2021 Caterham 620S - "Kato"

[Croc]

 

I was approached late last year to take on a new project, a 2021 Caterham 620S that an owner was ready to move on after he had his track day fill of it plus it was problematic on a few things.   As my long term 2010 Caterham CSR260 was in early discussions for moving on, I said yes to this 620. 

 

This is not my first time with a 620.  I had a week with a 620R in Spain/Portugal back in 2017 here

 

 

Standard spec is a 2L Duratec with supercharger for 309hp.  It has the Caterham sports seats with integrated seat heaters.  Full FIA cage.  Gearbox is the standard 5 speed Miata Box (620Rs get the Sadev) - 5th gear is an overdrive.  Rear end is 3.9 using the BMW/Titan LSD diff (BMW housing with Titan internals).  Upgraded brake package.  13 inch wheels (plus an extra set).  So a good spec.  The 620S actually has a better suspension set up than the 620R.  Its far more compliant for road and good for track in all conditions, unlike the 620R which is rock hard - too hard in damp/wet conditions.  Rocky Mountain Caterham has had good results from converting 620 spec cars to a 420 Cup spring/shock package - may do this down the road.  

 

 

However, it suffered the usual 620 engine issues of that era - running too cold, throttle response issues, etc.  The previous owner had worked with Partridge Green Motorsport (PGM) to install their standard package to make everything work.  Owner claimed it developed 350hp but a chat with Andy at PGM confirmed that they never did a dyno session with the car - just uploaded a new base ECU map.  So seat of the pants says power is somewhere in upper 200s.  I have the MBE/SBD ECU dongle that came with the car and plan to address that over winter with a refined tune.  For now it goes very nicely.

 

 

I have called this car "Kato" after the valet character to Inspector Clouseau in the Pink Panther movies.  If you recall this is the guy that would jump out from behind hiding spots and try to kill Inspector Clouseau who would promptly yell "Not now Kato!"   Thats exactly what it was like to drive this car initially.  You try to put the power down coming out of a corner and then the effing thing would attempt to murder you resulting in some frantic hand movements, lots of toning & tightening of my chocolate starfish, with lots of steering wheel action to avoid the impending crash as I am yelling at the car "Not now you stupid t***!"  It really was evil to drive and had more issues than a politician with an STD.  

 

The 620S had some odd problems - the differential and the brake system. 

 

The differential was only 1 wheel drive under load - evidence of the Titan/BMW LSD diff failing early.  The transition from 2 to 1 to 2 wheel drive as the friction plates held then released then reacquired lock was...errr....exciting.   These diffs are notorious for failing and requiring rebuild and replacement.  I was not going to do a like for like replacement since you are lucky if you get 10,000 miles life out of this particular diff (shame on Caterham offering such a substandard product.  The 620R gets the Ford 7" diff as standard since it has to integrate with the Sadev sequential - a 620S does not unless you special order.  Instead, Josh at Rocky Mountain Caterham, set me up with a Road & Race Transmission UK solution - a new BMW housing with a Drexler LSD internal.  This is better than the Ford 7" diff (Sierra/Merkur/Capri) as I would not have to replace driveshafts/hubs to make work so ultimately cheaper since it was plug and play with the existing rear end structure.  Also it allowed me to lower the final drive to 3.62 which gives more top end for track and brings more of the gear set into play to dent its frantic power delivery when the supercharger kicks in.  

 

 

The brakes were another issue.  The prior owner claimed he was replacing rear brake pads after every 2-4 days on track.  None of my 7 Caterhams have ever gone through pads like that.  You should be able to get 10,000+ track miles out of a set of rear pads.  He had installed a Wilwood master cylinder in tandem with the regular Caterham race master cylinder - so two proportioning valves controlling brakes, which was a new one for me.  My initial drive confirmed something was wrong as the brakes felt very weird.  The diagnosis was one or more of the following:

1) The Caterham brake master cylinder internals were assembled backwards to proportion more braking effort to the rear instead of the front.  Unusual but I have seen it twice before.

2) Rear brakes were constantly dragging on rear disks.

3) Owner was a long time Porsche track guy and was not used to the unassisted brakes of a Caterham and overbraking. 

My solution was get rid of the Wilwood and replace the existing Caterham master cylinder with a new one and all new brake fluid.  It was confirmed the rear brakes were not grabbing.  Calipers tested fine. New pads to my preferred spec.  Car brakes as it should now. 

 

 

There were other gremlins.  The front wing supports were custom steel as the prior owner wanted to run a particular large diameter spec version of Hoosier slicks on track.  This obviously created some interesting handling characteristics with the now high unsprung weight on the front end.  The solution was twofold:

1) Go to the standard Caterham front wing upright but go for the 15 inch wheel version since that has greater clearance when used with a 13 inch wheel for varying tire sizes.  Usual brute force bending method to give inner tire wall clearance.

2) Use a different set of Hoosier slicks for dry conditions.  I also have a set of Avon hand grooved (mirroring the former Avon ZZR) intermediates for damp/mild wet conditions on the spare wheels.  

 

I added a few enhancements - high rear brake light, new LED rear lights, electrical cut off switch, new belts that were in date, and ACES shift lights.

 

First days on track were fraught as we chased electrical gremlins eventually found in two spots - wires to starter motor failing under load and (weirdly) a faulty rollover switch, which was promptly removed.  

 

 

 

First go around with the suspension set up was mostly successful.  Powerflex bushings all round.  Set up mirrors my UK 420R.  Cross weighted across the front with sand bags weighted to fat old me in the driver seat.  Having another go at tweaking set up this weekend for some enhancements based on track testing.  

 

 

Car drives as it should now.  Playing tag with another well sorted 420R (with a very skilled and experienced driver - take a bow @simon450) at NJMP Thunderbolt had us both down in the 1min21s territory.  

 

 

The rubber gaskets around the dials in the below photo were fixed with Amazon replacements - 5c a gasket.

 

 

However, it confirmed a few things.  Firstly, it is nowhere near as composed to drive as a Caterham CSR chassis.  The De Dion rear end chassis cars really do struggle to put the power down coming out of a corner when you have more than 250hp.  There are a lot of wheel waggles to keep a 620 on track and on the preferred line (think of milking the cow or being a 15 year old boy again).  The CSR by comparison absorbs every bump, goes where told and does not require much wheel waggling.  You can point a CSR at a kerb on track and it just absorbs without fuss or wheel reaction.  You cannot do that with a De Dion car. You have to work a 620 far more to do the same lap times as an equivalent engined CSR on the same track.

 

Secondly, the power delivery of this car is peaky.  Once you hit the required revs then supercharger kicks in hard.  It does not have the torque steer effect I recall the 620R having in 2017, probably because I changed final drive down plus gearbox is 5 speed rather than the Sadev I had in 2017.  But you have to drive it like the old 1980s cars which had bucket turbos with enormous lag (like my Ford Escort Cosworth RS).  But if you try to do that by keeping revs elevated and the SC on song then you get wheelspin.  Grab a higher gear to control the wheelspin then you are not in the power band sweet spot that you need to be to get out of a corner quickly - you are back to 420 levels of power at that point trying to grind up the revs to get back into the power band.  It reconfirms a theory I have long had - around a tight track a 420 is just as fast as a 620 - something I proved previously at Anglesey where I hung on to the back of a 620R in my UK 420R.  The 620 is definitely not slow but more work needed on my driving technique to get the most out of the car.   

 

More to follow as I continue to refine the suspension set up and sort it further.  

 

 

[mrmustang]

Looking forward to this thread as I myself dive deep into a car I used to own back in 2001-2003, sold to fund a business, and bought back just this past week 2 days shy of 23 years, with only 4,984 miles added in that time. Oh, mine still wears the tires I installed in 2001 

 

 

Bill

[Scott_]

Awesome, can't wait to follow the updated on the project.

 

Scott

[Croc]

20 hours ago, Scott_ said:

Awesome, can't wait to follow the updated on the project.

 

 

Not much more to do.  It just has to be sorted so it is reliable.  I think I am close on that.  A dyno session to get to a better tune with more hp is an option but not really needed.  It drives nicely on the current tune - suitable for road or track.  I do need to get a paint guy to touch up the front top bar of the roll cage as the windscreen has taken the orange paint back to bare metal - you always need to put helicopter blade tape there to prevent that.  

 

Cars like this need fettling to be reliable and turn key.  Once you get there then not a lot is needed top keep them there.  

[Ian7]

" ... with integrated seat heaters. "    LOL

[CBuff]

Standing point by from me. See you in njmp in a few weeks. 

[Croc]

8 minutes ago, Ian7 said:

" ... with integrated seat heaters. "    LOL

 

I know, I had the same reaction.  However, on those frosty morning drives my tush will be just tushy! 

[Ian7]

2 hours ago, Croc said:

 

I know, I had the same reaction.  However, on those frosty morning drives my tush will be just tushy! 

 

2 of my 3 Caterhams only had one seat :-)  Add lightness! LOL