Engine fragility

[jackb_ms]

In my last posting, Low compression engine & Supercharger, Hoopy argued the fragility of the K, when asking for big power, is the result of high revs, above the “standards red line” (9000 rpm for a K is well pass the red line).

 

My aim is to have more power & more torque without having a high revving engine. This is why the supercharger is the road I’m following. I’m aiming for 220bhp with strict minimum of mods to the engine.

 

My point is, if I want 220bhp, at normal revs (4000rpm), will my engine (VVC) suffer the same way as the high revving high power output engine.

 

Which are the real factors leading to an engine failure? Rev or Power?

 

Waiting with impatience your thought.

 

Jack

 

[F355GTS]

Jack

 

if it's any help I know of an Elise with a VVC that's been modified by turbo technics with a Supercharger and is running approx 220BHP, might be worth talking to them

 

Mark

[Tony C]

In a very basic way - if more power is required more force is required on the top of the pistons, or the same force more often. This will be obtained either by increasing pressure in the combustion chambers or revs. Increasing the pressure on the pistons will increase the pressure on every other surface in the combustion chambers too, which will be trying to expand the whole shooting match. The K Series engine is a ladder design, which will be stretched to breaking point eventually - BOOM

 

Unfortunately it's impossible to get a quart out of a pint pot 😬

 

BRG Brooklands Aero Screen SV 😬 It is only with the heart that one can see rightly; what is essential is invisible to the eye. (Antoine de Saint-Exupery)

[V7 SLR]

Surely you can't add a S/C to any engine without lowering the CR. 🤔

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[jackb_ms]

Well this is the question i'm asking.

 

Jack

[jackb_ms]

Mark

 

Could i have a contact e-mail of this gentleman you speek about?

I will love to see an TT installation. I might be able to copy it 😬

 

Jack

[jackb_ms]

Mark

 

Could i have a contact e-mail of this gentleman you speek about?

I will love to see an TT installation. I might be able to copy it 😬

 

Jack

[jackb_ms]

Mark

 

Could i have a contact e-mail of this gentleman you speek about?

I will love to see an TT installation. I might be able to copy it 😬

 

Jack

[scooby dooby doo]

eventually you'll need a stronger block, ie and iron. eventually even cossie blocks can't cope and you need the uprated cossie RS500 block. I think that's good for 500+ though....

 

HOOPY

R706KGU Hoopylight R

[oilyhands]

To supercharge the K to any useful level you will need to significantly drop the CR, there is little scope to do this with the stock rods and pistons and the stock pistons will collapse under the increased BMEP. This means using a shorter and if possible steel rod together with a forged or hypereutectic piston, this will necessarily increase the rod angle and the skirt of the piston will be perilously close to exiting the bottom of the bore. TT and QED can supply suitable rods and pistons but I know TT have put a lot of effort into getting the engines to stay together, I know of two other ametuer built engines, one VVC one VHPD that have been supercharged, not entirely without incident.

 

Oily

[tcrawford]

Jack,

 

The max compresion ratio you can run is 8-1, if you exceed this

detonation becomes a very serious problem.

The K- series might even need less CR.

If you wish to run higher CR then you are in the world of intercoolers

and or water injection.

Personally if a customer aproached me with this request i would do my

best to dissuade him from this idea on these particular engines.

Hope this helps,

tcrawford.

[F355GTS]

Jack

 

YHM

 

Mark

[Paul D Jones]

My aim is to have more power & more torque without having a high revving engine. This is why the supercharger is the road I’m following. I’m aiming for 220bhp with strict minimum of mods to the engine.

 

Fit a 2ltr Duratec minimal mods ie mild cams TB's etc and you should have 220 SBD Dynoed one in this state of tune at 219bhp or 203bhp with standard cams.

 

Paul.

 

 

 

Paul.

See My Car Here

[Peter Carmichael]

I know, I know. I go on about Ks, but...

 

...some setting the record straight is in order.

 

... I will be a bit literal in reading jackb_ms's original posting, but I don't mean anything by it.

 

Initial question talked about revs above standard use. All engines used in such manner will start eating into their reserves of reliability. The K was an exponent of the virtues of light reciprocating componentry such that it is excellent at revving and is a generational leap compared to what was around at the time of its design. It is built light to rev to a certain degree. Take it further and the problems start. Revs give rise to vibration. Modal resonances with the vibrations are difficult to model, so to an extent you have to put up with what you get. The K, as it was, didn't have a lot of rigidity in the block (no webs) and didn't have a lot of dowelling holidng the various layers together in alignment. The new Ks have had most of that fixed.

 

So what do revs mean to a K? A 1.6 bog standard is comfortable to 8000rpm. No problem. Caterham sell the Supersports with the rev limit set at 7600rpm. Yes, the head gaskets cause problems but in my own experience any compromise of the cooling system (leak, airlock, dodgy fan switch) brings on the troubles. The installation with the wet sump is dodgy at maintaining its oil temperature. Take those problems away and reliability isn't a problem. Add in the mods to the latest Ks with a modified silicone bead pattern on the head gasket and the improved dowelling and they are reliable... at up to 8000rpm and up to 180bhp.

 

Above ~180bhp the pistons are suspect. They can't handle the heat, pressure and reciprocating loads and the ring lands fail. You need forged pistons... but that is about it. There are loads of R400 and Superlight Rs out there, both racers and road/trackday cars that survive very well on a regular diet of 8000rpm, no problem. Note that most of those cars are dry sumped.

 

Now look at my notorious ex-engine that ran for 12,000 miles until some plonker mis-fitted an alternator. It made 253 bhp @8900. It was revved on several occasions to 10,500 rpm. It kept running. It made 220bhp at... wait for it ... 7000rpm.

 

Which brings us back to jackb_ms's:

I’m aiming for 220bhp with strict minimum of mods to the engine.

Yup. Got me there.

 

And also:

if I want 220bhp, at normal revs (4000rpm), will my engine (VVC) suffer the same way as the high revving high power output engine.

Interesting. Taking you literally regarding the 4000rpm (which i appreciate is a "reductio ad absurdam" argument) that would require 289lbft of torque. From a 1.8 litre engine that would require 160lbft/litre. Naturally aspirated engines can at best expect 96lbft/litre out of a four valve design. You are asking for 1.67 times that figure, equating to more than 1.67 times the cylinder filling and requiring very good intercooling. You will have to drop the compression a lot, which drops the overall efficiency further. Maybe you are looking at 1.3 bar of boost (very roughly speaking). Which brings us back to the intercooling problem.

 

So far we have new pistons, new conrods, all new plenum arrangements to take 2 bar positive pressure and a plumbing and intercooling problem.

 

Lets ignore all that practicality stuff. Would it be worse for reliability? Erm. Probably. The mode of failure would be different, but it is in the nature of engineering that if you optimise for a set of operating circumstances, radically changing those circumstances probably breaks more than one thing. The BMEP of 220bhp at 4000 instead of 7000rpm is seen in the torque figure. This hurts the ring lands by a factor of 1.7 compared to a natasp K. While we are shortening the rods we can take a bit more out to accomodate a thicker crown to the piston and a deeper land.

 

Your modes of vibration are different because of the lower revs, but the bangs are bigger. Instead of the principal reciprocating forces being resolved through the crankshaft (second order vibrations carried through to the block) you now have a larger pressure from each combustion event. With two combustion events per revolution, that could potentially excite a resonance at double the reciprocating frequency. Admittedly a natasp engine gets that to a degree anyway, but the 1.7 times multiplier might do the damage. The crankshaft seems to have a resonance at or around the 4000rpm mark. You just need to fit a race clutch to hear the grief it sends down the drivetrain. So we probably need a steel crank (the cast crank wouldn't take it for very long) and we might want a heavy flywheel to smooth out the bumps and a hefty harmonic damper to prevent the pulley end of the crank from whipping about.

 

The development work to accommodate the VVC gubbins while all of this is going on is probably not worth the effort so you would junk it in favour of fixed cam timing. It would still need porting.

 

Oh, and the liners would also have to cope with the big pressures. And while you are at it, some oil spray under the pistons might be quite an idea.

 

Chances are that in development, or given the slightest dodgy drop of fuel that this thing is going to detonate, so all our safety factors have to go up as well, which means more metal in spaces that just don't have room for it... the pistons are already eating up space in the block that doesn't exist.

 

... Check out the Brodie Brittain K300T conversion. I know its turbo rather than supercharged, but it gets close with 285lbft @4250 rpm. That is 230bhp at 4250rpm.

 

Turbo Technics supercharged conversions aren't marketed with an option close to this. The nearest is the TT260 which runs 0.7 bar, but is only producing 125bhp at 4000 rpm. I have the dyno plots from the TT Elise/Exige that they managed to get 270bhp from... up until it blew up. You have to wait until 5700rpm to get 220 bhp. Interestingly, if you are prepared to rev the TT260 to just 5700rpm, banking your 220bhp, you would have got almost exactly the same performance from my natasp engine revving to 6700 rpm and holding a lower gear. Used in that mode both engines would be comprehensively trounced by a VHPD being used to 8000rpm.

 

Right. Near as I can make them, those are the facts. What conclusions?? 🤔

 

 

[Peter Carmichael]

Conclusions:

1. The forced induction conversions add complexity and as one off installations increase the chance of inadvertant cock up

2. The forced induction conversions require radical reworking of the engine internals.

3. The relatively simpler and better proven option of a VHPD engine (or equivalent DVA conversion) used to its full potential will be enough to persuade you into the upper rev band of the forced induction conversions to keep up.

4. Reliability comes as much from attention to detail in installation as from the raw engine spec.

5. Or as others have pointed out, an 1800 k-series is not the right engine to be attempting to get 220bhp from without revving it.

 

Hope this helps. It is meant to be helpful.

 

Edited by - Peter Carmichael on 11 Sep 2003 23:31:10

[jackb_ms]

Peter,

 

I just print your posting and have a very careful read about it later on.

 

The "220 bhp @ 4000 rpm" was just a figure explaining what i would like from my engine is low down power. I'm not interested in an engine which produces 250bhp @ 8000rpm. It will be useless to me as the only time I get to use those rpm is on circuit. And I’m not an aficionado of track days.

 

I understand as well that a forced air system is for likely to be less reliable than a normally aspirated one, remember the Maserati Bi-turbo of the 80’s.

 

From what I understand if I wish to pursue my supercharged investigation I need to turn to the duratec

 

Jack

[AMMO]

Get a NA 220bhp Duratec. The added bonus is that you will have none of the potential problems associated by pushing what was originally a 1400 cc engine to well beyond what it was designed to do.

 

I heard a rumour yesterday that the Duratec was originally designed by Cosworth as a four cylinder turbo F1 engine (a la Megatron). Don't know if this is true or not. Looking at the internals, they do look like race engine parts from a few years ago.

 

I am truly in awe of what Oily and Peter have managed to do with the K-Series. However it is an engine I cannot get excited about. If you were starting from scratch with a forced induction project even the humble Zetec would be a better starting point. In fact, I think Power Engineering in Uxbridge were making either supercharged or turboed 1800 Zetecs. Can't remember now.

 

Only my opinion. I know many will not agree.

 

AMMO

[New Barbie]

Jack

 

If you are not into track days, why do you need so much power ?

 

220bhp in a Caterham is a lot - too much for even fast road blatting for the most part. If you decide on a forced induction solution, either K or Duratec, you're effectively out on your own and probably won't be able to use the power anyway.

 

I'd go a high spec K route, have reliability, plenty of power and use the surplus money on a load of track days where you can really enjoy the car. My car started as a SuperSport 1.6K, now converted to roller TBs and more mods to come. Each new iteration provides a bit more power and noise, much more fun than trying to bolt in an odd Duratec.

 

 

shrewdcookie - my site

[I.Mupferit]

A predictable response from me I suppose but I can't help agreeing with Ammo that, if it were me, it would have to be a Duratec and I don't agree that upgrading a K is "more fun than trying to bolt in an odd Duratec".

 

I guess it all depends where you derive your fun from when owning a 7; is it all driving, is it messing about with upgrades etc or a combination of both?

 

I fall, very much, into the latter category and had huge enjoyment in the past year from a total re-build followed, this Summer, by a few thousand miles blatting.

 

For me, the joy of owning this car is the mind boggling number of upgrades, improvements and modifications it is possible to do, and keep on doing.

 

I love the idea of dropping in an engine with the potential of the Duratec, just because I can, but do also agree that when you are getting up into the realms of 220 Bhp + it is, perhaps, getting beyond the skills of your average person to use properly on the road.

 

So, one day when I run out of upgrades on the Zetec........ Duratec here I come 😬 😬 😬

 

Brent

 

Zetec

 

[RiF]

After 3 years of looking and planning for me Duratec has to be the solution.

Engine 226bhp with just mild cam changes and pocketed pistons, an easily obtainable engine and parts, reliability (well that is my hope), 7200 rpm to get the max bhp is still classed as very low reving and incredible torque.

I have not tried pushing the car at all, 4500rpm to run in is still very fast with that amount of torque.

 

Make your life simple, go for technology that is there and get the car built so you can DRIVE it 😬

 

Richard in France

At last my bright yellow 226bhp Duratec 7 is on the road, with internal kevlar/carbon panels and pushrod suspension 😬 😬 😬.for pictures

[Peter Carmichael]

A further point is that big torque at low revs is *difficult to drive*...

 

Doesn't get mentioned a lot, that one. Does it?

 

This is another reductio ad absurdam argument.

 

Let's consider an appropriate amount of power for any given situation. 60mph 4th gear (six speed box?), 4000rpm. That requires about 16bhp to keep the car ploughing through the air. With 285lbft on tap, you have a toe twitch to access 220bhp. A surplus of 200 bhp over the steady state requirement. 350bhp/tonne. If you are mid-corner on a slippery surface, what happens when you hit a bump? Does your foot bounce on the pedal? Do you get double the required horsepower just from a tenth of the remaining pedal movement being used.

 

Maybe you avoid this situation by changing up a gear or two. You're in sixth at 3000rpm. With a nasty wheezy supercharged 4 banger, off cam. The engine idles at 1000rpm. You are changing up at 3000rpm just to avoid excessive power.

 

As I stated, it is a reductio ad absurdam argument. By exaggerating the trait I am hoping to inform the debate.

 

With a high revver, the range from idle to max revs is much higher. You have stated this as a disadvantage, whereas I claim it as an advantage. With a high revving natasp, you restrict the power by selecting the higher gear. You select a gear appropriate for circumstances. Pootling in 6th; only 60 horsepower available. Drop it down to 4th 113 horsepower available. 3rd for 135 horsepower. (as much as a standard Superlight wrung out to the red line... i.e. this pretty damn rapid), 2nd for 214 horsepower (which is loopy and you are still only at 6700rpm and won't have to change gear until 83mph). If you stuck with 3rd, the power builds as the revs climb and you are very quickly at 75 mph and 214 bhp again and don't have to change gear until 105mph).

 

(All figures taken approximately from my 250bhp engine plots).

 

The point is that demanding power becomes an act of will rather than a whim. With great power comes great responsibility etc.

[Bare]

Wow... you've really got some engine there Mate!

Absolutely amazing given that Factory prepared FULL race Toyota 20V's manage 265hp (arguably;-)for Formula Atlantic use.. but these things cost well over $50,000 EACH and require 'at least ' one 'Refresh' per season.. as expected from an engine developed for max useable racetrack power where cost is is simply not a consideration .

You are obviously Very skilled to squeeze that amount of serious power from an engine design that is 'not one of the Better designs.. Even the Maxda penned Duratec is Leagues better .. prolly even Renaults.

[Peter Carmichael]

DVA did the squeezing. I just specced everything strong enough to hold it together... and then I blew it up because of a thrown alternator belt. The engine cost was under £8k, including £2k of strengthening work that Powertrain don't believe is necessary and that Scholar probably do better for £200. The installation cost with custom flywheels, R500 dry sump system, custom clutch release slave cylinder, exhaust and gearbox rebuilds added a load of money but the total was still under £14K, installed, set up and running. It ran a clear torque advantage across the rev range compared to Jason Krebs' R500 (that measured 243 bhp) measured on the same (Emerald) roling road. The rebuild cost I am facing at the moment is ~£2K.

 

My engine was not subjected to race use. It did a few sprints and some trackdays, and it won me the club sprint championship last year. The head was developed to the same spec as Mike Bees 240+bhp 1688cc K-series. This is why DVA (oilyhands) has such a rave following over here.

 

Interesting you choose the Toyota 20V for comparison. There are a stack of opinions that reckon that a balls out race head is better off with four valves per cylinder than five. Just look at all F1 designs... The regs allow five valves (as a maximum), but all that I know of use only 4 valves. The Toyota is a 1600cc capacity for Formula Atlantic with 81mm bore and 77mm stroke. This is minimally different to the K series 80mm bore. The k-series didn't necessarily have performance in mind when the head was developed, but there was enough meat in it to get the ports flowing up to about 138cfm at 10in. The port angle is quite shallow, even for the VVC/VHPD heads.

 

With the longer stroke of the 1798cc K, the power comes in lower down the rev range, saving problems from occurring in the valvetrain. My guess would be that the Formula Atlantic engine makes its 265bhp at ~10,200rpm using the usual fag packet mathematics. It will always cost a lot to extract the last little bit from any design, so $50,000 dollars for a works engine sounds about right.

[jackb_ms]

Richard

 

I would be very interested in the tech spec of your engine and the cost involved in it as well.

I'll be in France end of October doing a round trip from Calais via Paris, Limoge, Anger, and Chatauroux (maybe not in this order).

Would it be possible to have a view at your Seven "En chair et en os"? And maybe a little spin?

 

Jack

[Bare]

Interesting.. thank you for the verbal trour.

That is a fair cost in your motor.. with apparent reason, of course.

Have examined the 20v toyota (that's why I used it as a reference point).. the OEM intake ports look large enought o fit a Tennis Ball.

Just seemed strange to be able extract such power from such a Prosaic engine.

To paraphrase Ettore Bugatti's famous Uttering : " a triumph of Craftsmanship over Design"

My neighbor has a lovely Honda S2000 roadster.. whixch as you know produces generous power (240hp at about 8900 I believe.. I am cautious about over-reving HIS toy;-) coupled to an absolutely exquisite shifter.

I repeatedly fantasize as to the logistics of shoehorning that engine/trans unit into the 7.. seems like it's a V tall engine tho.

But the 5 year 'no questions asked' Factory Warantee.. gives some indication of the 'shopping car' reliability built in. On the other hand the s2000 CAR is awfully nice .. could get really attached to the Mod cons (silence, temp control even AC fer Gawds sake)) and the performance/feel is certainly 7 like, to say the least.

Lotsa Toys.. never enough time or Money :-)