Recommended total advance for 2.8?

[Mod_Squad!]

Hello Darksiders,
It's been a while since I've been on here. Life's been busy and I play with the Alpine whenever I get a chance. Recently I replaced the distributor as I've always had a problem with the one in it over advancing. At least I think that's what the problem is.... When I get into the 3,000-3,500 rpm range I get some strange running resistance. I've run the gamut (in my limited brain space) of what the problems could be. Ive gone through 3 distributoors and 3 carbs and I'm nowhere nearer to a solution. In fact, this past weekend it appears that I may have made matters worse...I installed a distributor that I just ordered from Performance Distributors. They advertise that they set up the distributor on a machine and base those settings on the engine info (cam, compression, fuel grade, etc. etc.) that you provide. Sounds awesome. I'll take one! Well, 3 months later I got it. Looks great. They indicate that it's set up to advance 24 degrees at 3,000 rpm's. I'm hoping that this isn't 'total' available advance. I had heard earlier that I needed 28 degrees 'total'. I set initial timing statically at 12 deg BTDC. After warm-up, when I accelerate into the 3,000 range it starts running like crap. After replacing so much equipment I'm wondering if my cam timing has been off from the beginning. Who knows...it was my first water cooled engine build. I've put 30K or so miles on the car but have always known that I'm only seeing 60% of it's potential and it's frustrating. I've had it to a few different mechanics, on their scopes, and they have no clue. The two times I took it to a dyno were useless as well. Anyone know any magic words? Advice? (Besides, 'You should get another hobby').
Thanks in advance (pun intended)
Bryan

 

[Barry]

Bryan,

A good starting point for normally aspirated 2-valve engines is 12 degrees initial / base advance plus 24 degrees of mechanical advance at 3,000 RPM for a total of 36 degrees. Another 12 degrees of vacuum advance would be in the ballpark.

ALL NUMBERS REFER TO CRANKSHAFT DEGREES!!!

 

[RootesRacer]

I would imagine 30 to 32 degrees would be what you want with higher than stock compression, 34 degrees otherwise.

Try timing the engine for 30 to 32 at the max mechanical advance point (perhaps 3500 RPM), then see if the engine accelerates better and performs better at wide open throttle, mid to high RPM. When setting the max mechanical advance, disconnect the vac advance line(s) as you may get some signal to them while revving the unloaded engine.

Forget how it runs down low since you can re-curve the dizzy to get your timing working down there later.

 

[Mod_Squad!]

Thanks guys. I need to see if the dist is curved for a total of 36 or a total of 24..

I will have another look at it later tonight.
Thanks again,
Bryan

 

[Mod_Squad!]

How do I go about setting the max mech advance? I assumed that I would have to send the dist back in and have it set up at the shop.

I did disect my original distributor just to see how it functioned. That thing ain't going back together anytime soon .

A few other things I might mention:

1) I’m pretty sure that no one else has had to go this route but just to get the initial 12 degrees I had to grind on my Offenhauser manifold and the vacuum advance canister to be able to rotate it enough.

2) I have a distributor cap that I sacrificed for testing purposes. I cut a hole in the top of it so I could see what the rotor was doing while it was running. It appears to me that it is getting the spark right at the trailing edge. I had assumed that it should get the spark at the leading edge or middle of the stator.

Thanks again,
Bryan

I would imagine 30 to 32 degrees would be what you want with higher than stock compression, 34 degrees otherwise.

Try timing the engine for 30 to 32 at the max mechanical advance point (perhaps 3500 RPM), then see if the engine accelerates better and performs better at wide open throttle, mid to high RPM. When setting the max mechanical advance, disconnect the vac advance line(s) as you may get some signal to them while revving the unloaded engine.

Forget how it runs down low since you can re-curve the dizzy to get your timing working down there later.

 

[RootesRacer]

You probably need the vacuum advance functional else the light load portion is going to be rather retarded.

The idle ignition should occur when the rotor tang is just leaving the cap terminal, the max timing point should be just as the rotor tang is entering the cap terminal.

If not, you need to remedy this first as you can loose spark energy jumping the rotor to cap gap.

Max timing is set by connecting a timing light to the motor and running the speed up till the ignition stops advancing (mech adv hits its stops).
You then set the timing to your max timing value, which is typically between 30 and 36 degrees BTDC.

You can then go back and see what the timing is at idle to see what the RPM advance rate is.

The bottom line to making WOT power is your max timing figure, so if the max timing figure doesnt work at idle or mid range, you may need to recurve the dizzy to make it happen.

 

[socorob]

It's very easy to put the distributor in wrong on the 2.8. A few people have done it. If it's in right you have room to turn it in either direction without it hitting anything. There's a post on here about putting it in correctly, make sure you have it in right before you go changing too many other things.

 

[WildBill]

You might think about checking your carb. You mention having to grind your offfy to get the distributor to fit - are you running a Holly 390. Is it a rebuilt unit? When do your secondaries open? Is it about 3,000 to 3,500? Following?? I didn't read how you came to the dizzy as the problem, what's telling you that??

Sorry the dyno didnt help, usually this kind of mystery problem is easily solved on a dyno, its a fantastic tuning device in the right hands. Any chance of locating another operator with CARB experience???

William Ramsey
1974 2800 5 Speed (Capri)
1973 2600 4 Speed (Capri)
---------------------------------------------------

Hello Darksiders,
It's been a while since I've been on here. Life's been busy and I play with the Alpine whenever I get a chance. Recently I replaced the distributor as I've always had a problem with the one in it over advancing. At least I think that's what the problem is.... When I get into the 3,000-3,500 rpm range I get some strange running resistance. I've run the gamut (in my limited brain space) of what the problems could be. Ive gone through 3 distributoors and 3 carbs and I'm nowhere nearer to a solution. In fact, this past weekend it appears that I may have made matters worse...I installed a distributor that I just ordered from Performance Distributors. They advertise that they set up the distributor on a machine and base those settings on the engine info (cam, compression, fuel grade, etc. etc.) that you provide. Sounds awesome. I'll take one! Well, 3 months later I got it. Looks great. They indicate that it's set up to advance 24 degrees at 3,000 rpm's. I'm hoping that this isn't 'total' available advance. I had heard earlier that I needed 28 degrees 'total'. I set initial timing statically at 12 deg BTDC. After warm-up, when I accelerate into the 3,000 range it starts running like crap. After replacing so much equipment I'm wondering if my cam timing has been off from the beginning. Who knows...it was my first water cooled engine build. I've put 30K or so miles on the car but have always known that I'm only seeing 60% of it's potential and it's frustrating. I've had it to a few different mechanics, on their scopes, and they have no clue. The two times I took it to a dyno were useless as well. Anyone know any magic words? Advice? (Besides, 'You should get another hobby').
Thanks in advance (pun intended)
Bryan

 

[socorob]

http://www.sunbeamalpine.org/forum/showthread.php?t=14740
see if any of this applies to your situation.

 

[Mod_Squad!]

Hi William,
It wouldn't surprise me if it's partially the carb but for now I'm pursuing the distributor. The carb is a new(not rebuilt) Holley 390. It's the 3rd ne actually. I've modded the Power valve. I'll watch and see when the secondaries open. The reason I think I originally had a distributor related problem was because of the feeback I got from a mechanic who put it on his scope. The distributor (I think) was over-advancing and crapping out when I got into the 3,500 or so range. I'm also sorry the dyno didn't work out either. I did 2 appointments ($$$$) there at the suggestion of the mechanic who I had gone to when I gave up trying to figure out this mess. Anyhooo...hopefully I'll be able to figure it out soon and get a few miles in before the snow flies!
Thanks for the tip.
Bryan

You might think about checking your carb. You mention having to grind your offfy to get the distributor to fit - are you running a Holly 390. Is it a rebuilt unit? When do your secondaries open? Is it about 3,000 to 3,500? Following?? I didn't read how you came to the dizzy as the problem, what's telling you that??

Sorry the dyno didnt help, usually this kind of mystery problem is easily solved on a dyno, its a fantastic tuning device in the right hands. Any chance of locating another operator with CARB experience???

William Ramsey
1974 2800 5 Speed (Capri)
1973 2600 4 Speed (Capri)
---------------------------------------------------

 

[Mod_Squad!]

Thanks for the link Robbie! That sounds a lot like what I'm experiencing. I'll have to read it a few more times to see if I can figure it out. It's hard enough trying to explain my situation when I obviously lack the capacity to truly understand timing. I definitely think that the link will be helpful. Makes me wish I wouldn't have ground on the Offy . Oh well.
Thanks again!
Bryan

 

[Mod_Squad!]

Well, I didn't get a chance to look at it last night. I do have another question though. When you dropped the distributor in, aligned with the rotor pointing at the 1 plug wire, did you have the crank pulley aligned with 12 deg BTDC or at 0 deg TDC? Also, was the star wheel in the distributor aligned wth the magnetic pickup?
Thanks again for all of your help.
Bryan

 

[Gitsmart]

Well, I didn't get a chance to look at it last night. I do have another question though. When you dropped the distributor in, aligned with the rotor pointing at the 1 plug wire, did you have the crank pulley aligned with 12 deg BTDC or at 0 deg TDC? Also, was the star wheel in the distributor aligned wth the magnetic pickup?
Thanks again for all of your help.
Bryan

The balancer should be at TDC, #1 piston at the top of the comp. stroke, from there you time it to 12 deg

 

[Mod_Squad!]

Thanks! Alrighty then. I'll give it a whirl at lunch time. I will set the crank at 0 deg, check that the #1 piston is at the top of it's stroke, pull the distributor and place it back in the bore, oriented as the illustration indicates, leave the dist loose, start her up and rotate the distributor til I'm idling at 12 deg BTDC, and I should be somewhat in business hopefully.
Thanks again to everyone for all the advice. I'll let you know how it goes.
Bryan

 

[RootesRacer]

Thanks! Alrighty then. I'll give it a whirl at lunch time. I will set the crank at 0 deg, check that the #1 piston is at the top of it's stroke, pull the distributor and place it back in the bore, oriented as the illustration indicates, leave the dist loose, start her up and rotate the distributor til I'm idling at 12 deg BTDC, and I should be somewhat in business hopefully.
Thanks again to everyone for all the advice. I'll let you know how it goes.
Bryan

You should still make sure you get full advance timing at higher RPM.

Far too often a lack of power is as the result that the mechanical advance is stuck, and you have relied on the idle timing to just "work out".

I always set my timing for full advance since max timing is pretty important and the timing curve varies from distributor to distributor even though they are supposed to be the same.

 

[Mod_Squad!]

I will do that. If I understand it that it....... As I understand it I should have my initial 12 deg + the 24 that's built in to the mech advance and say, maybe 10 or so built in to the vacuum advance so I should top out, timing-wise, in the 46-ish deg BTDC when I have the car above, say, 4,500 rpm's.
I should see a steady, linear, increase in timing advance from 12 deg BTDC to 36 deg BTDC as I accelerate from idle to 3,000 rpm's. Am I even close in my assumptions? Well, I guess I'll see in a few minutes..... Thanks again!
Bryan

 

[V6 JOSE]

Hi Bryan,

I know that it might be redundant to say to make sure the piston in on the compression stroke, but the piston will always be at the top when the pully timimg mark is at the top. Just make sure is it the compression stroke.

Jose

Thanks! Alrighty then. I'll give it a whirl at lunch time. I will set the crank at 0 deg, check that the #1 piston is at the top of it's stroke, pull the distributor and place it back in the bore, oriented as the illustration indicates, leave the dist loose, start her up and rotate the distributor til I'm idling at 12 deg BTDC, and I should be somewhat in business hopefully.
Thanks again to everyone for all the advice. I'll let you know how it goes.
Bryan

 

[RootesRacer]

I will do that. If I understand it that it....... As I understand it I should have my initial 12 deg + the 24 that's built in to the mech advance and say, maybe 10 or so built in to the vacuum advance so I should top out, timing-wise, in the 46-ish deg BTDC when I have the car above, say, 4,500 rpm's.
I should see a steady, linear, increase in timing advance from 12 deg BTDC to 36 deg BTDC as I accelerate from idle to 3,000 rpm's. Am I even close in my assumptions? Well, I guess I'll see in a few minutes..... Thanks again!
Bryan

Technically you could get as high as 46 (with 12 base, 24 mech and 10 vac), but you should set and test your max timing with the vac advance disconnected.
In actuality, the 30 to 36 degrees your engine needs is at higher RPM and at wide open throttle, which you will not have any vacuum adv signal, so you will in fact get the base plus the max mech advance only.

Personally I think 36 degrees (12 base and 24 mech) is too much for a performance 2.8, I'd try 32 degrees (take down to 8 base) and do some dyno testing with a stethoscope to determine if the extra 4 degrees (2 degrees at a time) is helpful, and if you are into knock.

The higher compression and volumetric efficiency you have (IE performance build), the less timing you will need, or at least the lesser timing the engine will tolerate prior to knock.

Most 60s and 70s engines have rather poor combustion chamber design and as a result are knock limited engines, meaning you have to run less than optimal timing to prevent knock.
This means its very important to tune to the octane level of the fuel you plan to ALWAYS run with, and be conservative with your final timing numbers to allow for a tank of bad fuel.

 

[Mod_Squad!]

Thanks for the informtion. I also thought that the vacuum advance was a transitional advance and wasn't really added into the total.

 

[Mod_Squad!]

Hey Jose!
Long time! Yeah, I figured it all sounded too easy . I'm on lunch and i's almost over. Looks like this will be an after work deal afterall. Shame, as the sun is out right now . Anyooo...how does one go about telling if it's on it's compression stroke. I'm trying to hold one thumb over the open spark plug hole but I'mnot feeling much. I imagine that if it's heading towards the end of it's compression stroke I would feel some pressure, correct? On the intake stoke I'd feel nothing because it would be pulling air through the intake system, correct?
Thanks,
Bryan