Thanks guys for all your help. It is nice being able to ask a question and get really good answers from people with knowledge. Thanks again!

 

Thanks guys for all your help. It is nice being able to ask a question and get really good answers from people with knowledge. Thanks again!

 

Thanks to Godspeed for furthering the points I was trying to convey in my questioning. <img src="images/icons/smile.gif" border="0">

A summary of points brought out thus far...

1. Know what psi the injectors are rated at. An injector rated at 44 psi will put out more at 58 psi.

2. Just because a calculation says 405 RWHP doesn't mean that it won't support more. Don't get so hung up in the calculations that you go out and buy bigger injectors just because calculations say that you are making 20-30 more HP than what calculations say your injectors will support at %80.

3. On the other hand, just because you can make the power doesn't mean that you aren't getting lean.

4. RPM does play a big part in how much power an injector will support. (Pulse widths) The lower in the RPM range that your peak HP is made the more power the injectors will support.

5. You must have a way to tune for larger injectors. A MAFT alone is not enough for the really large injectors. This is not to say that 50 lb injectors can't run just fine with a bone stock engine. They can, you just have to get the Ltrims back in line by whatever means necessary.

6. Picking injectors is not an exact science. As with anything else concerning fuel systems, more than enough is better than not enough.

7. Flow rate is not the only thing that seperates injectors. Spray patterns vary too but this is not to say that a different than stock pattern won't work just fine. There have been MANY folks to successfully use SVO injectors in these engine (myself included.)

[ February 07, 2002: Message edited by: Colonel ]</p>

 

[quote]The bottom line is stock fuel injectors are fine for almost all of the 346ci heads/cam setups, and 36#ers are fine for everything else.<hr></blockquote>

Terry is correct, injector choice doesn't need to be complicated. Don't let "in theory calculations" scare you off. They are good and serve a purpose, but the average enthusiast doesn't need to obsess over them.

 

One thing real quick. MAFT's can fix up to about 15% in either direction right? Just curious here but if that is true a MAFT would have a huge range of fixing things with out reprogramming. This is what I think it might look like..

28lb would be good from 275rwhp (325 rwhp @ 80% -15% because of the MAFT) up to 405rwhp (100% duty cycle)
36lb from 350rwhp – 520rwhp
42lb from 410rwhp - 605rwhp

Am I way off base with this?

 

[quote]Originally posted by LIL SS:
<strong>One thing real quick. MAFT's can fix up to about 15% in either direction right? Just curious here but if that is true a MAFT would have a huge range of fixing things with out reprogramming. This is what I think it might look like..

28lb would be good from 275rwhp (325 rwhp @ 80% -15% because of the MAFT) up to 405rwhp (100% duty cycle)
36lb from 350rwhp – 520rwhp
42lb from 410rwhp - 605rwhp

Am I way off base with this?</strong><hr></blockquote>

See my site:

www.vetteguru.com for maft info, and also www.vetteguru.com/mods/howto

here is a pic of the maft settings:

you can tune to 35% lean and 20% rich on BASE, and bring in 14% rich and 12 lean on WOT pot.



[ November 28, 2001: Message edited by: kewlbrz ]</p>

 

what if you are say 12% l-trims on the stock 98 injectors...worth going to the SVO 30s and tune accordingly with the MAFT?

 

[quote]Jeremy,
Thank for the info.. I figured the 375 to be on the bottle. I didn't think as high as 415rwhp.. I also didn't know about the 45hp loss instead of 15%..<hr></blockquote>

If you're only expecting 375RWHP on the bottle then stock 28# injectors should be fine. If you want a little more protection go with the SVO 30#'s and that should be plenty of fuel.

-Jeremy

[ November 28, 2001: Message edited by: Godspeed ]</p>

 

[quote]Originally posted by Matt98SS:
<strong>what if you are say 12% l-trims on the stock 98 injectors...worth going to the SVO 30s and tune accordingly with the MAFT?</strong><hr></blockquote>

With a ported MAF, I had +20 LTrims. With SVO 30#'s, I have -4, corrected to near zero with the MAFT & ATAP. I needed the extra fuel margin cause I have a dry shot N20.

 

What are SVO 30's rated at on LS1 Fuel pressure?
TIA
Sean

[ February 07, 2002: Message edited by: Seandogg ]</p>

 

check out my website

look at top..under calculators

I think I have wrote a clac for that there.

pain's website

I believe they work out to be around 36 #'s , but check again

 

Nice program. <img src="gr_images/icons/cool.gif" border="0">

I see my Lucas 42.5 lb injectors will flow better than 50 lbs if I can maintain 60 psi to them.

 

PaiN - nice webstite.

When MTI was dyno tuning my 422, we originally tried the stock 2000 injectors. The car basically died at about 5500 RPM - was leaning out severely. The injectors were replaced with SVO 36# units, and the car picked up about 10-15 RWHP all the way from 5000-6800 RPM <img src="gr_eek2.gif" border="0"> - the only other adjustment was to correct the engine tuning for the larger injectors. I wonder if I might even need to go larger if I ever step up to the S1 cam.

Forgive me if I am typing funny, but just got out of the hospital. Ain't gonna be able to drive for about 1.5-2 weeks. <img src="gr_sad.gif" border="0">

 

Weather Guy: What HP were you making at 5000 rpm before and after the injector swap?

 

[quote]Originally posted by Ragtop 99:
<strong>Weather Guy: What HP were you making at 5000 rpm before and after the injector swap?</strong><hr></blockquote>

Actually I just went back and looked through a couple of the dyno graphs. I posted some info that was a bit incorrect. Here is the CORRECT information - goes to show you what can happen when you rely on memory, especially today.

Here's what they were: (the following values are *uncorrected* and with the cutout closed; cutout open was worth 10-13 more RWHP than numbers shown below):

Below 5500 RPM: no change
5500 RPM: 502.37 RWHP afterwards, 501.95 before
5750 RPM: 510.77 RWHP afterwards, 502.33 before
6000 RPM: 514.64 RWHP afterwards, 502.59 before
6250 RPM: 513.69 RWHP afterwards, 490.07 before
<img src="gr_eek2.gif" border="0">
6500 RPM: 499.49 RWHP afterwards, 480.45 before
6600 RPM: 489.89 RWHP afterwards, 462.11 before
6750 RPM: before case not run that high in RPMs (too lean), but following the curve looks like at least 35 HP lower <img src="gr_eek2.gif" border="0">

Thus we start at about 5500 with about a 1 RWHP gain, reach 8 by 5750, 12 by 6000, 23 by 6250, 19 at 6500, and about 35 at 6750. That much difference could be worth 0.25 in the quarter for a good driver.

 

[quote]Originally posted by RPM WS6:
<strong>This is a good post. I haven’t done a lot of investigation into injectors yet as I feel that with my planned setup for next year I’ll only be in the 340/350 RWHP range (A4) and I don’t think I even need to worry about injectors yet.

But I have a friend with a 5.0 stang (I know it’s a totally different motor) who always swears by increasing injector size even on a stock na motor. When I told him I was going to try and support about 400 FWHP on my stock 26lb injectors he nearly freaked! I know he was thinking in 5.0 terms, but he is very knowable and I trust his opinion. So my question is, is he totally off base when it comes to LS1s, or does he have a point? He recommended somewhere around 36lb for my setup “at least”. I think that’s really going over board. My fuel trims are no where near maxed out now and I’m at about 310 RWHP now, so with adding only about 30 to 40 more RWHP, is this something I should even consider?</strong><hr></blockquote>


Ford is not the same as Chevy. nuff said.
<img src="graemlins/gr_zzz.gif" border="0" alt="[boring]" />

 

[quote]Originally posted by WeatherGuy:
<strong>PaiN - nice webstite.

When MTI was dyno tuning my 422, we originally tried the stock 2000 injectors. The car basically died at about 5500 RPM - was leaning out severely. The injectors were replaced with SVO 36# units, and the car picked up about 10-15 RWHP all the way from 5000-6800 RPM <img src="gr_eek2.gif" border="0"> - the only other adjustment was to correct the engine tuning for the larger injectors. I wonder if I might even need to go larger if I ever step up to the S1 cam.

Forgive me if I am typing funny, but just got out of the hospital. Ain't gonna be able to drive for about 1.5-2 weeks. <img src="gr_sad.gif" border="0"> </strong><hr></blockquote>


Thanks man...I'll finish the site one day <img src="gr_stretch.gif" border="0">

I took a tip from the Colonel, and picked me up some flow matched 42# injectors...like he said If I can keep the pressure head at about 60 they are equivilant to 50# injectors. That should be good for a lil sumtin sumtin.

<img src="gr_stretch.gif" border="0">

 

Originally posted by Godspeed

Exactly RPM is very important and as I'm sure you are aware this is where calculating injector pulse width comes into play. At 6000RPM you only have 10ms to deliver fuel. If the PCM is calling for an injector pulse width of 20ms then all the fuel isn't going to make it in.


Is this correct? It would seem to me that at 6000 rpms, which is 100 revs per second, you get one rev every 10ms.. but you only need to spray on the intake stroke so don't you get twice this much time to get the job done? i.e. at 6000 rpms you have 20ms, not 10?

Or am I missing something?

 

[quote]Originally posted by Trevor D:
<strong>
Did your friend take into the consideration the higher fuel pressure that the LS1 sees? If I remember correctly, I was told that the FMS 30 lb/hr injectors are actually 36 lb/hr injectors w/ our fuel pressure. With that being said, I'd HATE to see what a set of 42 lb/hr injectors are with our 58-60 psi of FP!</strong><hr></blockquote>


I run 42# injectors on my 422 with no problems.. at peak, I run a 60% duty cycle with excellent response at idle and trims of 2-3%

 

The intake stroke is half of a revolution or 5ms at 6000 rpm. Depending on valve timing though, there could be and most likely will be more than 5ms to fill the cylinder.