Injector question

[IanSzgatti]

I found a formula for calculating injector size for any engine. So the whole formula looks like this

HP x BSFC = lbhr divide by #of inj. divide by .8 to get final injector size.

thats awsome.. thanks for that


Instead of starting a new thread, I have another question that will be a breeze to answer....
when i get these 3400 intakes im going to start taking some metal out of them.... thing is, I don't know how much is too much...
I ported my SP intakes once, and then did it AGAIN! After the second time, i feel like I lost some mid range, until about 4500 rpm when i could feel a noticeable increase... i understand the gearing and all.... but i think i created worse flow in some ways...
I want to port the 3.4 stuff though... so i'd like to know how some of you have done the LIM runners... im guessing i'll just go get some really long dremmel style bits?? i dont want to ruin atomization of the fuel or something... or create too much turbulence...etc

[JMo60]

But I thought the DSM guys use our MAF's from 3100's and such as an upgrade?

touche' its an epihany

[IsaacHayes]

But I thought the DSM guys use our MAF's from 3100's and such as an upgrade?

[JMo60]

Dont quote me on this, but im fairly sure that Jap MAF sensors run on a 5 volt reference, and GM is the oddball that runs on frequency

[91parkave]

the reason for that is that MAF sensor cars supposedly run off of a frequency, and not 5volt reference

True but you forgot the SAFc is also made for cars with MAF's its got the formula's for most jap cars that are MAF equipped but matching that to the SAFC with a GM maf and then matching a ouput signal as well that the ECU can read best of luck

[IsaacHayes]

Save your money on the mail order tuned ECM. Use that for better intakes, heads, cam, etc. Then when you are ready to get serious and have done that work, get a tuner. It's worth it in the end to do it right. Then you can always adjust it for any mod you do and really, really fine tune it. And any other vehicle you own. Laptops can be found cheap. Sometimes free if you look in the right places.

[JMo60]

My SAFC isnt worth a damn, I still havent been able to figure out how to use with GM maf systems i just use it for to monitor other engine paramters

the reason for that is that MAF sensor cars supposedly run off of a frequency, and not 5volt reference

[lampy]

Injector size formula

I found a formula for calculating injector size for any engine.
HP x BSFC = pounds of fuel per hour

HP is horse power your engine will produce (be realistic)

BSFC is Brake Specific Fuel Consumption, (how efficient the engine is)
naturally aspirated carbed use .48-.55, NA EFI use.45-.50,
forced induction carbed use .62-.66, forced ind. EFI use .60-.65
Example 300 hp x .50 = 150 lbhr.
Divide 150 by number of injectors 150/6= 25 lbhr
The 25 lbhr is at max duty cycle to produce 300 hp. You want to run the injector at about 80% so divide 25lbhr by .8 to get the final lbhr for your injector.
25lbhr /.8 = 31.25lb hr
So the whole formula looks like this HP x BSFC = lbhr divide by #of inj. divide by .8 to get final injector size.
Found this info in a book called "Building & tuning high-performance Electronic Fuel Injection" Author Ben Strader.
I'm not sure how to find the exact BSFC But the book gave the numbers I posted. It's a pretty cool book with alot of info on how the sensors and computer work together.

[91parkave]

good deal remember cars that run 15psi+ can use 60lb injectors, but any N/A v6 stock displacment motor that runs on gasoline wont need more than 36lb injectors at the most. good luck on your mods though.

[IanSzgatti]

91parkave... if you happen to read this... what the hell is a PCV mod...

[IanSzgatti]

Remember you are not driving it WOT all the time so you need accurate idle and part throttle AFR

tuning seems to expensive.. first you need the DHP, which as i've seen seems to be the best for my application, then i'd need a laptop computer or something.... thats like 1300 bucks....
for the price, im just thinking i should try to order one of those PCMs buddys got here on the site...i've blown a hundred bucks on lots of useless shit, so i guess that would be worth it.
im going to f%#k my transmission good... i can feel it coming. anyways, thanks for the suggestions...

the guy that told me this stuff is actually a good tech. lots of experience, but NOT a tuner... he is still insisting though, so i need to find the best way to explain to him that he's wrong... because on your guys word here im not going to strap those fire hoses on my car if it's going to run like ass... i dont care about my transmission, but i dont want cylinder washing.

[IsaacHayes]

Funny that you say the stock tune is on the rich side. Cause with my 3400 lower, and 3500 upper, the BLM's are still pulling fuel back. I figured it would be adding fuel over the stock tune, but it's not.


Don't swap any bigger injectors. Especially not 60lbs!! LOL
Just people that do 3400 swaps that use the 22.5lb and higher FPR without putting their old back in notice that it doesn't run that well. Some say it's fine but if they were to swap back to stock it would be better.

You are not at the limit of the ECM yet. And when you are and NEED bigger injectors you will still need to tune for them. Remember you are not driving it WOT all the time so you need accurate idle and part throttle AFR. You don't want to be flooding the crank case with fuel and thinning out your oil and ruining your bottom end. Or fouling up your plugs and dirtying up everything.

[IanSzgatti]

ok thanks

[91parkave]

My SAFC isnt worth a damn, I still havent been able to figure out how to use with GM maf systems i just use it for to monitor other engine paramters

[JMo60]

Especially if your car has MAF. it will compensate pretty well fuel wise for what mods you have