Sbeckman7's Project: BR1

[mooseheadm5]

You can make a linkage gear shift, so I wouldn't worry about that too much.

BTW, the input shaft for the diff isn't centered, so be sure to take that into account.

You won't really need to put the engine completely behind the front axle, so I would just put it where it makes sense. You may need to dry sump it or weld up a custom oil pan (if you don't want to weld up an aluminum one, you can get the pan from an E12 to cut up.)

Definitely start the frame at the subframe mounting points. That is the only way to do it. You can temporarily install metal blocks fro your subframe bushings, but I wouldn't leave it like that. When you go to actually drive it, substitute poly bushings..

[nnarth212]

You can make a linkage gear shift, so I wouldn't worry about that too much.....

Yeah-- think FWD, my CRX had a 4' long shift linkage.... weird to us BMW guys.

[sbeckman7]

Ok, thanks a lot for the input. I guess I'll conquer that one in the future. If the Diff/input shafts arent centered, I was thinking I would just use 2 u-joints to align the shaft. Should I keep the guibo disc?

[tsmall07]

I don't thing there is any need for a guibo (or center bearing, obviously) with how light the car is and how short the DS will be. You just need to make sure your u-joint angles aren't too extreme.

You might have to make a custom yoke to mate the trans to the DS without it though. I don't know.

[mooseheadm5]

You just need to make sure your u-joint angles aren't too extreme.

Definitely You may need to go to a CV joint setup or risk short driveshaft U joint life. A guibo is probably not necessary, but it is not a bad idea as it will absorb some of the flex and punishment that you will dish out.

[tsmall07]

Also, if you make a custom DS you'll want to make sure you get it balanced. Even a short DS can cause problems at high speed if it's unbalanced.

[sbeckman7]

thanks everyone. Where do you get custom df's or cv joints?

[tsmall07]

thanks everyone. Where do you get custom df's or cv joints?

If you wind up needing a custom yoke to mate to the trans, it would be a lot smarter to just use the guibo.

You can cut down a stock drive shaft and weld it back together (very carfully) and then have it balanced. There is probably a shop near you that does this, but I don't know where one would be. Try asking around at local machine shops.

[sbeckman7]

thanks, will do.

[warezdog]

just google driveshaft specialists tons of them out there independent now that the franchise died, cost you around $150 typically.

[sbeckman7]

great, that seems pretty reasonable (even if it is only for a 1 foot long pipe )

[sbeckman7]

So, just in case anyone was wondering, the length of an m30b34 + Getrag 265, measured from the front of the pulley to the back of the shift lever, is about 57.5". That means I'm going with my 99 inch wheelbase.

[mooseheadm5]

You can shorten the shift assembly quite a bit if you like.

[sbeckman7]

Well I could but I feel that 99 inches is a pretty good sized wheelbase if its going to be fairly wide as well. What do you think?

[sbeckman7]

Is there an accurate way to estimate the drop in ride hight once the vehicle is built? I dont want to have a dune buggy or scraper car. Are spring rates reliable measurements? I feel like the preload would upset the accuracy of their ratings.

[tsmall07]

You should use adjustable coil-overs for this project. That way you can set the height where you want. I don't know what spring rates you should use for such a light car. I would research other home-built racers and kit cars for a starting point.

[C.R. Krieger]

Is there an accurate way to estimate the drop in ride hight once the vehicle is built? I dont want to have a dune buggy or scraper car. Are spring rates reliable measurements? I feel like the preload would upset the accuracy of their ratings.

You have to have a sprung vehicle weight in order to use the spring rates. It's pounds per inch, remember? After that, it's fairly a straightforward calculation.

Preload shouldn't affect it at all if it's a constant rate spring. All you're doing is compressing it some. The rate should be constant until the coils contact one another.

Any thoughts of using the ps rack with out attaching the pump?

I trust, since you now have the subframe lying on the floor, that you know there is no rack.

[sbeckman7]

Any thoughts of using the ps rack with out attaching the pump?

I trust, since you now have the subframe lying on the floor, that you know there is no rack.

Yeah, poor word choice

So If I decide to go coilovers, I'd just get the Ground Control setup that my friend got for his e30. Would I theoretically be able to lower the top of the strut towers without changing the ride height? (Seems like I should be). Could I both lower the tops of the strut towers and lower the ride height?

[C.R. Krieger]

So If I decide to go coilovers, I'd just get the Ground Control setup that my friend got for his e30. Would I theoretically be able to lower the top of the strut towers without changing the ride height? (Seems like I should be). Could I both lower the tops of the strut towers and lower the ride height?

Since you're building the body, you can make the ride height anything you want.

I think you need to proceed in some kind of logical order before making suspension decisions. Start with all the parts you plan to put into the thing so you can find out how much it will weigh. THEN think about springs - unless you're already committed to making it as heavy as an E30 ...

[sbeckman7]

Thats good advice. The only problem is I'm not sure how much the stuff weighs. I've seen estimates for an m30b34 ranging from 315 to about 450. The transmission I would guess weights about 80 pounds, the diff probably around 100, and wheels probably around 20 each (?). Then there is the issue of the tubing itself. I will be using 1.5" 1020 Mild Steel for the majority of the construction, but I'm thinking about going up to two inches for the two main beams on the bottom, running from the front to rear subframes on either side. If anyone on here has experience with metalworking, the more feedback the merrier. I have read through many of those locost seven forums but they all use 1" square tubing, but my car will weigh much more and I prefer the added strength of circular tube. I know that Caterham uses a mix of square and cirular tubing, and this might also be a prefferred approach if it means an easier time mounting things like seat rails, fuel tank, dash, etc., and if it proves to be more cost effective.

[sbeckman7]

Minor update: Created the two main bottom pipes in CAD this afternoon that will be forming the base of the car and connecting the front and rear subframes. I'll try to attach pictures later, this computer doesnt have the necessary software. Also in CAD, although not at all related to this project, I've finished the dimensions for the block and pistons of my 7.3L flat 12 project. Same bore and stroke ratio as a 917... Figured it was best to start with a well proven configuration

[CJ_VAC]

What shocks/springs are you going to use? The stock front struts aren't going to be kit car friendly, i.e they will force a high hoodline, also will allow for a lot of travel so make sure you plan accordingly with respect to tire clearance

[sbeckman7]

What shocks/springs are you going to use? The stock front struts aren't going to be kit car friendly, i.e they will force a high hoodline, also will allow for a lot of travel so make sure you plan accordingly with respect to tire clearance

Not going to have a body Ill post some more up to date design sketches later, but it wont have much of anything. Cycle fenders and maybe a few fiberglass panels. Oh, I really want to order some parts from you when the engine is ready to go in. I think I'm going to do 12:1 pistons, a stage 2 head, and rod bolts.

What springs would you recommend? The only reason i would change the springs is to lower the top of the strut tower and stiffen the ride. I want the top of the strut tower as low as possible for cosmetic reasons, but any ideas on lowering springs (or perhaps better, coil-overs) would be really appreciated. I still find suspension stuff fairly daunting.

[tsmall07]

First, you don't account for wheels, tires, brakes, shocks, etc. for spring calculations. There's a reason it's called unsprung weight.

Second, what wall thickness will your tubing be. Is 1.5" the ID or OD? Once you have that information, you can easily find a lbs/ft number and be able to calculate a fairly accurate weight for the vehicle. BTW, you need to use DOM tubing for this project. You can go lighter if you use chrom-moly tubing but it is more spendy.

You need to get yourself a pipe master and/or a tubing notcher. Your life will be made much easier. You can get the tabs and brackets you'll need (for seats and mounting components) from Blue Torch Fab.

Visit Pirate4x4.com for tips on building a tube chassis. Their end use is different, but many of the techniques are the same. You can get a lot of information from the forums as well as the Tech Garage link on the main page.

[CJ_VAC]

Well the problem with lowering springs is you are going to need different shocks because you are changing the amount of suspension travel available. However, the car will probably weigh half of an E28, so you help yourself out there. Personally I would do something custom in the front, since you are building the frame to suit. The reason they are so high is for tire clearance. If you spaced the wheels out and used a coil over (getting rid of the spring perch) you could get away with something that has the proper travel and wasn't so high.

Feel free to ask away on any questions you have with the frame/suspension/brakes/engine...I'm a mechanical engineer by trade

[Tammer in Philly]

What shocks/springs are you going to use? The stock front struts aren't going to be kit car friendly, i.e they will force a high hoodline, also will allow for a lot of travel so make sure you plan accordingly with respect to tire clearance

Not going to have a body :) Ill post some more up to date design sketches later, but it wont have much of anything. Cycle fenders and maybe a few fiberglass panels. Oh, I really want to order some parts from you when the engine is ready to go in. I think I'm going to do 12:1 pistons, a stage 2 head, and rod bolts.

What springs would you recommend? The only reason i would change the springs is to lower the top of the strut tower and stiffen the ride. I want the top of the strut tower as low as possible for cosmetic reasons, but any ideas on lowering springs (or perhaps better, coil-overs) would be really appreciated. I still find suspension stuff fairly daunting.

There are a million off-the-shelf coilover setups with rod-end upper and lower connections that you could use with a custom double-A-arm setup. Since you're building a tube frame, you can locate those anywhere you want and probably make it work with a stock steering arm. That will cut several inches of height out of your design without costing much in terms of suspension travel if you spec the pieces appropriately. At the low target weight, you're not going to need very stiff springs and ride quality won't suffer even if suspension travel is shortened somewhat.

-tammer

[sbeckman7]

Tyler, Tammer, and CJ: thank you so much for your knowledge. Below is the image of my updated design. I plan to incorporate the struts into the sweeping architecture of the two main beams on the side (there will be plenty more support, I just wanted to draw a rough idea). This is why I am continuing to use the front struts; it is the essence of an e28 in a new body. That said, the problem with knowing the weight is I don’t know how much pipe I will be using, or even what type. I have decided on DOM, and I was thinking of using 1.5” OD for the main two x-pipes on the sides and the two rails running along the bottom of the car. I came to this conclusion after seeing many of those Locost Sevens being successful with 1” square piping, and then adding strength to compensate for a much heavier engine and drivetrain. That said, I’m essentially guessing. I’m not sure how to chose the metal because I have never done anything like this. That’s why your information is so valuable! I will definitely get that pipe master, and I already have a hole saw notcher (although it was a $50 Harbor Freight POS), but I would be really interested if you guys have any equations or techniques as to deciding on a metal thickness and weight. Thanks again.

Spence

[tsmall07]

Is your design based on any calculations or just what looks cool? You will need a lot more bracing than what is shown. Also, you need to stick with as many straight pieces as possible. You won't be able to bend those long radius pieces at home and it may be hard to find someone to do it.

If I were in your shoes, I'd get some 2" 1/8" wall DOM and start to make the main frame that everything will attach to. Then again, I'm a design-as-I-go kind of guy. This is supposed to be an engineering project, right? I don't think seat-of-the-pants fab work will fly.

[tsmall07]

What type of tubing bender do you plan to use (manual or hydraulic)? FYI, you can't use a pipe bender. If you plan to use a manual bender, you better weigh a lot and have big muscles. You can get plans on ebay to turn a manual bender into a hydraulic bender using the cylinder from an engine hoist.

[sbeckman7]

As of now my design is based just on what looks best. Part of the project is to make the design unique and nice looking. I realize I wont be able to have those sweeping angles created easily… Maybe I will either find a place around here that can do that or make three sharper angles. I'm a design-as-I-go guy as well, but I realize I do need more of a plan before I start building this thing. That’s why I came here. And like I said, I plan on having much more support, I just didn’t draw it in the sketch because I was focusing on the main pieces.