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Post by spud on Feb 2, 2020 11:19:31 GMT -8
I started this one so i could tell a few things that have helped me. Weight transfer is all about changing “ instant center” . So if you start searching that topic, you get to the “ point” quicker. Six cylinder springs, are Specifically LOW RATE springs. They are longer unloaded, being low rate, they squeeze down more with the weight of the car, and conversely lift farther when unloaded when engine torque transfers into the chassis, lifting the front of the car. They start as taller springs unloaded, compress down to the ride height and then extend back further when unloaded . Of course you have to have adequate shock travel. My early jav had the hi rate red strip springs. They sucked cuz the front end was always high, and only lifted a bit and then the shocks hit full extension. These springs are stupid, and are not too high a rate in reallity. They take maybe 175 lbs to compress an inch. Now what i did was i found some six banger rambler american springs. About the same free length but much softer. Maybe 100lbs to compress an inch. If that much...i Put them in, got a nice drop in suspension height. They extend against the shock easily, so i screwed some shock stud extensions on the shocks to make em even longer and got more front end lift. All of this allows instant center to move rearward rapidly under hard acceleration. You can loosen and grease the upper a arm frame and trunion pivot point bolts for quicker response. Remove the front sway bar. Make sure your strut bushings are soft and flexible. 90/10 shocks allow minimum restriction to rise and maximum restriction to spring compression. Hi rate springs are stiffer, compression and extension travel is lmited. They store and release all their energy with very little travel. So instant center stays more centered. You want instant center to move rearward, over the rear tires, if you go too far you drag the fuel tank🤯, so its like riding a wheelie on your bike. I think the trunnion suspension is a great drag suspension. It can give a lot of weight transfer easilly with the right spring and shock. The 70 up is ok, you just apply the same principles. Longer, low rate springs were easy to find in small ford cars. Fact is amc blatantly copied the ford layout for trans am racing. If i could do pictures i would show you how i made the amc spring perch fit mustang springs. I know this is a “ modification” so i think amc spirits with the four cylinder were the lowest rate amc spring you could get to fit a jav/ amx... couple that with a 90/10 shock with a extension for greater length and no sway bar, and loosen and grease upper a arm bushings you should get a big improvement in instant center travel. These are modifications if you choose to see it that way, but they are also chassis tuning, and if its ok to “ tune” your engine, chassis tweeks should not hurt feelings too much...
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Post by spud on Feb 2, 2020 11:56:41 GMT -8
Now i know you like factory, but i like to cheat. If you want to help the rear suspension, focus on stiffening the front half of the spring. You can clamp it solid. You can take out the rubber and plastics and clamp the separate leaves together. You can also wrap the front half with a lot of electrical tape. A solid front bushing helps. Fully adjustable rear shocks are a solid investment, this should be an area you won’t feel that your cheating...If your more ruthless in your “ tuning” you can cheat your ass off and put some stock looking 200/lb per inch springs in there. I took my stock springs and used only the main leaf and put ford mustang boss 302 200 inch/ lb springs under it. How that happened was the ford springs are 4 leaf, i cut they eyes off of the main leaf to match the length of the amc second leaf, then bolted the amc main leaf to it and clamped it ONLY on the front of the spring. Let the back half free! So, I got a spring with less arch, very stiff and about the stock ride height. Maybe a tad more. Major reduction in 60 ft times once the shocks were dialed in. Yes its cheating in some respect. But its the idea that a stiffer rear. Spring really does a lot of good.
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Post by n2ojoe on Feb 2, 2020 15:42:22 GMT -8
Thanks Spud, I agree with ya. I texted Rich this morning after seeing his post to give him shit. What kind of wisdom does he hope to find over there? Like the first reply of bigger tires on the front and limit straps to keep the front from rising. WTF!?!
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Post by n2ojoe on Feb 2, 2020 15:45:09 GMT -8
And, it's not like I'm some angel either lol. I resisted the urge to even post my new engine build on here because I don't know who will see it from "over there". 😁
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Post by n2ojoe on Feb 2, 2020 15:56:36 GMT -8
I'm working on a new set of torque links to replace the factory stuff right now, with heim joints in a short chromoly tube so there is adjustment for preload. I have some custom valved SC397 shocks on there now that have really helped too. A big problem is the 58% front weight bias. It needs some rear ballast, I think the improvement in the 60' will offset the extra weight.
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Post by spud on Feb 2, 2020 16:02:07 GMT -8
Limiting front end rise has a point. Point is to keep instant center from moving so far it unloads the tires. Its usually a strategy for hi powered cars with good traction to start with to keep the car from gaining too much lift to quick... Larger diameter front tires do two things, they shorten “ roll out” to trip the beams faster for a slight time/ reaction reduction, and the generally have less rolling resistance than shorter tires. I dont really think either is going to help you guys out. Besides they are not to much a factory situation. Another thing you may consider is deeper ratios in the rear will limit tirespin and increase torque load transfered to chassis, and i know you guys are limited buy as deep a ratio as you can get away with will do wonderfull things. You can also get some traction by altering spring load on the rear. This is tricky business and you gotta scale the tires to see where you are at. The ring and pinion make the passenger side tire try to lift so treaking the weight load bias to the passenger side can get you a gain. Having someone video your car as it launches can provide extremly good info on chassis tuning, particularly shock tuning. Watching for body lift, sw or squat on the rear tells you which way to go. I could go on but the best thing that i can recomend for detailed in depth study of your suspension action, after you have video’d and analyized it should be interpretted with info available on chassis tuning readily available in book form from summit or amazon, i cannot stress the fascinating technology available in some of these books. Tuning a factory stock musclecar is as sophisticated or even more so than any machine
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Post by spud on Feb 2, 2020 16:09:08 GMT -8
The weight bias of an amx isnt a bad thing in my opinion. There are much worse weight distributions out there. The trick is to get the chassis to “adjust “ it over the rear axle when you launch.
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Post by n2ojoe on Feb 2, 2020 16:27:51 GMT -8
It would be different if the cars were on slicks, actually applying leverage to the I.C. point in the chassis. These stick shift cars on Polyglas tires require tons of clutch slippage to get the balance happy at launch, though the same suspension tuning techniques do apply. I am all too aware of the physics, and have been trying to relate this same info to Rich for his benefit, so it's on him for asking on that forum. Lower power cars need more rear weight bias and more front travel. My "stock suspension" Mustang front travel gets limited to 1" on a good track with up to 50 extra lbs front ballast to run 1.10 60' times on a 275/60/15 radial without wheelie bars. The pure stock cars are way easier IMO. I believe his question was more aimed at outside the box tricks, not just the basic practices. Rich's car is a 1969, and he has a pretty slick sealed bearing pivot in his trunions. Stuff like that is more the question, and the kind of thing that the innovators generally don't want to share.
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Post by spud on Feb 2, 2020 17:11:27 GMT -8
Lol. So i figure i’m talking to someone who knows quite a bit more than me. One thing i used to do to really shitty tires was soak em down in tread softener. Of course they got harder when they dried out. Maybe you could use a good adjustable pressure plate set on cook? I use to launch my 401 javelin at about 1500 rpm by letting out the clutch steady and pretty quick and roll on the throttle as the front end rose, it would lift and carry a tire as it rolled out. Was kinda slow in the 60 ft but it did hook.
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Post by n2ojoe on Feb 2, 2020 17:19:33 GMT -8
Now ya got it, soft launches with finesse. I've heard of a few guys applying WD40 to their worn tires then wrapping them in Saran Wrap and letting them soak for a few days. Wheels up launches on Polyglass are possible!
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Post by n2ojoe on Feb 2, 2020 17:23:35 GMT -8
Here is another not so well known trick. The Clutch Tamer started out as an idea and an adjustable screen door cylinder. It works like a 90/10 shock for your clutch pedal to consistently control the release. clutchtamer.com/
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Post by spud on Feb 2, 2020 17:29:32 GMT -8
I get this tire dope called “ hot lap “ . It does work but it ruins your tires eventually. Its like crack cocaine for your tires. They need a bigger longer treatment every time and they are fried in short order. The clutch tamer idea is not new. I tried it years ago with an old clutch slave cylinder and brake fluid . I never got it sorted out. If i got the launch half decent the rest of the gear changes were too soft.
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Post by Captain Awesome on Feb 2, 2020 17:39:13 GMT -8
I used to run a "Junkster" set of short of 60s so I had gear. Anywho, I used to spray the tires with VHT and burn it in. Those old crispy tires got soft again after several applications.
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Post by spud on Feb 3, 2020 8:41:19 GMT -8
Did they stay soft with vht? I used that hot lap shit until the tire started flinging chunks of rubber off.
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Post by Captain Awesome on Feb 3, 2020 10:46:39 GMT -8
I had to keep retreating them every race day. I saw someone talking about that Hot Lap stuff. They say it's the way to go. Wish I coulda tried it.
I see guys talking about the ol' "Washer bottle" trick to spray VHT on their tires. I think that way sucks, but the never tried it cause they think it'll gum up the lines. Welp, we put VHT in cheap spray bottles. Stuff was in there for years. Never plugged up.
We liked spraying it the whole way around the tires evenly, rolling the car forward and getting that bare spot.
I know the first few times we'd go way back in the pits and do burnouts, then recoat, getting it in the tread. we tried a bunch of dif ways. That way work with me since I'm a no cash racer. My tires were $10 for the pair at the swap meet. Since I have 2.56 gear, I run a 22" tall tire. Not much tire to bite with. Even new fresh rubber it's a shit tire. VHT was the only way I ran whooping low 14s instead of mid 15s.
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