So I read the post on injector sizes which is stickied at the top, and came out with two numbers, and I'm curious which is right, and what injectors would work. First a little background:

My engine is a 385 stroker, HSR intake, AFR 195 heads, compresison of around 10.5:1.

The first of the two numbers I've gotten is derived from HP * .50 / 8. I'm expecting 500-550HP at the crank at the max, so that works out to 34.37, so rounding up I'd get #36 injectors.

What worries me, is that there is another post, in which someone says to use this equasion:

injector flow = [(engine Hp)] x BSFC / 6.4

Which works out to 42.96. That's a rather large difference between 34.37 and 42.96.... So which should I go for? Would overkill be a bad thing, just running the injectors at a shorter duty cycle shouldn't hurt them.

Also, I can't find information on what type of connector and specific part numbers of injectors that will work, I keep hearing about Ford and Bosch injectors... but there are quite a few with different connectors and heights. Any information would be greatly appriciated.


Edit: Nevermind found my answer.

 

For the benefit of others who might be wondering the same thing:
The two equations for fuel injector sizing are really the same equation! BSFC = 0.50 for typical SBCs and the 6.4 = 8 injectors at 80% duty cycle (DC). The equation in full is:
injector size = [(eng HP) * BSFC] / [(# of injectors)*DC]
for example, if you expect to make 500 engine Hp, we get: 39#/hr injectors.
Now you could buy 36#/hr injectors (rated at 45psi) and run them at 54psi with an AFPR.

 

if you are looking to run closer to 500hp this is what you will need:
hp at the flywheel: 500hp
BSFC: 0.5
max duty cycle 80%
43.5psi
39lb or 40lb injector
If you are going to be closer to 550hp
you will need a 42lb injector

 

if you have the 87 TPI setup you have EV1 style connectors
Delphi is the manufacture all others re-labl & re-sell Delphi injectors
the HP to CC or pound info is correct

 

PS
always choose larger then what you need (like a battery)
you can set the flow in your programing to the correct # and adjust your fuel regulator accordingly it is much better not to go above 80% duty cycle and over working your injectors

 

here is a really good calculator that I use. BFSC from my understanding can be between .4 and .5 on NA motors. I never got a straight answer from that, depends on whom you talk to....but this site even has a chart, move your mouse over chart to read specific numbers.
http://www.gtsparkplugs.com/InjectorSizeCalc.html

oh, and for the duty cycle percent... use decimal style. like 80% is 0.80. (that confuses me every time for some reason, lol)

 

The link you sent on injector sizing is perfect..
you have to decide if you current car up-grade is your final
if your engine is rated @400 HP
it is wise to plan ahead so choose 500HP
it is wise to select 0.50lbs BFSC
it is wise to stay under 80% injector duty cycle
your injectors will easily accomplish their job if you select above your calculation within reason

you can adjust your fuel pressure and your ECU injector rate flow

If i were you I would read all the horror stories.. I found many import & domestic engines trying to save money buying Venom injectors

Delphi is the manufacture.. aftermarket performance like MSD, holley purchase from Delphi

 

as i mentioned in my post...at 500hp with 0.5 BFSC he is going to need an injector that is about 39lb, and the bosch injectors would definitely be the way to go.

 

I called fuel injector connection and told them exactly what I had/how much power I was expecting, and they sold me a set of injectors. I don't actually recall what size they were, but in a day or two when they get here I'll post what they are :P.

I do know they're bosch ford injectors.. that's all I can recall though.

 

Alright my injectors arrived. They are ford red top 30lb injectors. Jon at fuel injector connection is the one who specced them out for me. I told him exactly what I had and how much hp I thought I was going to make. This does seem a bit low after reading the posts here... but fic comes highly reccomended from this forum so ill trust he knows what he is talking about.

 

if you plan on running 400hp the 30lb injectors will be fine

 

I told him 500-550hp... does fuel injector connection not know wtf they are talking about and should I return them?

 

you should absolutely return them


If you really have 500 HP
you will stress 30# injectors way over 80%

you cant get every pound rating out there so you knew you need around 36 - 39 #
so get 40# injectors the moral of the story is it is safe to go over you can use a AFPR
or cut the # rate back in your prom

unlike using a carb that is to big

just like a battery if you only need 300CCA to start your car
and you buy a 900CCA battery the battery will easily and effectively accomplish it's job

PS you will need to upgrade your fuel lines to 1/2 and I hope you have a real fuel pump

I fried a brand new projection pump with 1 full throttle run

 

Ok, for the third time....if you are going to run approx 400hp then a 30lb injector will be fine.
If you are looking to run between 500 and 550hp then you need at least 39-42lb. Go and check out any calculator. Ours is not up and running on our website yet otherwise i would tell you to go there....but go to RC fuel injection and plug in your numbers and you will see what you will come up with. Their calculator is reliable!!!!


www.southbayfuelinjectors.com

 

you could prob get 460 FWHP out of 30lb injectors but that would be 80%DC and the AFPR set to about 60lbs

 

I dont want to get to critical here but, I don't believe that combo makes anywhere near 550. heads and cam ls1's have a tough time doing it. Stock pistons, etc.. its lower believe me. Look at TPI-Formula350s profile. He has more engine than you and runs the red Ford. If you got red tops they are 32 because ford rates them at 39.15.. At 43.5fp they are 32. You have a AFPR and your DS climbs increase the pressure.. At 58 they are like 36. When you talked to FIC did you go over your engine build? He knows what these make and would steer you to the right injector which will support your motor. This is a street car, Right? How long are you going to be at WOT anyway to worry about if the injectors jump to 90DS? Who told you you have more HP than a new ls7 anyway. Here's what you do put it on a scanner and see what the injectors run at. Do not over inject a motor. All you will do is make more problems.. Be honest and list all your mods just to make sure. I built a ton of these so I will tell you honestly what I think. Also look at this link from Golen Engines.. DOES YOUR ENGINE COMPARE TO THIS>
http://www.golenengineservice.com/sp...402_550tk.html

 

Lingenfelter tuned My 92 Z28 383 475hp 490fpt With 30lbs injtrs
ran fine for 8 or 9 years.

 

for a street car i would not want to use a bigger than necessary injector, unburned hydrocarbons washing down cyl walls. ending up in oil etc will prematurely ruin your engine. I laugh when I hear put in big ones and tune it down, this is such HS, the Bosch 42 doesn't work below 1.2 ms so you can't get it lean enough on idle. All you get is a loaded up idle.. All the formulas are great especially RC Eng.. as southbay said its reliable.. But, the first figure needed to calculate the right injector is HP. So if the HP is off by 20% the injector will be off also. So, the only way to know if your right, is to guess close and then scan it. When you get accurate numbers then you can get accurate injectors.

 

I told FIC exactly what was done to my engine, and told him what the engine builder who built the long block thought it would make (500+hp). He did not argue/correct me, so who knows. This is a street car, so I'm going to spend very little time at WOT, probably only when I'm at the track.

Here are my mods:
385 stroker engine
HSR Intake, stock throttle body
Flat top pistons with decked block
AFR 195 heads, port/plolished with, 64cc chambers
10.5:1-11.0-1 compression guesstimate by machinest.
3200rpm torque converter
I'm 99% sure this is the cam I got:
http://www.compcams.com/Cam_Specs/Ca...?csid=210&sb=0
I'll have to find the spec sheet and make sure, but it's either that one, or one level down from that.
2-1/4 dual exhaust (I know this is a limiting point here)

Anything I missed just ask.

 

Sounds like a nice engine, your cam is one size larger comp XFI then mine..I dont see it making 550HP. Something closer to 475 at the flywheel sounds more like it. Only way you know for sure is on a dyno.

Here are my mods:
385 stroker engine
HSR Intake, stock throttle body
Flat top pistons with decked block
AFR 195 heads, port/plolished with, 64cc chambers
10.5:1-11.0-1 compression guesstimate by machinest.
3200rpm torque converter
I'm 99% sure this is the cam I got:
http://www.compcams.com/Cam_Specs/Ca...?csid=210&sb=0
I'll have to find the spec sheet and make sure, but it's either that one, or one level down from that.
2-1/4 dual exhaust (I know this is a limiting point here)

Anything I missed just ask.[/QUOTE]

 

Any sound clips?

 

Hmm, I'll have to wait until I get it up and running and dyno it. The injectors were reasonably cheap (compared to how much money I have in the rest of the car) so maybe I'll just put them in and keep an eye on them, I can always replace them if I start getting near their limit.

You said you had one size smaller cam, how does it start and idle? I've never run a fuel injected car with a big cam before.

Unfortunately not, the car isn't running yet! I'll post one if I ever get it running though.

 

engine is still being built , goes on the engine stand dyno in a week or 2

 

the HSR is Great start... I welded a 3/16 bead to mine to accept a 1206 race intake port to match my heads
if you purchase heads with a 1206 port... your HSR Intake will not cover the 1206 intake port and leave a gap

i just ran your cam timings in software engine dyno as a simple guideline
that cam makes no scene for a stroker motor and makes no power compared to a comp cam 08 306 8
your compression will not be above 10.5 with only flat tops and 64CC

I have .125 domes with 64CC and make 10.90 -11.00

your engine maybe 479HP 30# injectors are still slightly small to support your combo unless you crank up you AFPR and over work your injectors
and who wants 50 - 60 PSI on their street car

I had 30# injectors @ 46 PSI on my engine for a week it was way to lean.
and had a lean knock no where near enough fuel supply
and I program myself and use my installed 02 meter I dont need someone to guess what I have

overall your car will be alot more fun to drive.. if only the 80'S did not smog
and cut the power

enjoy

 

i agree but don't agree. 58psi fuel pressure is better since the head pressure of the stock pump is 65, all chevys with ls engines run 58psi from the factory. The injectors at 58 will be 36 and will idle perfect and support that engine. Give them a try at that pressure you wont hurt them

 

I do not have a stock pump I do not have a useless in tank pump
I have a Aeromotive external pump And i do not need my pressure any where near 50PSI or 60PSI
my combo is flawless

is this the reason why you need to crank your 30# injectors up that high
if you re set your PSI to 35 - 40 your engine is most likely starving if you have over 475HP that would indicate you are over working your injectors

unless you have a brand that really flows 30# @ 50PSI

you only need to jump up to that pressure if your injectors are to small
or if you have a forced induction combo

I have yet to see a better performance cranking up my pressure that high on any combo I built

 

[QUOTE=88gta3508;4412028]I do not have a stock pump I do not have a useless in tank pump

my combo is flawless ....lmfao!

He'll be fine with 30lb injectors at 58lbs

 

[quote=TPI-Formula350-;4412044]
YES he WILL still slightly to small injector size


LMAO what are you laughing at hm ohhhhhhhhh your combo must be making at least 900HP I did not know that was U ROCK U LOL

 

If Lingenfelter says it works then it works

no I dont make 900 HP ..lol.. more like 475 FWHP... but Thanks

 

Now here is the question that I notice no one is really mentioned. Is the numbers fly wheel horse or rear wheel horse. That would make a difference. A motor producing 500 flywheel may only make 400 rear wheel. So then the calculations for the correct injector size changes. There is no specification listed which one to base numbers off of.
I based my numbers off of my rear wheel horse, and the numbers came out to 30lbs, if I base off flywheel , I need more like 38-40lbs. Need to take that into consideration.

 

True... I was refering to flywheel HP but with the AFPR set to 58lbs.....If he runs stock fuel pressure he'll need a bigger injector like u stated.. I was just sayn he could use 30's if he bumped his pressure upto approx 58lbs making 460-470 FWHP.. reading ur sig I see your makiing 494HP and using 30's yourself...
How do u like that 280XFI cam??, having that cam installed in my new 383

 

yeah, I made just under 500 flywheel horse (and about 380 hp at the rear wheels).....with the 30's on mine...my tuner (since I don't tune the computer myself) suggest the 30's and I went with them...hopefully mine aren't too small either...but I think I based mine off rear wheel power. I run 45psi on the lines.. but it runs out alright, no dead spots and doesn't feel like it's running out of fuel.
LOVE LOVE the cam. Runs out great. little doggy out of the hole, but get it around 2600-3000 rpm it start pulling hard, and runs out to 6500rpm, and still pulling hard when I shift. Sounds awesome at idle, very nice lope, and is streetable for sure still.