I have an edelbrock victor jr that we converted to EFI, and it seems to be acting strangely to say the least.

One day it will pull 247 gm/sec at the maf, the next it will pull 160, and the next 190. It has a slight miss at idle, and the number 1 and 2 header pipes are hot, but cold in relation to the others. I can put my hand on those pipes and hold it for 5 sec or so, where with the others I can only barely touch my hand to the pipes before I burn myself.

I thinnk it's related to the way I designed my plenum. It's 374 cui, the front of the box starts right infront of the carb flange, and it extends about 4.5" past the rear of the flange. Total length is about 10". I'm thinking all the air is rushing to the rear of the plenum, and then only feeding the rear cylinders properly.

I am in the process of making a new plenum, but want to make sure I am on the right track. It will be a 3.5" mandrel pipe that will dump straight down into the runners, with maybe 7" of pipe after the bend. Should be approx. 250 cui volume, with a straight shot down into the manifold floor. Will still have slight turbulance favoring the rear runners, but we plan on countering that some with a single baffle in the center of the plenum tube.

This is all on a 305, all the mods in my sig.

ALso something I'm not sure on, my BLM's are approx 126-130 when colder closed loop, and when running temp closed loop they will increase to about 150 or so. What would give it this trait, and what would be the best way to correct it?

Thanks for any help you guys can provide

 

Gotta pic?. They're worth a million, or is it thousand words...

Sounds like either the MAF is seeing alot of turbulence, or is dieing. The cold cylinders sound like a mechanical problem, thou it can be EFI related.

Dead valve springs could explain both, thou.

 

This is the clearest one I could find showing plenum positioning.

The springs are brand new lunati ones that they recommended to go with the cam, I hope it's not them. The documentation that came with the new heads said that lapping valves isn't needed with the new castings and new valves, I hope they are right. I'm gonna get a leakdown tester sometime this next week so I can verify that they are sealing up.

I have already verified that the cyl is getting spark, and got it to jump a 1.25" gap before it jumped thru the wire and shocked me. So that's gotta be at least 60,000 volts there. The plugs looked nice and clean, with a small amount of fuel on them. Any "home remidies" you know of for checking injector flow without pulling them out? I know snap-on makes a tester that sees how much pressure drops when an injector is activated for a certain PW, but it's big $$$ that I don't have now

I'll look into the turbulence thing too. I was in somewhat of a hurry when I pieced together the CAI, so there are some angles in there I can probably eliminate or lessen.

If the maf is dying, could that also explain the odd block learn numbers?

 

Here's the clearest shot I can find of the CAI. I'll see if I can't get a better one tomorrow.

The MAF is right after the elbow and rubber bellows, then it snakes down thru the fender to where the filter sits right under the driver's side battery tray.

I'm thinking of converting to SD to remove the small MAF from the intake stream and get more of a straight shot for the air intake, but I'd like to gain more experience in the MAF tuning first. Not to mention the fact that I almost have the resolution maxed out with minimal WOT tuning and missing on 2 cyl's.

 

After looking at this for a while, you might just have too much plenum.

You've gone to great lenghts to improve cylinder filling, and maybe have gone too far. Your valve selection looks to be about the largest possible. You may actually be pretty well shrouding the valves, in which case you have to limit the possible air flow or your just going to kill the cylinder filling.

As far as the rear wall goes, being 4.5" past the end of the manifold is kind of excesive. 1.5x the runner's width would be plenty. And unless your really spinning it way up high to actually need that much plenum reducing it some in this case might help.

 

Thanks for the replies grumpy, I'm actually in the process of making the new plenum as we speak. So I can let you know how it works out with that. Since I cannot find any definate theory or formulas anywhere on sizing, I'm gonna swing to the opposite side of the spectrum and join the folks running little to no plenum and see where that leaves me. The new plenum will be approx. 170 cui, reducing my effective fill by almost 200 cui.

I found some back posts of a massive plenum that you have for your GN, have you installed that yet? How does it run compared to the stock one?

 

I haven't installed the *biggie*, yet.
I plan on doing that within the near future thou. I'm also going with my *no* runner theory, which means some more machining.
The one I have is about equal to CID.

BTW, did you have many headaches with AE on that one?.

I hope you plan on posting what the differences are in VE, PE, and AE from your expeiments, be interesting to compare notes.

 

NO runners??? Should definately be interesting What do you expect to see from going that route?

I had all kinds of headaches, but I think they had more to do with the cylinders missing. I found the number 2 plug was loose on the injector, so that explains the heavy intermittent miss there. My AE was up to about 30% under 1200rpm, and it still didn't feel right.

I'll post up my notes as I progress, and definately keep up to date on here.

 

Well, nothing difinitive yet, just thought I'd post up some progress. The new plenum is complete and on the engine, the miss is taken care of, and I got the injector angle about 2* off vertical. Fired it up, and it idles much more smoothly and as soon as I crack the butterflys the revs shoot up instantly.

The idle surges some, but I also don't have the MAF plugged in yet and have 2 minor vacuum leaks to take care of. All 8 header pipes are HOT now, so I'm assuming that the larger plenum was the cause of the colder pipes in the front half of the banks. I also redid all my fuel lines with double flares this time for added security.

Maybe tomorrow I'll get the CAI fitted up to the new TB position and then do some data logging. I'm guessing that I won't need anywhere near as much AE, and I may even be able to reduce my total fuel delivery.

 

Interestingly enough on another list Doug from Holley, mentioned this, in reference to their new manifold.
I'm wondering if it's a product of having two small butterflies, and imparting too much inertia into the incoming air. A Monoblade might be the way to fly.


As far as no runners, mine is a Turbo application, and my theory at the moment is that they make an engine peaky. And that means for where ever it helps, there are some areas where it will hurt. Cylinder filling for me isn't an issue, so in theory sans runners should even make for a flatter torque curve. My current manifold has some serious short runners, and the only thing left is not having any.

 

Great post and glad to hear it running better.
I always wonder about making a setup like that and how it would run.

 

You've turned a central intake into a log style intake.... that's an issue that'll be hard to fix. Might want to try the monoblade like was suggested.
As for the holding the header, that sounds to me like no fuel or too much fuel or too much timing. Move the injectors around and see if the cold headers follow. I'm just suggesting this because it's hard to believe that you're able to hold the header even if it was getting next to nothing for air = rich cool exhaust.
I think the only way to get good air to all cylinders is to have a 4 barrel TB directly on top of the plenum.
As for the MAF, scrap it and go SD if it's giving you troubles right off the bat.
The BLMs shouldn't be at 150, that's the computer thinking or knowing that the engine is WAY leanner than predicted. Result is lots of fuel dumped in. It's hard to say exactly what's going on with your setup but I'd first find all the mechanical problems before getting to deep into the tune. As a side note, there should be a coolant temp table fuel adjustment but I'm not the person to ask about where that table is in the calibration.

 

I have only time to loose, so I'm gonna play around with this setup as much as I can to see how good I can get it to run

I think I have the air distribution issue taken care of with the small plenum. I made it even smaller than planned, probably 120 cui total volume. I also placed the TB at an angle where I think it will fill the plenum more evenly. If not, I'm gonna try a 3.5" mandrel bent elbow on a carb flange with a monoblade TB, and if that still doesn't work I'll drop the $$$ on the 4 blade TB. The cheapest I can find them is $400 though, so I'd like to avoid that route if I can. I think I have the great majority of the bugs worked out (mechanically speaking). I won't know for sure whats going on until I start my logs, but it idles much smoother, all 8 primaries are extremely hot like they should be, and the throttle is very very very responsive. I think my remaining problems are going to be found in the tune.

I'm gonna play with the MAF as well to see how well I can get it going, but I think eventually I would like to switch to SD both for the higher resolution and to get the restriction out of the intake tract. Unless it turns out that the MAF is shot, then the conversion will be sped up

If things go well tomorrow, I'll try and find some time to snap some pics to post up.

Grumpy, did he mention how they plan to correct their problem? Maybe I could borrow their engineering to suppliment my backyard engineering

Thanks for the interest and the tips guys

EDIT: I just reread my original post, and thought I should mention that the new plenum is also an aluminum box style. If that doesn't work out, then I have this to make the new plenum out of.

 

He infered it was minor and that no one would really notice. Didn't sound like there were any plans to get it any better.

If you want to talk manifolds, try finding Ollie Morris. He used to work at Offenhauser. Now he knows about airflow. The problem with alot of the older manifold designs was casting the darn things. Even the leaders are sticking with sand, when foam is the real way to go, IMO.

Sometimes, your alot better off with *shearing* walls then trying to get real smooth radii. When you start to try and bend air with like your mandrel tubing, it stats to impart alot of inertia, into the air.

http://home.woh.rr.com/brucesgn/manifolds/

If you look at the one view of where it's on the manifold you can see how much of a box mine is. And how it continues back past the lower manifolds opening. That *other* manifold that looks like a huge box is the next step.

 

HMmm id like to make a suggestion. dont use round tubing. Use oval tubbing. Yeah you heard me right. Use oval tubing. It has moe even air speed less inertial problems and typically is has more even flow distrobution throghtout its radi. then dont think round. round is a horiable shape for air to distribute evenly.

Bruce those are some interesting modifications to that manifold. Ive got something ill send you pics of soon for my honda. Try to think of an air compressor. Small distrobution lines and a large pressure tank. Its an interesting take. Longer runner then most honda folks are running and a slightly smaller plenum but from the fleunt anylisys it looks like itll kick some ***.

As for the un even air distrobution. Its possiable that the airflow was so distrubed and ythe plenum was so overly large that you surge volumes were completely beyond what the engine could handle. remeber its all pressure waves. with a plenum that big i would think you might have created soem temporary stand off issues in front of the TB from the pressure wave inside the plenum.

 

On a side note; a large plenum has lower average air speed velocities so distribution to cylinders that need air is usually cured with a large plenum. Small plenums have increased air speed which will keep a turbulant air flow but seriously, turbulance in the intake is RARELY an issue. Just look at how long it takes airflow to become laminer through a round pipe.... WAY longer than your intake runners and port.
The only time I'd use a smallish plenum with a bent tube adaptor and mono-blade is if I were running boast.
I bet the holley stealthram has distribution issues where the front cylinders are getting less air, then the rear, and the middles are getting the most. This is usually the case with a log style manifold that doesn't have any taper and a perpindicular throttle/ram port enterance. The rear distribution of a stealthram is improved by extending the plenum back. That looks like what you did, but you have some funky issues with too much plenum volume and in the wrong place. I bet if you shifted the whole assembly forward where you only had a couple inchs overhang and the rest was over the front of the engine that you'd have better results.... but then the hood clearance becomes an issue.
lol, this stuff is still magic don't let any engineer tell you it isn't! Trial and error... even the newest intakes have issues because of there packaging constraints.
I'd like to simulate the airflow but I don't have a good enough picture of the intake to make any dimensions. The monoblade manderal pipe could be simulated pretty easily... but it's father's day so give me a week or so. Unless funstick would want to do it...hint hint

 

WOW, thanks for all the info guys! As far as the simulation stuff goes, that would be really cool if you could do that. I'll get some pics of the new plenum mounted ASAP.

Funstick, If I went with the oval tubing I could probably use my twin blade TB again. Good idea or bad?

So does this mean that my current small volume squarish box is probably better off than a round plenum would be?

 

IMO, yes.
But, the only way to know for sure, is to build both and compare them.

FWIW, as a valve cracks open, the inital influx of air starts off looking like a tornado forming, at the end of the runner, in some engines.
The is nothing that isn't turbulent in the plenum, from what I've seen.

Often the best indication of what's going on, is looking at the staining that goes on. It's alot trickier then in the carb days, but often there's hints about what's going on.

 

Hmm ive been way to swamped at work to get to the place where i have acess to fluent. what i have learned is that fluent is an excelent program for working with stabil flow modes it no so good at transient states.

I can tell you from my experiences doing design work on my own cylinder heads, intake, exhuast headers, etc etc etc is that think of a big tank with a vacum.

If you have a 10 gallon tank with a vacum of 28in hg and you open a 1inch diameter valve air speed will approach ( for instance) 180fps

but do that with a 100 gallon tank at 28 in hg and whammo that AFS gooe from 180fps to around 500fps.

with the same size opening.

Once the pessure in the plenum had stabilized the airflow distrobution would have most likely been fiarly similar port to port and in fact been quite good. But the transient state change in mean pressure and the forward running pressure waves were most likely reflecting back into the TB cuasing some stand off issues. and with the differing air sampling rates of the cylinders comming into play here and the constantly changng RPM i really doubt things would ever settle down enough to have them work out smoothly.

Theres to many dynamics going on at one time to be 100% sue of anything but my eperience doing I.C.E. research suggest otherwise.

the hond intake i have on my car looks radically diffeent from what everbody else is running. but it works very very well. Thinking outside the box helps a bit.

As for running the Oval tubbing with a twin blade TB yeah the tendencys of oval tubing to laminarize airflow and collect it and the way it behaves would most certianly be just fine.

comming towads the actual Carb plenum or manifold carb flange entrance at this point would require some careful stepping of the pipe from oval to suqare., i would think that starting the transition at least 7-8 inches from the opening of the intake manifold itslef would proboaly yeild best results. you want time for the air to plume out and fill the Plenum already existing in the manfiold to distribute and fill it evenly. Although as bruce siad i wouldnt be to stressed about it being prefectly radioused as i would making sure that is was more or less just divided evenly.

i domnt really have much more to offer on the subject Sorry.

Also sorry for my absence lately been busy with wok, got bit by a deer tick and got lime disease and life in genral has been a big PITA

Ill make an effort to be around more.

 

So I probably had a ton of turbulence in the plenum from the large size, and by the time I was sucking enough air to facilitate such a large plenum it was time to shift. Pretty interesting. That explains why it would stumble and accellerate very strangely, and then throw you back in the seat hard at about 4500 rpm.

Here's a few pics of the new plenum. Any thoughts on if the TB angle is going to help with even cylinder fill? My guess is that at low engine speeds it will fill the plenum normally, and then at higher speeds it will kind of "aim" the air down to the runners. I can't tell a difference in primary pipe temps by hand, I'm gonna borrow a pyrometer sometime soon and get an accurate measurement.

Also, please excuse the messy fuel lines and the RTV mess. I've been experimenting, changing, fixing, and modifying without stopping to clean up my mess as I go. The rails have been thru 4 rail angle adjustments, so the bends look kind of messy now

Funstick, that stinks about the lime disease. How bad did it get before they caught it? Is that the disease that causes nausea, weakness, and temporary paralysis?

 

dos

 

tres

 

Header tubes in the front were on average of 150* colder than the rear 3 on the initial startup, not certain how they compare now after a little tuning the idle. Ominous_87 thinks that I need to get different plugs in the motor so I'm going to do that probably Tuesday and see if that takes care of my stutter problem under cruise, yet no stutter under acceleration.

 

Just for comparison's sake, here's the old monster.

 

Have you done anything to smooth out the transition from the plenum to the intake or is it just a flat plate mounted to the top of the carb flange?

Steve

 

Flat plate so far, I'm waiting to see how this works out for me. Why, you gots some ideas for me?

The plenum is 6x7x4.25, and then I have the triangle chopped off the front of it.

 

I was just thinking that the transition into the intake may be causing some adverse turbulance. The fourbarrel tb is looking pretty good as far as being the best performance choice for the manifoild your using.

Steve