FUEL RETURN PIPE (RV8 4:6 INJ)

Viper · Post by **Viper** » Wed Feb 11, 2009 11:16 am

Hi Guys, would it be appropriate to T in the fuel return pipe from the Swirl Pot in-between the tank outlet and low pressure pump (Carter) at the rear of the car instead of trying to plum it in directly into the tank?

Ian Anderson · Post by **Ian Anderson** » Wed Feb 11, 2009 1:46 pm

Yes you could but not a good idea

Reason you should not is that the HP pump will heat up the fuel, also more heat from the fuel rail and this would then not be returned to the tank to use the large tank volume as a heat soak.

Reason 2
Of you manage to suck air into the LP pump while cornering / braking etc the air will never clear as it willget pumped via the LP to the swirl then back from the swirl to the T - only for it to then be sucked back through the LP pump and repeat the cycle untill yu only have air.

Ian

Viper · Post by **Viper** » Thu Feb 12, 2009 9:20 am

Ian that all makes perfect sense many thanks for that. As you may have guessed it's a Cobra Replica and I was thinking of placing the swirl pot up front out of the engine bay which would solve the heat problem (Eaton M112), but not so good in the event of a front end smash!!

You then still have the air problem of course, the tank is a 77lt stainless jobie mounted over the rear axle in my case so no chance of removing it. So I guess I will have to feed the fuel back into the tank by way of the silicone elbows from the Aston Roller filer cap to the tank.

Cheers Eric.

chodjinn · Post by **chodjinn** » Thu Feb 12, 2009 10:13 am

Any particular reason why you can't put the swirl pot in the boot? They're not that big really. And I'm assuming that since most cobras run carbs, the factory tanks don't come with a return fitting, bah! Should be ok plumbing the return downstream of the filler like you mentioned.

Ian Anderson · Post by **Ian Anderson** » Thu Feb 12, 2009 1:06 pm

I Agree

If you are running carbs why do you need a swirl pot?
Presumably you are not sloshing the fuel too much under braking etc so if the outlet is at the bottom of the tank just do tank to pump to carb. (Pump at back of car would be better as they prefer to push rather than suck)

If you have the pump at the front you are more likely to get a vapour lock between the tank and pump - especially if the fuel pipe runs near a source of heat.

If you are running EFi then you can again do away with the LP pump and swirl and just mount the HP pump at the tank outlet and run the return back to the tank / filler pipe. After all this is the way most modern production cars run - and they do that very successfully.

On the GT40 it is different as the tanks are long and narrow and run fore and aft so as soon as you hit the brakes from 1/2 tank down and the fuel sloshes forward and the pump sucks air (The tanks could do with a load of balffles or explosafe foam) (Problem is with the foam your fuel level sensor does not work!)

Ian

Viper · Post by **Viper** » Fri Feb 13, 2009 9:59 am

chodjinn wrote:Any particular reason why you can't put the swirl pot in the boot? They're not that big really. And I'm assuming that since most cobras run carbs, the factory tanks don't come with a return fitting, bah! Should be ok plumbing the return downstream of the filler like you mentioned.

chodjinn, yes most Cobras do run carb's but I am changing from a 475 Holly to injection because of the super charger I am fitting after the injection is sorted and running (Mega-Squirt) by Phil Ringwood. I have put in brackets on previous post Eaton M112 when I replied to Ian. I personally would never put anything in the boot petrol related as most Cobra owners that do have a constant petrol smell as you do with series 1/2/3 Jaguars where pumps are in the boot. My tank is not a factory unit it's purpose built and at the time of the build I did not think I would ever be converting to injection at a later date. If you have a look at Ian's reply he has given a couple of good reasons why the return needs to go directly into the tank at some point.
Thanks Eric.

chodjinn · Post by **chodjinn** » Fri Feb 13, 2009 10:36 am

well can't you just get an extra return fitting welded to the tank?

I've also got me a Phil Ringwood Megasquirt but it's not been out of the box in over a year lol! That should be fun trying to get that to work ;p)

Viper · Post by **Viper** » Fri Feb 13, 2009 10:53 am

Hi Ian, sorry did not make myself clear, I am converting from 475 Holly to Eaton super charger after I have got the mega-squirt in jection sorted & running. Advise on this site and from Eaton themselves not to run a draw through configuration as regards fuel as like the LP Carter fuel pump it blows more than it sucks (stop me if you have herd this story!) so if the manifold between the carb a compressor is not very short with no bends you are in danger of igniting fuel/air build up at the mouth of the blower, one back fire and the bonnet is gone!! So hence fitting injection along with MSN ignition. Also the issue of seals breaking down with petrol contamination inside the blower re the Eaton.

Okay then my present set up with carb was, tank with baffles outlet to filter, onto Carter 9 psi pump fitted below the level of the tank under car at rear, as you say gravity feed, onto the front of the car with adjustable Fuel King regulator/Filter under bonnet to run the old Holly at around 6psi. As that was all in place hence my choice to fit the swirl pot/HP Sytec pump/injection filter some where at the front of the vehicle possibly in the mouth or under the wheel arch so no heat issues arise but as I said previously not to good in the event of a front end smash.

As you say possibly don't need a swirl pot but I do some track days from time to time which obviously involves heavy cornering & braking so I would rather have pot and the necessary LP pump in place so I don't have to revisit that area if a fuel starvation problem occurs.

May be best to fit all these units at the rear of the car under the tank perhaps which would then solve all the issues.
Many thanks guys forr your input Eric.

topcatcustom · Post by **topcatcustom** » Fri Feb 13, 2009 11:24 am

With regards to running the blower wet- i.e. draw through it is a risk but also very common! The Janspeed twin turbo systems (on carbs) are also draw through as are all dragsters and old skool style blower set ups (like mine!)

You end up with a plenum full of compressed air and fuel- effectively a bomb that you hope will only keep going off inside the cylinders or as you said- you can say goodbye to your bonnet! (Unless you have a backfire valve fitted which is pretty much common sense anyway!)

Viper · Post by **Viper** » Fri Feb 13, 2009 11:25 am

chodjinn wrote:well can't you just get an extra return fitting welded to the tank?

I've also got me a Phil Ringwood Megasquirt but it's not been out of the box in over a year lol! That should be fun trying to get that to work ;p)

Well, very risky welding any petrol tank and this one cant ever be removed from the car unless of course I take the body off, hence I went for a purpose built jobbie in stainless (17+ galls) as opposed to an ally tank (11 galls) which due tend to powder as time goes on. As said should be able to feed the return in below one of the Aston Roller filer caps so all will be well I think

. Yes I was wondering myself weather the Mega-Squirt unit will ever run

have made up the loom & connections so heres hoping.

Viper · Post by **Viper** » Fri Feb 13, 2009 11:50 am

topcatproduction wrote:With regards to running the blower wet- i.e. draw through it is a risk but also very common! The Janspeed twin turbo systems (on carbs) are also draw through as are all dragsters and old skool style blower set ups (like mine!)

You end up with a plenum full of compressed air and fuel- effectively a bomb that you hope will only keep going off inside the cylinders or as you said- you can say goodbye to your bonnet! (Unless you have a backfire valve fitted which is pretty much common sense anyway!)

.

Topcat, quick question on that subject is a dump valve the same thing as a backfire valve? I assume a valve of some sort has to be fitted between the blower & the RV8 Plenum chamber in my case (double plenum) if manifold pressure increases beyond normal parameters.
perhaps you could help me on that one. I see Demon Tweeks do a 70mm dia stainless link with a threaded coller to take such a valve

Eric.

topcatcustom · Post by **topcatcustom** » Fri Feb 13, 2009 12:47 pm

I know you have bypass valves on some eatons and dry blowers but obviously not on a wet set up as you would be blowing petrol mix out!!! The speed of a supercharger is directly proportional to engine speed so I dont think there is really a worry of getting a pressure surge like you could (?) with a turbo...

Viper · Post by **Viper** » Sat Feb 14, 2009 2:09 pm

topcatproduction wrote:I know you have bypass valves on some eatons and dry blowers but obviously not on a wet set up as you would be blowing petrol mix out!!! The speed of a supercharger is directly proportional to engine speed so I dont think there is really a worry of getting a pressure surge like you could (?) with a turbo...

Thanks for that info, think the smaller Eaton's like M45 have a integral valve from memory but not the M112, so won't need any type of blow off valve if running dry then top cat, more money saved

Eric.

topcatcustom · Post by **topcatcustom** » Sat Feb 14, 2009 4:08 pm

With regards to welding the tank- my old chap used to drain them and leave it to stand to dry out then fill with water up to just underneath the level where he would weld and do it that way. Also once it is full of water flash a flame over the filler hole whilst standing back- just incase! (there would only be a tiny bit of vapor left in there if any once it is nearly full of water)

But he doesn't seem to think tweice about doing stuff like that where I would be dubious! Always worked though!

TC

Ian Anderson · Post by **Ian Anderson** » Sat Feb 14, 2009 4:36 pm

On your filler line
Does it go
Filler cap
Flex hose
Straight / curved pipe
Flex hose
Tank inlet?

If so
Remove the straight / curved pipe and t into this for the return

You may also find that youhave a breather pipe in there too and at a push this could be used but not that desirable

I have als seen people that have removed their fuel gauge sender

drilled through the top and fitted a return pipe through this and then welded / braised the pipe inplace before refitting the sender and connecting up the flexable hose / return .

Always more than one way to skin a car (or is that a snake in you case!)

Ian