KnifeySpoony

TPS swapped thanks to @sltous - seems to have fixed this issue. Only did a short drive, but similar to my last neighborhood test drive that clearly elicited the issue. I think issue is solved. So it would seem that as the TPS got hot (remember on a RBTB car, it's attached directly to the roller barrels which are attached directly to the head, so it gets quite hot), it would malfunction over that part of its range. I don't know enough about how potentiometers work to explain that, but that's what I'm going with. Hopefully it was just a dud TPS and I won't have to replace every ~3k miles, but it may just be a hazard of being mounted to the rollers, as opposed to being more isolated on a plenum setup.

Going to swap tps today thanks to a very generous forum member. Will report back.

What were your tps symptoms?

Ugh, new problem... so did a trackday yesterday, no engine issues all day, though I was struggling with a leaky brake reservoir cap. Will have to make another thread for that issue. Driving back from Sonoma, started getting a severe hesitation at partial throttle - basically from 0-5% throttle, tip in feels normal, however it's like from 5-20% throttle, no fuel is being added, and the car hesitates severely/will not accelerate at all. If I keep gradually opening the throttle, once its gets past about 20% or so, then it's like it catches, I get a surge, then the rest of the throttle travel is normal. Car pulls hard and smooth to redline. When I get the hesitation, it's interesting in that if I keep the throttle depressed at that position, and press in the clutch, the revs do not climb at all as they normally would when the load is removed. Today I test drove around my neighborhood - when engine is cold it's not doing it at all. Even when the water got up to temp it wasn't doing it initially, but as I continued driving for more than 5-10min, it started up again consistently. No popping from exhaust. No smoke that I can tell. I checked the TPS (FWIW I'm on CC roller barrels) with easimap - idle voltage is correct, and it seems to be sweeping/responding normal with throttle. Jiggling wires to the TPS while connected did not show any voltage fluctuation. I swapped out the sparkplugs and no change. Plugs I ran yesterday seem to look OK but 2 of them look different than the other 2. Any thoughts? Bad 02 sensor? Bad TPS? Something else?

Mine is a 2020/2021 build - not sure if you have the newer style "race" oil cooler or the older style that mounts in front of the water rad. That could be a factor. Also, I have the 420R "race" nose cone with extra opening for the oil cooler. This could be contributing as well. On cold morning drives to the track I block off the opening, which does bump up oil temps about 10deg F on the freeway. However, on a particular cold fall AM drive to Laguna I was seeing 108F steady state on the freeway at 70mph. That's COLD. Cold enough for me to fear for my engine. 2 days ago AM drive to track was seeing 125F on freeway in about 55deg ambient. These temps are in the oil tank, btw- I'm not sure of the delta before/after the cooler. I can only hope oil is 50deg hotter in the bearings. I have read about people putting inline thermostats to the oil rad with little change in temps, so I abandoned that idea. My water temp runs rock solid at 197F when underway. Not sure which thermostat I have- it's the one that came fitted as standard. The reality is I think the car is cooled for racing. And in particular, drafting. The 420R race cars (now called UK championship) run the exact same nosecone and cooler setup AFAIK. They have to run nose to tail and not overheat. This means that in any other situation, the car will be overcooled. I'm ok with that as I only drive my car on the street to/from the track and I'm ok with the compromise. However, for a pure street car, I think a oil/water (modine) style cooler is superior.

I see higher lateral g in higher speed corners actually. I think this is typical?

What oil temps are you seeing on the street?

Just don't install an oil temp gauge and ignorance is bliss. If you aspire to track it, then dry sump is certainly an asset.

Dry sump and uprated brakes are for track work. You will never need them on the street. There is no downside to uprated brakes on the street, but they are unnecessary. However, dry sump is actually a downside for a street driven car. Your oil will be perpetually overcooled.

The standard bar is shorter and more likely to fold in a rollover. Since you're short, the height isn't really an issue though.

Shift lights are kind of pointless on a street car (and not that necessary even on a track car). I would consider the trackday rollbar, even if you never/seldom track it. How tall are you? Lowered floors if over 5'11" methinks. Also, i would go 13" wheels - looks better on ans s3, and better performance/ride quality.

Heck, buy two.

OK I registered for the 10/6 Sonoma day, so I can give a ride if you want. That goes for you too Gallognacio, either 10/6 or 10/15. Typically I'm trying for PR in first couple AM sessions with better track conditions, then after that I'm happy to give rides.

If I make it to 10/6, you're welcome to ride along to see what a 1:45 pace feels like.

IMO if you want the coolest, most bonkers car then the 620R is it, assuming you're willing to accept the significant downsides of a sequential when driving around town. Otherwise get a 420 with 5 speed.

Optioning a sequential on a 420R is not a simple matter - definitely will be some faffing/DIY to get it done (above and beyond the normal amount in a 7 build). If you really want a sequential, unless you're willing to tackle a project, I'd just get a 620R (factory build of course). A sequential is very hardcore, what most (other than 7 nutjobs like us) would consider a track-only option in a car. I would highly recommend against it for a solely street driven car unless you are a real nutter. Coming from a bmw and a subaru, I don't know if you realize how raw and aggressive even a rather tame 7 is. You certainly don't need to have a sequential for it to be exciting.

No need to notify me at all. Rather I would need to notify you if I end up registering and attending that day, so you would know if it's worth showing up. If I do go, all you need to do it find me there and I will give you a ride.

oh I might also be at Sonoma 10/6 if you can make that (a thursday)

Yes, I can show you the car on a weekend evening. But unfortunately there's nowhere to drive around where I live.

I'm fairly certain I could scare the shit out of him in boring-old 200whp 420. Come to Sonoma 10/15 if you want a ride along...

Yes - caveat is that my experience is only with roots-style blowers, I've never driven a centrifugal. Although the torque delivery is linear; ie there isn't a high boost threshold like there is with some turbo setups, there IS boost lag like with a turbo, albeit limited. You don't get that instantaneous throttle response that you get with a well -tuned NA motor. With a roots blower, boost is bypassed with closed/neutral throttle, and there is a delay until it builds pressure when mashing the gas. It's small, and many people don't even notice it. They're great for street cars IMO. But for me there is nothing like the instant hit from an NA motor, especially one with ITBs.

re: 420 vs 620 - other than the ability to build it (which was a big priority), I am not a fan of the response of forced induction engines. Also, supercharger heat soak is a power killer on a track-driven car, which is my car's main purpose. So the hottest naturally aspirated version was the most appealing to me. If you want a stoplight-to-stoplight or onramp champ, then the 620 is surely the way to go. From what I read, many people with a 620 find it frightening to drive, as it so easily overwhelms traction. It's not for beginners. Remember unlike all the other high HP cars out there today, a 7 has no nannies... re: S vs R pack - I think the most important part of the R pack is the LSD - IMO it's a mandatory feature for any moderately powerful seven. Driving a 7 with the throttle is a big part of the experience, and it's just not the same with an open diff. Of course, other R pack components are also worthwhile additions for a car that will be driven hard or near/at the limit. If you plan on having a cruiser, that will be street driven at no more than 7/10ths, then S pack may be more appropriate. If you intend to track the car, then it's an easy decision. A 7 is a surprisingly capable and performant car. Even a 420 is very quick at legal speeds (before hitting aero drag) and can easily overwhelm its rear tires in a curve in 3rd gear. If you intend to really explore its performance capabilities, you will need to go to a track. Only much more powerful or serious machinery can keep up with a well driven 420 on track.

. Model differences as well as S/R differences are shows on Caterham's site and configurator. Go the the UK page and play with their configurator to see all the options. One big difference between 420 and 620 is that 620 is factory-build only, so if you want to build (as I did) then 620 is off the table. Also 620 is RHD drive only. I am in Newark. If you want to do a test fit, I'm happy to oblige.

HOD. I'm on the fence though, as I'm already registered for 10/15 with Lightspeed. HOD also turns me off with their "membership" fee, and their high prices in general. Although they do keep the groups from getting too crowded I think.

This is one of the things that helped me solidify my decision to get a 7. It also has me wanting a M3W bad - my plan is to get one when I'm ready to slow down after the 7. AKA my retirement car.