endrop - for all your online needs

Tuning turbo time!

Currently reading:
Tuning turbo time!

Munkul said:
no offence but that sounds like tosh. Theres no way a returned system will have less air in than a returnless system.

Yes possibly an uprated FPR will be better than standard, but tbh I have watched my fuel pressure gauge like a hawk on the dyno and never saw any fluctuations apart from when at idle.
Click to expand...

just stuff ive read... they always use return systems on aftermarket stuff ive seen.

my reason behind the less air in the return system is the injectors are at the bottom of the rail. air will float to the top of the rail, and as the fuel is pumped through the rail then back to the tank... any air collected should go back to the tank rather then be trapped.
 
theres a good reason for returned systems on aftermarket stuff. You usually use a rising rate regulator (same as standard) which needs a vacuum line... are you going to run the vacuum line to the rear of the tank just to mount the FPR there? Nope.

If I were changing the stock mk2 FPR i'd use a fixed rate one with no vacuum line though, and keep it returnless and in the rear.

You arent thinking properly - if air manages to get into the system from the engine end, it wont be the air you worry about - it will be the fuel pissing everywhere when you start up :D

Air taken in from any system changes will either hang around regardless of return or not, or be pushed out of the injectors within a few minutes of running.
 
Last edited:
Munkul said:
theres a good reason for returned systems on aftermarket stuff. You usually use a rising rate regulator (same as standard) which needs a vacuum line... are you going to run the vacuum line to the rear of the tank just to mount the FPR there? Nope.

If I were changing the stock mk2 FPR i'd use a fixed rate one with no vacuum line though, and keep it returnless and in the rear.

You arent thinking properly - if air manages to get into the system from the engine end, it wont be the air you worry about - it will be the fuel pissing everywhere when you start up :D

Air taken in from any system changes will either hang around regardless of return or not, or be pushed out of the injectors within a few minutes of running.
Click to expand...

maybe so :)

out of interest... why would you use a fixed pressure regulator?
I have always been told that raising rate regulator are a must on a turbo car. (because turbos need good pressure to keep them working well against boost and also because they need rather large injectors for the engine capacity so would be crap at idle)
 
Last edited:
If there was a return line in place i'd definitely go rising rate. That way you can have 4bar at peak power and 1bar idle (or whatever) so you can keep your injector duty reasonably high for smooth idle and bottom end.

But IMO (and this is just opinion mind) its more hassle than its worth to plumb in a new line, when you could keep 4bar constant pressure, and just suffer a bit of idle quality if you have big injectors and low duty.

At the moment, once warmed up the idle with 3.5 bar and 240cc injectors is absolutely fine. Although i might be wrong and it go totally crap with .5bar more :D

So yeah theres more than one way of skinning a cat. I agree with you, a proper rising rate system is better.
 
yup yup that's what I was getting at. the cinqs have a return system. a lot of seis don't. going returnless for me is like taking a step back and having to pay for it lol.

I have 250cc injectors that run about 1.5bar at idle and still bit rich on idle :( runs rough if I lean it slightly.
guess mixture is better on the 16valvers
 
craigb244 said:
I have always been told that raising rate regulator are a must on a turbo car. (because turbos need good pressure to keep them working well against boost and also because they need rather large injectors for the engine capacity so would be crap at idle)
Click to expand...

The A Graham Bell book notes 4 different kinds of FPR. Of the rising rate regulator he states "........[it] is used in low budget low boost applications (up to about 7psi) when forced induction is added to an otherwise stock n/a engine................[it] is at best a band-aid solution......"
A Graham Bell Forced Induction Performance Tuning Haynes, London, pp.205-6.

He comes down in favour of a non-referenced adjustable regulator. The HP book I have, Street Turbocharging, says much the same.

To some extent you can compensate for the idle issue with pulse width. If you run out of idle, you stage a second set of injectors.

IIRC, Dave Walker remarks that you don't actually get much more flow out of most injectors if you run them past 4 bar, (but don't quote me on that).
 
fingers99 said:
The A Graham Bell book notes 4 different kinds of FPR. Of the rising rate regulator he states "........[it] is used in low budget low boost applications (up to about 7psi) when forced induction is added to an otherwise stock n/a engine................[it] is at best a band-aid solution......"
A Graham Bell Forced Induction Performance Tuning Haynes, London, pp.205-6.

He comes down in favour of a non-referenced adjustable regulator. The HP book I have, Street Turbocharging, says much the same.

To some extent you can compensate for the idle issue with pulse width. If you run out of idle, you stage a second set of injectors.

IIRC, Dave Walker remarks that you don't actually get much more flow out of most injectors if you run them past 4 bar, (but don't quote me on that).
Click to expand...


you are right that the pressure does not really do much the the flow (when increasing)
but what you are describing is cheapo ways of turboing cars.

people can use rising rate regulators to increase fuel pressure once on boost to get enough fuel. this usually goes along side larger injectors (they set the fpr to run lower then standard pressure while off boost to keep the fueling right)

you cant compensate for large injectors by pulse width. you get to a point were the pulse width is shorter then the opening time of the injector. this leads to a injector that kind of spits random amounts of fuel and causes huge idle problems.

all production turbo cars ive seen have a way of increasing fuel pressure be it rising rate regulator or a fuel pump that is PWM controlled by the ecu.
they NEED them to be able to supply enough fuel on boost while keeping a reasonable idle.

staged injection on production cars is rare. manufactures would avoid doing that at because of the huge cost involved and reliability issues.
 
Last edited:
megasquirt can run stage. i tried it and dont like it. maps look ugly and the reliability issues come from the fact there will be twice as many hoses, twice as many wires, twice as many injector drivers. its twice as likely to fail.

also the way stage work is there is a small injector for idle. then the large comes on once needed along with the smaller injector (they both go at the same pulse width)
problem with this (imho) is that if a wire/driver/injector fails then that cylinder will still be firing with a extremely lean condition with a good chance of putting hole in piston.

with one injector. if the driver or a wire fails then the injector will simply not inject fuel.

anyway the problem of over size injectors is easily fixed by running sequential injection and rising rate fuel pressure regulators.
 
I'd not want to do it with squirt -- at least, not without popping on a RR and then............ Mind you, I'd not like to run many of the set-ups people put on turbo cars!

The staged injection set ups I've seen stage further up the fuel load ramp. The first injector handles the initial load (but will still idle just fine -- bigger than a n/a injector, but not too big) the second comes into play further up.

Strange that almost everyone except folk running megasquirt say there's nothing to be gained (except emissions) from sequential.

I've never had an injection driver fail (or a post 60s coil driver!) so to me it really doesn't seem an issue.

Anyone know what the 1.4 16v guides are made of?
 
Last edited:
:confused: its very simple. Double the parts = double the chance of failure. Just as craig said. Also, double the cost.... unless you're not using larger expensive ones.

There IS nothing to be gained except emissions and smoother idle :rolleyes:

Unless you spend a LOT of time and money on R&D you arent going to get a staged setup to make any more power than a conventional single rail setup.

Why is that you mostly only see staged setups on massive power cars? Because anything else (including every 1242 build ever seen on here) doesnt need it - you can get suitably sized injectors and fuel pressure ranges to work absolutely fine.

Complicated doesnt always mean better.
 
Last edited:
Of course it doesn't. Please do not put words into my poor little mouth. I was -- as the possessor of the biggest Pico injectors available -- obviously not commenting on the lack of availability of sufficiently large injectors for the FIRE engines.

The R&D thing is a good point, but power always costs money. The angle of the second set of injectors is obviously parallel, so there's only size and spray pattern to take into account. Second hand injectors are cheap, so it's down to fab and mapping......... Still it's not something I plan to be doing.

If double the parts = double the risk of failure and the risk of failure is minimal, who cares? It's like one of those tabloid medical scares. I'd hope for adequate safety systems in a decent ECU to cover lean states, anyway.

Now, what are those valve guides made of?
 
You must log in or register to reply here.

Similar threads

S
Tuning Turbo choice
Replies
0
Views
316
Suplanter
S
Bill95
Technical Seicento 1.2 8v 75 Turbo conversion
Replies
1
Views
1K
Mrbee
M
S
Technical Timing belt change
Replies
8
Views
916
Sabbas
S
D
  • Question
Tuning Flywheel timing marks
Replies
5
Views
1K
Dirk007
D
W
Technical Seicento engine swap and turbo questions
Replies
0
Views
1K
WEB
W
Back
Top