350 LT1 What injector size?

[BrazilianZ28Camaro]

Hello friends,

Few months ago I built this 350 LT1 for a buddy and I did the following modifications to hopefully build a broad torque curve and make about 350HP.

The car finally went to the Chassis Dyno and we got 287 RWHP (68 RWHP inprovement over stock). Looks like we got the power desired,but the engine was assembled with stock injectors, and due the fact all our pump gas have 25% ethanol blended, I suggested he to buy higher flow injetors, the 26 lbs/h Accels in this case.

Funny thing is, these injectors ran leaner than the stock GM 24lbs/h on the dyno . Now he asking me if 30lbs/h injectors will make more power and set the lambda on 87 wich might make more power.

I'd like to hear from you sugestions and real life experiences about what injector flow we need to make more power and work with the stock Camaro ECU.

This is the friend's letter to Summit tech:



Dear Sirs,
I had purchased 8 fuel injectors ACC-150826, 26 lbs/hr, order 3326694, to improve the engine of my 95 Camaro LT1.
The engine has mild modifications with the following items (a lot of them bought from Summit):

Piston Mahle CLE 2243497020 (10.8:1 CR)
Camshaft 07-465-8 (218/222 lift 560"/560"-113 LCA 109 ICL)
Rocker arm set 17001-16 (1.6 ratio)
Valve Springs 981-16
No cat
Body Throttle: reworked to 48 mm
The Heads had been port matched and pocket ported keeping the original valves (intake and exhaust)
Stock ECU

According to GM, the original injectors have 24 lbs/hr and Accel-150826 26 lbs/hr.
Last february , 4th, I put the car on a dyno to check power and torque output after the modifications
Results:
GM injectors
287.21 HP @ 5500 rpm (peak, wheel horse power)
417.85 Nm @ 3500 rpm (peak) =308.19 lbft
Accel ACC- 1500826
275.28 HP @ 5250 rpm (peak, whp)
411.68 Nm @ 3500 rpm (peak) = 303.64 lbft

For my surprise the engine was better with the old GM injectors than with ACC-150826.
The O2 sensor (lambda) indicated 90 with the GM injectors (24 lbs/hr) and 94 with ACC-150826 (26 lbs/hr)
As power peak, torque and lambda were matching with each other in both cases, we had tested both injectors on a flow tester at 43 psi (free flow).
The results are:
GM= 240 cc/min. Capacity= 25,37 lbs/hr (near of 24 stated by GM)
ACC= 200 cc/min. Capacity= 21,14 lbs/hr ( almost 20% less than 26 lbs/hr)
The fluid test density was 0.8 in both cases.
According to your informations, no modifications should be done to my ECU for ACC-150826 injectors.
Conclusion: the engine is working lean with the ACC injectors

4 years ago i had tested the stock engine and I got 219 HP @ 5000 rpm (whp). I’m really surprised with the power and torque after the modifications. I never expected get 30% more power over the stock engine.

The Torque curve is flat and the engine has 280 lbft @ 2000 rpm. My Camaro has 6 speed manual trans and I can drive it at 1500 on 6th smoothly.
When I made the upgrade I wanted a car with high torque at low rpm and with a reasonable power and I got it!
To be perfect I need the right injectors. What is your recommendation?

Thank you

[S10LS2]

No modifications to ecu.. Is this the car you posted a while back about on here that had some issues? It is a fairly heavily modified lt1 350 compared to stock, would be a fair assumption? I think I know the answer here but I will ask anyway, There is no tune file or log file you are going to post? If you think accel injectors run anywhere close to the same settings as the stock injectors you have a long tough road ahead of you.. Not trying to be negative towards you at all, but you are just guessing on what you think the engine needs. What did the wideband read? 90 all the way thru until peak torque? Or leaner at the top? Where is the wideband mounted? What is the fuel pressure? Are you running them both at 43psi? How is the fuel pressure referenced? What are the voltage offsets in a stock file compared to what accel may, or probably does not publish? The ecu is still setup stock and the cam is far from stock? If you did not use a wideband you did read the factory narrowband voltages at least I hope? What is the commanded afr in power enrichment mode? Accel injectors will not perform the same as the GM injectors.. Flow test them both and see.. Why do you think you need larger injectors anyway? 24lbs is probably enough for this engine.. Where is the pulse width and duty cycle on the injectors at? And there are alot better injectors out there nowadays than those accel rebranded injectors.. The stock 24 were better.. Why not just adjust either the ve table or maf table to desired afr test it .. readjust map or maf test again.. Till your lamda equals commanded.

[S10LS2]

I am sorry I guess I am not understanding how you can run a modified heads, cam, TB,and injectors on a stock ecu, with no adjustment to the proper fueling tables. Or has the ecu been previously tund , just not with the new injectors?

[ap72]

When was your car retuned? The stock injectors may be adequate as is or may just require a bump in fuel pressure. What is the data logging telling you?

[2seater]

It seems pretty clear from the OP that the injectors were independently tested and the new ones are seriously deficient? No amount of tuning will fix that issue. It is absolutely true the system must be tuned to match the new conditions when that gets straightened out. I am not familiar with the ECM for this application but my slightly earlier GM ECM programming has an input for the injector flow rate to get the base fueling in the ballpark. Tune from there. It does seem close with the stock injectors and I agree the simple thing to do is ramp up the pressure first, if that works, great, plus it will give you an actual target flow rate if new injectors are installed.

[BrazilianZ28Camaro]

This car is the same I posted before, just now its finally dynoed.

This engine isn't heavily modified from stock, just a one step bigger cam, a mild head work, roller rockers and slight bigger throttle body. Cat was removed.

The ECU isn't retuned because nobody here have the software that comunicate with OBD1 system. I'm a carb guy, not a EFI tuner, I just build this engine for my friend and I'm helping he with answers.

The lambda was measured at the pipes and wasn't logged with the dyno graph, unfortunatelly.

The fuel pressure is at 43 psi at the rail. How can we increase the fuel pressure on the stock system? Will a fuel regulator be needed?

[1989TransAm]

Stock style adjustable fuel regulators are available. At least they were at one time when I was doing this.

[ap72]

Tuning is essential. You're probably leaving more on the table than what you already gained without tuning it. Either find a way to work with the factory ecu or replace it with one you can work with.

[2seater]

I would try Tuner Pro RT for OBD1 for logging from the ALDL. Also try Gearhead EFI for the proper code to be able to read and modify tables, I am too much of a neophyte to give any concrete information but that is what I use for my '90 GM ECM.