Late Model 4-link Vs Modified 4-link; Want To Pick Your Brain

wanabe

Active Member
1.Why does a 4-link lm run a lift arm (torque arm) and a 4-link mod uses a pull bar? (mostly)

2.Why are the majority of 4-link lm running 4 bar 4 bar, majority of mods running 4 bar z-link?

3. Why does swing arm lm run pull bar, 4-link lm run torque arm?

4. Why run a limiter chain or 6th spring on mod if pull bar has rubber stopper for the compression?

5. Aren't most mods using a 90-10 shock on rear, but the stuff you read on 4-link lm says not to unless you have wheel hop on braking. But, doesn't the swing arm lm run a 90-10?

6. 4-link vs. 2-link: Is rearsteer the only advantage to a four link? Can you make a 2-link act like a 4 bar?

7. What is the advantage to running a swing arm? Why would having the springs on the bars be desireable? I know it's fast, why???

8. Last one... How on earth does Rayburn make a panhard bar thats mounted backwards work so good? I don't see the benifit to that at all. Where does the sidebite come from? Where's the mechanics of the chassis roll?

Not a pop quiz! I wouldn't be smart enough to grade the answers! Seriously though, I just want to know what you think. It seems to me that modified suspension set-ups are very trendy, for the most part. Meaning that most front runners are 4 bar z-link with a pull bar and alot of times a 6th coil. Then you have your less common 2-link or leafspring. But in the latemodels, a 4-link may dominate or a Rayburn style swing arm with a backwards panhard bar may dominate, right. Never a 2-link or a leaf. None of this is an arguing point, or a slam on a certain type of suspension. Just observation.

Thanks for reading. Hope you take the time to post what you think.
Craig.
 
well i know almost all Shaw modifieds are 4 bar 4 bar. And I know the Calvert City track champ in mods runs 4 bar 4 bar with a torque arm instead of a pull bar. At the rayburn seminar he talked about running a J bar instead or the purple pan bar when its slick. he runs his j bar to the left and the pan bar goes the opposite way. Modifieds dont run the small pullbar springs because they arent legal. lots of mods run 90-10's. the 6th coil on a mod helps going into the corner when you are on the brakes, it keeps the pinion from going over center. i think swingarm cars are better on bigger tracks like pevely, paducah, calvert, etc. I think the springs being on the swingarms give you more bite because the springs push the rear end into the ground. also, i think rayburn uses swingarm because it is harder to mess up than 4 bar, less adjustments.
 
Craig,my opinions on some of your question start with the difference in tires,LM to mod.Cars about same weight, most good mod,s have more power than they can hook up and need a more radical setup.Lm tires wider and have taller sidewall and bigger roll out.Average LM doesnt have alot more power than good mod motors.but have more tire to hook up similar power. Rayburn car with right pan bar dont make alot of side bite,thats why they go on wet,big cushion tracks or momentom tracks.They also use a 10/90 or 10/14 wrap up shock because it runs from rearend to back of car instead of front. I,ve had 4bar and swing/arm LM,s both were good,the trick is getting 4bar good in wet,rough,and swingarm good when dry,and figuring what changes to make to match track conditions. I think swingarm is easier to drive. Ialso think the reason most mods are 4bar instead of swingarm is 4bar with jbar or straight bar is more radical setup to c ompensate for not enough bite from tires. My one finger typing has wore me out for now,hope this helped some,Ed B.
 
well i know almost all Shaw modifieds are 4 bar 4 bar. And I know the Calvert City track champ in mods runs 4 bar 4 bar with a torque arm instead of a pull bar. At the rayburn seminar he talked about running a J bar instead or the purple pan bar when its slick. he runs his j bar to the left and the pan bar goes the opposite way. Modifieds dont run the small pullbar springs because they arent legal. lots of mods run 90-10's. the 6th coil on a mod helps going into the corner when you are on the brakes, it keeps the pinion from going over center. i think swingarm cars are better on bigger tracks like pevely, paducah, calvert, etc. I think the springs being on the swingarms give you more bite because the springs push the rear end into the ground. also, i think rayburn uses swingarm because it is harder to mess up than 4 bar, less adjustments.


Jimmy,

Thanks for the reply. I think you may have misunderstood what my questions were. I know why mods don't run small springs, and that the 6th coil stops the rear end from gaining too much pinion angle, and that lots of mods run 90-10 shocks.
My questions were:a.)why run a 6th coil when your pull bar already has a stop(big rubber bushing) on the compression side(braking) b.) why do mods run a 90-10 so often and GRT(for example) says not to unless you have severe wheel hop (under braking.) c.)I didn't mention mods running small springs on the pull bar. d.) did you sell your Impressive? Sounded like an awesome deal.
Thanks again. Craig.
 
Craig,my opinions on some of your question start with the difference in tires,LM to mod.Cars about same weight, most good mod,s have more power than they can hook up and need a more radical setup.Lm tires wider and have taller sidewall and bigger roll out.Average LM doesnt have alot more power than good mod motors.but have more tire to hook up similar power. Rayburn car with right pan bar dont make alot of side bite,thats why they go on wet,big cushion tracks or momentom tracks.They also use a 10/90 or 10/14 wrap up shock because it runs from rearend to back of car instead of front. I,ve had 4bar and swing/arm LM,s both were good,the trick is getting 4bar good in wet,rough,and swingarm good when dry,and figuring what changes to make to match track conditions. I think swingarm is easier to drive. Ialso think the reason most mods are 4bar instead of swingarm is 4bar with jbar or straight bar is more radical setup to c ompensate for not enough bite from tires. My one finger typing has wore me out for now,hope this helped some,Ed B.

Thanks Ed, good to here from you. Hope things are well. Miss pitting next to you guys.
Couldn't you make a swing arm as radical as a 4-link with bar angles?
Thanks, Craig.
 
1.Why does a 4-link lm run a lift arm (torque arm) and a 4-link mod uses a pull bar? (mostly)

2.Why are the majority of 4-link lm running 4 bar 4 bar, majority of mods running 4 bar z-link?

3. Why does swing arm lm run pull bar, 4-link lm run torque arm?

4. Why run a limiter chain or 6th spring on mod if pull bar has rubber stopper for the compression?

5. Aren't most mods using a 90-10 shock on rear, but the stuff you read on 4-link lm says not to unless you have wheel hop on braking. But, doesn't the swing arm lm run a 90-10?

6. 4-link vs. 2-link: Is rearsteer the only advantage to a four link? Can you make a 2-link act like a 4 bar?

7. What is the advantage to running a swing arm? Why would having the springs on the bars be desireable? I know it's fast, why???

8. Last one... How on earth does Rayburn make a panhard bar thats mounted backwards work so good? I don't see the benifit to that at all. Where does the sidebite come from? Where's the mechanics of the chassis roll?

Not a pop quiz! I wouldn't be smart enough to grade the answers! Seriously though, I just want to know what you think. It seems to me that modified suspension set-ups are very trendy, for the most part. Meaning that most front runners are 4 bar z-link with a pull bar and alot of times a 6th coil. Then you have your less common 2-link or leafspring. But in the latemodels, a 4-link may dominate or a Rayburn style swing arm with a backwards panhard bar may dominate, right. Never a 2-link or a leaf. None of this is an arguing point, or a slam on a certain type of suspension. Just observation.

Thanks for reading. Hope you take the time to post what you think.
Craig.

1) A four link LM has a lot of radical rear suspension movement causing the pull bar to bind. There have been a few sucsessful attempts on running a pull bar with the 4-bar (pierce) but it takes a lot of careful planning.

2) The reason for putting a z link is to minimize rollsteer on either type. You can can do the same thing with a four bar setup it is just easier to z link it.

3) The swing arm suspeension does not move around near as much as a four bar so a pull bar can be used. There is no other type of torque dampner available that provides as much forward bit as a pull bar. (minus clamped up leaf stack springs)

4) I have a different opinion than most on the limiter chain. I think it is on there to break the car loose by lifting the rear tires off the ground when the brakes are applied extremely hard so if your car is a little tight you can use it to help you turn. the rubber snuber on your pullbar will also lift your rear tires off the ground which is why it is so surprising that so many people still use it.

5) Most Lm 4-bars use a 76-2 or something close to that on the torque arm which helps control brake forces. If that is not enough then you add the 90-10. the rayburns use a 0-14 because there is no dampner inside the pull bar, same as your modified.

6) you can make anything work however you want but the major diference of the 2 link is that fact that the birdcages are mounted solid to the axles tube and do not handle the bumps as well as a floating birdcage. there are other reason but typed too long already. lol

7) A swing arm with the springs mounted on the trailing arms put the springs on a motion ratio. the ends of the spring are heading in different directions making the chassis "feel" like the spring is softer on roll and acceleration

8) J bars are backwards!!!!!:D :D :D :D :eek: :eek: :eek:

I know these answers are vague but i am sure if you asked more detailed questions these guys that know a whole lot more about this stuff than i do can probably help you out.
 
Craig,Ithink you can make a swing as radical by softening right springs and putting jbar on,but you somtimes too radical makes car hard to drive in traffic.finding the balance between too tight and too loose is the hardest set up to hit. Ihave a friend in peoria that always had 4bar lm,he built a swingarm car ,it also had all the 4bar mounts,he rented a track to test on,tested swingarm stuff with stop watch,he said car was o.k but didnt feel that fast, put 4bar shock behind stuff on and tested on stop watch,cor was hiking left front and pulling motor hard,his comments were thats real fast now,he was consistantly 3tenths slower on 4bar.my point is sometimes what you feel isnt always fastest,both types are sucsessful if you can dial them in but too radical may look cool but might not be fastest. Also Ithink some people forget a racecar has a front end also and dont work on it.seen alot of cars so tight you have to slide the rear on slick to make it around corner,when rollin corner and steerin front end is much faster. I think I have been guilty of that set up more than once.LOL. We got a new car from Bill West and it has swingam and 4bar both so we will probabley try both this year. might be in for a few headaches but we like a challenge. Ed B.
 
Craig,Ithink you can make a swing as radical by softening right springs and putting jbar on,but you somtimes too radical makes car hard to drive in traffic.finding the balance between too tight and too loose is the hardest set up to hit. Ihave a friend in peoria that always had 4bar lm,he built a swingarm car ,it also had all the 4bar mounts,he rented a track to test on,tested swingarm stuff with stop watch,he said car was o.k but didnt feel that fast, put 4bar shock behind stuff on and tested on stop watch,cor was hiking left front and pulling motor hard,his comments were thats real fast now,he was consistantly 3tenths slower on 4bar.my point is sometimes what you feel isnt always fastest,both types are sucsessful if you can dial them in but too radical may look cool but might not be fastest. Also Ithink some people forget a racecar has a front end also and dont work on it.seen alot of cars so tight you have to slide the rear on slick to make it around corner,when rollin corner and steerin front end is much faster. I think I have been guilty of that set up more than once.LOL. We got a new car from Bill West and it has swingam and 4bar both so we will probabley try both this year. might be in for a few headaches but we like a challenge. Ed B.

Ed, thanks. I agree with you. We live off of the stopwatch every Sat. night. We time everyone else, too. Also, GRT book says 70 percent of chassis handling is in front end. I hope you enjoy alot of success with the new car! Thanks for all of the input. Gives me things to think about. The winter time drives me crazy. Love to hear other perspectives on suspension mechanics, keeps the tunnel vision away. I hope this post gets alot of good info out of you guys that have been racing awhile.Craig.
 
1)

7) A swing arm with the springs mounted on the trailing arms put the springs on a motion ratio. the ends of the spring are heading in different directions making the chassis "feel" like the spring is softer on roll and acceleration

Thanks for the input. I understand why it feels softer than the spring is rated. But where's the advantage? Why would heavy springs on the trailing arms be better than soft springs on the bird cages or the rear end. Why not just run a z-link with softer springs. There has to be a specific reason. A theory of swing arm suspention.
The only thing I can think of is that the stroke of the spring is less, due to it being closer to the fulcrum of the bar. Therefore, the car is always on the spring. Even when its "up on the bars."
I thank you again for your volunteered time and knowledge. I hope to hear from lots of people with some sort of input or other susp. ?'s for you guys to read and answer.Craig
 




Back
Top