Bit of a technical question...

[andygo]

We race a formula ford 1600 and despite fitting several different engines over the course of the past couple of years still have a bit of a issue with acceleration.

Basically second and third gear acceleration is slightly lacking. We have tried different gear ratios etc, but I wonder if the diff ratio could be a factor. Although the overall gear ratio is the same, we are using a diff ratio of 13/37 in the Hewland box, whilst most ff1600's use a 10/31 or 10/31. Can the diff ratio affect the way the car acclerates, even though, as I say, the overall ratio is equalised by virtue of different gear ratios?

I ask this, as a few years ago, when running my boys in karting, there were a range of sprockets available to suit different toothed engine sprockets.

[n3il123]

might be worth asking over at ten-tenths as there seem to be quite a few UK racers over there?

[anonymous-user]

It makes no difference, as the torque will equalise out at the wheels.

Are you sure you are gearing the car properly? Making use of the largest area under the curve, and not using peak power as your shift point.

[mattikake]

Are the electrics still the same? Could easily be a voltage issue. You'd be surprised how much a dodgy feed from any input sensor or output sensor to the ECU can produce seemingly random results in something that should be a mechanical issue...

[andygo]

mattikake said:

Are the electrics still the same? Could easily be a voltage issue. You'd be surprised how much a dodgy feed from any input sensor or output sensor to the ECU can produce seemingly random results in something that should be a mechanical issue...

FF1600 uses the Kent engine as used in such cars as Capri's, Escort mk1 Mexicos etc. We run it on points!

[Scuffers]

andygo said:

mattikake said:

Are the electrics still the same? Could easily be a voltage issue. You'd be surprised how much a dodgy feed from any input sensor or output sensor to the ECU can produce seemingly random results in something that should be a mechanical issue...

FF1600 uses the Kent engine as used in such cars as Capri's, Escort mk1 Mexicos etc. We run it on points!

As said, unless your diff gears are significantly worn/poor (and thus creating looses), so long as the overall ratio's are the same should make no odds.

only think I would look at is putting the car on a dyno and doing several power runs in different gears, this may show up any gearbox related issues if the plot's are not all the same, also worth checking that the engines timing is not doing odd stuff, had issues with this on Twinks where the vibrations at certain RPM's would wind the distributors advance back with a corresponding power loss.

[andygo]

We have had the same issue ever since we bought the car brand new 3 years ago, fitted with a brand new Hewland box. I just have a feeling that it must make a difference somewhere as why would different diff ratios be available?

The 2 engines we used at the weekend have pretty much identical power and torque figures, one engine actually being fresh off the dyno..

I'm going to call Hewland later and see what there answer is - they must know!

[mattikake]

lol sorry. I didn't realise the engine was quite that old!

[A911DOM]

I dont know if you've had any luck with this yet, but my mechanic over here in Belgium is a Formula Ford dabbler himself and a race engineer of some years.

I reckon he may be able to throw a few more suggestions for you to try if you're stuck.

And yes, you can speak to him in English despite him being a German, in a Flemish area mainly dealing with French speaking customers

If you want the number give me a shout.

Edited by A911DOM on Tuesday 9th November 12:35

[stevesingo]

Something that may make a small difference is that in using the 13/37 as opposed to 10/31, the diameter of the crown wheel and to a lesser extent the pinion is larger, This both heavier is terms of total mass, but it will also have more inertia overall as the extra mass is further from the centre.

Just a thought.

Steve

[number 46]

I don't think that the diff. ratio will make that much of a difference, you just need to use the correct gear ratios to keep the engine in the power band and not have too much of a rev drop between gears. A Kent 1600 power band would be between 4000 and 6500 revs I would think, your dyno sheets should tell that. You need to change you ratio list to match the diff ratio. I have a FF2000 which has a 9/31 instead of the usaul 10/31 diff and just use the appropriate ratio list.

[andygo]

I am pretty sure the ratios themselves are ok, they have been checked and double checked..

There is a clip here from last weekends Walter Hayes that shows what happens - despite being nearly on the guy in fronts gearbox, he cannot tow up to him. The engine has really good dyno figures so pretty sure its not the engine somehow. rolling resistance is fine - all wheels spin freely and easily...



http://www.youtube.com/watch?v=SKh64m1Sqdc&fea...

Ended in tears here as he was punted off into the armco.

[350Matt]

stevesingo said:

Something that may make a small difference is that in using the 13/37 as opposed to 10/31, the diameter of the crown wheel and to a lesser extent the pinion is larger, This both heavier is terms of total mass, but it will also have more inertia overall as the extra mass is further from the centre.

Just a thought.

Steve

I 'd say your're right, transient acceleration is very difficult to measure on a normal chassis dyno as you need to measure power on the ramp up not at steady state and it takes more power to accelerate a larger diameter / mass due to the larger inertia also while its 'only' a diff I suspect its still doing a few thousand Rpm so a few hundred grammes can easily cost a few HP in power required to accelerate it.

[andygo]

I've just spoken to Hewland, and our diff, although it is the largets is actually 50 grammes lighter than the other 2 diffs available. There would be no appreciable difference in power losses throughout the 3 diffs as they all run at about 97% efficiency.

So back to the drawing board. Thanks for all you interest and input guys!

[Scuffers]

350Matt said:

stevesingo said:

Something that may make a small difference is that in using the 13/37 as opposed to 10/31, the diameter of the crown wheel and to a lesser extent the pinion is larger, This both heavier is terms of total mass, but it will also have more inertia overall as the extra mass is further from the centre.

Just a thought.

Steve

I 'd say your're right, transient acceleration is very difficult to measure on a normal chassis dyno as you need to measure power on the ramp up not at steady state and it takes more power to accelerate a larger diameter / mass due to the larger inertia also while its 'only' a diff I suspect its still doing a few thousand Rpm so a few hundred grammes can easily cost a few HP in power required to accelerate it.

depends on the dyno....

I use TDi's Rotatest, it's a hub-dyno, so no rollers, tieing down, etc. with this you can do steady state, rising ramp rate, falling ramp rate, programmed test 'route' etc.

I still think the OP's issue is probably engine related, and at a guess, vibration issues.

[number 46]

Not easy to till from the video, but the engine sounds ok. It looks like you may have a data logging dash, if so, take a look at that to check the engine revs and especially, the rev drop between 2nd, 3rd and 4th, it may be that the ratios are too far apart and the engine revs are dropping below the power band on each change. get hold of a ratio sheet from one of the big teams or hewland for that year/type of car to use as a guide. One thing to remember about FF is that they do not have much power, so you have to try to scrub of as little speed as possible and to get on the power as soon as possible, your exit speed is everything. Looking at the video it looks like you are not blipping the throttle on the downchange and the car looks out of shape in the braking areas, so you are not back on the power smoothly and quickly enough coming out of the corners, with FF cars with so little power, the slightest delay in getting on the power again and the loss of momentum compared to the guy in front can make a huge difference. It may also be worth using luminition instead of points if the rules allow as that may also cause a lack of power under load when racing, your engine builder should be able to advise on that. If that fails bore the engine out to 3 litres and starve the driver to safe weight !!!

[andygo]

We have spent ages loking at ratios and are pretty happy with them. Our engine builder tells us there is no appreciable difference between points and solid state until 7500rpm.If he thought there was an advantage with electronic ignition, he would obviously say so. We keep with points as we generally dont have a problem with them, and they are easy to swap or spot a potential issue with. Electronics either work or not and can fail with no warning.

I'm only talking about finding maybe a couple of tenths per lap - as it is the car has held the lap record at Oulton for over 3 years, so its not that bad and looking at the results of the weekend, was probably good for a top 3rd or fourth out of some 115 entries..

Think the car is a little out of shaep under braking as he brakes pretty late, and from watching him is generally on the gas very early. He has driven in SCCA, F3, Zetecs with some success. He did the first ever Duratec race, but used a zetec car and finished 6th overall, despite giving away a chunk of power and weight....

Did a round of club F3 and put it on the front row 1st time in the car - he's pretty handy!

Edited by andygo on Tuesday 9th November 16:16

Edited by andygo on Tuesday 9th November 16:18

[number 46]

Seems the driver has quitie alot of experience then !! Maybe take the car to a rolling road to check the engine performance under load, it sounds good on the video though?? If it is down on power when racing that may explain the lack of performance. You can only change/check all the usuals things like plugs. leads, distributor cap, coil or the carb ??!! It is amazing how any one of those things being old/tired can cause an engine performance drop, but only out on track during a race.

[andygo]

We have changed EVERYTHING! Engine (4 versions from Neil Bold, probably top builder of Kents in the UK) all ancilliries (we have 2 identical angines, complete), ratios, even run with parallel tracking to minimise tyre scrub. Use Lucas racing ATF in the gearbox. Drained it after 3 races and as usual looks like new, the magnetic drain plug has no bits of dogring, swarf etc attached. In fact we are on the same 'as new' dog rings after 3 seasons which is pretty good afaik..

Car has superb traction off the line, and in the wet for instance can qually over a second ahead of the rest.

Driver weighs 70kg, car is 2kg over min weight limit. Doing our head in!

Edited by andygo on Tuesday 9th November 17:09

[Scuffers]

do you have any logging that covers engine parameters?

ie. ignition timing/IAT's/oil pressure/temp/etc. ?