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Upgrade from 19lb to 22lb/24lb injectors supercharged LB9?
I am putting a paxton on my LB9 (please don't tell me how bad paxton's are, i've read a lot about them already..) and I was wondering if I should upgrade my fuel injectors to 22lb or 24lb LT1 injectors since I found a place that will sell them pretty cheap.
I have a basically stock car right now .. except for the N20, but was planning on doing the following soon:
well.. should I bother with new injectors (mine are 19lb and have over 100k on them)?
I was thinking of getting both a set of 22lb and of 24 and using the 22 for now, and upgrading to the 24 later when I install what is listed there. my current mods are in my sig, thanks.
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89GTA5spd – Came: Completely Stock w/ 3.42’s, rear disks, dual cats, LB9 305, T5, bad paint & interior. I did: Conical K&N w/cust piping, TPIS Airfoil, Ported Plenum/Runners, TB By-pass, Home Made AFPR, MSD Cap/Rotor, Jet Fan Switch, 180 T-stat, , Flowmaster 3” Cat-back, Eibach 1” Drop, KYB’s, Hotchkis STB, BFG 255 Comp T/A’s, AC Plugs, NOS TPI (custom) Kit , Sony CD Deck, Orion Amp, Fosgate 10’s, 1991 GTA interior, new paint. I have but have yet to put on: Alston Bolt on SFC’s, Paxton SN-92. Soon: Mallory Hyfire, Autometer Phantom Elec. FP guage, N20 Guage, Boost Guage, Fuel Pressure Safety Switch, Bottle Blanket. Not So Soon: L98 w/ alum heads. Always a work in progress..
I don't have much experience with superchargers, but I would say that the 19 lb stock ones would be insufficient for your needs once your mods are done. You can only crank your AFPR up so high with the 19 lb injectors before they start giving up. The stock 19 lb injectors for that year were pretty weak, and would begin to have erratic pintle operation above a certain pressure level. You expect that the flow would increase with added pressure, which it does for a while, but above around 60 to 65 psi those injectors can't deal with the pressure.
I replaced my 19 lb injectors with F*rd 24 lb injectors from Bosch on my 89 IROC.
So I guess I really need injectors then.. I guess I'll order a set tommorow. I was only planning on running 6lbs of boost, maybe more later if I got it re-built (10 max). I was also thinking that maybe my stock 19lbs have been part of the somewhat erratic idle i am getting (checked TPS, IAC, vacuum leaks, etc, etc, etc..).
So 24lbs definately? I am really on a budget (which you should never be if you want to go fast ) so if those will get my by for the time being i am fine with them even if they are a little small.. originally i thought that 24 might be overkill.
24#s. I'd go with Ford SVOs. I've heard from a lot of people they are actually 26#ers on our car. You can use the SVOs for up to 10#s of boost on our engines (maybe even more).
Theyre in summit by the way
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91 Formula 1LE 1 of 46
305 TPI 5speed
1LE/G92/WS6
Paxton SN92 supercharger, Ford SVO 24#injectors, Crane AFPR,SLP airfoil, ported/polished plenum, March alt. pulley,Crane Gold 1.6rrs,MSD coil,MSD6AL (5400rpm limit),Holley 9mm wires,Ac delco R43ts plugs,custom chip,Bosch O2sensor,SLP 1 5/8" headers,SLP catback,shortened shifter,3:73s w/Auburn posi,180* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Well, it looks like I am going to go with the 24# injectors. Everyone seems to agree. Unfortunately, I can't afford SVO's.. so a used set of LT1 24# will have to do for now.
Will my stock pump hold up? I am going to put a electric f.p. guage (not full sweep) inside my car as well as a boost guage (these guages seem absolutely neccesary), and I will watch the FP closely, but I am worried about my stock pump, would it be better to install a new pump or go with an inline ...? I would much rather go with an inline cause I don't want to drop the tank. Would the inline be really expensive? Where can you buy them? Thanks for all the help, putting the extra power in my car makes me nervous about breaking it.
I drove a 91 Z28 with a Paxton supercharged LB9 auto. The car's only other mod was a cat-back system and he was running #26 injectors, and thats up here at 5280 feet!
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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End
<font face="Verdana, Arial" size="2">Originally posted by 89GTA5spd: Just ordered the 24# LT1 injectors a few minutes ago.. They will be shipped tommorow, so hopefully I'll get them by the end of the week!</font>
Shoulda went bigger!! The 24# LT1's will WORK but not to the full potential of the car if you run 10lbs of boost! The 24# SVO's would have been a good choice because with GM fuel pressure they run like 26# and if you bump the pressure a bit more you can get them to run like 27#-28#!!
I know I should have gone bigger, but I got these for $36 shipped. I am out of money and still need an ignition box, a fuel pressure safety switch (for N20), a boost guage, a nitrous guage and a f.p. guage. I am sure these will work better than my tired 19lb injectors..
.. and I am only going to run ~6psi for now.
to keep my car together .
[This message has been edited by 89GTA5spd (edited April 19, 2001).]
The problem with running larger injectors is that you will lose low end throttle response -- it will feel sluggish. The only viable solution is with EPROM programming, but only to a certain extent. This will not solve the problem entirely. It's basically a give and take situation -- you cannot have both low and high end optimized.
My 305 is driven daily. I did not want to sacrifice low end response. My best time of a 12.04 was run with 19# injectors. The problem is that I'm exceeding 85 percent injector duty cycle at ~3,000 rpm, which is not good. By 4,000 rpm, I'm at 100 percent duty cycle -- the injectors are constantly flowing. This will lead to premature failure.
Another solution is installing an FMU. This unit will increase fuel pressure proportionally with boost. The problem is again overtaxing the injectors and quite possibly locking them up at extremely high pressures.
My solution is the Carroll Superfueler system. This system adds three supplemental fuel injectors. By using this system, I plan on retaining my 19# injectors, reducing my maximum injector duty cycle to 85 percent AND running a constant 850mV O2 sensor readings throughout my rpm range (up to 6,000 rpm).
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Willie
Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
Former Paxton (6-psig): 12.57 @ 111 mph.
Former Paxton (6-psig) & former 50-hp nitrous: 12.04 @ 114 mph.
Current ATI D1SC (Initially 10-psig): Projecting high 11's.
Future ATI D1SC (15-psig): Gotta catch them pesky 26-psig boosted TTA's!!
You should be ok with the 24#ers and 6#s of boost. No need to worry about the stock pump unless it's giving you problems. Just watch FP under boost. If it doesnt fall you're ok.
Actually Willie, my low end isnt that bad with the 24#ers. I guess it's because of all that custom prom work though. But put it this way, I don't get traction until 3rd gear at around 70mph.
) so if those will get my by for the time being i am fine with them even if they are a little small.. originally i thought that 24 might be overkill. 
