Front subframe design - suspension/steering experts please provide input

[J-Ville VR-4]

Its not that advanced tech, but this section of the forum is a little skimpy lately and could use some new topics.

I had lunch today with my friend Dan, who started a company that sells kits for mounting LSX engines into miatas. Dan and his partner Richard (both good friends of mine) designed and build all parts of the kits, which include a tube steel front subframe. Anyways, I threw out the idea of making a new front subframe for my car since I'm tearing it all apart now anyway, and he said he would be happy to take on the project. He knows his way around a 3/S - his wife owns one, and he has helped me out with my car and other 3/S's from time to time, so this should be no real problem. Dan has some cad software that he uses to design the subframes, so they are easily duplicated, which means he will be able to make more to sell if any of you are interested.

I started this thread to discuss what improvements could be designed into a new front subframe. I'll start out with the obvious: it will thankfully drop some weight off the front end of the car, I'm estimating around 15-20lbs maybe. It will be mild steel, chromemoly is not an option.

The control arms mount to the chassis, so I assume changing suspension geometry is out of the question. Would it be worthwhile into designing control arm mounting points off of the subframe instead of using the stock chassis points?

I'd like to provide a little more room in the rear to accomodate room for 4" exhaust to fit back there correctly, this shouldnt be a problem at all. Also, I will be sure to make this design much more friendly regarding the tight clearances involved when removing/reinstalling the transmission if possible.

The steering rack: Would there be any benefit to repositioning the steering rack at all? I thought I read awhile back that moving the rack forward/back affects the amount of ackermann steering a car will have, would it be beneficial to mess with this? I guess I need to dust off my old Carroll Smith books.

Engine mounts: I have maximal performance solid mounts in my car now, and I am very happy with their performance, so I plan on designing solid mounts into this design as well. I remember the stock motor mounts that bolt to the block are hideously oversized (isnt there turbo clearance issues with these for some TD05 guys?), I will consider making new pieces that are smaller and less obtrusive.

Bushings: The stock subframe has bushings, correct? I see no real need for bushings anywhere on there. I really wish I had my car torn up right now to the point where I can access my subframe better at the moment so I could be more certain about some of the things I bring up, but I'd rather start planning this asap.

Anything else anybody can think of?

[ah4449]

Look into allowing a little more room between the oil filter housing and the subframe, basically where the oil cooler fittings thread on. Main reason for bringing this up is I just put on an aftermarket SMOC and used AN fittings and had to buy another set of 90 degree adaptors other than the ones I already had because there wasn't enough room... The fittings still didn't hang down past the oil pan or anything they looked perfect until I tried to put the subframe piece back on, which was where the problem was...

And I would definitely be interested in a modified/redone subframe, I hate those stock pieces; pending price and all that normal stuff.

My .02...

[J-Ville VR-4]

I finally tore my car down to start on everything - the engine should be out next week sometime, the only thing holding me back on doing that is clearing room in my garage for the engine stand, lol. Once the engine is out I need to bug Dan a bit more, then we will make a jig for the subframe and get to work on building the new one.

I was hoping for a little more input than this on the subject, but not really expecting any. Its probably going to be a pretty straightforward build anyways, I think I have covered most of the ideas I'd like to incorporate into the new design already.

Bottom line - I'm really going to have to nag Dan to get started on this, as he is really concentrating on getting his next LS1 miata up and running great for some big miata meet at the tail of the dragon in a couple of weeks. So that means it probably wont get started for another month, which is fine with me because I have TONS of other projects to work on with my car in the meantime. I do want to get started as soon as possible on it still.

[BBBBill]

I'm interested. I just can't offer any intelligent suggestions as I don't know the platform well enough. Just try to incorporate the above suggestions, make it strong, and try to save some weight while not breaking the bank in the process. If you can get some potential suspension geometry improvements, so much the better. I recall someone developing some improvements for the last generation of Camaros/Firebirds that paid great dividends in handling for a fairly miserly amount of $.

[Workin On It]

I'm with devils mentor on this it would be great to have the option to swap the motor or use a flip forward (clamshell) hood. It could really open up a lot of room and a lot more possibilities. A longitudinal setup would be a really sweet possibility. Its something I've considered for awhile.

Greg

[zba857]

i would think it would save a lot more than 15lbs. Yes the subframe has bushings. Are you just talking about the longitudinal straps, like the tranny support member and the one next to the oil filter? I think you are talking about the front subframe, so disregard. Would this include the straps? If this could include mounting provisions for aftermarket steering racks that would be prime.

Why no cromemoly?

How much??

[niterydr]

I have a chromemoly front "subframe".
The 2 pieces that go from the steering rack area up to the front of the car, and that front crosspiece that goes near the radiator.

Saved about 15lbs, we can even sell them with a chromemoly front motor mount.

Wasn't that expensive, but no-one was interested at the time.

Some pictures can be seen here from last season when I still had the twin setup:
http://www.lseperformance.com/galler...g2_itemId=2130

[J-Ville VR-4]

Originally Posted by Devils Mentor

Sounds like a hand full Bro... Good Luck with it all... If you need help let me know...

Here is an Idea though, what about a complete Tubed front end, meaning Forward of the Firewall to tip... That would be the Shit!!! Would leave so much open for all kinds of options (motor swaps, Coil over crossovers use, so so so much more) plus it will give some greatly need open air/room... Should not be any harder, just a little more material... That would be the BEST way to go!!! IMHO of course, but we all know that matters the MOST on here



DM

A complete tubed front end would be a SHITLOAD more work and design involved, I would have to redesign EVERYTHING, which involves all of the suspension geometry, way more mounting points for stuf like body panels and the other engine mounts, crash safety design, etc. All this design is WAY more complicated then it may seem and would take much longer to do than I want to spend.
If I was making a purpose built track car I'd consider it, but my car is being built for the street, and I do want to get it running sometime this century

Originally Posted by Workin On It

I'm with devils mentor on this it would be great to have the option to swap the motor or use a flip forward (clamshell) hood. It could really open up a lot of room and a lot more possibilities. A longitudinal setup would be a really sweet possibility. Its something I've considered for awhile.

Greg

As I said with DM's post, I'm not looking to redesign the whole front end, its fine how it is. I DEFINITELY am not out to do any radical design changes like rotate the engine layout and have to find a different drivetrain to go with it. This is just for a simple redesign of a bolt-in part.

Originally Posted by zba857

i would think it would save a lot more than 15lbs. Yes the subframe has bushings. Are you just talking about the longitudinal straps, like the tranny support member and the one next to the oil filter? I think you are talking about the front subframe, so disregard. Would this include the straps? If this could include mounting provisions for aftermarket steering racks that would be prime.

Why no cromemoly?

How much??

I'm talking about building the 2 longitudinal straps and the 2 transverse ones - the front support that has the front motor mount and runs parallel to the radiator, and the rear "dinosaur bone" as my buddy calls it, that has the steering rack running through it.

Using an aftermarket steering rack, now thats a great idea that had not occured to me, thanks for that idea! I am deleting my all wheel steering so the rack will be more comparable to most other cars out there.
I will look into a few different options here:

1)I will look into some inexpensive racks out there, like some ford or chevy racks, I'm sure they cost loads less then even our reman'd racks do. Cheap is good!

2)I'd like to consider a rack that has has a much better ratio (I think thats the correct term). In other words, a rack that requires fewer rotations of the steering wheel to get from lock to lock.

3)This probably is the least practical option for me since its really straying away from the original design of the car, but I'll at least look into it, it might be more do-able than I think: Adapting an electric rack or a hydraulic/electric rack from an MR2/S2000, etc. It would be nice to delete the power steering pump and beltline altogether, but I dont know if the electric rack is up to the task of the extra weight and wider tires, or it might require some extra sensors in the steering wheel or input from the ecu, or is might just be simply crazy expensive.

4)Are there any aftermarket steering racks out there that would be suitable? I've never looked into this subject really.

Chances are (I'm just being realistic and trying to stick to my goals) a different steering rack is not going to be incorporated into the design, but I'm NOT ruling it out - its worth looking into.

Oh, and chromemoly is not an option for us at the moment because none of us have any experience with it, and they are not ready to begin using it yet.

Originally Posted by niterydr

I have a chromemoly front "subframe".
The 2 pieces that go from the steering rack area up to the front of the car, and that front crosspiece that goes near the radiator.

Saved about 15lbs, we can even sell them with a chromemoly front motor mount.

Wasn't that expensive, but no-one was interested at the time.

Some pictures can be seen here from last season when I still had the twin setup:
http://www.lseperformance.com/galler...g2_itemId=2130

I assume subframe isnt the best term for what I am describing? I never did like suspension and chassis terminology, hehe. What is it called then?

Thanks for the pics! Out of curiosity, what was the price on that? If the price is right, I may just end up buying one from you instead of going through the hassle of building it