Ultralite impressions

[Kitcat]

JohnK was kind enough to let me take his Ultralite for a road test yesterday.

 

I liked that it started, nothing fell off and we got home under our own power. Given my recent history w/sevens that's big!

 

Stuff I liked a lot; very slick/quick shifter. Always was able to find the right gear. Even after 200 track miles in my track Cat, I am lost occasionally as to wh/of the 6 speeds I am in and where the gear I want is. No problemo, I will learn it-but on John's there was no learning curve.

 

Nice progressive clutch.

Great exhaust sound.

Tach, smack in front of my eyes, easy to monitor.

Vastly fewer creaks, rattles, groans, etc. Not BMW like but much tighter than any se7en I have owned.

 

Stuff I was neutral about: It is less of a rocket ship that I expected. In part because we were mostly cruising highly populated areas so I cldnt get on it. Like all VTEC's power is an on/off proposition. From 6K-8K it makes serious power. Below, modest. And I was usually below. Also, compared to the Civics etc I have driven, the VTEC power change is much more noticeable, perhaps due to the light weight.

 

Seating position-much higher than my butt-on-the-floor Caterhams and Birkin. For better, and worse. Better view, but felt a bit less a part of the car.

 

Stuff I didnt like as much as my other cars: Steering wheel sits real low, ya kinda reach down to your lap for it. Perhaps because the seat was so high? I did like the feel and speed w/which wheel turned the car, just not location.

 

Brakes, not much feel and took a lot of effort to get the car stopped. John says new grippyer pads are under review.

 

Unknowns: handling-didn't really push it. Something about driving in a residential area, w/cold tires on a irreplaceable car with the owner next to ya that adds an element of driving discretion for wh/I am not otherwise known for:).

 

Bottom line: fun se7en that wonderfully captures the spirit and soul of all the se7ens I have owned to date. I'd be happy to have it in my garage!

[WestTexasS2K]

I'm sure John will join the discussion.

On the steering wheel sound like its mounted under the dash bar. In this position which most are mounted there can put the wheel very low. My last car I mounted it above the bar I think this a much better position. You can easily get in and out with steering wheel on. It can require some adjusting of the pedal assy to fit it. I agree also that stock vtec point is a bit high for a light car. An Apexi piggyback tuner can be used to lower vtec to 5000 this makes the transition less abrupt. There are other systems that do the same thing. Apexi is the cheapest way to go on a stock motor. Fuel curve can be tweaked as well with it. You can gain 15-20hp with fuel tuning.

Gearing is also very important. I'm not sure what gear he has in the car. I recommend 4:11 or my favorite 4:44. This will help beef up the weak bottom end torque curve of the f20c motor.

Seating is usually very low. 3" from the floor. I have to sit on pillows to see over the dash myself. I'm not sure what seats are installed. Maybe John can fill in that info. If stock seats it just might be the way they are mounted that varies from my experience.

Brakes can be improved with some compound changes. They really require some heat to start working. I usually drag my brakes for a few blocks to get heat in them this usually will improve brake grip very quickly. I found Wilwood recommendations didn't work for me. I used there friction data sheets and went from there.

[JohnK]

 

And what Se7en owner wouldn't be flattered to have someone with more

driving experience than his own review his work?

 

I remember all the trials you've endured (read: 'had to pay for'), particularly with the Birkin. Considering the 6+years I've been at this car, I certainly share the sense of relief that it behaved without problems, particularly during your drive (Who's law is it that says “Things will choose to fail just when you try to demonstrate to someone else how they work.”?)

 

Kudos to Honda. Everyone accepts that they do absolutely great engines, and now with the S2000, transmissions as well.

Builder's choice of this drive train was a major reason I chose his kit.

 

As above, and,

I guessed at the piston size the master cylinder should have (5/8” IIRC) and came out OK; neither too small, making the throw too long, nor too large, making it quick but heavy. Note that the stock damper mechanism was removed from the slave cylinder (Honda fitted this for the general consumer who might let the clutch out too abruptly and stall the engine at drive-away, probably concerned about all the bad press re the engine's lack of low end torque(UNTRUE!) ).

 

Something NOT said was of any difficulty with the footwell controls. Sitting in the car some years ago, Mike had noted that the footwell was narrower than that of his Caterham Super Sprint, and he was wearing narrow racing shoes at the time. This time he was wearing ordinary street/track/trainer shoes and made no mention of any problem operating the pedals which pleased me.

When I got the kit, I couldn't see any way of configuring the footwell controls that would not make them awkward to use. Guided by a mock up of the space and cutouts from the soles of a pair of size 10-C shoes, I used the cutouts to figure out where the pedals should be for easy use, and especially for being able to heel & toe comfortably. The thing that killed using the hang-down configuration was the combination of narrow footwell width and the presence of the steering column. These two pictures show the pedal layout that Mike used and above the pedals you can see the where the steering column sits – so its easy to see that, with the pedals hanging down, you get either a properly positioned brake pedal or a steering column in front of the driver.

 

https://www.dropbox.com/s/gegh84b2gmcv7i1/Pedals_Brake_vs_SteeringCol_a.JPG?dl=0

https://www.dropbox.com/s/u0yf7tmajzrjk44/Pedals_Brake_vs_SteeringCol_b.JPG?dl=0

 

The cost here was modifying the chassis to support floor-mounted pedal assemblies. I managed to find a bit of room for the master cylinders by extending the front of the footwell (unused space isn't easy to find in a Se7en!) Challenging.

 

https://www.dropbox.com/s/57mvhylsfzj0itw/Pedals_RoomFor.jpg?dl=0

 

Kudos to the Builder for his choice of muffler, plus the wonderful sonics produced by nearly any very highly tuned engine.

 

 

Took some thought, planning and work as shown in

https://www.dropbox.com/s/rl8lurrrsftzujw/ChassisMod_Dash.JPG?dl=0

Vertical pieces support bonded bushes which connect to the dash for shock/vibration isolation.

 

 

 

Thanks to EviLRome0 's post “heim joints ...” and his reference to Gary at Fastener Specialties. For a mere $550 I replaced all these rod ends with FK brand CMX series pieces that had teflon inserts. I machined pairs of trammel points of the right diameters and fabricated them so that the could be bolted to the bench – taking one suspension link at a time off the (aligned) car, I was able to capture the length with high precision, bolt the points to the bench, pull the suspension link off the points, swap the rod ends, and then use the bolted-down points as the reference fixture to ensure that I transferred the length as it had been on the car. There was quite a difference in feel as well as a huge reduction in noise, both of which made all the work worthwhile. The little noise that remains is due to the front and rear anti-roll bar links which I've yet to switch.

Also, there was a concerted overall effort to make sure that nothing in the car was free to flap about or rattle.

 

 

Powderbrake, who also happens to own a Corvette (of course strictly for comparison purposes), wrote me when I announced that I was buying an S2K kit; “Congratulations! Now you will fear no man at the stoplight.”

 

It really is potentially a very very fast car, and driving it quite quickly will be effortless not only due to its considerable power but also its very smooth delivery of that power, save perhaps through the VTEC band . However at present it may as well be dragging a boat anchor behind it.

 

When you, as Honda et ala., design a power train, you engineer the thing so that engine's power band, the sizes of the steps between the gear ratios, differential ratio and the wheel size are matched in such a way, that the driver can access max or near max power everywhere in the car's road speed range.

 

The S2000 was designed with a 4.10 differential . The Builder delivered my car with a 3.54 differential which is such a high ratio that it, as Mike could tell, emasculates the performance. I think this reflects negligence, if not ignorance, on the part of the Builder that is just inexcusable. Therefore, in order to get it to perform like it's capable of, I'm looking at time required to locate a 4.11 differential from the right model Subaru (thanks for the data on the different models, Loren), spending the several hundred dollars to acquire it, and days of pretty difficult work to do the swap – all, of course, provided there are no surprises along the way. The only good side is that this is a no-question fix; make this change and I'll have the “rocket ship” Mike expected.

 

 

Agreed. I anticipate that the last 2K on the tach will be an exercise in personal reflex management, once I swap for the right differential. But let me comment on an experience here. In the past I had a 250 cc Ducati Diana MK II that was tricked out and performed REAL well. Then I bought an '87 Honda Hurricane 600 . . . and for quite a while I pretty much thought of the throttle, at anything over 5K, as an on-off switch. I eventually learned that you really did have throttle control there, but it took more than a little maturation of skills on my part before I got there.

 

 

For the track, it's intuitively obvious when you're out there (depending on how much intuition your rear end has built into it) that the lower in the car you sit, the better positioned you are to control the car. And by being as low as you can get, you're doing your part to make the vertical CG of the car as low as possible – which is the best thing you can do to make the car handle better.

 

In my car, driver height is limited by the fact that the engine, as wonderful as I think it is, is really tall, not to mention it being ~ 200 lbs. heavier than what you had in your Caterham Super Sprint. I mounted the seat only high enough so I could see over the hood, as well as getting it tilted back as much as I could so the driver was as far from the steering wheel as I could manage.

 

For me this issue is a considerable compromise. Not yet having had track time, I have questions about being able to see things like corner apexes and making judgments about depth. Looking at approaching corners from the ride height of my sport bike this was never a problem, but in my car I'm now finding it is. I can guess that on the track, you know where things are from practice and memory. However I've got so many really fantastic roads nearby that I know and enjoy, I put more of a premium on being able to see, both the road and its hazards.

 

With respect to feeling connected to the car; I'm certain the choice of seat bears a lot on this. The UltraShield ProDrag 12020 that came with my kit is sound and I tied it quite rigidly to the chassis, but it's hardly what you'd call 'designed for a road racer'. But then this helps one understand why more suitable looking units are on the order of $1K. I just noticed that there's quite a gap right at the hips, that even with the seat belt being there, conveys a 'lack of connectedness' when you're cornering. Probably time for judicious application of yet more padding ('rebond'), or upgrade to a 'spensive chair.

Edited December 29, 2016 by JohnK

[JohnK]

 

Root of this problem is that the chassis was designed with a frame member right where it would have been most appropriate to put the steering column – so you had to put the wheel either higher or lower than you'd like - which lead to a lot of agonizing on my part.

I reviewed a bunch of pics and one caught my attention as to what I did NOT like,

https://www.dropbox.com/s/ehd0vtvktfdpjwa/DrivingPositions_Chad_rm4.jpg?dl=0

which, to my eye, looks awkward.

 

and others that indicated a low position was probably not awful

https://www.dropbox.com/s/h6m5g3tk2lkpaqi/da02DrivingPos00cat-superlight-R.jpg?dl=0

compared to what I implemented

https://www.dropbox.com/s/pjwx1x2ew7hf4pp/da01DrivingPosition.JPG?dl=0

 

However, compare

https://www.dropbox.com/s/pxqn8p5jx2ymx03/DrivingPosition_caterham-superlight-500.jpg?dl=0

and

https://www.dropbox.com/s/hdcyaddcwb28gxk/DrivingPosition_Chad_rm11.jpg?dl=0

 

Does the light blue Cat have the steering wheel raised? Anyway, it seems there's not a clearly better way to place the steering wheel, other than right in front of the driver.

 

 

Just thinking about my car, it seems like the wheel should be higher - but at the time the cost of doing the chassis modification was just too much. Along with that, experience over several hundred miles out in the country in familiar sport bike haunts surprised me. I started with my hands at 10:00 and 2:00, but found myself holding the wheel below 9:00 and 3:00 as the miles went by, because it was obviously more comfortable and offered the best sense of control. Two things contribute here: with an 11:1 steering ratio very little movement of the wheel is necessary, and with assisted steering there's need for only very little force to turn the car - which means no need for compensating body posture. My sense is that, if you're reaching up toward the level of your shoulders, the ergonomics point to more effort, and vice versa for when your hands are lower. Sitting in the car when it's not running, I don't have to shift my posture to turn the wheel against the force of the steering.

 

One thing about the steering not commented on by Mike was its effect on the car's drivability at speed. On one stretch of moderately bumpy two-lane asphalt we got to well over 90 MPH (I was too busy holding my hat and glasses on to get a good look at the speedo) and there was no report that the car felt darty or twitchy. Absence of complaint in this regard made me feel that I'd gotten the steering right – 11:1 assisted steering in these conditions, not done properly, will make placing the car on the road where you want it difficult and make the car feel unstable. (N.B., The 11:1 ratio translates, with around 22 degrees of lock and 6 degrees of Ackermann at the inside wheel, to 1 1/3 turns lock to lock.)

 

I'd read so often of people complaining about how weak the brakes were in their Caterhams, I figured you just used more force slowing down a Se7en. Apparently, Mike's Caterhams have been different, so I just placed an order for some racing (rather than street) pads. Friction will be much higher but at the cost of shortening the life of the brake rotors. We'll see how much.

FWIW – when I designed my brake system (starting with a blank sheet of paper and Puhn's Brake Handbook) I had the rotors and hats machined to my specs by Coleman Racing Products (http://www.colemanracing.com/Default.aspx), who offer the service of machining brake parts like rotors and hats to customer specs. Cost-wise this was made much easier by finding close approximations from their considerable stock of blanks. Just looking at all the different rotors you can start from teaches you lots about brakes. They were recommended by Wilwood whom I chose to source the calipers. Happily, I find that Coleman is still in business, looks to be doing well, and and has added Spindles to their catalog of items you can get modified to your needs. Yet another set of options for the builder and fabricator.

 

 

 

And the owner is indeed most grateful!

 

The final major item to dial in is handling balance.

The car god spake that race cars will understeer initially and oversteer finally, and the transition between the two states will be at the condition where the car is reaching the limit of its cornering ability. Time spent in a Boxter made it apparent to me that this is indeed gospel to be followed most ardently by the tuner.

We'll see how well I can achieve this. Clearly, achieving this will be an occasion for inviting a second test drive.

 

Many thanks for the feedback Mike, and, hey, S1Steve ! don't forget you're also on the list for a test drive!

 

 

__________________

'97 Caterham Super Sprint, 1700 Crossflow-sold

'09 Birkin S3, Duratec street car

'03 Caterham Zetec track car

Edited December 29, 2016 by JohnK

[WestTexasS2K]

John I have a few 4:11 on the shelf. One that is brand new from a WRX.

[BusaNostra]

John I have a few 4:11 on the shelf. One that is brand new from a WRX.

 

What if you have 3.90?

[Mondo]

Stock Honda S2000 is a 4.1 diff (on 17in wheels). I have 3.9 and can spin the tires in first... great at freeway speeds. I bought the 3.9 because it's the strongest of suburu's diffs and Loren has gone thru several 4.11s (with forced induction). And I'd like to go that route at some point too.

I'm wondering if 1st is pretty useless with that low ratio... 2nd & 3rd would pull harder I guess.

[JohnK]

Loren,

Thanks much, and I'm interested in a 4.11 (either kind of LSD is OK), but need to weigh shipping (to 45227) into the cost versus that of a local purchase. Also, I'm not in any hurry, so if you're traveling sometime that may help. Contact me via PM. Thanks again.

Cheers.

John K

[JohnK]

Mondo,

Worked out the figures: at 7K 1st is 34 MPH, 2nd is 53, 3rd 73, 4th 93, 5th 114, and 6th 141. Chuck said he was clocked at 140 and it was still climbing, so 4.11 seems like a good fit. Plus that, I'll guess that Honda lined things up pretty optimally with respect to the power band.

John K

[WestTexasS2K]

Mondo the 3.90 isnt any stronger than the 4:11 units or 4:44 units. Its true we trashed a few diffs during 1 Lap with the supercharged engine and the R160 diff. We upgraded to the R180 diff from STI and have had no more problems with the diff. My personal preference for my cars with a stock NA motor is the 4:44. Now if I were going to go on a 2000 mile tour with a group and was going to be doing 70-75 for hours on end then I would swap to the 4:11 or 3:90. The motor could care less about the increased rpm but your ears will care.

 

John It is true that Honda used the 4:10 stock form. Honda does make alot of compromises as well. Most aftermarket tuners will run 4:56 gears in the S2000 for improved perfromance. If you are going to use you car for any kind of DE events or Autox I would recommend the 4:44 if you are going to run the 17" tires. If you are going to run a 15 inch slick for these type of events a 4:11 will work ok because your final drive ratio will be lower because of the shorter tire.

 

Now if your intended use for the car is mostly cruising driving up and down the highway 90 percent of the time with a few track days a year thrown in for fun then the 4:11 will be fine. Your math is correct on the gearing. The one thing those formulas dont account for is wind drag which is significant in a 7.

 

When Chuck was clocked at 140 he was at Run and Gun. He was running a 13 in rim and tire. I would have to run the numbers but his gearing was way down there. I was running 17" street tires and I was clocked at 137 in the same stretch with 4:44 in my car.

[BusaNostra]

I have a 3.90 and you are right - it'll bleed your ears.

Mine is Sierra diff with quaife.

[powderbrake]

I have the 4:44, and it is awesome off the line. People that I have given rides have been astounded by the acceleration. Of course the noise and wind rush of a seven are new to them and adds to the experience. You do have to shift rather quickly to stay out of the rev limiter.

 

What Loren says it true, that many hours on the highway may seem a bit noisy, but heck, the wind is the big noise in these cars at highway speeds.

 

I found the 4:44 to be my limiting factor at the 1/4 mile drag races. I peaked out just a bit early and needed to shift near the finish. I believe a 4:11 would have given me a better time, or perhaps a higher speed. I always ended up at around 106mph, even though the times went from 12.6 to 13.x This was always with 17" wheels, and the Falken 615's in 245/45 R17. I am also not skilled at drags, only having run them a few times at Run & Gun. I am sure some more pactice, stickier tires and more horsepower would always help.

 

If I had to do it all over, I might go for the 4:11, as I am no longer doing any track days or drags, and use it mostly for blats on twisty roads, and some daily driver runs in good weather. On the other hand, I love it the way it is. I put on some new Falken 615k's on this summer, and they made a huge change in performance. Tires don't really wear out on my Ultralite, they tend to get hard and slippery, so this time I had them heat cycled at Tire Rack before delivery. Maybe that will extend the sticky life.

[rnr]

Does anyone know the cruising rpms at say 70mph with the 3.9, 4.11 and 4.44 offhand?

 

I dont know what diff is in my car but it is at ~4k rpm at 70mph (GPS verified)

[powderbrake]

Does anyone know the cruising rpms at say 70mph with the 3.9, 4.11 and 4.44 offhand?

 

I dont know what diff is in my car but it is at ~4k rpm at 70mph (GPS verified)

 

My rpms are about 4000 at 70 mph

[WestTexasS2K]

Ap1 Trans in 6th has a drive ratio of .081

Ap2 Trans in 6th has a ratio of .0763

 

Measure your tire height and the. Plug the numbers into an online gears calculator.

 

Example .081 gear 4:44 diff 25.5 in tire should be 3317 rpm.

26 inch tire is 3253.

[JohnK]

Loren,

Thx for all the great info and recomendations. While I've got some really fine Se7en roads that I enjoy, I also designed the brakes to accept 13" wheels, and hope to spend time at local tracks. However, I'll have to dry sump the engine before I can run such wheels - so that's a bit in the future. Given this, and based on your feedback, it sounds like 4.11 is a balanced fit. And, from your earlier posts, I'll plan on making ABS bushes and reinforcing the fwd mount. In the back of my mind is a worry about compatibility with the inboard brakes I have and any differences there may be with the diffs you have. Are the castings all identical, particularly re the side bearing retainers? I'll send pics if necessary.

Cheers,

John K

[WestTexasS2K]

John i think the 4:11 with 13" will be great combo . As long as you stay with the R160 they are dimensionally the same from the eighties till today. The R180 is wider in the diff section but will bolt into the car. It requires different axles too the STI axles have a bigger shaft and are a little shorter. There are fewer gear choices for the R180.

 

I recommend some sort of diff brace to reduce torsional twist. I'm finishing one today Ill post a pic so you can get an idea of how I have done them. I think it will clear your inboard brakes.

[JohnK]

John i think the 4:11 with 13" will be great combo . As long as you stay with the R160 they are dimensionally the same from the eighties till today. The R180 is wider in the diff section but will bolt into the car. It requires different axles too the STI axles have a bigger shaft and are a little shorter. There are fewer gear choices for the R180.

 

I recommend some sort of diff brace to reduce torsional twist. I'm finishing one today Ill post a pic so you can get an idea of how I have done them. I think it will clear your inboard brakes.

 

Good to hear and thx again. Still lots of work ahead, but as they say, "When the journey is as important as the destination."

 

- What are the characteristics/dimensions that let you identify a diff as an R160?

I'm assuming I've got an R160, and am much relieved to hear that I don't have to worry about small differences among the different models other than ratio and LSD.

 

- Look fwd to seeing your design for the diff brace and will certainly implement such when I do the swap. While things are apart, have you run into anything that suggests that a stiffening of the rear of the chassis would be worthwhile? Chuck mentioned that the rocking of the diff was in some part due to flex in the rear of the chassis, and I'm feeding the loads from my rear AR Bar into the section that's part of the diff's rear support.

 

-Making progress on suspension balance. Will detail how I got there when I get it nailed. I'll wager that what I'm finding will be generally useful, especially for Ultralite owners.

 

Cheers,

John K

[WestTexasS2K]

Your car will have the R160 mine and 7evin are the only ones with R180 units. We are the only ones running higher horsepower cars as far as I know.

 

Diffs have the tendency to tear the sheet metal that hold the front of the diff up on the front. The rocking back and forth overtime will just fatigue that U shape brace that the diff is mounted in. The factory Subaru cars had a 3 foot arm across that front portion of that U brace. That obviously will not work on our cars. So my solution is to put a wider brace on the back of the U shaped support and tie into the chassis behind the seats. This really helps eliminate the rocking motion and prevents the nose from breaking. I ran out of material to finish the diff support tonight Ill have to pick up more on Tues.

[rnr]

I posted a picture of my diff brace (copied from Mondo) and the reinforced front mounting point at http://www.rahulnair.net/blog/2012/02/02/difficult-times/