Croc

For a newbie to this forum you multi-quote responses like a pro! I have always believed the 420 is the sweet spot of the range. Most power that is realistically usable on the road and enough to make life good on the track. The range topping cars of 620 and CSR (yes it is still available for order despite it being off-list) are just too powerful for the road. The 620 is a monster on track as the torque effect on the rear wheels makes it a really tricky power delivery to manage - the deDion rear end is unable to handle 620 levels of power. The deDion handles power up to around 250hp and then is outmatched. Any higher than 250hp then really you need the CSR independent rear end to put the power down.

Welcome Henry! Heat is only an issue on the Caterham CSR260 or 620 models. I melted my shoe sole in a 620R on track. I also had to remove aluminum sheeting (undertray) and install vents for my CSR260 as I was burning my arms and legs on the cockpit chassis tubes. However, I also have a 420R that I keep in the UK for backroads and trackdays and I have never had a heat issue in that car. No special efforts needed for a 420 - it will be fine as is out of the box. Cheers mike

That works. Works quite well! Nice one Charlie. You can also apologize to Vlad in September!

@CBuff you are taking this way too seriously. We could be busting @Vovchandr’s chops right now. 😛

I think you are on to something. What about a play on Caterham…Cat7….PUSSY

What about MUPPET1? Has an AirForce One vibe to it? Vlad, I think I owe you drinks in Millville in September for being such a good sport!

ok…..third drink down. Fourth on the way… @Vovchandr what about: SLOW. Sums up your driving and the fact your wife laps a circuit quicker than you in a Caterham. COMPENS8. I just ordered this on a V12 Lamborghini but things being proportional should work here. @JohnCh gave me the idea. LITEW8. Car or driver. Works well. BROKEN. Could be the car after it’s oil analysis or you after this thread. Hold on, let me order another drink… @S1Steve do you want one?

oops. Someone had that plate I was thinking of? Mazda maybe? Drinking wards off the air pollution here. #blameCanada

@S1Steve had LowFlyin on his S1. I was banned in NJ from that one.

Only halfway down second drink here. I have some great ideas already. I had SE7EN in NJ on my old yellow Caterham? What about 3MINS? Quite flexible - lap time, patience, breakdown interval, bedroom,…..

For you? Let me get a second drink down for inspiration and a third for comedy…

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I agree. If I was doing this as a professional racing effort, I believe the 2.4L (with the 94mm crank) is superior because the higher rev limit achievable is more usable in a race environment. Its just a very rare engine in the US racing community - probably as the race classes don't fit it that well, being focused around protoypes. The Caterham racing here is either 420R or SCCA spec (Zetec engine - loosely approximating Sigma 150).

I read through your posts and I do agree with a lot of your logic but there are other factors you do not mention - it was a compromise in the end. Bear with my explanation as I did not make a crank decision on the engine and have everything else be decided from that. We started with stated objectives of what we wanted the engine to be and then come at it logically. Crankshaft was a fairly early decision but not the first. During the planning stage for this project, we tried to identify the 'sweet spot' between engine displacement (2.3 vs 2.4 vs 2.5), the stroke and where we thought the power/torque curves would end up relative to the revs needed for the end objective. The core of the debate was the 2.4L Duratec with a higher rev compared with the 2.5L with lower revs - which was best? A number of UK engine builders and one German race team believe the 2.4L Duratec approach is the right one - essentially validating your observations. Some of the open prototype classes that run the Duratec in the US favor the 2.5L approach. The displacement decision was a major determinant of end crankshaft spec. I wanted bulk power/torque but also wanted durability as I am not planning to rebuild this engine each month. Lower revs is consistent with durability objective. A lot of the difference in the thinking for a final decision came down to the circuits where the car is running, gearing options and durability objectives. In the end we took the 2.5L approach. This allows us to maximize torque. On the circuits the car is likely to be running and the gearing selected (to provide the best compromise for the tracks) the max revs will be 7800rpm. In reality I will never get that high. Optimal gear change point is 7300rpm. We achieved our engine objective with a 7500rpm limit. For the majority of the tracks the car will be expected to run, a torque bias in the engine focus will be a big advantage. Another advantage of this approach is lower revs lengthened the expected refresh cycle for the engine - so cheaper for me in the long run. Given this is not a class race car, these are all acceptable compromises. If I was a professional race team, my decision would be different. I would want a higher rev band and limit. But I don't have a major sponsor allowing rebuilds once or twice or more a year. So I am happy with my approach as it is a reasonable compromise and I don't think I give much away in terms of end performance. As it is I think I am going to be at the limits of a CSR chassis so any more engine performance would just be wasted. A torque focused engine will be easier to drive in that context. I agree with you on choice of pistons and quality of internals. My engine will not have the internals of a standard Ford Focus or Ford Ranger! Being cheap on quality parts just comes back to burn you in the end.

ECU is not yet tuned to engine. We will need to have a session on the dyno/rolling road. It is not a locked Caterham ECU but one we can freely tune. Its a custom forged 100mm crankshaft. It is not off the shelf production Ford part. I believe it derives from a racing program. Standard Caterham roller barrels. Same as on a CSR260. Plenty of air flow for my purposes.

Thanks Ian - will upload both files shortly once I get more coffee.

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Ian - will send you a PM note with my email address and I can upload it to the USA7s library section with credits to you. I am pretty sure I can upload a spreadsheet....

Have you seen this site for ideas as you develop your plans? Building a Sevenesque Roadster - plans

Absolutely brilliant story and photos. Thank you for sharing.

Yes I saw it but I find it confusing. Its not a well written ad. They should have run the provenance to ground with research and documentation. That would have a huge effect on value. The other thing is that it seems to be only driven a short time in 2017 - so is it sorted or not? HP seems 50hp and 0.1L displacement above what should be expected from the engine description? Lots of questions that I need to go back and review again.

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Sometimes these cars just have times of the month and you have no idea why things happen. Glad it resolved itself for you.

Oh how I can relate to this!!!! Great minds make the same mistake.