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MG TD TF 1500 - 1953 MGTD max gas consumption

Own 1953 MGTD
Does anyone have an idea of max gasoline consumption through 1.25 SU carbs.

Based on my rough calculations I get about 22-25 miles per gallon depending where and how

at 60 miles per hour that comes out to about 2.7-2.4 gph

therefore a correctly spec'd out fuel pump should be no more then 3-4gph at 1.5psi

why is the stock original SU fuel pump then 9.6 gph at 1.5 psi?

is my logic screwy? and buy an auxiliary pump with 15gph rating?

Michael Balahutrak

The only thing I can think of is filling from empty. A steady state is one thing. But you want it to start quickly. Listen to your fuel pump when you first turn the ignition on after a long rest period (days?).

Also temperature could effect the output too. Maybe you also want 2x the high demand for marginal error?
Christopher Couper

There is no downside to having a pump with more GPH than necessary, and since the pump isn't designed specifically for an MG TD there is overhead built in for other applications. Also if there's an issue in the system like overheating fuel lines, being able to pump more will be an advantage.
Steve Simmons

Though max flow maybe 9.(?) you have hydraulic friction loss based on the size and run of the lines and fittings. The pumps are not positive displacement pumps. If they were they would blow the weakest link between the pump and carburetors apart. Also depending on the fuel type and load more gallonage would be required ie if running straight methanol for racing would literally double the fuel load requirements on a similar displacement engine. As Chris intimated the pumps are not XPAG specific. These were put on nearly every British car built in that period. From I’m guessing the diminutive Croseley to AC, AH, Jaguar, Rolls Royce and everything in between. All requiring different fuel requirements. Then there are also industrial engine uses. Race applications, various carburetor sizes, lines sizes etc. that would also have to be considered. A larger rated pump also
Means it doesn’t have to work as hard to keep flow rates up. Allowing cooling cycles for the pumps electrics which would prolong its service life
W A Chasser

Last week installed the pump supplied by Moss and it stated to cause weeping around the banjo washers. Then a few days later the Grose-Jet s could not stop the flow.

I must believe that the new pump supplied by Moss is overrated - in flow rate and pressure

Any better suggestions or supply?

I have been fighting this for 3 days to no success
Michael Balahutrak

Michael - A couple of points
you mentioned-
'at 60 miles per hour that comes out to about 2.7-2.4 gph'
Yep ok - but at that same speed uphill or on full throttle it'll use 2 or 3 times more fuel than that and that's where the pump needs to be able to supply that extra fuel.
Second point is where have you got your fuel pump mounted. ---------- S.U. had high pressure and low pressure pumps
The LP pumps mount in the engine bay and are good suckers to lift the fuel from the tank and supply it at low pressure to the carbs -----
The HP pumps mount at the rear at tank level and pump at a higher pressure to push the fuel uphill from the rear to the carbs.
"IF" you happen to have a HP pump mounted in the engine bay it will overwhelm the carburettors with too much pressure.

willy
William Revit

The Moss pump is rated at 25 GPH which seems as overkill?
Michael Balahutrak

Not really an overkill- the gph is it's max flow rate.
Flow rate has nothing to do with pressure.
That pump ,at 25GPH would be a good all round pump that would be enough to feed a modded MGB or similar, you can never have too much flow---it's too much pressure that causes flooding/leaks.


William Revit

Good point thanks Willi. Merv
M Hyde

I hear everyone about the gph being some what irrelevant except in the case when the Grose jet will not shut - then suddenly there is a whole lot more fuel then you need or can consume.

Of course the pressure is important because that is what stresses the Grose jet. If it is more then the 1-3 psi you are asking for trouble and then the volume gets into it.

I installed the Grose because it was touted as being the best alternative to the Viton needles. Also installed the Nitrophyl float. The float does not float level but a bit lopsided - is this normal? Do they need to be balanced by removing material?

Probably these fuel pumps Moss sells were for the newer cars but for our older MG from 1953 I would have liked to see a better specified pump closer to our utilization rate - pressure and flow.

I am looking for one that better approximates this need.
Michael Balahutrak

Michael
Have you got this new pump mounted down the back in the original spot
William Revit

The issue isn't the gross jet or the volume. It is the pressure which is overpowering the float. I do not know which pump Moss sent you but 3 PSI is the maximum that the floats will handle without being over powered. Most small generic pumps are made in many configurations with different pressures, different volumes and equally important if you are mounting it near the original position in the engine compartment..different dry lift capabilities. I have some posi flow pumps from NAPA installed as back up pumps on my cars and although they look the same the one on my TR8 has a higher pressure rating than the ones on my MG's. Just because Moss sold it to you doesn't mean it will work for your application.
L E D LaVerne

This thread was discussed between 11/10/2024 and 13/12/2024

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