StudyTime

How does the sequence of fuel injectors firing come to play in swapping the firing order?

I'd see on a TPI car just swappin the wires because they are batch fire, but what does the LT1 ECM need done as it is SPFI?

Ben T.

engineermike

Ben, swapping the wires would work.

The only problem is that the computer adjusts the fuel for the entire bank of injectors. If you swap the injector wires for 4 and 7, then instead of correcting the fuel for, say, 1, 3, 5, and 7, which are all left bank, the computer would be adjusting the fuel for 1, 3, 5, and 4, which are 3 left and 1 right bank.

Would this make any real difference? I doubt anyone would ever know the difference.

Mike

dnz28

thats what Im thinking.

SStrokerAce

Might and it might not.

It's going to play with the part throttle operation more than anything.

Someone should really try this on their own car and accept the results if they are bad.

Bret

jimlab

How is the injector firing of a sequential or bank/bank system affected by swapping the #4 and #7 cylinders? I would assume that a sequential system would require swapping the injector wires also, but what about a bank/bank system? If it fires all four injectors on one side of the engine, isn't it going to be out of synch with the #4 and #7 swap, firing the injectors on the opposite side while firing the spark plug for that cylinder after swapping the wires?

IllusionalTA

If one of you guys' will finance it i woudln't mind throwing it in before the motor goes in.. ALready have DFI I'd like to know myself..

chucks97ss

So Bret, what is your secret discovery? Is it the fact that the LT1 has a step nosed cam just like every other late model sbc roller block? Or is it the fact that it has an extended dowel pin to drive the opti? Or maybe the fact that you have to reduce the dowel pin size if eliminating the opti to plug the cover? Or maybe you've put a cam sync in a belt drive to trigger an edist fired by a crank trigger igniting 8 coil packs? The 4-7 swap has been around for many a year now. It is no "new" discovery here... GM just finally caught on to what Fords been doing right all along.

Later
Chuck

SStrokerAce

Seems like you are still a bit edgy over the "engineering" thing that Fred even backed me up on. As I said LOVE THE NAME!
Chuck, I could care less if we get along or not. I don't want to get into anything because it's not worth it to me at all, I gotta take a nap and pull another long day/night at the shop.

It's some of those things you mentioned for sure. Buy a cam and put it in a block and you will know for sure.

It's been around a longer than a year, just more of a commercial item now.

Thanks for the imput.

Bret

LameRandomName

Stroker -

I'm not sure that I agree that having an O2 sensor read 3+1 cylinders is really going to screw things up. In fact, I'd have to wonder if it wouldn't in fact help to give the computer back some more "balanced" information.

So, am I misunderstanding what's going on there? Why is it a negative?


Also, you mentioned that if you had an aftermarket controller that you would be "golden".

What would you be able to do that makes the difference?


Finally, I've been trying to figure out what the LT1 issues are.

The crank shouldn't know the difference.
Neither should anything in the bottom end, not that I can see.

I understand that the valve timing would change because you are swapping out two firing events, so that's the entire cycle that changes.

I can't see where it's anything to do with the opti, because the camshaft itself is identical and behaves the same way, except for those two lobes being opposite.


All I can think of is that you need to wreck out the air pump system completely in order to have clearance to run two wires in the opposite direction than they began in, but you alluded to something OTHER than the wires.


I'm just stumped.

Any help?


BTW, the reason I am asking is because I have been wondering what you would get if you completely optomized everything that you could in the LT1, even down to high performance coatings, both friction and heat. The idea of the LT1 working better with different timing events interests me, and the thousand dollar cam doesn't really scare me.

jimlab

Neither do I. The O2 sensors are still reading the output of 4 cylinders each. It's not like they have any idea which cylinders are firing and when... exhaust flows past, they read the oxygen levels. Pretty simple.

I'm not sure why this is an issue either. If you simply swap the plugs for #4 and #7, the computer shouldn't care. As long as the Opti is still spinning, everything should be copasetic as far as the PCM is concerned.

Nope.

The only problem I can think of is if the injectors are firing sequentially and #4 fires when #7 should fire and vice-versa. That's not an issue with an aftermarket bank/bank system, but I don't know enough about how the stock PCM controls the injectors to know if this is a problem.

A 4/7 cam isn't a thousand dollars, and even an LS1-lobe order cam shouldn't be over $800.

I think I'll be one of the first to buy the LS1-order cam, but I can almost guarantee that someone else will have an engine running with one before I do.

Hot Rod Hawk

LSM did this three years ago. Petty played with it and it stayed pretty tight liped till they started selling test dyno motors
I have a friend that has bought a couple of these test pieces from petty.
He put the sb2 cyl heads & intake on a 331 inch sbc ran 8.12 @172 at 3000 pounds. ThEn he switched the deal to the 4/7 swap and ran 7.91!
On a non related bit he just went 412 inches 4/7 sb2 and ran 9.23 on motor and with 32 jets in the fogger boggied out a 7.59 at 191 on ten inch tires at 2600 pounds testing at Bradington a month ago

SStrokerAce

Thanks for the answers Jim.


Yeah the custom firing order LT1 cam is $750 or so so it's not outrageous but not cheap at the same time.

The little issues with this I'm not going to let out, it's a simple setup if you do it on a SBC but a LT1 is a little bit more work.

Bret

OneFlyn95z28

We also have a firing order picked out for my new motor. Pro Stock Racers found more power and less crank breakage with the order they are using also. I want to say it is 1-8-7-3-6-5-4-2. I have all of them scanned some where. There are 8 firing orders for the SBC twisted crank shaft

Correct me If I am wrong but the LS1 is and old GM firing order?

Cadallac comes to mind?

SABLT194

I don't think the PCM would be a serious drawback. It would only affect idle and cruise situations. And, if it did tend to skew things a bit, just set up a nice lil Open Loop program and she'll run just fine. My guess is that anyone going with this much of a change won't be super particular about maintaining a perfect 14.7 AFR while taking the Z to the grocery store. Running Open Loop can work just fine. Just need to recheck things with a WB fairly often to make sure nothing has changed. Heck you guys squeeking the last little bit out of NA LT1's have probably already ditched the MAF and tuned Speed Density so it would be just 1 more step for mankind.

Steve

96Z28SS

Jim there is no difference in the 2 eDist boxes they are exactly the same only difference is that the LS1 part number comes with the LS1 coil harness mating connectors. I think just recently they list the box as the same part number, but the harness are 2 different part numbers. You can check with FAST on that but I'm pretty sure the boxes are the same you just change the pins on the harness.

Also in the Setup menu or System config menu, (I can't remember) in the FAST system you can change the firing order to anything you want.

Rob