FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: aj on April 14, 2019, 11:02:42 AM
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After dyno sheet showed lean condition during 2 pulls (A/F in 15-16 range), I decided to borescope at Brent's suggestions...which then led to pulling heads off. I'll deal with shop that ran dyno'ed with lean condition (yes, inexcusable).
After removing heads, I saw odd, bad, and truly ugly things. :'(. I've posted a few photos and would appreciate thoughts/comments from experienced folks on the following:
The Odd:
First thing I noticed was sticky dark oil residue on tops of all pistons and back side of all intake valve. Also could see on tops of piston oil pattern where it bulk oil was migrating across top of piston much like water on a windshield. That led to investigation of PCV tubes and fitting (stock CJ resto stuff) where I found evidence of oil. Oil baffles had been from the stock CJ cast valve covers to clear the rockers. My understanding if IF motor was inhaling large volume of oil, that would greatly increase chance of detonation.
The Bad:
Signs of detonation. I'm no expert of forensics but it appears the detonation was extensive enough to escape the past the head gaskets and leave combustion residue including the sticky dark oil residue on the block-to-head mating surface beyond the metal ring of the head gasket.
The Truly Ugly:
Two fairly deep scratches in #8 from two small pieces of debris that embedded into side of piston just above top ring. I don't know if the debris could have been caused by detonation or lean condition. (Side Note: When new valve guides were installed, it broke/chipped bits of the head's guide boss as the guide was pressed in. I've always been leary a small chunk of the guide boss could further crack off and get inhaled. But I would have expected to see a bigger piece of loose guide boss than the very small pieces of debris that caused scratch.)
Pulled the number 8 rod/piston and bearing and crank look fine.
At first it appeared I could simply clean up the oily residue and address the PCV issue and retry on dyno (obviously at different shop) using higher octane, richer carb setting, etc. But upon discovery of the scratches, looks like ill need bore job and bigger pistons.
I don't know if the lean condition and detonation caused the debris that led to scratches...of if they're separate and unrelated.
So I suspect I'll be boring as needed and new pistons. Dadgum it.
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Well, that sucks, sorry to see all that. A couple of comments. If the oil on the deck is sneaking by the head gasket seal around each cylinder, probably its from detonation lifting the head or gasket a bit to allow that. If I had to guess, oil in the cylinder and on the valves is probably from an intake gasket leak. Those two problems are easily fixed. The big deal is the damage to #8, those scratches look pretty deep. But you could just bore and/or power hone that one cylinder and go a step bigger on the one piston. One piston that's 0.010" or 0.015" oversize won't be enough to affect the balance, and the engine will never know the difference. Also, do your best to determine where the debris that caused the scratches in the cylinder wall came from; best bet is something obvious, like left over material from porting on the heads and/or intake that didn't get completely removed.
It really makes me mad when I hear of incompetent dyno work. It's not that hard to take care of an engine on the dyno. The A/F numbers are a big red flag, and you always want to run race gas on the dyno, because even if you do run lean, you won't hurt the engine if you're running 110+ octane. Sounds like your dyno operator didn't know what he was doing...
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Ouch ! All that on a stokish build is hard to understand.
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Check ring land dimensions, you may find those piston are beat up worse than they look
Sorry to hear about it. I think you may have had more than a jetting issue the way it went hard lean, maybe fuel supply? Float level? PV too small a number and closed? Combined with DCR too high? Regardless Dyno operator should have shut it down, but recommend some deep thought before the next one
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Agree - scratches that deep would be more likely from debris than detonation. Piston tops and valves don't really look as bad as they could. Also agree that getting a measure of ring clearance should be part of forensics.
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Can that A/F happen from secondaries not opening up? We don't talk about 2V's here, but what happens when you WOT a big engine with one, and it hits a point of no more acceleration? Does it go lean?
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Can that A/F happen from secondaries not opening up? We don't talk about 2V's here, but what happens when you WOT a big engine with one, and it hits a point of no more acceleration? Does it go lean?
LOL!
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Can that A/F happen from secondaries not opening up? We don't talk about 2V's here, but what happens when you WOT a big engine with one, and it hits a point of no more acceleration? Does it go lean?
LOL!
Evidently, you don't know either.
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They tend to roll rich when secondary opening is delayed. If you get to a point where vacuum from too small a carb exceeds power valve settings you can pull back lean, but we do not see that often - except on oval track race cars in those "two barrel" classes.
This just looks to be dead lean. Possibly a serious and repeated supply problem or a float stuck "closed"? I have had engines run out of fuel in the middle of a dyno pull and not seen that level of damage. You can clearly hear an issue when something goes wrong - and abort the pull in an instant.
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They tend to roll rich when secondary opening is delayed. If you get to a point where vacuum from too small a carb exceeds power valve settings you can pull back lean, but we do not see that often - except on oval track race cars in those "two barrel" classes.
Oval track carbs, especially 390's are going to do that anyway as they have a .130 HSAB. They come pre-jacked up in order to work for their intended purpose, no doubt why oval track is truly it's own branch with highly specialized folks working there.
Evidently, you don't know either.
Sure......
How does an engine pull fuel from a carburetor?
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How does an engine pull fuel from a carburetor?
It totally sucks?
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How does an engine pull fuel from a carburetor?
It totally sucks?
Wrong! :lol: Now he'll go into "depression", maybe because we put too low pressure on him. Can't stroke everyone's ego.
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How does an engine pull fuel from a carburetor?
It totally sucks?
Wrong! :lol: Now he'll go into "depression", maybe because we put too low pressure on him. Can't stroke everyone's ego.
if it doesn't suck , please explain how Idle circuit works ? lol
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Pressure differential.
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How does an engine pull fuel from a carburetor?
It totally sucks?
Wrong! :lol: Now he'll go into "depression", maybe because we put too low pressure on him. Can't stroke everyone's ego.
Hey, what did I ever do to you? The only thing that depresses me about this forum is the ever-dwindling lack of humor too many members exhibit. I guess there is truth behind the old fart crotchety meme.
It's good to have an ego. It keeps you grounded, aware, and forward-focused. Just ask Jay.
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Pressure differential.
You mean, like when you suck a drink through a straw?
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My question was a valid one. Barry treated it as such. I have a '67 Mercury that came with a 350 cfm 2V on its 390. You can accelerate it in second gear until it just stops increasing speed. I wonder what the mixture is doing.
So Drew, I realize spending a month on a tuna boat in a sausage fest with all those sweaty mens gets you a little askew, but let's not get into theory. Just the facts, ma'am. Put a stock 350 cfm 2V on your Galaxie and run it down the road in 2nd until its done, and data log the A/F so we know what's really going on. What is learned, is learned by all. Don't let your ego get in the way. Again.
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Don't do it Drew. A Chevy motor in your Galaxie? Anyway, a stock 352 with a 2bbl will run out of valve train b4 it ever leans out.
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It's running out of fuel. If it feels like it just gives up, or comes to some RPM and just "flat lines" - it's most likely out of fuel. Lean out, whatever - it's lacking fuel. The first 351C I put in the Falcon, before I went to a full cell/return fuel system, flat lined in 2nd at 5200 with 5 psi of fuel pressure at the carb (650DP Holley). The pickup out of the tank was 3/8" but it necked down to 1/4" as it passed through the plate that mounted on the stock tank. Got another tank, drilled the sump and installed a #8 bulk head with a #8 bulk head in the top for a return line, ran new lines with a return regulator - 6800 in first two gears no problem.
>You mean, like when you suck a drink through a straw?
Sorta. There is a column of air sitting over the carb that varies in weight depending on how the atmosphere feels on that day/that time. The piston starts down, intake valve is opening and creating a low pressure area in the cylinder. The weight of the air above the carb plus the restrictions between there and the cylinder along with piston speed affect how much air actually gets to make it trough the carb to pick up fuel and deliver it to the cylinder. No "suckage", the piston movement creates to opportunity for air to start moving. Since it has weight, it has inertia so now you can start thinking about the effort required to get the column moving, what speed it can reach, what happens when the valve closes - inertia means the air/fuel is still moving even with nowhere to go - and all that stuff.
Why as a bracket racer my weather station updates the prediction computer every 30 seconds with air density, water grains, RH, temp, baro pressure, etc. The amount and quality of air available to make power varies by the minute.
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Don't do it Drew. A Chevy motor in your Galaxie?
Funny boy. Fixed.
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Hey, what did I ever do to you? The only thing that depresses me about this forum is the ever-dwindling lack of humor too many members exhibit. I guess there is truth behind the old fart crotchety meme.
It's good to have an ego. It keeps you grounded, aware, and forward-focused. Just ask Jay.
I'm thinking that there's plenty of humor on this forum. Maybe just not your kind of humor... ;)
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My question was a valid one. Barry treated it as such. I have a '67 Mercury that came with a 350 cfm 2V on its 390. You can accelerate it in second gear until it just stops increasing speed. I wonder what the mixture is doing.
I actually thought you were joking when you posted the original question..... *shrugs*
When it became obvious that you were not joking and were serious I asked the question of how an engine gets it's fuel from a carburetor. Not for the sake of delving into theory, it was with the intention that you would figure out how to answer your own question, as that is often more rewarding than being spoonfed an answer that you may or may not believe anyway.
So Drew, I realize spending a month on a tuna boat in a sausage fest with all those sweaty mens gets you a little askew, but let's not get into theory. Just the facts, ma'am. Put a stock 350 cfm 2V on your Galaxie and run it down the road in 2nd until its done, and data log the A/F so we know what's really going on. What is learned, is learned by all. Don't let your ego get in the way. Again.
If this was your idea at humor, I'll admit, I don't really get it, seems like you were trying to be intentionally insulting so I just ignored it. If this was indeed your idea of humor, I can see why you do not find the place very funny.
I haven't bothered datalogging anything as I'm too lazy to drive around with a laptop attached to the O2. I still visually note the O2 meter and have tested out literally hundreds of carburetors in the last few years this way. There is certainly a lot to learn from this, more to learn by making big changes to the calibration and seeing where and why the engine does what.
My LM2 has the capabilities, and one of these days I'll do it with some of the more common carb combinations I build just for the sake of having a print out.
Running out of air, is running out of air.
Carburetors meter fuel into the air as it passes the venturi, calling it sucking/blowing/depression/etc is just semantics and not terribly important to the fact that if air becomes the limiting factor it wouldn't go lean unless there is a calibration issue or the carb is magically getting unmetered air from somewhere else.
Calibration issues like jet/pvcr too small, HSAB/emulsion waaaay too much, etc. (or as Chris mentioned, the engine is running out of supplied fuel)
As Barry mentioned, if anything secondaries not opening cause the engine to go rich due to pulling harder through the venturi than the carb was designed for. Maybe some instance does it differently, but I haven't witnessed this.
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The problem with having a reputation is that some people think I'm still joking when I'm just curious. In-depth carburetion science is an area I really haven't delved into, as my main interest the last few years revolves around restoration techniques and parts refurbishing (you know, like carb plating). We all have our areas of expertise.
In this particular case I was trying to come up with one more idea for the original poster to consider concerning his lean A/F. I really don't know what happens if the secondaries don't open. Once again, trying to think outside the box gets the lid slammed on my fingers.
My first car had an 8k rpm small block with a 750 double pumper. The "power range" was 4k on up. During the week commuting to school I drove with the secondaries disconnected, as the low end driveability was much better without them. The engine was pretty well finished at 5k, though. I never really knew what, if any, damage I was doing at that particular point. So I'm curious. Or was. Really don't give a shit anymore. Thanks.
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Without secondary opening, it's just run out of air. It's a lean out as the engine would just run out of fuel and air to keep going. But you'd have to be hammering it to get there, just driving around on a 2 bbl isn't going to make any difference. IMHO what happened on the dyno was just what the other engine guys said - nobody bothered to check the A/F on a light pull to see if the carb was even close to right. If I'm worried about the jetting on a new carb on a bigger engine, I'd just go up 2 steps front and rear - rather be fat than other. Most Holley's, though, work well enough right out of the box. The old 650DP on the Falcon is stock front, two steps up in the back for best MPH.
Talking carb is fun, and frustrating sometimes. I love the tunnel ram, as much for the "1200 CFM is too much for a 302" as anything else. :) "Would you put a 275 CFM 2 bbl on a 4 cylinder?" "Sure." So why not 2 of them on an 8 cylinder?" "Oh."
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You can only go lean if you don't have enough fuel . Except for a forced induction application , the maximum amount of "potential air flow " is limited by the cubic inches and maximum rpm so you aren't facing "too much air" so to speak , just too little fuel due to supply or calibration. When you limit air entry to less than the maximum air flow capacity of the engine , the vacuum "pull" on the carburetor is greater ( similar to a choke) and the engine goes rich unless the calibration is changed to correct it.
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Any whooo...in closing, I’ve decided to make the 4 hour drive to Kuntz & Co. for version 2.0 of this build. I need to focus on rest of the car (paint , susp, etc). I’ll circle back with those follow up dyno numbers in a couple months.
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At the request of several members I've deleted some non-pertinent posts in this thread. Let's try to keep it on topic, folks...