The V8 Owners Forum -

Hi All,

I have now fitted the 4.6 RV8 into the MGB, which still has the standard SU fuel pump, electronic version. I am getting a problem which feels very much like fuel starvation with air getting into the system and then the car stops. After a while it will start and go for a bit.

RPI say I need a Facet Red Top pump. Does anyone have an opinion on this?

Also do I need a fuel regulator, if so why and how do I set it up?


Roger

If its an electric pump you can run it into a container for 30 seconds, measure the amount of fuel then double it. This will be the flow in cc per minute.

Use the following formula to work out the engine requirements

Flow in CC per minute = BHP x 4.7

If your motor makes 240 BHP you would need 1130 CC at WOT per minute. I would round this up to something like 1400 CC to be safe.

I am running a 4.6 in a Land Rover on twin 2" SU's. Producing 250BHP with a standard SD1 in-tank pump.

I have no known issues with the pump being unable to deliver the necessary fuel.

I did have issues, which turned out to be a knackered pump, so I fitted a new one.

Chris.

sidecar wrote:If its an electric pump you can run it into a container for 30 seconds, measure the amount of fuel then double it. This will be the flow in cc per minute.

Use the following formula to work out the engine requirements

Flow in CC per minute = BHP x 4.7

If your motor makes 240 BHP you would need 1130 CC at WOT per minute. I would round this up to something like 1400 CC to be safe.

When you do this test make sure you take the feed from the end of the single pipe that feeds the carb. This will take system resistance into account.

Edelbrock do a really nice pump that has a reg built in. Real steel sell them.

I work on a formula of 100cc in 10 seconds per 100hp. So that makes 1440 cc per minute which agree's with Petes formula.
Perry

Hi
"RPI say I need a Facet Red Top pump. Does anyone have an opinion on this?"
Yes, looks like RPI have Facet red top pumps for sale! I wouldn't deduce anything else from this.
Personally I would go for Perry's recomendation, Facet red tops are OK but nothing special, usually they are paired with filter king regulators, again OK but not brilliant. The Edelbroch will have plenty of capacity and the regulator is designed to work as part of the pump so should give good results.
Best regards
Mike

Yes, I understand the comment on RPI, but Roger Williams in his book also suggests the Facet Red Top among others.

I will do the test tomorrow. Real Steel do not list an Edelbrock electric pump on their website; I will ring them tomorrow also.

Can anyone explain what a fuel regulator is for, Roger Williams says one should not really be necessary on a road car. My understanding is that the pump stops when the pressure is such that the carb no longer needs fuel.... or something like that....


Roger

Facet Red top is 36 Gallons per hour or about 165 litres per hour
(specced at about 46GPH but ths is American gallons)
Or 165 000 cc per hour
or 2750 cc per minute

I use 15cc per hp per minute it maxes out at about 183 / 185 horsesAlso why a regulator?

A carburettor is set up to expect a fuel flow in as Xpsi - that way the float need and seat will seal - increase the pressure and you can flood the carburettor by forcing fuel past the needle and seat.

The regulator can come preset or adjustable and with a gauge to confirm the pressure

Ian

Roger.S wrote:Yes, I understand the comment on RPI, but Roger Williams in his book also suggests the Facet Red Top among others. I will do the test tomorrow. Real Steel do not list an Edelbrock electric pump on their website; I will ring them tomorrow also. Can anyone explain what a fuel regulator is for, Roger Williams says one should not really be necessary on a road car. My understanding is that the pump stops when the pressure is such that the carb no longer needs fuel.... or something like that.... Roger

The red top pumps are probably OK but you need to check the PSI of the fuel that it delivers, 6.5 PSI is really the max that your carb will take. If you go over this figure then you will need a regulator to bring the pressure down and this opens another can of worms!

There are two types of regulator, dead-head and bypass. The dead-head type just shuts down when the pressure is too high, this can cause the pump to stall, many pumps do not like this, it makes them noisy and shortens their life. The bypass style does not stall the pump but it does require a return feed back to the fuel tank.

You can avoid all this by using a pump with a low PSI outlet, that way you do not need a regulator at all.

I ran my stage III 4.6 with a Facet Silver Top for ages, it had no regulator and it was fine. From memory the pump was rated at 150 BHP and 30 US gallons per hour. I measured the flow and it did tally up with the stated flow.

With regards to the max BHP I think that Facet have put a huge safety margin into their figures because my engine was making around 285 BHP at the time and it never had a problem. (I run at WOT quite often!)

My formula also indicated that the pump would be OK. (I measured it at 1.8 litres per minute). You may ask why bother with high pressure pumps in the first place, well they do have there uses, drag cars that pull a lot of G as they leave the line will have fuelling issues if the pump is marginal with regards to pressure, to get round this the pressure is kept high in the fuel line all the way up to the carb, the regulator reduces the pressure just before the fuel in fed to the carb. In the end I did change the pump for an Edelbrock electric jobbie because I wanted plenty of fuel flow capacity in reserve for the NOS system that I was fitting.

I must say that the Edlebrock pump is a nice bit of kit, it is very quiet, the low pressure version of it does not require a regulator either and can be stalled as it has its own internal regulator. One thing to note is that the pump does not come with any fuel unions, you can buy these with various bends in them to suit your needs. This is the pump that I now use, it’s not exactly cheap! (The 1791 model) http://www.edelbrock.com/automotive_new ... main.shtml

My old pump is either this STS504 or this STC505 http://www.fuelsystem.co.uk/web-facet.pdf

My old pump is kicking about doing nothing, if you want it make me an offer, I don’t want much for it! (I live in Wokingham)

Thanks again all,

I’m learning a lot very quickly; if this is a ‘steep learning curve’ I’m getting vertigo!

I talked to Burlen Technical (they make SU carbs and fuel pumps now) who said the MGB pump I have should do two pints a minute.

I did the suggested test at the carb and got less than one pint per minute! Did it at the pump and got more than two! The offending article was the fuel filter before the carb. Took this out and ran her for forty miles: the car went fine. Of course I am going gingerly as I am running in.

This standard late MGB pump was also used in the factory MGBGTV8 but that only had 137 bhp of low compression Land Rover power, of course. It was also good enough for my 3.5 SD1 engine, perhaps 180 bhp, but by Sidecar and Perry’s figures will not cope with 200bhp+.

However the silver top should do fine, the Facet BHP figures are indeed very, very low, perhaps by 100%, if the flow rates are right (which Sidecar has tested). (I’m having a mental block with Ian’s figures; I keep being out by a factor of ten!).

Also talked to Real Steel who no longer stock the Edelbrock pump, but they mentioned figures of 5.5psi (ideal) and 6.0 (maximum), for the carb, confirming the information on this thread.

So, I have bought one of these: http://www.burtonpower.com/fac480530.html , and hopefully this will last me the duration, also it has a fuel filter so I can be rid of the in line filter. Thanks for the thought Sidecar, I decide I deserved a new one.

Btw, there are two different Silver Top models and different suppliers quote different psi’s for the same model.

Many thanks, hopefully that’s another ‘problem’ solved. Or do I mean ‘opportunity’, or ‘challenge’?

Roger

Well done for sorting it out, quite often these things turn out to be something simple, its just finding it that can be a pain!

There are, of course bigger SU pumps. The Jag 4.2 one? Even saw a sort of double effort on a Rolls. Two bodies with a single chamber.