1979 top speed

[lm48]

I have a 79 with a rebuild 1800 cylinder head and a knock off weber carb with some custom links between fist and second barrel. After 1 year of hard working I drove the car for about 400 mile with no issue so I decided to check top speed. With stock weber copy at 80 mph to 85 the engine will starve. After the installation of the custom link allowing a early open on second barel there was a impressive gain on acceleration and speed. I was cruzing at 90 mph at 4000 RPM and I decided to keep pulsing the gas, 100 110 and then at 120 I back of even there was some more left. Is possible that the speedometer to be wrong or i was realy going that fast. looking at other cars I was by far the fastes one on I75 Florida going south.I have standard 13" rims and tires. I am back in the garage with a blow up head gasket on cyl 3.

[Danno]

How were you doing 90 at 4k? Having a more powerful engine doesn't change ratios and it seems like I'm at about 65 at 3300 or so in 5th gear. I'll have to dbl check that soon, maybe my memory is off.

[spiderrey]

Your car should top out at 108 or 110.

[divace73]

to get accurate (more so anyway) use a GPS unit, then you'll know for sure

[lm48]

I was thinking that if is a mechanical speedometer, standard rims and tires the speed should be not much different. I will need to barrow a GPS because I alway use the iPhone. But is not much what can be checked know because I need new head gasket

[Zulu]

I was thinking that if is a mechanical speedometer, standard rims and tires the speed should be not much different. I will need to barrow a GPS because I alway use the iPhone. But is not much what can be checked know because I need new head gasket

There are a couple apps for the iPhone that use its GPS to measure speed.

[vandor]

If everything was working normally then an indicated 120 mph is likely close to a true 110-112 mph.
However, as others said, at 4000 rpm you are likely doing 70-75mph, not 90, so your speedo may have more error than it originally had.

[lm48]

Can the speedometer be re-calibrated?

[divace73]

yes they can, I know a few mobs here in Oz can do them and have to assume they can be done in the states as well..

[TX82FIAT]

I would think the speedo is off a little given the RPMs as well. 4000 RPM is about 75 on my car. The speedo does read about 10-12 MPH off depending on speed because of the 15" wheels. With that said, have fun and be safe out there. If you were traveling at 120 in a Spider on a public open road and something in the 33 year old vehicles steering, braking, suspension, hubs, axles, tires did go wrong.... It would not be a good day!

[carl]

Not only can the speedo be off but the tachs are not that accurate either. With a 3.9 axle ratio in my 124 coupe I'm showing about 73mph at 4,000rpm. I know the speed is right, I double checked with my daughters Iphone...no clue if the tach is right.

carl

[RRoller123]

I never been over 60mph, it really smooths out at around 3000 rpms (~50-55mph) and I like it that way!

[lm48]

Mystery solved. The 79 spidometer go to 80 mph and the 80 spidometer go to 140 mph for the same nidle travel, becouse my transmission is 79 then the 80 mph speedo should be the one to be use. I did replace the speedo with the corect one and drove the car for 100 miles today. I checked the speed with GPS and is perfect. So the 120 reading was around 70 to 75. Driving a fiat convertable it feels like fling at 70.

[JEEPER]

Mystery solved. The 79 spidometer go to 80 mph and the 80 spidometer go to 140 mph for the same nidle travel, becouse my transmission is 79 then the 80 mph speedo should be the one to be use. I did replace the speedo with the corect one and drove the car for 100 miles today. I checked the speed with GPS and is perfect. So the 120 reading was around 70 to 75. Driving a fiat convertable it feels like fling at 70.

That is strange. I have a 79 built in Oct 78 and it has a 140 MPH speedo. I bought it new. It now has 20,000 on it.

[srwilson]

My 79 has a 140 speedo too.