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SP250 top speed

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John-B
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SP250 top speed

Post by John-B »

George Zdanko, I must protest!

Your DM article shows the SP250’s top speed as 120mph, less than the Majestic Major’s 123mph.

According to the Automobile Catalog http://www.automobile-catalog.com/make/ ... /1964.html the factory-declared top speed was 124mph but I have seen early road tests giving 125mph and 126mph.

I myself have achieved 134mph in about 1970 on the M4 late at night, slightly downhill going west from the Bath roundabout A46 junction towards Bristol (at least that’s what the speedometer said before I chickened out, passing cars doing 70mph in a flash).

The SP250 should always beat the Majestic Major’s top speed, surely?

Regards

John-B on the forum

The thought of being chased by a five tonne hulk at 123mph horrifies me. (Actually, the Majestic Major is one of my favourite designs, after the DJ254. In my view the SP 250 is quirky, beautiful in parts.)

I've often thought about the relationship of tyre circumference and speed. When I bought my car in 1968 it had Michelin X 165x15 tyres with hard, low tread, a small diameter and circumference. I changed them to Avon 185x15 with a much larger diameter and circumference.

So when the gears are rotating and showing a certain speed on the speedo, the larger tyres are covering a greater distance, ie greater speed, say up from 134mph to 145mph. I don't believe that, but the larger circumference wouldn't be reducing the recorded speed down to the factory 124mph, would it?

Sonus
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Re: SP250 top speed

Post by Sonus »

I managed 194km/t in my TVR Vixen with a stock Daimler V8 engine in 4th with a salisbury 3.31:1 diff and 195/65/15 tires on the autobahn this September. I might have been able to pull av few more km/t with a longer straight, but the engine was increasing it's revs very slowly and it was dark. All measured with a GPS. It did less in 5th gear which is 0.8 overdrive. My car has been rolling road measured to 106bhp at the wheels and 138bhp at the flywheel.

A.N.Other
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Re: SP250 top speed

Post by A.N.Other »

Part of the magic of driving an old car is the the fact that nothing is for real when it comes to the dials.
Always allow at least 15% on the optimistic side. The good thing is the ride quality makes you think the guages are to be believed.
Thirty years ago I was led to think it was 200 miles door to door when visiting relatives in Stowmarket. The odometer on the latest rep Mobil reads 194 and has relatively reduced over 12 cars. The route is the same just the accuracy has improved or the pot holes have got deeper.
Colin,
I may be slow but I’m rough as well !

Ian Slade
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Re: SP250 top speed

Post by Ian Slade »

It really depends on which Spec, and the tyres fitted, with 165x 15 the speedo over reads, with 185 x15 it under reads, a "A" sec is just about 18cwt in running order and a "C" spec is 23 cwt, unfortunately GPS wasn't available in the early 60's, the best way is to check the rev counter accuracy with a stroboscope then work out the speed in any given rpm on the tyre circumference. Way back in the early 70's an "A" spec was reputed to have achieved 140mph with a 22% overdrive fitted in the Birmingham area, though what tyres was never indicated, I achieved about 130 mph in third gear at 7250rpm on 185 x 15 at Greenham Common airbase before the cruise missile kerfuffle.
Last edited by Ian Slade on Fri Nov 02, 2018 5:23 am, edited 1 time in total.
Owner since the 70's, Genghis is slightly to my left.

simonp
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Re: SP250 top speed

Post by simonp »

Having owned two Majestic Majors as well an an SP250 it would not surprise me at all if the Majors were faster. Certainly faster than Ford Galaxy 7 litres and 130mph seen on mine.

SimonP
Daimler SP 250 - "To feel its eager response as you open up is to know a new motoring adventure"(Sales brochure) The adventure continues!

tjt77
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Re: SP250 top speed

Post by tjt77 »

I dont know about potential top speed of an SP 250.. but Im fairly sure the 'stated' power output of the 4 1/2 litre V8 is less than what it actually produces.. whereas the 2 1/2 is about right @140 bhp.. Id think it would take 150 HP + to get the SP250 up to anything above 125 MPH.. I do know that a 4 1/2 V8 when fitted to the 2 1/2 litre body with manual overdrive box and 3.77 diff will outperform a mildly tuned 3.8 or std 4.2 inline 6 powered Jag by a huge margin.. and will hit 140 MPH on the speedo on a decent straight.. as to what 'actual' speed that is.. speculative.. the majestic major engine is immensely powerful if assembled properly.. and will pull strongly up to 6,000 rpms in standard form .

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