Min size of an effective surge tank?

[thomasbl]

I was wondering if anyone had thoughts about the minimum capacity a surge tank would need to be to remain effective?
I know its one of those "how long is a peice of string" questions but...
Ill be using a pierburg prepump, bosch high pressure pump for my 1G in the RA28.
There is a surge tank for sale on ebay that will fit nicely in the eng bay but it only hols about half a litre?
What are your thoughts?

[bansheebuzz]

if you lift pump will flow more than you hp pump then it will be fine

[DoctorDubb]

I would also be interested to see the outcome in this,as i was looking at the same setup. Thomas have you got the model(part) numbers of the pumps you were looking at running? I was looking at the Bosch 910 (130L / hour) and the pierburg pump (no model number) (100L/hour) and was concerned with the fact that we would run into problems with the prepump not putting out as much as the EFI pump. Were you looking at another pierburg pump?

[LeeRoy]

"how long is a peice of string"

I believe the answer is 2x half its length

if you lift pump will flow more than you hp pump then it will be fine

Are you sure thats right? i'm pretty sure it's the other way around as your hp pump will be only working at its hardest so to speak when your at hi-rpm wheras the lift pump is just designed to fill the surge tank and when you cruise it fills that surge up and then when you give it a squirt the hp pump sucks from the surge tank.

If you wanna find out what a good size is then work out how much fuel your car would use at full rpm in a minute and then have a surge tank that could hold your supply fuel for say 30 seconds as the lift pump will still be pumping the whole time. This will also depend where your fuel return line goes to. Keep in mind that the fuel return will contain hot fuel.

I'm sure one of those Ebay ones would suffice.

- LeeRoy

[myne]

Figure out the rate which the engine uses fuel at its max power.
I guess you could work it out by the size of the injectors in CC/min *.8 (80% duty cycle) * # of injectors.

So my 4agze would flow, at the absolute max 365 * .8 * 4 = 1168cc/min

I guess, a surge tank should hold a fair amount, say a minute's worth + a bit for slack.
So for my engine, for total piece of mind, I'd pick 1.5-2L.

*note* I dont actually have any experience with this, but it makes sense to me.

[LeeRoy]

...concerned with the fact that we would run into problems with the prepump not putting out as much as the EFI pump.

It doesnt matter cause your never having the pumps pump at their max flow rate. Especially if you run the fuel return back to the surge tank. It's like saying you drive at rev limiter 24/7 which you don't. The lift pump is just to fill the surge tank back up after the hp pump empties it a little.

- LeeRoy

[roadsailing]

i'd say a litre, 1.5 for overkill.

and dont put it in your engine bay!

[kingmick]

a 1litre one will do it no prob! the other thing to look at is the temps in summer. As you will need your return from the fuel rail to go to your surge tank, you will have very hot fuel at the rail in no time flat. if you go bigger in the tank then you can go straight back to the tank with the return fuel. So for a very little out lay of money{bigger tank} you will get more HP and a safer system. hot fuel dosnt need much of a spark to ignite hot fuel.

[thomasbl]

Thanks for the response guys.
I am definately aiming to stay clear of hot fuel, and if this means maybe going to a bigger tank then i will do so.

shinybluesteel- What is the justification behind not putting the surge tank in the engine bay? I need to avoid having it inside the car for engineering etc. Any other thoughts on options for placement on a ra28?

Thanks heaps..
Tom

["Z" UTE]

Tom, the surge tank I used in the engine bay of the 1G-GTE powered RA28 Celica, had a capacity of about 600 ml.. Never had a problem with heat, as it was mounted on the wiper motor side.

That actually works out to about 6 kilometres worth of fuel at cruising.

Giving it a bit of stick, maybe 3 kilometres of fuel.

With your pre pump always filling the surge tank, and your fuel rail bypass also going back to the surge, it will never get anywhere near close to empty.

shinybluesteel. The car is an RA28, real bad for vapours in the cabin, if any of the fuel lines leak.

cheers Chuck.

[roadsailing]

OK, should have explained myself a bit better to begin with.

The only thing worse than putting the surge tank in the engine bay is putting it in the boot/hatch, i;d suggest putting it under the car beside the fuel tank, then any issues with the surge tank will already be be issue with the fuel tank.

hold on, the surge tank is in the boot or behind the rear seat in XA2Xs isn't it? there still might be a way to mount the surge outside the car, or you might even be able to build an internal surge tank. If your car has a vertical tank, as opposed ot a lay flat tankm then the need for a surge tank is reduced somewhat. for what its worth, i don't get surge in my sprinter using the standard carby pickup unless i have less than a quarter tank of fuel, and plan on just running a properly baffled pickup to avoid this.

anyway, there are two main reasons to not have the surge tank in the engine bay

1. it will get hot like everything else in the engine bay

2. it you hit something head on (pretty hard i must say) then there is a chance that it will rupture, and make your crash slightly worse.

if you need to put it in the engine bay, make sure it is sturdy and has no fittings that can break off from shock or vibration, and does not have mounting tags welded on to it as these can tear out.

hope this helpos, i think i started rambling there

[thomasbl]

Yeah, i see where you are coming from.
The ra23's have an upright tank in the boot, not so much of a hassle there. The ra28s have a flatter tank which sits under the floor of the rear of the car. There is not a heap of space there to fit a surge tank as the exhaust runs down one side and i hope to mount the pre-pump under there too.

At this stage, i would rather not go go down the intank pump road, it seems like a bit more hassle at this stage.
Thanks for the help.
TOM

[TA-022]

similar to Toy77 ill be moving rear muffler further to centre of car. Then mounting surge tank and pumps in a box in stock mufflers place.

[willwal98]

If you are making the surge tank yourself and are going to use a return line from your rail have it enter near the top and have your lift pump enter near the bottom. That will help seperate your hot fuel. Don't forget to angle them in towards the side to get a swirling effect. Let me know if you want a diagram

[Billzilla]

if you lift pump will flow more than you hp pump then it will be fine

Well I hope so - the engine won't run otherwise!


Half a litre should be about as small as you want to go for shorter corners. One litre is plenty big enough.