Learn me EFI for SBC

In reply to MadScientistMatt :

Understanding what did what in a carb- yea- that one needs to know what part does what.  But even if you have a rich misfire, it will at least trend rich on some of the cylinders unless all of them are dead rich.  At at least on it's way to a rich misfire, it will go rich quickly.  And a lean misfire will just go lean quickly.

And for me, I would not bother with a gauge- can't look at it and drive at the same time, let alone know how rich/lean it's actually doing.  Have to collect data to do it well.

Still, it's a lot better than guessing.

tripower4speed said:

Thanks to everyone that has posted! @nermalsnert I have started a build thread and will update it to get us to the current day status.

@Pete. (l33t FS) I have been thinking about a Quickfuel as a possible solution, but I am growing weary of messing with it. I had the OEM Holley 780 restored, along with the stock distributor and have dialed everything in as best I can without having to mod the IFR circuit which I think is the next step to solve the off idle stumble. It all worked great on the Dyno and I was happy with the power and Tq numbers but the drivability is a different story.

Your statements that the engine has been on the dyno and that you are happy with the power and torque make one wonder whether this is a stock LT-1 or not. I'm guessing that you might not have dynoed it if it was stock, and probably would have a pretty good idea of what to expect.

How is the engine set up? Big cam, lumpy idle? We'd love to get the specs.

How much vacuum does the engine pull at idle?

What is your idle speed?

How far open are the throttle blades at idle?

How much of the progression slots are visible from below with the blades in the idle position?

What is your base ignition timing?

Im guessing that the engine is pulling less vacuum than stock at idle, which means the butterflies have to be propped open more to maintain airflow, which means the progression circuit is exposed before it should be, which means there's less fuel available at tip-in, which means it goes lean and stumbles right off idle.

If that's the case, there are a couple of cheap, easy, non-EFI tricks you could try, like adding more base timing, or drilling small holes in the primary butterflies. Either (or both) of those would bring the idle speed up so that you could close the butterflies back down where they belong, and bring the progression circuit into play just as the throttles are opening.

In reply to DarkMonohue :

Drilling holes in the throttle plates works wonders, but also represents a vacuum leak before the main circuit comes into play, so it will run lean on tip-in.  This can be fixed by getting a pin vise set and drilling out the idle feed restrictors a little at a time until it clears up, assuming you don't have a metering block that had replaceable jets there.  Another trick if you only need to go a little is to open the secondaries a little more at idle.

I've been to the "make the bottom of the page camshaft drivable on the street" rodeo a few times 

Timing... most engines I played with seemed to like about 20-22 degrees at idle and 36 or so "all in", not counting vacuum advance (which should not be connected to manifold vacuum).  The really hairy engines had non vacuum distributors.

Part of the problem with this is hot starting.  The bigger and higher compression the engine, the worse it can be.  This is where you really need a switch panel so you can get the engine spinning with the starter before you switch the ignition on.  You can approximate this with a normally closed momentary switch (like a brake light switch) on the left side, so you can shut off the ignition while you crank it with the key, but this seems like an additional failure point to me.  90% of the time it's a non issue, seemed to only really be a problem with high compression big blocks.

While we are playing with wiring...  One feature that I love is an underhood starter button.  If you have an engine with mechanical roller lifters, you find yourself adjusting the valves a lot, even if to just check that lash didnt suddenly open up somewhere and you need to investigate why.  It's SO luxurious to bump the engine with an underhood button, vs trying to rotate the engine with a ratchet on a bolt that really is too small to try to turn an engine over with.  And one man compression testing is a ton faster, too!

In reply to lotusseven7 (Forum Supporter) :

That is the plan!

https://youtube.com/shorts/Sbv8ojpX8M8?feature=share

MadScientistMatt said:

What's the end goal for the EFI? Make a race engine easier to live with, better mileage, combine a lot of separate black boxes into one central tuning point, support boost or nitrous, wow factor, or what? Different answers can call for very different hardware.

Its definitely all about drivability and ease of use/tuning. I do NOT want to spend my life tuning EFI, or playing with a carb to get mediocre results. I am fussy about getting it right and EFI should allow for a more consistently good running car under varying conditions. Hot and cold starts should be better, and so should part throttle driving. WOT performace in theory should be noticably better and that is fine with me.

Opti said:

I think LT1 guys are running the 411 PCM with a specific vortec distributor (so no crank trigger, just a cam sensor). I barely read into it but I think there was some tradeoffs, like maybe only batch.

You could probably adapt an LT1 PCM and fbody harness pretty easily, the 94s and 95s are sequential injection, flashable, tuning software is incredibly cheap (free) and simple and have no crank signal and it's made to run a SBC, figure out the distributor and I'd bet all the sensor for inputs probably bolt right up to a gen 1 SBC. Back in the day people were converting LT1 intakes to work on gen 1s, you need a distributor hole and bolt pattern redrilled (not sure what they were doing about the water neck), the benefit is they are good manifolds and very cheap ( I think I have 3 because they aren't worth selling)

Another option is TPI swtup, made specifically for a gen 1 but performance from a stock setup isn't great and IIRC tunig requires chips, which has its following and solutions do exist but I've never looked into it so I can't comment on it, but bonus points for being beautiful. I like them so much I have a setup in my garage even though I have nothing to bolt it to

TPI is an interesting option but not for this car. I am OK with fuel rails, but want to maintain a 4150 style throttle body and the stock air cleaner.

Shavarsh said:

The purpose of the conversion is important. I started my speeduino conversion because of heat induced inconsistencies with my carb performance. Lo and behold long after converting to efi we put that carb (summit brand autolite) on another car and had exactly the same issues. Switched to a demon carb and all issues went away. I still have the efi on my car(and am pleased with my conversion), but it is likely that I could have switched carbs and been just as happy. This would have saved me some money. I also suspect a holley sniper would have suited my needs just fine as well.

 

I think it would be fun to use a tpi manifold and a dropbear speeduino ecu if we are throwing out ideas :)

I have really enjoyed your build thread! Read it front to back and found it very enjoyable. I love early small bumper Pintos, in fact the first fast car I ever rode in was in about 1978, it was an early Pinto with twin Webers, widened steel wheels and some sort of sticky tires all set up for slalom. 

I am really torn about ditching the old school in favor of EFI because I do love the simplicity of this car. Thing is I have already spent the $$ to restore the stock carb and distributor and so feeling a little fed up messing with it. On the other hand, back when these cars were new they ran just fine and everybody made due, so I know its possible to dial it in. Also, mt GTO with a Tri Power runs fantastic, albeit a little hard to modulate between two and six barrel without blowing the tires off. If this car ran that good I likely would just leave it alone.

As far as the TPI, I get it, but not for this car.

What is a dropbear speeduino?

JMcD said:

Couple data points that might be helpful:
 

I did a MS2 roll your own approach and described it here

https://nastyz28.com/threads/24x-sbc-crank-trigger-conversions.329776/page-2#post-3813801
 

My application is a relatively high strung 377ci SBC in a dedicated auto-x car. 
 

Gimp's application is similar but his setup is a bit more plug and play. Details somewhere in here:

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/1981-camaro-c-prepared-build/59501/page1/

 

agreed with port > tbi in every way except if you are trying to go EFI as cheap as absolutely possible (and have a low power engine)

Thank you, looks like I have some reading to do!

Pete. (l33t FS) said:

Another trick if you only need to go a little is to open the secondaries a little more at idle.

Oh, now that is tidy.  That's simplicity itself.  And totally reversible.