Picking fuel injectors... - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
LinkBack Thread Tools
post #1 of 5 (permalink) Old 08-13-2012, 09:18 AM Thread Starter
Registered User
 
Join Date: May 2012
Location: Buffalo
Posts: 22
Picking fuel injectors...

Hey guys,

I'm working on an '87 5.0 and it's going to be a stroker (347 I believe). I've heard the stock injectors won't work... what determines fuel injector requirement?

Also, is there anything out there with info relating to bearing clearance (what I'd be looking for with plastigauge measurements)?

Thanks!
Danny K is offline  
Sponsored Links
Advertisement
 
post #2 of 5 (permalink) Old 08-13-2012, 10:06 AM
Registered User
 
Join Date: Aug 2010
Posts: 251
Re: Picking fuel injectors...

Need more info on your build, but i'll guess you will need 24# injectors at least. and a MAF calibrated for them.

Get your self a Hayns manual. 20 bucks for lots of that little info that you need. torque specs, clearances, wiring diagrams, ect. Not everything you'll need to know but well worth the money. IIRC oil clearance is .0015"-.0035".
firehorse5_0 is offline  
post #3 of 5 (permalink) Old 08-13-2012, 11:22 AM
Registered User
 
Join Date: Jan 2008
Location: Seattle, WA area
Posts: 10,299
Re: Picking fuel injectors...

Danny - Here's the full scoop, and you'll be able to understand everything that goes into injector and system sizing if you want to understand it. Injector sizing is based on the maximum horsepower (HP) you need to feed, and the efficiency of the engine that's making it. The efficiency is generally measured in brake-specific fuel consumption (BSFC), and for a typical street/strip 347 will be in the neighborhood of .50 to .52 pounds of fuel per hour per HP. So, now you see how you can roughly figure how much fuel your engine will need, as 100 HP at .50 PPH would be (100hp x .50) = 50 pounds of fuel per hour. You can also use this figure for sizing your fuel pump and lines.

So, to turn this into injector size, we also consider other factors, such as the extra fuel when the engine is cold, extra fuel for acceleration enrichment (pump shot), and system degradation. We use a rule-of-thumb of 15% to compensate for these additional requirements. This buffer is called Duty Cycle (DC), and is the amount of time the injectors are ON (open) for normal full-power operation - leaving that extra buffer. So, we are looking for injectors that can supply full power at 85% DC. That leaves us with a simple formula:
(HP * BSFC) / (#Injectors * DC) = PPH per Injector
An example of this would be a 347, making 450 peak HP, with matched and efficient intake, heads, piston dish and exhaust for better BSFC of .50, and port injected with 8 injectors. The calculation would be:
(450 * .50) / (8 * .85) =
225 / 6.8 = 33.088
We can round that off to 33 pounds-per-hour per injector. To convert to CC/minute for injectors rated that way, it's roughly 10.5 cc per PPH, so:
33 * 10.5 = 346.5 CC/min

As we can alter fuel pressure to change flow rate, we could use 32 pound injectors with about 3 psi extra fuel pressure to get 33 lb/hour - if necessary. The extra margin with our 85% DC may be sufficient with 32 PPH injectors. Likewise, we could use 380cc or larger injectors and drop the pressure a bit.

For your bearings, use minimum to average stock clearances for street operation, and only larger (max stock) clearances if you are planning to rev really high. The extra clearance is to allow more oil to leak past the bearings for cooling with very high power or revs, or extended power modes like offshore boat racing. HTH

David

-=≡ If it was easy everyone would do it ≡=-
[size=1]HotShotsJava.com Hot Shots Java Coffeehouse, Poulsbo ,WA fair trade and 100% organic. Voted best espresso and coffee![/size]
PSIG is offline  
 
post #4 of 5 (permalink) Old 08-13-2012, 01:21 PM
Registered User
 
Join Date: Aug 2010
Posts: 251
Re: Picking fuel injectors...

Memory has failed me. Alowed .001-.002 on#1, and .0005- .0024 on the rest.
firehorse5_0 is offline  
post #5 of 5 (permalink) Old 08-13-2012, 02:16 PM
Registered User
 
Join Date: Feb 2004
Posts: 3,658
Re: Picking fuel injectors...

I second what David said - and remember, going a little bigger is okay but don't go much bigger or you'll never get the car to idle properly, because injectors have a minimum amount of time required to open and close and also a minimum amount of fuel they can inject, so it's possible just opening and immediately closing a too-large injector (min open time) may still be too rich for a good idle.

Wesley

Operation EFI:
http://connecting-rods.blogspot.com
thekingofazle is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Muscle Forums : Ford Muscle Cars Tech Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Fuel Injectors bugpuckey Falcon Pages 1 09-05-2011 08:27 PM
5.0 fuel injectors indianjoe Mustang Pages (1979-1995) 1 04-08-2009 03:22 PM
fuel injectors flocko Mustang Pages (1979-1995) 2 05-02-2008 04:04 PM
NEW FUEL INJECTORS SPEEDLEECH All Ford Techboard 2 09-10-2003 09:50 PM
5.8 fuel injectors help Modified Mark Late Model EFI Techboard 3 08-07-2002 09:13 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome