Injector sizing

[szewczyd]

I right now have PTE 780's and my injector duty cycle is 97% and I am only running 20 psi. I am planning on stepping up to a larger size and I am planning on steping up my turbo to a gt35r. I was thinking about doing 1000cc injectors would these be an overkill, also if I don't get the gt35r right away will the 1000cc be way to much for my sc61? What do you guys suggest?

 

[crunchymilk]

since you're running DSMLink get the biggest you can find. With a simple clicks of the mouse they behave like stock, but provide all the fuel you'll need. Why put yourself in a position to have to buy bigger later? Buy as big as you can find.

 

[pneumo]

What a coincidence, I just got fic 1000's to go with my new GT35. I guess it's a good match. Before this I had Denso 720's with a 50 trim and it was pushing over 95% DC at 25psi on pump gas.

 

[szewczyd]

Awesome guys you both were great help! I guess now I need to shop for some 1000cc injectors!

 

[99gst_racer]

szewczyd & pneumo - What are your guys' airflow numbers? (lbs/min)? And what's your AFR looking like?

 

[szewczyd]

I am unsure of my airflow numbers and my afr casue my wideband is being dumb and I don't really have much of a tune right now, I am waiting to go to AMS on July 26th for a full tune.

 

[pneumo]

I was seeing about 2200Hz on a hacked 2G maf, if that helps any. No wideband, so I don't know the actual A/F ratio, but my eprom chip is set to 10.8 and I leaned out the SAFC by about 5%.

 

[2gGSX]

I was seeing about 2200Hz on a hacked 2G maf, if that helps any. No wideband, so I don't know the actual A/F ratio, but my eprom chip is set to 10.8 and I leaned out the SAFC by about 5%.

95% IDC on Denso 720's (which actually tend to flow more, but assume 720) with a 10.8:1 AFR (if the chip is working correctly) gives you approximately 49.46 lbs/min airflow (assuming .76 spec gravity for pump). That puts you near the limit of the 50 trim, so you've got yourself a crazy setup going.

The GT35R is rated for a bit over 60 lb/min airflow (http://not2fast.wryday.com/turbo/maps/gt35rcompress.gif) Thus, to get a max of 95% IDC at 10.8:1 w/ a .76 specific gravity flowing the full 60 lb/min airflow, each injector should flow 873 cc/min (60 / 10.8 / .95 * 454 / .76 / 4 = 873). In all actuality you will be flowing 830 cc/min each injector, for an overall flow of 199.2 lph. Thus, you should also double check that your fuel pump can support this number at whatever boost level you're looking to run to even get the 60 lbs/min.

Let me know if you need help figuring anything else out.

 

[pneumo]

95% IDC on Denso 720's (which actually tend to flow more, but assume 720) with a 10.8:1 AFR (if the chip is working correctly) gives you approximately 49.46 lbs/min airflow (assuming .76 spec gravity for pump). That puts you near the limit of the 50 trim, so you've got yourself a crazy setup going.

HAD myself a crazy setup, yes. It got wheelspin on a roll in first gear when the weather was cool. I sold off the major mods, put the car back to stock for smog, now I'm building up a bigger setup.

The GT35R is rated for a bit over 60 lb/min airflow [url, Thus, to get a max of 95% IDC at 10.8:1 w/ a .76 specific gravity flowing the full 60 lb/min airflow, each injector should flow 873 cc/min (60 / 10.8 / .95 * 454 / .76 / 4 = 873). In all actuality you will be flowing 830 cc/min each injector, for an overall flow of 199.2 lph. Thus, you should also double check that your fuel pump can support this number at whatever boost level you're looking to run to even get the 60 lbs/min.

My thoughts exactly. OK so check my math, please.

I'm running a Supra pump which is rated at 290lph@43psi and 260lph@58 psi according to the tech tips at RRE. I figure the pump should put out around 240lph with a base pressure of 40psi plus about 25psi of boost. I'd like a little safety margin in case I go crazy and try to use 30psi of boost on pump gas. Add in a few psi of pressure drop through the fuel lines + filter and the flow might (guesstimate) be down around 220lph. FIC rates their injectors at 48psi, so factoring a base pressure of 40 brings their flow down to 913cc.

 

[2gGSX]

The Supra pump I'm guessing will be fine, but I'll run through the calculations for you. Based on my data (from an excel sheet on here, verified by Kevin Jewer's tables), you can model the flow of a rewired Supra pump from 43 to 73 psi fuel pressure fairly accurately with the equation y=388.8789/[1+.11554e^(.023059625x)]. Thus, at 25 psi boost, or 68 psi fuel pressure (43 + 25 = 68) you will flow 250.2 lph. Once again assuming the data is correct the equation will give a very accurate number for x fuel pressure between 43 and 73 psi fuel pressure.

I would keep your base fuel pressure at the stock 43 psi unless you have your own reasons--your pump will be able to handle your injectors and then some. Even if you do lose some flow through the lines, filter and what not, you will be completely fine running your injectors to 100% IDC (or beyond, theoretically).

Let me know if you need anything else.