Does anybody know what the stock injector size is on the 95 and 96 - 99 Northstars?

Also, if I want to upgrade to bigger size injectors, which options do I have for good quality and value for money?

[This message has been edited by 88GTS (edited 10-30-2007).]

I believe the stock northstar injector is 23.5#/hr.

Thanks Ramdge!

Anybody with recommendations on a good brand and/or source for high flow injectors? Will any Ford Mustang injectors work?

BTW, here is an easy to use Injector Flow Calculator: http://www.z31.com/software/injector.pl

I had a set flow tested and they were 21.6 lbs.

According to Allen at CHRFab the stock northstar injectors are 19lbs/hr.

quote Originally posted by Zac88GT: According to Allen at CHRFab the stock northstar injectors are 19lbs/hr.

Either that's wrong, he tested 4.0 injectors, or stock injectors go static at WOT. That is not enough to support 300hp with any margin.

The only number I've heard and used is 23.5#/hr. When I switched to 24# injectors, there wasn't any noticeable difference in the tune. FWIW...

http://www.injectorservices...taPix/rp17091728.jpg

The stock injectors i pulled out of my motor are Rochester 17091728's. Rated at 202cc/min @ 3 bar, which converts to roughly 19lbs/hr @ 45psi.

http://kgparts.com/kgimages...chester/17091728.jpg

~22.5lb/hr

But I don't trust flow rate checks from used injectors. Who knows whether the cleaning opened the orifices to the same size as new or not.

I can't believe a 19lb/hr injector would be used... The 4.6 ford DOHC (260-300hp) uses 24lb/hr injectors. The LT1 (275-300hp) uses 24lb/hr injectors. 3.4 DOHC (4.6 - 2cyl) uses 24lb/hr injectors. So either cadillac has some crazy BSFC or they're running static.

I guess the values vary depending on where you look. It would make sense that they were 22-24 but i just bought a set of 24's from an LT1 and i'd like to think that they are a little bigger than stock so i don't feel like i wasted my money, hahahaha. This page seems to have a whole lot of info and they list the stockers at 19.2 lbs/h
http://users.erols.com/srweiss/tableifc.htm

If I use the calculator ( http://www.z31.com/software/injector.pl ) for the stock 300 hp Northstar, I get the following based on conservative factory parameters:

- for a Duty Cycle = 0.85 and BSFC = 0.50, the injectors should be 22.1 lbs/hour
- for a Duty Cycle = 0.85 and BSFC = 0.55, the injectors should be 24.3 lbs/hour

...which indicates the 23.5 lbs/hour to be an "accurate" number. The 19 lbs/hour injectors will either run lean or at 100% duty cycle at WOT & RPM.

quote Originally posted by ryan.hess: Either that's wrong, he tested 4.0 injectors, or stock injectors go static at WOT. That is not enough to support 300hp with any margin. The only number I've heard and used is 23.5#/hr. When I switched to 24# injectors, there wasn't any noticeable difference in the tune. FWIW...

There is confusion because 95 inj are rated at 300 Kpa or 43.5 psi and are rated at 23 # per hour and are part number 17091474 or 17109386.

But 98 injectors ( my motor with 95 pcm) is rated at 350 Kpa or 50.8 psi and are part number 17091728 and are rated at 21.4 #/hr.
That small difference of 7% takes about 16% more pressure if you were to try and use 98 inj with a 95 pcm and raise the system pressure to
get the smaller inj to flow like the bigger ones. Flow is proportional to square root of pressure ratio.
If you take the pressure into account, the 21.4 # inj make sense cause they are used at a higher pressure.

Good source for inj is Motor Man inj here in Mich at 989-644-2695 or on web. About $25 ea.

frankc5r
retired engineer Corvette C6R racecar

So you're saying 98 injectors are 21.4lb/hr @ 43.5psi, but installed in a 50.8psi system - giving 23.1lb/hr effective delivery?

If so, I was not aware they increased the fuel pressure during the 95-99 model years.

quote Originally posted by ryan.hess: So you're saying 98 injectors are 21.4lb/hr @ 43.5psi, but installed in a 50.8psi system - giving 23.1lb/hr effective delivery? If so, I was not aware they increased the fuel pressure during the 95-99 model years.

Exactly. I am not sure what year they change but they did. I have shop manuals for both years and it shows the key on
pressure as being different numbers ( 43.5 vs 50.8) and if u look up the the fuel press reg, they have different numbers.
I ended up getting rebuilt 95 inj for my 98 motor and buying a new fpr for 95 motor and when installed, the key on pressure was 43.5 psi
- the exact 95 spec

my northstar w/ 288 cams is running Ford Motorsports 30 lb/hr at the stock fuel pressure (45psi). runs like it's ass is on fire..

So, John, what injectors would you run with the 272 cams I have from you? Same 30lbs, stock or something else?

Been working out some idling issues and a clutch problem as well.

-dave

[This message has been edited by IXSLR8 (edited 11-24-2008).]

quote Originally posted by IXSLR8: So, John, what injectors would you run with the 272 cams I have from you? Same 30lbs, stock or something else? Been working out some idling issues and a clutch problem as well. -dave

I believe that you can get away with even a stock ECM from caddy when running the 272 cams (300hp stock cams are 266), so the stock injectors should do you just fine too. Its with the 288 and up that you will need 30# injectors and a better Air-intake system with a longer set of headers to help compensate for the bigger/longer duration of the cams...

JG

The injector size you need is only determined by the amount of power you are making (amount of air you are moving).

quote Originally posted by frankc5r: Exactly. I am not sure what year they change but they did. I have shop manuals for both years and it shows the key on pressure as being different numbers ( 43.5 vs 50.8) and if u look up the the fuel press reg, they have different numbers. I ended up getting rebuilt 95 inj for my 98 motor and buying a new fpr for 95 motor and when installed, the key on pressure was 43.5 psi - the exact 95 spec

[This message has been edited by Erik (edited 11-24-2008).]

quote Originally posted by Will: The injector size you need is only determined by the amount of power you are making (amount of air you are moving).

Not only that, but the amount of time you have to inject fuel in.

You need bigger injectors when you're turning the engine faster- you run out of time before the next cycle.

Thanks for the input.

I suppose I should have the injectors all tested just to make sure they are flowing right. They sat in the N* for a couple of years before it made it into my fiero swap.

quote Originally posted by KurtAKX: Not only that, but the amount of time you have to inject fuel in. You need bigger injectors when you're turning the engine faster- you run out of time before the next cycle.

If you need the same amount of fuel per cycle, then you're making the same torque. If you spin the engine faster and keep making the same torque, you're making more power. If you just spin the same engine faster, torque & fuel consumption will drop as RPM increases, and you won't require a bigger injector.

Power is the determiner of injector size.