hey guys


I just recently bought a 91 z28 with a 350 roller engine in it it has a 350 roller bottom end with the 305 upper end on it ( heads intake etc)

I know the 5.0 vin f engine uses the 19 lb injector and i think the 5.7 vin 8 used the 22 lb i think or 23 lb


will the car run lean with the 19lb injectors and keep me fom getting the best tune out of it or has the ecm got enough control in the block learn table to add more fuel to keep it stable with out running too lean?

 

There have been a couple posts on this. Basically you still should have the 305 memcal (computer) and it has 19lb injectors programmed into it. IF you get a 350 memcal (big difference from the 305) you should switch out to 22lb injectors.

If you leave it as-is, your motor "should" be fine. I have the same motor as you (350 block with 305 heads, injectors, and computer) and my A/F is perfect.

 

The system may adapt well enough to run respectably once it achieves closed loop and writes some new table data, but will always tend to be lean.

The most appropriate repair would be to install the proper injectors and reprogram the ECM. The injectors are the more expensive part, but since the '91 likely had Multecs, it may only be a matter of time before you'll need injectors anyway.

Reprogramming is easy, and you can either get a factory 350TPI CALPAK (new or used), or far better yet, burn your own. Check the DIY-PROM board for information on that.

 

You need a 350 memcal. The limp home mode and esc circuitry inside the memcal are different between a 305 and 350.

Unless you plan to change the injectors, you can get away with running the 19 lbers on your 350 by having the injector size in the prom changed to 19.

On more thing, you need to make sure that you have a 350 knock sensor, as the 305 knock sensor is different as well.

 

Not in '86.

Good point on the KS. The 305 KS is going to be way too "loud".

 

Correct, 86 doesn't have the esc circuitry on the memcal. The 85-89 models had an external ESC mounted on the firewall.

He is talking about a 91 though... or did I miss something?

 

My 89 has a 355-everything (block, heads) but i still have the 305 injectors (basically the whole TPI setup has not been changed..yet) and ECM with a chip for 19lb injectors supplied by Jasper and made by FastChip. My rig runs pretty well except for, what feels like, a lean out condition around 3500RPM and up. I'm going to upgrade the whole intake, injectors, KC, and "custom" chip early next year. I didn't think I'd need to replace the ECM but after reding this thread I'm wondering...is that something that may need to happen?

 

thanks guys for the info


What i am going to do is while the top end of the engine is down i am going to install some 28 lb injectors ( stock for the GN) i have gotten some extra to make a set of 8 and have those put in.

then i'm gonna have a custom chip cut for the new injectors. i figured if i'm gonna put in bigger injectors put in some that will give me room to grow if i make changes to the car( BOOST ) so i will have extra fuel to handle it.

do you think i still need to get a L98 memcal and KS


i also found out from the original owner the heads are from a 350 car so the only thing from the 305 are sensors and intake. he also told me it has a aftermarket cam in it dunno about specs

if i get more info i will post

i understand the concepts of FI and all i just don't know what works well for these engines and set-ups

give me SFI and a turbo and i can make it boogie

 

Yes, you still need an different prom and knock sensor. Needs to be off a 90-92 350 regardless of whether or not its going to be reprogrammed.

 

Get an adjustable fuel pressure regulator and increase the fuel pressure to about 55lbs. It's more than Ideal for your needs.

I'm not 100 % sure but I think the 90-92 speed density fuel maps for the ECM Calibrations are the same for a 5.0 tand a 5.7

I'm running a bit more than stock internals. 355 CID with Cam, Headers, Heads, pistons ect... I still have the stock TPI unit, injectors, ECM, prom, mem-cal,knock sensor, smog pump ect.. My car runs much stronger than I expected with this induction even though I ported it and installed a larger throttle body. My car runs perfect and I'm not a dummazz either.. lol . I've been playing with hot rods since the seventies and I'm a G.M. tech with 30 years experiance.

 

Raising your fuel pressure to 55 psi will bring 19 lb injectors up to 21.36, which should be close enough to run ok. However, you are putting alot of stress on your fuel pump that isn't necessary. Dropping the tank to change a bad pump is a royal pain in the ***.

The calibrations for a 5.0 and 5.7 are very different. Yes, the car will run with the wrong one, but plenty of things will be off.

90Formula-X-F, I am pretty sure that if you were to datalog your car while driving around in a variety of conditions, you wouldn't be as happy with the results. Just because you have a strong running combo doens't mean its running perfectly.

 

thanks for the info guys


I really don't want to raise the FP up to make up for the diffrence in injectors. IMO thats a BAND-AID for the problem.

The turbo regal guys do it all the time. but i don't thats why i have 55 lb injectors in my GN. plenty of fuel.


also i will change the KS and memcal.


I also want the fuel pump to live a nice long happy life since it's a new one. i do know how much of a PITA changing one out can be

i also figured the program for a 305 is gonna be diffrent than a 350. Thats why i asked if the car would be ok to drive when i get it put back together long enough to have it correct witht he right parts.

 

As far as that goes, it is kind of a bandaid, but I see it as different from what most of the turbo regal guys do. I for instance, as I would assume you also have a walboro 340 which is the high pressure 255lph pump. It is designed to be able to handle higher pressures than what the stock pump is. The reason it is so common to adjust fp w/ these cars is that there is no real wot learning in the chips, and unless you get the car dyno tuned, it is hard to get a chip that will have a perfect a/f with all of your individual mods. Some of the guys are getting them pretty good now, but it still allows you to get your wot a/f where you need it w/ different boost levels and such(very critical w/ these cars) The car will learn at part throttle, but we max out the maf pretty quickly so all of the tuning is done in tables that cant even tell exactly how much air is coming into the motor.

Well, I guess that was more than I inteneded to say, but basically, it is being used for tuning w/ components that are made to support it, not being used to cover up a problem w/ parts that are not made to work together.

Ben

 

Actually I don't consider it a band aid. It is common practice to do so. Manufacturors rate the same injector based on different fuel pressures. The Bosch ones I'm going to install in my car are rated at 28.55# by Ford with 39PSI pressure. GM rates it at 30# at 43.5 PSI.

What you don't want to do is exceed the duty cycle. Either on the low end or the high end. This will cause problems. As long as one stays within the duty cycle range I do not see a problem with adjusting the fuel pressure.

 

As far as the buicks go.... The stock MAF will only read 255 grams/ second. well that problem can be solved by going with a LS1 MAF and using the MAF TRANSLATOR from bob bailey. you use a his Eprom ( EXTENDER) and the ECM can control fuel @ wot up to 512 Grams/second. then he offers a Extender extreeme eprom that will allow the ecm to read 765 grams/second. and these chips also have some more functions in them too like

128 BL lock @ wot
TCC lock up @ wot @ set speed from 45 mph up
Open Loop idle.
BLM adjust for injector constant.
Low Gear spark advance + - 4 degrees
Low gear fuel

there is more stuff in the chip that is user friendly. The neat thing about thing is you can make the changes while sitting in the driver's seat and never have to remove the Eprom from the ECM

Call Mike licht @full throttle speed & style

But i was refering to raising the FP up on the Z28 as a band-aid not the buicks. In my case i still think it's a band-aid. cause if the Eprom is tuned correctly you don't need to make any adjustments on FP


Thats just my opinion guys.

 

I agree to an extent. There is nothing wrong w/ adjusting fuel pressure, but I would rather have a prom that is programed for what I have and make fp changes for fine tuning.

Also, not to say whether or not the pump can handle it, or if it is hard on the pump, but just because different fuel injectors are rated at different fuel pressures doesnt mean that the pump can handle the pressures that you want to run an injector at. I do believe that a 305 prom and injectors can run a 350 w/ the fp turned up, but I dont think it is ideal, or gm would have just used the same injectors on each, and used different tuning, or regulators.

Ben