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  #1 (permalink)  
Old 11-25-2007, 07:17 AM
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Default hey jmarsey

i understand you are running your car at the minimum ride height. how is that working on the street?

what are you using for track rims and tires. compmotives are nice but with tires they weigh 47# each. i'm going to need another set if the $$$ holds out.

ref. your clutch/tranny. i'm looking at the 53 series tilton setup which requires tranny w/chevy bolt pattern and input shaft. did you use the chevy tranny or ford? also, i believe you had to shorten your input shaft?

i've mocked up the dry sump pump and it fit nicely with some milling on the bracket. i'd post pics if i could figure out how.
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Old 11-25-2007, 10:27 AM
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"i understand you are running your car at the minimum ride height. how is that working on the street?"

I have tried various ride heights on street and track. Current settings are front: 4.25Ē rear: 5.5Ē This may sound low for the street but itís actually quite high for the JBL. On the track you can run F: 3.75Ē R: 4.5Ē The important thing is that you maintain .75Ē to 1Ē of rake. The car really likes that setting. If you drop the rear too much, the car will not steer or track nearly as well. If you are running the Hoosiers on the track you can set chassis a bit lower due to the lower profile.

A few things to keep in mind: Tire clearance will ultimately determine ride height especially the rear. The front is really a non issue. When the body is bonded to the chassis, you can look at the relationship between ride height and rear tire clearance and set the altitude of the rear clip, by lifting it up or down, and set accordingly. If that relationship, (between top of tire / clearance to wheel opening / desired lowest ride height), is incorrect, you will be limited by tire rub. Under hard acceleration these car really weight-transfer to the rear, almost too good. You will want to experiment with spring rates and damper settings as I have. I can give more data on that subject. I have found that the car can take a lot of rear spring, and the front, quite the opposite. Good double adjustable dampers are a must. Street tires should be the Michelins. Donít buy the Dunlaps as they are less $ and ok but the tread pattern will make the car hunt. On a side note, I am converting to a quick ratio power rack, much like the one on my spec racer. This comes down to driver's style and how the car is used but in my opinion, the manual 4t-lock to lock is way too slow for any kind of driving under 100mph. But I'm used to shifter karts and now my FFR spec car, which is 2.5 turns, and like the faster steering. You won't be able to catch the car IMHO. See what you think of the steering ratio. I'd be curious.

"what are you using for track rims and tires. compmotives are nice but with tires they weigh 47# each. i'm going to need another set if the $$$ holds out."

Iím running the Hoosiers on compomitive wheels. I donít know how much track experience you have in these types of cars, but I would say wheel / tire weight is a non issue unless you are going to be competing in a race series / time trials, and can drive the car at 90% or more. Otherwise, youíll be giving 1k+ per wheel to BBS for a custom piece. The compomotives are very reasonable for a true modular wheel that you can simply bolt on, and besides, how much weight savings are we talking about? The tire weighs whatever it weighs so the wheel is the variable. A lightweight wheel of this type can be very pricey. The compomotives are also extremely strong.

"ref. your clutch/tranny. i'm looking at the 53 series tilton setup which requires tranny w/chevy bolt pattern and input shaft. did you use the chevy tranny or ford? also, i believe you had to shorten your input shaft?"

Yes. I already recommended a few folks to help you with that chore. It is a Ford / Chevy combo but not hard to do. I could tell how itís done but I would rather you work with a tech at Tilton as we may have setup differences. You should work with a professional(s) if you want the tranny to shift smoothly. Make sure you sweep the bellhousing and check alignment. Run a needle bearing input also. Iím running a TKO-2 RR. I included some pics so you can see the transition plate.


"i've mocked up the dry sump pump and it fit nicely with some milling on the bracket. i'd post pics if i could figure out how."

Posting pics here is pretty easy, just search the topic and you should get examples of how-to. I would love to see what youíre doing!








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Old 11-25-2007, 07:56 PM
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Default

i was curious on your ride height. i was under the impression it was you who was running the min., maybe it was someone else. i'm already into the fenders on the rear, but there is a lip on the underneath side that i may knock off which should give a little extra room. the car was designed for lower and i'd like to run it there for track use but like you said, the fenders are the limiting factor it seems, i may drop it down and try bump rubbers. i wonder how the suspension reacts to a higher ride height. maybe richard will chime in here.
i had to ask about the tires. it didn't cost anything.
you know, when i first drove the car i was surprised at how slow the steering was at lower speeds, but figured that is what was designed so it must be good. didn't seem to be too bad on the highway doing the straight and narrow although on track it could be different as you say. nothing like a sneeze/fart lane change. there is probably a compromise with steering effort. let me know which rack you use i might change mine out.
ref. the clutch/tranny, i am familiar with the setup but someone had to cut there input shaft and whatever and i am trying to avoid the pitfalls. i plan on making some calls first of the week, should be no problem. as a note i will prob. stay with the 3.** 1st to reduce wear on the clutch.
so you're a kart racer. we're racing in the tag class now with the parilla's. lot of racing and fun for the money. do heartland park, gateway, mid america, hallet. can't wait to get the jbl on track though.
pics should be forthcoming, just have to shrink them.
thanks for the info and pics, i like looking at cool stuff.
i'm looking for a quick release for the clutch line if you come across anything. i found one but was pricey.
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  #4 (permalink)  
Old 11-26-2007, 07:27 PM
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Gentlemen,

A couple of my thoughts. (which you all can take with the grain of salt they are worth.)

1. Steering ratio. It may seem slow to you. That is because you are not driving fast enough. Really now. The 2.5 rack is going to be too fast for tracks like Willow. It would be better to use shorter steering arms on the uprights. (If you will notice, there is plenty of room for more holes on the part.)

2. Ride height. The 2395mm WB (95 inch) chassis was designed for a 4 inch front and 5.5 rear ride height. (This is measured at the front bulkhead and at the rear most bulkhead.) The geometry is correct at this dimension. The lower you go, the more camber change you will find in the travel. But remember the camber curves are optimised already for normally available race radials. But you guys can do what you wish to make the thing work.

3. Spring rates. It s all a matter of of driving style. The front end seems stiff until you go really deep under braking and turn in. Then it makes sense. the rear seems soft until you pick up the throttle pre-apex and are full on it at the apex. Then the weight transfer will make sense.

But only if you drive the car the same way I do. It is a non ground effect-pure mechanical grip piece.

The dynamics are very basic and you just have to hammer this chassis. It demands forward thrust to achieve ultimate lateral G's. It demands heavy braking on slow speed turn in to work correctly.

Now you guys can set the thing up any way you wish to go fast as the chassis is pretty adjustable and forgiving.

But I designed it to suit my way of driving a non aero car.
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Old 11-27-2007, 06:31 PM
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welcome richard,

1. i'd agree with you on the steering. maneuvering around the drive and pulling in and out of traffic it seemed slower than what i was used to, compared to the jetta which has variable steering. like i said, at speed, highway speed, on-off ramp, and the turnaround it seemed normal with my limited experience.

2. your web site indicates other ride heights for stage 1,2 & 3. is your above recommendation the preferred height?

3. i believe my car is set up with 50# stiffer springs in the back than what is recommended. i did notice at hiway speed going over a rise in the road enough to upset the suspension that the front would settle real quick while the rear would take noticeably longer to drop to ride height where it would stay. kind of different because i have never experienced this before. is this normal or a function of the carreras and spring setup? i'm not sure what the damping and rebound settings are.

listen richard, anytime you want to give advice i'm all ears. we are pretty fortunate to have your input.

thanks again, mark.
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Old 11-27-2007, 07:52 PM
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Hi Mark,

First let me address your statement about the rear not settling after a rise.

Remember, due to where you are sitting relative to the polar moment you are going to feel that the front is settling quicker than the the rear as you are quite a bit aft of the rotation point. So take this into account as you look to set up the chassis.

The rear spring rate on your chassis is normally 325>375 depending on the track. (The slower the exits the higher the rate.)

I do not know what dampers Dave had on the car. But it sounds to me that the bump rate on the rear might be a bit too high or you are being fooled by the dynamics. John's recommendation of a good set of double adjustables is a very good one as you can dick with the settings and figure out what is going on. (Or you can go so far out in left field that the car becomes undrivable. Has happened to me a number of times.)

Secondly, The web site setup info really speaks to the SWB chassis. The LWB chassis was designed for a 4in. front and a 5.5in. rear ride height. In other words, the geometry (Camber curves) are optimal at that ride height. And as an aside, if you use the undertrays, it is the good for underbody flow and does reduce lift. (But 3 and 4.5 is better for aero.)

The best thing for you to do is to give me a ring and we can discuss what you are feeling in the chassis and I can give you setup direction relative to that info.

Please understand that I like to get feedback on the setup and development work that you guys are doing out there.

After all, that is why I did the car. For folks like you to have fun and go fast.

Send me an email and I will give you my numbers.
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Old 11-27-2007, 10:23 PM
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John,
It sounds like you are going to have to drive your car much faster here on out to make the suspesion work properly. It's much more clear now. Just hammer that thing, and remember... It's a "non ground effect-pure mechanical grip piece." I love it. Wish I had one of those.
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Old 11-28-2007, 09:36 AM
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Duane,

John does not have to drive any "faster" to make the chassis/suspension work properly.

But he has the high ratio front rockers which are designed for very heavy braking and turn in. If you do not load the front suspension hard enough with his setup you will get initial understeer and then mid corner oversteer because you are not able to pick up the throttle early enough.

If I recall correctly you have a non ground effect pure mechanical grip piece as well.

The only reason that I mention that these chassis (Meaning most all of the "Cobra's" out there are non ground effect Morris Clements excluded ) is that much information that you read these days on line or in books about race chassis setup is speaking of more current designs and they do have some ground effect. (Even SCCA H production Bugeye sprites do nowadays.)

Even a little air management changes things quite dramatically and if you follow some of the current advise you will chase your tail quite a bit indeed.

And yes, John just needs to hammer that thing. That is what it was designed for after all.
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Old 11-28-2007, 05:37 PM
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Just having some fun with both of you guys.
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Old 11-28-2007, 06:26 PM
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Quote:
Originally Posted by decooney
Just having some fun with both of you guys.
I know.

But you really do need to get John to hammer that thang. (In my best NASCAR accent)

I have not seen him backwards yet.

I only did half a lap at Fernley and I got it that way. ( In my own defense the brake bias was set for a sane person)

Work on him for me would you.

The insanity needs support now and again.

And from observing you drive~you are the perfect choice to carry the torch.
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Old 11-28-2007, 06:47 PM
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Richard,

I know this ďstuffĒ drives you nuts, and right around happy hour too, but the thing is, when I read threads like this I think about the age-old question, one that I never asked myself from the onset, of how is the car "actually" going to be driven and what can the driver tolerate, or compromise on, in terms of chassis setup for what ever percentage the driver actually uses the car between both street & track (I would say the same logic would apply to engine building aswell). Also, you really canít have a dual purpose all-in-1 track/street car. Not really. In a nutshell it just doesnít work as the two setups are obviously at odds. That is just my limited opinion. What works on the street takes away from the track and vice versa.

However, one could have another set of dampers and springs pre-set to ride height via corner scaled, pre-determine basic chassis settings, along with your track wheels (track engine & gearset, ), so one could do a simple basic starting point changeover from street to track, and try to have the best of both worlds. This would be my all-in-1 car approach.

I think it is important here to keep in mind that unless the car is a committed, what did you call itÖ. ďa non ground effect pure mechanical grip pieceĒ ( I love that definition ) track car, then some concessions have to be made in both discussion and recommendations, otherwise, one will chase their tail to some degree.

I am learning a lot about the my JBL via driving the FFR spec racer. The spec is a committed single purpose-built track car and, although quirky, there are some aspects that work very well, surprisingly, for a ďcobraĒ. No question, the bossJBL is a bad ass track car, but to really make it sing on the track, I would end up loosing my street car drivability and trashing the body over time, unfortunately. So presently I am trying to get the JBL to drive on the street as well as the spec car drives on the track, if that makes any sense. The JBL is, and has always been, more of a prototype to me that I just canít seem to stop dickín with. Oh yes, 4400 miles later, I do love driving it and the more I tweak it, the better it drives. Currently, itís awesome to drive except for the steering ratio but that is more a personal preference.

So, to sum this up in understandable terms; what comes to mind regarding threads like this? Two, actually three things come to mind:

1. If you want to track & race your cobra, and drive on the street, you need two cobras; a spec racer (for the NASA Challenge Series), or a committed NAPMGP-track vehicle preferably a JBL, and your favorite street cobra Ö.. take your pick.

2. If I were to do it all again, I would build a JBL for the track, committed, the way you designed the car, and build a nice FFR street car with cup holders and a luggage rack for overnighters.

3. If I were really nuts, Iíd keep the spec and the bossJBL, and build another JBL for time-trials.

Good times Richard and talk soon, John

PS, I have had the JBL backwards twice and I must say it was the smoothest flattest spin I've ever experienced.
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Old 11-29-2007, 09:38 AM
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John,

You are quite correct. There is a big difference in a pure track car and a road car. (If you wish to make them both optimal that is.)

Your approach with 2 sets of everything would work well on the JBL as you would not have to make any other changes outside of camber and toe settings. (And the engine/gearbox/rear gear. )

I think the 2.5 rack for road use would be OK but I have some concerns about 75 mph crusing comfort. The car really does not need much steering input at speed as you know.

First I would add in a bit more caster than the 3 degrees that I spec. More like 4.5>5 degrees and see how the low speed steering is before you change the rack.

The front wheel rates are a bit high for road use as well. Are you running the 175 springs or the 150's? With your rockers I think that 150 or even 125's might be the best rates.

I bet the spec racer is interesting to drive. Anytime that you have limited motor like that you really have to rethink how you drive. Momentum is very important as I am sure you have found out and really requires entirely different chassis think to work well.
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Old 11-29-2007, 01:13 PM
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Hi Richard,

Yes, I currently have the caster set 5+ degrees and steering is still very light with minimal input at 80mph. I like more caster and feels good to me. You are right on front springs with the high ratio rockers, you had me switch to the 150# a while ago. The front of the car really floats nice, in a good way, and stays up well under braking.

The spec is a total momentum car and good practice for me. Like you say, with any low HP car, forces you to be smooth and drive a clean consistent line. They are sprung pretty stiff, use no bars, but they work better than you would imagine. They typically run a little faster lap time than a front running CMC car. Right now, the JBL is a lot of car for me to just run around the track with, but, Iím sure the day will come again. In the meantime Iím hammering the kart and the spec. So donít loose faith.

Talk soon, John

PS, As you know, tires usually take more than 1/2 lap before they come in.....
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Old 11-30-2007, 08:55 AM
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Cool move to the bay area

Quote:
Originally Posted by Richard Hudgins

John does not have to drive any "faster" to make the chassis/suspension work properly.
ok... I just have to start looking for a job in the bay area so I can spend some more time with John... and learn how to drive this car correctly
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Old 11-30-2007, 09:08 AM
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Hey Chris,

If you ever plan a visit to Napa / Sonoma area, let me know. I will show you the beautiful wine country via bossJBL style. Great driving here and Infinion Raceway is only 20 minutes away, at 55 of course.

Talk soon, John
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