Timing/vacuum advance/HP questions
 

Hi guys,
I had my car at the track the other night,first time out since the 400 was rebuilt. I made a few passes,then increased my initial timing from 12 to 14,then from 14 to 16. Each increase my MPH went up,around 92 MPH at 12,96 to 97 while at 16 degrees.
Ok,now today while driving on the street,it lugs and bucks slightly while cruising in 4th (Muncie 4-speed tranny). My engine builder had put one of those Crane dist. curve/adjustable vacuum advance kits in the distributor when he had the engine. Silver springs installed ,I believe. Advance connected to manifold source currently. This is a stock breaker point distributor ,BTW
OK,logic would tell me that the engine wants less timing at cruise,seeing how it ran good at 12 initial while street cruising before. So now I should adjust vacuum advance to take advance out at cruise,right?
Also,how much initial can I give it? I was tempted to go another 2 degrees advance at the track,and see if MPH increased,but I'm afraid I would not hear the detonation if it started.
I would like to check cetrifugal advance also,so I did buy a dial back timing light,just have to wait for it to arrive.
I have never really played with these curves before,so it's all new to me.I just want to make sure I'm doing the right thing here?
Thanks,Drake

Limit the travel of the vacuum can rod. Some of those adjustable units are for the spring pressure, some for the distance the rod travels. In any case, limit the movement of the rod to apprx 1/8" or .125". There are lots of ways to close down the window and limit the travel of the rod. Some vacuum advance cans even come with a "cam" that goes under the screw that holds the unit down, which allows for adjustments.

We use a MIG welder here to add some material to the "window", then a round chainsaw file to open it up to about 1/8" of travel. This is a good starting point, and will limit the advance form the vacuum unit to about 10 degrees. You can open up the window for more if needed?......Cliff

Thanks Cliff.
Do you think I should try to go to 18 initial ? Seems like nobody else runs this high,that I see. I would wait till I went to the track next time though to do this. Seems like the seat of the pants meter don't work too well!
I figure in the mean time I'll throw my piston stop in there and check to see if the timing mark on the stock dampener is accurate.

Do you have a new balancer? I didn't replace mine at build time and it started to slip, throwing timing way off. All seems well after having replaced it (though my plugs are now toast)

forget about intitial timing and concentrate on the TOTAL timing, and at what RPM it is all in at..................you need to find out what mechanical advance your distributor is supplying at a given RPM........most stock distrijbutors will get you 18-22 mechanical........you can taylor your total by limiting or adding either initial or mechanical, as well as spring tension to get the TOTAL desired for best performance....

my old 400 liked about 40 TOTAL for best performance.....every engine will be different...

Good advice. I would throw timing at it till it slows up or pings, then bring it back to the last setting where it ran the best without detonation, THEN look at the initial setting, add vacuum advance, etc.....Cliff

Sounds good. I don't have a dailback light yet though.It's on it's way. The distributor was recurved by the engine builder on a dist. machine,but because of other problems I have run into with it,I don't quite trust what was done to it,and I would rather double check it myself.
Ok,should I try putting lighter springs in so that timing comes in sooner then ? Like I said I am missing the silver springs out of the Crane kit that I was given,so I assume that is what the engine guy put in there. Crane says two silvers starts advance at 600 RPM,all in by 2200.
Greg,I'm using the stock dampner,thats why I figure if I check it with the piston stop<it should let me know if it's off at all.

Yep I agree with mike and others dont worry about initial.. total is what u are looking for.. Be good to know what weights and center plate numbers u have that will give u a good idea whats in the dist for timing... Its always good to watch the mph at the track then back it down 2* from best setting...

Thanks guys. If I have some time this weekend,I'll see what I have in there. I have to put the new stiffer points in anyway.
I'll be going back to the track in a week or two,I'll let you know how it turns out.

I figured you would run faster with your combo and you probably will with more tunning.
I know a guy that has a 79TA 400 4spd with 3.23's runs 14.30-14.60 at 96-98 mph with a 8.1.1 400 with 6X4's and a 268H compcam.

Good luck and keep us posted.

16-22 is pretty normal for initial and 34-38 total all in by 2500rpm or earlier just make sure its not coming in at idle or close to it, That engine should rip pretty good!

I don't know if that is good news,or bad ! LOL
I'm sure,over time,that it will get better ET wise. I plan on getting RA manifolds (stock logs right now),and some better tires(F70/14 Sears radials for now). I have to really baby it off the line right now,as you can imagine. My goal with the present set up was 14.0 @ 98,so I will keep plugging away at the tuning part. Plus keeping it stock appearing was always a priority during the build,so I know I sacrificed a little right there.
If it was not the original engine,trans,rear,I would probably be a little harder on it too,but I bought this car to have fun.
I really need to get a tach also,just too hard to be consistant without one,with a 4-speed.
Thanks,Drake

Drake
The good news is that you are in the 14's. Which is very respectful in my opinion. With your combo (stock logs) you should be in the 13.8-13.9 range which is even better news. Just keep tunning and working on the 60ft time. Get the 60 ft down to 2.0-2.1 and you'll be in the 13's. 4speeds a hard to launch consistently, but practice, practice and more practice and you will be there.

At last I had some time to work on this thing! This 400 has been running like crap the past week or two,I didn't even want to drive it.
The timing mark was jumping around constantly,and idle kept fluctuating about 100 RPM,so working on the curves was useless with a light and tach. Last night I ended up putting the tightest, "blue",springs in,I figured maybe having the lighter ones in had my mechanical coming in too early,and causeing the timing jumping at idle? I also adjusted the limiter plate on my Crane vacuum advance to the last notch tight,so now I am only getting 9-10 degrees vacuum advance at idle. Timing and idle are now steady,and I even got it to idle down to 600 RPM without a problem,I bumped it back up to about 650 though,in case I turn the A/C on. Before last night I couldn't get it to idle below 750 or so. Not bad for a Crower 60242,IMO. Initial set at 20,mechanical comes in at 850,I never did get a "all in" or total,it was very early in the AM,so I didn't want to wake the neiborhood.
Took it for a test drive,and ended up staying out about 1 hour because it was running so good.:D I'll try to get to the track again Wed. and get some updated ET's.I know there is a more to be gained with some dialing in,I was just trying to get this thing streetable again,I did more head scratching then tuning. LOL
Thanks for the help guys,and thanks again for the E-mail Geoff!;)