I have a 1986 IROCZ with a 1991 L98 engine that has 190 AFR 75cc heads, a holley stealth ram intake manifold, 1gc211-D1SC Procharger, MSD 6BTM, MSD distributer and coil. It has a fresh rebuild on the stock bottom end. I will be running 8 lbs of boost. This car will be a summer daily driver with very limited 1/4 mile action. I currently have Accel 24# injectors and a 1 5/8" tube headers, no cat, 2.5 or 3" exhaust. I am going to start to assemble the engine soon and I'm looking for a reccommendation on injectors.

I won't be touching the bottom end for one or two years.

Thanks for your help.

 

What computer will be controlling them?
What are your upgrade plans in the future? current and future HP goals?
Have you ever tuned an ECM before?

That stuff will affect which injectors you should consider.

 

What computer will be controlling them? The stock one.

What are your upgrade plans in the future? current and future HP goals?
My upgrade plans for the future are to build a bullet proof bottom end, replace the rear end with a 9" when the stock one goes. I spent a lot of money on my transmission, so I hope it holds.

Have you ever tuned an ECM before? I have never tuned an ECM, but I was told about a person who does. I'm not sure if he is a sponsor and I don't want to advertise for a person who might take business from a sponsor, but I'm lead to believe that he is very reputable.

My goals for the future are to beat my friend's 99 Z28 and he has been working and planning it for years. I don't think I will ever beat him and, if he is correct, his car should have 800+ HP. I don't really have any particular goal and I figure I will be able to trade up from the D1SC and the AFRs in the future. I'm planning on going to a 1 3/4 header system in the future, but, I don't want it to be loud. It will always be a work in progress and I don't know if it will ever hit the track or a dyno. I'm just having fun. And, oh ya', beating Fords and Dodges. I have a white 86 IROC that is desperately in need of painting, no rust, but a lowered Hotchkins suspension, otherwise just a slow looking third gen.

Thanks,

Steve

 

The stock computer will not work because it is MAF and you will max out the system before hitting PE mode (higher TPS position). Swapping to speed density is an option.

I would start with 60#/hr or larger injectors.

Let the tuner know it is a MAF computer and the MAF will be maxed out before PE mode is active. Not easy to tune. Personally, I wouldn't even try running and tuning that computer and would swap it out for an SD computer. The MAF is only good for lower HP numbers than what you are targeting.

 

Thanks, that's good to know. Where would I get a cheap, new speed density computer?

 

60's will be more than enough for that setup right now. Depending on your cam, it looks as if you will be in the 575 hp range on motor at 8 psi. You can handle that with 42lb injectors, but 60's will leave room for growth down the road. They usually are good for about 700hp, but my buddy used them to 700whp on his truck, but at high LSx pressure so they were more like 72's. They have some capability. If you ever want to run with an 800+HP 4th gen, you may need to get a set of 72's or 80 lb injectors to be sure you have enough. 80's should be good for near 1000hp on gas. I think I'm only at 40-45% cycle duty and I estimate I have 800-850hp on motor.

You can run a 91-92 ECM and run code $59 to run the boost. Its a nice setup and cheap. Thats what i use. The biggest problem is finding a 91-92 Speed density TPI memcal and stock chip system to plug into the new adapter you need to plug in burnt chips. 305 ones are much more common and will work. 350 ones when found can be rather pricey.

Repin your stock harness to plug into the ECM. You will need an extra connector pack for this conversion. Its not that hard, just takes little time to pop out the wires from the stock connectors and move them to the new pin locations. 730 ecm from 91-92 has 3 connectors on it, while 86-89 have only 2.

 

I agree with Orr89RocZ about the choice of injectors.
I forgot about the 730 ECM Memcal becoming so obsolete and expensive. One option is to use a 4.3 V6 MEMCAL and do the jumper wire needed for V8 fueling. Since the 4.3 and 5.7 have the same bore then the knock sensor ckt is tuned the same (in theory).

Three reasons I started coding boost for the 427_ECM (95 truck, etc) was that they are cheap with a 5.0, 5.7, or 7.4 MEMCAL, can control the E-trans, and use peak-and-hold or saturated V8 injectors. Sad part is that I haven't continued testing the code in months. If you kept the MAF setup then you could use Dimented24x7's code modification that uses the LT1 or LSx MAF (I forget). This would get you started with boost and do the fuel right until you went too high with HP. If I was doing a boost setup and didn't know coding and wanted an E-trans I think this would be a great place to start for cheap.

Another option is the Megasquirt II or Megasquirt III. The III is looking nice because it can do COP ignition and sequential fueling. It is nice for tuning intakes with runner-to-runner fuel distribution problems, but not all that necessary. If they could add the E-trans stuff it would be a nice replacement for the LSx engines and the all expensive tuning software.

 

I agree. 42s or 60s will work for you.

You don't need to convert to SD if you want to stay with MAF.

This can be handled with an appropriate MAF and either a double or triple range tune, depending upon the chosen injector size and ultimate power goals. There's more than one way to skin a cat.

On 8.5 intercooled psi (or 11 psi hot boost), I'm running about 90% duty on 42s now. 60s will give you some room to grow.

 

The only problem with that using the stock ECM is that you lose resolution. Extending the range by 3 means resolution goes down by 3. The stock TPI MAF is analog, and all the newer stuff went digital frequency signal.
What are you running for a MAF in your setup? Did you re-code or just divide the tables to extend range?

Dimented24x7's $0D code uses an LS1 MAF with 16 bit code. So it has excellent resolution and range (512 gm/sec => approx. 700HP)

 

I ordered the FAST 60# injectors. what about a 950 Holley or an 004 002 Bigg Stuff 3 computer?

 

Good questions.

Yes with this method with the 165 ecm you are still limited by the 8 bit A/D converter. This results in an A/D resolution of 0.02 volts per bit.

The output of the A/D is first multiplied by a factor to convert to counts and is then input to the MAF tables for interpolation to determine the airflow corresponding to the voltage, afterwards it is filtered to produce the aiflow signal in grams/sec.

Since the output of an analog sensor is roughly parabolic with respect to voltage, a 0.02 volt or 1 bit change represents a very small flow difference at the bottom of the sensor's range. The resolution is therefore variable over the sensors range which is independent of any scaling.

With a standard 3" housing diameter, the working resolution is on the order of 0.25 gm/sec per bit in the normal drivebility range.

As the housing diameter increases, this may go to about 0.5 gm/sec per bit, which is still rather insignificant due to the subsequent interpolation and filtering of the signal.

Resolution really isn't a problem.

I've also reworked the number of MAF tables and number of rows per table to permit up to 65 fixed 0.08 volt tuning increments across all of the tables.

This was done to increase the number of tuning points available in the low airflow region to provide more tuning flexibility for larger diameter housings, or to accomodate any non-linearity in the sensor's output due to bends or turbulent flow.

I'm using an analog maf from Blowerworks. Depending upon the housing diameter, this sensor can support a 0-510 gm/sec range, 0-765 gm/sec range or beyond if required.

Another comment on resolution:

At the high end of the 510 gm/sec range with a standard housing, 0.02 volts or 1 bit represents about an 8.5 gm/sec airflow change.

Therefore it is possible for the air flow to change as much as 8.5 gm/sec without any reaction from the ecm to provide additional fuel. At 510 gm/sec airflow, an 8.5 gm/sec change represents only 1.6%. Even in the extreme cases, a 1.6% fueling error should be acceptable.