19# Injectors Enough For This Combo?

ratio411 · Jul 5, 2012

I am rebuilding a 5.0, no stroke, .030" overbore. 306 cid

E303 cam
Edelbrock Performer heads (170 intake runners) (1.90/1.60 valves)
Shooting for 9.5 or 10.0 compression with Probe forged pistons.
Factory Cobra (GT40) intake. (1" phenolic spacer)
65mm TB
Stock 1994 70mm MAF
Aftermarket headers, ORH, MAC Flowpath exhaust.
Auto trans, and 4.10 gears.

I planned on keeping the 19# injectors, figuring everything was so mild, they would do fine.
My oldest son keeps insisting that I will need 24# injectors.

What do you think?

We are hoping for 300 rear wheel HP out of this combo.
Do you think we will be close without doing a stroker?

RangerJoe · Jul 5, 2012

http://www.rceng.com/technical.aspx

According to this calculator....no, 19lbs will not be enough for 340hp (about 300 rwhp). I think that you would have to run about 50lbs of pressure and 100% duty cycle to keep up. 24's would probably be a good idea. I do think I have seen a few guys making close to that on 19's, but who knows if it was safe or not.

Joe

ratio411 · Jul 5, 2012

Thanks for the input Joe.

Actually the 300 rwhp is not accurate info.
I was just saying that we were hoping for 300 rwhp.
Actually I have no idea what the combo is going to do.

So, the 19# injectors will work IF the HP ends up under 300 rw, but if we do reach our goal, 24# would be advised?

Rick 91GT · Jul 5, 2012

Youll need to run them at higher base pressure to make them work, Id personally feel more comfortable with a 24lb inj on that combo.

RangerJoe · Jul 5, 2012

Rick 91GT said:
Youll need to run them at higher base pressure to make them work, Id personally feel more comfortable with a 24lb inj on that combo.

Expert advise right there.

Joe

ratio411 · Jul 5, 2012

Thanks guys!
Will do... 24s shouldn't be too hard to come by.
I have a yard I go to that gets in trucks, and I might just pull a set off a 460.

Do you feel that a 306 set up like this might have a chance at 300 rwhp?
I know that it's harder with the increased parasitic losses of the AOD, but we're hopeful.

We just bought the heads today.
They were previously on an engine, and it appears they have been ported.
Do brand new Edelbrocks have light porting done to them, or are these signs of port work a sure sign that they have been worked on?
The owner had someone else build his engine, and didn't know a lifter from a roller rocker, so I couldn't get anything out of him.
They look like they got a port match anyway...

ratio411 · Jul 5, 2012

These are the heads.
I don't know if the roller rockers are 1.6 or 1.7...
I googled the part number, a Ford number, and the info is mixed.
Some results said they were 1.6, and some said 1.7.
Most all said they were stock on 93-95 Cobras.

jrichker · Jul 5, 2012

Fuel injector sizing & injector photos

Revised 11-Dec-2011 to add larger injector sizes to injector table

Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines at the flywheel.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See http://users.erols.com/srweiss/ to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.

With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.

Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure

Diagram courtesy of Tmoss & Stang&2birds

ratio411 · Jul 9, 2012

No one has an opinion of rwhp this combo might make?

oz · Jul 10, 2012

I think you'll see 300 rwhp pretty easily (see my combo below).

Get the 24 or even 30 # injectors and at least a 190 lph fuel pump. I actually have my very lightly used Walbro 190 lph availble if you're interested (~1k miles on it). I put a 255 lph pump in when I added my blower and have not yet sold the Walbro 190. I also have an adjustable pressure regulator for the stock '87 - '93 rails that I'm parting with (I'm using the larger '94-'95 rails on my blown combo). PM me if you're interested in either/both.

I made 300 hp prior to adding a blower and my combo is:
Stock 5.0 liter short block (9:1 compression)
PowerHeads CNC Ported Stock E7TE Heads (1.90"/1.60" valves)
Ford Racing 1.6:1 Roller Rocker Arms
Hand Ported Cobra Intake w/ 1/2" spacer
Comp Cams XE270HR Cam (.512" lift, 218°/224° @ .050", 114° lobe separation)
Ford Racing 65 mm Throttle Body
Pro-M 75 mm MAFS
Ford Racing 24 lb/hr injectors
MAC Equal Length Shorty Headers
MAC Off Road H Pipe
MAC Cat Back
190 lph fuel pump
Accel 300+ Capacitive Discharge Ignition
Custom AutoLogic Chip by Don Walsh Jr.

oz · Jul 10, 2012

Oh, forgot - you have 1.7 rocker arms.... just do a Google search of the part number (F3ZE-6529)....

Maryland Stang · Jul 10, 2012

ratio411 said:
No one has an opinion of rwhp this combo might make?

Honestly with the exception of the heads you're using Ford's lowest performance cam and factory parts through an AOD. 255 to 265 HP.

a91what · Jul 10, 2012

sadly i have to agree i am going to put 1.7s on my car becouse i run the e303 cam. The cam does sound really good but does not make the power i was looking for. I highly suggest degreeing in the cam to get every drop you can out of it.

Rick 91GT · Jul 10, 2012

It will all come down to the tq converter....that will make or break your combo.

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