[cobalt327]

Originally Posted by 454C10

Well, then it seems you did know of oem smogger engines that needed 40 degrees of timing. (since you have the book).

All that needs to be "known" about the book, is it's from 1976.

38-40 degrees timing is a spec given to be used in what they deem a high performance drag engine. Using old fulie heads, not smogger heads, w/domed pistons and "good" gas, in a race vehicle- the title gives you a hint at what the book was aiming to do.

The heads/pistons/fuel used is a far cry from smogger-type specs. Take a close look at the cover. Does that engine look to have smog heads?

Regardless, you are in error if you think that OEM heads make best power at 40 BTDC in anything approaching normal conditions and circumstances.

[Rickracer]

Bottom line here is: "If your motor needs 40° total timing, there are quite a few ponies left on the table in the overall combo" ,

[red65mustang]

I want to stay out of your 40* debate but a part of it is due to a "points" dist spark (joules) energy characteristics at high rpms and the small plug gap in that now dated book reference...

or,,LOL are you both just bumping the thread so it can reach the 3000 readers level!!!

agree with rick,,,,clear to me that the 8.1 magazine motor is built for a shot of nitrous!!!!
and it ain't gona be 40 then!!!!

[454C10]

Originally Posted by cobalt327

All that needs to be "known" about the book, is it's from 1976.

38-40 degrees timing is a spec given to be used in what they deem a high performance drag engine. Using old fulie heads, not smogger heads, w/domed pistons and "good" gas, in a race vehicle- the title gives you a hint at what the book was aiming to do.

The heads/pistons/fuel used is a far cry from smogger-type specs. Take a close look at the cover. Does that engine look to have smog heads?

Regardless, you are in error if you think that OEM heads make best power at 40 BTDC in anything approaching normal conditions and circumstances.

The same information is published in the 1994 version of the book. besides a book written right at the point of smogger engines should have good real time tuning experience. The book wasn't referring to the picture on the front cover. the 38 to 42 spec was intended for "street engines". The "race setup" was 38 to 40 as recommended by "chevy engineers".

Well, looks like we will disagree on this one. "Slow burn heads" just need more timing for max power, it is that simple. And BBC's need even more timing. Sure, the old smogger engines will still run with 36 degrees but will be a little short on max power.

[cobalt327]

You’ve (unsuccessfully) taken my comment out of context, but to no avail.

The thread is about an iron (993) headed SBC in a Jeep.

At post 168 you chime in w/a very helpful “a 383 I read about in a car rag made max power at 40 degrees” or words to that effect. (An odd-ball build that was obviously made for a supercharger or was just lame to begin with- who builds an engine w/8.1:1 CR and puts a cam in it w/almost 240 degrees @ 0.050”?)

Then about 10 posts later, you (very helpfully ) back up and pull out a book that hasn’t seen a revision (reprinting the same thing is a reprint- not a revision) since it was printed in 1976, that references 40 or 38 to 42 or whatever degrees of timing. For max power in a drag engine. W/pop-ups and a points-type ignition.

If you have something worthwhile to contribute, then I’m sure everyone would like to hear it.

But being a troll helps no one- especially yourself.

[Rickracer]

Originally Posted by 454C10

... "Slow burn heads" just need more timing for max power, it is that simple....

Agreed, which strengthens my above post...40° is leaving power on the table in the overall combo....

Originally Posted by 454C10

...And BBC's need even more timing..

That is a blanket statement that just doesn't agree with the facts. My 427 ran the quickest ETs with the exact same timing curve as my 327, 18° initial, 36° total, this is after very thorough back to back drag strip testing.

[cobalt327]

Originally Posted by Rickracer

Agreed, which strengthens my above post...40° is leaving power on the table in the overall combo....


That is a blanket statement that just doesn't agree with the facts. My 427 ran the quickest ETs with the exact same timing curve as my 327, 18° initial, 36° total, this is after very thorough back to back drag strip testing.

FWIW (and this isn't just to agree w/you) my 468 that had 360's on it (PP heads but ported, mild hydraulic cam, stock valves) made its best MPH at the track (113) w/34 degrees. I later changed to 215's and found I needed a bit more timing, settling finally on 35 degrees. It was built for a Blazer, but I broke it in, in my Camaro for S&G's.

Too bad the OP doesn't have a BBC in his little blue Jeep- this thread probably wouldn't exist! But the thread (w/one not notable exception) HAS been informative, w/good give and take, a few good laughs and just plain good ol' FUN!

I've not thought as much about vacuum readings or timing in quite a while, and it is refreshing.

[cobalt327]

Back on topic.

I see that Blue has 369 casting heads, so I was in error when I said 993's above- I thought I saw that on this thread, and had jotted them down as such, but oh well.

I have no experience w/369's. Mor Tec has them as:

33417369...90-up...350..........Gen.I Goodwrench crate motor,"Hecho en Mexico", 76cc

I'm guessing they're not the swirl port-type heads, but more like standard, run o' the mill-port heads.

That said, does anyone have any particulars on these heads?

[Blue84JeepCJ7]

Originally Posted by cobalt327

Back on topic.

I see that Blue has 369 casting heads, so I was in error when I said 993's above- I thought I saw that on this thread, and had jotted them down as such, but oh well.

I have no experience w/369's. Mor Tec has them as:

33417369...90-up...350..........Gen.I Goodwrench crate motor,"Hecho en Mexico", 76cc

I'm guessing they're not the swirl port-type heads, but more like standard, run o' the mill-port heads.

That said, does anyone have any particulars on these heads?

This seems to be what I have!!!

getting old iron heads to flow? (SBC)

[Blue84JeepCJ7]

Originally Posted by red65mustang

set the base at your normal idle rpms and then back off the idle rpms linkage screw to the lowest rpms possible till it barely runs (ignore the idle) and check to confirm with your light that it is still the same base setting
(to confirm there is no cent added at idle rpms)

I did confirm that the cent looks to come in at 1,200 rpm which them jumps to 16deg! From a low rpm up to 1,999rpm I get 12deg right now as my new setting with 39deg in at 3,000rpm. If I recall Thursday I got something like 34deg at 2,500rpm with all in at 39deg by 3,000rpm. I think I posted that somewhere above but not sure if I changed the base since then.

[Blue84JeepCJ7]

Originally Posted by Frisco

The "all in" RPM will be best if kept between 2500-3000 RPM.

Mine is set to 39deg all in by 3,000.

The maximum timing with NO vacuum advance added should be around 38 degrees.

Mine is 39 deg with 12 initial. Anything over 12 initial brings the total above 40.

Because of the cam you are running, the initial timing should be around 16-18 degrees. I suggest the 18 degree setting.

See above answer.

You should also be using FULL manifold vacuum advance. Adjust it so that you limit the amount of added vacuum advance to 10 degrees.

I am but I need to check on why I am only getting 2deg advance. Maybe an obstruction inside the dist.

The hesitation you are getting could be because the timing is off OR because you need additional pump shot.......[or adjust the accelerator pump linkage for an Edelbrock style carb.

I will check on this too!

Your initial timing should be checked at or below 800 RPM to insure that no centrifugal advance is being introduced.

Done!

Lower the idle RPM so that it is at or below 800 RPM in DRIVE if an automatic...

Done!

The air/idle screws should end up being very close in their respective adjustment to each other.

I'll check on this too after I finish the undone items above.

[Frisco]

Originally Posted by Blue84JeepCJ7

I did confirm that the cent looks to come in at 1,200 rpm which them jumps to 16deg! From a low rpm up to 1,999rpm I get 12deg right now as my new setting with 39deg in at 3,000rpm. If I recall Thursday I got something like 34deg at 2,500rpm with all in at 39deg by 3,000rpm. I think I posted that somewhere above but not sure if I changed the base since then.

When watching the timing curve as the RPM increases, the timing should show a gradual increase as the RPM is increased. You stated that it "JUMPS". This is an indication that the advance plate is sticking.

Originally Posted by Blue84JeepCJ7

Mine is 39 deg with 12 initial. Anything over 12 initial brings the total above 40

Assuming that those readings are with the vacuum advance dis-connected and plugged, you are showing a built in mechanical advance of 27 degrees (39-12). I don't know of any distributor that incorporates that much mechanical advance. Most GM's are limited to 20 degrees. There are some distributors that have 24 degrees.

To get the spread reduced between the initial and the full mechanical advance you will have to limit the amount of travel of the mechanical advance plate. This can be accomplished either with small bushings in the slots or by shortening the length of the slots by welding them up. Doing this will enable you to get the initial up to a more desirable 18 degrees while limiting the total mechanical to 36-38 degrees. Once again, the "all in" @whatever RPM is controlled by the return springs and/or the weight of the advance weights. It is very common to get an acceptable reading by swapping out the return springs. The springs can be mis-matched as well. i.e. I have found that one light spring and one medium spring will work well in a GM HEI to keep the "all in" RPM close to the often desired 2600 RPM figure. Going to the 3000 RPM figure is Ok, but is a little high in my opinion for max power under typical street driving condition. A lot will depend on your typical cruise RPM's as to what the "all in" RPM should work best.

Originally Posted by Blue84JeepCJ7

I am but I need to check on why I am only getting 2deg advance. Maybe an obstruction inside the dist.

Read the adjusting instructions for the vacuum advance cannister. Set the cannister to the max for your initial adjustment. Check how much you actually get at idle RPM. If greater than 10-12 degrees, adjust accordingly.

If you are still limited to 2 degrees, I think you will find that there is something binding or restricting the advance mechanism.

[cobalt327]

Good advice, all.

FWIW, w/the dist. cap off, you should be able to draw by mouth (or use a MityVac-type hand operated vacuum pump) on the disconnected end of the hose to the vacuum can, to watch the vacuum advance work.

By doing this you will easily be able to discern any lack of movement and by "assisting" the movement by hand as vacuum is being applied, you will see if there's a impediment to the action of the plate.

[454C10]

Originally Posted by cobalt327

You’ve (unsuccessfully) taken my comment out of context, but to no avail.

The thread is about an iron (993) headed SBC in a Jeep.

At post 168 you chime in w/a very helpful “a 383 I read about in a car rag made max power at 40 degrees” or words to that effect. (An odd-ball build that was obviously made for a supercharger or was just lame to begin with- who builds an engine w/8.1:1 CR and puts a cam in it w/almost 240 degrees @ 0.050”?)

Then about 10 posts later, you (very helpfully ) back up and pull out a book that hasn’t seen a revision (reprinting the same thing is a reprint- not a revision) since it was printed in 1976, that references 40 or 38 to 42 or whatever degrees of timing. For max power in a drag engine. W/pop-ups and a points-type ignition.

If you have something worthwhile to contribute, then I’m sure everyone would like to hear it.

But being a troll helps no one- especially yourself.

You are taking this discussion way to personal. I'm a member on this forum and I have the right to disagree with your "no oem head requires 40 degrees" of timing statement. Calling me names (troll) has no place on this site. Grow up. It's about time.

[red65mustang]

Frisco,
he has a accell 71100 and it doesn't say if 28c is possible setting,,,(new it was 24c),,,"see enclosed instructions for centrifugal changes"

http://www.accel-ignition.com/pdf/71000.pdf

blue,
yes you want the cent to start around 12-1300 because that's when the convertor starts to grab and put a load on the motor

lol, clear as mud instructions????
71100 has some form of a "vacuum advance lock out feature" for race only for plate control (and plug the body hole?),,,
I don't know what it is,,,how it works,,,,but it could ber why the vac adv units are not working....