Whitey

Thanks for the info Smitty. I need a 2 inch spacer and am looking around for one. I am just not ready to buy it new....yet.
Are you staying at Brower?
We are heading there on Friday. Hope to see ya there Dwight

articfriends

I wil be at brower all weekend,look for a red 06 duramax 4dr pulling a 272 baja named "never enough_____?" or if out on the water flag me down,Smitty

SB

I'm not sure if you accounted for the following:

Don't forget to subtract boost psi (intake psi) from fuel psi to figure out actual psi at injector .

Example: 75psi fuel measured at rail minus 10psi boost = 65psi actual at injector.

Whitey

See ya there!
Dwight

articfriends

I've never accounted for that but you bring up a very interesting point and something for us all to think about factoring in. Kurt will be watching his a.f.r and egt's on the dyno when making his pulls plus adjusting his fuel tables so he probably won't melt motor down if injectors turn out to be too small but it would suck if he had to rip motor apart and change them half way thru his dyno session,Smitty

articfriends

I ran my numbers thru the calculator,unfortunately I don't have bsfc from the dyno because Crockett doesn't measure it when doing EFI motors.
I'm using 63lb injectors at 75 psi under boost,they become 82.7lb injectors from 75psi and 77lb injectors if pressure is changed signifigantly from the 10 psi of boost I'm running to 65psi.
82.7lb inj will support1058hp at.5bsfc,882hp at .6bsfc 77lb inj will support 985hp at .5bsfc,821hp at .6bsfc
My motor made 944hp/962ft lbs tq with a correction factor under 2% so either my bsfc is between .5-.55 or dyno was incorrect. I do know that Crockett checked the calibration after we made 900 plus ft lbs in the first pull to 4800 rpm's because he was in disbelief,Smitty

SB

I believe the .6 BSFC's used really aren't accurate anymore. Remember how people thought near .5 was normal for NA BBC ? Well, today we are in the lower .400's due to better components and better understanding of stuff. Oh, and this is with carb's too .

Now, add into the equation much more effecient centrifugal SC's with big intercoolers and the .6 BSFC's (typical roots , carb's, older engine parts) for the most part dissappear.

Also, old thinking said 'add way more fuel then you need' to keep detonation at a minimum.

Anyway - as you can see with your math, a difference in injector needed at .5BSFC is much different tha at .6BSFC.

Those equations are to give you a baseline to go from when deciding what injector size you'll need when planning an engine build.

Last important notes:

1) You need to know what psi the manufacturer uses when rating each certain injector

2) You need to know how accurate / close to those ratings your injectors actually are. Some manufacturers/models of injectors are a lot 'looser tolerance' than others.

3) The dyno or vehicle w/measuring equipment will ultimately tell you what's happening.

SB

Smitty - did he atleast use the fuel flow meter ? If not, I guess this explains why no BSFC's.

cstraub

Smitty,
You may want to check these guys out:
www.metalax.com

Elite Marine

Great info guys. I fear i may be a little small on the injector sizing, I'd rather go larger with less fuel pressure.

60 Lb/Hr injectors should be correct.