rb26 injectors into rb25?

[ANVIL]

what all is involved in putting rb26 injectors into an rb25? are they a direct replacement? i read some where the rb25 are i think 270cc and the rb26 is 440cc. i might be able to score some for real cheap locally and was wondering if it would be worth it.

[Darius]

Won't be a direct drop in. RB25s are side feeds and RB26s are top feeds. Stock RB25s are 370cc btw. If you're getting new injectors, spend the money on some decent side feeds.

[Kansei240sx]

This is somewhat related, but i've never really heard the answer from anyone.

What is the max power a factory RB25 fuel rail can support? To me the design of the stock rail seems decent, and most people upgrade without even wondering what the stock ones can handle, they just convert impedance and styles from side to top feed and an aftermarket rail.

I was wondering how far i can go with the stock rail and good uprated side feed injectors to keep it simple, and then use Toyota's badass fuel rail connectors so i dont have to worry about gay worm drive clamp connectors coming loose and fuel going all over the engine.

[Darius]

Increasing the diameter of the fuel rail depends on the hp goal you have and what pump you're running. If the pump can deliver the fuel flow you need at the pressure you need it, then increasing the size of the fuel rail won't do anything for performance.

For example, 660cc/min injectors pump about 1.04 gpm through a 1/4" line or so. The head loss in about 20ft of line is ~3.8 ft which is 1.65 psi. Add in fitting losses and it is probably somewhere in the neighborhood of 5 psi.

It is an exercise in hydraulics that I will get into this winter.

[Kansei240sx]

Increasing the diameter of the fuel rail depends on the hp goal you have and what pump you're running. If the pump can deliver the fuel flow you need at the pressure you need it, then increasing the size of the fuel rail won't do anything for performance.

For example, 660cc/min injectors pump about 1.04 gpm through a 1/4" line or so. The head loss in about 20ft of line is ~3.8 ft which is 1.65 psi. Add in fitting losses and it is probably somewhere in the neighborhood of 5 psi.

It is an exercise in hydraulics that I will get into this winter.

I understand that much, my question was what the limits in power were for the factory fuel rail.

I still intend on using a factory fuel rail because its easier and the fittings i am going to use are basically maintenance free and easy to take apart. So i dont need to buy an assload of those expensive A/N fittings, although hydraulic fittings are much cheaper with same thread pitches, and material, they're just not anodized red and blue. They're black.

[Darius]

When you start pushing upwards of 700-800 hp and running methanol with 1200+cc/min injectors, then upgrading the fuel rail will be worth it. So save your dough

[wawazat8402]

IMO, swapping to RB26 injectors on a 25 isnt worth the hassle. In all actuality, the purple sidefeeds found in S13 and S14 SRs are closer to 400-410cc when flowed on a bench. Maybe pick up a couple of sets of S15 SR injectors, I believe they are 480cc injectors and would be a direct drop in.

[StricNyne]

well u need rb26 fuel rail, and obviously rb26 inj, then you need to wire in resistors, also to mount the rb26 rail to the rb25 intake you need to fab up new tabs, i recently did this....

[Carl H]

if you remove the 5/16" feed tubes on the rails its plain to see that the inner bores are quite substantial, coupled with a larger bore fitting on the rail it should support quite a bit of power no worries.ive heard of sr guys running upto around 600hp before the stock rail becomes a limit, guess it depends on the injector size as well.

[wawazat8402]

Ive always wondered if an RB rail would max out sooner due to total system flow over an SR. If they max out at 600hp, hypothetically, say they are running 1000cc injectors. (This is just a guess, Ive never looked into what size injectors the 4 cyl guys run to hit those numbers.) If run at 90% IDC say theyre using 900cc's of fuel, again, completely guessed numbers because I dont care to calculate the actual flow at 85% IDC. Thats 3600cc's needed to flow the the rail just for consumption by the engine.

If we use 800s for the same 600whp at 90% IDC, which I will arbitrarily state as flowing 720cc into the engine. Thats 4320cc's total system flow through the rail for engine consumption. Does that mean our rail, if the same diameter and flow rate as an SR rail, will max out on smaller injectors than the SR guys can get by with or is my reasoning on this completely off base?

[Carl H]

also have to take into account total fuel pump flow...a walboro 255 doesnt support a true 255 liters per hour unless its supplied with like 14v constant.i did the math awhile back while talking to gawdzilla and we speculated that a 255lph pump (supra or otherwise) will max out on 660cc injectors or so.on my setup with the bosch 040 (crammed in tank), greddy 720cc injectors the fuel pump could almost be maxed assuming 100% duty (ended up we calculated something around 295lph required from the pump).

[Darius]

i did the math awhile back while talking to gawdzilla and we speculated that a 255lph pump (supra or otherwise) will max out on 660cc injectors or so.

It is good to hear that because I did the same calcs and came out at about the same answer. That was assuming 12V to the Supra TT pump right? And when you say max out, do you mean 100% duty cycle or like 85-90?

[Carl H]

hrum now that i think about it i dont remember the details wether we used 100% duty or 80% cutoff...I'll see if i can dig up my rough estimates later.and yes we did assume standard 12v supply to supra pump.

[ANVIL]

well u need rb26 fuel rail, and obviously rb26 inj, then you need to wire in resistors, also to mount the rb26 rail to the rb25 intake you need to fab up new tabs, i recently did this....

what was the reason u decided to go with this injector setup? was it worth it? how difficult was it?

i was just thinking about it because i can probablly get that set up for cheap but if it takes so much work i might as well save up and buy some nice injector/fuel rail setup

[BoostFab]

i urge everyone not to push your injectors over 85% duty cycle. a surge will push your injectors over that and will cause the injector to lock open. kill the injectors fast and causing the engine to flood.

[StricNyne]

i did it cause i am running a rb26 power fc with rb26 harness just made life eaiser for me especially when i want to upgrade to cheaper top feeds