[frankenvette]

At the end of the season I had an issue with carburation and during the process of eliminating an off idle bog, I recurved my distributor. My ignition system is mechanical, Mallory Unilite, and it was recommended I use as much initial as possible, all in at 38* by 3000rpm. The engine is a 70 LT1, 383 stroker, old school. I ended up at 20* initial at 750rpm idle, all in at 3000rpm at 38*, a steep curve. The engine really perked up on the low end, and I lost nothing on the high end. The engines in a 63 Vette street rod, with Hooker side pipes and 2.5" inserts. Needless to say, the pipes are loud. I haven't noticed any sputters and haven't heard any detonation, but still wonder if the initial is too much for the street. I pulled the plugs after a couple hundred miles and they are not fat or lean, pretty clean burn. Anyone else running a similar set up?

 

[xntrik]

At the end of the season I had an issue with carburation and during the process of eliminating an off idle bog, I recurved my distributor. My ignition system is mechanical, Mallory Unilite, and it was recommended I use as much initial as possible, all in at 38* by 3000rpm. The engine is a 70 LT1, 383 stroker, old school. I ended up at 20* initial at 750rpm idle, all in at 3000rpm at 38*, a steep curve. The engine really perked up on the low end, and I lost nothing on the high end. The engines in a 63 Vette street rod, with Hooker side pipes and 2.5" inserts. Needless to say, the pipes are loud. I haven't noticed any sputters and haven't heard any detonation, but still wonder if the initial is too much for the street. I pulled the plugs after a couple hundred miles and they are not fat or lean, pretty clean burn. Anyone else running a similar set up?

Edit note: Often times damaging detonation can occur without our hearing it.

Old school means old style heads?? Lots of newer chambers need only 32-34* total for best top end pull. Also what is your vacuum can curve is doing.

If you find that less total is better, then maybe you could get less centrifugal and keep the initial.

Newer computer cars actually run a different spark timing in high gear mid rpm full throttle pulls, compared to lower gears, to avoid detonation.

When I was doing a lot of distributor curves, I found that high initial with no centrifugal advance before 1100 was beneficial especially with a stick car.

Then kicking in full advance by 2500 to 3000 depending on the individual set up.

Sometimes one soft spring snugged up, then a tighter spring very loose on the post, will make the first part of the centrifugal curve come on quickly, and then when the second spring hits the post the rate of advance change is slowed. What you get is an arc rather than a straight line increase when graphed, and it peaks 500 higher to the same amount. This makes the low end have lots of advance quickly for snappy response without over timing the mid range.

When the weather gets hot, all that timing might be too much.

Some Chevy guys found that running manifold vacuum to the can pumped up the low rpm timing enough to make a difference, and when they hit the throttle, it disappears and the centrifugal takes over...... just something else to try..

Funny about all this stuff...... EVERY engine is a tad different when you drive it.

I've seen some that are so "on the edge" that putting two people in the back seat is enough load to make it ping..

 

[frankenvette]

No vacumn, mechanical distributor. Vacumn at idle is 13hg for carb tuning purposes. Old school fulie 461x iron heads. I am using one light spring and one heavy spring, using a slower advance, not straight line. I have been told that some engines stutter off the line on a slow start, indicating some detonation when hearing is a problem. Never experienced this. I can run a lesser initial, but the low end suffers. Running 3:08 rear and 2.20 first in a rock crusher makes off line cumbersome anyway. After 3000, the engine builds the torque and ponies the way it should, and thats what I want with the set up. I thought I once saw a detonation detector that simple bolted to the block and you calibrated it to the normal sounds of the engine, and when the sounds weren't right, a red light came on. Maybe? Anyway, ran the engine with this set up at 90* temps late fall (global warming?) and no signs, maybe just being paranoid. You know what they say, just because your paranoid doesn't mean they're not out to get you!

Thanks xntrik

 

[Sean's]

Yeah Im listen here . Good stuff ! Wonderin about the Pic Bubble gum Card's ? What'd they call those ? Weird Racers ? I cant remember !
I still draw those Guy's ! Veiney Eye ball's , Racey Pointy Hair Waves . Huge Head's Stickin over the Top of There T- Bucket Wind Sheild,s .
I love those Guy's ! My oldest, boy Draw's ! But He like's too Draw Nude women and Dragon's ! Go figure ! Im not sure why ?

Ok Yeah generally speakin on Full advance Timming . Just wanted Too point out . That Elevation , Compression , How well the Head's Flow . All affect how far you can advance Timming .

On Vw's we runn A Basic 32 Deg* Total advance At 3500 RPM . If head's are Hemi Cut , Ported Polished , 9-1 CCR or lil Less . Along with I live In the High Desert << Higher Elevation's above Sea level . You can, easily advance 34* Too 36* . << with mechanically Advanced Dizzy !

But At 36 Deg* If I run Down the Mountain . Too Say Out skirts of Barstow Ca. <<, Dry Lake Bedd Area Below Sea Level , on say a warm day ? It's a Noticeable Difference . Im Runnin 9-1 CCR

After a Hard Runn 100+ Mph For 2 or 3 Mile's, across dry lake . Start gettin the Blow by Smell . Dip stick Runnin Lil warm . Hot Oil smell . Head Temp's , are up !

Now on H20 Pumpers . I notice the Water Temp's are up . Get a Lil Radiator smell too um . Get a Lil Sluggish , on Bogged pulls from down low Etc.

Point Im trying Too make Is Total Advanced timming Is a Happy medium . <<< Found Some where between , Below Sea level , and Above Sea level .

Up, and down Mountains << are good Test , of where Timming should be .

But then I live in a Region where I have Both extreme's , at my back door . I Have Higher Elevation's Of Lake Arrow Head / AKA Big Bear Mnt . With lower elevation's of the desert floor , all within 20 miles, or less of each other . << Kinda make's it easier too play with .

Sean

 

[automotive breath]

... I have been told that some engines stutter off the line on a slow start, indicating some detonation when hearing is a problem...

I do detonation testing on bracket race engines. Normally detonation
shows up first at low RPM when piston speed is low and the engine
is working hard to get the car moving.

It's not possible to here the detonation because we run open exhaust.
I use a lighted magnifying glass designed for reading plugs. It works
great, look for tiny specs on the porcelain. The specs are normally
dark, if the problem is severe enough they will appear as and an
aluminum color.

Fixing the problem with reduced ignition advance or more fuel are
options but this will hinder performance.

 

[xntrik]

No vacumn, mechanical distributor. Vacumn at idle is 13hg for carb tuning purposes. Old school fulie 461x iron heads. I am using one light spring and one heavy spring, using a slower advance, not straight line. I have been told that some engines stutter off the line on a slow start, indicating some detonation when hearing is a problem. Never experienced this. I can run a lesser initial, but the low end suffers. Running 3:08 rear and 2.20 first in a rock crusher makes off line cumbersome anyway. After 3000, the engine builds the torque and ponies the way it should, and thats what I want with the set up. I thought I once saw a detonation detector that simple bolted to the block and you calibrated it to the normal sounds of the engine, and when the sounds weren't right, a red light came on. Maybe? Anyway, ran the engine with this set up at 90* temps late fall (global warming?) and no signs, maybe just being paranoid. You know what they say, just because your paranoid doesn't mean they're not out to get you!

Thanks xntrik

:welcome: Don't forget my note about off idle advance with the stick shift. Sometimes jerking, hesitation, or clutch chatter is caused by fluctuating advance as the clutch comes out. That is varied by the shape of the weight arm.

Also note how to set the tension on double springs for varying advance. :welcome:

 

[frankenvette]

All good stuff guys, thanks.

xntrik comment:

"When I was doing a lot of distributor curves, I found that high initial with no centrifugal advance before 1100 was beneficial especially with a stick car".

This is what I have set up now, not a straight line curve:

750rpm - 20*
1000rpm - 23*
1500rpm - 29*
2000rpm - 32*
2500rpm - 35*
3000rpm - 38* all in
(was 18* iniitial, all in at 2500 at 40*)

Vacumum

13hg @ Idle
1800rpm - 20hg
2250rpm - 22hg
2500rpm - 22hg
Generel driving in the 17-22hg
Quick accelaration - drops to 1-3hg quickly, then builds with acceleration

Carb - Holley 3310-10

Primaries - 70
PV - 85
Secondary spring - purple (1915-6950)
Idle - 750rpm @ 13hg
(adjusted with new AirGap manifold)

Again, thanks for the tips guys!

 

[Guy Hiltz]

Youve got the right idea,set your total timing to where it works best and let initial fall where it may.If you have a cam with lots of duration this may be the only way to get it to work right.You should be able to hear any detonation,it wont happen at WOT,more likely to happen at part throttle.

 

[xntrik]

NO vacuum advance, mechanical distributor only. :thumbup:

You are picking up 3* advance at 1000 rpm.... I'd try to eliminate that, especially on a stick shift car.

In other words, 20* at 1000 then start getting advance from there up.

First thing you have to do is put tighter springs on it to stop advancing that soon.

The weights might turn out to be wrong too. Wrong shape and too light it maybe. Tighter springs will make your curve come in slower and peak higher 3500 or so.

A heavier weight will also start advancing sooner, which means you need tighter springs,etc.. yada yada.... so what is probably needed is a different shaped weight arm. The fairly straight part that pushes on the elongated diamond shaped part on the distributor shaft. So as the advance occurs, it will kick in faster due to the arm radius change.

edited, reread his post, and corrected my misunderstanding.

 

[frankenvette]

xntrik, was thinking the lighter initial spring was needed to get more timing quicker to eliminate detonation. Are you saying I should have 20* up to 1000rpm, then have more timing come in? The set up I had before changing the manifold was 12* initial, and all in never stopped. I went to 3500rpm and was showing 42*, that's what started down the dizzy path. Like I said, the engine is better with this set up, wondering if I can get more and don't want detonation.

 

[xntrik]

xntrik, was thinking the lighter initial spring was needed to get more timing quicker to eliminate detonation. Are you saying I should have 20* up to 1000rpm, then have more timing come in? The set up I had before changing the manifold was 12* initial, and all in never stopped. I went to 3500rpm and was showing 42*, that's what started down the dizzy path. Like I said, the engine is better with this set up, wondering if I can get more and don't want detonation.

Timing coming in too fast usually aggravates detonation.

Yes, but you are getting timing advance starting at too low an rpm. That means tighter springs to overcome the weights throwing-out so soon.

Then the weights have to be changed/altered to give you the curve you want. You don't want to too many centrifugal degrees and reaching full advance at too high an rpm. That is the shape of the arm.

Kits are just kits. They are usually better than stock, but are often a compromise to perfection.

Are you having trouble with ping now to worry about it?

 

[frankenvette]

No trouble's now, just have loud exhaust and didn't want to risk not knowing, so I posted my set up to see if I should change it. I couldn't get any of the combinations that Mallory suggested to work, so had to use my own combination. Maybe I'll check the weights. The engine's got a monster top end.

automotive breath, will check the plugs next time with a magnifying glass, thanks for the tip.