310R vs 420R

[James2]

I'm about to have to decide on the spec of the new kit I ordered early last year. I currently have a 310R which I love, but have always wanted to build my own (well, help to build my own anyway) so the 310 was bought second hand at the time of ordering the new one because I didn't want to wait a year.

The plan all along was that the new one would be a 420R, giving me the excitement of a more powerful engine to look forward to in the new one. I went down to Crawley last Friday to drive two 420s, one a 5 speed and one a 6 speed, ostensibly to decide which gearbox I wanted to specify for my 420.

Well, the gearbox choice was easy for me (6 speed, as I have in the 310, frantic but fun) but I ended up with a whole different and entirely unexpected dilemma. I loved the power of the 420, incredible, and I see why so many people love it. But I found I preferred the characteristics of the Sigma engine in the 310. Obviously now I want the characteristics I enjoy, with the power as well!!

The 310 just feels more instantly responsive. The 420 feels smoother and more refined, as well as much faster, but I'm not really looking for smooth and refined in my Caterham. The 310 feels more like a racing engine. The 420 feels like a heavier flywheel (guess it will be in a bigger engine) and therefore not as responsive when you first push the loud pedal, although it seriously picks its skirts up once you get going.

So I'm wondering whether I should get another 310 and look at upgrading the power (can you safely and reliably get another 20-30 bhp out of the Sigma?), or maybe I could make some changes to the Duratec engine to make it feel a bit more racy? I'm not very techy (yet!) so any thoughts gratefully received.

I hope I don't upset any 420 owners by the way, it's an incredible car and I loved driving it, and I see why they are so popular. I guess I just want it all!

Most use will be on the roads by the way, but with the odd track day thrown in. I know that I will find the 310 lacking power on the track, but I'm sensible enough to know I will generally find myself holding back in the 420 on the roads.

The other thing is the financial aspect. Having had a quick look at second hand values, it looks to me like a 420, whilst a bigger initial outlay, holds its value much stronger. Have I got that right?

Thank you all!

James

 

[elie boone]

You could always go and test drive a Pemier Power 200 bhp Sigma, the difference between a 270 and a 420 is 6.5K that will get you a long way to upgrade the engine.

[SM25T]

Get Premier Power to tweak your existing engine.

[James2]

Oooh, a consensus emerging already! Thank you!

[Alan Reeves]

a 420 is likely to cost a lot less than a power upgrade. I think you might just get used to the power and delivery

though would a lightweight flywheel do the job re responsiveness ?

Also a 6 speed box with the 420 would make a big difference me thinks...

 

[Domus]

I concur, save money and weight by buying the Sigma, then give that money to Stuart at Premier Power.  

[Alan Reeves]

i see you have done the 6 sp thing, oh these decisions....

Garth went the 200 upgrade route so comments from him might help, 

 

[ChrisC]

I think your right to try before you buy, I had a 150 Sigma with a 5 speed before my current 420R 6 speed, however it was built as a 360R 6 speed kit.   

Instantly I missing the 150 Sigma character, the noise from the TBs was amazing and the car felt more balanced.   The 360R engine felt bigger/heavier had more vibration, and yet some how lacked character.   I spent plenty of time tracking down my cars vibrations, and miles also made the experience smoother, but there was still this something lacking.     For me the upgrade to the 420R has replaced most of that character, but I would say not to the same level as the 150 Sigma engines character.   I assume this is the difference between a stock and upgraded cams.

For me the gearbox thing was easy, my first Caterham was a 6 speed, and I missed it.

To add more character to a 420R what about the Roller Barrel TB upgrade, you might struggle to find one to test drive, however there are more R400D's out there with this upgrade, so a test drive or ride form a fellow member might be possible. 

If I was making your decision it would be more about build or upgrade?   I would not build a 310 and then upgrade it, if I already owned a perfectly good 310.  Upgrading a new build would void your warranty (unless CC approved upgrades) so you would be stuck for 2 years post registration before you could upgrade a 310.    Only the 270, 360 and 420 provide an official upgrade path which can be done during the warranty period.    I had significant issues with unrelated components during my warranty period, so I wouldn't dismiss this lightly. 

If your heart is not set on building, then Premier Power would be my next phone call.    For me building was the itch I needed to scratch. 

[ChrisC]

Also there is a way to make a 420 more urgent and have less hesitation.   Get the map converted from manifold pressure to throttle position sensor and have the map custom tuned at the same time.   It can only be done using the locked Caterham ECU by a company with the software/keys, i.e. Track and Road, or a using replacement unlocked ECU.      Again this is something that has to wait for your warranty period to expire  

[Chris300]

Interesting point on throttle lag. I have a 2014 Supersport R (upgraded to 210), so same engine as the 420. The slow throttle response is very noticeable and Caterham say this is characteristic of this engine and i will have to get used to it (purchased March last year from CC). I was looking to get the car tuned to see if this will fix the problem. ChrisC have you done this successfully? I have a lightened flywheel and not sure if anything else on the engine will prevent tuning/remapping away the issue. If this does resolve the problem, the 420 would be a great bit of kit. Also considered roller barrels, but have tempered my upgraditis to some other less expensive elements.

[K7 VCT]

Just a note, having a 310s car myself.

I looked into getting throttle bodies fitted, but as its running variable cam timing, that also means new ecu etc etc.

The cost would pass the £5000 mark, and need much setting up on a rolling road.

I have a light weight fly wheel and 5 speed Mazda box.

The throttle response s instantaneous.

I had tried a 360r and 420s with 6 and 5 speeds.

BTW the factory stock or modified car will always retain ore more value than an aftermarket modified car.

GP cars in kent have had a premier power modded 7 from Oxfordshire for many months.

Its your money and your car , so choose away.

 

Best of luck.

[ChrisC]

This is back to my comments on the stock map / setup / ECU used by CC thread.  CC need an ECU that will work with all component tolerances involved, but the ECU used does not learn these components, so as a compromise they use a combination of manifold vacuum and throttle position determine the need for the engine to idle.  If the throttle position is approximately closed and a vacuum is being pulled in the manifold idle is assumed.   This leads to a hesitation around idle part / light throttle openings, making it east to stall or have hesitation, i.e. idle is assumed incorrectly by the ECU.    Giving the ECU clear instruction (i.e. use more throttle) and all is fine, the ECU knows what to do.  

I did all my research on yellow Blatchat for my 150 before it was upgraded, and read the story where CC abandoned this setup for the 150 Sigma in favor of a pure throttle pot voltage setup, but this means there is only one setup that works (well).   I have had a fair few fellow members come to me to setup Sigma 150's, all have been amazed by the result.   The advantage the 150 Sigma has is the throttle pot has adjustment, sadly the 360/420 has no adjustment in this component.  

So CC can't use this where the components have no adjustment, only a small percentage would work well, and the rest would have running problems so they stick with the compromised setup, which is fine.

There are plenty of Duratec owners who have posted that Track and Road have transformed the drivability of their cars without the need for any ECU upgrade.   I understand why other rolling roads can't offer this service because of the locked ECU, meaning they are at a disadvantage here.   Personally I will have this done in the near future, but I have more pressing issues to resolve first.  I have observed the hesitation on Easymap and as much as possible reduced it on my car, but its still there to a lesser extent.    But a word of caution, if you have it done the setup is specific to the components you have fitted, change a faulty throttle position sensor will need the map adjusting again. 

[mossy7]

Last year I had a run out in Premier Power's F200 Tivct Sigma with Stuart and can only conclude it's an absolute beast! If you like the fizzy high rev pull of the 310R rather than the slightly softer pull of some Duratec installations than you really need to check it out. It's perfectly docile at low revs around town but pulls hard, revs like a buzz saw and OMG the noise is unbelievable! It's an amazing bit of engine building that also seems reliable as Stuart is often out and about in it at national meets and track days, frequently giving test drives to anyone interested. Definitely recommend a call to him. 

[James2]

Massively useful and interesting feedback everyone, thank you.

Premier Power sounds very interesting indeed!

[BigCol]

Similar things (and maybe one or two other options) are talked about here...

also consider Dave Gemzoe’s EcoBoost conversion (alluded to the thread by Simon.Rogers who hasn’t commercialised his version) - similar cost to a 200bhp PP upgrade with headroom for upgrading more if that’s not enough!

that will be my preferred route when I get Executive Approval  

[diggerman]

I built a 150SV in 2010. It took a year or so for Caterham to get the mapping right and I ended up upgrading the transmission to BMW - the silent diff, bliss.

The car has now completed Just short of 30,000 miles having toured, France, Belgium, Germany, Switzerland, Spain, isle of Man and most of the UK. That version of the Sigma with throttle bodies is outrageously raucous complete with over-run pops and bangs, but it has been completely reliable and if anything, gets better with age.

I have driven Premier Powers 175 with throttle bodies and a light flywheel. If you want a completely crazy car, that's the power unit to go for and the only alternative to the 150 I would consider. Give Stuart at PP a call and spend your cash on his upgrade. He's a nice bloke too!

Peter

 

[sjl1]

Chris

really interesting comments about the Duratec throttle  lag, my 360r has this and its really noticeable so pleased to hear the explanation. Its booked into Caterham for a cam upgrade at the end of the month so am looking forward to the difference, will see if the lag improves at all and will investigate the remap suggestion further. Oh, and i will reroute the sump breather

Regards the OP about 310 vs Duratec, having had a 270 and upgraded it to a 310, completely agree its a great engine and very exciting and enjoyable to drive, almost as nice as my old K series. I upgraded to the Duratec because the sigma has little low down torque and does run out of puff on the track, the Duratec has a lot more grunt and you do notice it. Economically i suspect upgrading to Duratec will save money over upgrading the sigma away from caterham (good as the premier power upgrades are). A 6 speed 420 is probably as far as you can easily go with a caterham unless you go 620 which just seems bonkers!

simon

 

 

 

[James2]

Many thanks for all your very sound advice Chris. I’ve only had the 310 for a year, and it’s my first Caterham so your experience of a range of models is invaluable.

Of course you are spot on when you say it makes no sense to replace a perfectly good 310 with a new 310 and then upgrade it. The plan was always to build a 420 so that I would experience a real step up when the new one was ready, but that was before I completely fell for the 310! And the one I have is lovely, really nicely built by Dan Piper (Caterham service manager) for himself in 2016, with some lovely bits on it and only 5k miles.

But I have the same itch to build that you did, and I intend to scratch it however bad for me that might be! My Dad turns 80 this year, and we’d like to build it together. He’s the expert and I’ll be his oily rag, and he’s as enthusiastic as ever so it will be a great shared experience (I hope!). And he’s given me the personal registration number which was the number plate that was on his father’s (my grandfather, who I sadly never met) Mk2 Jag when it was bought new, which has been retained in his family ever since. So I’ll have a Caterham built by my Dad, with the registration number that came from my Grandfather, and I’ll keep it for the long term. So it does make sense for me!

Because I’m still a newbie as far as Caterham ownership is concerned, the novelty of the 310 experience has far from worn off, so I think I can be patient and wait for the warranty period to expire before upgrading, but that longer term strategy sounds very appealing at the moment.

In the meantime I’m having a lot of fun thinking through the possibilities. Sometimes the anticipation is at least as enjoyable as the experience!

Thanks again,

James

[tomwood]

Why not build a 420R and then after the build have it upgraded so it has the roller barrel throttle conversion. Caterham will do it for you so the car remains under warranty etc. They may even let you build the car in kit form and fit the roller barrels yourself. Not sure about that, you’d need to ask.

i built a 360R and then had Caterham upgrade it to 420 spec + the roller barrels on top. It’s a completely different thing to drive now being both more rapid and more responsive (and much louder).

Tom

 

[DougBaker]

What is the weight difference/saving between the Sigma and Duratech engines?

[CtrMint]

I'm going to add my 2 pence here, but please take it with a pinch of salt.

I recently bought my 420 R kit over other specifications including the 310 and 360 as I wanted the dry sump from Caterham.  This wasn't because I'll be pulling high g on regular track days, but because I felt the dry sump system had greater clearance under the car, i.e. the dry sump underneath the block isn't as exposed as the wet sump pan.  

Like I say, take with a pinch of salt.

[Golf Juliet Tango]

What is the weight difference/saving between the Sigma and Duratec engines?

An important question. 

[mossy7]

Based on Roadsport spec, i.e. Leather seats and windscreen etc, half tank of fuel and weighed on a DVSA calibrated weigh bridge and at Northampton Motorsport. vehicle only:

S3 Sigma engined 140- 560 kg 

S3 Duratec 360 - 585 kg

Andy

[ScottR400D]

From the figures on CC’s web pages, for what that’s worth, about 20kg. 

[DJ.]

The Sigma wet sump has noticeably more clearance than the Duratec. I know of someone who upgraded went on a favourite oute and cracked the 2 litre Sevens sump.