new engine tuning

[nilak]

IÂ’m preparing and engine swap to a 383 from a 350 in a 91 Corvette TPI. What would be the precautions I have to take for tuning the ECM ?
for example if the mixture is way off or wrong timing I could get knocks or backfire into the intake. Or should I avoid WOT until I improve the VE and timing maps gradually?
Obviously the mixture will need to be properly set up at the end but you wonÂ’t know until you datalog it. Another thing IÂ’ve noticed the corvette uses quite high spark advance however (some cells show even 46 deg) thatÂ’s only at low rpm low load, but maybe itÂ’s better to start tuning with up to say 32 degrees?
the new engine has a mild cam 0.5 lift, 112 LSA, 68cc chambers 9.8 compression, 440ccm bosch injectors,
so quite different configuration, if the tuning is way off it might not even start

[In-Tech]

Hiya,
There is never a reason to change injectors on a stock TPI setup. You can never out flow the runners. They are the restriction.

Change the cu in constant and start with the stock VE table and injectors, adjust from there. You will find where you run out of air in the VE table due to the restriction of the stock runners and intake. You can change injectors if you so desire, calamity arises from there.

[Fast355]

Hiya,
There is never a reason to change injectors on a stock TPI setup. You can never out flow the runners. They are the restriction.

Change the cu in constant and start with the stock VE table and injectors, adjust from there. You will find where you run out of air in the VE table due to the restriction of the stock runners and intake. You can change injectors if you so desire, calamity arises from there.

I dunno I made 350 rwhp with stock TPI runners, plenum and throttle body on a 383. I know the stock 305 injectors never would have supported that.

[steveo]

the timing shouldn't be far off enough to cause damage at low loads.

the timing you run has a lot to do with the compression and combustion chamber design

the fuel mixture shouldn't be far off enough at low load to cause issues either as long as you account for the displacement difference somewhere

[In-Tech]

I dunno I made 350 rwhp with stock TPI runners, plenum and throttle body on a 383. I know the stock 305 injectors never would have supported that.

Ha ha, well, ya got me there. I didn't think we were talking about 19lb injectors. I'll be quiet :)

[nilak]

btw the current injectors are bosch yellow-orrange, probably 19-20lb. I could go with the large diameter runners from asm but it would make it more difficult when working on the car

[steveo]

i wouldn't run those injectors, too small. you'll want something in the 24-26lb range i bet

[NomakeWan]

If the part number on the injectors is 0-280-155-700 or 0-280-155-710, neither of those will be correct. Previous owner of my '90 Corvette installed those thinking they were drop-in replacements for the factory L98, only to make the thing run even worse than before. They were causing a severe lean condition on the factory tune. Fortunately since otherwise my 350 is stock it was just a matter of me correcting the injector values in the tune and I was back in business. But since you're building a 383 and have the ability to choose, I agree with steveo that you should be running a bigger injector. At least a 0-280-155-715 (22lb). For my '95 LT1 I have a set of FIC 32lbs, but that's because I intend to run E85 in it.

Best of luck with the build!

[nilak]

i wouldn't run those injectors, too small. you'll want something in the 24-26lb range i bet
I just bought 42lb 🤦🏻*♂️

[sanderson231]

Pontiac Fieros came with a 2.8L V-6 rated for 140 HP. GM later made a 3.4L V-6 using the same heads with similar intake and exhaust. This engine was rated for 160 HP. The displacement increased by 21% and HP increased by 14%

I contemplated bore and stroking a 2.3L DOHC Quad 4 to 2.6L which is a 13% increase in displacement. I bought the DynaSIM software to check this out. It predicted an increase in HP from 191 to 205 or 7%. When you put a bigger displacement engine on the same intake, same heads, same cam and same exhaust, the volumetric efficiencies go down and you don't get as much of a HP from the displacement increase as you you might hope.

Based on the ECM calibration data that In-Tech posted, the 350 TPI has a peak air flow of 1876 lbs/hr at 5600 rpm (73.8 volumetric efficiency) 100 kPa and 30 'F ambient. With an air fuel ratio of 12.5:1 the fuel requirement per injector is 18.8 lbs/hr. The OEM 350 TPI injectors are 22 lbs/hr. A 383 has 9.4% more displacement than a 350. Steveo's recommendation of 24-26 lb/hr injectors feels right to me

[nilak]

Now the question is if I could use these https://www.summitracing.com/parts/bch-0280155968 or I will have to buy something else. My concern is at idle it is going to need half BPW like below 1ms which could not be supported by the ecm/power module. Otherwise a short injection time may mean faster burn I think.

[sanderson231]

Now the question is if I could use these https://www.summitracing.com/parts/bch-0280155968 or I will have to buy something else. My concern is at idle it is going to need half BPW like below 1ms which could not be supported by the ecm/power module. Otherwise a short injection time may mean faster burn I think.

That injector is rated for 29.5 lbs/hr which might work. You might want to try Motor Man Fuel Injection Supply. I bought Bosch injectors for a 4.9L Cadillac from them and they were very reasonably priced. I think $25 each. Bosch 0280155869 are rated for 25.4 lbs/hr.

[nilak]

18920
If I modify PE, increasing afr slightly may increase torque, setting it to 14.7 seems a significant change that may increase combustion temperature too much.

[sanderson231]

You don't want to go anywhere close to 14.7:1. If you did run there at WOT there will probably be knock and the best case scenario is that the knock sensor would detects it and the PCM would pulls timing. The worst case scenario is engine damage.

During PE you need excess fuel to ensure that all the oxygen in the mixture is consumed. Otherwise you leave power on the table. Excess fuel also protects the engine. Your new engine is not a big step-out from the 350 that is in the car. GM spent countless hours on the dyno developing the power enrichment and spark timing value that are in the calibration. There is little reason for change. Keep it simple. Change the displacement per cylinder from 711 to 784. Change the fuel injector flow rate to match what ever fuel injector are installed.

[nilak]

You don't want to go anywhere close to 14.7:1. If you did run there at WOT there will probably be knock and the best case scenario is that the knock sensor would detects it and the PCM would pulls timing. The worst case scenario is engine damage.

During PE you need excess fuel to ensure that all the oxygen in the mixture is consumed. Otherwise you leave power on the table. Excess fuel also protects the engine. Your new engine is not a big step-out from the 350 that is in the car. GM spent countless hours on the dyno developing the power enrichment and spark timing value that are in the calibration. There is little reason for change. Keep it simple. Change the displacement per cylinder from 711 to 784. Change the fuel injector flow rate to match what ever fuel injector are installed.
Thank you
PE delay was suggested by a member. I’m exploring possibilities. Until the new engine comes I want to prepare the ground. As you said it’s better to keep it simple.

[sanderson231]

If you want to tweak the PE air fuel ratio in search of more power then you will need to invest in a wide band O2 sensor (really an air fuel ratio sensor) otherwise you are flying blind.

[Fast355]

You don't want to go anywhere close to 14.7:1. If you did run there at WOT there will probably be knock and the best case scenario is that the knock sensor would detects it and the PCM would pulls timing. The worst case scenario is engine damage.

During PE you need excess fuel to ensure that all the oxygen in the mixture is consumed. Otherwise you leave power on the table. Excess fuel also protects the engine. Your new engine is not a big step-out from the 350 that is in the car. GM spent countless hours on the dyno developing the power enrichment and spark timing value that are in the calibration. There is little reason for change. Keep it simple. Change the displacement per cylinder from 711 to 784. Change the fuel injector flow rate to match what ever fuel injector are installed.

The OE GM tune on 350 ran up to 60 seconds at WOT before PE enabled. Most of the 0411/P59 truck calibrations are set that way. Timing map is backed off a bit until PE enables then GM puts timing into them. I enabled my PE alot sooner because I wanted more power but it was a fuel saving measure for trucks towing heavy trailers.

[sanderson231]

I looked at the AXCN calibration for a 91 vette. There is no parameter related to PE delay. It looks like PE is enabled with TPS greater than 70.3 %. It does look like the AFR is very rich in PE mode.