Technical What'll it do mister?

[smart51]

What would you expect the top speed of a 500R with a 594cc engine and 28IMB carburettor to be? The D was said to do 59 MPH, the F/L would do 60. The R with the 24IMB was quoted at 62 MPH. What do the extra 5 BHP give me?

For reference, I set the timing on the car on Saturday and found that it would only do 62 MPH on the dual carriageway. Today, I advanced the timing 2° and the top speed on the same stretch of road is now 65, both using the GPS on my phone. I think it should be able to give a little more. What does yours do?

 

[JumpJet]

I've gotten mine up to about 70 before I chicken out, but it gets a little squirrely above 60; a combination of my sloppy steering box and the tiny non-radial tires). I don't really love cruising at those speeds with it though. For reference, I have a 594cc motor with a few little mods. I'm guesstimating it makes 25-30hp.

 

[lazylobster]

I have a R with 594 and 28 carb. She'll do 70 on the motorway no prob. But I keep her in the cruise at 100kmh (62) And use the extra 8mph for over taking when required!

 

[dangfiat]

My 500F with a somewhat tired stock 650 will do 65mph (albeit with 2 reasonably large dudes onboard). It's lowered & has a steering rack from the 126P installed, so handling at that speed was fairly confident

 

[Bigvtwin996]

I got my N up to just over 30 once that was exciting....
the books say it will do about 50 but I assume down hill with the wind behind

 

[smart51]

I got my N up to just over 30 once that was exciting....
the books say it will do about 50 but I assume down hill with the wind behind

I saw an old booklet by The Times which put the 0-60 time of the F as 299.5s - 5 minutes. It also said 0 - 50 was 26s. By subtraction, 50 - 60 took 4 1/2 minutes or about 4 miles of straight and level road. Your N may well do 50, you just need a lot of patience to get there.

 

[smart51]

As the joke goes: in 1965, Fiat gave the 500 another half a horsepower, allowing it to reach 60 MPH. The 0-60 time didn't come until 1966, though, as they had to do it twice and average the times.

 

[Bigvtwin996]

well... I actually think the 0 -60 - 0 times are much more exciting...
if it takes 20 seconds to get to 60 but 45 to reach 0 again....
since following a modern car it would be very interesting if they had to do an emergency stop.

 

[smart51]

I took it out and did 3 runs yesterday, nudging the timing a couple of degrees for each run. It made no difference. On the same road at the same point, it had reached it's top speed of 62 MPH according to my phone GPS. I reckon it must be a bit down on power. If the timing is making no difference, it must be air flow or fuel. The air filter is new (as is the carb base for what it's worth). The carb is clean and seems to be in good repair. I did reset the float height from about 4mm to 8mm (which is correct for the 28 IMB). Could it be running lean at WOT, which is why a previous owner tweaked the float up a bit?

 

[Goldnrust]

I would suggest putting your timing back down to whatever the lowest value that produced the best top speed, or even a couple of degrees back from there.

Running excessive timing will only put extra stress on the engine components and increase the chance of detonation/knock which can cause engine damage.

The timing curve on mechanical distributer is a compromise, often a little more advance right at the top of the rev range will allow for a little extra power, but doing that would mean that the mid range, where the engine makes peak torque would then be over advanced. So you might get a higher top speed, but actually loose a little mid range punch.

You could check the air fuel mixture at full throttle by doing a plug reading. You’ll need to run fresh new spark plugs and to run the car flat out for while, then cut the engine (don’t let it idle or drive gently. It must go from flat out to off within a few seconds) and once it’s cooled remove the spark plugs and inspect the colour. From there you can get a guide as to what the fuelling is like.

If you feel the car is a bit down on power though, and most noticeable flat out at the top of the rev range where it’s trying to draw the most air, then it’s possibly also worth checking that the air filter is nice and clean, and that the passages inside the fan housing that feed it are clear of oily gunk might be a good move. Likewise checking that the exhaust is not at all blocked and is flowing freely might help.

You could also do a compression test to help gauge the healthiness of your engine. There’s a myriad of ways to make these little cars faster, but no point looking at that till you know you’re starting point is sound.

 

[smart51]

This is fun. I started to remove the tinwork that holds the air filter to check for blockages and was looking at the throttle linkage, which made me wonder. Is the throttle opening fully? Putting a weight on the accelerator pedal showed that it wasn't. Taking up 1mm of slack in the throttle cable and strategically cutting out the carpet round the pedal has allowed it to open further, but not fully. The carpet behind the pedal stop is worth 2 MPH. Retarding the timing by the 2° I'd advanced it gave me another 1, taking me to the heady heights of 65 MPH.

With the pedal now literally to the metal, The throttle still has a couple of millimetres to go before hitting the end stop. I'd have to lift the carpet to adjust the cable on the other end of the throttle pedal, so that's something for another day. It suggests my estimate of 67 or 68 MPH top speed is not far off, and that my engine is running about right.

 

[Goldnrust]

Ah yes, not getting full throttle really wouldn't help!

Presuming you've got no more slack in the cable, I wonder if you've got a mismatch of throttle linkages (if I remember rightly your car has a swapped engine?). Even with a couple of mm of slack in the cable, my throttle is open to the stop a way before the pedal hits the floor?

 

[smart51]

Ah yes, not getting full throttle really wouldn't help!

Presuming you've got no more slack in the cable, I wonder if you've got a mismatch of throttle linkages (if I remember rightly your car has a swapped engine?). Even with a couple of mm of slack in the cable, my throttle is open to the stop a way before the pedal hits the floor?

That's interesting. The 500R came with the 594cc engine from the factory. AFAIK mine has the original engine. I wonder if either the pedal or some part of the rear linkage has been swapped at some point. There isn't a lot of pedal travel; though it does come to a positive stop when your foot is off it. Is there some kind of adjustment on the pedal (or stop) so that it can come up a bit further to give it more travel?

 

[Goldnrust]

If you lift the pedal by hand will it come up any further?

There is a stop built into the pedal yes, so it can only come so far up. I believe the pedal linkage pushes against a stop on the bracket on LHD cars. On RHD cars theres an arm coming off the pedal linkage that pushes against the floor.

There's no adjustment beyond the cable clamp on the engine.

Could be worth digging around by the pedals, compare yours to images online. Could be as simple as the carpet stuck between the arm and its stop limiting the upwards travel? The pedal itself could be bent?

 

[vitorio]

Interesting stuff, i need to try mine with GPS once i get new brake shoes fitted. I've had it slightly over 50 on the speedo, but at that point i was passing a lorry (which never really keep to their 50 limit over here), so either my speedo is way off, or this was a fluke.

Either way, i'd assume with the 650 in there i should be able to hit 65-70, but im still going through all the bits and bobs and finding small things to be fixed.

 

[smart51]

Interesting stuff, i need to try mine with GPS once i get new brake shoes fitted. I've had it slightly over 50 on the speedo, but at that point i was passing a lorry (which never really keep to their 50 limit over here), so either my speedo is way off, or this was a fluke.

Either way, i'd assume with the 650 in there i should be able to hit 65-70, but im still going through all the bits and bobs and finding small things to be fixed.

My speedo reads about 10% over, so while it says km/h not MPH, in truth it is neither. When it says 50 km/h, the GPS says 28 MPH; the right hand edge of the red second gear circle is 30 MPH. 70 km/h on the dial is 39 MPH and 90 km/h is 50. In an odd way, it is more usefully a MPH speedo than km/h.

 

[vitorio]

My speedo reads about 10% over, so while it says km/h not MPH, in truth it is neither. When it says 50 km/h, the GPS says 28 MPH; the right hand edge of the red first gear circle is 30 MPH. 70 km/h on the dial is 39 MPH and 90 km/h is 50. In an odd way, it is more usefully a MPH speedo than km/h.

Yeah im in KMH country, all my MPH numbers on here are crude in-my-head conversions. Ill also add that i have no idea about whether the bits on my car wind up giving a proper ratio, tyres look stock, its got a 650 and a syncro engine, and i think a stock 500L square speedo (which to me seems like am imprecise device to begin with). I should get a tacho in today which combined with a few GPS measurements might help me guage my speed more accurately on the road