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10-31-2013, 01:56 PM | #76 |
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Well the car is pretty light bit if it is breaking, I think understeer will be the last thing on his mind :P
But really, valid questions. I've driven numerous FSAE cars with about the same distribution and we had no issue with either. Braking concerns can be dialed out through suspension geometry, as can much of the understeer concerns. Now with the 'anti-understeer' geometry solutions aimed toward track speeds, it'll probably push at low speed.
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10-31-2013, 10:51 PM | #77 | |
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Quote:
In steady state cornering, rear weight bias gives oversteer if the roll stiffness and tires are the same front to rear. So with rear weight bias, the designer is always battling oversteer. That is why larger tires are almost universally found at the back of cars with mid or rear engines. I'm sure you have seen Porsche 911s lift the inside front wheel in a corner. This is because to tone down the oversteer the front is made very stiff (done with swaybar). It is hard to draw conclusions from what you see modern race teams doing unless you have a thorough understanding of the rules and their implications. For instance LeMans P1 cars are sometimes using the same tires front and rear. This is because the rules will not permit bigger tires, so by putting 4 of the biggest tires on the car, the tires can be run longer before changes, a big factor in endurance racing. Anyway, the car does not have any understeer, and turns in very well (contributing is the car's low polar moment of inertia). On corner exit, happy throttle will bring the tail out easily. It is very easy to go stupid fast. The wide track, generous wheelbase and low center of mass make you look like a much better driver than you are -lol. |
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10-31-2013, 11:21 PM | #78 |
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"Well the car is pretty light bit if it is breaking, I think understeer will be the last thing on his mind :P
But really, valid questions. I've driven numerous FSAE cars with about the same distribution and we had no issue with either. Braking concerns can be dialed out through suspension geometry, as can much of the understeer concerns. Now with the 'anti-understeer' geometry solutions aimed toward track speeds, it'll probably push at low speed." I have suspension experience - it's what I do! -lol I will not claim to know it all by a long stretch. One of the most intriguing things to me is that cars (in the absence of significant downforce/lift influence) oversteer more with increasing speed. I used to think that to maintain high speed, the rear tires are being worked harder (bikes at Daytona spin the rear tire at top speed!) so they can't contribute as much to cornering. It makes sense, but in no way explains that front wheel drive cars do the same.... Maybe yaw aero? Maybe front tire slip angle differences? Anyway, I will soon be testing the high speed handling and expect to be able to deal with oversteer (with aero if needed). High speed oversteer - especially with trailing throttle - is something a give a lot of thought to - anal plotting of rate curves, etc. Imo it is unacceptable. I have done a good job on 5 different designs in the past with V8s out back, but you can bet that I am really appreciating the light weight and low mass of the Subaru engine! Already planning a 600hp EJ25 version. Probably come in 50 lb lighter... yesss! |
11-01-2013, 09:57 AM | #79 | ||
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Quote:
Our (the one I codrive) F500 car is very neutral at speed but pushes like a pig during heavy braking and low speed sections. It "feels" like there just isn't enough weight on the front. As both of you have stated, neutrality @ speed is indeed a strength. Keep in mind, we don't get up above 60 mph very often. I guess jdogma's concerns are with tracking his car. Low speed, like you see @ an AX, is not an issue. Our F500 is 47.5/52.5 w/driver and we push really bad w/the wheel cranked and moving slowly. Power on after a heavy breaking zone @ low speed = push. It also means your line was wrong and you were probably too greedy. Our F500 friend/competitor has less problems in this area. I've driven his car and it feels more willing to turn (no doubt aided by slight difference in design) and I know he is much closer to 50/50. W/some redneck engineering and the necessity to make the 800 lb min weight for our class, I wear 30 lbs of ankle weight. It seems to aid significantly to the car's ability to turn in during heavy breaking. I guess my experience, though minimal and AX related, makes me think the 40/60 is too much. Quote:
Anyways, good stuff. I'm learning some things and I like that. |
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11-01-2013, 02:38 PM | #80 |
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K.Linchpin, it sounds like your issue could be addressed through means other than playing with weight distribution. Perhaps one of the Carroll Smith books would provide some possible adjustments to test.
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11-01-2013, 03:00 PM | #81 |
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"I wear 30 lbs of ankle weight. It seems to aid significantly to the car's ability to turn in during heavy breaking"
That is really funny to me for some reason! I wonder about the weighting being damped by your body rather than being attached rigidly to the chassis. If the car does not turn in well, typically that would mean too much load on the outside front resulting in it not being able to give more grip, so typically people add less front sway bar, or soften front springs or soften low speed shock compression on the outside front to get it to turn in. Others may add toe out. Conversely, things that make the rear grip poorly usually help turn in. I don't think this is the best way to go, but in autocross it has worked for me. I put a big swaybar on the back of an Alfa GTV and let the rear tire pressures down to about 10 lb cold and kicked as. My autocross experience was that best success came from making the car rotate easily - heavy oversteer is best. When I had a car that was winning it was almost impossible to drive it in a straight line. I am not doubting your results, and have seen instances when engineers do the opposite of what theory dictates and get good results. The F500 car - does it have a diff? No diff or spool makes car just go straight at low speed with no weight up front. Go-Karts lift often lift a rear wheel via chassis flex to aid turning. What I mean by trailing throttle: transitioning from high speed into a corner - you lift the throttle and turn in a bit at the same time. Some trail braking may be included. During these times you are trying to lose some speed and you don't want it all tail happy. If you want to learn, read Mark Ortiz's newsletters. He writes a column in Race Car Engineering Magazine and publishes monthly newsletter about suspension. EVilTwinMotorsports.com has most of them. I am on his mailing list and get them. PM me and I will give you his email address. Imo he is the best out there that is opening his mouth. He backs up ideas with sound reasoning and solid math and often evidence as well. He has been very kind to me, answering questions - even did a newsletter on a banked turn math question I had - and eyeballing designs. I try not to abuse his good nature because he makes his living as a suspension consultant. |
11-01-2013, 03:59 PM | #82 |
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Here's a direct link to index of Chassis Newsletters by Mark Ortiz on EvilTwinMotorsports.
Here's a working link on archive.org to Part 1 of their Suspension 101 article that seems to be a broken on their site. Looks like there are 13 years of articles for me to catch up on =) |
11-05-2013, 12:09 PM | #83 |
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I love this thread...
How difficult would it be to integrate some banned F1 technology by having the exhaust gasses working in conjunction with the rear aero? *looks at the EZ30R and Ver.8 gearbox sitting in the garage and gets ideas* |
11-05-2013, 12:57 PM | #84 | |
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Quote:
The exhaust is currently being repositioned a bit toward the center to allow for additional structure that had to be put in for tail support. It could be introduced into the diffuser floor which may or may not help even more. Look forward to aero testing, but not likely before next year. Don't even have the sensors I want yet. A concern I have with exhaust enhanced aero is that it will reward the pro driver who has the nads to stay on the throttle when the normal person's foot is lifting, and conversely spank the guy who lifts by decreasing downforce when it is needed most. |
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11-08-2013, 12:23 PM | #85 |
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Any updates on the Niprotec?
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11-11-2013, 06:43 PM | #86 |
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Sorry DK, they are in the prototype stage. I can not say for certain that they will ever be offered as coil-over substitutes. They have characteristics I like: They are very light, they have rising rate characteristics and you can change spring rate by turning a hex. There are some things I don't like as well: I can not get the initial stiffness I desire on the front. Although I can get the ultimate stiffness, the initial stiffness is insufficient to tune the low speed handling the way I want (without sway bars). The car is overly aggressive on turn-in and I can not get the front springs to start out stiff enough. This is due to an inherent gas spring characteristic of being just stiff enough initially to maintain desired static ride height. I could use a front sway bar to give roll-only stiffness, but we have very large front aero loads and that requires a platform that is initially pretty stiff. I have some tricks to try (like a secondary chamber) and will get the car properly sorted, hopefully with the gas springs. I will post updates on the suspension development if you want.
If you want something for your car, I can get you QA-1 aluminum small body coilovers (I am a dealer and will give you a discount), and appropriate springs. I would need to know stroke lengths, fully compressed length and motion ratios for front and rear along with car weight and weight distribution (or corner weights). Would also want to know your approximate desired ride height and usage. I am assuming no significant aero loads in your case. |
12-06-2013, 03:26 AM | #87 |
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Coming along nicely! Keep up the good work!
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12-15-2013, 01:40 PM | #88 |
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For DK: Had to go to a 0 droop front spring setup. I noticed a problem (difference) with the Niprotek gas springs is that the initial stiffness over a small, incremental movement can not be easily changed without affecting ride height. I should have known that because gas spring characteristics are that they have a rising rate curve, with the initial rate being very flat. By changing the final gas volume, you can steepen the curve, but the initial change over a small movement is still very flat. What this means is that I can not adjust the handling of the car with the springs (by stiffening the front) without limiting droop. Thankfully this is only an issue on the front. I accomplished the 0 droop by limiting the amount of oil in the system - over pressurized the gas springs, then let oil out of the units until the front sat on ride height blocks. The travel is not truly limited as in most ) droop systems, but the spring action is. Now I can stiffen the front as much as I want without changing the ride height. I have the handling pretty well balanced now and the 0 droop repercussions are not noticed. What it can do at the front is give the car corner exit understeer, which is not a big problem if it does occur. At the rear, 0 droop is a bad idea because it can give corner entry oversteer of the snap variety.
In other news, the details are being cleaned up, I have someone to do the upholstery, and the car is very quick. At 16 lb of boost, I estimate around 500 hp. The dry weight with fire system in is about 1660 lb, so the acceleration is great. With cold tires, you get wheelspin when it hits around 4000 rpm in third ~60mph. Last edited by jdogma; 12-15-2013 at 01:45 PM. |
12-28-2013, 07:30 PM | #89 |
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12-28-2013, 11:24 PM | #90 |
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.049 wall 1- 1/2 and 1- 1/4 OD 3003 alloy
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12-29-2013, 02:58 PM | #91 |
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How will your build compare to other quick track ready cars. Something along the lines of a track special that you can take from the show room floor? something like the
Leguna Seca: Exige 260 cup: Z06: How about to something even more track specific like a Caterham: Radical SR1: Or an Arial Atom: Or compared to an actual race car like a Stohr 1000: |
12-30-2013, 04:11 PM | #92 |
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Track performance can be roughly estimated by power to weight ratio, so I calculated those for the cars you mentioned plus a few others. The Carma Wolf has very friendly handling and effective too, due to the very significant aero package and the wide track. We will be racing the car in NASA this season. We have a test/tune day scheduled for Jan 11th and our first race should be at Barber Motorsports Park Feb 15th. Lap times will tell, but I predict after a season's worth of development that nothing in the list should come close except for the LMP2 car, and that costs $1million plus. I will be bragging big time if we can equal LeMans Prototype lap times - lol!
Last edited by jdogma; 12-30-2013 at 04:27 PM. |
12-31-2013, 02:30 PM | #93 | |
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I enjoy reading GRM. Please take this thing to the GRM Ultimate Track car challenge! FFR took an early production example of the 818 to that event. That's a car that I was/am very excited about since you can build one, get high levels of performance, and don't need $50k in the bank. The fact that it got beaten, pretty handidly, by a Dodge Neon, is a little upsetting, but as you have eluded to, Power to weight makes a big difference and the Neon's 600HP surely trump the 818's 300 Hp. Anyways, the event is a big mashup of track cars and street cars all grouped together, so it's interesting to see how fast various cars (and drivers) are to one another. Let us know how the Test n tune goes. |
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01-01-2014, 05:09 PM | #94 |
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"I, like many others on here enjoy working on my Subaru and making it a more competent Street car & track car."
You and most guys here are the modern hot rodders and that is why I came here. You guys have learned a lot about these drivetrains and I have a lot to learn. |
01-01-2014, 05:22 PM | #95 |
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""Please take this thing to the GRM Ultimate Track car challenge! FFR took an early production example of the 818 to that event. That's a car that I was/am very excited about since you can build one, get high levels of performance, and don't need $50k in the bank. The fact that it got beaten, pretty handidly, by a Dodge Neon, is a little upsetting, but as you have eluded to, Power to weight makes a big difference and the Neon's 600HP surely trump the 818's 300 Hp."
We will try to run the season in NASA's Super Unlimited class. Super Unlimited is pretty much anything with 4 wheels and fenders, so we will be lucky to do well. It would be a mistake to underestimate the competition in a class where almost anything goes. There is a race at VIR, so if we go I will certainly post lap times. The first race is at Barber Motorsports Park Feb 15-16th and we hope to make it. lol - 600 hp Neon has got to be a handful! Thanks for the upbeat post. Will let you know how the test and tune goes - hope nothing breaks. Right now I'm just praying for dry weather 'caus all we have is a set of slicks... |
01-01-2014, 05:39 PM | #96 |
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01-04-2014, 07:59 PM | #97 |
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Yeah, Doug is a great guy and his SRT4 is a solid FWD car. With that being said, I am not impressed with what the 818 turned in at UTCC. I think it still has a lot to improve upon without getting into my main area of power.
Last edited by Homemade WRX; 01-08-2014 at 08:40 AM. |
01-08-2014, 01:16 AM | #98 | |
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Quote:
They had lots of problems. First, the decided to use the weak 5 speed with slicks.... I think they lost 3rd in the 2nd session or something like that. I personally, would've gone out on R comps to get the car remotely dialed in before going to slicks. D |
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01-09-2014, 12:20 PM | #99 |
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Well, at least they got some good R&D in. Keep in mind, it was designed around the 5mt. I don't know for sure, but I don't think there was any development work done around using the 6MT.
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01-09-2014, 02:48 PM | #100 | |
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We have our 1st track say test coming up Sat. It's supposed to rain and all we have is a set of slicks. Should be interesting - ha! Thanks, John |
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