This is my first post and I apologize for being so long winded here. I have a 1996 LT4 Competition Yellow Corvette with many modifications. I bought the car like this back in May and am ironing out the little problems with the car. I know, I know, this isn't a Camaro, but it is an LT motor!

My number 3-6 cylinders were causing the headers to dimly glow at night. During the daytime, there is no sign of glowing. This initiated some questions on a Corvette board and the advice I got was that it is either retarded timing or running lean. At idle, the car does not run lean, but I don't know about throughout the rpm band. The car currently has stock injectors (26 lb). I had quite a few folks say that these injectors were wayyyyy to small for this setup and recommended 36 lb. Sooo, I'm looking at 36 lb. If I get the 36 lb, I've been told that a new tune will be needed and that scares me a little. I'm comfortable wrenching, but electronic controls have me concerned. I'm just looking for advice from the experts here on what is a good tuner for me and my application? Will the car need new tune with 36 lb injectors? How hard is it to tune?

Here are the details of the motor and ignition setup if that is needed and this is what was posted on the other forum:

Thanks for all of the info and keep it coming! Sorry for the long post, but this might help in diagnosing a problem, if one exists.

I checked the pressure while not running and it is a solid 36 - 37 psi. I had some NGK TR6 plugs in it for a few hundred miles and they were very black, but these are cool plugs. I use TR55's and they are doing very well. When I look at the ground strap, they are very light in color, but the ignition system is what I believe is causing this. Right now the TR55's are set at .050. I do believe that the stock injectors are stock. Here is a picture of them, so if they don't appear to be stock, please let me know.



The motor is not a stock DRM 480 package. The previous owner started out with this and added some really beefy parts to the motor. The only DRM work that remains is the machine work on the block. Here is a list of items added later. All of this info came from the previous owner.

Crank, rods, and pistons were replaced with an all forged rotating assembly. The pistons are ROSS and hold about 190 psi compression.

Cam and pushrods are Crane with lift of .555/.570. Don't know the other specs.

Heads have been ported, bigger valves, double springs, titanium retainer, and the flow is about 280. Crane Gold 1.6 RR's added.

Intake has been port matched to the heads and 58 mm tb. TB is 58 mm.







Ignition is MSD Dig 6 Plus Controller (Part 6520) with Accel Coil, and MSD opti.

Nitrous system, NX MAF wet system, FJO progressive controller, fuel pressure regulator switch, with bottle warmer. All the good stuff. Here are 2 picturs.





Meziere HD electric water pump.

I'm beginning to think the car needs a custom tune. Is this something that I can do?

 

Wow, I feel like an outcast already!!

I was referred to this site due to all of the expertise on tuning. Anyone have some insight????

 

First you have to decide if you really want to tune it yourself. You will have a learning curve, and with the number of mods done to the car, its going to take you a while to get the hang of it. Changing the injector flow constant for the 36 #/HR injectors is pretty straight forward, but you have to verify the results. Yes... if you change the injector size, you must enter that information in the program.

Your fuel pressure is not adequate IF that is measured at WOT/max engine load/max RPM. You should have at least 41psi under those conditions. The check procedure would be to measure the fuel pressure at idle, with the vacuum line off the fuel pressure regulator. Should be in the range of 41-47psi, with 43.5 being the desired pressure. Reattach the vacuum line to the FPR and pressure should drop in proportion to intake manifold vacuum. 6-8psi drop on a stock cam would be normal, but with the cam you list (limited data) you're probably going to see less of a drop. But ON THE ROAD, at WOT you should see the same fuel pressure you measured at idle without the vacuum line attached.

A 26 #/HR injector is going to hit 90% duty cycle at about 390 flywheel HP, so yes... you need something more than the 26's. To get your approximate, minimum injector size, multiply your estimated flywheel HP by 0.07

Example: 450 flywheel HP x 0.07 = 31.5 #/HR.

There is nothing wrong with using a larger injector than you need, as long as you don't get ridiculous. The stock PCM seems to be able to provide a decent idle with 42 #/HR injectors.

To provide more info on injector sizing, you have to provide more info on the engine. Full cam specs (intake and exhaust duration at 0.05" lift, gross lift using the specific rocker ratio you are running, and lobe separation angle). Then you need to include some info about head flow in the 0.500-0.650" lift range. The fact that the pistons can hold 190psi compression is not really relavant.

[EDIT: Not sure why, but I thought you had an OBD-I conversion. That's why I listed the OBD-I programs shown below. If you are still running OBD-II, I can revise these links]

For tuning, you have 2 choices:
-LT1_Edit
http://www.carputing.com/

-TunerCat
http://www.tunercat.com/

In order to evaluate your tune, you need scanning software:

-pcmcomm
(bundled with LT1_Edit)

-TTS DataMaster:
http://www.ttspowersystems.com/

-FreeScan:
http://www.andywhittaker.com/

-EFILive V4
can't find my link to that one.

If you decide against tuning yourself, go to the Supporting Vendor Index and look up the popular mail order tuners, including pcmforless, MadZ28 and Trifecta

The NGK TR6 is not a very cool plug.... its one step colder than stock, and good for nitrous and heavily modified normally aspirated engines. Your engine should not be fouling them.

 

Let me give you some additional basic help.

Your injectors are sized just fine and you do not need to go larger unless you are going to be going WOT above 4.5K or so. Only then will the car have issues with going lean. Get the car tuned first and THEN change the injectors. To do drivability tuning, your injectors will do just fine.

Regarding your idle issues, I would figure that you need to take a look at the TB bypass to make sure all your idle is going into your idle plenum. Do a search for throttle body bypass. Mucho been said. It is a start but a VERY good start to determine where you stand. Unless all your air is going through your idle plenum, easily you will have idle problems especially with a larger cam. Correcting this will help with the individual cylinder AFR.

This is a start but, my friend, you have some work cut out for you. I have many hours under my belt tuning but learned a lot by going to this forum and reading old posts.

After what I have given you, I would start by doing some things Injuneer and I suggested and hearing from you on your progress. Definitely get a scanner as Injuneer suggested.

 

You can adjust the individual cylinder fueling in your tune if need be. I would look into replacing the injectors with some 36lb fast units. Go on youtube and look at videos of the spray patterns to see why fasts are new delphi 3 type injectors. You may have some trash in them or the injectors may be having driver problems, they are a wear item. The stockers are ok up to a point and then you will run out of fuel. Tuning for them is as easy as can be. You can have it in shape with about two flashes, you just need to change one number and thats it.

The only other things that causes the tubes to glow besides improper fuel (rich will do it especially with an exhaust leak), is improper timing (retarded), or in some cases weak spark or missfire. What happens here is it doesnt finish burning in the chamber and goes out still on fire into the header.

As has been mentioned before, it could be a distrobution issue caused by your camshaft. You could probably fix this fairly easily by adding a couple % fuel to those cylinders and quite possibly closing down the throttle body (although i have no idea how it is adjusted at current).

IMO, the first thing anybody should have when modifying an efi car is logging and tuning software, maybe even if the car is stock. Its really not that hard. You can read old posts here or start new ones with your questions or problems as they arise. Mail order tunes are ok, but they have a bit of trouble addressing the small things and tuning your car to your driving style from a remote location (critical for a4's more than m6). I like tuner cats, freescan, and tts datamaster for the job.

 

Thanks for some very good advice!! Someone said that there is a great deal of tuning knowledge here and you are not letting me down.

The car runs very well, but I'm just trying to get the tuning and timing all tightened up. My main concern is to not go lean and cause engine damage. The CHP from Doug Rippie is stated to be 470 (DRM 480 package), but with the additional mods done, it I'm guessing over 500 w/o nitrous. The car runs 12.0 - 12.1 1/4 in the 118 - 120 range right now. So, assuming 500 is close, don't I need 36 lb (500 * .07)? So anything over 514.29 chp would need more than 36 lb?

I found a set of real white (36 lb) Bosch III injectors for $250 shipped. These are the newer design with improved atomization. Is this a good deal?

I looked at the links, but the only tuner I could find for my car (OBDII) was through tunercat (Jet). I saw a Jet Power Control Module Stage 2 and Jet Performance Dynamic Spectrum Tuner / Programmer. I think the dynamic tuner is what is needed here. Is this the correct tuner? If so, how hard is it to use??

Since the car has a MSD Dig 6 box, I can retard the timing up to, I think 12*. I turned the dial back to 0 or no retard, so the computer is not being overridden when the NO2 system has been activated. When running the fuel pressure is right on 39 and when driving, it is 40 - 41. When the car is off, but the fuel rails primed, it is 36 - 37. All of this is taken from a pod gage and the censor is pictured in the previous post.

Winter is coming up and this is sounding like it could be a very fun winter project. The car is used for liesure, so if it is down for a few months for tuning and injector swapping that is OK.

Again, thanks for the great advice and being patient with a novice tuner. Some days I wish this thing was carbed!!

 

I'd probably switch it over to obd1 to allow acess to free/cheaper programs. I am not sure of the logistics of it on a vette but I am sure that information is available freely if you look. I will be the first to admit I dont know vette stuff.

36lb injectors will cover quite a bit, my latest 355 combo made about 540fwhp and did not max out the injectors although the duty cycle was somewhere in the high 70's low 80's. My fast injectors flow a little more than they are rated at, they are exactly like the white 36lb ones you are looking at. 250 isnt too bad, I gave 300 for a new set last year from texas speed.

I would stick with 36lb injectors over the 42's. While 42's will idle ok I think thats right around the point where low speed and idle operation begins to get a little funky due to the ms resolution of the stock pcm. If you can find a deal on a set of 42's though they will give you a little bit of room to grow. I cannot understand with your current setup how you are able to keep from leaning out at high rpm though if your inectors are in fact stock. You might consider having them flowed or if you can find somebody with a scanner to check duty cycle that would be another way.

Now for a little lesson on fuel injectors. If you have never seen them in action before side by side it will be. Fuel injector connection does very good work as well.

http://www.youtube.com/watch?v=Emnax...eature=related


None of the tuning programs the material isnt that difficult, but there is a mountain of it for you to digest before you get a good understanding of what happens when and why.

 

Somehow I thought you had an OBD-I conversion, and that's why I listed what I did. Since you have OBD-II:

LT1_Edit (OBD-II version - same link as posted above)

The JET program software is correct. That is the OBD-II version of TunerCat.

Virtually any OBD-II scanning software will work. AutoTap is a decent setup.

http://www.autotap.com/

 

Is there any way to tell what lb they are by pulling one of them? What confuses me is that the car seems to run rich. When I used the TR6's, it would literally leave black soot marks on the garage floor about 2 feet from the rear. With the TR55's, it does not do this. I'll try to post some pictures of the 6's with 200 miles on them and show you the TR55's with 300 miles on them. By reading the plugs, the timing is just slightly retarded, by looking at the strike mark on the ground strap.

One more thing to mention is that when the car is dropping in rpm in gear (using the motor to slow down) it sometimes pops. It is not backfiring, but just a light pop. I'll see if I can get this recorded for you.

I'm going to call a tune shop that was recommended to me and see what kind of service that they can give me. If it pans out, I'm going to go with the 36 lb and have them do a tune for me. After reading up on tuning, I'd better leave that to the professionals.

The only reason that the nitrous system works well, is because it is a wet system. Fuel is mixed with the NO2 in the MAF, so it does not run lean.

The problem seems to be when the car is used just on motor.

Thanks again for all of the advice and I'll keep you updated.

Now I am impressed, a 355, all motor, making 540 rwhp is incredible!!

 

No no flywheel hp. I couldnt afford the gas and the stock pcm wouldnt work if it made 540rwhp n/a. I drive this sucker every day about 100 miles. Knocks down 22mpg avg doing half city half highway. I thought you were talking of 500 flywheel hp in your post you will not hit 500rwhp n/a unless there is something you're not telling. When you calculate injectors you go by flywheel hp.

Tuning shops are not the answer, if you get it tuned on the dyno it is going to be lean on the race track 99% of the time. Your problems are drivability problems it sounds like. Most of the time all they do is fix up the wot fueling tables and leave most of the rest if it alone.

When you would run lean would be wot without the nitrous. When the injectors max out they start acting really funny and eventually it will just lean out.

Tuning is not hard! One change at a time and check the results, you will get it very close very quickly. The pcm has all sort of dummy proofing on it, it is very hard to get it to do certain things outside of stock because of how it is programmed. I do not trust or believe in tuner shops for the most part. I have seen some completely terrible and dangerous (engine damaging) work done by "reputable" tuners. I have also seen people pay up 500 dollars and the "tuner" cant seem to fix an issue so he tells them its a mechanical problem or that the pcm cant be adjusted for whatever the trouble is so they walk away 500 poorer with a car that runs like ****, and magically when the right person is pecking the keys the problem goes away and the car runs great .

On the popping and soot marks, let me guess this is right after startup? It sounds to me like your open loop target air fuel ratio tables need to be leaned out as most do especially with a healthy cam. The popping is from being over rich, and you probably have an exhaust leak. It was worse with the cold plugs because they are too cold to keep themselves clean and were fouling due to the rich condition. I would swap to the autolites (103 or 104 cant remember) for a stock lt1, they are harder to foul than the ngk's. You will not hurt it staying with a stock heat plug while you're off the nitrous. On the nitrous you'll want to go with something like a tr6. In general a good nitrous/race plug is much too cold for cruising. Part of the fun of nitrous is swapping plugs . It is always going to smell nasty and gassy from the pipes if you have removed the cats, that is just part of it with cammed lt1's. There are fixes but mileage is going to suffer most likely, and I am not really a huge fan of some fixes as they freak the computer out a litte bit and cause problems in certain cases.

If I was going to do tuning and spend money on getting it running right I would do an obd1 conversion and tune it myself on the street/track. I know on the obd2 f-cars that all you do is buy an obd1 pcm solder in a 3 cent resistor from radio shack and it is plug and play I have done this about 30 times. I would give that a hard look before I bought obd2 stuff thats 5x the money. The reason i cant tell you for sure is i am fuzzy but remembering something about certain cars having gauge options that dont work correctly with older pcms? If your gauges are all analogue it should be all good.

The thing about injectors is they can be modified, you can take the same injector, make it anything from 19-48# and you wont be able to tell squat by looking at them. Only way to know for sure is to have them flowed.