Hi folks:

I am building my FD from Stock Twin into a Single T04, What size of injecotors should I use in order to have best performance and it last?


thank you for your help

JGTC89

 

A good fuel pump with 550cc/1600cc, 850/850, 850/1600cc. Depends on how much power you want to make and if youre going to go the whole way thru and do the entire fuel system...

Jay7...

 

The short version....

Take your target rear wheel horsepower (rwhp) and multiply by 10.
This is your required fuel in cc/minute.

Let's say you want 400 rwhp.

400 x 10 = 4000 cc/min of fuel required.

On my car, I did 2 x 550 and 2 x 1600 for approx 4300 cc/min of fuel and I'm basically just over 90% on my duty cycles.

Now, as to which COMBO of injectors... here are my thoughts...

stock primary 550s provides a nice idle and you can install stock 850s in the primary location with a little work for cheap and get more fuel.

For secondary injectors, 850-->1300 overbores are cheap, but I am not 100% of reliability with the overbores. You can go with a 1600 cc/min setup, but then you have to buy a new rail, new fittings and hoses, and a new fuel pressure reg. This adds up fast.

The KEY question is what is your target rear wheel HP?

 

To expand further... here is my recommended upgrade path... Keep in mind these are ESTIMATES. If you plan to be right on a breakpoint, you may wanna go with the next size up.

Assumptions:
- Close to stock fuel pressure levels
- You are not replacing gasoline with other fuel sources like methanol injection (at high enough mixtures that it is a major fuel source in the motor)
- You have an upgraded pump system that can deliver enough flow volume and won't fade at the top end!!!!! (VERY IMPORTANT)

Stock = 550/850 and will support about 270 rwhp
FREE - no need for any upgrades

Upgrade 1 = 850/850 and will support about 320 rwhp
Cheap - used injectors can be purchased and cleaned professionally and installed into a slightly modified primary fuel rail. Buy yourself a fuel pump from a Supra for a drop-in upgrade.

Upgrade 2 = 550/1300 and will support about 350 rwhp
Cheap - Buy 850s overbored to 1300s (or pay to have your stock 850s modded) and install in the stock secondary rail. Buy yourself a fuel pump from a Supra for a drop-in upgrade.

Upgrade 3 = 550/1600 and will support about 410 rwhp
Somewhat expensive but in my opinion, the "right" way to do it - Buy an aftermarket secondary fuel rail, aftermarket fuel pressure regulator (1:1 boost compensating type), aftermarket fittings as needed, 1600 cc/min injectors, and resistors to use with the injectors. Wire it up, test it out. The Supra pump is getting to be at its limits at the 400+ rwhp levels. Your fuel pressure may have slight fade as you near redline. This is the area where you may wanna think about dual pumps or a less-drop-in and more race style setup for the fuel pump(s). Rewiring the pump to draw directly off the battery with larger wiring may help.

Upgrade 4 = 850/1300 and will support about 410 rwhp
Cheap - Put your stock 850s in the modded primary rail and buy a set of overbored 1300s from someone else's car. The Supra pump is getting to be at its limits at the 400+ rwhp levels. Your fuel pressure may have slight fade as you near redline. This is the area where you may wanna think about dual pumps or a less-drop-in and more race style setup for the fuel pump(s). Rewiring the pump to draw directly off the battery with larger wiring may help.

Upgrade 5 = 850/1600 and will support about 470 rwhp
Somewhat expensive - Your stock secondaries become your new primaries in a modded rail. Buy an aftermarket secondary fuel rail, aftermarket fuel pressure regulator (1:1 boost compensating type), aftermarket fittings as needed, 1600 cc/min injectors, and resistors to use with the injectors. Wire it up, test it out. The Supra pump is getting to be at its limits at the 400+ rwhp levels and is probably not going to cut it up here. This is the area where you may wanna think about dual pumps or a less-drop-in and more race style setup for the fuel pump(s). Rewiring the pump to draw directly off the battery with larger wiring may help.




500+
If you're going for 500+ rwhp, I really hope you're not getting the meat of your advice off this post

 

This sounds low to me.

Let's begin with what 100% duty cycle gives and correct at the end. Assume 2800cc/min or 2.8L/min from stock injectors. Fuel's specific gravity is roughly 0.75, giving 2.1kg/min. At 11:1 AFR, we'd need 23kg/min of air. That's just over 50lbs/min, and our old rule of 7.5rwhp per lb of air states 375rwhp. Drop the duty cycle to 85%, and we're still pushing almost 320rwhp.

What's wrong with this reasoning?

 

Eh, nothing is wrong with your calcs. I'm sure someone has probably done 320 rwhp on the stock setup.

My little estimate is just a rough one and errs on the side of safety. 8D

 

Kenne Belle boost-a-pump is another option if you need a ton of fuel. It works very well on a Supra TT pump. My friend had a 600whp setup on his VR-4 with that, although it would probably only do like 500 on an Rx-7