TBI injection still has the manifold mixture distribution problems of a carb. Running to an averaged afr likely is running a cylinder or more lean which is missfiring especially when you lean it out more. Going the other way to a little rich may help. Idle and cruise can be hard to smooth out with a bigger cam for either a carb ot TBI. The manifold can count for a lot of this so knowing what you're using and modifacation or spacer usage not to mention cam timing is needed information.

Bogie

 

I’m running a bigger single plane intake to help alleviate fuel reversion. Cam timing I’m not sure about as this is a crate motor I bought. Cam isn’t that big, I’ll look up specs but makes 14” of vacuum at idle. Motor made 448/473 on the dyno.

 

In the sense that "you're dammned if you do and dammed if you don't"; a large single plane wants to run at high RPM, this is where they demonstrate a flow advantage over a dual plane plus being spacious inside reduces flow velocities especially under the RPMs of the torque peak. These propositions encourage fuel and air separation and port AFR differentiation everywhere except at the top end.

Much has been written, especially by David Vizard, about how to "level up" single plane distributions at lower RPM, it takes the welding in and shaping of passage dividers into the plenum to try and recover street drivability. I'm still not convinced about the usefullness of this effort after all these years, that being a lot of work for minimal gains.

While your engine shows good power up on top, you aren't using it that way. The configuration while great if you drive on a dyno is not really in tune to the way you state that you use it and likely can't be brought to 'heel' in this configuration. This is an old problem of trying to run race bread engine on the street. In the good old days the solution was to gear down to spin the motor faster and use a manual gear box to manage revs against road speed keeping revs to the high side regardless of road speed. Today an answer does lie in port injection, this takes the vagrancies of variable mixture ratios do to passage and porting foibles away, reducing the passages and ports to only conductiing air so each cylinder gets the same mixture ratio.

Varible mixture ratio's by cylinder with wet intake manifolding systems is an old and difficult problem to solve. I often refer to it as being "lots of mayhem in a surprisingly little distance".

Bogie

 

I agree with Bogie it sounds like a distribution anomaly. If lean makes it worse richer should make it better. Are you running a PCV valve? If you are is it connected to an intake runner or the plenum? If it is connected to an intake runner it will make that cylinder lean. What do the plugs look like?

 

The pcv is connected to the plenum. Is there a way to upload photos on here without a third party site? The plugs don’t all look the same so reversion makes sense.

 

Below is a article with a chart showing a visual spark plug wear check/cause.

Also check for carbon at the head/boots as indication of bad plug sealing ring or stripped head threads.

With the engine off pull your wires one at a time and run your hand down the length looking for frays, discoloration, or ripples. Make sure your caps all click tight with no slop and squeeze if there is some. They should require a bit of force to be removed from the cap/plug. Use a bit of electrode grease whenever checking plugs to make removal easier.

https://motorizedbicyclebuilder.com/how-to-read-your-spark-plug/

 

Iv had this issue with several different ignition systems. Currently I’m running a pro billet msd and their super conductor wires. The miss is less noticeable when I run vacuum advance, it gets worse without no vacuum advance.

 

Have you thought about dumping the vac advance, go mechanical, can play with spring combs to dial it in? Can control speed of the advance, or curve, same/same


Run the pro billet msd, mechanical advance, healthy camed stroker motor
Pep

 

I have but the motor is 99% street driven also so a lot of idling, not sure if that makes a difference. I stop making vacuum about where my initial is at 22*.

 

If it’s locked out you don’t run advance springs tho? Right? It would just be stuck at 34* ?

 

If it’s locked out you don’t run advance springs tho? Right? It would just be stuck at 34* ?

No ....Mechanical advance provides a curve thur the RPM range.

What's with the keyboard you use .............’s


Instead of typing a book, here is an example p3
https://documents.holley.com/frm289..._85795_857951_85773_85783_85793_85791_85786_85771_857931_857731_857831_0519.pdf

 

Are you saying you're using the EZ EFI for fuel only and you're cruising at an AFR of 13.5? If yes, then why and why?

 

Yes for fuel only it doesn’t control my timing like some newer self learning tbi kits. With leaner afr’s at cruise the lean misfire gets louder. Then over 14afr cruise it will want to buck and surge and actual afr starts swinging all over. The car runs great besides this slight Miss I’m describing. And I miss understood the question about just running mechanical timing and pulling the vac hose, for some reason I thought u meant locking it out. But the misfire at cruise is worse without the extra timing from the vac can.

 

Any reason you don't just give it more vacuum advance, see if it cures the problem?? As long as you don't have detonation it is fine.

I don't see how eliminating the vacuum advance is going to help anything at all.

Lean mixtures burn slower, that's why the vacuum advance helps so much, because it adds timing specifically when the engine operation is typically leaner - idle and cruise/part throttle.

Any reason you don't just richen it up a bit at cruise, as this may be just as easy and effective cure??

Hopefully you haven't got some pre-determined "target A/F ratio" you think you need to hit at cruise and are totally focused on trying to achieve it....give the engine what it is telling you it wants...not what your brain thinks it ought to have.

 

You can’t run dual planes with tbi you get horrible fuel reversion. I had an rpm air gap on there when I first put the efi on and had lots of drive ability problems from it.

 

Where do you get this idea? Hopefully not those dip****s on Engine Masters.

There is a difference between running on a dyno and running on the street. A single plane intake is never going to be happy at low RPM.

Reversion is mostly a cam induced problem that is telling you the engine isn't making enough RPM. Reversion comes from two problems those being a late closing intake valve, and/or excessive overlap.

Large cams in terms of duration especially older cam designs where a lot of duration is in opening and closing ramps encourage reversion. This is because the piston has come a long way up on the compression stroke while the intake valve remains open. At lower RPMs under the torque peak, as a quick and dirty measure, the rising piston develops more force on the induction system than that of the mixture velocity. This pumps the previously inducted mixture back through the intake system to arrive at the classic event called reversion. In really severe cases you can see a fuel cloud sitting above the air horn. To some extent a carb moderates this as it fuels the air going in and the mixture going out so it naturally adds richness as some of the mixture standoff cloud is drawn in with fresh air to be fueled again. EFI type TBI not so much, it is adding fuel to a prescribed time interval and is adjusting the mixture ratio so it doesn't add fuel based on pressure differences in the venturi thus it leans this event out. The answer with fuel injection is less duration larglely a function of reducing the degrees of the ramps, and adding lift. This is something roller cams are good at flat tappets not so much as this increases the loads on the valve train which increases wear that with today's low zinc oils find intolerable.


The other issue is overlap this can be roughly seen in the Lobe Seperation Angle that being less LSA indicates the Lobe Center Angles are closer together thus the intake and exhaust valves are both open at the same time for a longer period of overlap through the Top Dead Center period of the piston as the exhaust cycle transitions to the intake cycle. As the LSA gets longer this is an indication of less overlap. Like I said this is a rough indication, you actually have to do the math from the cam card to see what the overlap actually is because the true amount against the LSA swings about the specific durations and LCA's of the lobe. The LCA compared to lobe duration gives you some idea of lobe shape being semetrical or not. Larger LSA's indicate less overlap, generally 110 degrees differentiates between a street or competition cam. Larger LSA's indicate less overlap and are more street friendly. Shorter LSA's are leaning to a competition tuned cam and engine thus are less street friendly the smaller the LSA gets. The function here is how much residual exhaust pressure remains when the intake valve opens. It is assumed that a race engine operating at high RPM and with a minimal back pressure exhaust will actually have a cylinder pressure depression under atmospheric at this point, thus that 'vacuum' will initiate an intake flow before the piston gets to TDC. For a street engine with a full exhaust system thus having back pressure, this doesn't happen, especially at street RPMs.Thus the residual exhaust pressure remaining with a high overlap, short LSA cam pushes mixture hanging in the valve pocket back into the intake track and perhaps is strong enough to shove it out the air horn with the same issues of fueling I prevously discussed.

So your engine is mismatached on several levels that basically have you running a race engine as a street cruiser and you're getting the headaches that come as a result of a vehicle and engine design missmatch to its end use. One way around this is to gear the rear end so at cruise it spins the engine really close to the torque peak RPM thus minimizing these reversion caused problems by eliminating the reversion causes. Others range from a combination of milder camthat for sure will quell this problem, a dual plane intake might be helpful by itself, a conversion to a port injection system may work as a standalone change, as well as going to a carb may help but likely not much unless tuned by a pro that understands all this stuff, which I suspect was missing when this set up was originally configured. Another thing that might help is adding some more edvance to the camto get the intake closed sooner. If your using 1.6 rockers going back to 1.5 might help. If you can overide the fuel trim to run richer in cruise may help. More advance on the lean mixture might help, but here your walking into a possible detonation issue, which could be already there as signalled by the miss fire.

You've just got a bunch of issues steming from the total design of this vehicle having too many missmatched ideas.

Bogie

 

I’m not stuck on any afr Iv ran it down to 13.3 at cruise and can still barely hear it. These r already pretty fat af numbers for cruise and I’m running vac advance but the the van is not adjustable on my pro billet msd. I’m wondering if I’m still getting a little fuel reversion and a few cylinders r lean because of it like was mentioned before. I’m tempted to throw a 1” spacer under the throttle body and see if that helps.

 

Sorry about the weird symbols when I post I’m not sure why it is doing that. They don’t show up until I post it. I’m using my iPhone to do this

 

I am having similar issues like you as well but I don't run EFI or TBI but just a holley carburetor on a edelbrock single plane intake and I have been chasing a misfire faint stuttering at lower rpm cruise around town that goes away at highway speeds and I have changed out pretty much my whole ignition stuff and several carb adjustments and a different carb to test and also trying to make for my fuel to be the coolest as it can be with installing a return line and some other things and I still can't figure out what the problem it and it started all of a sudden in May and have never been able to trouble shoot what it is and still working on it. Hope you figure out what yours is.

I know for some part I thinks its half of it with the fuel they have nowadays as three years ago my truck was no different then what it was last year in May of 2018 and stuff always ran fine as it was and all I did was a new engine build and last summer I started to have fuel boiling issues after shutoff and under hood temperatures never affected that before but I was able to run fine through the summer then at the fall I swapped out carbs to one with a choke tower for colder weather and it ran and did fine but once it started to get hotter temperatures outside in May of this year then things just went downhill and have spent the last several months making upgrades to this and that and still no change so I have yet to find out what my issue is. Hope your fine yours soon. From what I have read the single plane intake has better fuel distribution vs a dual plain and I would believe that as my plugs I recently took out on my single plane almost all looked identical as compared to in the past the dual plane intake plugs there were be some that would be leaner or richer then others depending on the cylinders location.

 

I started my last post before Bogie sent his, and as usual, he explained the issue much clearer and definitively than I - LOL. I think we are both saying the same thing though, just in a round about manner.

 

Holley and fast both make intakes for their tbi kits and they r both single plane intakes. They both suggest the use of a single plane intake. Like I said I had a dual plane on there before and it ran like ****. The fuel is being injected at 43psi not 7 and is already atomized unlike a carb. You do not see the low end draw backs nearly like u do on a carb and single plane.

 

Holley and fast both make intakes for their tbi kits and they r both single plane intakes. They both suggest the use of a single plane intake. Like I said I had a dual plane on there before and it ran like ****. The fuel is being injected at 43psi not 7 and is already atomized unlike a carb. You do not see the low end draw backs nearly like u do on a carb and single plane.

Your response that I put in bold identifies your misunderstanding of what is happenning. The fuel pressure could be at 100psi and the vapor will still change to droplets if there isn't enough air flow. I do understand that Holley and Fast recommend a part for you to buy - but please keep in mind that they are not going to tell you that their system doesn't work with a particular part. And the dual plane Air Gap intake you had creates the same issue due to it is not heated by the coolant. The entire concept of an Air Gap intake is a marketing ploy with exception of one type of situation. If you search here for Air Gap issues, then you'll find many complaints of exactly what you have going on now.

The long runners of your Super Vic generate some additional air flow over a 'normal' heated dual plane, but only at higher rpm's - usually 3000+. Without re-reading your initial post, IIRC your issue disappears once you're over 2500 or 3000 rpms, correct? If you'd like, I can find some articles on the x-tau factor. In a nutshell though, Boyle's law PV=nRT explains quite clearly why the fuel vapor turns to puddles at low rpm's (low pressure) in a cold (low temp) intake. Increase either the pressure (more rpm's or throttle plate opened further) or hotter intake (heated) and the problem will disappear.

If you were to take your Super Vic and put 8 injectors in each runner within an inch of the head's intake port, then issue the would be 90% gone due to the time needed for the fuel vapor to change to droplets would not be long enough for the state change to occur.


Please don't take my comments as derogatory, rude or condescending. I'm trying to explain the myth to some of the marketing ploys made by magazine articles, TV shows and internet hoopla.

FWIW, if you lived nearby, then I'd let you borrow the Holley 300-36 high rise dual plane that I have kicking around on a shelf so you'd see for yourself that your issue would be gone. I'm sure you can pickup a used dual plane cheap - they are not hard to find. And yes, the dual plane will give up some top end go, but even a turd bomb intake will run better on the street than you your Super Vic for cruising.

Sincerely - Jim


edit : forgot to mention - your comment that your fuel at 43 psi is atomized unlike a carb, is incorrect. The fuel from a carb is atomized when it working correctly - again, that darn Boyle's law.

 

I’m with u tho bogie on the port injection and also that it’s a distribution problem but if I change fuel systems again I will yank this thing out and ls the car. This motor is anything from a race motor also, it’s a pretty mild 450 horse roller motor, very streetable. .528 Intake .536 Exhaust
221 Intake / 226 Exhaust duration
@ .050 - 110 degree lobe separation
Pretty mild cam also.

 

Think of a mild cam as around 200 degress at .050 lift with lift around .45 inch. The concept of of making over 370 horses from a Gen I, 350 without resorting to radical cams and compressions ratios above 11.5 just didn't exist before 1996 within the context of the 23 degree head. From my old age historical view calling a cam with 221/226 degrees at oh-fifty with .528/.536 lift "mild" is a new fangled concept, which is mostly allowed by modern application of all the elements of the Sir Harry Recardo patent design wedge chamber of the late 1920's and 30's. The picture that runs with my header is a 1954 Ford small Y block which used all of his design except for the beak from the quench side to run up beyween the valves. This was the last year it was used even in partial form as the finance people took over the company and refused to pay the royalty to use the design. Sir Harry's work on the flathead chamber design is what kept the old Ford flat head minimally viable through 1953. Starting in 1955 Ford simpled the chamber to escape the design payments. Most manufacturer's avoided the patent chamber designs altogether at considerable performance cost. To get power they resorted to very high compression ratios and for the day a lot of cam. The price was high fuel consumption and emissions. Chevrolet copied the concepts of the Recardo chamber on the SBC as close as one could and stand a chance of surviving a court challange for patent infringement. The end result being a historical monument to efficiency and power production till the SMOG era heads where everybody lost their way as if no one in automotive engineering circles never read "The High Speed Internal Combustion Engine" by Sir Harry. But the SBC in total design and with its double quench chamber put most everybody elses motor on the trailer, including the much vaunted hemi. It took a really big inch hemi to run with a lot smaller SBC and that due to weight, size, and cost was a closed end proposition.

So anyway a lot of words to get at saying I guess first is don't get complacent about what it takes to get modern power and secondly recognize the physics haven't changed only the engineering solution gets better in closing the gap between the doable and theoretical. With the latter thought,improved fuel atomization hasn' changed the physics going on in the manifold and ports. That being centrifugal force throws heavier molecules of flow to the outside of any turn and fuel in any state from liquid to pure gas is heavier than air so at any direction change the mixture ceases to be homogeneous. The next problem is local pressure changes in the flow where changes in flow direction or disruptions of protrusions into or away from thr flow, mismatches of surfaces result in 'micro' pressure changes which cause the fuel to drop out of the mixture. These are conditions that are not dependent upon the state of atomization so much as molar weights of various compounds, velocities, and pressures. A good analogy about micro velocity and pressures changes in the port's flows is piston movement; that is usually measured in an average speed of moving the length of the stroke to engine RPM. But if you look at micro or instant piston velocity by crankshaft degree you get a very different picture of what is going on as piston velocity varies widely by degree of rotation.

Valve angle to the bore center alsocounts for a lot, hence lesser angle heads make better power, that's not to say elinimation of the chamber is healpful in that regard, though there are some succesfull attemps at this but its a whole different engineering approach in all the elements of the design.

I don' know about your symbol problem, my old Apple did that now and again, I stumbled through a solution but because of stumbling in the dark, I don't know what it was.

Bogie

 

What manifold are you using??

I would think the Holley Strip Dominator would be your best bet.

 

I’m using the super vic

 

Let me add some more direct questions and thoughts.

Are you runnng a 6AL box of any body's?

- A 6AL without specific grounds on each head and the intake will seek ground through the electronics which in mild conditions will disrupt the spark but this is usually ramdom. In bad cases some critical component in the ignition system stops working altogether.

- At the other end if you aren't using a 6AL in your situation of a lot of cam and low revs a multiple spark, extreme energy box might help fire a lagging cylinder by supplying multiple opportunities to strike a light.

Other thoughts:

- Is this a flat tappet cam, if so a lobe and tappet may be going away.

- A stem seal leaking oil and fouling a plug.

- This brings up the condition of each plug as to what the insulator looks like. Normally I look for the color of lightly toasted bread as a sign that combustion is occuring correctly in terms of mixture, oil pull over, compression pressure, plug heat range, time on cold start enrichment, etc. This color is not necessarily uniform around the insulator. Insulators running darker are being overfuled or oiled or the heat range is too cold. Insulators runnng lighter are seeing a lean mixture or the heat range is too high. An insulator once fouled will generally not come back, this can be true of a cleanish looking plug that was once fouled.

- Injected engines do tend to look dryer on the plug insulator than carbed engines, carbs tend to be sloppy with cold start and dropped throttle changes which shows up as making the insulator darker than what you see with EFI when even when the AFRs read correctly. Aluminum heads also contribute to this since they move heat faster than iron they can run the plugs colder than expected for their heat range.

- Cylinders may not be running at the same temperature which really is a simple fact. The front two sit right where the pump delivers cooled coolant, so they tend to run colder that the others. The rears generally run hotter simply because the coolant gets warmer with each cylinder it cools. I like a 4 corner return on the Gen I and II Chevy as it speeds up the process of eliminating heated coolant from the rear of the block. This leads me to the hottest runnng combustion chambers in the middle where the exhausts are adjacent to each other. A lot of attention is put into cooling this area and rightly so. But if you have modern or modifed head gaskets that put more coolant return here but are not racing the engine you can get an excessivly cooled spot here.

All of this comes back to how the engine is used, while you make think this engine is mild it is infact more a thoroughbred than a draft animal. These can be testy when lugging the wagon insted of dragging it.

Bogie

 

Ok I think I’m understanding what you two are saying about the intakes, and sounds like possibly a Vic jr would have been the better bet if I was to run a single plain like the efi company suggest. I typically cruise in the 2500rpm range. The insulators in my plugs are white with a ring of soot around the top of the threads and about a 1/4 to 1/2 way up the ground strap and then clean. I run bkr6e ngk’s but have just put in a set of bkr5e’s to see if it could handle going one range hotter. I also run 92 non ethonal

 

Ok I think I’m understanding what you two are saying about the intakes, and sounds like possibly a Vic jr would have been the better bet if I was to run a single plain like the efi company suggest. I typically cruise in the 2500rpm range. The insulators in my plugs are white with a ring of soot around the top of the threads and about a 1/4 to 1/2 way up the ground strap and then clean. I run bkr6e ngk’s but have just put in a set of bkr5e’s to see if it could handle going one range hotter. I also run 92 non ethanol fuel if that matters. And I have a msd 6a but don’t use it to keep down in wire and clutter and have a ready to run pro billet because it produces the square wave rpm signal I need. I thought the msd box quit working around 2000 rpms and I cruise above that rpm with a 4 spd. Thanks for the help guys, obviously I have a kindergarten thought process to this compared to you guys

 

As far as learning it just keeps on going, we're all nside that process somewhere.

A square wave box like a 6AL needs each head and the intake grounded. To some extent this precautionary but even many of the manufacturer's of this stuff buries a statement in the fine print or on line. It turns out that the top end fasteners bon't necessarily make the electrical bonds between parts conductive enough for these abrupt wave forms and/or power levels of these ignitions. The fasteners have lubrication and sealers on the threads and under their heads that in a static situation can measure a decent ground but when slammed with the duty of grounding the what was delivered to the plugs often proves insufficient. certainly this much potential will find a ground path somewhere; since electricity is a game of potentials not so much as one of absolutes these harsh wave forms will guord out through whatever path is available which can be back through the ignition system primary wiring. Aside from being electrically and physically clean these top end grounds only need be of number 10 wire as these are not carrying the large starter currents which should be with a battery sized cable mounted as close to the starter as reasonable but not from its mounting bolts for structural reasons of not permitting the starter movement on its mounts.

The MSD multi strike does stop that somewhere in the 2000 to 3000 range. This thought an also bring up what your combustion chamber looks like. The head provides the roof shape, the gasket thickness and distance of the piston crown from the block deck set the squish/quench clearance with the piston crown shape making a contribution to this and the flame travel speed. A big danger lurking here is using so called "rebuilder pistons" these have a short compression height to return zero decked blocks to GM's standard .025 inch crown to deck clearance. While fine for an iron head by the time you run the recommended head gasket thickness with a aluminum head the compression ratio is considerably reduced and the squish/quench that we like to hold not wider than .040 inch becomes greater that ideal. One of the fall outs of this is less chamber turbulance which reduces fuel and air mixing which increases detonation sensitivity, makes lighting off the mixture more difficult, requires running a richer mixture as with the cold choke operation just to get something that burns, the excess fuel just gets wasted. The point here is the need to know part numbers of what's under the heads as this is a common place to find a mix of parts that aren't working well together. My shot at a high energy multi-strike ignition was a Hail Mary shot that these can often be used to mask lower RPM combustion problems.

Your description of the spark plugs does not agree with the AFR readings. The cause can be a range of things from a faulty reading on the AFR to way too hot a heat range on the plugs. Typically EFI produces a cleaner looking plug than a carb all other things being set correctly so to some extent beauty is in the eye of the beholder. But what you're seeing needs some deeper investigation and thought. Also, it doesnt sound like there are a lot of miles on these plugs, but one would think at least the missfiring plug would show some darker color. The dark on the bottom of the threaded portion is normal that doesn't run as hot as the insulator so like the chamber walls it carbons up a little. You might want to idle this in the dark to see some of the spark leaks out before getting to the plugs.

I did not spell or grammer check this so my appoligies for any hard to read spots.

Bogie