Top gear mph/1000rpm on a 403 etc.

David.H · #1 (**permalink**) 23-06-15, 03:45 PM

What mph/1000 would I expect on a non o/d 403 (1953). I'm investigating one (LOY555. Anyone know it? It has not much history, the seller has bought a 400 apparently). I'm looking for a car to use & I take my present cars overseas quite often & a good cruising speed is essential. Also what is the 100A engine like on modern fuels...does it suffer from overheating/ vaporisation?
DGH

dave dale · #2 (**permalink**) 23-06-15, 05:19 PM

Hi David. I have had my 403 since 1999 and I had an overdrive fitted in 2002. Can't help with a direct answer to your question until I next take the car out but, if it is any help, in overdrive the rev. counter reads 2400 approx. at 70 m.p.h. Fitting the Laycock 'J' Type O/D was the best thing thing I have ever done - it transformed the car. I also take my car abroad a lot. Went to Prague (from London) last year and needed to use fast roads there and back. Would have been miserable without the O/D. Have covered 100000 miles as of this summer and wouldn't have been such a joy without the O/D.
If you get the car, and are within striking distance of London, you are very welcome to come out in my 403. Good luck.
Dave Dale.

Quote:

Originally Posted by David.H

What mph/1000 would I expect on a non o/d 403 (1953). I'm investigating one (LOY555. Anyone know it? It has not much history, the seller has bought a 400 apparently). I'm looking for a car to use & I take my present cars overseas quite often & a good cruising speed is essential. Also what is the 100A engine like on modern fuels...does it suffer from overheating/ vaporisation?
DGH

2valvehead · #3 (**permalink**) 23-06-15, 05:46 PM

Depends what crown wheel and pinion is in the differential. The standard ratio will give c20mph/1000 revs on a Michelin X tyre. The overdrive bumps this up to c25mph/1000. The o/d does make a huge difference; especially if you are thinking of some serious journeys. Less revs = better mpg + less wear all round.

David.H · #4 (**permalink**) 23-06-15, 08:23 PM

Thanks for that information.
At the moment I have a ZA Magnette & changed the final drive from 4.55:1 (around 15mph:1000!) to 3.9:1 from an MGA mk2 -this meant I was able to cruise at 70-75 (around 4000rpm) & get 32mpg on the Autobahn last year! An overdrive is difficult to fit to the ZA without transmission tunnel surgery.
O/D has to be the way to go, my old TR3A was useless without it! So I have to factor that in to my costs!
Further to fuel, does the head need to be "unleaded" or just use the additive &98 octane?
David