hey grumpy do I need bigger injectors?

[grumpyvette]

"I swapped my stock 350 engine for a 383 with bigger heads and a bigger cam and re-installed my old TPI intake and stock injectors and its just not running correctly, any ideas ?"?



obviously you need to check for vacuum leaks bad electrical connections, faulty ignition timing curves a badly adjusted CPU or low fuel pressure and any mechanical or electrical issues first,and verify every system is working correctly, that theres no mechanical issues like a cam installed incorrectly or a worn cam lobe, low fuel pressure a defective injector, a broken piston ring, a restrictive exhaust,
Id suggest pulling trouble codes and doing a compression check and verifying the ignition advance etc
your horsepower is based on how much fuel/air mix you can efficiently burn per second, you'll burn about 12-15 pounds of air per pound of fuel, all modifications that increase power concentrate either on increasing efficiency like increasing compression or reducing friction , or increasing exhaust scavenging or on burning a greater amount of that fuel/air mix per revolution, such as increased displacement or packing the cylinders with higher pressure like a super charger or a turbo, or increasing the number of power strokes per second, like with longer duration cams,
the most common reason , a new 383 stroker,with a larger duration cam, installed in place of a stock 350 sbc won,t run as expected is failure to realize the new engine combo will need to run at a higher average rpm, and it will require noticeably more air and fuel to make that extra hp,if you just went from 240hp in a stock TPI and built a 470 hp 383 thats a 100% increase in hp it only makes sense that the injector size must jump up to almost double the original flow rate to compensate also,
and the new cam is very likely to require a different ignition advance and CPU tune plus a higher stall converter and a 3.54:1-3.73:1 rear gear should be used so the engine can spend most of its time in the higher average rpm range the cams designed for, all the changes were made so you could burn MORE FUEL and AIR in each power stroke and have MORE power strokes per minute, one of the most common mistakes,is not swapping to a matched rear gear and higher rpm torque converter stall speed,followed buy guys not upgrading the exhaust and understanding the need to upgrade the injector size to supply the higher demands for fuel and air the new engine will maker because its going to need to be supplied with more fuel to maintain the correct fuel/air ratio.the most important and effective performance asset you have is simply your ability to ask yourself questions, the ability to think logically isolate and test components carefully and doing the research if its required to find the best answer's you'll need.
actually 36 lb- 42 lb injectors are very commonly used on the better 383 engine builds, one of the most common problems I see is guys trying to reuse stock 24 lb injectors to build a 400hp plus engine that results in a constant lean upper rpm condition that eventually results in detonation damaging pistons but always results in lower power than expected
ALWAYS TEST ALL YOUR INJECTORS OHMS RESISTANCE, WITH A MULTI METER, IF YOUR ENGINE RUNS BADLY ,INDIVIDUALLY< THEY SHOULD ALL BE VERY CLOSE TO EQUAL, ANY THAT ARE NOT NEED TO BE REPLACED
heres a basic chart on injector size and expected power levels, you should see reached before potential higher rpm lean condition
heres a bit of advice! so many times I get called over to help in some project, only to find the problems the guys hoping I can solve could have been avoided entirely ,
if the guy whos at this point is going partially insane, had only bothered to carefully read the details or installation instructions.

many times youll see the guy ordered the wrong part number, and theres a very similar component that exactly matches the concept ,
hes currently waist deep into, only to find the component he ordered is not compatible with the rest of the parts, hes working with.
Ive seen guys order high impedance injectors that are installed on a controller designed for low impedance injectors

http://fuelinjectorclinic.com/faqs

You can measure the resistance across the two electrical terminals of the injector. If the resistance is between 1.5 and 4.0 Ohm you have low impedance injectors. If the resistance is between 8 and 16 Ohm you have high impedance injectors.

https://www.hotrod.com/articles/hrdp-1211-low-impedance-vs-high-impedance-fuel-injectors/

Low impedance (peak and hold) injectors have a resistance of between 2 and 4 ohms. High impedance(saturated) injectors have a resistance of between 10 and 14 ohms. Low impedance and high impedance injectors cannot be used interchangeably without modification of the injector drivers.

What are the differences between low impedance/peak & hold and high impedance/saturated injectors?

The older fat body style low impedance injectors (1.5 to 4.0 Ohm) used to have faster open and close times due to the type of electrical signal pattern emitted by an ECU equipped with proper P&H signal transmitters. This “Peak and Hold” injector signal typically uses a high (4 amp) initial current to open the injector, and which reduces to a lower (1 amp) current to keep the injector open until the pulse ends. Since this method put less total current into the coil, the coil heated up less and was therefore more reliable. Since the “hold” or lower current part of the signal has created a weaker magnetic field, the injector will also close more quickly.

High impedance injectors (10 to 16 Ohm) are triggered by a low (typically around 1.2 amps) constant current signal and kept open by the same constant (saturated) current for the entire cycle. Most OEM injectors today are high impedance injectors being driven by saturated injector signals from the ECU since car manufacturers are most interested in the simpler saturated signal which is more cost effective to produce when building ECU’s, especially where there is no apparent loss of drivability or performance.


https://www.summitracing.com/parts/...MIsMryyOf_3gIVjoTICh1o7wzhEAQYAiABEgKO9fD_BwE

https://www.summitracing.com/parts/...MInIGXief_3gIVy-DICh1rpgH3EAYYAiABEgJLafD_BwE
24 lb/hr 326 hp
30 lb/hr 408 hp
32 lb/hr 435 hp
39 lb/hr 530 hp
42 lb/hr 571 hp
https://fuelinjectorclinic.com/flow-calculator

https://www.injectorrx.com/injector-size-calculator/

https://www.witchhunter.com/injectorcalc1.php

http://www.raceworks.com.au/calculators/injector-hp-calculator/

http://www.rcfuelinjection.com/Technical

http://www.enginelabs.com/news/calculating-fuel-demands-and-injector-sizing-with-efi-university/
watch these videos

http://www.youtube.com/watch?v=l2ne6AVn ... re=related

http://www.youtube.com/watch?v=aIUJbTXN ... re=related

http://www.youtube.com/watch?v=49WXmzfO ... e=youtu.be

viewtopic.php?f=32&t=3429&p=9084#p9084

HERES SOME THREADS TO HELP YOU LOCATE YOUR PROBLEM
http://forum.grumpysperformance.com/viewtopic.php?f=55&t=1200

viewtopic.php?f=44&t=38

viewtopic.php?f=32&t=596

viewtopic.php?f=44&t=773

viewtopic.php?f=80&t=728

viewtopic.php?f=32&t=168

http://www.hotrod.com/articles/innovate-air-fuel-ratio-meter/

viewtopic.php?f=44&t=5575

 

[Grumpy]

Id suggest the 24lb for a basically stock 350 TPI application

THESE LOOK STOCK (I'm using a similar 36 lb rated set in my 383 currently)
https://www.ebay.com/i/391440066276?chn=ps&dispItem=1

, if it takes you more than an hour or so to swap injectors out you need a great deal more practice
http://garage.grumpysperformance.com/index.php?threads/my-current-corvettes-383-combo.430/

calculators
https://fuelinjectorclinic.com/flow-calculator

https://www.injectorrx.com/injector-size-calculator/

https://www.witchhunter.com/injectorcalc1.php

http://www.raceworks.com.au/calculators/injector-hp-calculator/

http://www.rcfuelinjection.com/Technical

http://www.enginelabs.com/news/calculating-fuel-demands-and-injector-sizing-with-efi-university/
http://www.blowerworks.net/

one major restriction to and TPI system running a stock MAF sensor is they are rather airflow restricted
due too both design and internal size, http://www.blowerworks.net/ sells custom 3" 3.5" and even 4" custom built MAF sensor designs,
obviously youll need a set of 30lb-50 lb injectors to keep up with the potential increased air flow and the controller that will also work with the custom parts

THESE DON,T (I ordered these for my BBC swap)
https://fuelinjectorconnection.com/products/24lb-bosch-3-for-tpi
https://www.highflowfuel.com/i-2390...MIoLrr3KCN2gIVTbjACh2JdgspEAAYASAAEgKqbPD_BwE
https://www.texas-speed.com/p-3973-fic-80lb-bosch-injectors-for-ls-ev14-set-of-8.aspx
basic fuel injector test
(pull your trouble codes and check battery voltage ,alternator output and ignition spark first)

(BTW it rarely hurts to drain old fuel thats over 4 months old and replace the cars fuel filter, then add two different brands of fuel injection cleaner and 6 oz of marvel mystery oil to as full tank of fresh high test gas to the car if its been sitting un-used for very long before you start testing for fuel injection related issues

now Ill assume your battery reads over 12 volts and the starter works, and easily spins the engine
the first step
find the fuel rail shrader valve and remove the cap and connect the fuel pressure gauge
if you turn on the ignition key to get the dash and accessories to light up but don,t start the engine,the fuel pump,
should briefly run to pressurize the fuel rail to about 38psi-42 psi,
this should stay at this pressure level for at least 5 minutes minimum, if it drops slowly your fuel rail is leaking fuel.
now the fuel pressure regulator may be defective or leaking, or in very rare cases the fuel pump may be defective ,
but the most likely cause is a fuel injector(s) stuck in the open position.
next pull the injector harness,

off a single injector at a time, press the wire bar to release the clip, retention, then pull it up and off, the noid light plugs into the harness,
use the spare injector pig tail

on the now disconnected injector ,connect the multi meter on ohms setting and it should read 11-13 ohms injector on each injector tested.
if it reads under 9 ohms or over 20 ohms its a defective injector
now use a couple 3 ft long test leads connect one too one of the pig tail test leads
https://www.walmart.com/ip/Uxcell-2...-Clips-Test-Jumper-Wire-1-5m-2-Color/45588242

and to 12 volts, connect the other pig tail lead too a different test lead and watch the fuel pressure gauge,with the key out of the ignition , you should have 38-42 psi of fuel rail pressure, watch carefully while you tap the second test lead to ground (the plenum or alternator case works) the fuel pressure should drop as you tap the ground pig tail lead, this verifies the injector function at least partially, if you don,t see the pressure drop the injectors not allowing fuel flow through it and should be replaced.
after you complete each injector test , turn the ignition key on, to re-pressurize the fuel trail and reconnect the harness to the previously tested injector,
repeat the noid light and pig-tail function fuel pressure test on each of the other injectors individually.

youll need a fuel pressure gauge and multi meter

it helps if you have a spare fuel injector pig-tail for testing

having a NOID light injector harness tester wont hurt either
https://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html

on the TPI and LT1 efi and many other EFI intakes,
theres a shrader valve,
that can be easily accessed to check fuel rail pressure,
dealing in facts you verify is always preferable.

GM part number for the complete fuel rail o-ring kit is 17111696

if your TPI FUEL PRESSURE REGULATOR DIAPHRAGM LEAKS youll find it difficult or impossible to be starting your car

heres a link to the correct o-rings they are light blue
NAPA sells them at times
all the o-rings on the fuel rails and injectors need to be dipped in thin oil so they insert and slide into place with less friction, this tends to greatly reduce the chance of the o-rings ripping, and yes you need the correct o-rings that fit correctly to begin with if you expect the rings to seal correctly
http://tpiparts.net/inc/sdetail/10950/300

17113544 - Injector Seals
17111696 - O-Ring Kit
22514722 - Fuel Inlet O-Ring
22516256 - Fuel Inlet O-Ring

http://garage.grumpysperformance.co...dding-a-fuel-pressure-gauge.15264/#post-88472

http://garage.grumpysperformance.co...njection-at-start-up-problem.7309/#post-24862

http://garage.grumpysperformance.co...oven-facts-if-your-in-doubt.13051/#post-84695

http://garage.grumpysperformance.com/index.php?threads/tpi-fuel-pressure-issue.10385/#post-42943

http://garage.grumpysperformance.co...-system-trouble-shooting-flow-chart-info.596/


http://users.erols.com/srweiss/tableifc.htm

either choice , of these would work
keep in mind the cpu will read the sensor data and modify the injector pulse duration,
to provide the engine with the intended fuel/air ratio, and the difference in the rated size is of zero concern as long as its properly tuned.
the rated size limits the upper flow rate but has almost no effect on mid and lower rpm flow.




https://www.corvetteactioncenter.co...il-removal-fuel-injector-replacement-827.html

http://garage.grumpysperformance.com/index.php?threads/diagnoseing-tpi-lt1-problems.1241/

http://garage.grumpysperformance.com/index.php?threads/my-current-corvettes-383-combo.430/

http://garage.grumpysperformance.co...ive-are-the-stock-tpi-engine-components.1509/

http://garage.grumpysperformance.com/index.php?threads/c4-corvettes-fuel-system-info.67/#post-37351

http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401&p=8895&hilit=start+sequence#p8895

http://garage.grumpysperformance.co...ey-grumpy-do-i-need-bigger-injectors.5583/#po

http://garage.grumpysperformance.com/index.php?threads/calculate-fuel-injector-size.1200/#post-4041

http://garage.grumpysperformance.co...easonably-effective-tpi-combo.1060/#post-2031

http://garage.grumpysperformance.co...-other-efi-intake-manifold-info.431/#post-530

http://garage.grumpysperformance.com/index.php?threads/can-you-get-there-with-tpi.10494/#post-44299

http://garage.grumpysperformance.co...g-tpi-crossfire-or-lt1-vette.1401/#post-39419

 

[Mark Bradley]

So you went from 350ci to 383ci or roughly increased the displacement by 10%.
If all things otherwise remained equal then you need to assess if the original system had 10% of headroom. If it does not have the headroom then you have two choices to increase the fuel delivery volume.... increase the injector volume with larger injectors or increase the fuel pressure to the back of the injectors.
In either case you will need update your delivery calculations.

 

[Grumpy]

theres not a single original component in the current corvette engine that was in the original 350,
the stock 1985 tpi had 22 lb injectors, and made about 230 hp
that corvettes used as a test mule,
my 383 has closer to 480- 500 hp and a good deal more with the wet nitrous system engaged
I've changed injectors from 22 lb to 32 lb then too 36 lb, I've got ported trick-flow heads,
boosted compression, a ported stealth-ram intake and a crane roller cam,
and a totally different scat rotating assembly, hooker headers , several sets of roller rockers,
several different exhaust systems etc.
theres no way a 10% boost in injector flow would come close to keeping up with demand.
I've checked and tested so many intake and cam combos over the last 20 years,I almost need to refer to notes, I've taken extensive notes ,
I've rebuilt the engine several times with new rings, bearings at least tested a dozen cams,
two sets of pistons, three sets of heads, 4 different intakes, but otherwise lost track.


http://garage.grumpysperformance.com/index.php?threads/my-current-corvettes-383-combo.430/

 

[Mark Bradley]

Note in my earlier message I said “if all things remained equal”.
So in addition to ~10% displacement you potentially increased the VE of the motor.
If your at 500hp your looking at much larger injectors... how many injectors are you running?

 

[Mark Bradley]

Yes it is a bit of over kill although I run eight 62# injectors on my 496 and never seem to saturate them.
I’m running them at 50 psi so I have plenty of capacity and can sustain 12.5 AFR at 6600 rpm.
Make sure you have enough capacity to allow the pental to settle and the coils to cool at WOT. You should target 70% duty cycle or so for the WOT max although if this will be a driver you need to equally keep an eye at the minimum injector time. Too low a minimum will result in difficulty getting a stable idle.
My 2 ¢

 

[Strictly Attitude]

 

[Strictly Attitude]

super budget guys decap injectors, triples the flow what I have seen on YouTube is you lose having a balanced set of injectors but gain a 75lb injector from a stock 22lb injector. Guy building 5.3l 6.0l turbo ls engines this way cheap and fast. Not saying this is ideal just saying it is out there happening and working to create fast cars.