Doing H/C upgrade w/UD pulley, LS6 manifold, LTs and ported TB. Should I upgrade injectors? If so, what size would be best or could I just stay w/stocks? Thanx.

 

Your tuner will have the best answer for your app.

 

It depends on what HP level you expect to be at after the engine work. Typically from what I read on here, you don't want to be more than 80% duty cycle on your injectors at WOT. Your tuner can tell you what your duty cycle is at the time of the dyno.

I have 471rwhp, 441rwtq. I'm running 80% duty cycle at WOT with my 36lb injectors. If I add more HP, or change injectors I will be going with a larger size for sure. Likely 42lb injectors.

Toque

 

What year is your Corvette? The 99s and maybe +/1 1 year model had 26 lb/hr injectors and they quickly run out of capacity. I just tuned a '99 FRC with headers and Vararam that was already at 83% injector duty cycle. For my '99 FRC I added 30 lb/hr SVO "redtop" injectors that actually flow 36 lb/hr at the LS1 fuel rail pressure of 58 psig. These injectors are adequate for my 467 rwhp setup.

If you have the larger 28 lb/hr injectors used in most other C5s (not the '98-99s) then you may be OK with them up to 420 rwhp or so (rough guess). If you don't want to wait until after the build to find out, then just go ahead and buy bigger flowing injectors. One note of caution is to get well known brands that have good flow data available. Your tuner can help you select a brand that he is familiar with.

edit:
Don't fall for the misconception that larger injectors will give you more power. The ECM will only command the amount of fuel that is necessary for the engine's airflow. Larger injectors are more difficult to tune at low flow (idle). There isn't any reason to go larger than what will meet your hp goal.

 

Fritzm, I have been following your build as it is similar to mine. If I recall, your setup is estimated to be around 420-430whp. Mine around 400whp for lack of long tubes and a slightly smaller cam. It does not seem like people change injectors for a H/C setup in that range.
I would defiantly talk to the expert where you are going for work/tuning. I will have no need to change mine from what I've been told. Hope that helps.

 

2000 vert, Heads PRC 2.5, .650 Patriot duals, cam TSP Torquer v.2: 232/234, .595/.598, 113 LSA. Guess i'll go w/tuner's opinion, but I think at this point I suspect larger will be needed due to increased airflow of manifold, CAI and LTs. Not going to change in a quest solely for more HP, just worried about starving.

 

from what I have seen, at around 420hp your going to be too close to 100% at WOT and anything more might become a lean situation. If I were you I would go ahead and go larger. You don't want them anywhere close to 100% because that means they are just staying open and fuel could be pooling on the intake valve. It would be a waist of time to get on a dyno and not have them ready to install anyway.

 

I just checked my tune files from two 2000 C5 convertibles that I tuned. Both of them have the 26 lb/hr injectors. You will absolutely need larger injectors for your build. My recommendation would be the 30 lb/hr "redtops" or you can discuss with your tuner. Good luck with the build. I have that same cam profile in my LS1. Great choice for daily driver that has a fair idle lope and lots of mid-range power.

 

From a number of searches I found this reference regarding injectors in C5's:

1997-1998 LS1 24.7 (3 bar) 28.5 (4 bar)
part number 12554271

1999-2000 LS1 22.3 (3 bar) 26.3 (4 bar)
part number 12555894

2001-2003 LS1/LS6 24.7 (3 bar) 28.5 (4 bar)
part number 12561462


lbs-hr.@3 bar = (43.51 psi)
lbs-hr.@4 bar = (58.02 psi)

 

Yes, I have seen this too. Much like the cam, the early models had slightly better injectors. But I guess they went down some starting 99. So it would be a good idea for OP to upgrade injectors.

 

Op an injector swap is definitely recommended. If you decide to upgrade the FAST 36lbers get the job done for most heads, and cam setups. If your planning for even more upgrades down the road it would be a bad idea to go a little larger.

 

I've read a lot of posts on the forum about injectors for applications in my expected HP range. It appears that 36# would be just right and allow for some additional minor HP upgrades. The concensus seems to be Ford SVO Red Top 30#'s which, at C5's stock fuel pressure of 58#, actually function at at 36#. Are remanufactured are worth a try. Seems that they are manufactured by Bosch. Anyone know?

 

So, if your spending lots of your hard-earned money on all your upgrades, why would you consider basically experimenting to see if rebuilt injectors "are worth a try"? Further, even if they DO "work", for how long? You're still buying used injectors after all.

Best use new.

 

It was a just a question my friend, if I may. I did not say I was buying remanufactured injectors, I asked 1) a question about remanufactured injectors, and 2) are the SVO red Tops manufactured by Bosch. As to 1) You have answered that, and thanx for that. As to 2) .

BTW, I found a formula that answers my need as to injector sizing. From Fast’s calculator for determining a NA engine’s injector needs, if you take approximate HP and multiply by .5 (apparently a constant), then divide by # of cyls, then divide by duty cycle, you get approximate injector size.

In my case, assuming HP is expected to be no more than 450 (to be somewhat overly optimistic and on the safe side), and a desired duty cycle of 80%, then: 450 x .5 = 225 /8 (# of cyls) = 28.125 /.80 (desired duty cycle) = 35.125 or 36# to be in range. This is also assuming the Fast calculator to be accurate, as to which I have no doubt as that is their business.

 

There are a number of fuel injector calculators on the web, use one of those. You're probably going to be in the 36-42 lb range. Just use your Google and find one or two of the calculators my friend.

 

Sounds about right.

 

Don't choose an injector unless you know for sure that it has well known flow data that your tuner is familiar with.

For what it's worth - I installed used 30# SVO injectors and they have worked just fine in my LS1 for the past 110,000 miles. Results may vary...

 

I've got a little over 400 rwhp/lbft.
After MEASURING my injectior duty cycle (83-87% WOT with stock 99 injectors) I replaced with 30# ford injectores ( measured duty cycle @ WOT 67 - 74% ).
I think its best to measure duty cycle first, then pick an injector accordingly.
Injector calculation charts are very useful but might not put you spot on.

 

Don't know how to do duty cycle estimate. I've gone to at least 6 different on-line injector calculators and used ranges from 400 to 450 crank HP to calculate @ 58lb pressure. The answer almost invariably ranges from 31 to 35 lbs at 80% duty cycle. So I believe that 36 lb injectors will suit my needs just fine.

I've found that SVO 30 lb red tops are rated at 43.5 lbs fuel pressure and will work out to 34.65 lbs at the 58 lb LS1 fuel pressure. I am therefore deciding whether I am going with Bosch 36 lb Green injectors, FAST 36 lb injectors or the red tops newer M-9593-BB302 30 lb. When I buy I will buy flow matched so my tuner will know.

As I also don't know what my final HP will be after mods, I am going by the reported HP results of several forum members who have mods similar to the ones I am doing and who have reported HP results in the 400 to 450 HP range.

Again, TSP Torquer v2 cam 232/234 595/598 LSA 113 w/upgraded chain, PRC 2.5 heads w/Partiot dual .650 springs w/Comp Cam trunion upgrade, catted long tube headers, LS6 intake (unported), ported Shaner 3 TB, K&N CAI w/upgraded LS6 85mm MAF, ported LS6 oil pump.