TheSamba.com :: View topic - Mechanical Vs. Electric fuel pump for turbo setup.

Fri Aug 05, 2011 7:05 am

I am wondering if it's actually easier to manage your fuel supply with the good old mechanical fuel pump than an electric one when boosting these vw engines. I'm not exactly sure how the mechanical fuel pump operates so I will have to research this, but since it's running off the engine wouldn't it pump more fuel as the engine revs higher? Thus supplying the engine with an adequate amount of fuel compare to and electrical fuel pump which is running at a fixed rate via regulator? I understand that these engines tend to lean out when a carburated drawthough setup is used since there is no precise air to fuel management. Anyone?

Fri Aug 05, 2011 7:34 am

you can't get by with the mechanical pump
the mechanical pump does increase psi with rpms, but it goes from like 3psi to 4psi.
you might be able to get away with a draw through system, but for a blow through, you need a pump capable of producing a few psi's greater than boost pressure.
best option is to run an electric pump with boost sensing fuel pressure regulator.

Fri Aug 05, 2011 7:43 am

You need to alter the stock fuel pump so that it's "boost referenced" or run a quality electric pump (NOT a woodpecker-style pump) and use a boost referenced regulator with it. The fuel pump has to maintain fuel pressure at around three pounds ahead of the boost setting

Running five or ten pounds of boost, you have to keep the fuel pump at three pounds in addition to the extra five or ten for the boost. A stock mechanical pump can work if it's altered, but only up to a point.

3.5 + X (where X is the boost number) = your required fuel pressure at all times. Anything less is gonna run the engine lean and cause big problems within a short amount of time.

Luck,

TC

Fri Aug 05, 2011 7:55 am

Just go fuel injection and forget carb and it solves fuel pump problem...

Dale

Fri Aug 05, 2011 9:35 am

Dale M. wrote: Just go fuel injection and forget carb and it solves fuel pump problem...

Dale

x2

Fri Aug 05, 2011 10:08 am

:-k There are different size engines be it for the street or strip or sand drags where a Turbo is used.

Some applications are a draw thru and others a push thru.

Generally a Turbo is under boost for less then 10 secs (recommended).

I have a street 1776cc Turbo/Weber DCOE draw thru system and have had it to 15lbs of boost for less then the 10 secs recommended.

A strip car would be going less then 10 secs in the 1/4 mile and have a fuel pump and larger jets strictly for that need.

That being said the question here is the fuel needed via the pump and press reg used. I have a Facett pump and the reg set at 2.5 lbs...never have run out of fuel.

Webers like 3.5 lbs max so I use that as a guide line.

Just my personal experience.

Steve (VW mechanic of 28 yrs)

Fri Aug 05, 2011 11:55 am

Sweet info guys, you all shed some good light on the subject. What I'm working with is an original rayjay turbo kit designed for the vw and in the manual it says it should only get up to about 9psi.

I had plans on modifying the design to a push through so I could incorporate a wastegate but now I'm thinking of just keeping it oldschool and original for simplicities sake since it's a carburated setup. Why try and fix something that not broken right?

Suggestions on a quality fuel pump? I have the empi one that thumps like a woodpecker and gets pretty warm. The cheapo reg I will probably toss for a holly as well.

Fri Aug 05, 2011 2:32 pm

:) I have a Rajay B25 model with a different exhaust housing to bring on the boost quicker. This model works fine for a 1600cc/1641/1776cc application.

Larger cyls would need the 40 or 60 model Rajay.

My intent and purpose was a street Turbo for that extra ooomph when you step on the gas.

Already had a 2180cc VW dragster for the strip so was covered at both ends...wear and tear.

Building a Turbo would highly recommend a NEW case...shuffle pin and all the inards balanced including a CW crank.

Just a part of my engine preps.

Steve

Fri Aug 05, 2011 3:41 pm

I also have the rayjay B25 on a 1500cc. I would definitely like to rebuild this engine cause I think the no.3 cyl got to hot when one of the previous owners had it cause it's knockin a bit. When I adjusted the valves the no.3 valves were nearly seized. It is evident the one of the previous owners neglected the oil.

What's a ballpark range for a good rebuild?

Fri Aug 05, 2011 5:21 pm

:) I'm retired now and not in the retail parts business anymore so cannot answer the cost to build one.

You can assemble one the cheap way or expensive way...take your pick. The results will show in the short or long run.

PM me and I will give you a breakdown on my engine and what might be a good setup for longevity needs.

Steve

Fri May 31, 2013 10:32 pm

HRVW wrote: :-k There are different size engines be it for the street or strip or sand drags where a Turbo is used.

Some applications are a draw thru and others a push thru.

Generally a Turbo is under boost for less then 10 secs (recommended).

I have a street 1776cc Turbo/Weber DCOE draw thru system and have had it to 15lbs of boost for less then the 10 secs recommended.

A strip car would be going less then 10 secs in the 1/4 mile and have a fuel pump and larger jets strictly for that need.

That being said the question here is the fuel needed via the pump and press reg used. I have a Facett pump and the reg set at 2.5 lbs...never have run out of fuel.

Webers like 3.5 lbs max so I use that as a guide line.

Just my personal experience.

Steve (VW mechanic of 28 yrs)

So you shouldn't need to put an new carb in it? Or just if your running it hard?? I'm confused

Sat Jun 01, 2013 5:43 am

Check out the 'Forced induction forums on www.shoptalkforums.com and you won't be so confused :wink: :wink: :lol:

Sat Jun 01, 2013 1:33 pm

:idea: Late followup here.

Size of the motor will determine what Turbo and Carb to use.

Stands to reason with larger pistons more fuel is needed otherwise a piston will take a dump if run lean thus the Carb size and Jets are critical.

With my 1776 Turbo engine the boost will come on and stay as long as I've got my foot in it under acceleration....pickup is Fast and only needed for Secs in order to gain speed then back to normal aspirated driving.

Nothing wrong with a 1600cc engine being Turboed that will give adequate 5lbs of Boost under a 5K RPM Redline and still live......I had one.

Over 5K RPM then a CW crank is recommended.

One thing I do have is a Water injection under Boost with 87 octaine gas.

A B25 will work just fine with a Weber DCOE 40 on a engine under 2000cc.

A matter of opinion and experience will sure to vary ......all depends on how the finished engine is run on the street/strip/dunes.