JAP spec fuel system

[adi2009]

just out of curiosity, at what point is it necessary to change the fuel system in the jap TT (injectors etc). can the 440cc injectors handle a single turbo setup aimed at about 500rwhp. is there any way in which the 550cc from the export mkiv be fitted to the jap mkiv.

 

what are the basic mods for the fuel system except changing the fuel pump

 

cheers

[Nic]

I had mine dynoed at 429.5hp running stock turbo's in parallel, using stock 440cc injectors with the addition of an uprated Walbro pump, HKS adjustable fuel regulator and E-manage. The fueling was sufficient but was nearing max duty cycle for the injectors, the car ran great for 6 months in the high HK temps, before I eventually installed an HKS rail and 680cc injectors.

 

Think you'd definitely need to fit bigger injectors if going for any more power than this with a single kit.

 

The UK spec 550cc injectors can be fitted on the j-spec fuel rail but you also need to fit the UK resistor pack as the UK injectors are Low Impedance as opposed to the j-spec ones which are High Impedance. I would also fit an uprated fuel pump, adjustable pressure regulator and electronics to map the fueling.

 

EDIT: Reference to injector capacity limit/hpdeleted to avoid confusion. (cheers Terry.)

[adi2009]

Hi Nic,

thanks a lot for the advice. anyways just though that i ll give u a background of the mods that i ll be performing.

 

walbro 255lph fuel pump

[adi2009]

Hi Nic,

thanks a lot for the advice. anyways just though that i ll give u a background of the mods that i ll be performing.

 

walbro 255lph fuel pump

manual boost controller

Greddy BCC

K&N intake

De-catted exhaust

(i have an adjustable Fuel pressure regualator but was told by someone that in a turbocharged application i can only use the boost variable fuel pressure regulator)

 

thanks

 

adi

[Nic]

Hi Nic,

thanks a lot for the advice. anyways just though that i ll give u a background of the mods that i ll be performing.

 

walbro 255lph fuel pump

manual boost controller

Greddy BCC

K&N intake

De-catted exhaust

(i have an adjustable Fuel pressure regualator but was told by someone that in a turbocharged application i can only use the boost variable fuel pressure regulator)

 

thanks

 

adi

 

Hi Adi

 

1. Walbro 255lph is a good choice.

 

2. You probably won't need the manual boost controller. Fitting a new exhaust and removing the cats should increase the boost sufficiently, it will probably increase it too high in fact and so you may need to fit a restrictor ring to decrease the boost to 1.1-1.2bar. Chris Wilson on the forum can supply you with de-cat pipes and restrictor ring.

 

3. Yes you'll need the fuel cut defender, many members fit the VFCC from Thor Racing, not sure how the Greddy compares on price but they both essentially do the same thing.

 

http://www.thor-racing.co.uk/THOR_Racing-44.asp

 

4. Personally I would save my money and keep the stock air filter. The K&N is poorer at filtering and will suck air from the hot engine bay which will reduce power slightly. The only real benefits over stock is the sound the K&N will produce.

 

5. The "de-catted exhaust" is this a full new exhaust or are you just decatting the stock exhaust? One of the first mods I'd do would be to fit an aftermarket exhaust and de-cat pipes.

 

6. The adjustable fuel pressure regulator allows the pressure of the fuel to the injectors to be increased ie. forcing a little more fuel through the same size injectors. It will do this across the whole rpm range though so it may mean you run slightly rich in areas. I have a Greddy e-manage fitted on my car which controls the air/fuel mix across the rev range, it also adjust the timing map. I cannot recommend the e-manage strongly enough, one of THE best mods I've made to my car and very resonable too (well it is in HK.)

[Nic]

Forgot to add a couple of things:

 

1. if you are fitting the new fuel pump, it would be a good idea to also fit a new fuel filter (new Toyota one), this is located underneath the car in line with the fuel pipe.

 

2. When you fit the decats/exhaust tyou also should fit a boost gauge so you can see what boost you are making.

 

3. And finally use a tuner who has a lot of experience of tuning Supra's to fit the parts and make sure everything is running properly. A run on a dyno would also be useful.

[Guest Terry S]

Nic you formula for the injectors is too close to the mark mate. That will be at a VERY high duty cycle unless you are running high static fuel pressure.

[Nic]

Nic you formula for the injectors is too close to the mark mate. That will be at a VERY high duty cycle unless you are running high static fuel pressure.

 

 

You're right Terry, which is why I said the injectors would 'max out at the equivalent hp...' Perhaps I didn't word it very well, I'll edit it so as not to cause confusion.

 

Mine dynoed at 429.5hp with 440cc injectors and was running low 90's duty cycle with the fuel pressure increased and A/F mapped by the e-manage.

[Guest Terry S]

Sorry mate I was "skip " reading.

[Nic]

Removed the reference to Injector cc limit/hp ratio, to avoid confusion.

 

Terry you definitely have more experience of this, so would be useful if you could explain injector sizing for Adi and others.

 

cheers

[Guest Terry S]

There is nothing magical to it, you need to understand the formula, and that 80-85% duty cycle is the Max you want to go to for sustained use. EG, if you were to achieve 440bhp on 440cc you would need around 75psi of fuel pressure, so if you were making 440 bhp @ 20psi boost, the static pressure in the rail would need to be 55psi. There are calulators on the web which allow you to punch in the cc, number of cylinders etc, to find the optimum size. This explanation is really simplified but I hope it helps.