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Last Post 13 Mar 2017 09:33 AM by  loosecannon
EMod MGB-GT build thread
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Bullitt2954
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24 Oct 2010 03:37 PM

loosecannon wrote:
I sliced off all the mounts I didn't need, welded on the ones I did and cut holes in the braces to lighten things up a little.
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Your new nickname is now officially "Swiss".........

loosecannon
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24 Oct 2010 06:31 PM
Bullitt2954 wrote:

loosecannon wrote:
I sliced off all the mounts I didn't need, welded on the ones I did and cut holes in the braces to lighten things up a little.
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Your new nickname is now officially "Swiss".........

We were going to paint it orange and call it "Orange Krush" but maybe "Swiss Cheese" would be better? ;)

loosecannon
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25 Oct 2010 05:29 PM

Ok, LOTS to report today. After Friday's big grindfest and weldathon, I had the weekend to ponder my work. It was bugging me that I left the rear differential brace on and that the 4 link suspension would bind when articulating. Then, the guys on the D/EMod Yahoo group pointed out that my 4" of ground clearance was double what I should be running. I decided to first drop the car to 2" of ground clearance then see where everything landed up. Here is the crossmember with 2 1/2" clearance:
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And the pedalbox in the foreground and oilpan in the background with 2" of clearance:
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And finally, I spent 7 hours grinding off and re-welding the work I had spent 7 hours doing on Friday. I removed the brace (losing several lbs unsprung weight) and changed the 4 link/panhard suspension to a triangulated 4 link (with no panhard, also unsprung weight). It now articulates nicely and doesn't move side to side at all.
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From the side, notice that I removed the bottom hole from the front mount because with the lowering of the car, I no longer used it:
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loosecannon
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26 Oct 2010 03:50 PM

Some of my unpainted parts are starting to rust so much of my time was spent with a spray bomb today. I did re-make the pushrods so they have nuts for adjusting and the rear ones I made longer so they don't change the angle as the suspension moves up and down. Rear pushrod:

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Front pushrod:
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47CP
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27 Oct 2010 06:51 AM

Your pace of work is shaming me for how long my car took.....looking great!

A few comments - take them for what you paid.

The 2 inch ground clearance is only going to work if you never have any type of a flat bottom or splitter at that height. I haven't closed it in yet, but the bottom of my car is competely flat, from edge to edge and from rear axle to splitter and 3 inch ground clearance is about as low as it will go. Any lower and it won't go on the trailer (I use about 18 feet of ramping to get a 4 degree apparach angle), won't go on the 2.5" high scales at Tours, won't go over minor bumps and etc at event sites. I don't think you will have a problem with your car at 2 inches, just letting you know in case you add a splitter and play with flat bottom aero.

I don't know much about straight 4 link rear ends, but a little about converging upper 4 link rear ends from my Mustang days. It seems like the only way to fix the converging one is to remove it, so I am curious why you added one? How do you locate your rear roll center on that? Or the instant center? On Mustangs, it was extremely high, like 15 inches or something, which could lead to a very high roll couple, or if both roll centers are too close to the CG, problems with weight transfer. How do you deal with bind in roll? Granted, your working travel is pretty short (can't compress more than 2 inches) but in the Mustang world, stiffening the bushings made it much, much worse than stock. Trust me, I have no knowledge of this type of suspension besides the OEM Mustang setup, which is pretty far from what you have, so I am not second guessing, just wondering.

Finally, make sure you have enough adjustment on your trailing arms to always be higher on the chassis side than the axle, at ride height. This is extremely important on 3 link setups, I would assume it would carry over to 4 link and would be really important with the shirt links on your car. It looks like you are OK, but is hard to tell from pictures. I ended up switching to a sliding type mount on one end on all my setups as well, finding that the 3/4" or 1" spacing on the holes was too course of an adjustment.

IMO, hope it helps, etc,

DaveW

loosecannon
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27 Oct 2010 12:36 PM
47CP wrote:

Your pace of work is shaming me for how long my car took.....looking great!

A few comments - take them for what you paid.

The 2 inch ground clearance is only going to work if you never have any type of a flat bottom or splitter at that height. I haven't closed it in yet, but the bottom of my car is competely flat, from edge to edge and from rear axle to splitter and 3 inch ground clearance is about as low as it will go. Any lower and it won't go on the trailer (I use about 18 feet of ramping to get a 4 degree apparach angle), won't go on the 2.5" high scales at Tours, won't go over minor bumps and etc at event sites. I don't think you will have a problem with your car at 2 inches, just letting you know in case you add a splitter and play with flat bottom aero.

I don't know much about straight 4 link rear ends, but a little about converging upper 4 link rear ends from my Mustang days. It seems like the only way to fix the converging one is to remove it, so I am curious why you added one? How do you locate your rear roll center on that? Or the instant center? On Mustangs, it was extremely high, like 15 inches or something, which could lead to a very high roll couple, or if both roll centers are too close to the CG, problems with weight transfer. How do you deal with bind in roll? Granted, your working travel is pretty short (can't compress more than 2 inches) but in the Mustang world, stiffening the bushings made it much, much worse than stock. Trust me, I have no knowledge of this type of suspension besides the OEM Mustang setup, which is pretty far from what you have, so I am not second guessing, just wondering.

Finally, make sure you have enough adjustment on your trailing arms to always be higher on the chassis side than the axle, at ride height. This is extremely important on 3 link setups, I would assume it would carry over to 4 link and would be really important with the shirt links on your car. It looks like you are OK, but is hard to tell from pictures. I ended up switching to a sliding type mount on one end on all my setups as well, finding that the 3/4" or 1" spacing on the holes was too course of an adjustment.

IMO, hope it helps, etc,

DaveW

Thanks for the compliment :) It makes me chuckle that when the car had 4" of ground clearance and a parallel 4 link/panhard bar, the D/E Mod guys said the car was too high and the 4 link wasn't as good as a 3 link or triangulated 4 link, and now that those are changed, you are saying the car is too low and the triangulated 4 link has problems. For the life of me I can't find the website that outlined the advantages and disadvantages of each rear suspension design but the triangulated 4 link was the better of the two for handling. As for bind in roll, the parallel 4 link would bind more than the triangulated one when I would move it through it's full range of motion. And concerning ride height, the faster D/E Mod guys are running as low as 1 1/2" ground clearance in Lincoln so my thoughts are to build the car so everything works good at that height (suspension geometry, etc) and raise the car up if necessary for bumpier lots. Remember, it's a pushrod suspension, I can raise ride height easily and with no change in spring rate or shock travel.

47CP
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27 Oct 2010 01:32 PM

loosecannon wrote:

Thanks for the compliment :) It makes me chuckle that when the car had 4" of ground clearance and a parallel 4 link/panhard bar, the D/E Mod guys said the car was too high and the 4 link wasn't as good as a 3 link or triangulated 4 link, and now that those are changed, you are saying the car is too low and the triangulated 4 link has problems. For the life of me I can't find the website that outlined the advantages and disadvantages of each rear suspension design but the triangulated 4 link was the better of the two for handling. As for bind in roll, the parallel 4 link would bind more than the triangulated one when I would move it through it's full range of motion. And concerning ride height, the faster D/E Mod guys are running as low as 1 1/2" ground clearance in Lincoln so my thoughts are to build the car so everything works good at that height (suspension geometry, etc) and raise the car up if necessary for bumpier lots. Remember, it's a pushrod suspension, I can raise ride height easily and with no change in spring rate or shock travel.

Hey, I never commented on ride height or rear suspension on the DMEM list, and I am just telling you things I have learned, some recently. I really don't plan on arguing with you to save you time and money so you can build a faster car when you run in my class.

I didn't say your car was too low and in fact specifically said I didn't think it was a problem. I also didn't say that there is anything wrong with a converging 4 link, I just don't understand how some of the angles work with them.

Having spent some time with powerful live axle cars, I would keep my eye on power delivery to the ground and how you can adjust the items that change that.

DaveW

loosecannon
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27 Oct 2010 02:30 PM

No, no Dave, I'm not arguing about anything, you know more about this stuff than I do. I'm trying to learn from others and am very new to 4 link suspension adjustment. Maybe I took a step backwards by changing to a tri-4 link but I don't really know until I drive the car. If I could do it all over, I would have made the links longer but it's too late for that. I also had packaging problems with the panhard bar and the Tri-4 solved those. I found the link to one of the articles about rear suspension design: http://www.automotivearticles.com/1...gn_2.shtml There was a discussion on the Lateral-G forum about Tri-4 links and this is what one aparently knowledgable person said:

"Roll Center Height: If you have one pair of angled links, the roll center height will be located at the virtual intersection of the two angled links. From a practical standpoint, with this design, you want to get this as low as possible. The Morrison designs put the upper, angled links at the height of the axle housing, which is better than most such designs which put brackets on top of the housing (unacceptable, IMO). Even better, as suggested by Herb Adams, is to make the lower links the angled pair, but this is more difficult to pull off from a structural and packaging standpoint.

Side View Swing Arm and Roll Steer: Viewing the suspension from the side, imagine extending the upper and lower links until they intersect in space. The line from this point to the center of the axle is the SVSA. The angle that this SVSA forms with the roll axis is important, because it determines whether you will have roll understeer, oversteer, neutral steer. If the SVSA is angled upward toward the front, you will have roll oversteer, which will make your car unpredictable and twitchy on turn-in. Some amount of roll understeer is generally considered desireable, but there are tradeoffs between achieving this and keeping the instant center higher to get more anti-squat. Also, keep in mind that the shorter the SVSA is, the more likely you are to suffer from brake hop.

Instant Center and Anti-Squat: The intersection of the upper and lower links in the side view, as described above, is the instant center. Draw a line from the point of the rear contact patch through this instant center, and find the intersection point with a horizontal line at the height of the center of gravity of the car. If this intersection point occurs forward of the front contact patch, you have less than 100% anti-squat, if it occurs between the contact patches, you have more than 100% anti-squat. Some amount of anti-squat is desirable, to help the car hook up on acceleration out of the corners. Just how much you want is debated, but if you can get close to 100% AS while still having roll understeer, you're doing pretty well.

Link Length: The shorter the links are, the more all of these parameters will change as the suspension moves, and the greater the chance that the suspension will start to bind up to a significant degree. From a practical standpoint, it's hard to have links that are too long.

Getting the optimum balance of all these parameters - even knowing what the optimum balance is, and what it feels like to the driver - is what makes suspension design hard. Build some adjustability in, for sure."

47CP
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27 Oct 2010 02:59 PM

The SVSA, IC and Anti's are the same as on a 3 link, it was the roll center I did not understand. I think you are going to want a pretty low RC in the rear so IMO keep an eye on leaving adjustment for this. Of course, rear RC depends on front RC and they both depend on GC which you may never know. :) I would say that most CP type cars are going to have rear RC's in the 4-10" range, but I have no idea how that translates to your lighter car.

Perhaps you can buy a Corvette to compensate for the short links? :) I don't think I would lose sleep over it. Mine are 46" or something crazy just becuase I could, but if you look at the overall small amount of total travel in the suspension and the range you are using in normal circumstances, the bad effects will be minimual. You will be no more than 2" of compression and only need 1.5" of droop (if that).

Thanks for the link to the article, I will read up on it.

EDIT: PS - please don't ever confuse me with someone knowing something again. :) I have years of Nationals results proving otherwise....

DaveW

loosecannon
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27 Oct 2010 08:32 PM

Unless somebody comes up with compelling evidence why my Tri-4 suspension won't work, I'm going to go with it and if it proves to be a dud, I have all next winter to correct it-and the winters up here in Manitoba are long ;) I think I'm going to try and make a rotissire to make working/painting the bottom of the car easier.

fd_racer
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27 Oct 2010 09:23 PM

Well I would say your 4 link is not a dud at all (at least what I can tell from the photos)... It looks almost the same as my 4 link on my car (just reversed, I have my straight links on top and angled ones on bottom)... So if that is any indicator, I really think you will be fine, just make sure you have no bind... You need 2" upward and 2" downward travel on a light EM car..... Keep an eye on your rocker arm set up (those can be a bit of a pain to tune) make sure your not past 1 to 1 ratio on squat and figure out where you are on roll (that will tell you how high your roll center needs to be, RC change will not be an easy/quick change (you should be around 5-8")...

Build is coming along good, keep it up....

Kiesel

47CP
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28 Oct 2010 06:49 AM
loosecannon wrote:

Unless somebody comes up with compelling evidence why my Tri-4 suspension won't work, I'm going to go with it and if it proves to be a dud, I have all next winter to correct it-and the winters up here in Manitoba are long ;) I think I'm going to try and make a rotissire to make working/painting the bottom of the car easier.

As long as there is no bind, I agree with Jeff K, the rear will be fine.

DaveW

loosecannon
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28 Oct 2010 12:43 PM
fd_racer wrote:

Well I would say your 4 link is not a dud at all (at least what I can tell from the photos)... It looks almost the same as my 4 link on my car (just reversed, I have my straight links on top and angled ones on bottom)... So if that is any indicator, I really think you will be fine, just make sure you have no bind... You need 2" upward and 2" downward travel on a light EM car..... Keep an eye on your rocker arm set up (those can be a bit of a pain to tune) make sure your not past 1 to 1 ratio on squat and figure out where you are on roll (that will tell you how high your roll center needs to be, RC change will not be an easy/quick change (you should be around 5-8")...

Build is coming along good, keep it up....

Kiesel

Thanks Jeff. If you check out that link in my previous post, they talk about the triangulated 4 link when the bottom links are the angled ones, it's called a Satchell link and aparently has a low roll center. Today I worked with sheet aluminum for the first time to make covers for the back. They aren't riveted yet because my rivet gun is nfg.

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47CP
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28 Oct 2010 01:19 PM

See, aluminum isn't so scary....:)

DaveW

loosecannon
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28 Oct 2010 05:12 PM
47CP wrote:

See, aluminum isn't so scary....:)

DaveW

You're right :) I got my rivet gun working and the cover is all put together and suprisingly strong. I think I will be making a lot more stuff out of aluminium (I have to pronounce it the british way now ;) ). Let's see, I can make a diffuser, airboxes, radiator deflectors, firewall and a few undertray pieces out of the shiny stuff.
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Also made a tow hook and discovered about half an inch thick patch of lead on the car:
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loosecannon
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29 Oct 2010 10:03 AM
Didn't have time to work on it today but here's a video of the car:
http://www.youtube.com/watch?v=tyT3GytphCw
47CP
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29 Oct 2010 10:19 AM

It sounds like your shop is attached to a bar with the music blaring :)

Looks great!

DaveW

loosecannon
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29 Oct 2010 01:32 PM
47CP wrote:

It sounds like your shop is attached to a bar with the music blaring :)

Looks great!

DaveW

For everybody who doesn't know, I own Speedworld Indoor Kart Track www.speedworld.ca and have a small area where I fix karts and work on my race car. We open at noon so I come in around 9:00 or 10:00, get the karts ready for racing then work on the car until customers arrive. Sometimes there will be 30 minutes here or there where no customers are racing and I tinker with the car some more. I would say I never work on the car more than 15 hours in a week, but I do spend more time than that thinking about it and how do make this or that. I get to watch karts race and stare at my MGB, planning my next move. There is a sound system so I get to play music while working on the car.

fd_racer
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30 Oct 2010 11:56 AM

very cool man....

if you have any audio needs let me know www.carvin.com

check us out...

Kiesel

Dave Hardy
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31 Oct 2010 11:09 AM
fd_racer wrote:

very cool man....

if you have any audio needs let me know www.carvin.com

check us out...

Kiesel

Jeff - I've had some Carvin gear. Good stuff. Ended up watching the manufacturing video on the website. Cool stuff. All of the CNC is cool, but didn't really surprise me. What did was the amount of handwork still involved. Nice to see that even with modern manufacturing doing the hogging, that the guitars are still hand sanded and finished.

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