of the main hoop routed. Mine are attached to what in essence is a rear strut bar (piece of cage tubing going between the rear shock towers), so obvjously I do not plan on adding additional rear shock tower reinforcement. Others have their down bars go to the rear fender.

The first thing that most people will say is there is no good compromise between a DD and a track car.

[zhp43867]

Okay, well I'm going to try to compromise anyway. I am going to strip all the tar and carpet out, and now I'm thinking about some black e46 manual seats. Then spray some sound insulation and tuffliner in the back, with dynamat extreme mat underneath the stock floormats in the front. So people who say that the bar gives all the stiffness they need are talking about roll cages? Which is better/stiffer, fender or strut tower? Where would you recommend getting the roll bar installed? I think I'm about 6 hours from you but if need be I will travel that far for the best deal/worksmanship.

[jlevie]

A full cage will stiffen the car quite a bit if you run the rear down tubes to a point above the rear springs and cross brace the rear tubes. A lot is sacrificed if you don't install the front half of the cage with door bars. In that case you wind up with just a roll bar.

A cage (or just a roll bar) isn't really compatible with using the car as a daily driver. Pick one or the other. Either make it a pure track car with a full cage or make it a daily driver with nothing.

[zhp43867]

A full cage will stiffen the car quite a bit if you run the rear down tubes to a point above the rear springs and cross brace the rear tubes. A lot is sacrificed if you don't install the front half of the cage with door bars. In that case you wind up with just a roll bar.

A cage (or just a roll bar) isn't really compatible with using the car as a daily driver. Pick one or the other. Either make it a pure track car with a full cage or make it a daily driver with nothing.

I understand that with a full cage, but why not the back bar? I don't need the rear seats. Is it just not worth it and why? Would a bolt in bar be much worse if the welded isn't doing "anything"?

Thanks

[Fast Frankie]

nah, plenty of cars run roll bars and are still DD material. I say you just replace the carpet, leave the tar (or dynamat like you described) and then you'll be fine.

It's just a roll bar so it won't affect getting in and out. Will stiffen up the rear, add some weight, and overall be fine. The only thing is headliner since you're going to want to take that out to put the bar in correctly.

[SkinnyVT]

Do a bolt in rollbar and a front strut bar and that should be all the chassis stiffening that you will need until you get more serious about tracking your car and put a full cage in. The chassis stiffness won't be the thing that holds you back from going faster.

I would do a bolt in bar because you can just sell it later when you want to do a proper cage(that time will come probably sooner than later). When you do the cage you will want it as far away from your head as possible and that means no headliner/moonroof.

My cage was done by Chris Howard in Boston. He does a lot of spec miata cages but obviously has the measurements worked out for e30's also.