TAC Tech => Mechanical => Topic started by: restlessgypsy on August 18, 2021, 07:50:03 PM
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My motor was rebuilt ( 72' block 400 ) stroked to 462CI. Ran good on the engine dyno, but have had issues since putting it back into the car. Running rich but runs good and hard. Rejetted the carb a few times, a little better, but still rich, plugs smell like gas and black, which goes into my other issue, excessive crankcase pressure ( after driving it for a while 2- 3 hours here and there, the dipstick has been pushed out almost 1/4" ) Oil has a hint of gas smell after a while too. Was told the rich condition could have washed the rings out to the point that they are not seated properly allowing unburnt fuel into the crankcase and the crankcase pressure pushing oil past the rings and into the combustion chamber. ( Quickfuel carb 780cfm ) Like I said, no problems that they detected on the dyno. I've been told too much backpressure, replace 2 1/2" exhaust with 3"...
Swap carb and see if it continues to run rich. Swap Pertronix Flame Thrower HEI with something else ( maybe not getting good enough spark ) Swapped in a DUI module, ignition coil, cap and rotor but haven't really tested it yet.
Talked on the phone with Mr. Butler ( Butler Performance , they didn't build the motor) He explained that this is sometimes an issue ( crankcase pressure ) and recommended getting breathers/oil separators for the valve covers and 90 degree smog tube fittings to mount into my drop base air filter housing, running a hose from each to the breathers to pull pressure. He said that should work. I have a friend that ran the pieces that are welded into your header collectors to pull excessive crankcase pressure. I have Headers too.
Anyone else with any of these issues, and advise? Thanks...
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Was the dyno for output testing or tuning setup? Often when they are seeking impressive figures it isn't the tune you want for continuous driving on the street at all rpm. Not that any of that helps too much after the fact.
*Honestly, I would say more for output testing, more so than tuning for street driving, which is all the car sees. I talked to the owner that performed the dyno and he suggested jetting down both primaries and secondaries at least 3 sizes. which I did. a lot of adjustment.
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Is there a PCV system in place?
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Just out of curiosity how many miles on this new engine and how hard is it being driven. Is it possible the rings need to seat a little better? If there is a lot of foot to the floor driving you will have more blow by and crank case pressure. For this reason it is not unusual to see scavenging pumps on some race cars to reduce crank case pressure. There are also tunable PCV valves to help control excess pressure, but I don’t think they help much on wide open throttle. http://wegner.com/
I would for sure get your mixture issues resolved first if it causing oil contamination.
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Is there a PCV system in place?
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Yes, I put a new one in just in case there was a problem with the new on that was in it.
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Just out of curiosity how many miles on this new engine and how hard is it being driven. Is it possible the rings need to seat a little better? If there is a lot of foot to the floor driving you will have more blow by and crank case pressure. For this reason it is not unusual to see scavenging pumps on some race cars to reduce crank case pressure. There are also tunable PCV valves to help control excess pressure, but I don’t think they help much on wide open throttle. http://wegner.com/
I would for sure get your mixture issues resolved first if it causing oil contamination.
I would say, maybe a couple hundred miles on it. I don't keep my foot in it all the time, but I will play from time to time. I love the torque and the feeling when the secondary's open, though I need to do some adjustments there, they don't always seem to open or it could just be me. I've been told to drive the hell out of it, but all the money invested in it makes me a little nervous, to the point I actually bought another 72' 400 standard bore block..I also just bought a new carb to check out, one of the new FST carbs.
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I had the same problem. I had a pcv. My problem was i didn't have any kinda breather on either of my valve covers. Once I put a breather from the valve cover to the breather pan. Cured the problem.
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I had the same problem. I had a pcv. My problem was i didn't have any kinda breather on either of my valve covers. Once I put a breather from the valve cover to the breather pan. Cured the problem.
I have a PCV and was running an open breather filter in each valve cover. But that's not enough. You ran a hose from your breather to your air filter housing? That's what i was advised to do, run a breather / oil separator in each valve cover running a hose from each to the smog tubes mounted in / under my air filter assembly.
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As noted by some other posters here, addressing the rich condition may be the priority at this point.
I use to think a new carb would solve many issues and like many of us after spending our hard earned money and putting our faith into a new carb we come to realize new carbs need tuning and in many cases reconfiguring. You noted making some main jet changes which is OK when tuning for WOT, however the impact on idle and cruise (which is where the engine will spend most of it's time) is not so effective with MJ changes. Do you have any specs sizes on the current carb you're running ie. Idle Feed Restrictor (IFR), High Speed Air Bleed (HSAB), Idle Air Bleed (IAB), Power Valve Channel Restrictor (PVCR) and vaccum opening rate?
Were AFR readings recorded when dyno'd (not that they would be the same in real driving conditions but it's a start)?
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FIRST thing I would do, is to test your cylinder pressure, and possibly perform a leak-down test. If those turn out bad, then you have issues and the motor probably needs to come out and be torn down.
If good, then the next thing I would suggest is have an oxygen sensor bung welded into the exhaust and hook up a wide-band oxygen sensor. You've had way too many changes based upon guesses and speculation, and the quickest most accurate way to assess you situation is with analyzing your exhaust gasses (with the o2 sensor).
Rich mixtures are WAY easier to ignite than are lean mixtures. MANY times when people state they are "rich" because "I can smell the gasoline" - they are actually running so lean that the spark can't ignite the gas and raw gas is dumping out the exhaust.
I have a good friend who has tuned - literally - several thousand fuel injected motors. But he has not messed with a carburetor in nearly 15 years. I spent a day with him, helping him sort out & tune the carb on an old truck he recently got. It started and ran pretty good, but we started looking closer at it. We used a wide-band O2 sensor and a chassis dyno to evaluate.
Just checking the idle mixture, it was very rich. The idle mixture screws were 2.5-turns out. With the O2 sensor to guide us, I got the idle mixture to average right at 14.0:1. After balancing the mixture screws, all they needed was slightly less than 1-turn out. In the end, we added 9 degrees of timing, closed off the idle mixtures screws significantly, and made a large increase in secondary jet sizing. The tune was THAT far off, and yet it still ran decently.
My point - TUNE! Tune before you whip out the VISA and start ordering parts that you may not need. I personally have an old Innovate wide-band system that I've been using for about 15 years. I've heard mixed things about AEM, but there are other brands out there as well. I install my Innovate when I'm tuning a car, then just remove it and plug the bung once I'm finished.
Good luck
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Now that's sound advice. any up-dates?