What mods did you make? Your profile shows a CC503 and LTs.

 

You log data or take your tuners word for it. A good way to check is a 2nd gear pull till red line while logging data. For C4's 86 to 94 Datamaster will allow you to use there data logger for free for the first 20 sessions but you will need a cable and a laptop. 92-95 can use Free Scan as well For the 96 OBDII you will need an OBDII complaint scan tool and are probably better off just getting the car dyno tuned unless you want to start tuning your own car.

http://www.monodax.com/mxscan.htm

http://www.andywhittaker.com/ECU/Fre...0/Default.aspx

http://www.ttspowersystems.com/DataM...downloads.html

 

PM sent

 

Have the 28# LT4 injectors on my MTI 396 LT1. 415RWHP/425RWTQ. Fuel pressure set at 50 with high flow cats - 53 with off road pipes on.

Low 11's 1/4 mile, low 7's 1/8 mile. 3000LB car weight. No problems with these injectors.

 

I rest my case!!!

 

Guys, I have 24LB injectors, guess I'll need new ones based on my build.

Can anyone tell me I don't. Please........

 

jsup, talk to alvin. he knows your setup, he knows hundreds like it. he's seen several thousand+ setups, he's been there done that.

when you told him you had 24#ers, when you ordered your chip -- what did he say?

mine are effectively 26.5# and i'm plenty fine. you may be on the cusp with some headroom to spare. really though -- datalogs will prove it out. like fd2blk said -- a 2nd gear pull thru WOT -- alvin will want to see 4 of these in a recording. (the other recording should be a 20 min. run, "normal driving"). i don't think there's any reason to panic right now.

the op has gone in the other direction - 30# is likely unnecessary and he;d have to adjust up the fuel pressure well past stock to get correct atomization. i honestly think you're fine for now -- again DATALOG IT.

 

The part is FMJ-47 Standard brand. I think they may even be 22#. I bought them from BADDUCK, he corrected me in PM. I'm trying to find out. There's little information on them on the Summit website.

It's all research at this point. I don't want to change them. I may have to change them.

 

you won't know anything until you actually datalog. so for now, relax, no worries. the formulas are too dependent on the BFSC value, and you have no real idea which value to insert -- the outcome varies widely. the formula tends to way overestimate the injector size needed. forget research -- 22# 0r 24# whichever -- DATALOG is mandatory, opinions are not.

 

The OP hasn't "gone" anywhere. Just gathering info to make a decision.

 

good, then stay put

 

I found that there are other things that play a role when looking at D.C.
"Inj.Flow Rate" (setting below actual inj. size)in the tables/tune, fuel pressure, "PE, AFR vs. RPM" (in the tables/tune), and rpm at which you look at DC. On mine w/24#s 350ci. and modded (see sig.) I was able to keep it below 90% DC from tweaking the above stated. It doesn't see almost 90% DC until I am up past 6k. The effect of increasing F.P, will lower DC. (compensations will then needed in the closed loop area of the tune).
Like tornado mentioned datlogs will answer the questions.

 

Yeah......I know that.

And the formula implies that the 28LB injectors isn't enough for 400 CHP......and I'm pretty certain that ain't right!

KW

 

I have stock LT-4 injectors on my 396 with 420 RWHP/ 400 RWTQ with zero problems.

 

I have quoted this before. Back when Motorsport Technoligies Inc. was still messing with LT's, Jayson, the owner, said 24's can support up to 450 chp n/a. So that is pretty much most head/cam combos.

 

I spoke to Alvin. He said that the 22LB "should be fine" but to get a data log. The only place this can hurt is at higher RPMs.

 

On the absolute best quench v8 (bsfc of .45) and at 90% duty cycle, 400 crank HP about 22-23# injectors with a WOT rail pressure of 50psi.

The calculator from rceng.com is the one everyone uses. There is no need for a 'different formula'. the BSFC is a huge thing to consider. Heat, bad quench, etc will all directly effect the BSFC of the engine in question. Folks like ski_dwn_it have run stupid-fast ETs with 24# injectors with no problem, while others have run the same ET's and needed much larger injectors because the motor wasn't as efficient, had cooling problems, etc.

My 355 for example, needed 36# injectors at 50psi to run 120mph passes because the boost + the iron sportsman-II heads put the BSFC
to something around .60, where my aluminum headed 358 with better
quench is much closer to .45-.50 max bsfc.

Quick math: 3600lbs fbody, 120mph 1/4 trap speed (my old car)
we can say is probably around 500 crank hp right? Well at near static
DC, .60 BSFC the calculator says about 36-37# injectors at 50psi. This is dead on with what my AFRs, DC, fuel pressure, combo, and trap time.

Same weight and trap speed, but better bsfc of .50 and the motor suddenly only needs 30# injectors. An 'amazing' built like ski_dwn_it's old motor which i'd guess was around .45, and it would only need around a 27# injector.

I'd post #s for the Corvette, but I won't drive the thing at the track until I like it at least as much as my fbody, which hopefully the powerdyne + 6speed will fix that. Last 2 years, I've hated the car. (n/a, 700R4)


Of course, we could ignore all the math and just say 'the stock injectors would work fine'.. I've seen plenty of those posts accepted by the general population

-- Joe

 

Step 1:

Fix the exhaust

Step 2:

Do a datalog

Step 3: worry about the injectors.

Seem reasonable.

I'm outta here.....off to the exhaust shot

 

 

Very true!

I got my 396 from MTI back in '98.....and they said at the time that stock injectors would suffice for their 396's with ported heads and the 306 cam that they used.

I went with 30LB SVO's anyway !

KW