Constructional Criticism Please :)

[73-TYPE-LT-LS1]

I know a few people here have said not to go with the Martz rear suspension due to the major potential of binding. Well I bought it anyway, but don't plan to use it as it came to me. Please view the pictures and read my ideas and then give me your input. I think a 3-link suspension is very do-able keeping 99% of the stock floor pan.


As you can see the upper bar would be removed and the 3rd link would come from the drive shaft loop. I'd be fabbing a bracket to sit on the top of it. I think this is where the stock floor pan would have to be cut. The loop is 1/4" thick so I think it will have good structural integrity. This bracket could also be welded to the floor pan for added strength. Which is more than likely what I would do.









On to another part of this that was mentioned. The LCA's are short. 15"'s to be exact. I did some measuring tonight and I think they could be increased to 19-21". Here is how.

Moving the front cross member forward 2" on the car. Above picture there is a hole in the mounting tab. It is supposed to bolt in to the stock leaf hole then get welded up. I'm not sure this one will work as I don't have the car in the air and the suspension off of it.


The stock front LCA bolt is at the 11" mark on the tape (Bellow pics). This could be moved 1" forward and then radius drilled making it adjustable.

The rear hole is at 26" on the tape (Bellow pics). It could easily be moved to the 29" mark again, radius drilled for easy angle adjustment. I have one concern with this though. In the second pic bellow, you can see moving the rear 3" would put the LCA 3/4" behind the center of the rear axle tube. Would this have any ill effects?







I would also be planing to use 3/4" Grade 8 bolts (As you can see from the pics) since the plan is 1000rwhp when the boost is up. This is another reason I want to be able to swap it back to a ladder bar/4-link style rear at the dragstrip on full slicks.



Comments/Ideas/Concers please let me know.

[Cdog]

I'm afraid I don't have much to add to your idea. But I congradulate you for thinking out of the box. Good luck.

[BRIAN]

Honestly why don'y you just try it as is and modify if it doesn't meet your needs. The reason I say YOUR needs is a lot of guys here are into serious cornering and feel every suspension should be designed to attack a slalom course, which is fine if that is what your intentions are. Problem is you mention you are building a 1000hp motor which would probably totally disrupt any handling characteristics when you hit that pedal in a turn staying within a stock floored car. Honestly what you have there will provide driveability with the traction you need. There has to be a trade off with that HP level in regards to traction and handling. I would even say it might not be enough. 1000hp and 335 size tires in a stock chassis is downright dangerous. Ask any drag chassis builder what they would recommend for a 1000hp motor. The HP ranges keep going up with the new technology but that chassis was never designed to handle it. I am not putting down your combo at all. I just feel you should design car for your needs not what the guy with a 3000lb 350hp high rev slalom style car likes.

[73-TYPE-LT-LS1]

Brian,


I'm not taking your input as a put down to my ideas. I agree a 3-link with 1000rwhp at a drag track is not the best idea. This nice thing is the motor setup is going to be a using a large T88 or T91 turbo so I will be able to drop a lot of boost. With the Gen7+ stand alone, I will also be able to have a few preset tunes based on a given boost setting. I will more than likely drop the boost on a road course when using the 3-link suspension setting.

In regard to the tire at the drag strip. Per Martz, once the car is mini tubbed, I will have 15" from inner fender lip to the frame rail. There are 4rth Gen F-bodies running 1.2x and 1.3x 60's on a 10.5 slick. Here is a quick little Turbo 4rth Gen on stock style rear suspension with a 10.5 tire. http://stenodracing.com/thunder04/ts_1.wmv

[MuscleRodz]

Your idea to modify the rear setup is a step in the right direction. I don't think the drive shaft loop will support rear end loading without a lot of reinforcing. Salt Racer, Mean 69, or Dennis can help you a lot better on the why's and how-to's. Lengthening the LCA's will help a lot to reduce roll steer and anti-squat problems. It will help even more to lengthen the convergence angle of the UCA's to improve AS. Trying to put 1000 hp to the pavement without a very well thought out rear suspension will be pointless to have except just to say you have it. I am know expert and I am still learning, just my "young grasshopper" opinion. If I have explained anything wrong guys, please correct me.

Mike

[Steve Chryssos]

The primary limitation of the stock Martz design revolves around the fact that they tried to minimize intrusion of the floorpan/rear seat area. As you are willing to cut into this area, your mods should help.

You may find that you want to raise that front crossmember as well as move it forward. Once you cut the floorpan and take some measurements, some of our suspension-rocket scientists should be able to help with calculations. Be sure to establish ride height before measuring.

[Einstein1]

The quality of that piece looks very well designed in my opinion How much does it cost?

[73-TYPE-LT-LS1]

Einstein,

I agree it is a very solid built piece with great workman ship. The kit starts at $1250. I ellected to do a few upgrades like adjustable shocks and Sway bar.

[Piet]

Very little input here... just watching the answers.
What kind of shocks/ springs are you planning on using (coil overs?)
Also... this is done without modifying the width of the frame rails?

I would consider a custom sway bar for off strip cornering. Remove for drag racing?
My other thought is.. connecting to the top of the driveshaft loop seems to give the torque a lot of leverage to pull on it... ever consider doing a "Y" to the base on either side of the loop?

Very intersting though... looks like a simple setup. I like simple.
Oh yeah... also wanted to say.... nice choice in cars!

[73-TYPE-LT-LS1]

Pete,

The shocks are adjustable coilovers.

The sway bar is pretty easily removable on this set up. (Not pictured, look at Martz website and you will see it)

No modifacations to the frame rails just a little cutting of the floor board above the DS loop if I do the proposed 3-link. Again, the bracket will be tied in to the floorpan at either the top or sides with .25" flat steel. I was also planing on bracing the bottom of the DS loop with some 4-6" 45* angles front and rear on both sides running up the DS loop.




Here is a bad drawing but will give you a visual.

[Salt Racer]

...The reason I say YOUR needs is a lot of guys here are into serious cornering and feel every suspension should be designed to attack a slalom course, which is fine if that is what your intentions are...

Good point, but your statement is not entirely true. Here's a quote from my own post from previous thread about this suspension.

"...You guys, there are TONS of info about rear suspension from the old board in archive section. Rather than just asking "what's best?", try doing some research by yourself. You're building a car for yourself, and you know better than anyone else how the car is going to be used (BE HONEST!). You don't need killer road race setup for just cruising around town. Even if you do OT events occasionally, properly setup leaf springs can kick some serious arse! Read what CarlC and JonB69FB have done in their F-bodies in this thread. https://www.pro-touring.com/forum/sh...ad.php?t=2358G...Learn what the advantages/disadvantages of different setups, and YOU decide what you need for YOUR car..."

I'm one of the most bull-headed guys on this board who are actually into running old irons on road courses and slaloms. Other guys are much more liberal. Personally, I'm not impressed by cool-looking cars anymore, unless the said vehicles can actually back up their good aesthetics with equally great performance capability. BUT, as long as owners are happy and have fun with those cars, it's great. I just do/express what I like and enjoy, and they should do the same. That's the way I see it.

Now I couldn't agree more about ultra high hp car in a stock chassis/body. Even if your name is Michael Schumacher, you'd have tough time using all of 1000hp in a stock-platform Camaro riding on "mere" 13.5" wide radials, let alone the potential safety issues. But I'm speaking from my point of view and my purposes (I don't drag race).

BTW, I wish I had a 3000lb 350hp high rev slalom style car. I have a 4300-lb, 230hp low rev luxury-looking car with road race style suspension. Not practical, but perfect for showcasing my suspension design. It'll be my rolling resume when I finish everything up.


Anyway, onto the design...
You'll need to gussset the hell out of that loop if you want to use it as UCA attachment point. There's a lot of leverage.

Where's the lateral locator? (PHB, Watt's, etc) Is the UCA in the mock up pic the PHB? If so, it looks kinda short to me.

Nobody can really give you any pointer on pickup points (ie, geometry) unless you mock everything up, including chassis/body & axle at the ride height, and you supply pickup point measurements. LCAs are pointing down slightly in the pic, but would they be at the same angle when you assemble the whole thing in a car? Don't assume anything. You've spent good amount of money on the system - do it right.

Tack weld that crossmember in the car as far forward as you can. Tack weld axle brackets on. You may have to alter them later (mainly height). Set the car at the ride height you want with wood blocks under subframes, calculate the tire rolling radius (roughly diameter/2 minus 0.7" or so) and set the axle centerline at that height. Mock up PHB. Then measure XYZ coordinates of each pickup points. Plot top view and side view of those coordinates on CAD or a scaled drawing.

After doing that, read this thread until you understand 85% of the technical content.
https://www.pro-touring.com/forum/showthread.php?t=203

That should give you a rough idea of what needs to be revised. Then I'd be more than happy to give you additional suggestions, etc.

[Norm Peterson]

Just to echo the concern about having the D/S loop carry the entire UCA load - I have lots of doubt, even at only street levels of grip. If you feed that load into the floorpan, you'll need to spread it out over some distance. What you're proposing as reinforcement is certainly do-able, but it's much like adding a suspension pickup bracket to a monocoque structure. Keep in mind that the stresses need to be kept fairly low, for reasons of fatigue life. As a really rough approximation of how much load is involved, that upper link carries a similar tension load under acceleration as either lower does in compression.

Actually, there's substantial argument for putting a bigger rear sta-bar on for your strip passes than you'd use for the street or any corner-carving events. What that does is use the engine torque reaction carried back through the chassis to return some of the load to the RR tire that the driveshaft torque reaction removed. Disconnecting the front bar will help this effect in addition to lowering the resistance to rise (the reason that everybody thinks of first is not the only reason). Given that the pavement is equally grippy in both wheel tracks, equally loaded rear tires will out-pull an unequally loaded pair with the same total load. Even with a spool.

Longer links will slow down the rate of change in the anti-squat, and converging the lowers makes the rollsteer less sensitive to changes in ride height.

Norm

[73-TYPE-LT-LS1]

Norm,

Regarding the load the UCA will see makes sense. The back seat will not be used do to the roll cage and other reasons. Perhaps I should think about tying the roll cage in to the mount. A Y coming off the middle cross bar or the inner bars that run from the main hoop to the floor.

[73-TYPE-LT-LS1]

Salt Racer,

I agree that with out true knowledge of where the pick up points are, you can't give me a real answer. I'm not sure I can provide that info for a few weeks, but I plan on doing just that.

I have been through that post about 5 times now. I do understand a decent amount of it and learn more each time I read it The one abreviation that I have not figured out that will probably help me understand more is SVSA.

[Norm Peterson]

Perhaps I should think about tying the roll cage in to the mount. A Y coming off the middle cross bar or the inner bars that run from the main hoop to the floor.

That's a much better approach. Can you tie the Y (or two separate diagonal tubes) directly to the D/S loop? I've seen variations of that in a few race car pics, and I might have one D/L'd and saved somewhere. Anyway, make sure that you are loading all of the tubes in tension/compression rather than in bending. Don't forget to leave enough room around the pickup bracket for access to and removal of the bolt.

Incidentally, SVSA is Side View Swing Arm, which is a virtual link that effectively describes the movement of the axle as seen in side view. It pivots about the Side View Instant Center (SVIC). Since the SVIC moves around a bit with suspension motion, the SVSA is not of constant length, and the resulting side-view axle motion is therefore not a true circular arc.

Norm

[yody]

The first thing I noticed when I read this post was that you HAVE to do something more to that loop to attach a upper link to it, but I see everyone else already responded to that. It is common knowledge that beefy rear sway bars help straight line acceleration and help reduce some of the uneven body twist that drag cars produce. I have seen 1 3/8 sway bars on the rear of grand nationals. There is some good info posted. Not all posts ge tthe attention of all these guys.

[baz67]

It is hard to tell by your mock up, but it looks like your SVSA would be exceptionaly long. I gather that by the length of the UCA and by your mounting it on the top of the driveshaft loop. That would lower you anit-squat somewhat.
Brian

[Steve Chryssos]

Norm,

Regarding the load the UCA will see makes sense. The back seat will not be used do to the roll cage and other reasons. Perhaps I should think about tying the roll cage in to the mount. A Y coming off the middle cross bar or the inner bars that run from the main hoop to the floor.

Both are probably too far forward. If you've bailed on the driveshaft hoop idea, and you are incorporating a roll cage, then you're on the right track. Don't worry too much about reinforcement for now. Get the pivots properly located and the reinforcement will become obvious. Maybe an upper crossmember tied into the rear down bars of the cage with a vertical mount that drops down to meet the third link--plus triangulation from the upper crossmember to the lower crossmember.
Whatever--you won't know for sure until you finalize the forward pivots.

[73-TYPE-LT-LS1]

FYI, The UCA shown is not the one I will be using. That was just used so people could understand what I was talking about.


I'll try and have some real numbers on the pick up points in the next few weeks.

[Mean 69]

I think a 3-link suspension is very do-able keeping 99% of the stock floor pan.

I am a little unclear on this statement. Where are you planning on locating the upper link, on the differential? I'd have to assume in the middle, in which case you need to plan on creating a tunnel for the UCA to live in while the car is under bump. It'll need to be quite a bit wider in the rear to accomodate roll of the rear axle, too.

If your lowers are parallel in plan view, I'd make certain they are not upward inclined (from rear to front) very much, if at all. You are on the right track by making them as long as possible, in my opinion this is a good thing. You are also on the right track in terms of reinforcing the UCA mount (front), just make certain that any triangulation nulls out longitudinal (i.e. along the vehicle centerline) forces, as this is basically all this mount will see.

Mark

P.S. Good stuff!