Even though my engine seems to run quite strong (especially since I put the 1 inch spacer under my Q-Jet) I just checked my timing with my new dial back timing light and digital rev counter and found that not all was well. Could there be even more power hidden in this motor? The Q-jet is running very nicely with the new rods and hanger (thanks to this and other boards). Now that I have the correct instruments to see what's actually going on I need to do this right - myself. I have been to 2 dyno tunes and this is the way my 401 is timed at the moment. Obviously the specs I gave them (10-12 initial and 32-34 by 2800) where not adhered to and aren't even close. Just to recap...this is a stock motor with a 425 spreadbore manifold with an 800 Q-Jet (AX rods B hangers) sitting on a 1 inch open hole spacer (which, by the way, increased power throughout the entire range - not just the top end). I use the best quality premium unleaded fuel (gas) which is rated at 98 Octane plus I use "104" brand octane booster. It's the best I can do fuel-wise. With the vacuum disconnected the static timing is 4 degrees at 600 rpm. The advance starts to move off at about 1200rpm and reaches a maximum of 20 degrees (!) at 2300rpm(!!). I used to have the vacuum advance hooked up to ported vacuum but I have a choice of ports so I can hook it up to manifold vacuum as well. The vacuum advance adds about 16 degrees but like I said I don't run it. If I increase the advance just by turning the distributor or re-connecting the advance to ported vacuum it pings all to hell - undriveable. I'd really like to sort this one out once and for all. Maybe I should try manifold vacuum? Bill S.
o No: Bill, I am no expert, but I would go back to stock settings with vacuum from carb and start there. Good luck Bill. Bill Bailey
Thanks Bill. I have it fairly close to stock as it is but with the vacuum dis-connected. I'm not getting enough advance according to general practice but if I give it more you could call me Sir Pingalot. During my lunch break I re connected the vacuum advance to a ported source and noticed a little more power (especially on take off). I'm not sure if that helps anyone diagnose my problem. Tonight when I get home I'll run up the timing light and the tach and see what is happening using the vacuum advance (but obviously with no load). Bill S.
Bill, what compression ratio are you running? If it's more than 9 to 1, maybe as much as 9.5 to 1,you may well run into pre-ignition problems. If fuel quality "down under" is anything like it is here in the states, you'll definitely be pinging with higher advance numbers. I recommend hooking the vacuum to a manifold source, but first set your timing to about 25 degrees with the advance "all in", (no vacuum). Don't worry to much about the initial timing, as hooking the vacuum advance to manifold vacuum will raise the timing at idle, just reset the curb idle as needed. This practice has given me good performance, and a smoother idle, what with the extra advance at idle. I've read that most of the pre-emissions GM (and other makes too) hook the vacuum advance up in the aformentioned manner and it helps overall driveability. I used to run my vacuum advance on all my engines to ported vacuum, but then read that this is usually on "emissions controlled" engines. As far as the 25 degrees total advance goes, that would be a good starting point, but you could go as much as needed untill you get pinging, then back off. Hope this helps... Zach
Zach. A 66 401 MT motor runs 10.25 compression. I would say that has quite a lot to do with my problems. So, let me see if I understand your suggestion... 1)disconnect vacuum. Set timing to 24 total at max advance (which in my case is about 2300 rpm). 2)connect the vacuum advance to a manifold source. This will raise my initial quite high but I will give it a go and see what happens. I'm half tempted to pack the distributor into my suitcase and bring it with me to the States! Thanks for the suggestions. I'll try anything at this stage. Bill S.
I used this set-up most recently on my ' 71 GS 455 (which I've since sold ) And it worked famously. What it does, is give you more advance at idle for better off the line response, and then gives you less vacuum advance under heavy loads, which is when you are more likely to encounter detonation in the first place, and when cruising at speed, gives you more advance once again, for better throttle response. I just finished checking out your site, and really enjoyed it!! When I get some pix of my ' 55 Special 4dr-hdtp, I'll send them to you. G'day.
G'day Zach :TU: . Did you see the 55 4 door I have just featured? I'm not sure if the nailhead behaves the same as the 455. The 455 seems to come from the factory with more advace to begin with. The stock initial timing for my Nailhead is 2.5 degrees. So taking it up to 10-12 is really gonna have an effect on it. Good or bad remains to be seen. I'll be interested to see what effect your method will have. Thanks again for the suggestions. Bill S. P.S. Glad you enjoyed BuickStreet.
Ok, this weekend I bought a crane adjustable vacuum cannister (which came with 3 sets of springs) and a set of weights (which also came with 3 sets of springs and a brass bush). I also bought a vacuum gauge. After many hours of trials and testing I finally managed to achieve what I think is an acceptable mechanical advance curve. With vacuum disconnected I have 10 degrees at 600 rpm all the way to about 1100 rpm where it starts to advance and achieves 31 degrees all in by 2750 rpm without pinging. The next looser springs will make it come in by 2300 which is too early and causes pinging. Now I have to work out the vacuum advance. Mind you the car seems to go quite hard with setting already and I would be happy with current power levels if there is no more to be gained by adding vacuum advance. I have much more power down low and it appears to be stronger through the entire range (especially at part throttle where it's really quite a lot stronger than before). My main problem is trying to choose a vacuum port from the carb. There are three and they all exhibit different characteristics. As I mentioned I purchased a 20 dollar vacuum gauge so I hooked it up and took some notes. Here is what I found.... Port 1: -20 HG at idle. -Idle increases when unplugged. -Maintains 20-25 HG when revved steadily -Drops to 10-15 when revved suddenly Port 2: -0 HG at idle. -no change when unplugged -Maintains 25 HG when revved steadily -Drops to 0 HG when revved suddenly Port 3: -0 HG at idle. -no change when unplugged -increases to 10 HG when revved steadily -increases to 10 HG when revved suddenly Revved steadily = slowly increasing the revs to about 3000 Revved suddenly = violent movement of the throttle usually to at least 3000-4000 rpm. All of this tells me nothing about what is happening when under load but at least they all have different characteristics which will help in identifying which is the preferred port for my vacuum advance. My questions are these... Is my initial plus mechanical advance acceptible and which port do I connect the vacuum advance to? I currently have it plugged into port 2 and I have noticed a little extra power down low (I think - it's hard to tell some times) and it seems a little smoother. I would happily run it without vacuum and not feel like I have sacrificed any power just a little smoothness. Thanks for your ongoing help with this. Bill S.
Bill, My guess would be port# 1. Give it a go on the street and let us know. Good luck Bill. Bill Bailey
I currently have the factory vacuum cannister which provides for 16 degrees of vacuum advance. Won't that be too much for it now with all the extra initial advance? I presume that port 1 has "full un-ported manifold vacuum". A pretty strong signal there. I'll try it and see what happens. Thanks Bill Bill S.
Port one is manifold vacuum. Port two is ported vacuum. Port three, I have no idea what that is. Ordinarily you use the ported vaccuum on newer motors, don't know about a Nailhead. If you tested it with the car moving you should see SOME vacuum at steady, part throttle. You don't have enough load on it at idle to see that though. My guess is hooking it up to manifold will give you too much advance at idle and low RPM. It sounds like you've set the mechanical advance curve and initial timing up so that you'd want to use the ported.
Bill, My Edelbrock 1407, 750 CFM has a port for mechanical advance and one for vacuum advance, depending on your your set up, you plug the one not used. Mine is the original stock distributer rebuilt by me with vacuum advance. Again much luck to you Bill. Bill Bailey
Thanks everyone. I'll try manifold vacuum and tune my Crane adjustable vacuum cannister to minimum advance. Any idea what a ballpark figure would be for vacuum advance? I'm guessing 6 degrees but will tune it to ping and then back a few degrees. Will let you know how I go. Bill S.
Hi Bill. I would go with port number one. It is as I described in my previous post. When under a load, vacuum advance will be minimized, due to lower vacuum, and will therefore be less likely to cause pinging under a load. As vehicle speed increases, load diminishes, and then more advance will "come on line" maintaining smooth performance. It's kind of a "see-saw" effect. Centrifugal advance does the bulk of the work of timing advance, and the vacuum "enhances" the effect. Keep in mind, that with the vacuum advance hooked to a manifold source, when the rpm's are at your mechanical advance limit ("all in"RPM) you may only see a slightly higher total advance value. I use a MAC tools timing light that is adjustable for doing these set-ups. I just set it to my desired total advance number, then point it at the timing mark, then turn the distributor till the TDC marks line up. Of course, you have to rev the engine up for a second, watch the marks, and then tweak a little, then re-read the marks untill you achieve the desired setting. Or, you can use a degreed "tape" on the balancer. Good luck, and I hope the pinger's stay away!:TU:
I wasn't going to have time to throw on the Crane adjustable vacuum cannister until the weekend so I decided to just try Port 1 as suggested. This motor has amazed me on several occasions by responding to my mods with more power and this was no exception. Once again I felt a healthy power increase. Now, from what I understand, any change in power levels below 10% probably can't be felt. That being the case I would have to say that re-attaching the factory vacuum cannister was worth at least a 10% increase - most noticeable down low (my poor tyre). From a standing start, in drive, I can smoke for several car lengths. I also have regained a lot of power when in low-stall (I drive around mostly in high stall). Before, I used to bog down slightly when 'performing' in low stall (I have a manual switch inside the car). Now (if it wasn't for the creeping at the lights) I'd be happier to leave it low stall more often. I really expected it to ping at 10 degrees but it doesn't. It does however ping at 12 degrees with the vacuum attached but I haven't tried 12 degrees without the vacuum advance (as suggested) so I tuned it back down to 10 and now I know that I am getting the maximum timing from the motor at this stage. I wonder how much is left in this 'ol Nailhead. All hail the Nailhead! Thanks for the advice. Once again it was 'spot on' correct. Stay tuned for more exciting adventures of...this Ozzylectra. By the way, I am the only Buick that I see driving around Adelaide (my home city) and I drive it every day so I'm really keeping the Buick flame burning down under. The humans seem to enjoy it too. They always want to creep forward looking for the make as Buick is only written on one place on the entire car. The hood. Fortunately, not many people get to see the hood and most have to recognise it from the tailight view :Brow: Bill S.
Thanks Bill. Couldn't have done it without V8Buick. The carb is running great, I've recurved the distributor, I have an internal switch pitch, what else can I do? ..o0 mumble mumble, nitrous, mumble, dual carbs, mumble mumble, posi, mmmm. Serious though, thanks everyone. Bill S.
dual quads hey bill how are you? i wnt down the road of 2+2 and it was a gas!! the only thing i can say is hold on to your wallet 2400 was awhat i paid and the carbs still needed work old floats and worn out linkage i ended up parting with it for 1800 oh well live and learn! g-day
G'day Craig. Owzitgarn mate? As you're probably aware I'm on way over to the States. Who knows what I'll be picking up. At that price I'm not sure I could afford it this time around but ya just never know what you'll find at a swap meet - right? The Hot Rod re-union will have a swap meet and I just know that I'm going to have to buy those finned Nailhead rocker covers that I just know will be there. Bill S.
