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ZZ4 & ZZ383 - no vacuum advance???? Header size??

 
Old 03-22-2011, 07:43 PM
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highschool67
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I still have dual point accel , mechanical advance, tach drive distributors on 2 of my hi hp vettes. Set for full advance and let it fall where it will at idle. Never had a problem overheating or hi rev point bounce.
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Old 03-22-2011, 08:19 PM
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Originally Posted by highschool67 View Post
I still have dual point accel , mechanical advance, tach drive distributors on 2 of my hi hp vettes. Set for full advance and let it fall where it will at idle. Never had a problem overheating or hi rev point bounce.
So, the only point where the timing is correct for best thermodynamic efficiency is at high RPM WOT.

Why????
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Old 03-22-2011, 10:05 PM
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GM has to honor warranties, and I bet the lack of vac advance is to keep 'em out of the detonation/ping mode...esp w the fast burn heads.

Just like the conservative cam timing in most crate engines...helping the valve train last thru warranty!!!
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Old 03-22-2011, 10:58 PM
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Originally Posted by mikem350 View Post
GM has to honor warranties, and I bet the lack of vac advance is to keep 'em out of the detonation/ping mode...esp w the fast burn heads.

Just like the conservative cam timing in most crate engines...helping the valve train last thru warranty!!!
Mike,

Valid point!

GM supplied the dist. with wmf62's ZZ4, and I checked it on my Sun Machine. It was a lazy dist., with full cent. advance of 21 crank degrees only being reached at 5200 crank rpm, although it was at 16 crank degrees @ 3000. As noted previously, this is not the dist. he used.

I also checked the vacuum advance on the above (although according to the spec document, it was not to be used):

0 deg. advance @ 4"

1 deg. dist. (2 deg. @ crank) @ 4.5"

10 deg. dist. (20 deg. @ crank) @ 7"

I still wonder why GM would even supply a vacuum advance dist., if the vacuum advance was not to be hooked up. If they were serious about you not using the vacuum advance, a pair of pliers or Visegrips on the vacuum canister inlet would of "fixed" that.

Plasticman
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Old 04-01-2011, 05:28 PM
  #25  
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Plasticman, did you ever reach a conclusion on this one?

Harry
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Old 04-01-2011, 05:53 PM
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Originally Posted by 66since71 View Post
Plasticman, did you ever reach a conclusion on this one?

Harry
Harry,

Nope! wmf62 is still dialing in his ZZ4 using his ACCEL efi and dist, so he will have to come up with the optimum ignition curve.

If and when I go with a new engine, I will do the same dialing in process, although mine will not be efi or electronic anything (still using points). So far the ZZ383 is not looking good from the standpoint of using my existing Offenhauser dual quad intake. The intake ports on the ZZ383 are Vortec style (but GM says that older standard intakes can be used - it has dual intake bolt patterns). However, comparing intake manifold gaskets (Fel-Pro 1255 Vortec type), with a "standard" large port manifold gasket shows lots of mismatch and only about 1/16" of manifold material at the gasket at the top of the port. The alternate would be to weld up my manifold at the top of the port runners (such as what Devildog did to use his original intake), but frankly that was not what I wanted to get in to.

John (plasticman)
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Old 04-01-2011, 06:16 PM
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John, thanks for the update.. I understand that AFR heads can duplicate Vortec performance and would fit pre Vortec manifold and accessories.. Might be worth checking out. It came up in my discusssions as a way of keeping 1966 "engine dress". Our plan was to use the zz383 short block, AFR heads and stock manifold and valve coves (L79). I may pull the trigger on the project this summer. Lots to do first though...
Keep us posted..

Harry
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Old 04-15-2011, 12:36 PM
  #28  
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John,
I would suggest using the crane adjustable advance kit along with a vacuum advance limiter. Something like http://www.kendrick-auto.com/ignition.htm (halfway down the page) I have a MSD 8360 in mine and had to build my own. The ZZ4 likes only about 8-10' of vacuum advance. The Stock HEI or pretty much all advance pods give 20' crank advance (10' dist adv), way more than the motor wants. I'm not a fan of the crane vac adv. limiter, I like to limit the end point rather than limit the starting point. Maybe use a light siver/light blue spring combination. You can disable the vac adv, but you will lower your fuel economy and you may need to tweek the carb settings to make up for the non-optimal lean issues at idle operating with retarded timing.

So I would be looking at something like:
~10' initial + 8' vac (~18') at `1000
~+21' mechanical at 3000 (all in)
~31 total at 3000
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Old 04-15-2011, 01:22 PM
  #29  
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Originally Posted by aquaroscoe View Post
John,
I would suggest using the crane adjustable advance kit along with a vacuum advance limiter. Something like http://www.kendrick-auto.com/ignition.htm (halfway down the page) I have a MSD 8360 in mine and had to build my own. The ZZ4 likes only about 8-10' of vacuum advance. The Stock HEI or pretty much all advance pods give 20' crank advance (10' dist adv), way more than the motor wants. I'm not a fan of the crane vac adv. limiter, I like to limit the end point rather than limit the starting point. Maybe use a light siver/light blue spring combination. You can disable the vac adv, but you will lower your fuel economy and you may need to tweek the carb settings to make up for the non-optimal lean issues at idle operating with retarded timing.

So I would be looking at something like:
~10' initial + 8' vac (~18') at `1000
~+21' mechanical at 3000 (all in)
~31 total at 3000
Thanks and I agree. Your curve (and info) looks good.

I am very familiar with the Crane adjustable advance units, and have one in my 62. I have a Sun Dist. Machine (and know how to use it).

Plasticman
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Old 04-15-2011, 04:06 PM
  #30  
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John,

I am not familiar with the finish on your Offy 2 x 4 intake, but increasing the flange area on my stock 2 x 4 was quite easy. I paid a heliarc welder $200 to lay 3/8" on the four intake flange edges.

Then I just used a old wood rasp to shape the aluminum weld. It looks like the original surface.

Joe


Originally Posted by Plasticman View Post
Harry,

Nope! wmf62 is still dialing in his ZZ4 using his ACCEL efi and dist, so he will have to come up with the optimum ignition curve.

If and when I go with a new engine, I will do the same dialing in process, although mine will not be efi or electronic anything (still using points). So far the ZZ383 is not looking good from the standpoint of using my existing Offenhauser dual quad intake. The intake ports on the ZZ383 are Vortec style (but GM says that older standard intakes can be used - it has dual intake bolt patterns). However, comparing intake manifold gaskets (Fel-Pro 1255 Vortec type), with a "standard" large port manifold gasket shows lots of mismatch and only about 1/16" of manifold material at the gasket at the top of the port. The alternate would be to weld up my manifold at the top of the port runners (such as what Devildog did to use his original intake), but frankly that was not what I wanted to get in to.

John (plasticman)
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Old 01-22-2016, 10:35 PM
  #31  
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Hey John...

I know this is an old thread...but I fired off my ZZ4 today..and tuned it out. Well I should say tuned at it..it doesn't quite suit me yet.

Everything is brand new...and the carburetor is a Quadrajet from SMI (Sean Murphy Induction) set up for a ZZ4 from dyno specs on previous ZZ4 apps.

...so I did a search and found this thread again, hoping to see if anyone had come up with a plan for the GMPP ZZ4 distributor to work well with vacuum advance. ( I just happen to have two new ZZ4 distributors).

It's times like these that a distributor machine would be really handy (and to know how to use it..lol)

I'm still wondering why GMPP put out an engine with instructions not to use the vac advance...

Thanks...Stan

Last edited by Stan's Customs; 01-22-2016 at 10:46 PM.
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Old 01-23-2016, 12:05 AM
  #32  
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Originally Posted by Plasticman View Post
Mike,

Valid point!

GM supplied the dist. with wmf62's ZZ4, and I checked it on my Sun Machine. It was a lazy dist., with full cent. advance of 21 crank degrees only being reached at 5200 crank rpm, although it was at 16 crank degrees @ 3000. As noted previously, this is not the dist. he used.

I also checked the vacuum advance on the above (although according to the spec document, it was not to be used):

0 deg. advance @ 4"

1 deg. dist. (2 deg. @ crank) @ 4.5"

10 deg. dist. (20 deg. @ crank) @ 7"

I still wonder why GM would even supply a vacuum advance dist., if the vacuum advance was not to be hooked up. If they were serious about you not using the vacuum advance, a pair of pliers or Visegrips on the vacuum canister inlet would of "fixed" that.

Plasticman
I don't claim to be an expert, but I have done a LOT of reading about ignition timing and I think I understand it pretty well. Articles written by John Hinckley, Duke Williams, and Lars have influenced my thinking on this topic.

It is is important to understand that vacuum advance (at least the common type tied to manifold vacuum) is only active at *idle* and at *vert light load cruise* conditions. Those are the only times when the engine has enough vacuum to activate vacuum advance.

So, if you application is racing, vacuum advance is not useful. However, if your application is street driving, vacuum advance is VERY useful. At light load where vacuum advance would be active, engines run smoother and cooler with lots of advance.

Typical GM vacuum cans add about 16 degrees of crank advance when the engine has high vacuum (idle and light load cruise). Lars feels that with today's fuels, it might be better to limit that to 10 degrees to prevent surging under cruise conditions.

However, I think all of the experts would agree that for street driving, vacuum advance is a good thing. The only effects will be at idle and light cruise, but for street driving these are pretty important operating conditions.
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Old 01-23-2016, 09:22 AM
  #33  
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Originally Posted by Stan's Customs View Post
Hey John...

I know this is an old thread...but I fired off my ZZ4 today..and tuned it out. Well I should say tuned at it..it doesn't quite suit me yet.

Everything is brand new...and the carburetor is a Quadrajet from SMI (Sean Murphy Induction) set up for a ZZ4 from dyno specs on previous ZZ4 apps.

...so I did a search and found this thread again, hoping to see if anyone had come up with a plan for the GMPP ZZ4 distributor to work well with vacuum advance. ( I just happen to have two new ZZ4 distributors).

It's times like these that a distributor machine would be really handy (and to know how to use it..lol)

I'm still wondering why GMPP put out an engine with instructions not to use the vac advance...

Thanks...Stan
Stan,

Bill is using an Accel EFI (port injection) and electronic dist. with his ZZ4 with the 1962 modified FI manifold / dog house (with a throttle body) system. He has up to 52 degrees "vacuum" advance dialed in with a "lean" fuel map programmed in, and has never seen any issues.

Here is his "vac." advance curve. Note that it reads off the MAP sensor, so it is showing pressure (shown in the left col.) rather than inches of vacuum. As shown below, his initial timing is 12 deg. BTDC. And the display shows "steps", whereas the onboard computer automatically "smooths" the curve between the steps:




Yes, 52 deg. may be too much advance with today's "gas", but it works for him.....

Plasticman

Last edited by Plasticman; 01-23-2016 at 01:03 PM.
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Old 01-23-2016, 10:52 AM
  #34  
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Originally Posted by GearheadJoe View Post
I don't claim to be an expert, but I have done a LOT of reading about ignition timing and I think I understand it pretty well. Articles written by John Hinckley, Duke Williams, and Lars have influenced my thinking on this topic.

It is is important to understand that vacuum advance (at least the common type tied to manifold vacuum) is only active at *idle* and at *vert light load cruise* conditions. Those are the only times when the engine has enough vacuum to activate vacuum advance.

So, if you application is racing, vacuum advance is not useful. However, if your application is street driving, vacuum advance is VERY useful. At light load where vacuum advance would be active, engines run smoother and cooler with lots of advance.

Typical GM vacuum cans add about 16 degrees of crank advance when the engine has high vacuum (idle and light load cruise). Lars feels that with today's fuels, it might be better to limit that to 10 degrees to prevent surging under cruise conditions.

However, I think all of the experts would agree that for street driving, vacuum advance is a good thing. The only effects will be at idle and light cruise, but for street driving these are pretty important operating conditions.
Joe,

I agree with what you are saying (I always custom tune the complete dist., including the vac. can, both on my Sun Machine and then finalized on the vehicle).

Plasticman
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Old 01-23-2016, 06:44 PM
  #35  
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Originally Posted by Stan's Customs View Post
I'm still wondering why GMPP put out an engine with instructions not to use the vac advance...

Thanks...Stan
Probably because the GMPP crate engines are supposed to be emissions-friendly, and emissions are lessened with reduced ignition advance; not having any vacuum advance also reduces the risk to GMPP of any warranty issues.
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Old 01-23-2016, 09:40 PM
  #36  
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Originally Posted by Stan's Customs View Post
Hey John...

I know this is an old thread...but I fired off my ZZ4 today..and tuned it out. Well I should say tuned at it..it doesn't quite suit me yet.

Everything is brand new...and the carburetor is a Quadrajet from SMI (Sean Murphy Induction) set up for a ZZ4 from dyno specs on previous ZZ4 apps.

...so I did a search and found this thread again, hoping to see if anyone had come up with a plan for the GMPP ZZ4 distributor to work well with vacuum advance. ( I just happen to have two new ZZ4 distributors).

It's times like these that a distributor machine would be really handy (and to know how to use it..lol)

I'm still wondering why GMPP put out an engine with instructions not to use the vac advance...

Thanks...Stan
I just finished incorporating the vacuum advance on my new 350. The machine shop set the total at 34 degrees for dyno runs, and it ran ok but was missing some response off idle and cruise passing where the extra advance helps.

Simply piping the B28 vacuum can added too much advance, with a highway load surge around 3500 to 4500 rpm. I added an aluminum plate on the vacuum advance tab with a slot to limit the advance (lots of photo options pop up with a search). The stock advance pin travel is 0.180", 16 degrees. I limited the pin to about 0.100" in the slot, about 9 degrees vacuum advance.

I had to reset the timing as the slot located the vacuum advance pin at both ends of travel.

10 degrees initial, 34 total at 2100 rpm (blue springs). Pipe the vacuum can and get 18 degrees at idle, and about 43 degrees total, under no load.

No surge and the response is much better. I would expect the ZZ4 to see a similar improved response.
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Old 01-23-2016, 09:44 PM
  #37  
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Yes, 52 deg. may be too much advance with today's "gas", but it works for him.....

Plasticman[/QUOTE]


Thanks for the update John...and thanks to other's input as well

I would think 52 deg. would be good on a carbureted engine too...but is been a loong time since I did much distributor work. Plus I don't have a clue what today's ethanol fuel does to old tuning habits.

I was hoping that some one had dialed in a ZZ4 with HEI...and had some particular centrifugal weight part numbers and a light vacuum advance part number they had used with some success.

I'm dreading a drawn out ordeal of hit or miss to dial in my ZZ4 hei distributor...(of course , I've only been working on this thing 11 years...so why get in a rush now, lol!)

I'm definitely going to run vacuum advance since this is a street cruiser and I want the advantages of cooler engine temps..and improved driveability in general. (better fuel economy won't hurt either...albeit not my primary goal).

Thanks...Stan..
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Old 01-23-2016, 09:50 PM
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Originally Posted by 63 340HP View Post
I just finished incorporating the vacuum advance on my new 350. The machine shop set the total at 34 degrees for dyno runs, and it ran ok but was missing some response off idle and cruise passing where the extra advance helps.

Simply piping the B28 vacuum can added too much advance, with a highway load surge around 3500 to 4500 rpm. I added an aluminum plate on the vacuum advance tab with a slot to limit the advance (lots of photo options pop up with a search). The stock advance pin travel is 0.180", 16 degrees. I limited the pin to about 0.100" in the slot, about 9 degrees vacuum advance.

I had to reset the timing as the slot located the vacuum advance pin at both ends of travel.

10 degrees initial, 34 total at 2100 rpm (blue springs). Pipe the vacuum can and get 18 degrees at idle, and about 43 degrees total, under no load.

No surge and the response is much better. I would expect the ZZ4 to see a similar improved response.
I missed this post..must have been typing mine....thanks for your input.

What are some particulars of your 350 engine...Cam, fuel delivery etc..?

Thanks...Stan

Last edited by Stan's Customs; 01-23-2016 at 10:17 PM.
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Old 01-23-2016, 10:21 PM
  #39  
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Originally Posted by Stan's Customs View Post
I missed his post..must have been typing mine....thanks for your input.

What are some particulars of your 350 engine...Cam etc..?

Thanks...Stan
The 350 is 0.040 over, about 10.5:1CR. Ported aluminum Bowtie heads with flattop pistons. The cam is a solid Isky custom grind. The dynamic CR is just under 8:1. Port matched Edelbrock C3BX intake and ported rams horns. With a 750 double pumper it fits a 14x3 air cleaner under the stock hood. 430 lbft at 4400, 421 Hp at 5500 and continues climbing (with headers). It lost a little low end torque with the exhaust manifolds but still has 300 plus lbft from 2600 to 6600.

The heads and pistons leave a nice open chamber for a fast burn, and combined with 91 octane the surge was the result with the 50 to 52 degree total advance with the full vacuum advance. The response was good, but the surge was not. It now runs better with the advance limited. The idle is also much more stable with the idle timing being stablized with the vacuum advance pin located in the 5/32 x 0.100 slot. 700 rpm idle and the Duntov style sound.
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Old 01-23-2016, 10:26 PM
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Originally Posted by 63 340HP View Post
The 350 is 0.040 over, about 10.5:1CR. Ported aluminum Bowtie heads with flattop pistons. The cam is a solid Isky custom grind. The dynamic CR is just under 8:1. Port matched Edelbrock C3BX intake and ported rams horns. With a 750 double pumper it fits a 14x3 air cleaner under the stock hood. 430 lbft at 4400, 421 Hp at 5500 and continues climbing (with headers). It lost a little low end torque with the exhaust manifolds but still has 300 plus lbft from 2600 to 6600.

The heads and pistons leave a nice open chamber for a fast burn, and combined with 91 octane the surge was the result with the 50 to 52 degree total advance with the full vacuum advance. The response was good, but the surge was not. It now runs better with the advance limited. The idle is also much more stable with the idle timing being stablized with the vacuum advance pin located in the 5/32 x 0.100 slot. 700 rpm idle and the Duntov style sound.
Good info...thanks for the help.

Best regards...Stan
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