dhirocz

OK, I have a perfectly fine running 383 in my '94 and I started a conversion to a big cube small block in my shop to install most likely next year. The problem that I currently have and will make worse is the factory MAF sensor.

I love MAF, and my descreened MAF with a tune from Ion has always done me very well. Problem I have is that I think it's a small restriction now when I go over 4500 RPM's or so (assumption), but I'm certain that with a motor that's 427 cubes or larger with a single plane, that MAF will act like a restrictor plate. I've looked into aftermarket MAF's and the general concensus is that while they work for some, they cause tuning problems and driveability problems for more than they help. The Z06 looked like an attractive alternative, but with it maxing the LT1 computer early and with a big small block, I have to assume that will happen even earlier in the RPM range. And with a larger engine that tuners arent accustomed to tuning, this may prose a serious problem. So Im considering a speed density setup.

I did a search and everything was inconclusive really. I've heard that I would need to swap harnesses, computers only, that the PCM had a switch in it, etc... and I'd really like to know for sure. If I need to swap harnesses, will the connectors from the engine harness to the chassis harness match up? Are any sensors different from the '94 OBD1 sensors? Anyway I can get the MAF tuned out of the '94 PCM so I can keep both O2 sensors? Some good info on this will be great.

Im considering running the engine with a MAF, and if I pick up any significant restriction which Im thinking I will at speed, then swapping to the SD. If I do that, I will dyno the differences before and after for reference and post the results. Thats a ways off though.

BTW I have a T-56, so I have no need for trans controls... even though the harness has the connector for a 4L60-E.

red94chicken

well since the maf cars also use a map sensor too.. i don't see why it couldn't be tuned to just run off the map sensor..

O J

I have a 94 converted to SD, but done with a FAST system, so I'm afraid I can't answer most of your questions. What I have heard though, is that all you need to do is tune out the MAF and tune the SD tables (since the PCM reverts to those when the MAF is disconnected), but that it's more difficult from a tuning standpoint. I would talk to Ion or the guys at PCMForLess about it, they could probably give you a good answer.

However, I would suggest you ask this in the computer section of the board, might get a little more play there.

engineermike

Instructions to convert a '94 to Speed Density:
1. Make sure the key is off.
2. Open the hood.
3. Unplug the MAF sensor.
4. Close the hood.

Seriously, it's that simple. The '94 ECM has all the SD programming built in in case the MAF fails. The SES light will come on, but you can turn that off using any tuning sofware (LT1edit, TunerCAT, Tunerpro). Of course, you will have to tune the VE table just like you would any modified SD vehicle.

The only caveat is that the '94-'95 ECM does not allow you to play with the Accel Shot (tip-in enrichment) like the '93 SD-only ECM does. If you have tip-in tuning problems, then you might have to switch to an older ECM.

To see what is required to swap, find the ECM pin-outs on the '93 and '94 and compare them. You might find that it's simply a plug-out/plug-in installation.

MichiganSkip

Here's what I can't figure . Why not INVEST in a SET of WB O2 A/F boxes like the Innovate or Dynojet or now FAST has a Dual WB setup. then you can go SD, and the LT1 Edit or TunerCat allows you to tune both sides individually( even right donw to individual cylinder balance). Seems to me to be money well spent if one dumps big $$$ in an engine. What's another 1K when we're looking at $$$$ for a motor.

dhirocz

Im a soldier. I dont make THAT much money. Building this motor is gonna cost me almost 10 grand to not cut corners. But it really isnt that much more than your typical high end 396...

Besides, Im the first person I know of to do this. I need to know if and how well the engine runs with the stock equipement before making changes. Anyone can install a SBC in an LT1 car with a different method of fuel management, but part of this is to make sure it works before making changes like that. If I didnt do it that way, it kind of defeats the purpose.

I was thinking that maybe the '93 ECM would fit in place of the '94. I'd have to check. I have access to one at home. At a minimum, if the pinouts are the same but the connectors are different, I could always get the connectors and replace the ones on the harness or add some for easy swapping. Just a thought.

engineermike

No offense, but I kinda' doubt it. That sort of thing is done all the time. Just a couple of weeks ago, I was running my '95 turbo car in SD mode to get a feel for whether or not a 2-bar SD tune would be feasable.

Mike

dhirocz

No, I didnt mean run speed density. I meant run a big cube small block using factory EFI equipment on a Gen 1 in an LT1 car. Everyone always says it cant be done... I already have bolted the thing to a motor. Now it's not a matter of 'if' it can be done, but how well it turns out.

Who knows? I might put it in there and the PCM goes nuts. But if you can use the stock PCM for a crazy cammed stroker, I dont see why not for a big cube street engine.

Jerm93z28

it should work and tune fine, you just wont be able to spin more than 7100 with it... the injection system doesnt care how much displacement the motor has, to a certain extent.
dump the maf and run it in SD.

engineermike

What do you plan to do for a distributor if it's a Gen 1?

dhirocz

Figured I'd tape an opti on. LOL No really I modified a stock timing cover by machining an adapter to sandwich it to the block, taking up the open space at the top where the water pump drive would be...machined it down the thickness of the spacer where the cover meets the block... then bolted an opti to it. I dont run spark through the opti and I have had zero reliability issues with it and dont think I will. It's all running stock type hardware with a few tweaks.

I think I came up with a better idea to block the intake and drive the oil pump with a dummy distributor. If I was using the opti for spark and had timing marks set with a keyed hub, I could also use the distributor for making minor spark changes and making an easier serviceable cap and rotor than the opti. Either way it keeps me from having to weld in the valley for a standoff for the oil pump drive adapter.

I have that part all figured out. Somehow though just unplugging the MAF and running in SD mode seems too easy... and maybe it is. I'm worried that since I have a single plane to tune for, tip in accel might need adjusting, and if I cant, that may pose a problem. I'm planning on making a call today sometime to see if it can be tuned out.

engineermike

If you figure out how to tune tip-in accel on a '94/'95, let us know. Lots of guys (including myself) have been trying to do that for years.

sbs

Non-redneck method:

1. Open tune in tunercat
2. Enable SD mode switch
3. Upload to PCM.

dhirocz

If I do I will post it. It shouldnt matter to me much, because from what I read, the majority of people with single plane intakes who have problems tuning tip-in are those running Accufab throttle bodies. I'm running a 58mm so tuning should be pretty straightforward. Like I said, the biggest issue will be with the PCM/ECM and deleting the MAF. I dont know if it's hurting me with a stroker by just being descreened, and I hope not, but we'll see. I'll post what I find out.

dhirocz

Now THAT's what I wanted to hear! Now my biggest question is, since I'm still finishing my 383 the way I wanted it (will eventually go into a 'vert when I finish the big motor) is do you guys think there will be any gains from switching to SD now with a cammed 383, or do you think that the gains are insignificant enough to not justify deleting the accuracy of the sensor?