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#1068651 - 11/19/20 12:00 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Marc I'd say the weight/size reduction between a comparably equipped A body and G body would be a little less than 5%.. My 72SS Chevelle was 3700 lb, SBC, TH350 and a 12 bolt with no A/C. The 86 SS with a SBC, T56, 8 1/2" is 3625, has power everything + A/C. I think when people look at the Gs gross they get a little confused by the 78-79 light weight A/G years, they were a good bit lighter than the later 82 up metric G's. It's difficult without a significant weight reduction diet to get a G less than 3400. Of course no driver weights included. My car is a fat G I agree, and no where to shed a few pounds without big dollars again.

Also need to remember the A and G were both the mid size car of their day. Much bigger and a little smaller were the other choices in a GM. When the car manufactures were mandated by the Feds to improve fuel economy and reduce emissions again in the late 70s GM shrunk down the A to become the A/G, later the G which became the last midsize with a frame and an old school chassis.
I'm just thankful I didn't buy that 1991 Lumina Z34 in 1991, bought my 86SS that year instead.
Bob

#1068656 - 11/19/20 03:35 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Hi Bob - The weight basis of comparison was the larger 1973-1977 A-bodies, which had about the same interior volume as the downsized 1978(+) A/G bodies. We know the 1973-1977 A-bodies transitioned seamlessly into the 1977(+) B-bodies with the frame, suspension, and drivetrains. So we could say GM did some sleight-of-hand in how they transitioned their body designations through those years. CAFE and OPEC - all of these arose from the 1975 Middle East oil crisis...

Yes, the A-bodies with the 305 in 1978 were right at 3,400lb as mine was. I think registration (in NY) showed 3,280lb, but I believe that was the dry shipping weight.

Last edited by MAP; 11/19/20 03:41 AM.
#1068657 - 11/19/20 04:11 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Originally Posted by MAP
Hi Buick,

Quote
Space is a major issue for G body rear suspensions. GM basically sacificed space away from the rear suspension in order to have more space for the rear seats and trunk. G bodies are mainly designed to be Grandma cars with focus on space and comfort, they never were intended for high performance which is always going to be a problem.

Just for an interesting comparison, Ford's Panther platform such as Crown Vics used C4L rear suspensions with a Watt's link until 2003 when the frame and suspension were completely redesigned. Post 2003, Panthers use parallel 4 link rear suspensions with a Watt's link.


Well said about A/G bodies! The GM design mandate was to scrub 800lb of weight from the car starting with the 1978 model year while minimizing the reduction in interior cabin volume. Hence, doors with much thinner section profiles, engine hard-up to the firewall, and not enough room for the rear suspension. "Grandma cars" definitely nails it, sadly. The Panthers put the WL atop the diff case, right? If so, we still have a very tall RCH.


The WL is mounted high so the RCH is still high. However, it still seems to perform better than the rear suspension in my Regal. Through I will say the CVPI does tire slip pretty bad when accelerating from gravel or wet dirt. It seems in many cases with cars, performance is sacificed for utility, that there is a performance / utility tradeoff. Most passenger cars leans more to the utility side.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1068658 - 11/19/20 05:29 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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mmc427ss Offline
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Here's a truck arm used on Al Unser Speedway 1st Gen Nova.
https://www.speedwaymotors.com/G-Comp-Unser-Edition-1962-67-Chevy-II-Nova-Rear-Suspension-Kit,232050.html

Also here is another Nova build. Pic is at the bottom of the page.
https://lateral-g.net/forums/showthread.php?t=58772&page=2

The truck arm always intrigued me.

Many years ago Dennis Kirbin along with a couple other investors did a repop of the GNX rear suspension and offered a kit to install it in any G-body. He had an open house event and a donor GN was on a rack getting the kit installed. I was able to walk along side as they fitted the kit into the car. Pretty cool. Kirbin always had gorgeous personal TRs, the one at the time was sitting outside with the GNX kit already installed. As we were leaving his open house a 500 mile GNX pulls up and parks, it was a fresh buy off a Buick dealership's floor, this is 2000. Have seen numerous original GNX over the years and still have a curiosity about how ASC McLaren engineered and threw 547 GNX together in short order. And did they think the torque arm was the answer or the novelty. Was there that much engineering or did they just adapt the 3rd gen F torque arm into a G. And yes the Kirbin GNX kit required a GNX catback system because of interference with the torque arms front crossmember if I remember correctly.

The Kirbin kit has been gone years ago. Some of the GNX alum rear covers show up occasionally. Not sure if it would be a better starting point for a torque arm or three link than the cover I dreamed up for a Watts on an 8 1/2".

As usual just kicking the can doing some musing about a cheap easy fix for the turd.
Bob

#1068672 - 11/20/20 08:00 PM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Hi Bob,

I hope I'm not being too repetitive in saying that the only disadvantage with all of these options is weight. We're going from heavy (i.e., stock) to heavier (i.e., non-C4L.) But the increase isn't huge: maybe 4%-15% or so, depending on the suspension solution you apply. If you drive mostly on smooth roads, that may work fine for you.

Best,
MAP

Last edited by MAP; 11/20/20 08:01 PM.
#1068686 - 11/22/20 02:06 AM Re: SS rear suspension: thoughts and musings [Re: Buick Runner]  
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Originally Posted by Buick Runner
The WL is mounted high so the RCH is still high. However, it still seems to perform better than the rear suspension in my Regal.
The Watt's link they added in 1998 must have helped, because my SS handled (overall) a lot better than my mom's 93 Marquis and it had the option handling package. I can't say one way or the other about what difference there was comparing front and rear handling though. Plus, I'm sure the tires on my SS were a lot better than those on the heavier Merc as well.

#1068689 - 11/22/20 03:37 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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In reading these last few posts involving WLs on Fords, I'm having a hard time discerning how it helped handling. Basically, anything that constrains the roll center to be in a certain place, whether it be a virtual intersection of link centerlines, or a real physical pivot of some sort (e.g., a PHR or a WL,) should perform equivalently. That's why I deliberately avoided approaching that topic from the hardware standpoint.

#1068693 - 11/22/20 11:46 PM Re: SS rear suspension: thoughts and musings [Re: BadSS]  
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Originally Posted by BadSS
Originally Posted by Buick Runner
The WL is mounted high so the RCH is still high. However, it still seems to perform better than the rear suspension in my Regal.
The Watt's link they added in 1998 must have helped, because my SS handled (overall) a lot better than my mom's 93 Marquis and it had the option handling package. I can't say one way or the other about what difference there was comparing front and rear handling though. Plus, I'm sure the tires on my SS were a lot better than those on the heavier Merc as well.


By 2003 Ford completely redesigned the frame and suspension for Panthers. A cast aluminum sub frame, rack and pinion steering, and coil over struts upfront with a switch to parallel 4 links in the rear. Plus being a police package, my Crown Vic has stiff springs, shocks, and 17 inch wheels, through thinner sway bars because of the stiffer springs. Of course comparing a police package car to a base V6 model Regal or a mid level Marquis to SS package isn't fair.

Last edited by Buick Runner; 11/22/20 11:57 PM.

SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1068705 - 11/23/20 07:57 PM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Interesting, Buick, but unless I'm missing something, I don't see any clear takeaways for the present conversation. Basically, a high RCH has problems, whether that happens through some virtual intersection of link centerlines, or a PHR, or a WL, or what-have-you. Conversely, any goodness in a given RCH will be independent of the means used to constrain it.

Last edited by MAP; 11/23/20 07:58 PM.
#1068712 - 11/24/20 08:28 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Sorry for the side tracking. I just think Panthers make an interesting comparasion and benchmark for improving G bodies. Afterall, Panthers are the last V8 powered, RWD, body on frame cars plus the early versions were constructed pretty similar to Gs while latter versions have a host of improvements.

I like to think that in some alternate timeline where GM kept producing body on frame cars to a much later date that they too would have recieved improvements to their frames and suspensions similar to Ford Panthers. It is unlikely Ford went to the trouble of adding a WL to mid C4L Panthers let alone completely change the rear to a P4L for late Panthers for giggles.

Personally I don't have any concern in a 3 link vs Watts fight nor did I intend to start one. It just seems that G body suspension upgrades boil down to making the best of a bad situation. The best solution is probably a completely redesigned new frame and suspension simiar to late Panthers. Sometimes you just have to start over.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1068720 - 11/25/20 07:42 PM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Hi Buick,

No problem. That comment about changing from the C4L to a parallel 4L with WL is an interesting one. I would say that if it didn't change the RCH, then the change was done for reasons other than performance - like maybe packaging?

I definitely agree that the OE A/G body chassis has so many shortcomings by modern standards that it is now cheaper and easier to fix them with a brand new performance-specific frame/suspension rather than a piecemeal fixing of the original.

But I would go even beyond this and re-engineer the whole car, by integrating the body with the frame and making big adjustments to the distribution of inertia within the car.

Best,
MAP

#1068733 - 11/27/20 04:00 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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So Marc after it's all been said and done about the poor C4L configuration on the G-body is there no real viable fix to improve upon it. I think we all understand after owning a G for a long time and making suspension changes that there is no WOW moment that is easy, affordable and doesn't involve cutting the car up.
Lowering the rear roll center, and increasing the rear tire width (available grip) seems to be my goal. And of course reducing the unsprung weight would be good but hard to do other than an IRS.

Not planning any major changes in the rear soon after spending a good bit of time and money on rear spring and shock combos looking for a bandaid. Rear roll center is what left to play with.
http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=1063953#Post1063953

Lance has been able to deal with the rear suspension ills via driver talent and seat time on track. LUCKY HIM. And with a fresh set of tires on his car he's very competitive against a field of very good cars, and drivers. Again I credit a lot of that to his driver skill and the 100s of runs at the autox.

Have been playing to improve the performance of my 1986 for soon to be thirty years. FIRST on that list more than two decades ago was front brakes which snowballs to the point of all that is left original of the rolling chassis is a modified frame and modified front LCAs. Also being a hands on, do it my way, and a little miserly, looking at all the info, choices, which leads down a path. I don't think I made many bad choices dealing with available parts at the time. Some parts were upgraded several times, but attribute that to the progressing technology and market interest in your particular car. Lucky for a G that it's a Chevy and a little brother of the A- body and they made a million of them. It took a little longer to get there than a few other cars but good parts are available to improve the G rolling chassis. today. But as mentioned it's still about polishing the turd.

Have looked at other rear systems we have mentioned here in this post and know there is no easy fix and no real winner in the various options, they all have a negative and positive side.
As I moved into the "golden years" the need to make a change in the rear suspension has become a non-issue. Just like the need to have 600 hp under the hood someday the 500 hp there now is more than enough to get me in trouble. Building an autox competitive car to run a couple times a year ain't going to happen, Lack of venues, especially this year, along with time and distance constraints limits driver seat time which effects driver skill.
So kinda stuck beating the car around some nice back roads in pothole heaven Pa. Seat time is limited to hitting that 90 you've run through many times to see if you can get it back after being to aggressive, or as the case last week, saving it.

Tires, the equalizer. The best money, unfortunately a big chunk, would be a 9 1/2 x18 wheel with a set of brand new 275/35x18 200 wear rated autox/street tires. That would be a noticeable handling upgrade, and the easy way out. But another compromise. I like the 255/50x16 Comp 2 tires on the car, more sidewall to deal with the poor roads, same tread width, section width, just a little taller than the 275/35x18 which helps keep a lowered car safe here. The big problem with tires is they age in front of your eyes. If you buy a 330 tire you would expect to get give or take 30 K life out of it without abusing it. If you put 2K a year on that tire it will last 15 years, not, it's junk way before the tread life is gone. My 330 rated Comp 2 only have 10K on them, a little over 5 years old, just getting down to the good handling tread depth but the compound has aged. Will replace in the Spring with some fresh hides. I learned this lesson the hard way with my previous set of BFG KDW tires, worthless for rear traction when they aged, junked when you got to the good depth of the tread. A 200 tire would be a good choice for me but unfortunately there is nothing available in the wheel size currently on the car.

Hoping this thread continues and we find some magic way of controlling the rear roll center without scraping the entire rolling chassis.
Bob




Last edited by mmc427ss; 11/27/20 04:03 AM.
#1068735 - Yesterday at 04:16 AM Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Hi Bob,

Well, the live axle won't hurt you as long as you drive on smooth sections of pavement. Ditto a high RCH. Use tires with a tallish, soft sidewall so that you low-pass the coupling of the sprung mass with the unsprung mass. If you go back to the post where I say a 1"-tall one-wheel bump pushes the chassis 0.3" to the side with an 18" RCH, another way of looking at what we're trying to do with a soft tire is to get all of this deflection to be absorbed in the tire's sidewall, rather than have it transmitted up to the sprung mass. This will allow the rear to track road roughness better than would be the case with stiff tires. It also helps push the car's handling balance toward oversteer, but by dialing-back rear roll stiffness, it shouldn't be hard to keep the car's balance where you want it.

But yes, I have to agree that if you want it all, then major surgery is in order.

Best,
MAP

#1068751 - 9 hours ago Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Hi Bob,

Just some further commentary here. The C4L live-axle factory design with its towering RCH definitely does some bad things kinematically, and therefore dynamically as well. On a smooth surface, however, these issues disappear, which explains why live axles are so competitive on tracks. I think I even said somewhere else that on perfectly flat surfaces, you might as well run a live axle up front too.

But bad things start to happen when you want good handling on rough surfaces, and especially when that roughness presents itself as difference-mode inputs on that axle as opposed to common-mode. This is where the live axle's high unsprung mass and the OE high RCH really hurt you.

I experimented with different RCHs on a rear live axle in a 1:7 (ish) scale model, with tires that had nearly infinite stiffness. One RCH I experimented with was so absurdly high that it put the COM right on the model's roll axis, so you'd get zero roll in any turn, even without sway bars. And it accomplished this goal admirably well. Handling on smooth surfaces was absolutely exemplary. But on rough surfaces, it bounced and skidded and convulsed sideways all over the place. As I reduced RCH, roll increased, but it handled better on rough surfaces. Handling was best when the RCH was zero.

So back to the OE C4L, the idea here is to use a generous helping of tire compliance to decouple the bad aspects of axle behavior from the tire contact patch. The greater this compliance, the better, although steering response is obviously softened. (This softening isn't a big detriment in the rear, IMO. Because of the way the rear gradually follows the front (relatively speaking) as we start a turn, the rear is much more tolerant of soft tires. It's the front where stiff tires are critical for quick steering response.) As I mentioned somewhere else, the best all-around solution is a very wide tire in combination with a soft, tall sidewall. Additional tire width increases the tire's torsional stiffness about z, thus reducing tire slip angle and improving the tire's steering transient response. And accomplishing all of this happens with no increase to the tire's transverse stiffness in y nor vertical stiffness in z, which is just what we'd like.

Again, I know this is no practical help when we've all already done all we can to stuff the widest tires that will fit in the rear...

Best,
MAP

Last edited by MAP; 9 hours ago.
#1068757 - 5 hours ago Re: SS rear suspension: thoughts and musings [Re: MAP]  
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Speaking of wide tires, notching the frame to allow wider rear tires to fit is a popular modification. However, I suspect that frame notching severely weakens the frame.

[Linked Image]

Besides the reduced material strength, those right angle cuts look to me as to be nasty stress risers.


Just for some fun, I wonder how converting a G body to a rear dually setup would affect handling? Such as this replica marauder villain car from Mad Max 2.

[Linked Image]


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
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