Sounds like to me you have more than one problem. One of them is the rings on a few of the cylinders did not break in correctly? Like someone else said that's a lot of difference between compression for a fresh motor. If it was me I would contact the builder and see if he will stand behind his work. 215 pounds is up there. 10:1 probably. Good luck.
You might check to make sure the secondaries on the Q-Jet are closing completely. It's not uncommon for them to stick open just a touch which will cause the engine to run rich. It's hard to check visually because the air valve should be held closed by vacuum at idle. You can usually get the butterflies to seat by flipping the secondary linkage or tapping the butterflies with the engine not running.
OK...someone please explain to me what the heck I am doing wrong. Today I pulled ONE spark plug and ran a compression test. Result 140 psi. FYI - that plug looked good. No oil fouling at all. Before, I had ALL the plugs out and the pressure went sky high on the test. Time to pull the rest (one at a time) and check the plug and cylinder pressure. Checked one entire head. All plugs look good. #8 plug looked the best (tan) and had the highest cylinder pressure of 142. 2-#140, 4-#137.5, 6-#140, 8-#142. Too late and too tired to check the other side. I am wondering if the shorter electrode in the new plugs are causing the popping or if there is oil in the exhaust system. I might drop the exhaust at the collectors tomorrow to check...might also run the engine with open pipes just to hear it run and see if it smokes from just headers. My neighbors will just love me revving the engine to 3000rpm...not.
on your popping problem, my brother in law had a Camaro with a bbc and it developed a pop in the exhaust shortly after building the engine went thru all the avenues and no luck. I was over one day and noticed the wire going to the dist was the original resistor wire which reduced voltage to the dist, changed out the wire to have 12 volts to the coil and no more popping issues. just a passing thought. hot rust
Good thought, but I do not have any resister or resistance wires on my truck. I will double check to make sure it is getting a full 12 volts.
Hard to say exactly what you could be doing wrong. Standard compression test. 1 . Warm engine preferably 2. Fully charged battery (I usually put a charger on it while testing) 3. Remove all plugs 4. Remove coil wire. 5. Block open throttle 6. Ready your gauge and pen&paper. Screw in your gauge to each plug hole And crank engine ( some say let gauge see 3 cycles some say more I usually go 5 cycles. I do that because I want to see max pressure and sometimes 4th one sees a minor increase but the 5th one as yet to show any movement.) Record and repeat the test on the same cylinder to ensure accuracy and same reading repeated. Move on to next cylinder. These things are mechanical, not mystical. When things don't make sense it's usually the methods or the equipment. I have no idea how you obtained a +200 reading and now see a reading in the 140s. 200 is way out of what's expected and a huge red flag. Anyone who routinely does compression tests would realize that. With reading your description of "dished pistons and large chambered heads " I was expecting to see 140-150 cranking compression.
At 240 PSI compression, you're gonna need premium fuel. I suspect the ultra high compression is partially caused by the oil being introduced into the fuel system. Also, Stimpy is right-on regarding the oil in the fuel [from the lack of baffle in the PCV] decreasing any octane you may have had in your shit-gas...I assume it's 87 octane. I always ran at least 91 and mostly 93 octane in my 406 with no problem. I wouldn't trust the timing marks.There have been many different timing covers with pointers, bolt-on pointers and even ones with a hole in 'em! Each vibration dampener has marks in different places to match up the the pointer...get a mis-match of parts [or have the outer ring slip on the dampener] and the timing marks will lie to you. I like to use a vacuum gauge to set the timing and then road-time it if the engine still pings. The oil baffle is a big deal.
yes,check that you have the correct PCV valve. I bought a car one time that had one in it that was too long. It was sucking oil off of the head surface. SBC are quite short. Almost all are the same for SBC.
I assume that after not using my compression gauge for many years, that it was somehow stuck/messed up inside, but now seems to be reading correctly, because I did it exactly as 31vicky said. Anyway, I feel much better about the normal readings...and the PVC valve issue is also corrected with the baffled valve covers. The smoke and popping are the next issues to tackle. I can't tell if the smoke is fuel or oil or both. Not really sure what to do or check. I will try and borrow a good leak down tester from somebody. Would that tell me if the rings are sealing or cracked? I'd also like to figure out if the carb is just running extremely rich. It sat for a long time between engine starts.
Carbs and today's fuel can be problematic. Recently I had a q-jet that operated flawlessly until one morning it didn't. It went from a long history of perfect to totally fucked overnight. These Things do happen. It can take a while to burn off oil if you had a lot of oil being sucked into the engine. Usually not as long as days, longer than a few mins but a few hours of running to burn it off. One way to tell is to watch the exhaust at night with headlights or trouble light. Oil burning will make a hazy cloud that grows and grows and it's easy to see with the back lighting against the darkness of night. The cloud can get as big as a house in calm air. Fuel smoke doesn't grow on itself. A fresh engine will burn some oil. Also The nose is a funny thing, an engine that's running too lean will smell off, burn a little and it's easily mistaken for richness to an untrained nostril. Funny that popping thru the exhaust is also a symptom of a lean condition. Think on that for a moment. You could always use an air fuel gauge too, it will advance your tuning to new levels. Tuning is a dance, a series of steps or adjustments repeated ever refining towards the optimal. It's not hard but it's not as easy as falling off a log. Your distributor needs/must do 3 things perfectly. 1. Provide you with maximum mechanical advance at the desired rpm, this accomplished by weights and spring. 2. Provide the correct timing at idle. 3. Come to resting stop that provides the correct timing to allow starting. More often than not, this requires some tweaking to get it right. The engines baseline vacuum needs to match to the various vacuum pots on your carb and advance units. If you have box stock pots that work well on a box stock engine creating a baseline of 20 inches at idle everything is fine, but if the baseline vacuum of your custom engine is 15 inches at idle those stock pots aren't behaving and causing you trouble. Quad jets are amazing carbs but they are not simple. They are infinitely adjustable but those are not simple turns of a screw adjustments. You'll need to speak fluent quad jet to get one working correctly on a custom engine. It's more than possible and you will be happy but it's not easy.
dont panic, ignore the popping, ignore the oily exhaust, set the timing without vac to the specs you were given, block all/any open vac openings. 1. do the leak down test, results? 2. save me looking what carb? was it on this or same size engine before? do you have a spare? 3. keep your fingers away from the vac advance 4. did you fit the inlet manifold?
when you did the first compression test did you have all the plugs out ?? if so that can cause a higher reading as the motor spins over faster from the lack of pumping resistance on the other 7 cylinders ,and the cam will start working better ( quicker overlap time so less cylinder bleed down ) . to get the proper numbers you have to do it one plug out at a time . kind of like my friends car it reads real high numbers because it uses a 16 v battery and a 12 v starter and spins over real quick , for use to do a compression test we have to use a 12v battery or the results are off . just brain food for the memory banks .
on rare ocassions if its sucking oil the oil can coat the exhaust pipe or muffler and make a overly rich environment and cause it to pop on deacelleration ) ( we have that happen on detroits when thye get old or just shopped and breaking in the rings ) it goes away after it all burns out , id the q jet a GM one or a Edlebroke one?
Can't say I read every post in this thread but did anyone mention checking the intake manifold gaskets?
I ran the leak down test. The Left bank looks really good. Left 1 - 85.3, 3-.91, 5-.91, 7-.92 Right bank is shaky, especially number 4. I checked it several times. I thought I broke the valve spring on #6, but maybe it was on #4 and I bent a valve? That still does not explain the other low readings, unless I have a leaking head gasket? Right 2-.77, 4-.65, 6-.77, 8-.91 What to do next...pull the head and have it checked?
Could you tell where the air was escaping to ? That's sort of the point of the leakdown test. The 2-4-6-8 side the side that's popping on deceleration ?
I listened to the exhaust and the intake and heard nothing...never thought to check the radiator for bubbles. I can hook up my compression gauge hose and run air into the cylinder to check that I want to eliminate oil in pipes as reason for smoke. I will run it and see if it smokes with cold exhaust. Then pull my exhaust pipes off the collectors and run it and see if it smoke with no exhaust pipes If it still smokes, then I will suspect a problem with the rings. Second, I think I should pull the head off and inspect the gasket to see if blown between cylinders 2,4,6. I can also pour thinner into head chamber and look for leaking around valve into the intake and exhaust runners. I really thought it was # 6 that had the broke valve spring, now I am not sure anymore...I'll should be able to tell if a valve hit the piston with the head off. I have no ide which side is popping. I have a crossover pipe right after the headers and the sound just seems generic in the exhaust. I'll check to see if I can isolate which side today. Can I pull a plug wire to eliminate the cylinders?
You can listen for air in the crankcase = Usually rings or an adjacent cylinder = head gasket between cylinders Or radiator = head gasket On your leak down results - 10% loss is considered good 30% loss is trouble . Your cranking compression test should have shown those high leakers as low cranking compression too. I can tell your not sure where to go next, and its hard to say for sure - none of your test results are consistent.
SO it gets better and worse... 1. Better - I always had a three "TIC Tic tic" sound right after start up. I swapped in a different starter and that noise went away...Good! 2. I ran it from cold and it smoked, but not as bad as the other day. It also did not pop so much when it was cold. I got one pop back. I do throw a lot of moisture out the exhaust. The smoke looks both white and blue. 3. Worse - I swapped my HEI back into the engine and set the timing the exact same 32 degrees and it runs like crap. At 2500 rpm it breaks up. (I thought it ran much better with the borrowed distributor.) It also popped a lot more with my distributor in it. I might try swapping just the caps. 4. I crawled under it while it was running and discovered a leaking header collector gasket. (FYI - running engines sound weird with your head right under the oil pan...!!!) The compression test did show those three leaking cylinders at 140 psi compared to 150 for a non-leaking cylinder. How do you listen for air? Stethoscope, bare ear, ? I ran the test at 80 PSI. I returned the leak down tool, but I can still hook up my compressor to the cylinders and run 130 PSI down them.
By hooking up the air line to cylinder you should be able to hear the air escaping as long as it's reasonably quiet where you're working. Assuming you have the valve covers off and hear the air coming up thru the drainback holes, it's the rings or piston or cracked cylinder wall, air noise in the intake manifold, it's a intake valve not seating, air out the exhaust, leaking exhaust valve or bubbling in the rad, blown gasket.
If you ran an 80 psi test and had 30% leak that should equate to 24psi escape. You've got to be able to ear that bare eared. A length of heater hose to your ear can help pinpoint it. And Yeah an exhaust leak was mentioned quite a few times here in your thread. They really do hurt things.
OK so I am probably off target here but is this an automatic , I had a 400sbc with a th400 that was smoking .Turned out to be a leaking diapham in the vacuum modulator sucking oil.
BAD NEWS is good. It turns out the hose for my compression gauge has a check ball in it, so no air was going into the cylinder...thus I heard none coming out. LUCKILY, I had just bought an adjustable stop bolt and using my handy dandy die set, I threaded the top of it to accept a hose connector and yes I can hear air clear as day running out the exhaust. SO...remove the head is obvious. Send it to a good machine shop and hope they can fix it. What do I look for in the bottom end. Will the piston be ruined? Could the rod and bearings be damaged too? How bad could it get...? I will check #2 and #6 before I tear it apart, just so see how they are leaking. I also bought a new HEI distributer today. What else should I do/test before I tear it apart?
I assume that you already did so, but before you pull the head, make double sure that the valves are all of the way closed. If the rockers are not loose, loosen them to make sure. Its a lot easier to double check than to pull the heads....
I double checked that I was at TDC, but I will do that too. There is so much air leaking that I am also wondering if I blew the gasket between cylinders. I might pull the plugs out of the adjoining cylinders and see if I can hear or feel air in them. They registered low too.
I am stumped..everybody has suggestions, and you are working very hard at fixing it..now you want to pull the head and take it to a GOOD machine shop.? why is the professional builder, that built your engine, not fixing it..?
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