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K series 1600 / Kent 1600 Sprint


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Bonsoir Eric,

I must say that the 115 bhp of my 1.6 standard K engine is really a screamer between 5500 rpm and 6700 rpm where it hits the limter. This is the rpm range where 16V engines make the difference on 8v's

. However the torque is not impressive and the Kent engine might be superior inthis domain.

Question for motor experts:

hitting the limiter = possible damage to the engine if being done often?




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6700 is mild revs for a K my 1600 ss was regularly at 7800 for three years and on strip down this winter for Forged piston fitment showed no damage whatsoever use a good synth oil ensure the oil is up to temp not just the water and let her at it Jez reckons they are OK for 8500 but that is madness however 7400 is absolutly fine.Problem is without an M3D you are stuck with the mems rev limit [bLATENT PLUG from satisfied user.]



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The fuel injected K, with mapped ignition is able to operate optimally throughout the rev range. The crossflow on carbs is compromised on fuelling and ignition timing. Getting a 3d mapped ignition is a worthwhile upgrade for a carbed car. At part throttle and snapping open the throttle the K is probably much better.


The k's rev range is higher. This means that to get the same amount of oomph out of it you have to rev it higher all the time. If in doubt just stay one gear lower. Stop thinking about an absolute number of revs and start thinking about proportion of rev range.


A 1.4SS K series has almost exactly the same power characteristics as a 1.6 Sprint crossflow up to 6000rpm. The 1.4SS K then has another 1000 and a bit revs to go where it just gets better and better.


Hitting the limiter does nasty things to the fuel air mixture. The limiter can work in three ways - cutting fuel, cutting sparks or cutting both. If it cuts fuel, you get a lean mixture because there is a lot of fuel hanging around in the inlet tract. If it cuts sparks, you get residue from an unburnt mixture. The worst consequence of hitting the limiter is that you tend to burn the valves at the seats, compromising the valve sealing. The crank is not the issue - it is just seeing a different frequency of vibration compared to normal.

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What is odd is how very different a K on standard plenum box feels from my 1700 XF despite not dramatically different power curves.


The XF feels like a wild, snarling, lumpy, LOUD bag of power that barks out of it's twin 40s as much as the tailpipe, it feels alive and full of primal urge.


The standard 1600K feels so smoooth, quiet and civilised in comparison, intake noise is minimal and despite a probable higher output it doesn't seem quite as soulfull somehow, more like the Tinman in "The wizard of OZ".


I suppose in all practical terms a K must be considered a better engine but... practicality is not the reason we love our sevens.



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I would disagree with:

I suppose in all practical terms a K must be considered a better engine


The good bits about the standard K compared to the XF are: light, light reciprocating mass, 16V head, simple construction, electronically controlled FI and ignition.


The very specific bad bit is the plenum chamber based induction.


The plenum chamber induction works well for emissions, but isn't good for a sporty engine as it kills all possibility of decent snap shut throttle response. The K throttle response isn't at all shabby in production car terms, but twin carbs can do better.


I think some crossflow enthusiasts do get confused when they equate bad manners with character. To my mind any fluffing in the power delivery, particularly midrange and part throttle is a fault to be fixed. Equally, poor throttle response is a fault to be fixed. The answer is of course to use throttle body fuel injection, where you get it all: throttle response; progression; noise; ultimate power. A throttle body equipped k-series is still just as practical, but has the added character, noise (naughty but nice) and throttle response.


Throttle body fuel injection can be fitted to a crossflow, but it will still be a heavy engine with an 8 valve head, with vulnerabilities when it is asked to rev beyond its design range. The cost of moving to fuel injection has to include a complete rejig of the fuelling system including a baffled fuel tank and fuel return piping. You need to be dedicated to take a crossflow Seven and convert it to FI, compared to the easy path of trading up.


So lets ignore carb-fed crossflows as they are so clearly an old hat technology - there is nothing that they do that cannot be done better and with ease with the modern alternatives; Weber DCOEs were old hat even in their heyday. It is worth observing that carb-fed bike engines seem to work quite well. What you have in the case of, say, the Blackbird is an engine developed to a single specification with a sophisticated and calibrated carb setup and with a sophisticated and appropriate ignition setup; you have a 4 valve per cylinder design with minute and exquisite attention paid to the detail required to achieve reliability and power at elevated rpm; you have the gearbox also. Because it is possible to transplant all of this into a car, the "carb-ness" of the installation is not an issue compared to the benefits. In the world of bikes, the top of the range is gradually progressing towards throttle body fuel injection as you might expect - for production bikes everything is obviously very cost sensitive.

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I don't know exactly the rev limiting strategy used by the MEMS. I have a technical manual at home that may give the answer. What is typical is for a preliminary soft cut to be implemented by cutting sparks for individual cylinders. This can work progressively by killing every 9th spark to start with and if the revs still rise, by progression to killing every 7th spark, every 5th spark and then every 3rd spark. This pattern allows each cylinder to recover by firing normally every now and again, for which the cylinder obviously needs normal fuelling.


Because the k-series injection is grouped, it is difficult to reduce the fuelling to a non-fired cylinder without affecting its paired cylinder that is going to fire on the next cycle. Typically, fuel cut is reserved for the hard cut rev limit.


The point of the soft cut is to give an obvious misfire that discourages going further on to the hard cut. The power drop may be enough to prevent the revs from rising any further.


Running on the limiter is a bad idea and should be avoided apart from in race situations where there is a proven time advantage to be had from holding on the limiter or when driving a hire car or courtesy car. You should view a rev-limiter as the least worst option . It is there to prevent the engine revving dangerously highly, but is in itself damaging.

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