Vette(s): 1975 C3 Red, T-Tops, Black Interior.
All I need is time and money! Getting there!
You can start there. It will still be a few weeks until I install mine. You will need to play with the timing a bit to find the right setting. A vacuum gauge may help. There are a few past threads describing how to do this. Ben listed a good procedure.
Use a dial back timing light,set it at 36 deg, take the motor to 3000 rpm with the vac adv. disconnected, when the mark on the dampner reads O on timing tab lock the dist. there, might have to reset idle,check intl.
timing by turning dial on light back to O, check timing at idle ,hook up vac.adv.take the car and wring it out,see what happens, should be real close.anips38482.8457523148
[QUOTE=anips]Use a dial back timing light,set it at 36 deg, take the motor to 3000 rpm with the vac adv. disconnected, when the mark on the dampner reads O on timing tab lock the dist. there, hook up vac. adv, might have to reset idle,check inst. timing by turning dial on light back to O, check timing at idle ,take the car and wring it out,see what happens, should be real close[/QUOTE]
anips.. no disrespect but I dont like this method.. you get your timing good for 3000 but not for idle..
most of us drive street cars and therefore we want the best off idle response .. so the best way is to tune your idle timing to the best.. then use springs of different strengths to tune your timing at later rpms.
if you had a distributor where the springs had not been replaced recently (which most people do) getting the timing to 36 at 3K could leave your initial timing at an incredibly low level.. and kill your off idle response.
Ben, no disrespect taken,what your telling me is that you don't agree with my method of timing a chev V-8, let me explain a little more , Chevy V-8's like to run somewhere around 36-38 degrees total mech. advance all in at about 3000 RPM, most distributors have depending what year have somewhere between 20-28 degree's built in, when you add in your initial setting that gives you your total, when I had my dist. built Performance Distributors built in 24 degs. so that makes my initial setting 12 degrees advanced. simple, as far as the weights and springs are concerned all they do is regulate how fast your advance comes in, heavy weights and light springs come in faster than heavy springs and lighter weights, you don't want it to fast to cause it to ping or too slow so that its a dog, the advance curve should be somewhere in the middle, but the total advance should remain the same, getting to the original post there was a cam change and question about initial timing, set the engine at total timing turn the dial on the light back to O and see where initial is at and go from there, do the math, subtract initial timing and that will give you built in adv.its a place to start, you folks with emission controls, EGR, smog pumps, etc. have to take that into consideration when timing the motor, the only emissions equipment my motors have is a PCV valve, with a new cam and emissions you might have do some distributor work. anips38482.8653240741
my problem isnt with the total timing concept.. my problem is that the method you described involves using an arbitrary figure.. of 36-38 in about 3000 RPM...
while this is a good starting point.. it isnt exact for every engine...
fuel quality, aluminum heads, individual variations in an engine block all affect your detonation threshold
if your timing springs are worn you will get your timing advanced too quick.. too strong it comes in too late.
so for example i have a worn 20 yr old dist that ive never changed springs in.. i get my timing to 36 @ 3000.. then check it at idle and its at 4 BTDC.. this is too low at idle.. even though it is correct at 3K
say i put some brand new strong springs in.. i get the timing to 36 @ 3000 and then drop it down to idle and its at 20 BTDC.. too high at idle..
so the problem i have is using an abitrary figure that is the "safe bet" for most engines and then trying to work backwards from there to get the idle timing right is a pain.
I prefer to work the other way around.. get the timing set at idle correctly.. using vacuum.. not just some arbitrary figure with a light.. then tuning the timing curve from there..
I really dont use a light for tuning.. i use it for reference after ive tuned.. or if im going to put things back exactly like it was.. but when retuning I dont use them. I set the idle timing by vacuum.. then use springs/weights/bushings to adjust the ramp rate from there.. I have tuned cars that detonatated above 34 deg @3K .. and ive tuned ones that didnt detonate until 41 @3K..
everyone has their method for doing this.. I think mine is a reliable and easy method for tuning every bit of timing you can get out of your car.. my grandfather and father taught me this method.. every person ive taught it too loves it.. if done right and thoroughly you will get every last bit of performance you can get.
if im working on joe blows 4 door sedan.. ill set it with a light and maybe give it a few more degrees at idle.. but ill use a safe arbitrary figure. when i tune my car... the light doesnt get used until im ready to record the timing figures for the current config.
Ben, if your method works for you and you get the performance you are looking for thats great, stick with it, but for the this debate I have to disagree, a Cup or Tour car that produce 6-700 hp and that run around all day at 8-8500 rpm with the equipment they run can run at 40+ degs. total advance, but we are talking about a mild street driven 350, the arbitrary figure of 36degs. that you speak of came down the mountain with Moses,its a fact, it states it in the GMPP catalog
and in "How to Hotrod a SB Chevy" dated 1972, pertty much the same today, in your post you stated weak springs would give you 4 BTDC and strong springs would give you 20 BTDC at Idle, you have it backwards, weak springs would allow the weights to extend outwards easier than strong springs giving you more advance, fact # 2, weights and springs play no role in initial timing and off idle responce, the reason for that is on most stock distributors the weights don't start to extend out thus advancing the timing until somewhere around 1200-1600 rpm, so unless your motor idles at those numbers they have no bearing, but what does have a role in initial timing and responce is your static initial setting and the vac. adv. dashpot that hangs on the side of the dist. so with my method you are setting the total and initial at the same time and getting a starting point if the initial is in question and adjust from there, now, this is my story and I'am sticking to it
[QUOTE=anips]in your post you stated weak springs would give you 4 BTDC and strong springs would give you 20 BTDC at Idle, you have it backwards, weak springs would allow the weights to extend outwards easier than strong springs giving you more advance, [/QUOTE]
you miss my point.. think of it this way.. i set a car with weak spring to 10 at idle.. and it gets to 36 @ 2600 rpm... now take the same one with strong springs.. it gets to 36 @ 3400 rpm.. so if I set the timing to 36 @ 3000 the strong strings car will be too high at idle and the weak springs car too low.. you are saying adjust your timing by turning the distributor to get your timing right at 3000 rpm.. when you do this it will change your idle timing. this is indisputable.
[QUOTE=anips]fact # 2, weights and springs play no role in initial timing and off idle responce, the reason for that is on most stock distributors the weights don't start to extend out thus advancing the timing until somewhere around 1200-1600 rpm,[/QUOTE]
my point exactly.. set you initial/idle timing to the best value for off idle response.. then use springs/weights to get to 36 @ 3000 if that is where you want to be.
[QUOTE=anips]you are setting the total and initial at the same time and getting a starting point if the initial is in question and adjust from there, now, this is my story and I'am sticking to it[/QUOTE]
I have no idea where you got the idea that i said set them both at the same time.
this is how i do it
this example is with an MSD dist.
set INITIAL timing to the minimum required to get peak MANIFOLD vacuum. you can turn your initial up further without vacuum increasing... dont do this. turn it back down until it drops from peak.. then back up to barely reach peak.
this gives you the BEST off idle response. the timing light figure from this will vary based on a number of factors. lets just use mine as an example. 15 deg at idle.
then i usually take the second weakest springs and second smallest limit bushing and install them in the distributor. I drive the car.. i let it warm up.. and then drive it up hill with it floored.. if I get detonation early but it clears up.. i use the next stronger springs.. if i get detonation and it doesnt clear up i use a larger limit bushing.
i keep doing this until i get no detonation.. on my 427 i am using the third weakest spring combo and the second smallest limit bushing..
I have great off idle response.. and great accleration through the power band.
so to summarize.. I set the IDLE timing and lock it down with the dist adjustment bolt.. then adjust wieghts/springs/bushings from there..
the way you are describing it is to set your timing to be correct at 3000 rpm... and live with the consequences of what it will do to your idle timing.
I say adjust your initial timing first.. then use weights/springs for adjust your high rpm timing.
I have no idea what the timing light would say my timing is @ 3000.. not that a cheap timing light is worth a damn for accuracy anyway.. I have access to a snap-on light that was just calibrated.. i took a reading from a car with it and compared to three other timing lights.. not a one of them was within 2 degrees..
I dont really know or care what the light would say at 3K.. what i do know is that when manifold vacuum is highest at idle.. the engine is "hungriest" for more fuel. this improves off idle response. there is a state that can be reached where timing and idle mix cause vaccum to be at its highest at idle.
then i also know that if I change my limit bushing to the smallest one.. i reach a threshold where it will always detonate.. i know it if put in the next weaker set of springs.. that i will detonate early.. and then even out..
so does it matter that it probably is not set to 36-38 at 3000... not really.. its as aggressive as my particular car will run... and thats all im concerned about.
assuming idle timing set to 10 btdc @ 1000 by light or vacuum.
weak spring car using figures in previous post..
this car gets 36 @ 2600 so it gains 26 deg over 1600 rpm or 1.625/100
so at 3000 it would be @ 42.5
turn this down to 36 at 3000 and you have shifted the total and initial timing both back by 6.5 degrees... leaving your idle timing at 3.5 which will run like a DEAD DOG..
now for the strong spring car..
it gains 26 degrees over 2400 rpm or 1.083/100
so at 3000 it would be 31.66 deg btdc.. then shifting this 4.33 ahead to get to 36 @ 3000 also advances your idle timing up 4.33 degrees.. this leaves you at 14.33 which is too high for most mild engines on pump gas.
contrast with this.. lets just assume for sake of argument that you had the car with weak springs (as most people with 20+ year old cars who havent replaced them do)
lets assume you set it to peak vacuum and it comes out to 10 deg btdc for idle timing. here you lock the timing adjustment bolt down and leave it alone. you rev the car to 3000 and the timing light read 42.5 degrees total...... then you get a new spring kit and change out your springs until you find a set that gets you to 36 @ 3000
when you drop it back to idle.. it is still correct.. when you rev it back up to 3000 it is still correct. no guessing. at this point it is CORRECT.. not pretty close.. and you have the best off idle response.. and 36 deg @ 3000
Ben and Ken, I believe we are talking apple's and orange's here from reading your latest posts, tell me if I'am wrong, I thought we were talking about a 78 with a cam change and a question about initial timing and I'am assuming he has a stock distrubitor with a vac. advance, not a MSD with no vac. advance and full mech. advance, but for the sake of the debate I will assume that all you have told me is correct, although I pertty much know how they opperate I don't fool around with weights and springs, why, because I don't have a distributor machine and if I did I wouldn't know how to opperate it, swapping springs and weights from a instruction sheet, the time it takes and not to mention what I would do if I dropped one of springs into never never land would really piss me off, so here's what I'd do, I would set my total timing at 36 degs., turn the dial back to 0 on the light, then check my initial, if I had lets say 3.5 initial, I would kill the motor, pull the distributor and take a ride to my engine builder and tell him I want 36 degs.total @ 3000 RPM with a Initial of 10-12 degs. and spin it on his machine, a couple hours later I'd go and pick it up, come home and reinstall, time my initial 10-12, DONE, and sleep good knowing it was right.
Ben, may be we are both missing the point, I'am running a tack drive HEI with vac adv. built by Performance Distributors out of Memphis Tenn, they requested my cu in, weight of the car, comp ratio,cam spec, trans, gear ratio, carb, what type of driving, and sent me a hand built to my spec's distributor with 24 mech.degs total BUILT into it, that means when the weights were fully extended could not go any further I had 24 degrees, no more advance out of the distributor,thats it,the spring- weight combination was as such as to allow a middle of the road advance curve with 24 degs.total all in at 3000 RPM, so the only way I'am going to get a total of 36 is to crank 12 degs into my static initial timing, so I drop in the dist. hook up the "dial back" timing light, turn the dial on the timing light to 36, bring the engine to 3000, lock it down when the mark on the dampner reads O on the timing tab, let it return to idle, turn the dial on the light to 0 and I now have a 12 degs static initial timing, (12+24=36) after a ride and If I felt 36 was to much I crank in 10 initial gives me 34 total at 3000, if I want more I crank in 14 and that gives me 38 mech degs. at 3000 and so on, after the initial 3000 RPM run up to get my starting point of 36 all I have to do is time it in the normal way at idle with the light set on O, like I said chevy's make the most power + or - 36 total on a mild to med. street machine, that doesn't include what the vac adv. brings to the party, anips38484.8890162037
bravo guys---have you ever looked in the factory service manuals at the spec sheets for distributers and at timing specs---so many different distributers,weights,vacuum advance and timing settings---different curves for both mechanical and vacuum advances---different initial and total timing settings depending on engine hp rating---wow---let's line them up on the 1320 and see who comes out on top----then we'll check mpg figures--marty (totally stock LS5--including dist timing)
Vette(s): 1972 Coupe
Anything, but Stock and more mods to come!
SSBC Force 10 Brakes, 3.73, TH350, 355 CID, Rack and Pinion, Vette Brakes suspension front and rear.
Well not to add to the debate, but Cam design, cam timing, engine stroke, plug type, plug gap, dwell time and coil type can be added into the mix to what an engine likes for timing. I'm not one for picking one way to time over another. I prefer to stick to initial, plus what ever is designed or set into my distributor and stick to a total advance.
I have never set timing the way Ben has described it, but it makes 100% sense to me. IF you think about it using manifold vacuum is the best way to set fuel air mixture on a carb at idle. However since I have never set dist advance as Ben has described I'm not sure how that would affect carb tuning. I guess what I am saying is I'm not sure how I would go about tackling which task first.
I have always set timing first and then went about tuing the carb. If you adjust the distributor first and tune it for max vacuum you would have to do some adjustment on carburetor, because rpm will rise as vacuum rises. so if you lower the idle rpm then I would suspect you would need to come back and adjust distributor again. I guess you could keep going back and forth like you do with a carb until the idle speed and distributor adjustment balance out and no changes occur to engine vacuum. Then from that point you could work on idle air fuel ratio for engine vacuum.
Ben, can you give me some insight because the ideal of tuning distributor advance is new to me and i'm not sure how carb tuning would play into that mix. You would think after working at Holley all these years I would have hear this method, but I have not and I would like to be educated and possibly learn something new.
Vette(s): 1975 C3 Red, T-Tops, Black Interior.
All I need is time and money! Getting there!
Yes, if you set the carb, then the timing, you will have to reset the carb again. And then that does mean you may need to recheck the timing. When you get them close to each other, you won't see one changing the other any more. But if they are way off, the differences can be huge. It is a balancing act. Everything is. Does this mean more work to get it just right? Yes. No way around it.
Part of the hang up between Ben and Joe comes with procedure. Joe is looking at 3000 RPM as a set point. Ben is not. Ben is using a entirely different method. Ben is looking for peaks. Joe may not find peaks at 3000 rpm, depending on the distributor settings. It MIGHT peak at 3000, it may be way past, and it may not have gotten to peak yet.
Joe is setting max mechanical advance up from inital. Ben is setting max timing, then adjusting mechanical advance back down to inital.
Both are say similar things, and getting similar results. Both methods work. But Joe is assuming the 36 is ideal at 3000 rpm. It may be, but may not depending on compression, ignition system, cam, etc. Ben's method take into account for all of these. Joe's is long run easier. Ben's takes more fiddling to get the weights and advance limits correct. You can't forget the vacuum advance. Without creating a specfic number, Ben takes that into account as well.
Bottom line, Joe's is easier to follow, and will create good results that will improve the way the engine runs, but leaves a few thing to assumptions. It deals with hard numbers. Ben's is more of a pain to make multiple test, but as a result does not make the assumptions that hard numbers can lead you into. But it does take the particular engine, car, drivetrain, weight, etc, and therfore may or may not make even more power.
One way helps a lot. The other way could buy not might help more. Are you after Big improvements, or absolute maximum improvements. Does this mean you might set the peak with vacuum and find the inital is too far off to get the car started when warm? Sure. Then you change initial weight stops and springs, and try again. Yes, more fiddling. And when you get all done, you may need a different carb set up. Possibly a jetting change. Of course that could screw up timing response. Again, it's a balancing act.
You could set up one engine perfect, and change the final drive or tire size and it would change. Lighter or heavier cars need different settings in identical built engines. And when we build engines there are hundrends of variations within the engine itself. There are no hard and fast rules. Just good guildlines. Most of us will never go that far. Serious racers do, and usually on a dyno. I'm still backing up Ben.
Ken, the numbers I used are hard numbers used by GM and just about every one else in Chevy land, never the less, the question I have is with Ben's method what if maybe you have a bad hole or two, maybe some leaky or burnt valves, weak valve springs,some worn guides,or a hidden vac. leak somewhere, marginal carb,can't forget a leaky head gasket, then what do you do? anips38486.6412037037
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