I am seriously considering swapping my miniram setup for a carb. Not expecting more power, just looking for more consistency when bracket racing. I did some searching and couldn't find much about keeping the computer and sensors and using them with the carb. It would be nice to data log the data for the CTS, IAT, Knock, O2 (step up to WB) and also the VSS. Is this possible once I unhook the injectors and take out the computer dizzy? Any one have any pointers??

 

Hmmm, carb sensors.

You can keep MAP and CTS. You can rig up TPS and IAT. Cam sensor (engine RPMs) will be questionable, as the factory computer uses a non-vacuum/mechanical advance distributor to provide that signal. Wideband O2 would require its own system, I believe, but I could be wrong about that. Knock sensor could be monitored, I suppose. VSS isn't part of the engine control system.

 

To take it a step farther, couldn't you keep the electronic distributor too? Not that I really want to, just thinking out loud! If you have IAT, CTS, TPS and MAP...isn't that all of the input that is needed for the distibutor?

 

If you wan't more consistency, disable closed loop.


Their is no benefit in switching from the miniram to a carb, unless you know how to tune a carb as good as hitting + or - with the laptop...

Now with that said, you could remove the miniram and replace it with a carb. Work out the fuel pressure, and use the ECM for spark control, and logging. As long as the ECM sees the distributor turning, that is all it needs.

You will want to run CLOSED LOOP, disable idle speed tables and spark correction for idle, and maybe a few other minor things. You will want a TPS signal and MAP signal for your advance curve. (if you are running MAF, switch to a MAP ecm).. You can zero out anything fueling related, or anything that would use spark to compensate for a fuel condition or idle condition. Would work out fairly well.

Wideband can go into the ECM with a patch for the bin.


Depending on the car, I like EFI, especially if it's paid for. For an aggressive setup, or starting from scratch sometimes it is hard to justify spending money on all the EFI stuff. Some things EFI sucks for, like tuning fuel on a large cam with a MAP sensor. I've learned over the years that you can't dismiss a CARB or EFI, they both have proven applications.

-- Joe

 

Joe:

Thanks for the input. I never gave much thought to keeping the distributor until just now. It seems like an interesting setup. I really have two main reasons for going to carb...

1) Consistency when bracket racing.
2) Changes next season (higher compression and stroke to 383).

I am a little old school, so carb tuning is much more natural to me. With that said, it is Traxion's old IROC that I own now. That thing runs! He sure knew what he was doing when it cam to tuning a car with MAP and a 240@50 cam on a 109LSA!

JEFF

 

Didn't some other guy buy that car from Tim?? I'm impressed the bottom end is still holding up.. Tim did get every bit he could out of that car.

Anyhow, your plan should work. Assuming you have the tuning stuff still for the car, you can zero out a lot of the stuff I mentioned. When you make the change head over to DIY-PROM and that can be discussed.

IMO, if you can know exactly what the advance curve looks like that is better than a guess.

-- Joe

 

Yeah, I bought it from that guy. He owned it for about 4-5 years, but only put a few hundred miles on it. I put that many on it in two years just on the dragstrip! Still the stock L98 short block. I put in new valve springs and just general maintenance. It is due for a rebuild soon. I just recently yanked out the original 700R4 and replaced it.

I don't have any DIY prom stuff...just a cable and datamaster. If I do decide to keep the distributor computer controlled, I will need to invest in all that. It is something to think about. I have a standard MSD pro billet from an old car. Maybe I will run it until next season when I do the rebuild and then convert it back to the computer controlled setup.

Thanks again for all of the input!

 

Other than the laptop, you'll need some sort of emulator and you will probably want to read his chip to get an idea of what the timing is currently.. Figure a few hundred bucks.

You'll probably get around $1,000 for the miniram/injectors/throttle body combo.

If you intend on using an electric fuel pump for the carb, and using the ECM to power it on and off you will need to keep the electronic dizzy. The ECM will prime the pump at key on, and keep the pump energized as long as it sees DRPs from the dizzy.. If you run a mechanical pump that doesn't matter, or you could splice the electric pump to power in RUN but I don't like the idea of a pump going with a stalled engine...

I also don't like a mechanical pump. Sometimes a car sitting for two weeks will result in a dead battery trying to get it to fire up with a mechanical pump.


-- Joe

 

You can keep the electronic distributor if you have TPS rigged up. Without TPS, you won't get proper advance from the ECM.

You can use the electronic distributor without TPS on the track, just set total timing (36 degrees with RPMs up). There isn't much advance built into the ignition control without the computer active (which it won't be without TPS), so starting may give you some kick-back when you have the timing advanced for total.

 

The only thing that worries me is what the ECM will try to do with spark at idle if the idle speed isn't dead nuts on with what the BIN is set to. It will reduce/add fuel, and advance/retard spark to try and get the idle speed set, which might make for an interesting running car.

If he has a copy of his bin online, I could probably zero out all the tables for him and mail him a prom, disable closed loop, basically make it a 'timing only' computer, but with TCC control, fuel pump control, etc.


Do you have preference on vac/mech dizzy's vs electronic, five7kid ?

-- Joe

 

This conversation is getting really interesting guys...especially for a guy like me who knows almost nothing about proms!! If I had a wish list, it would look like this...

Keep my existing timing curve (it shouldn't change much with a carb)
Keep my ability to data log the various sensors (and be able to use a WB O2)
Keep the computer controlling the fuel pump and the TCC (vats is disabled) and the fans.

Joe,

Your offer is very generous and I think I would be willing to pay for a prom like that. I have no idea how to get the .bin extracted. I have some copies of Tim's bin files, but I am not sure which is the current one (if any). How would I get them to you so you could look at them?? What software would I need for making changes to the timing curve in the future? Tunercats?

Thanks guys! Keep the ideas flowing!

JEFF

 

Hi Jeff,

You would want to use tunercat or tunerpro. Tunerpro is free.

I wouldn't charge for any sort of labor or anything, but if you wanted to reimburse me for postage and the cost of a blank chip that would be fine.

You can email me the bin files, however you need to determine which one is the one you are using. (although if the advance curve didn't change it might not matter).. I think I have an image of Tim's advance curve from some years ago.. He, like me, used a lot of cruise and decel advance. He may have zero'd out the PE spark adder, and done it all in the main table. (I do that as well).

I'm not that great with carbs, but EFI was always second nature to me. I'm going to try and make an effort with the carb for a little while anyhow on my 2nd gen, just because it's better to be well rounded.

-- Joe

 

Joe,

I have the bins saved on my work computer. I'll look at them and see if there is anyway to tell which one is the newest. I'll send you an email and then we can square away the details.

I do have some datamaster logs that I did recently. Tim is running a ton of advance at cruise and partial throttle...close to 50 degrees advance. I had a similar timing setup on my solid lifter 406 years ago (low compression and too much cam for the cylinder heads!). I followed what was in a David Vizard book, and it worked well. I think Tim was doing the same thing.

JEFF

 

50 degrees? That is impossible. You can't have more than 45 on an electronic dizzy. hrmm. I wonder .

-- Joe

 

If you don't have TPS hooked up, the computer will go into "limp home" mode. The only advance you will get will be what is built into the ignition control module.

Unless you've moved away from the original idea of putting a carb on.

If you aren't running a computer induction system, such as TPI or computer controlled carb, I would use a vacuum/mechanical advance distributor. But, using a computer distributor on a track-only car would be very similar to using a locked-out advance distributor, with a slight advantage of less advance at start and low RPMs. I don't know if it would be enough to avoid starter kick-back.

I did run a computer distributor with a non-computer carb a couple of years ago. I rigged up a TPS to give the computer that info so it would control timing. It worked okay, but the computer controlled carb worked better, so I put it back on.

 

Joe,
I am not sure about the 45 degrees advance max. I thought it was showing 48 degrees in the datalog...I would have to go back and check. On my 406, I was using an HEI. I believe it was 16 degrees at the balancer, 20 degrees built into the distributor and 12 more from the vacuum advance can. That was 15 years ago, so my memory is a little shady.

five7kid,
I am planning on adapting the TPS sensor to the carb. I have seen some kits out there, but they are like $80. I think I can do it cheaper than that.

 

On an electronic dizzy, the rotor is fixed. The advance happens by firing the coil when it thinks the rotor is xx degrees from TDC.

Now say you want to fire the coil at 50 degrees BTDC of cylinder #8, well the rotor is closer to the terminal of the #1 cylinder than it is to the #8 terminal, and since electrical current will follow the closest path to ground it will fire the #1 cylinder.


You have 720 degrees of firing, 90 degrees between each terminal. 45 degrees is in the dead center (could go either way)..

Rules are different for mechanical. The rotor actually moves closer to the terminal

-- Joe