As far as I know my `72 350-4Bbl motors ignition is completely stock (points and all). I have always had a problem with spark knock with anything more than 6 deg. initial timing. The motor was re-built ~20K miles ago by someone else and it has a different (energy) cam. The vacuum advance is connected to the lower driver side of the Q-Jet. I see no difference in timing whether the vacuum is plugged or connected. I've installed a John Osborne 800 cfm a few weeks ago (will go on the 455 when done). Here is the timing information I gathered today. Initial timing - reads 10* for about 10 seconds after throttle blip... but reads 8* after that, the idle is 800 --> 750 rpm in neutral. At 1000 rpm - 12* At 1500 rpm - 16* estimated At 2000 rpm - 20* estimated At 2500 rpm - 21* estimated At 3000 rpm - 24* estimated No change after 3000 rpm, the vacuum was connected for all readings. Additional note: My paint close to the headers is burned indicating lean or retarded timing. I thought with the new carb. I'd try to bump the timing a bit; maybe it was lean before? The new Q-jet (with no change in timing, 6* initial) was .3 sec. quicker in the 1/4 mile. Todays drive proved that 12* initial causes spark knock when motor is 190* or more, so I reduced it some for the readings above this afternoon.
Hey Cray, I have a '71 350-2 auto trans. The manuals state 10deg initial timing on it. It ran from the factory that way, it should run fine now at 10deg. I'd say there's a problem somwhere. Have you tried replacing the points, condenser, rotor, cap? What about spark plugs? As for timing curve, from when I've read and asked, it's about the same as the 455's. 34-36deg in by 2600rpm. I run on 12* initial, then with the curve kit I put in, it runs around 14* idle (N) and 12* (D). Have it all in by 2600 and runs perfect. Initial timing on the 350's can make all the difference in 'spunk'. If you don't mind spending a lil but getting a bit in return, maybe think about getting a Pertronix kit and an open air cleaner w/ K&N filter (if you don't already run a 360* cleaner). The reason you don't see a diff when the vac advance is plugged or not when setting timming is because it's a ported vacuum, that doesn't start to open up until your on it a lil. In a nutshell, check everything in the distrib, and the spark plugs. You may have worn out parts, or the wrong heat range plug in there. I noticed when I upgraded my ignition I went from R45's to R43's. Hope some of this helps Scott p.s. One last thing, did you reset the idle mix screws after you swaped carbs back and forth? err on the rich side...
I did not re-adjust the idle mixture with the new Q-jet, since it ran stronger, I will check it though. About a year ago I replaced the points and condencer they should be fine. No sure I got the dwell exactly right though? I'm not sure which plugs I used probably what ever the book called for. How would the heat range effect spark knock? The car runs fine, but it has always had a tendency to spark knock easily, specially when hot. If the AC is on on a hot day it will spark knock with 6* initial.
Are you having this problem on both premium and regular gas? A low compression 72 should be able to handle about 10*-12* or more initial timing with no problems....... What do you know about the rebuild???? Compression? I'm kind of thinking it may have a multi-keyway timing set, and it's set wrong Also, could be high compression pistons [10:1] and not enough overlap on the cam to bleed off the excess cylinder pressure...... Also, it could have a carbon build-up problem If it were my engine, I'd start with points/plugs... Use the accell brand. [yes, the yellow plugs,,, there a little "cooler"] Then a tank full of premium gasoline. If the problem persists, I'd then pull the front cover and spec the cam out with a timing wheel to make sure it's not set too far advanced. Also might try a cooler thermostat.
Waaaaait a minuteuzzled: What do you mean "energy" cam???????? Are you running a "Cam Dynamics" brand energizer or high energy cam??????? If so, that may be your problem..... Cam Dynamics builds cams with very little overlap and tight lobe centers designed to increase cylinder pressure in low compression engines. Also, if I remember correctly, they have about 6* advance built into the cam..... Find out exactly what cam your using, also what compression pistons went into the rebuild, and let me know.
Darryl & Scott, I don't know any more about the cam than I already stated, thats the problem when the car changes hands a couple of times after the work is done. I do know the cranking compression is on the low side for all cylinders, ~110 psi.! Leak down testing shows only 1% leakdown. I guess the valve timing of the cam is such that pressure is bled off more than with the stock cam with the same low compression it came with from the factory. I always run 93 octane to minimize any pinging. I think the engine still has the stock pistons and the block was honed and ringed. I don't think there's carbon buildup, I've poured water down the carb. while revving it, and I exercise the engine often. I am running headers and a 360* 4" K&N filter.
Cray, A year is abit for point/condenser set IMO, replace them with Delco parts. They're cheap, can put all new distrib parts on for less then 40$ Heck, if you can do w/o a cap you save about 15-20$.. Also ajust your dwell! Stock is 30 +/- 2*, so 28-32. Plugs can effect knock, just like after upgrading to Pertronix here, when I ran high load passes it would knock and in high temps too. Go down a heat range or two.. Plugs that get too hot cause nasty probs just like to cold a plug. You saying that the problem is worse when it's hot out or with the AC on, the engine just gets hotter and the plugs load up.. I'm with Daryl also on the cam, might wanna pull it to nab the numbers off it and go hunting.. It's one way to findout what the thing is doing inside there. Pressure and leakdown are both good, 110 i think is a lil low but still if they're all runnin the same it shouldn't matter much. Unless you have a hot cam in there or somebody went crazy with the engine, it should run fine set to factory specs on 87octane. Make sure to reset the carb mixture screws.. Best do it with a vacuum gauge routed to the manifold. Run it a tad rich and it'll be yer best friend. Lean mixes cause high heat, and all kinds of probs as well. Hence why it's better to run a lil rich then lean. Just set it for highest vac on both sides. Excercising the engine is the fun part. :Brow: Scott
OK, that helps some.... 110 psi does seem low... really low. I just did a 71, re-ring job with an iski 262 cam installed straight up [4* advance built into the cam] and I got 122 psi avg on all cyl's. I set the initial timing at 10*, and a distributor re-curve kit that gave 32* total [without the vacuum advance hooked up]... With the vac, it's close to 40*....[HEI distributor] Not a bit of ping..... Something is up with your engine..... How much "cam" is in there???? Is it really lopey, window rattler, slightly hotter than stock???? Try to give me an idea of just how raticle it is... I'm still thinking the cam is installed out of time.... Perhapse a poorly manufactured timing set.... It happens that way sometimes. Fatten up the carb for sure, that will help to cool it down. Also, look around for a cheap used HEI for a buick 350... Junk-yard maybe. Just drop it in bone stock and see what happens. The HEI is a far superior unit to the points distributor. If you see an improvement with the HEI, consider keeping it, and beefing it up. Ultimately, you may be looking at a cam swap. No, not cheap, but it's worth it to get it right. Let's hope it dont go that far... It would be nice if you could solve the problem without opening up the engine, but I think you may have to.
I'm planning to swap this engine soon, with the 455 on the engine stand within 3 months (projects going too slow). I have a HEI and I could install it and I could swap the 455 dist. gear with the current one in the 350. I've been tempted to do this. The engine has a nice little lope, but not rough. You know, it sounds really good when you first fire it up then smoothes out some ... after it gets warmed up.
HEI..... Go for it... If you have a bigger radiator for the 455, this would be a good time to swap that as well OK, so we have a mild thumper cam in an 8.5:1 motor, that pings at anything over 6* of initial timing, and you run it on premium gas at all times. We know it's jetted a little lean,,, fatten it up... see if that helps. Is it actually running hot? Has the radiator been serviced? Is the thermostat good? .....Where are you taking the temp reading from? The intake manifold coolant passage I presume... I feel were quickly narrowing it down.... One of 3 things... #1, carb too lean #2, problem with the cooling system... Blocked radiator, bad water pump, stuck thermostat, etc. #3, The cam is installed too far advanced... How does it run [ping] and perform if you back the timing down to, say, 2* or 4* ??? Big drop in power? Still ping? Go ahead and install the HEI, and some cooler plugs... Like I said, I like the accell plugs [personal expirence] as it could be a spark related problem... Sure cant hurto No:
do you have a temp gauge on it? I had some pinging problems... put a temp gauge on it and found out it was running at 240deg!!! After I fixed the colling prob it never gets past 210... usually nowhere even close. just a thought.
O.K. I going out for some testing today. I've got a temperature guage (mounted under the dash) and will record the temperature at the front of the intake, I also have a pyrometer to measure the temperature at the head (just before the header). I'm running 93 octane and will test what I have before changing any hard parts. I'll play with the timing (plugged and unpluged vac. adv.) and how it relates to pinging and record perfmance (AP22 performance meter). It's ~60 degrees out today, I'll post the update later today.:laugh: uzzled: :jd:
One thing you want to do for sure is replace the thermostat. The stock 72 smog motor thermostat is 195* for both 350 and 455. You want a 180*, or even possibly a 160* thermostat, that they used in the older 60's cars before smog equipment. Another possibility - outer ring on balancer has slipped on the dry, cracked, 30 yr old rubber?
Testing results Lots of testing today:Brow: First temperature readings at various timing settings, the engine was allowed to idle at each setting to stablize temperatures: initial timing/temp. at head/water temp. taken at intake. Note, the temperature of the head (at the exhaust) was taken from the #1 location, readings from this cylinder were consistantly 40* more than cylinder #2. 2/419/191 6/403/187 8/403/183 10/398/180 These readings were taken at idle in park. I did not experience any pinging today the engine never got over 195*, the high today was maybe 68*. I figure I'm running lean with these high temperatures at the head. I did (6) test runs today, each test consisted of a 2-way timing average. These (first four) results were done with the dist. vac. plugged. The time between speeds was chosen to eliminate tire spin, each run was timed between 15 and 70 mph, 0 - 60 times listed second. All times were done electronically to eliminate human error. timing / 15-70 mph / 0-60 mph 2.5*- 7.90 sec. / 7.15 sec. 5* - 7.50 sec. / 6.98 sec. 7.5* - 8.10 sec. / 7.33 sec. 8* - 7.45 sec. / 6.98 sec. It turns out the car ran just as well if not better with the dist. vac. plugged?? Here are the runs with the dist. hooked up, the timing was set to 8* (the best result from above). 8* - 7.60 sec. / 7.00 sec I then checked the vac. with the gauge and adjusted the idle mixture. It turns out the initial adjustment was 2.9 turns out. This resulted in 14.2 to 15.8 psi. range of vac. Trial and error showed that 3.5 turns out gave more vac., new range between was between 15.5 to 16.8 psi. One more test run: 8* - 7.85 sec. / 7.05 sec. QUESTIONS: I always forget?? On a Q-Jet if idle mixture screws are turned in (clockwise) will this make the engine more rich or lean?? How is do you make the mixture more rich?? I don't know yet what jets or rods are in the carb. it was prepped by John Osborne. If the jet size goes from .073 to a larger number will that provide a richer condition? How do you change the jets on a Q-Jet and will the rods need to be changed if the jets are?? Do you have to take the carb. off the engine or take the top 1/2 off the carb? Thanks!
Impressive! I never do testing like that.. lol So when you got the carb it was running lean, 2.9 turns out. You adjusted it to 3.5 turns out. That richens up the idle mixture and gives better vacuum. It should also make the engine run cooler, as well as increase the idle rpm a bit. Turning the screws in leans it, outward richens it. You can change the secondary hanger and rods with the engine running if you wanted to and they're easy to identify by letters. Changing the primary side tho requires you pop the top off. Thinner rods, richer circut I believe. The vac advance is ported so it only comes on after your on it a bit and does nothing at idle. It runs better with it disconnected I think because you don't get to much advance when your on it. What alot of people do (myself included) is set the initial timming and then recruve the dist weights and springs to get 34-36 total in by around 26-2800rpm. Initial + Dist = Total. Then nab a adjustable vac advance and plug it to the manifold port and get it set nicely. What you end up with is good takeoff and idle mileage combined with good hwy perf... I think your pinging problem should be about fixed since you've richened up the carb. Tho only a warm day will tell that story. I'd go for 10* initial timming and see what she does, if all is well, head to 12. Shouldn't have to go above 12 tho. I couldn't notice a diff when I played with it up to 16*.. Impressive that these old monster cars have nice 0-60 times ain't it.. hehe Scott
Thanks Scott. I should go ahead and install that HEI. Here's what I think I have to do (corrections or specifics requested): 1--remove old dist. and remove gear 2--remove resistor wire and replace with 10 AWG. 3--install 350 gear on HEI dist. (was set-up for a 455). 4--install dist. I know this has been covered before but can't recall the details. Anyone else use the AP-22 Performance Meter? Excellent capability to cost ratio. For less than $300 you get many features to evaluate performance, calibrate the unit with actual drag strip times and download data to the PC for more fun.
Here's a couple of thoughts on your testing: 1. Vacuum advance only works at part throttle. At WOT, vacuum drops to near zero and there is no vacuum advance as part of the total timing. Only initial and centrifugal advance contribute at WOT. 2. Idle mixture screws are just that, IDLE. They don't affect the mixture ratio once you're moving at part throttle or WOT. And they affect the mixture quantity not the air/fuel ratio . 3. If you really want to mess with the rods and jets, go buy the Doug Roe book. It's too much for a post, that's why it takes a book.
Been thinking a lot about the timing thing this week. Why not first mark the damper where the total timing you want is then rev. the engine to say 2500 rpm and rotate the dist. so this new mark is aligned with the 0 on the pointer? This would eliminate the guesswork relating to the total advance. I've decided to upgrade to the HEI (on the 350), what is the resistor wire connected too on a `72 Buick Skylark? I assume ... the positive side of the coil and the ignition switch, and I should replace it with a 10 awg. copper wire. Also wondering about the tach. My tach was upgraded to be compatible with points or HEI about a year ago. Can I just route the wire from the neg. side of the old coil to the tachometer labeled connection on the HEI? Thanks!
Craig, The resistor wire runs from the + side of the coil to the firewall connector( drivers side, down low). Along the way there is a wire that tees off the resistor wire to the "R" terminal on the starter solenoid( eliminate this). The firewall connector comes apart( bolt in the middle) The wire has a special barb type clip that can be released from the rear with a pair of needle nose pliers. You can either unsolder the clip from the resistor wire and use it on your 10 gauge wire or you can buy a replacement clip from NAPA or you can order the entire wire with proper clip and HEI connector from Year One(L00510). Your Tach wire hooks to the Tach terminal on the HEI cap. Hope that helps.
Larry, that makes it clear. Eliminate the wire that runs to the starter that "T's" with the resistor wire. Replace the resistor wire, that connects to the positive wire on the coil, with a 10 awg or so wire. It is so clear now :eek2:
