What is considered the limit on the SPI injector

[lowtechguy]

And how do you overcome?

By increasing fuel pressure?

Secondly, if you have the standard submerged pump (1.0bar) plus an external inline pump of 2.0bar would this make 3.0bar at the regulator?

Or would there be other tricks like wider fuel lines (more fuel is moving with the same pressure from the pump) or is this the bodge way?

Any other tips or tricks people can share?

[oldschool]

Frome experience it is about 80bhp before the injector struggles to give more fuel.

If you want to increase fuel pressure you will have to change the submerged pump by a 3 bar one.

The fuel lines might need increaseing when going to an extreme power increase.

[lowtechguy]

What would you estimate the potential of the injector after 3bar only? 90bhp? more? As I am aware that double the pressure does not double the flow.

[j333evo]

I do not know the max of the standard injector but it is standard prectice on tuned cars to increase pressure to get more fuel, the integrale is fitted as standard with adjustable regulator so when you do a mild boost upgrade you increase fuel from 2.5 to 3.2bar to compensate, after that a 255l/h Walbro uprated pump is fitted, before really extreme applications that run twin pumps.

this brings me nicely on to this; by changing the pump to a"3bar" I use the term loosely you will get no more pressure as the pressure on SPi models in controlled by the regulator found inside the throttle body. Pumps are rated for the flow per hour and maximum pressure they can do, so you find in fact the so called 3 bar pumps are rated to a max of 5bar. As for the standard in tank pump as found on Spi models, i have found that this is a Walbro pump and I wouldn't be surprised if it was just a low rate flow wise pump regulated to the Fiat set up ie as per Fiat workshop manual 0.8-1.2bar, a fairly big parameter.

To increase fuel pressure on a SPi car you have to get an accurate fuel pressure gauge and plumb it in before the regulator as it needs to measure the pressure up stream of the regulator. So this is easiest to do by removing the fuel pipe in and putting gauge inline before the throttle body and then with the throttle body top off you can follow the fuel through the throttle body to where it exits to the return pipe. You will then see the regulator which is normally sealed with blue wax, pick it out and you will see a small IIRC 3mm allen bolt turn clock wise to increase pressure.

I have experimented on the SPi reg in Cento's and found its usable max was about 1.8 bar before it was fully locked and therefore was no longer regulating but was actually stopping fuel from passing altogether.

Therefore if you wish to have a higher setting you need to go to an after market fuel pressure regulator, I ran a SARD one on my turbo Cinq and Emma's turbo Cinq runs one as well to get 3bar at 2nd injector and we set primary injector to 1.3bar. There are other makes like FSI from www.fuelsystem.co.uk. I got my SARD from eBay as you can get them for about £60 delivered from abroad as they are about £120 from UK suppliers cgi.ebay.co.uk/NEW-UNIVERSAL-JDM-SARD-RACING-FUEL-PRESSURE-REGULATOR_W0QQitemZ250113635647QQihZ015QQcategoryZ4311

As this would be on a N/A Spi model and as such do not need to go to the complexities of running two different pressures in two different places i would then either remove the standard regulator or just open it up as much as possible so that it is offering no resistance to the fuel flow, plumb the regulator on the RETURN line as remember it creates the pressure upstream so has to be after the throttle body to create the pressure change and then feed the return from the regulator back into the tank return line.

On the turbo Cinqs we used the Walbro fuel pumps as fitted to Ford Escort RS2000/Granada/Sierra 2.8i V6 etc, again as found on the in tank application list found on ITP050 www.fuelsystem.co.uk/itplist210205.pdf

HTH

Aaron.

[lowtechguy]

Pucka post mate thank you! Very detailed, i'm sure it will help many others too! :-)

[oldschool]

lowtechguy said:

What would you estimate the potential of the injector after 3bar only? 90bhp? more? As I am aware that double the pressure does not double the flow.

I wouldn't want to estimate anything really. If I get through the expense of increasing the fuel pressure I would go the extra mile and MPI it. Manifolds etc are available from any scrapyard ans with a drill, a couple of drill bits and a some files an adapter plate is easily done to fit the manifold on an SPI head.

A couple of people have done it and some more are in process of doing it. The results are quite good.