would i benefit from 24lb injectors?

axeman · Mar 10, 2004

so far, even with my minimal mods, it seems that my car likes 51lbs(vac off) of fuel. of course, that could be that the injectors have 160k miles on them and have seen better days. i am thinking about upgrading my mass air meter and wondering if i should step up injectors while i'm at it. even if i don't need to step up, would it hurt me or benefit me at all? i am looking for performance gains, not really worried about gas milage, running a little rich at idle, emissions, etc.........

ECU5.0 · Mar 10, 2004

wow, 52 psi vac off...my car likes 42 vac off...well thats what i run atleast and dont have any problems. id like to know also. i was thinkin about gettin the kit from jegs that is a new computer, mass air, and 24 lb injectors if i need them.

Mike86Stang · Mar 10, 2004

I'd say do it personally... like I said before in another post... my car even just with an exhuast, Intake,TB & MAF liked 52PSI with vac ON

Of course my injectors have more miles on them than yours do.... but just the same. I think you should go for it.

ninety15.0 · Mar 11, 2004

Are you running an AFPR? If so i would say go for it...i think you have enough mods to make use of the #24's especially because they have 160k on em. the only problem is that they are very expensive and it would suck to have it hurt your performance. But if you are running an AFPR you could always turn the pres. down a little bit.

BlackFox5.0 · Mar 11, 2004

Injectors are not exspensive if you know what to look for. I got mine used for $40 siped

IMissMy93Fox · Mar 11, 2004

Go for the 24's that way you don't have to worry about it again for a while.

willys1 · Mar 11, 2004

You guys say your running with 51,,52 psi,and the engine likes it,How do you know? I have full exhaust maf,65tb,,should I increase mine? Its got 36,000miles.,,,,,,Axeman,have you run the 1/4 yet with the 430's?

axeman · Mar 11, 2004

yes i am running an AFPR. injectors are not that expensive because alot of people sell injectors along with the calibrated mass air meter for a good deal. the reason i know my car likes that pressure is from doing a little tuning at the track. that's the only way you can really tell.

willys1,
last summer i ran my 28" street tires with 3.73's and the best i could run was 14.1. i did run with the 4.30's and same street tires a couple of weeks ago and i ran a 13.74. 28" tires really kill your gear ratio. i'm going to the track again this saturday and i'm running my 26" et streets. so, we'll see what happens compared to my previous best on the same et streets. lets just hope i don't run out of gear. i'm going to be ordering new slicks in a couple of weeks, so i may end up buying the new 27" et streets.

Rick 91GT · Mar 11, 2004

Mark here's a formula for ya...

fuel delivery (lbs/hr) = 19 times the square root of [new pressure/calibration pressure]

so your 19#injector right now at WOT is acting like a 22#

I say go for it or 30# and 80mm MAF

axeman · Mar 12, 2004

Rick 91GT said:
Mark here's a formula for ya...

fuel delivery (lbs/hr) = 19 times the square root of [new pressure/calibration pressure]

so your 19#injector right now at WOT is acting like a 22#

I say go for it or 30# and 80mm MAF

a while ago i came across a calculator that gave you that exact information. i was looking for it and could not find it again for the life of me. thank you rickki.

whitemustang89 · Mar 12, 2004

id say go with the new injectors youll only benifit from it

gt90stang · Mar 12, 2004

Hi,

I recently used my Tweecer RT to datalog my NA 306 with H/C/I and 24# injectors. The injector duty cycle was 75% at WOT and high RPM. With 19# injectors it would be at 95% duty cycle (much too high 85% = max. you should run). I run 40# FP with a stock regulator and 190 L/Hr pump.

Once you switch to 24# injectors and/or H/C/I you will have to deal with lots of driveability and idle issues using a stock PCM. All the load tables get hosed and you run more advance sooner due to this. Also all the ISC data in the PCM is way off compared to stock H/C/I and that is what messes with the idle. Most people either work around or just live with these issues. I tuned them out with Tweecer.

Good Luck, Don

axeman · Mar 13, 2004

if i would step up to a 24lb injector, what % duty cycle will i be at. i want a new throttle body too, and wondering if i should wait on injectors until i go to a 30lb.

gt90stang · Mar 14, 2004

axeman,

I don't know because I never datalogged my setup until I put in my new 306. However, 19# injectors can work up to 300 HP at stock 40# fp and even up to 340 HP at 50# fp. At 40# fp these injector can do:

19# 300hp
24# 380hp
30# 470hp
42# 660hp

On your setup I'd go with a larger MAF and TB.

Good Luck, Don

Rick 91GT · Mar 14, 2004

gt90stang said:
axeman,

I don't know because I never datalogged my setup until I put in my new 306. However, 19# injectors can work up to 300 HP at stock 40# fp and even up to 340 HP at 50# fp. At 40# fp these injector can do:

19# 300hp
24# 380hp
30# 470hp
42# 660hp

On your setup I'd go with a larger MAF and TB.

Good Luck, Don

That chart is so off, if you use real world results........

I made around 330RWHP and my 30#'s were at 85% at 6600rpm, 46psi of fuel

gt90stang · Mar 14, 2004

Rick 91GT,

Those are fwhp numbers assuming 90% duty cycle and not rwhp. Also how did you measure your injector duty cycle? Versions of Tweecer software before 1.3A7 had inflated injector pulse widths and duty cycles.

Real World = Edelbrock Performer package = 300 FWHP with 19# injectors.

Don

Rick 91GT · Mar 14, 2004

Well I ran a Speedbrain, that kept track of many features including duty cycle and air fuel ratio...it was right inline with the readings from a wide ban on the dyno.

I have always been told you really don't want to use for the 80% of the injector...

Most of the P/S guys use a 42#inj and are pushing the 80% duty cylce with 415-430RWHP

Don I know you can run 300RWHP on a 19# inj, however I feel it is pushing it and a 24# would be much better. The inj chart has changed over the last 5 years, I remember when a 30# was for a blower car, now you see 50-55# in healthy NA cars.

gt90stang · Mar 14, 2004

Rick 91GT,

I think we are pretty much in agreement as the numbers I posted were absolute maximum FWHP numbers. Yes, normally you don't want to exceed 85% injector duty cycle.

I just feel that with his combo he can keep the 19# injectors for now and get improved performance with a larger MMF and TB. He will also avoid some driveability issues staying with the 19# injectors.

Don

raph130 · Nov 19, 2004

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