Author Topic: I'm going to adjust my timing from smog factory settings  (Read 489 times)

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Offline Winningbago

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After lurking on this board for quite some time I've learned a ton that I hadn't ever known before.

I just rebuilt my quadrajet and the engine is running better than it ever has. I purchased a digital timing light via amazon and will be checking my initial timing (with distributor vacuum unplugged and hose capped) This should be 4 degrees BTDC as per the air cleaner housing

I'm going to be following in cncsparky's footsteps, who was himself following in the footsteps of Jim83Itasca. It seems the majority of the problems our 454's have is due to the timing profile that our engines came with. Here's what I'll be doing;


From what I've read, our 454's have 4 degrees timing BTDC at idle (with distributor vacuum unplugged). Our distributor weights supposedly put out about 16 degrees advance when fully operated. My centerweight is a "383" and my flyweights are "48" to the best of my research these are simply identification markings, but each number obviously means its different from another somehow. I'm going to be bumping my initial timing from 4 degrees BTDC to ~10 degrees BTDC. I'm also going to be purchasing the new HEI distributor that has the "correct weights" (a 375 centerweight and 41 flyweights) This is supposedly supposed to give out 22 degrees of mechanical advance.    In addition to this, I'm experimenting with moving my distributor vacuum signal to manifold instead of ported vacuum. I tested out manifold vacuum on it today and it seemed a little smoother, but nothing really discernible.

From everything I've read, the increase in initial timing (from 4* to 10*), the increase in mechanical advance (from 16* to 22*) will make this old bird more efficient and run cooler at idle and normal driving.


Does anyone have any more insight into this? I know Rick seems very knowledgeable about timing but any advice is appreciated!

Offline Oz

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Re: I'm going to adjust my timing from smog factory settings
« Reply #1 on: April 23, 2021, 01:29 PM »
Amazing what can be done by tweaking things grom the knowledge and experience others share!

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #2 on: April 24, 2021, 02:09 AM »
So, I checked the advance at idle today with my new dial-back timing light. I hooked the timing light to the #5 cylinder wire and used the timing marker underneath the rig. I disconnected the vacuum advance on the distributor and plugged the hose. The air cleaner housing spec says it should be 4* BTDC is factory advance at 700rpm idle. Mine was 12* BTDC at ~610rpm

I then hooked up manifold vacuum directly to the distributor advance canister then crawled back underneath and the timing light showed it was 24* BTDC and the RPM's had raised to ~720rpm

The engine sounded just fine. No pinging or any unusual sound... Here's my issue though... I don't know the history of this rig, and presumably someone changed the timing. If that were the case then great, it gives me something to go by...

My other thought is that the harmonic balancer has slipped or otherwise delaminated at some point and the timing marks are shifted... The only way to verify the harmonic balancer is accurate is to get the #1 cylinder to TDC on the compression stroke and ensure the timing mark lines up at 0* on the timing marker


Does ANYONE have any idea how likely these harmonic balancers are to slip? Or an easier way to verify that timing is correct?

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #3 on: April 25, 2021, 02:16 AM »
Well I updated what my new emissions diagram will look like. I'm uploading the stock original (with AIR pump removed from diagram already), and the "after" that I modified via MS Paint.

The differences are: EGR, EFE, and AIR pump removal. With those removed I'll have no need to route any vacuum hoses to the thermal vacuum switches/valves that normally control the EGR and Distributor timing. I'm moving my distributor timing from ported vacuum to manifold vacuum.

The charcoal canister will remain, the only change is moving the "red and white" vacuum hose that was attached to the EGR line.

The "blue" vacuum line (letter H on the carb) was originally used for the distributor delay valve, and since it will go unused I'm going to cap that off.


If anyone has any questions please feel free to ask, or chime in with any words of wisdom!

Offline Eyez Open

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Re: I'm going to adjust my timing from smog factory settings
« Reply #4 on: April 25, 2021, 06:43 PM »
It looks like your on target? Do you intend on respringing the mechanical weights? I can tell you each and every engine is a bit different and with that being said I went with 12 static which was enough for me all the way around. Perhaps some lazy day i will get some crane springs and tinker with the curve and play with the vacuum advance.

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #5 on: April 25, 2021, 08:27 PM »
So my plan is to buy the distributor that Cncsparky and Jim83Itasca have mentioned and recommend (ACDelco 93440806) this has 22* mechanical advance

I’ll have to play around with different springs to ensure my full advance comes in by 3000rpms (preferably a little lower, like 2600-2800)

I’m in the process now of ensuring my harmonic balancer is accurate and hasn’t slipped though. Whoever had the rig before me set the timing to a little over 12*BTDC and I don’t know if that was on purpose or slippage

Offline tmsnyder

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Re: I'm going to adjust my timing from smog factory settings
« Reply #6 on: April 25, 2021, 11:16 PM »
If you want to check the balancer to verify TDC, you would need to get #5 to TDC, with a piston stop for instance and check that the mark is at 0 degrees.

You wrote: "My other thought is that the harmonic balancer has slipped or otherwise delaminated at some point and the timing marks are shifted... The only way to verify the harmonic balancer is accurate is to get the #1 cylinder to TDC on the compression stroke and ensure the timing mark lines up at 0* on the timing marker"

Not #1.   In your case on the P30 chassis the marker is set up to read #5.

What you're doing is exactly what I did to my P30 chassis motorhome about 4-5 years ago.  I put it back to pre-smog timing using a very inexpensive spring and weight kit and adjustable vacuum can from Summit. All in, I think it was about $40.  There's no need to change out the whole distributor.  The HEI is a great distributor.

Timing a gasoline engine is something that they figured out more than 100 years ago, but b/c of bs emission rules the chevy engineers had to mess up the timing and fuel mixtures in order to try to prevent certain types of pollutants from forming.   They form when you have a hot combustion, in other words when the engine is operating most efficiently.  Also the reason why the compression ratio was lowered.   So the smog engine you have was timed in a very strange way.  They had to throw efficiency out the window in order to improve emissions.  I'm not going to try to describe it, I won't do it justice. 

That said, before the smog BS,  10-12 degrees of initial timing at idle with the vacuum line plugged, plus the mechanical timing "all in" at some rpm you choose with the springs (I liked the timing to come in early on the 454, the lowest rpm option for the springs, lightest springs) and you should have 34-36 of advance without any vacuum advance added.  This is 99.9% of your timing problem solved.   If you want to back into it, use the number from the spring and weight kit, subtract that from 34-36 and that's the initial timing you need to set.

The last step is the vacuum advance which is adjustable, so add that into the mix (hook up the vacuum) and drive it into some hills with the doghouse open, where you are under partial throttle.  If it pings, adjust the vacuum can to add less timing.   If it's not pinging, maybe try to add some timing with the adjustment.  Play with it until you feel like it's about right but then back it off so it's on the safe side.   Once you cover up the doghouse it's hard to hear it, and you might get a bad tank of gas.  Or they may only have a lower octane gas somewhere.  Better to be on the safe side with the vacuum advance.   The vacuum can though is really not critical to your mpg, it's not going to make your mpg go from 5mpg to 8mpg.   It's just not that significant. Maybe it helps a little, not much though.   I have a mechanic friend that swears it's not even needed.  Mechanical advance, 34-36 degrees total and send it.


Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #7 on: April 25, 2021, 11:43 PM »
Hey tmsnyder!

I've read many of your posts long before I was a member here so it's assuring to get your input! Yes you're absolutely correct about using the #5 cylinder, I had even thought about this after I posted it, so I'm glad you reminded me.

I wasn't going to be changing from an HEI distributor, merely buying a new one that had the 375 centerplate and 41 weights that cncsparky and jim83itasca used that deliver 22* mechanical advance, and then I'll use your suggestion of a spring kit to find the combination that delivers that 22* advance at a reasonable RPM.

I'm fully with you on the Smog vs Efficiency thing. It's ironic that to get better emissions in these rigs you have to burn more gasoline. The stock 4* BTDC timing these 454's have are the main reason for the cracked exhaust manifolds!


Let's assume my 12* BTDC initial timing is accurate and my harmonic balancer hasn't slipped for a minute: When I plug my distributor vacuum advance to manifold vacuum my timing raises to ~730rpm (~630rpm with ported/no vacuum), and it honestly sounds better! When idling at that 730rpm my timing WITH manifold vacuum advance is ~24* BTDC. I idled for about 30 minutes and the gauge never raised past normal, the engine sounded better than ever, and there was no pinging/detonation when I revved it. I'm pretty happy about this so far and will continue experimenting.   When the throttle is pressed (like during acceleration) the manifold vacuum drops and the mechanical weights get to work advancing. It is only at cruising speed that MAX advance timing takes place.

I had read that the peak efficiency at cruising speed is roughly 52* BTDC, with my setup I should be getting near that but I'll probably retard the timing a bit just to offset the chance of bad gas or altitude issues. Any thoughts on this?

Offline Eyez Open

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Re: I'm going to adjust my timing from smog factory settings
« Reply #8 on: April 26, 2021, 03:26 PM »

For the sake of yourself and others, set your base timing at 12 hook up your vacuum timing and spin the RPMs to 1000 and take a timing light and get a read. I think you will be shocked. As to your mech friend we that is him and I have vastly different opinions on vacuum timing that is where the fuel econ come from..never forget the mechanical advance works to acceleration...there is no vacuum available under acceleration..

It starts with base timing your idle should jump quite a bit, then it is turned down to 700 rpm and then the idle speed mixture screws are turned down to meet the lower fuel needs...or turned up these older rigs have been Hodgepodge for many many yrs. Getting a Rochester back on its idle circuit can be challenging and most RV carbs are not running on the idle circuts.

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #9 on: April 26, 2021, 04:08 PM »
While I haven't seen what the actual timing is at 1000rpm's with manifold vacuum hooked up I have revved it to 3000rpms and there were no odd sounds.. My friend is coming by sometime this week so that I can do just that (he'll sit in drivers seat and press pedal while I'm underneath)

Part of my information I'm getting is from "Lars" who has a seemingly very high reputation among all the Chevy forums. My research is also based on cncsparky and jim83itasca's findings, which in part also come from Lars amongst others.

You're correct about no vacuum during acceleration, this is where the mechanical advance takes over in its place until reaching cruise speed. From everything I can find, ported vacuum primarily used until emissions standards took over. In addition to that everything I've found all states that 454's best run at 36-38* BTDC all in, but this figure does NOT include vacuum advance as that's mainly used during idle and cruising where the mixture is leaner and needs more advance.

Here is an interesting article by Lars that describes why he states what he does. This article helped lead me to my conclusions: (the link is a Ford site but the article is by Lars, a retired GM engineer)

https://www.460ford.com/threads/timing-vacuum-advance-101-good-article-by-gm-engineer.117504/

Offline Eyez Open

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Re: I'm going to adjust my timing from smog factory settings
« Reply #10 on: April 26, 2021, 05:43 PM »

Yes, i do understand your references and each and every person's thought process on this subject. My thoughts comes directly from the late 60's/80's trying to keep those old carbs and ignition systems in order. Since that time ive updated my thoughts with Cliff Ruggles information along with the engineer coined the ignition man....

It should say the emission control system would really be a system designed to "burn off" poorly setup carbs or ignition systems. Make no mistakes few back in the day really understood carbs and millions upon millions did not relish spending the money to get their carb in tune..just get by was the thought. Hence a system that would burn off any sloppy carb or ignition system mess, an imperfect answer to a big problem..but it worked.

Each time you set up a new curve put the brakes on full, mash the pedal and see what happens...it is also known as a butt torque meter. If the engine is sluggish not enough timing, if the engine rattles and bangs to much timing..lol nice terminology. Ohh you know when you have it right when the engine pops to attention under braking power and the brakes strain to hold her...Put it back in neutral and the engine should just jump to the accelerator when called upon.

Always attempt this under a well heat soaked engine and a good set of brakes.Below is a link to the man who was on the original engineering team...a bit terse but he cuts thru the BS. Along with Mr Ruggles site.

https://www.davessmallbodyheis.com/

https://cliffshighperformance.com/simplemachinesforum/


Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #11 on: April 26, 2021, 06:28 PM »
Thanks Eyez, I've read much of what Ignitionman (aka Dave Ray) has said and he fully agrees to use manifold vacuum instead of ported. Cliff Ruggles DOES say that he PREFERS ported vacuum so it's a toss up.

I get what both are saying and it's all very interesting, but so far everything I've read (with the exception of Cliff Ruggles) says that manifold vacuum is the way to go... I am leaning towards manifold vacuum because it's been explained much more thoroughly the benefits and the reasoning behind that idea, versus other's that state "it comes from the factory ported, so use ported vacuum."     The factory also states the timing should be 4* BTDC which as we know is terrible for our engines, so the factory doesn't always have YOUR best intentions in mind, just theirs and the EPA's.


If you can provide me with some links that are relevant to your thoughts on this I'll definitely read them. I'm not arrogant and my mind is always open to new ideas! I'd be especially interested in any articles or whatnot that say that ported vacuum is preferable :-) Thanks!


EDIT:   Dave Ray (aka Ignitionman) states this:

"Please, the vacuum advance should be run on FULL MANIFOLD VACUUM SOURING ONLY, NOT PORTED VACUUM.

Then, with initial set to 14 degrees, and vacuum advance set to 10 degrees, IDLE degrees should be 24.

With a 14 initial, and the 41/375 weight/center combo of 22, the total would end up 36 degrees total.

At acceleration, the vacuum advance degrees would go away, then come back in as the engine goes to no load cruise. Total of 36, vacuum advance on no load only, 10, no load cruise 46.

800 is a very high idle rpm."

Here is the link to that forum thread: https://www.chevelles.com/threads/hei-distributor-advance-mechanical-and-vacuum.1103684/

Offline Oz

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Re: I'm going to adjust my timing from smog factory settings
« Reply #12 on: April 26, 2021, 08:01 PM »
Please use the "reply" button, not the "quote" button, when replying to the previous post.

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #13 on: April 30, 2021, 11:00 PM »
Eyez, do you have any links that would be helpful in understanding why you choose ported vacuum? I'd be interested in reading them :-)

Offline Eyez Open

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Re: I'm going to adjust my timing from smog factory settings
« Reply #14 on: April 30, 2021, 11:49 PM »
In not sure I stated ported vacuum, actually I use manifold vacuum simply because of Rays advice. After all that is his expertise. Your last post seems quite correct.
https://www.hotrod.com/articles/quick-tech-still-need-vacuum-advance/

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #15 on: May 01, 2021, 02:33 AM »
My mistake! I've been doing a ton of reading on this subject lately and I might have confused what I had read with something you wrote. One thing that confuses me is that Cliff Ruggles says he recommends ported vacuum over manifold and yet everything else written by someone credible says the opposite! I know Cliff is much more experienced and knowledgeable than I am about these systems so I'm going to read more about what he says about it to see where I'm not making the connection haha


Do you by chance have any suggestions or advice for me or my setup? I just received my new HEI distributor and it did indeed come with the 375 centerplate and 41 weights that I've seen recommended everywhere so that gives me a jump off point, just curious if you have any advice since you've gone down this road before

Offline Eyez Open

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Re: I'm going to adjust my timing from smog factory settings
« Reply #16 on: May 01, 2021, 12:28 PM »
I'm not to much of a blogger, in addition tuneups were not a labor of love or a hobby..and you are tuning up your engine "opinion" One thing I would take into consideration most of the material your reading revolves around higher compression engines with aggressive cams. There all riding a fine line of combustion efficiency and detonation. You Will not find to many tuning up a low compression small cam 454. Always keep that in mind.

I wish I had finished up a tune so I could state some results but I cannot. Just playing around with the factory timing on my engine was pretty eye popping, I have my base at 15 now with vacuum it runs at 27 at idle...no ping no valve train rattle and pulls quite hard.That is a lot of advance..I'm still not comfortable...

I fully intend to get the crane advance setup, shoot for 36 at 2500. It will be interesting to say the least. I cannot help but to wonder if 40 is acceptable. No matter what you do trim the carb each and every time you make a adjustment, it might not like small changes. Once you reach your max timing let the engine run-up another 5/700 rpm and watch your timing closely, if it jumps something is wrong don't let that get by you.

Monitor your heat along the way, and be ready for your engine to act like a temperamental child. It will surprise you at some point, these transitions are ra rarely seamless. W%




.

.
 

Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #17 on: May 03, 2021, 04:04 AM »
Great point! You're absolutely correct that nearly all the information I'm finding is for street cars and only a tiny bit for motorhomes... these are indeed low compression beasts not meant for high revs or performance.

A few questions;

Why aren't you comfortable with your timing at 27 at idle? What is your idle RPM?

Do you know what your mechanical advance is, like how many degrees of advance that gives your engine?

Can you elaborate on what you mean by trim the carb after each adjustment?

I want to make sure I'm reading the next part right; do you mean to give the engine an addition 5/700 rpm after reaching max timing advance by pressing the gas pedal?


Earlier in your post you mentioned that you're wondering if 40 is acceptable and that certainly seems so, as your cruising advance will be near 50. My setup now is 12* at base and 24* with manifold vacuum at idle, and with the new 375/41 weights will be 34* (without vacuum advance hooked up), I like that you set your timing a little more at base and it's working well, that gives me some ideas

Thanks again Eyez Open!

Offline tmsnyder

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Re: I'm going to adjust my timing from smog factory settings
« Reply #18 on: May 03, 2021, 07:55 AM »

I had read that the peak efficiency at cruising speed is roughly 52* BTDC, with my setup I should be getting near that but I'll probably retard the timing a bit just to offset the chance of bad gas or altitude issues. Any thoughts on this?

I've read, and it makes sense to me, that with today's fuels not being the same as fuel 40 years ago, they will ping with what used to be considered a normal amount of vacuum advance.  So if you put in an adjustable vacuum advance canister, keep an ear open for pinging under partial throttle.  You might have to back off the timing added by the vacuum advance.  You might not be able to get 52 without pinging.

What I do is set initial + mechanical = 34-36 degrees using a timing light at a RPM high enough that the mechanical advance is fully advanced.  Should be 2000 to 3000.   Then add the vacuum and drive it.  If there's pinging under partial throttle, I'll reduce the timing added by the adjustable vacuum canister until it disappears.

And to be perfectly honest, if I'm on the road and hear pinging for whatever reason, I'll yank and plug the vacuum advance.  I just drove from NY to FL recently with no vacuum advance attached and got 8.80 mpg.  The vacuum advance doesn't really do much for mpg if you've got pre-smog weights and springs installed.



Offline Winningbago

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Re: I'm going to adjust my timing from smog factory settings
« Reply #19 on: May 03, 2021, 12:05 PM »
Thanks tmsnyder!

The different fuel today is a great point and I will definitely be taking that into consideration. My concern is not being able to hear any slight pinging as the engine/clutch fan is already so loud, and with road noise and the interior making noise I'm afraid I might not hear things going awry.

I will probably put my settings to a more conservative low-to-mid 40's at cruising just for safety and until I'm more comfortable with my engine and its nuances.

The new weights I have should give 22* mechanical advance but you're right about the springs, I'll have to experiment with a curving kit to find the combination of lighter springs that work best and give that mechanical advance at a lower RPM versus the 4000 RPM springs the new distributor came with. It's too bad that this is such old technology because I can't find anyone near my that does distributor re-curving, and the turnaround time sending my distributor to someone is not only expensive but appears to take several weeks at a minimum :-(

Offline Eyez Open

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Re: I'm going to adjust my timing from smog factory settings
« Reply #20 on: May 04, 2021, 11:53 AM »
There are times on just hates to stick his nose into the middle of things, now tell a seasoned mechanic he's not tuning up a engine right goes hand in hand with telling your wife she looks fat in her new dress.
A RV engine is going to operate 95 % of it life below 3000 rpm, vacuum controls the timing down there for the most of that journey its called cruise. Dialing in max advance is critical yes but cruise is where the money is at.
 
I will be the very first to admit setting the initial up at 15 and defeating the vacuum is prudent when chasing the drag strip, not so much when chasing economy. Actually getting the combustion correct would be the proper thought process, if getting it right at idle and 3000 is important then 1500/2000 is critical.

The only reason mechanical advance exists would be due to lack of vacuum under acceleration, and why I eluded to hot engines be tuned up. There whole existence revolves around acceleration. Take some time to optimize your lower rpm vacuum timing, this is done by using the crane adjustable vacuum can kit and it has the springs to boot.

As to trimming the carb, as mentioned above the first thing is to get the carb on its idle circuit, then trim it out using the idle jets, each time you do a major recurve you go back a recheck how the carb responds to this new curve from. idle on up. It's not complicated at all, if the engine bogs a smidge off idle with your new curve an enrichment may be needed or maybe leaned out. It's a combination of both timing and carb adjustments to this new timing.It can be quite fun or interesting or frustrating... W% W%

Here https://cliffshighperformance.com/simplemachinesforum/index.php?topic=3349.0

Ohh look and here well discussed here, https://www.classicwinnebagos.com/forum/index.php?topic=8305.0

great article on this pinging/detonation topic..https://www.enginelabs.com/engine-tech/misunderstood-causes-of-detonation-in-high-performance-applications/


https://www.enginebuildermag.com/2013/11/impact-of-todays-fuels-n-carbureted-engines/

Most modern fuel injected ­engines have a computer – controlled ignition system that has been programed with a spark advance curve suited for today’s gasoline, plus it provides the spark plug with the higher current and longer duration spark that is needed to prevent misfire problems. But the ignition system that most carburetor- equipped engines came with can prove to be marginal with today’s reformulated gas blends.
Today’s gasoline burns somewhat faster than the leaded gas of days past, but it needs a hotter spark to ignite it. The ignition spark advance curve that is programmed into the PCM of a typical modern fuel-injected domestic V8 engine would also work quite well with a vintage carburetor- equipped engine.

A typical vintage Ford or Chevy small block (with a mild camshaft) will perform well with a spark advance curve that has 12 degrees initial timing plus 24 degrees of
mechanical advance all in by 3,600 rpm with an additional 10 to 12 degrees from the vacuum advance.

A great summary on vacuum advance....https://www.chevelles.com/threads/ignition-101.189195/