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MG MGA - 100 MPH for real?

I am just into mg's and read yesterday that stock MGA's were capable of doing 100 mph. Just wondering if this was an, "oh thank you god the speedo hit 100 and the car didn't explode", or if it is a "sustainable traveling speed for a decent amount of time sans praying 100 mph." Also, i plan to drop an 1800 into my soon to be restoring A, were early b's capable of such speeds?


Anyone?

Jon
Jackpine

If you put an 1800 and a 3.9 rear end into your MGA, you will be able to cruise at 100mph without any problems. I have that setup plus a 5 speed and at 80mph I am doing about 3000-3400 rpm.(Not sure of exact rpm) I have to watch my speedo as I always seem to travel at 80 mph and I need to let off the gas. With that setup and the age of your car and the way it will look, get ready to start collecting speeding tickets. So far, I have been lucky and have not got one yet!!!
JEFF BECKER

I think Jeff's speedo is a little optimistic I have a 3.9 diff and I need 4000 RPM to do 80MPH. Mine is still the 1600cc but pulls this diff easily and I cruise a lot at 80MPH when travelling to the south of France each year.
Bob (robert) I am turning? yes I once owned an MGWasp!!

With an 1800cc engine you will easily surpass 100MPH, assuming you have geared the car for it. I have an early 3-main 1800 engine mated to the stock MGA 4-speed transmission and 3.9:1 rear end. I can take the car to redline in top gear without any real effort. Offhand I don't remember what that speed is, but it is easily attainable. Admittedly I haven't actually pushed it to top speed but I have been close and the car was still pulling strong. With a stock 1500 or 1600 it would be a bit tough to cruise at those kinds of speeds but the car would be more desirable to collectors with the original powerplant. You will also have an easier time keeping the engine cool with the smaller bore.
Steve Simmons

My '64 when new, was quite capable of 100 mph and on several occasions, sustained this speed for about sixty miles or so, with no problems. I've never had my MGA over seventy--as I'm a bit older and wiser now. I avoid interstate highways, and only indulge in nice rural drives now.
R. L Carleen

Bob, I will check my speedo. Remember this is a five speed not a four speed. When in 5th the rpm drops way down. The speedo has been callbrated on a rolling dyamo and is on the mark.
JEFF BECKER

I've done 90+ on a public road in a bog standard '59 roadster and it was just about out of leg. As I recall, it was in the orange and had I taken it to the red, it may have done the time. I was 17 when I did this and I haven't had the desire to do it again. In my experience, it's best not to think about what's happening inside the engine when it's wound that tight. As I've said before,

"Racing this car [MGA coupe] is like arm-wrestling your grandmother. Sure, you can do it, but if something breaks, you're going to feel bad and it's going to be expensive to fix." - Me
Kemper

100 mph no problem, keeping it there leads to problems especially with the 3.1 dif.

I was silly enough to race along the motorway against a slightly modified B with my 'hot' MGA 1600. I saw the B off and remember seeing about 7000 rpm and 115 mph before sudden loss of power due to head cracking between cyls 2 and 3 bought things to a halt.

Always wished for a 4.1 diff.

Ian f





Ian Fraser

Ian,

I suppose that you meant a 4.3:1 Differential?
I assume from your email address that your MGA is a Coupe?
I understand that the 1600 coupe could just reach 100 MPH in standard trim (albeit for a short time). The roadster just fell short of 100 MPH.

Mick
Mick Anderson

oops yes

4.3:1 diff in my MGA 1600 'ragtop' (since sold <sad>)

The Coupe is still in a container waiting a rebuild, 1800 + o/d + 3.909:1 banjo diff.

I'll be too bloody old by the time I've finished it to drive at 115 mph!

Road tests at the time gave varying results, but it would seem that 100mph was within the grasp (or gasp) of all MGA's.

Cheers
ian F

Ian Fraser

We were driving at betwen 95 - 100 through France a few years ago, top down. In the end, we just got fed up of the buffeting and noise so slowed down.

This was with 1500 and 4.3:1. The main worry was that it took so long to get up to speed and there was no spare acceleration left to get out of trouble!

dan
Dan Smithers

Yes Jeff I think the 5 speed ought to knock about 10% off so I would expect the revs to be in the region of 3500 to 3600. Wish I had one!
Bob (robert) I am turning? yes I once owned an MGWasp!!

I was in SCCA (late '60s) for a while with a '58 MGA running a '62 Mark II engine (1622 CC). The transmission and differential were stock, but it was no problem to cruise at 80 mph. The speedo wasn't that reliable, but as far as top end goes, I can recall a mid-60s Mustang one night and our little horseplay from stoplight to stoplight until we caught one that didn't turn yellow and I overtook the Mustang and passed him only to see red lights in the mirror and a very angry policeman who noted "I was doing 95 mph and not gaining on you". Thankfully, I got off with a stern warning (better defined as a good ass chewing). I don't recommend this sort of action on the street, by the way, but I was young then.

MGBs with stock (non-OD) transmissions and rear ends could easily exceed 100 mph. I had a '70 that I cruised many times (in perfect open road conditions with no traffic) at 105. As I recall, the specs on that model of B showed top end at 103 mph which was where you touched the red line. On a couple of occasions, I had it to 115 mph.
Rick Penland

My first 'B' a '1965 with wire wheels, Dunlop radials, 165/R14 hit 6200 rpm down a long grade. Speedometer showed 115.
Accurate?
Dunno.
But fun.
SF
Dwight
DCM McCullough

The 1500 coupe was the first MG to do 100 MPH in stock form. My 57 coupe will just touch 100 on a good day, but 5800 RPM is a bit beyond my comfort level. My old 74 BGT would top out at about 105 at around 5400 RPM. My current 68 B is a little too shaky to go that fast (or maybe I'm a little too shaky).

Bill
Bill Boorse

I had a 1960 MGA 1600 Roadster when it was just two years old and when the motorways were new.

I always kept the engine in tune, garages were expensive and couldn't get it right. With the hood down flat out she would do an indicated 103mph and with the hood up 110mph.

It was certainly a good one, I beat a Twin Cam to a Jazz club one night. The owner wanted to know what I had under the bonnet.

It was always the best car I ever had, that's why I'm doing it again - same model same chariot red.

Pete
Pete Tipping

About 6 months after I restored my 1500 back in 1973 I got into a flat out race with a Triumph TR3 on a flat Texas Highway one night and ran for about 20 miles at wide open. Neither one of us could pull away from the other which kind of surprised me since the TR3 had more power but unfortunately I discovered the weak link in my "A", the rocker shaft failed and I ended up driving 75 miles home on 3 cylinders. Gist of the story, perfectly tuned and fresh MGA 1500, indicated 97 miles per hour, no more.
John Nelson
John Nelson

Just so you know most of you low landers are a bit spoiled.

At altitude ~5000 feet, the best I could accomplish with a stock 1500 with the hood up was about 95. This was down hill with a tail wind too. I had more room on the tach but not enough go to use it all.

j

John B

Hello DCM McCullough,
Provided the given peformance data was factory establihed at 19mph per 1000RPM, at 6200 RPM 115 MPH
should be reachable. But a I think yours was a really well tuned exemple.
Renou

Renou

I am sure DCM's 115 mph was actually possible. My 110mph reported above with hood up, was actually with the rev counter red lined but I know the car was still accelerating. I just couldn't let it explode! It's us engineers we can't bring ourselves to abuse machinery...

Pete
Pete Tipping

Standard MGA were originally geared for highest possible velocity at the peak of the power curve. This may still be a desireable objective today, so if you want slower running engine for quiet cruising, you would need an overdrive top gear (OD or 5-speed), but use direct drive 4th gear for accelleration, hill climbing, or ultimate top speed.

With standard 4.3 to 1 final drive (MGA 1500/1600) and original tire size, 6000 RPM is 102 MPH. Original top speed spec for those cars was 91 MPH and 97 MPH respectively.

For the 1600-MK-II with 4.1 to 1 final drive, 6000 RPM is 107 MPH. Original top speed spec for that model was 103 MPH, which is why the final drive ratio was different (to avoid over-reving the engine).

The 3.909 to 1 ratio was a (rare) factory option for any MGA. With original tire size this would give 112 MPH at 6000 RPM (if you warm the engine over enough to ever get there). For the Twin Cam folks (or racing specials) 3.909:1 gives 134 MPH at 7200 RPM, but could vary a little with tire size.

These days the 3.909 final drive gears are getting to be much more common in MGA, as direct swap gears are readily available from pre-1968 MGB. Most people use the cars for casual road cruising as opposed to top speed runs, so lowering the final drive ratio doesn't hurt much, evcn with a stock original engine. If you tweak the engine for a bit more torque and power,the lower final drive ratio is generally desireable to prevent over-reving.
Barney Gaylord

Keep in mind that top speed is as much a result of aerodynamics as it is of RPM vs gearing. At the redline the engine's horsepower is dropping off and the ability to pull the car through the air is diminished. It's easy to rev an engine to the limit while standing still, but under load it's a different matter. The A coupe had a higher top end than the roadster because it had a lower coefficient of drag and was therefore easier to pull through the air. That's why many racers put hardtops on their cars.
Bill
Bill Boorse

I run my 1958 1500 fitted with the 1800 engine, Sierra 5-speed box and standard 4.3:1 differential. I have been making a few notes of RPM/speed readings these last 2 nights on the way back from work (no nice policemen to chat to!). From the data gathered so far I seem to be running about 47/48revs/1mph in 5th. This gives the following (*) so far tested and as best as the eye can judge. The rest are linear assumptions.

40mph = 1880-1900rpm *
50mph = 2350-2400rpm *
60mph = 2820-2900rpm *
70mph = 3300-3350rpm *
80mph = 3750-3850rpm (I was in a 50mph zone)
90mph = 4230-4350rpm -"-
100mph = 4700-4800rpm -"-

Coming home a different route tomorrow by the motorway for the remainder!

Steve
Steve Gyles

John B just hit 110 in the red 58 roadster coming UP the hill from C470 going east on 285 at an elevation of 5500ft. (GPS confirmed) Wasn't out of motor traffic slowed me down. Figure she is good for about 135 @ 8000rpm. (.390 rear) The 4 speed slows me down, Advance has a 5 speed that will fit for only $150.
12a engine.
R J Brown

Barney offered good information - top speed is governed by how high the engine will pull as well as by aerodynamic drag (as noted, the coupe is considerably better than the roadster).

One shouldn't forget that at the 6000 RPM red line the engine is already well past the power peak, and running it higher (you won't get much past 6250 or so even if your valve springs are still in good shape) gets you less, not more power.

A stock coupe with 4.3 is in the 105 MPH bracket, maybe 5 MPH more with an MGB engine, but that's pulling over red line.

The guys that have fitted OD or 5 speeds are the only ones that could really test for aerodynamic limits rather than engine rev limited top speed.

BTW, if you remove the windscreen, the roadster is back on top aerodynamically. I took a dead stock low port 90 BHP Triumph TR-2 out on the track and managed an honest 110 MPH at 5500 RPM (500 past redline). Decidedly scary going into a hairpin corner with only drum brakes at that speed.

The race car has been clocked on track around 130 MPH, but that is limited by length of straight (I am not hitting red line, which is 7800, by the end of the straight) - Twincams at Le Mans with improved engines, although with less power than I have, made it into the 140s on Mulsanne.

A final note - claims about top speed are pretty dubious unless you have GPS confirmation. Speedometers were notoriously inaccurate. Some tachometers were better, but only some. We used to get clocked at the race track by radar - but I doubt you'd like to try that on the street just for accuracy, given the likely consequence from the guy clocking you.....the one in the car with the cherry on top.
Bill Spohn

Sorry. How do you guys do it? I spend half my life flying military jet fighters at max throttle and full burner. I've been Mach 2 more times than you can shake a stick at. I've flown M0.95 at 50-100feet across your desert in California (Red Flag). I even sent in an application to Richard Noble to drive his supersonic car in his world record attempt, but I can't put my foot on the floor and take my lovely old 'A' beyond 4000RPM. She was handling like a dream, but I cannot go that extra 'mile'. What is stopping me?

Steve
Steve Gyles

Steve:

Well, based on your life history, it's probably not fear. Dare I say...love?

Regards,
M.D.
'57 Coupe
M. D.

Hi, 100 MPH ? Easy, 1892cc, 5 speed box, 3.9:1 diff = 23mph @1000rpm, approx 125+ bhp lets you cruise at 90, press the loud pedal and it keeps going. I dont know how fast, I chickened out at 120mph. You need a Coupe for aerodynamics and more comfort but I'm sure its possible in a roadster.


Terry
Terry Drinkwater

Steve G.
From your post I'd say it wasn't fear that keeps you from doing it, likely Love of the "A" or the fact that if she breaks you've either got to fix her yourself or foot the bill yourself.... Just a thought from an "old aircraft mechanic"
John Nelson

Steve
In your list you missed out your short and (so far) unsuccessful attempts at flying the A at 4 inches from the take off ramps installed around the airfield. It sounds to me now like your real problem is that you are not going fast enough in the A and that you are hitting a stall immediately on take off (a normal experience when making an aggressive short field TO). Is it alos possible that with 4000 RPM, the noise level in your car resembles take-off volumes in a Jet and you switch to automaton mode?Unfortunately in the A you are obviously missing some standard aeroplane technology aids, and without a stall warning buzzer you can't figure out what is the problem and correct the rate of climb.

You need to do a little less stick shaking, and get the foot HARD down on the organ pedal, and ease back on the (not shaking) stick more gently, then maybe the old girl will manage to stay off the ground a bit longer!

Just a suggestion!

Dominic
dominic clancy

I think John is probably nearer the mark. I suspect it is the fear of breaking it. I have always had the view that these old long stroke engines were not for revving hard. I guess I just need someone to assure me that 4500-5000 rpm is not going to send a con rod through the crankcase. I don't have any problem with my new Beamer, I will quite happily take it up to the red line. There is just this mental barrier I have to break through - a lot harder than the sound barrier! Like many things in life, once I've done it once I am sure I will be on a roll.

Steve
Steve Gyles

Hi Steve

Your engine will happily rev to 6000, even in standard form, the standard cam may run out of puff at around 5500. If your engine has the 'flat' webbed crank it is forged steel and is used in many race engines that rev to 7500. Don't blow it up on my account but I'm sure you can push it a little more!
My next project is a race replica with 1950cc cross flow engine, 175 bhp is possible at a cost.

Regards Terry
Terry Drinkwater

Thanks Terry. I will report back in due course.

Steve
Steve Gyles

Somewhere I read that the MG crank was forged while the lesser HP B series engines had cast cranks. No telling what is in which engine after 50 years though.

Chuck
Chuck Schaefer

Terry

Got it through my psychological barrier today and up to 4300rpm. Unfortunately only in 4th at the time and in a 50mph zone.

Steve
Steve Gyles

I remember in 1967 hitting 95+ in my first car, a '60 1600, before my mother got worried and asked to go slower. I recall clearly the feeling there was easily more speed to be had. My mother's smile surprised the crap out of me....She was way too old for this. Now that I'm closer to 60 than 50, she wasn't really old at all. I never could get rid of the shimmy ay 60 to 65mph. Over or below that range was smooth running.
Doug
D Sjostrom

Steve

You can do it - really. Assuming you have good oil, filter and oil pressure over say 50psi, no smoke out the back - we other members will guarantee 5000rpm is just fine! Try it briefly in 2nd/3rd to get the taste...

Do that, report in and then we can urge you on to greater heights.

Peter
Pete Tipping

Peter

You are right. Nothing wrong with my engine health -60psi. Took it up to 5000rpm in 3rd on the way to work.

Steve
Steve Gyles

Oh so near. Just went out for a lunchtime spin. An indicated 98mph at just over 4600rpm (Sierra 5-speed box) when I had to lift for traffic and my turn-off. The car was so stable and smooth. Not a hint of vibration anywhere.

There is always tomorrow.

Steve
Steve Gyles

Isn't it just the best car you ever had?
Congratulations on the bravery - now be careful!

Pete
Pete Tipping

My recent ever so nearly attempt (98mph) proved all the old parts could take it. It was the 6 month old alternator that could not cope! - see my pulsing headlights thread.

Steve
Steve Gyles

"If your engine has the 'flat' webbed crank it is forged steel and is used in many race engines that rev to 7500."

But not without modification, Terry.

The intermediate rods will have serious problems over 6500 unless the crank is crossdrilled. You used to be able to buy a factory nitrided cross-drilled crank (I must be getting old, I used to be able to reel off the part numbers without looking them up).

Stock MGA engines will happily pull to 6000, although the cam is 'all in' by 5000 - and flat to about 5500 where it starts to drop off quickly.
Bill Spohn

This thread was discussed between 02/04/2006 and 16/04/2006

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