Ask Phil #11 – Hi Phil! I’m curious as to the background of the SR5. The car seems like a great idea to me. A lower stressed engine that would be great for track days where the owner isn’t as concerned about getting every last bit out of power to weight. However, it seems it never really took off. I’d like to know what were the thoughts behind the SR5 and why you think it never caught on? The car was also available as a roller and able to accommodate a Sadev which I found to be something Radical doesn’t typically do and was wondering if they were trying to tap a new market with this approach? My interest comes from owning SR8 Chassis 42 as a roller and looking to swap in a Honda K24 and a Sadev transaxle. Thanks! Joe (@JoeP)
Hi Joe, SR5 design and build was initially driven from the European market racing series.
We were looking to increase sales by expanding into other categories.
Several things were moving in European sales. The VdV endurance series, run by the Eric Van der Vyver organization, was a very successful series in early 2000’s. It was a 4-6 hour race with the main cars being Norma or Ligier FIA CN category. Most of these used a carbon tub with a lot more downforce, and automotive based engines for longer life. They were a step between a radical tube frame and LMP (Le Mans Prototype).
Hugely popular series, but hard fought, but IMHO, they just went too far with authority, rules, etc., etc..
Gotta keep it fun and achievable.
However main CN championship chose Honda motor and then, as they do, regulations caused issues.
They decided not only to keep motors entirely standard, but also to limit revs., so CN Honda motors had lower Rev limit than road cars in the name of reliability. However, the regulations guys did not look at the circuits, or look at an “on power histogram”, or how the V tech valve operation affected the power delivered.
To go fast, you had to keep motor above 5900-6200, which is the area the valves open more, and below now 8000. If you take 500 rpm off top of revs., you reduce the power band to 1800 rpm instead of 2500.
There were cases of rev limiters actually damaging engines. A lot of the French circuits have tight hairpins, if you have V tech coming in at 6000 – you gotta be in first gear – if you then look at rest of track and ratios available – with the max speed available from a motor with good torque – the biggest step down is always 2nd – down to 1st – and over Rev the motor on down shift.
With standard pistons, over rev on downshifts pulls the wrist pin out the piston! Mugen offered completely identical piston to standard but forged not cast, same compression, but scrutineers would not allow it! Consequently, the best year for grids and racers, there were 54 Honda motors blown up! So VdV started to get known as an expensive formula, that and most teams were over the top serious about prep for 6 hour races – they really were sprint cars, so cost a lot to keep going fast. It needed a more balanced and flexible view on regs for design and cost consideration to take the cutting-edge lightness out of play and put in some durability and commonality and availability of parts.
Also, the cars were very fast, but on a knife edge handling wise, similar to F3, difficult for the average gentleman driver to cope with. Beautiful in many ways, but a self-defeating prophecy. They had to employ young hot shoes to be competitive in the team, too much like the European Le Mans Series… very costly.
Eventually they allowed a very light Peugeot turbo motor in that more or less killed the series.
Think the moral of that is – Think about the customer experience!
At same time whilst all this was developing… We went along to the headline event back then, a double 6 hr. event at Magny-Cours. Saturday 6 hours finishing at dusk, park ferme overnight, Sunday 6 hours straight away in the morning, straight out of overnight jail for the cars – no prep, on the grid, re start the race. We had our Belgian dealer and others there. For the 2 litre class limit, we actually built a 2 litre V8! Horrible bodge design, using very tall and heavy piston crowns but it was a quick job to just see how the car went (don’t forget, this is the time we were flying on sales and success, and we were drunk with it!). Also, Mick and I raced the first black and gold turbo SR3 (this was the first Radical to break the Nürburgring track record) before it did Nürburgring. It was a rocket ship on straights but a hand full through a whole lap (with 3 hairpins). Out of first 10 places I think radicals took 6 of them, with our motorcycle engined cars that they had allowed in their series to make big numbers of entrants. I believe we were 1-2-3 – 5- 7- 9 or something like. And following that…Wait for it… We never sold another motorcycle engine car for the next 2 – 3 years in France until we took another specialist French dealer. The 2 litre V8, was approved for series, initially, so we built it in 3 months – and it was promptly banned!
So, as we were not allowed to beat them, so we had to join them, and build the Honda engine SR5.
I did find the Honda motor kind of heavy and tall, about 140 kg and huge power to be had at quite some cost. Guess it wasn’t “Radical” enough? I wanted it to work, I love Honda products, I have had at least 7 Honda motorcycles, My son James has same model as I had when I was 19, a 1969 CB450 black bomber, loved that bike, torsion bar valve springs etc., etc..
The SR5 did have a design flaw that I discovered in the workshop one day. One engine bay tube was moved from SR8 chassis to accommodate Honda motor – it was a disaster, engine bay flexed, I saw it as a new car was balancing on a jack without a bolt on crossmember on, and although it was rocking there was another movement going on, it didn’t take long to spot after that, cross member was saving it, but it needed updating.
Regarding the Sadev transmission, it was never used in the SR5 because the drive shaft center of the differential is a long way to the rear in the car, and the SR3 /8 / 5 chassis and body (position of the wheel arches) is very short wheelbase due to motorcycle origins. The SR8 gearbox has driveshaft at front of gearbox. The CN / Honda / Sadev (and Revolution) have ~12” longer wheel base to accommodate the transmission geometry.
So, good car, but all these things need selling, and overcoming, and volume wins favour in small excitable companies, I guess.