K series gearing

[p.mole1]

After another spectacular failure at getting more power out of a K series I now have another problem.I have a six speed gearbox and seems a 3.9 diff. My car is producing it's max power around 6/6500 rpm so that equates to about 105mph in top!.

Were all K series models fitted with this diff. My options are mess around with the cam timing to try and lift the maximum power up the rev range and a another expensive trip to a rolling road. Change the cams to Piper 285's and use my Janspeed solid tappet head. Even I should be able to get 150 bhp at about 7000 rpm with that. Change the diff but that would knock out the speedo calibration. I must admit I'm getting a bit sick of throwing time and money at it and am giving serious consideration of putting back to standard, selling all the tuning bits and buying a Megabusa, sorry, I just can't afford the right sort of 7.

[Jonathan Kay]

Were all K series models fitted with this diff.

No. What ratio would you like?

Change the diff but that would knock out the speedo calibration.

I'd prioritise getting the gearing right. Then sort out the speedometer. What type have you got... mechanical off the gearbox. electronic off the gearbox, electronic off a wheel? And which dash?

Jonathan

[Roadsport06]

6 speed were usually using a 3.62 diff. 3.9 was for a 5 speed.

[p.mole1]

The manual says it's 16.7 mph per 1000rpm so about 18 mph would be ideal? however if I could raise the maximum power up to 7/7500 rpm that would give me a around 120 mph which is high enough. The speedo is cable driven from the gear box. I really don't want to spend any more money on it. Anyone know what diff the K series R 300 had, In theory my car should have had more power than one of these?

The only reason I can come up with is my cam timing,however it is exactly the same on my 1.8 as it was on my 1.4 and that produced peak power at 7500 rpm, I just can't fathom it out. I am sure the R 300 made around 160 @ 7000rpm that would give a top speed of around 115/120 mph which would be ideal.

The car has fantastic low and midrange power in fact it's blistering but it does not feel like it has hotter cams fitted, there is no step in power anywhere higher up in the rev range

[p.mole1]

My car was a 1.4 Supersport

[Jonathan Kay]

The speedo is cable driven from the gear box. I really don't want to spend any more money on it.

Cheapest solutions for accurate display of speed with that are:

• Add marks at known speeds to the instrument using Letraset or similar, or:
• Use a GPS device such as a smart 'phone or dedicated satnav.

Jonathan

[p.mole1]

Thanks Jonathan, 

I'm off to the Alps on monday with my mountain bike. But I'm going to give some serious consideration to selling my Caterham, putting all back to standard as a 1.4  or 1.8 Supersport and cut my losses.

[Jonathan Kay]

I'm off to the Alps on monday with my mountain bike.

But is the gearing right for your top end power output?

:-)

Have fun.

Jonathan

[Roadsport06]

Speedo would be easy to sort. Getting the diff out is straight forward and the likes of SPC will get the diff sorted. I imagine with the 3.9 diff and 6 speed combination you're finding the gears incredibly close and motorway driving not nice with the revs being high.

[revilla]

Speed at maximum power RPM probably doesn't correspond to top speed.

[p.mole1]

Thanks at the minute my car acceralates rapidly to around 105 mph in 6th then it stops. It's under geared for were the power is at the minute. I had a screen on at Cadwell and although it gets to its top much faster it's no faster down the straights than my 1.4 was! that was peaking in 5th. I might see if I can get a diff on the cheap, unfortunately I have do all the work myself, I can't afford to pay other people.I don't find low gearing an issue on motorways, I always wear ear defenders and am used to motorbikes. If only I could find were my missing 15/20 Bhp and  revs revs have disappeared to. The Injectors are fine and have plenty capacity left, fuel pressure is fine, compression  is fine and equal across all four cylinders. I found my water leak, it was the water rail, I'm not using a drop of oil and oil pressure is 40psi / at idle 65 psi at higher revs at 100 degrees. Water temps never got above 80 degrees until leaving the track. Also the engine was very free to rotate once built up so I don't think it's tight running clearances.

[The_ASH]

Just a thought but do you still have a windscreen fitted, I’ve always found with Sevens that the greater the screen drag as the speed rises has pretty much the effect on top end speed you describe, quick to a point and then ‘brick wall’, running with an aeroscreen after being used to the same car with full screen I remember getting to the point of triggering the bottom two or three shift lights in 5th (with a type 9 5 speed, 3.9 diff and maybe 130hp). My memory of what the shift light settings were is blurred but I think the first light would have triggered at 6300ish with the standard mems cut being at 6800 (I had Piper 633’s on a 1600K using the standard Mems 3 ecu, shift lights were Ecliptech from Oz best I’ve found).

[p.mole1]

I may gain a bit extra with the screen off but I was surprised the top speed was no greater than my 1.4! I'm going to Croft in August with my friends cheap as chips Westfield bath tub with a Toyota 1.6 its putting out 175 bhp its going to blow the doors off mine! whats worse it didn't even cost a 1/3rd of my car. I got a feeling there is going to be some p*** taking I hope I don't get lapped.

[p.mole1]

I'm going to try and my car looked at by Gemzoe Motorsport and see if we can get anywhere. If not I give up and will probably sell it. At least my wife would be happy as she hates it!

[revilla]

Just had a random off-the-wall thought. Not trying to be patronising or anything, just throwing in an idea which may be a load of rubbish...

The stock cam timing on my VVC engines was dreadful. The exhaust cam was 10° retarded and the rear inlet cams were a full 17° retarded. Sorting that out with offset dowels certainly gave it an extra kick but it was in no way crippled as it was. Still had in excess of 120mph out of it is an SV on the Autobahn with windscreen, wife and a weeks worth of luggage. So I find it hard to believe that having taken care to time the cams you could be far enough out to cause what you're experiencing.

Been trying to sort out replacement pistons and conrods for my own engine and it occurred to me... Where did your pistons and rods come from? I know you've taken lots of pictures of your build, do you have any of the conrods showing the part numbers? You couldn't possibly have ended up with the shorter, lower compression rods used on the turbo engine and used to detune the 160 to cope with poor fuel quality in Mexico engines? These would drop your compression ratio from 10.5:1 down to 9.2:1 and I've a feeling this would rob you of top end power and move peak torque down the rev range. These were I believe fitted with the 160 pistons in production, so it would be easy to accidentally use these on the basis that the pistons were 160s. I've been offered sone myself while trying to source some standard rods.

At 131.1mm instead of 133.1mm to piston would sit 2mm lower in the bore at TDC than with a standard N/A rod. The big end journal sizes are identical so it would fit and might not look obviously wrong. Do you have any photographs of the assembled bottom end at TDC?

As I say, just throwing a random thought in, feel free to throw it back out again if you want!

[revilla]

Just looked again at your picture on the other thread. They don't look like 160 pistons and your compressions look pretty high.

[SLR No.77]

Mr. Mole, first of all get your car to Dave Gemzoe and start by having him sort out your corner weighting and geometry. Secondly, lose the angst. Thirdly, with the power you have and your close gearing, with some additional driver training (whatever your current level) you’ll have no issues holding your head high at Croft.

Yes your car should have a 3.62 diff with the 6 speed, but it hasn’t. Maybe stop concerning with ultimate top speed and work out where you can go quicker elsewhere, then later maybe consider the 3.62 diff if you still have the car.

NB. No intention to be patronising, just saying it as I see it.

[p.mole1]

Hi Revilla,

Thanks for your help, I'm open to any ideas and no it's certainly not patronising. I could be missing something really simple. I know the pistons and rods are fine as they came from Dave Andrews, they were second hand 160 VVC and came with new piston rings.Dave has always given me his time and has been extremely helpful even when dealing with simpletons!. The car performed really quite well at Cadwell but I could tell the power was tailing off too early, but it was much easier to drive than the 1.4 

I seem to have the handling pretty well sorted, I managed to get rid of the bump steer and set the suspension with a tape measure, have managed to dial out the under steer. I have not touched the camber but I now have no issues with the handling.  The brakes are now awesome combination of Mintex and Ferodo pads.

I have done all the work myself and have turned a very poor handling car with mediocre brakes into something reasonable and have gained a lot of satisfaction doing the work. Plus I can't really afford to pay anyone to do it for me. I hoping Dave at Gemzoe can find the missing power,With any luck it could be camshaft timing incompetence, I would be more than happy if it matches a R300 or comes close.    

[Bricol]

My 1600 K with a whole 142.3bhp would hit the limiter in 6th  . . . windscreen, heated leather seats, stowed full hood, 3.9 CWP, 6spd box - equated to 126mph . . . private land, where conditions allow, etc etc

I've nothing useful to add - but something not quite right - unless you're too hung up on max power/torque revs - mine revved beyond if thrashed hard enough ;-)

 

[Gnockoff]

I think you have answered your own question.  You say it's undergeared for the power so even if you had 300bhp, with that gearing, the car wouldn't go much above what it does. No doubt the acceleration would be blistering.  Change the diff to a 3.62 or lower and the top speed will go up, but acceleration times will drop, your choice.

[p.mole1]

Just came back from Croft and I was only 1 second a lap faster than last year with my 1.4. To add insult to injury my mates bath tub took off down the straights and made my car look like a Micra and his is an early one with Cortina hubs and a live axle, it must weigh a fair bit. It has a 4 AG 1.6 Toyota engine with poorly jetted carbs and the manifold has horrendous steps in it just to rub salt into wounds, it must have been thrown together. Good job mine brakes and corners a bit better or it would have been embarrassing.

 At the end of the straights my car was no faster than last year, At Cadwell it would hit 100 on the straights with the windscreen on, I had no screen on at Croft it just hits a wall at about 100 which coinsides with the maximum power at around 6000 rpm. It has been dynoed twice and is making between 145/150 bhp depending on the dyno,( I have been told that is about the ballpark figure for my spec engine ) both highly respected operators. I would like to keep the gearing as it is but raise the peak power to around 7/7500 rpm.

I have a Janspeed/PTP cylinder head in the garage, gas flowed but with standard valves,solid tappets and steel spring caps, I was thinking about fitting a pair of Piper 285 solid tappet cams to raise the power band and see if I can squeeze a bit more power out of it, what could I realistically expect ? (Not over inflated rolling road figures) I am trying to decide wether to put it back to standard and sell all my parts off or give it one last go

 

[TRP]

What’s your current cylinder head spec (cams, valve sizes, porting?) and exhaust manifold? What does your power plot look like? My old 1600ss pulled to the limiter in 4th (5 speed box) easily! If you use 285 cams with an otherwise standard head the ports won’t flow enough to see the gains they could offer especially higher up the Rev range. Handling wise if you haven’t had the car corner weighted and the camber set correctly there’s probably a lot to be gained there too and probably worth asking Dave to sort if your going to see him!

[p.mole1]

Hi my current cylinder head is bog standard apart from the valve seats in the chamber cleaned up and the valve seats in the ports cleaned up, the jenvey throttle bodies were matched to the ports and I have a Power speed 4-2-1, Emerald Ecu and vernier cam wheels. My power is very linear and it made maximum power at the wheels at 6000 rpm and its gone by 6500 rpm. We spent time with different ram pipes and cam timing but the gains were out weighed by the losses. As a road car it's fantastic but its no good on the track. My 1.4 was a storming engine it had power all the way to the limiter at 7800 just not enough of it it. Made maximum power at 7500 rpm which suited the gearing. I niaively thought that the same cams would produce a similar power curve albeit slightly lower down the rev range not this low! I really don't want to spend any more money on it . I have a pair of solid Piper 744 cams they 280 deg duration 70 degrees overlap but quite low lift at 9.1mm I was thinking of trying these but they may be a bit too wild? although my engine should be safe to about 7800 rpm I'm not after huge power hike I just need to extend my power band up to 7500 rpm

No problems with the handling I've corrected the bump steer , tracking, have not corner weighted the car but set it with a tape measure which is 90% good enough for me.