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.

DarkMonohue said:

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.

@Darkmonahue I am happy with the dyno results, made 373HP and 410TQ, compression was lowered to 10.3:1, cam is a small comp cams 224/230 hydraulic flat tappet. I'm still running the stock points distributor, vac advance and the original Holley 780.

It pulls 15-16" vacuum at idle, and idle is set to 750 RPM. I have not pulled the carb to look at T slots, but considering doing just that.

Base timing is currently about 18 degrees and I have 10 degrees vac advance at idle with full manifold vacuum. Not ideal in this case with a manual trans, but there is no ported source on the carb.

Since my last post I spent a bunch of time looking into various EFI conversions and also, after letting the cost of the efi conversion sink in, started looking into modifying or replacing the current Holley 780.

 Holley Terminator X Stealth, with Hyperspark ignition and stick fuel tank module looks like about the best option for this car and costs about $3300 USD. Multi port, while better appears to be about 50% more $$, and will be probably 20% better across the board, but I think the costs may outweigh the benefits in this case. Now I am leaning towards a progression ignition, wideband AFR,  and fixing or replacing the stock carb.

Oh man, if you're still on points, an MSD 6AL will really make the engine happy.  And since the points won't be passing much current, they will last much much longer.

I've found that the MSD's tach output is a very solid base for EFI systems to get a signal from, too, if you're planning on running fuel only.

Tell  me more about the engine.  Factory old-school?  Cam?  Anything different or upgraded?  Sorry if you already did and I missed it.

One simple way to do it is with a marine EFI intake.  The downside is that I don't think they were installed on anything but Vortec heads, so they won't bolt up to older heads.  Pair that intake with a factory Vortec PCM and jailbreak it for tuning.  Factory PCMs have thousands of times more controls than aftermarket, and they're way more accurate.  The downside is that it takes money and know-how to tune it right.

TBI units are fine, but they're basically an electronically-controlled carb.  Quite honestly, a finely-tuned Qjet is probably every bit as good as a TBI injection.  One of the big benefits to port injection is that your intake design has less of an impact on power, torque, and driveability because the runners only carry air.  They don't have the design needs of the extra mass of fuel, and the shape/turns in the runner that can cause fuel to come out of suspension.

I have also seen several where you just take a single-plane intake and drill the runners.  You can buy injector bosses and just TIG them in place.

In reply to Curtis73 (Forum Supporter) :

My bad experience with a port injected single plane intake suggests that it practically requires sequential injection, which raises the stakes as far as what you need sensor wise and computer wise.  The nice thing about TBI compared to batch fire port injection, with short runners, is that it won't have weird low load drivability issues when the reversion at idle blows all of one cylinders' fuel back up into the plenum for another cylinder to get.

A small cam would help but what's the fun in that?

In reply to Pete. (l33t FS) :

I love a good rumpity cam.

If his SBC isn't far from stock, he might be wise to look into a BBC factory TBI.  The SBC TBI is pretty awful.  It flows fine dry (no injectors), but wet flow is about 390 cfm.  I would also not use a TBI ECM.  They are PROM chip, incredibly sensitive to anything deviating from stock, and not very manageable.  Maybe a megasquirt?

Downside to the factory TBI is that they use low-pressure nozzles.  I refuse to call them injectors, because they just squirt mostly liquid fuel.  Back in the 80s, there were plenty of folks who ditched the TBI and went back to a Qjet and picked up a couple MPG and a few more HP.  The TBI was not a necessary upgrade.  The Qjet was still meeting EPA and CARB emissions limits by a fair margin as late as 1989.  The only reason GM switched was because everyone else already hade EFI and they wanted to be like Ford and Toyota.  A guy I fish with a lot was on the team that engineered the TBI at the Rochester Delphi plant.  He apologizes profusely for the TBI.  It was slapped together, poorly engineered, and never did work the way they wanted it to.  It at least made the marketing team happy until they could come up with better port injection.

The TBI also needed to idle rich of stoich in order to run smoothly.  Poor atomization.

The thing with the Q-jets is that it's very difficult to do the kind of error monitoring that was going to be required in the nearterm. 

In reply to Pete. (l33t FS) :

About 15 years ago, I would have called myself the Qjet whisperer.  I read everything Cliff Ruggles ever wrote, learned from my buddy (also ironically named Cliff) from his experience at Rochester Delphi, and was friends with a fellow Qjet fanboi when I lived in L.A.  He and I went balls-deep on a 454 build that made 437hp with a Qjet in an 81 C2500 and it passed a smog test... after about 12 tries. Not bad for an engine that started with less than half that hp.  I had modified probably 300 Qjets, and I was darn near a master with them, but I understand they are daunting to the layperson.  I'm pretty ticked at myself for not keeping my skills honed with them.