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  #1  
Old 10-23-2011, 01:46 PM
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john briggs john briggs is offline
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Default Think Im gonna call this season "the year of going back to school!"

Havent been on here much this year, spent all my time in the shop trying to make a modified work. Last fall, when the homemade chassis showed up, I thought, "we will put it together for him and just get him some laps"... After the season started, I said "Bygod, were gonna win some of these damn things!" At the end of the season, I said "Thank god this season is over!"
List of stuff that happened:

Mechanical fuel pump arm wore in half (with a moly coated eccentric) and burned #8 piston way up on my 340 with 30 year old pistons that nobody had on the shelf. New sleeve in the block needed.

360 was put together...mistake is I reused the Cosmetic gaskets. engine ran 5 shows and then leaked water into #4 and 6 cylinders. Resulting in a broken piston in #6 cylinder without damaging the bore. New piston took three weaks from KB and wasnt fixed till late Augest.

Dropped a 100 over 340 in the car from the hobby car from two years ago and it blew the cylinder wall out of it the #5 cylinder in hotlaps. Bigger cam and Alcohol was not a good mix for the thin-walled engine, but it gave me two seasons before.

Now am building two engines for next year. They are 360 stroked, 340 mains with good cranks, good rods, and 30 over blocks. Should work out well. Bought a 2002 GRT chassis and found a reverse mount bert bellhousing on ebay that is a much lighter piece than the lakewood that we run now. We build our own sheetmetal and we will take advantage of all the area that we can get away with till they catch me! Quickchange is on the way and we might go chase the USMTS shows next season. Wish us Luck! cause we are gonna need it!!!!!!!!
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  #2  
Old 10-23-2011, 02:11 PM
dirtmopar44 dirtmopar44 is offline
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John I have never had problem reusing those gaskets. As I have said on here before the gasket bore needs to be as close to the cyl bore as possable never more than .030. I also use studs and tq short bolts to 120lb and long bolts to 110lb. The gaskets that I bought from Huges had a 4.180 bore and I had the same issue you talked about. Bought some from FBO that were closer to my bore and have never had issue again. Hope this helps.Mike
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  #3  
Old 10-23-2011, 02:46 PM
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That exactly what the guys a cosmetic said! I am now a dealer for them and buy direct, although there was no mark-up to save and solved the problem. I use studs and go to 105 on everybody.
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  #4  
Old 10-23-2011, 09:22 PM
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cageman cageman is offline
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You better get some more to go usmts, that wont cut it. Been there done that.
I have gotten my gaskets right from cometic also, and I get them the same bore size, or close to it. I am still using my first set. I might retire them this year, just cause.
I think my fuel pump arm might be on its last leg too, 10 years of racing, got my moneys worth I guess, but it is just about wore through.
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  #5  
Old 10-23-2011, 11:04 PM
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Yep, them boys are fast, but we wont get faster if we dont go, know what I mean? Gone to a belt drive power steering/fuel set up and new set of indy heads are on the way also... We stayed on the same lap with most of those guys this year, but we need to up the game to run with them next season. Most of those guys are running around here at any given time. Going to a lift bar cause I think that is faster than a pull bar too.
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  #6  
Old 10-24-2011, 01:11 AM
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I was gonna lift bar my car last year, but IMCA disallowed them. My car is basically a mastersbilt late minus the lift bar, so it would have been easy, but it never happened.
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  #7  
Old 10-24-2011, 05:14 PM
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I really think the lift bar is the way to go. Just make much more sence than the pull bar deal. We came upn with some wild rear mounts last year that shot us strait to the front and the little car made hay. We are faster in, faster thru the middle ans just a smude faster than most off, I want to really work on comming off next season. As for the engine stuff, Im now just trying to build reliability. We were never outran, we we outspent, but not really outrun.
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  #8  
Old 10-24-2011, 06:11 PM
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Don't you run the lift bar with the pullbar? The lift bars I have seen made the car freer on entry. Most of the people that had them on have taken them off, that I have helped with anyway. The lift bar slows down the forward rotation of the rear when you decelerate right?
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  #9  
Old 10-24-2011, 08:53 PM
340king 340king is offline
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Idea Lift Bars

The way I see this whole lift bar thing working is simply due to instant center preservation. What I am talking about is watch a video of a typical 4 link rear suspension and see the angle that the pull bar ends up at. It is typically it is less than 8°. That provides nearly zero lift to the chassis.

http://www.youtube.com/watch?v=45hpB...eature=related

http://www.youtube.com/watch?v=LF68o...eature=related

What happens is the lifting of the left rear pulls the bar down to that low angle. The the only lifting on the chassis is the upper bars on the 4 link. The problem with them is that they tend to have instant centers behind the rear axle. That means they only lift the rear of the car. To make the best use of that, chassis designers went to extremely high rear weight percentages. This helped, but then the pendulum effect came into play. Now the cars tended to be too loose on dry slick tracks and the cars tended to be stop and go cars.

As the suspension science has evolved for the 4 link modified, the need to maintain some lift in the chassis after lifting with the upper bars was complete was needed. Enter the lift bar or 5th coil. As the rear end rolls back under the forces of acceleration, the 5th coil maintains its lifting point or point of action. Even if the pull bar is dead flat, the lift bar is lifting in the middle of the car. This means that less rear weight is needed. If you look at the current crop of USMTS cars, they mostly sport smaller fuel cells. That is partially because they don't need as much rear weight as they used. That would seem odd with the HP they run.

If you notice, they try to keep the left front tire on the ground these days. That is because if they lift in the middle of the car, the rear tires can carry the whole car's weight. If you lift with just the upper bars, then the instant center will dictate that you are lifting the rear weight or left rear weight only. That means that at best you can get something like 1,400 lbs on the rear tires. If you can lift in the middle of the car, then you can put close to 2,000 lbs on the rear tires. The weight is more balanced between the two rear tires also with the pull bar.

Think back to the tire traction circles and how adding weight increased grip, but not proportionally. As you add weight, the amount of grip does not go up as fast. So one tire with 2,000 lbs of weight on it has less grip than two tires with 1,000 lbs each. That is part of the secret of making the 5th coil work on the mods; spreading the tire loading more evenly.

At least that is my take on it.
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  #10  
Old 10-25-2011, 09:16 AM
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moparallen moparallen is offline
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I guess we are talking about two different things, or using it two different ways. The fifth arm is attached to the center of the rear end housing offset to the right. It extends to the front of the car to a point real close to the rear of the trans housing. It is suspended from an upper cross bar by a chain with a rubber bumper. When the driver lets off the throttle the bar and chain controls how fast the rear rotates back forward. It is supposed to free up the car on entry. Some of the guys here say it makes the car too loose?

I have seen some that look close to what Late Models run that use a shock and spring above the bar. That would provide resistance and move the lift point father forward. This is the type you are talking about? Would not putting a long pullbar with 2 springs that work in opposite directions do the same thing?
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  #11  
Old 10-25-2011, 10:51 AM
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Yes, The lift bar I am talking about is the old "5th" coil. We ran them years ago before the 4-bar thing came around. They will make you loose going in, but you have to adjust it to fit the track/car/driver. The were simple, reliable, and easy to adjust... And I remember car pulling both fronts off the ground coming off the corner with 54 rear percentage.
We built last years car with 1994 technology, cause thats what I knew at the time. I was very surprized to find that it was as fast or faster than 2010 stuff. Who would have thunk?
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  #12  
Old 10-27-2011, 06:20 PM
340king 340king is offline
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Thumbs up Geometry

Allen, the geometry dictates that when the pull bar drops to say 8° that the resulting upward lift is only 14% of the total. On my car the normal pull bar force was about 1,500 lbs. So the upward lift force at the point of intersection of the pull bar with the frame is 208.76 lbs. That isn't much by itself. That is why lower bar angles are so important.

With the fifth coil or lift arm, that force is changed to nearly 500 lbs of lift. This is due to the torque multiplication that the gear ratio gives us being reacted to by the torque/5th coil arm. I used a 3 foot arm for simplicity in math. Here is how I did it. My car has the pull bar mounted one foot above the center line of the axle. It is mounted at about 16°, so I used the Cosine function to determine that my 1,500 lb force had a horizontal force of 1,442 lbs. That creates a moment of (1,442 lbs)(1')= 1442 ftlbs. I then divided that by my 3' lever arm to get the resulting force of 481 lbs.

The forces available on a USMTS car are much greater since they make so much more torque.

If we use a rear weight of say 58% on a 2,500 lb car, then the actual static weight on the rear tires is 1450 lbs. If we lift the rear of the car we will lift a significant portion of the weight. If we lift ahead of the center of gravity, we will add front weight to the static weight of the rear tires. That means that we could in effect have 1,930 lbs of weight on the rear tires, with an engine like mine or more with the USMTS monsters.

Now this is an over simplified way to do the math. It is actually more complex, but I think it illustrates how the lift arm can add traction to the car.

On the more simple 3 link car, the intersection of the three links form what is known as the instant center. That is the point where the car thinks all the forces are acting. That point on well designed cars is in front of the center of gravity. On good tracks, you can create a very similar affect by summing all the forces at that point. The upward lifting forces of the lower links contribute as well. You can lift the entire chassis with a 3 link in the same manner as the lift arm setup.

The issue has always been that in order to get a 3 link or lift arm car to hook hard enough on the gas it had to be really loose on corner entry. The four link cars used bar angles and floating/bird caged rear ends to create forward bite by loading the left rear tire on corner exit. That gave them the advantage over the lift arm and three link cars since they could load that left rear in all track conditions.

The real answer seems to be using a four link to initiate the forward bite and then transitioning over to the lift arm to carry that bite farther down the straight. It also allowed for the loosening that you mentioned which can aid in driving the car deep into the corners on dry slick. I know this sounds backward, but the fastest cars on dry slick can and do drive deep into the corner before they have to drop the speed to turn. Just watch the big dogs sometime at a big show with a dry slick track. They are super smooth and they roll in deep, regardless of the suspension type.

Any time you are sideways on dry slick you are too slow. You can't be pitching the car in. If you do; you scrub off speed. Running in at a smooth yaw is OK, that isn't sideways.

As for running 1994 technology against the newer stuff, well that is what Cageman and I have been doing with my old three link car the past several years. I think I have found a way to make the three link work very well on any kind of track surface. More to come on that subject in the future I hope.
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  #13  
Old 10-27-2011, 09:08 PM
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cageman cageman is offline
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In my 340, I have no power, and the car was designed for ump with soft tires back in 03, so add in big motor. So I shortened the pull bar, and I like it. Dont know the math, I think I just got lucky, all I know is I didnt like the long pull bar, and I like the 12 inch long pull bar, I can feel the tires better.
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  #14  
Old 10-27-2011, 11:31 PM
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Are you running a 90/10? As far as the new technology, I honestly belive that the materials/machine work have gotten better with better availibility to all that want it, but I also stongly belive that the "monkey see=monkey do" has strongly affected the modified world.

Dont get me wrong here guys, Im no wizard, but I watch guys change their cars cause Bone runs this setup or Hughes has this on his stuff... I think it all comes back to the most predictable car wins. The four bar cars can be blistering fast every once and a while, but they dont hit it every time, nor did we with our simple stuff, but we were way more consistant than they were.
As far as the best setup? Hell, we might be back on leafs in two years!
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