It's my understning that all factory tpi's were batch fire. is that true? also, does anyone make sequential fire injection systems?

 

This belongs in the ECM board, but yes they were all batch.

Why do you want sequential?

-- Joe

 

I'm mainly just trying to find out what is available, I know that many aftermarket EFI systems are batch fire, but I didn't know of any sequential fire systems

-Eric

 

Several of the newer aftermarket ones are sequential.

 

Can I add a dumb question that is related? In a batch fire system, isn't a LOT of fuel being wasted by injecting it to cylinders that aren't on the intake stroke? It would seem that SEFI would be hundreds of percent more efficient than batch for that reason, but it's not like you would double your gas mileage just going to SEFI-- how does a batch fire system still get good economy even with all that fuel being sent where it is not needed?

 

From my understanding batch fire doesn't inject extra fuel when it's not needed, it's just not necessarily at the right time. So you may have a little cloud of fuel sitting above a closed valve for a split second which then gets sucked into the cylinder when the valve opens.

 

that was my understanding too, I want to eventully build a maximum effort monster motor, so I'm trying to find ot the pro's and cons of all of the different induction methods.

 

All L98 engines were batch fire. 93 LT1 was also batch fire (as was 92 LT1 in the vette). In 94 the LT1 switch over to sequential fire. You might check out the HP/MPG differences between these years, I'm not sure exactly what kind of gains seuqnetial fire has over batch. I'm sure it's somewhat more efficient but I dont know how much. LS1 and all newer engines are sequential fire.

 

According to fueleconomy.gov
the 1989 z28 got 15/23
the 1993 z28 got 15/22,
the 1994 z28 got 15/22
the 2002 LS1 z28 got 16/23....

I expected alot of difference between the l98 batch fire, LT1 batch fire, LT1 sequential fire and the LS1s....

 

It's my understanding that the sequential fire injection systems work better under 3500 rpm for emissions and ever so slightly better fuel mileage. Above 3500 rpm there is no difference.

 

I'm trying to remember, is batch fire all eight injectors at once, or four at a time?

 

Seems like most aftermarket stuff I've seen is bank to back batch fire, so 4 then 4 then 4... SEFI is much better for an engine with a big cam mostly for low rpms or idle, I'm guessing because of the lack of air velocity and/or reversions.

 

I question how accurate those "really" are. For example, an 89 IROC or Formula 350 with 2.77 gears had the same rating as the heavier GTA with 3.27 gears.

An 88 Corvette with a manual is rated for 15/22. Now how is it that the much lighter Corvette with a manual and 3.07 gears has a worse fuel economy rating than an IROC?

LT1's always seemed to get whatever their rated mileage was. LS1's tend to do better. Upper 20's. Some with the manuals get 30. Very few L98's in F-bodies get more than 20.

 

I've thought that too!

....and fueleconomy.gov has gotta be off. I know several people who have all mentioned the accuracy of that site at one time or another. For what it's worth though. My mild L98 with ZZ4 cam and 3.27 gears made 22 mpg on the 5 hour trip down to Atlanta. My buddy's 500(nitrous) LT1/6spd/3.42 made 30 mpg. Trust me, we all compared mileage and receipts. It was legit. It pissed me off.Hah!

 

The only reason you should need sequential fire is if you have a lopey cam and you need better low speed fuel control. Batch fire systems keep the valve head cooler and can improve efficiency by allowing fuel to vaporize on the back of a hot valve. At higher rpm's there's no benefit to sfi because the time required to inject the correct amount of fuel can exceed the amount of time the valve is open.

 

ACCEL's "Thruster" (Gen-7) is selectable batch/sequential. In order to utilize the sequential feature you will have to run their dual-sync distributor. ACCEL claims 15% more horsepower due to fuel efficiancy below 3000 rpm on most setups
Check out www.accel-dfi.com
Good luck!

 

My big stuff 3 system is sequential, just need the sensors to do it. In my case an MSD I got used with the standard trigger per plug wire terminal plus a single pulse per dist. rotation to signify cylinder 1.

 

F.A.S.T. also offers sequential fuel inj. Dont know the details, though.

 

https://www.thirdgen.org/forums/tpi/...-opinions.html

Read ^

Several members discuss fuel economy increases with just a PCM swap
Batch -> Sequential

 

Its my understanding that almost all new cars use SFI. There has to be a reason for that.

 

As per the technitions at FAST, the overall power difference is so miniscule in comparrison between Sequential and Batch, that below 900hp it is not necessary and a waste. Not to mention that it is a lot more costly than batch fire when you take into account all the sensors, and that most any high end aftermarket system that offers sequential is loads and away more expensive. Perfect comparrison, the FAST Classic Bank2Bank and the XFI. Thousand dollar difference.

I would trust the experts on this, and FAST said not to waste your time or money.

Brett

 

I believe that in sequential fire, the injector fires right after the valve closes. So that the heat of the back of the valve vaporizes the fuel before the valve opens and sucks in the intake charge.

 

There has to be a dyno comparison somewhere but IMO the efficiency and driveability of some pretty ridiculous combos on SFI is amazing.

I personally cannot wait to ditch OBDI batch for OBDII SFI