i am building a 355 TPI set-up i was wondering if 40lb injectors or 28lbs would be better. i am going to be putting a stockish type cam in. just wanted to see what would be more worth my while.



Steve

 

There are several online calculators for this. There is some science behind picking injector size. Its not one of them black magic things like cam and heads.
http://www.witchhunter.com/injectorcalc1.php4

A 28lbs would support up to around 360 hp.

 

30 lbs would be enough. I am running 30's and making 470 horse

 

Are you guys running some kind of fuel management? My expirience is that the stock ECM wont handle more than 24#. We tried MSD 55#, Vortech 36# and even Accel 26# and none worked out for us. We ended up using Ford's (green) 24#

 

IS'NT FORD GREEN TOPS 42 NOT 24
BLUE TOPS ARE 24
RED TOPS ARE 30

 

I'm running 30 lbs red tops with my stock 7730 computer and my own custom chips. No problems here. The stock computer will handle any high impedance injectors (16 ohms each). It will not work with low impedance injectors (4 ohms).

 

but will having the bigger injector be over kill. like will the stock computer think its the smaller injectors and start flooding the engine. or should i reprogram the chip so that it would run better. or would it be better to just use the smaller ones.

 

probably should use the smaller ones, imo

 

to be honest with you i think that if your gonna spend the money on the injectors i would go with something better the stock injectors are only 19 lbs per hour

 

If you go bigger than stock (1 or 2 lbs "should" be ok, may little rich on some sidess... but it will work)
But if you go 28lbs or 40bs you need to change that in the PROM orelse it will run all rich and you could take a bath behind your car..
If you go bigger, its the best to change it in the prom to proper fuelling..

 

From my understanding, too big of an injector will not beable to handle the small injector pulses by the ecm at low speeds/low loads. you can have 60 lb injectors and program the ecm to say it has 60 lb injectors but it still doesnt mean everything is gonna be ok. Low speeds/low loads on mild motors require little fuel but the ecm cant inject that amount with big injectors. Theres only so little fuel that a big injector can squirt out.

You can error on the larger side if need be but cant be too much larger than needed. for stockish type cam 355, 24 lb injectors is all you need. 28's are overkill but usable. 40's are very hot cammed 383 level *500hp* I plan to run 42's on my car and i could probly get away with 36's

whatever you choose, its best that you program the ecm for the injector you use. stock 350 bin is 22lb injectors. you can run 24's ok on stock programming but its gonna be rich

 

ok then that would explain why the car is running rich now. i already have both injectors the 28lb and the 40lb so i think i will be using the 28lb. but if i reprogram the ecm for the 28lb would it run ok or still over kill

 

it should be ok. what make injector is that? i never heard of 28's before unless its LS1 injector

 

Hmm.... starting to get worried on my injectors then... The one who sold me them told me that it would be fine to use larger injectors if I change the inj. constant in the prom.. maybe thats why Im having trouble with my car ?!

Thread about my problem : https://www.thirdgen.org/forums/tpi/...m-shaking.html

Dont want to buy smaller injectors if it isnt my problem.. payed alot for thoose injectors i have now,, changed them last year....

 

you know i am not sure who makes them i bought them from one guy on here ill have to look to see if i still have the pm
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ok found the pm he said they are 19# injectors are those stock?

 

Yes you are right, sorry for the missunderstanding. 24# are blue!

Stock prom and larger than 24# in our tests wont work

 

19lbs injectors are stock for a Chevy 305 TPI and a Ford 302.

 

ok so 19# is the stock ones

 

Im running Ford 30s in my stock computer chipped 89 formula 350.
No probs at all. its a huge ci small block tho...

 

do you notice any power gains from having the bigger ones in or not really

 

Bigger injectors will not give you more power by themselves. Bigger injectors will only give you more fuel. If you have the air to go with it, they will allow the engine to make more power by keeping it from going lean. If you dont need the extra fuel, then the engine will be harder to tune, because it will run richer.