I'm looking into 24# injectors for my 350 c.i. gta TPI setup. Do you recommend upgrading to 24# injectors? What kind of gains can I expect by upgrading to these, and will I have to modify the computer at all?

 

Installing 24#/hr injectors in place of the factory 22#/hr injectors will gain you nothing on a stock or nearly stock 350 TPI.

If you go ahead with the 24s, the ECM probably has enough range to correct the PW and take a bit of fuel away from the calculation w/o throwing a code.

 

Well it's got roller rockers, lunati cam, CAI , hooker LT headers, stock injectors.. I ran a 13.01 @ 116mph so I'm pushing way more hp and tq than stock 225.. It really hauls *** as it is with the T5, but I've heard mixed things about aftermarket injectors.. If it won't really benefit my car's performance, then I won't get them

 

I wouldn't mess with 'em if yours are working ok.

 

Ditto
On a side note the ECM can handle the 24# upgrade without any modifications. Nothing above that though.

 

If the gains really won't be worthwhile then I'll just keep my stock injectors and give em a great big cleaning. If the gains are significant and show a noticeable difference in boost then maybe I'll give them a shot in the long run.

 

Well, ya gotta remember that all they do is add fuel. Either they add enough, or they don't. Black and white. It's not like a little bigger adds performance, and a little smaller restricts performance.

I can't think of a situation where someone went from 22 to 24 for performance. They're just so close in size. Most people who upgrade to 24 (like me) do it because they're cheap, easy to find, and often better quality. My 22 pound stockers were going bad, so I upgraded to 24. Is wasn't for performance.

 

Abubaca,

So your saying the 24 are cheap, better quality, and easier to find. What brand of injectors did you go with? Reason for asking I think my injectors in my 89 350 L98 Iroc are going bad. I am looking into getting new ones or having my old ones flushed out. For the price of $120 to have them flushed I would rather spend that towards new injectors. Your injectors what brand and how much was the price on these if you can recall, thanks in advance.

I see now you have the Ford/Bosh III injectors what did you do to have your computer programmed accordingly for the new 24#?

Thanks for the info and update TIMMYS89GTA

 

theres a place called fuel injector connection.
I am getting a set of the bosch III's from them (i think like $180) for the set.
Run a search for FIC and you should find their site.

 

I could be wrong, but my thought was that the LSx style injectors were considered "type 3".

Regardless, I got Ford/Bosch 24# pounders, new off Ebay from Blue Oval Motorsports.

When I initially put them in, they ran fine with the stock programming. I had been toying with a custom tune for awhile, and used this injector swap as an excuse to do so. That being said, I never actually had a problem with the stock tune. Ya gotta remember, ideally our ECM doesn't need to make any adjustments, but it has the ability to do so in case of problems. When you rely on this adjustment to compensate FOR KNOWN CHANGES like an injector swap, it may adjust and run fine. The issue is that now if down the road somewhere you have a problem, the computer may already be compensating for the injectors, and it may not have enough room to make the necessary changes to fix whatever new problem has come up.

 

If you are under 90% duty cycle on your 22# there will be no change. If over 90 % then the 24# will not go static and lean out your mixture.

If you have tuned your bin (Wot) for the 22# and were lean, you are going now to be richer.

At idle there can be issues with richness, after changing to ANY size newer designed injector. The idle blm's can go high even if the mixture is correct to rich.

A 10 degree change in idle timing, changed my O2 swings, from 600 mv (20 degrees total) to zero mv (30 degree total), This small change is the difference between normal idle and way rich.

I run the 24# on a mild 383.

 

why ?????
please explain this to me. I am having this problem on my LB9, and so are many people on the corvette forum with their L98's, all with new injectors.

My cell 0 is especially bad. no vacuum leaks. nothing obvious. I'm considering a heated o2 sensor, but the motor and prom are stock, so this doesn't make sense.

why would it dump fuel?? it's like the o2 sensor is not reading correctly.

 

The stock tune (bin) is matched (calibrated) to a stock 198* fuel injector, the new stuff takes a different (calibration).

 

but going on the assumption the size of the injector is the same, how are the new injectors different from the old multiteks?
are they flowing different at the same pulse rate?
or is something else different?
are they faster acting?

if they flow the same, or even close to the same, the computer should be able to compensate.....

 

At very low flow rates, just above 1.59 ms (the stock minimum flow setting) the injector pulse of the 80's injectors (pintle type) act very different then the newer (disc type). The stock ECM tune is setup to compensate for a relatively heavy and slow acting pintle. When you install a disc type, the disc has less mass and is alot faster to react. The fixed constants and tables setup specifically to deal with this pintle slowness at low speed (software fix) are now over kill because the injector was "fixed" by redesign so the software "fix" is not needed and now causes problems.

At higher Flow rates the differences are not as much.

 

ok, what then causes the BLM;s to slowly rise??
why doesn't the computer see the richness and start pulling back fuel ?
rather it see's the opposite, and keeps adding fuel.

I understand what your saying, but shouldn't the o2 see this and self correct?

 

The blm's will rise anytime the average O2 output is low (closed loop), below the 450 mv level. The computers (ECM) assumption is that less oxygen means more burning from more fuel and that the opposite is true that more oxygen means less burning and less fuel.

If there is more oxygen for any reason, air vacuum leak or exhaust leak, the O2 will sense the extra oxygen and try to add more fuel.

There are at least two ways for the O2 to be "lied to" the first is a cold O2 sensor, at a low exhaust temp the O2 mv are lower. This is why they used a heated O2 sensor on newer systems.

At Idle you can see this on a data log, under a certain low rpm (under a 1000) the O2 mv will drop but the engine idles the same (open loop) or blm's start to rise (closed loop).

The new type of 4 hole disc injectors atomize the fuel better (a finer mist). This better burning mixture, allows less fuel to do more work, less raw liquid fuel passing through the engine. That makes for less fuel to burn in the exhaust pipe, making a lot cooler pipe and O2.

If you can see a video of an 80's injector, at a low injector pulse, it is more of a squirt of liquid then a mist, almost a dribble.

The second way is, too much cam overlap, intake air is pulled into the exhaust. The EX valve closing point has the most effect on this, that is why the Lope center angle on computer cams is 112 plus not 106 or less.

This is my view, I will entertain any other thought on this.

On my engine a 5 degree change in spark advance at idle will change the O2 sensor output from 600 mv to 300 mv (20 to 25).

 

pandin, very nice write-up. One thing to keep in mind is that the BLMs will keep you at or near 14.7"1 AFR while cruising around. However, at WOT, my scanner always tells me that I am is fuel cell 15 and the BLM is always defaulted to 128 (the perfect BLM for 14.7 AFR). Therefore, the BLM value is not used for fueling at WOT. Instead, the ECM goes into power enrichment mode, and the ECM consults the fuel enrichmnet table to add the extra fuel that is required while in PE mode. This table goes by engine RPM.

For this reason, I always recommend an adjustable fuel pressure regulator when mods are made to an EFI car. With the AFPR and a wide band O2 sensor, you can dial in 12.8 AFR and any other AFR of your pleasure. The problem here is that WB O2 sensors are expensive. But if someone is strongly interested in doing their own tuning, a WB O2 sensor is a must.