NewB Contest: Spot the error

[Bwk2000]

JT:
Actually, Chrysler had already developed their anti-smog kit for use with select test vehicles in 1963 (prototype testing really). Simply marketed as their “Clean Air Package”, so they must have cared. - Part of it was a vacuum advance valve … I have no information whether or not Datsun also “cared” in 1964.

[JT68]

Again, you can hook it up as you please, but manifold vac will not do the engine any good.

At a minimum, it is going to tend to make it idle fast because there is so much manifold vacuum and advance. To fix that you’d have to retard the distributor position which will affect final timing, or live with over advance at idle.

Again, the Chrysler lore isn’t really relevant to 60’s Nissan.

We’ve been tuning roadster engines since 1978 and recurving roadster distributors since 1990. Respectfully, we’ve kinda have it figured out.

The purpose for the vacuum advance is throttle response and efficiency under light load. Nissan was certainly trying to make performance cars in 67. The emissions stuff was added in 68 per federal regs.

No matter what you prefer, hooking it up to manifold vacuum is incorrect per Nissan.

[redroadster]

The vacuum advance in a 64-67 roadster isn't an emissions device. Nissan (and no mfg) cared about emissions in 1964 - The early engines had crankcase "draft tubes"!

The vacuum advance is intended to increase timing under light load to improve throttle response.

This is pretty much spot on:

"Under a light load and part throttle conditions, timing can be advanced. This improves throttle response and makes the engine more efficient. It also helps the engine run cooler. The vacuum advance provides this benefit BEFORE the Mechanical Advance provides Total Timing."

Ok maybe I misunderstood your post on ots function , but
Yes it was mandated in 65 on most US high pollution If a low fuel ride cars foreign manu's given longer to comply this per my Mitsubishi Eng. performance training , Vr4-eclipse turbo etc , and Nissans Eng perf course , I remember it as a kid techs hating having to deal with vacuum advance .
Its a big deal as advanced a bit to much you will cook ,detonate the cyl under full load .

They explain it this way your at the bottom of a short hill / steep slope ,about 30 ' to the top you have to take short powerful steps to get up , but if you get a run at it you can take big strides and easily assend
,But if the slope is long ,keeps going up try the long strides it wipes you out it cant be done.
the long stride are the same as advancing ign timing farther than it can be to obtain high or max power/ performance
Answer this: the ign timing Is set before TDC , but what degree do you need the biggest part of the combustion to occur( pressure in the piston) after TDC..... 45 degrees , 60 degrees, 90 degrees or 100- 110 degrees @ full power ?

The PVC valve IN 67 heat riser valves in 68

[JT68]

Don't know what this means: "The PVC valve IN 67 heat riser valves in 68" There is no PCV "valve" on a roadster, only the VC tube over to the carbs. No heat risers on roadster either. How is this relevant to Datsun roadsters?

I'm not sure the other question is particularly practical since literally every roadster engine is different regarding cam,CR/cam timing, piston type, fuel type&quality, rpm, temp, elevation and a dozen other variables, but in general you want peak pressure to develop just after TDC to maximize power. That is the whole reason for ignition BTDC, to start the flame front early "enough" for peak pressure to develop an instant after the crank is heading down. So if you mean what is a good "total timing number", somewhere in the 34-45 range typically- 34/35 is a good safe number for roadsters. As you go past that, you will make more power to a point until the timing is so early that max pressure is developed before the piston reaches the top-in that case the engine is definitely not working efficiently and power will be off and detonation/damage can occur. Optimizing total timing is really best done on a dyno under controlled conditions. Then you remove a few degrees for safety.

Definitely a good contest.

[Bwk2000]

JT:

Ok. Let me try a different approach.

This article is an exemption given by The State of California Air Resources Board allowing the swap of Hitachi carbs to Weber ones on some older emission controlled Datsuns.

Original text found here:
https://ww2.arb.ca.gov/sites/default/fi ... 133-11.pdf

1B7B221C-FB1C-4353-A1DC-8F40D4AD4581.jpeg

With the inclusion of this article, I’ve now provided three independently verifiable sources confirming that General Motors, Chrysler, Ford and Datsun all identify ported distributor vacuum advance as an emission control system - Because, that’s what it is.

Now, there are certainly non-emission benefits to it, namely part-throttle operations, but there is also a bigger negative one. That is the extra heat generated by the engine under a lean burn condition at idle when no vacuum advance is present. Whether you are idling or just stuck in slow moving traffic, that accounts for a significant portion of normal vehicle operations. Ported vacuum advances make those situations much worse.

Going back to the original post and eBay pictures, it’s clear the owner has removed all the pollution control equipment and the car is essentially in a pre-Smog control state … Except, for the ported vacuum advance connection, which again, is clearly designed as a pollution control feature. Whether it existed that way before is somewhat mute, as the mid to late ‘60s was a transition era to impending emissions control legislation which all auto manufacturers knew was coming and were already adjusting for.

An article in the early ‘60s described Los Angeles as: The only City in the world where you can wake up in the morning and hear the birds cough. - John T. Middleton, (California Air Pollution Research Center) - A submission to support vehicle emission controls legislation.

Finally, this isn’t about me or what I want to do. It’s about the original post and two pictures on eBay; trying to find something wrong that can damage that engine over time. Yes, the vacuum advance is hooked up to the manifold instead of the pollution controlled specified location on the carb. But, since all the other pollution control equipment has been removed, it wouldn’t do any harm to the engine and can yield heat reducing benefits. As I stated earlier, sometimes it works, sometimes it doesn’t - All depends on the specific car. With the rest of the pollution control equipment removed, it wouldn’t necessarily be wrong to make that change - But it certainly wouldn’t damage the engine.

[JT68]

Call it whatever you like. A gold vacuum booster thingy, doesn't matter, if you want the oem distributor to work to optimize street drivability, the vacuum advance needs to function properly, Jhayden correctly pointed out a newb error on an otherwise nice looking car. If you are optimizing a race engine there is no need for a vacuum advance.

A distributor which is purely mechanical has only rpm as the input, so it has no load or throttle position input. Manufacturers added vac advance to provide improved part throttle response and efficiency. That isn't about emissions.

Citing an emissions statute regarding a 2 barrel progressive carb (with an accelerator pump) on 70's 510's and trucks is just as irrelevant as discussing Vette and Chevelle timing advance requirements. Really?

For the benefit of the rest of 311's newbs and experts, If you want it to run the best it can, we'd suggest you hook up the vacuum advance properly to the carb port and set the final timing correctly. That will result in improved performance, efficiency and drivability . Hooking it up wrong is simply a step backwards. Incorrect timing can certainly damage your engine and may cause piston failure over time. - I'm pretty sure that was the point of the original post.

If you need help with a rebuilt and recurved distributor, a programmable distributor, or how to set final timing or anything else distributor related, we are glad to help as always

[Bwk2000]

…Citing an emissions statute regarding a 2 barrel progressive carb (with an accelerator pump) on 70's 510's and trucks is just as irrelevant as discussing Vette and Chevelle timing advance requirements. Really? …

Why yes, really! Allow me to explain.

Perhaps my previous posts and references were too long to read in their entirety. If you had, you would realize the point I was trying to make: Namely, not only are ported vacuum advances an emission control feature, but they are common across the auto manufacturing industry since inception. They are not limited to specific carbs, engine displacements or brands, but are mostly universal. They all work basically the same way, achieve the same end state through the same means and are all hard on the engine at idle or in slow moving traffic.

If you can achieve a reasonable idle without sacrificing timing, switching to manifold vacuum can provide tangible benefits, which various subject matter experts (some of which I’ve referenced) agree on, and may outweigh the potential downside (part throttle operation). Yet again, car dependant of course (you won’t know until you try).

We may not agree, and that’s fine, I can respect that. But, the repetitive belittling from the start of what is otherwise an alternate, but informed opinion by another member here, along with an air of condescension, probably wasn’t the best way to go - You can decide.

Looking back, I guess I didn’t make this reply much shorter - Apologies.

[unklpat]

Wait, shouldn't there be a discussion as to if the cam inside the distributor has been changed, and add that to the argument regarding the incorrect vacuum line? Pat

[Bwk2000]

Wait, shouldn't there be a discussion as to if the cam inside the distributor has been changed, and add that to the argument regarding the incorrect vacuum line? Pat

An excellent point.

[GeoffM]

The first emissions control devise was the exhaust pipe.

[Bwk2000]

The first emissions control devise was the exhaust pipe.

Lol … touché!

[redroadster]

The first emissions control devise was the exhaust pipe.

Ok federally mandated emmissions control device.per the clean air act
We disagree , Ill leave it there
Dont forget to have 96. 97 octane fuel in the tank ( it was when Roadsters were produced ) when you set ign timing as thats critical
And the only way IMO To know your best advance and when it is at rpm is was a sun dist machine dist off the car ...you cant hear detonation , but you can hear extreme detonation

[JT68]

I'm not sure why guys who try to help the "less experienced" understand the way these systems are designed to work (correctly) are called arrogant or condescending. Providing years (decades) of expertise and advice for free.

The title of the thread is correct..it is an error. The original poster correctly recognized it as one. Simple as that.

[Bwk2000]

I'm not sure why guys who try to help the "less experienced" understand the way these systems are designed to work (correctly) are called arrogant …

Although I never used the word ‘arrogant’, you are not wrong …

[jhayden]

The title of the thread is correct..it is an error ... Simple as that.

to corroborate JT's point here:

"...29. Hooking up your vacuum lines wrong. If you have a '67 or earlier or are running a later car without the emission control distributor (you've replaced or recurved your distributor) the vacuum line should run from the CARBURETOR to the distributor, NOT from the MANIFOLD to the distributor. The manifold vacuum fitting should only be used when you want to check the engine's vacuum." p.220.1, "The 35 Biggest Mistakes You Can Make," Catalog Insert, Rallye Enterprises, Ltd., 1988.

As a sidebar, how many of us who have been around roadsters for roughly half a century could complete the list of "35 Biggest Mistakes?" Would we list the same items? The Catalog Insert is still highly recommended reading, and may even bring back some old memories ("Yeah, there was that time the little wire inside the distributor broke right in the middle of downtown, and ...).

Thank you to all who have contributed -- none of us should take this forum and the work that goes into it for granted.

Jon