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MG MGB GT V8 Factory Originals Technical - Standard bhp ?
|Could someone please tell me what BHP a factory standard MGBGTV8 should have and what 0-60 time I should be getting.|
I have a 1975 r/b factory V8 and the garage that services it tells me it seems to be slower than the other V8s they look after.
Also, if you tune the standard engine, what sort of improvements should this bring in terms of performance ?
I don't know what a std V8 should do 0-60 and I don't want to put the sort of shock loads on my transmission that a full blooded 0-60 requires. How about a 50-70 time? Easy - cruise along at 50mph in 3rd or 4th then give it wide open throttle and time how long it takes to reach 70. This puts much less strain on the 'box and eliminates variations between cars due to gear changes etc. How long have you had the car and how many miles has it done? Is this a new problem or something that's developed? On my old V8 I found a lot of casting flash in the inlet manifold that was partially blocking the inlet tract. I'm driving down to Somerset tonight so I'll try the 50-70 time thing.
I think these cars can be a long way off tune and still feel quick, I still havn't got my present V8 to be as quick as the one I sold six months ago.
|Its my first V8 so I have nothing to compare it with. There does not seem to be a problem per se - it runs fine albeit that it often does not idle properly, preferring to stall unless I've got my foot on the gas. However, I was expecting it to be a bit quicker (given the size of the car and engine). At the moment its hardly any faster than a friend's Citroen Saxo VTR - so when the garage made their comment it got me thinking.|
It has done 67,000 genuine miles and has been very well looked after with a very good history.
Your mileage may you in the window for worn tappet/camshaft/stretched timing chain problems. Have a look at
RPI reckon this problem will occur between 60-80k miles. When I had it I had cylinders 7 and 8 operating at about 50% and tappetty noises on startup
|I believe the factory V-8's had 137 hp with a 8.7:1 compression ratio. I have the 0-60 time at home I'll see if I can find it for you.|
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|0-60 mph = 8.25 seconds. Source - Motor Trend October 1973|
|137bhp DIN is correct, with 190.5 lbs ft of torque at 3000rpm. The comnpression was set at 8.26 to 1 and the engine was set up by the Land Rover development engineers to run on UK 94RON octane fuels.|
The average acceleration times in the rather unrepresentitive 0 to 60 mph dash were just over 8 seconds, but of note was the road test version used by Motor which recorded 7.7 seconds. I raise this point to illustrate the variations in power actually achieved with the V8 engine. Almost always the quoted power is exceeded once the engine has covered about 20k miles, sometimes by a significant margin.
On the rolling road something around 110 bhp is the average at the wheels, yet it is not unusual to have a well run in example still at a standard spec give another 10 to 12 bhp at the wheels and place it firmly in the SD1 power bracket. Adding the K&N filter kit releases a similar amount of extra power.
Bear the above variations in mind and remember one overall fact with the V8 and that is it's ability to achieve about 90% of the outright performance without having to bounce of rev limits in every gear.
|Roger, my rover v8 'opened up' just as you say after about 10K miles. Everyone else I've talked to has had a similar experience. Why do these motors do this so much? I'm just wondering ... I have had many rebuilt motors over the years and I rarely noticed any such effect, and certainly not nearly to the extent that seems to occur with the Rover. Just wondering.|
|It seems from Roger's note therefore that mine might be a little slow / underpowered. What might be the causes of this anyone ? How could I remedy it ?|
Philip, how did you get on with your 50-70 test. I would be very interested to know.
I think that the homologation of the engines was done with lower mileage engines, leading to lower and in many respects more realistic representation of power. The fact that this specific design clearly has greater internal friction to start with may be a design issue, leading to extended life later.
The other fact is that with 8 cylinders dragging there is greater potential for loss than on a 4 pot motor. Clearly if you lose a miserly 3 bhp per cylinder on a 4 cylinder motor you have a potential 12bhp gain later. Worthwile but hardly that big if the engine is a 140bhp current 2 litre type. Now if the V8 at 137bhp has the same 3 bhp per cylinder loss then when run in you suddenly have a 24 bhp gain which you certtainly do feel.
My experience with V8 and other multi cylinder engines is too small to know, but I imagine that many of the other US V8's will display similar changes after bedding in. Comments anyone?
It is also easy for power to be lost due to many simple things being worn or out of calibration. I say it often, but fully believe in it, that a session on a rolling road will identify most faults and once fixed usually find a sizeable chunk of hidden/lost power.
This thread was discussed between 09/06/2000 and 12/06/2000
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