best wa vs gm way ??

[Francis F.]

the new G M crate motor is installed and running,I have two questions for our NCRS engine guy's
1) how to solve the height issue of the carb. air cleaner now being used ? in order to close the hood I need to reduce height by about 1*

2) timing set up....G M spec sheet says run engine @ 650 rpm,set timing to 10*BTDC,with vac.disconnected (as per normal)
they say to leave vac disconnected.This setting will produce 32*degrees total advance at W O T."this engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve..".. notes the Dist .#93440806 came supplied on the engine with a vac. can ....do you suppose GM advises this to cover the emission side of thei after market business ?
I am all ears for the proper /best way to set up the engine. Just for information 350/330HP coupled to an orig.1966 powerglide engine,..,our goal is to have a good running engine and a very family driveable corvette.(not looking to take to the races)

hope you can chime in Duke and Joe Lucia and others,
Francis

[Jim T.]

Re: best wa vs gm way ??

I do not know what type of air cleaner you are using. I have a crate engine installed in my 1970, it is a ZZ1 which when later ZZ engines (ZZ2, ZZ3, and ZZ4) were available their intakes were lower for air cleaner installation. I installed on my ZZ1 a Corvette type open element using a Holley double pumper 650 carb and it has no clearance problems with the hood. The air cleaner is the same type open filter that came on my 1968 327/350 L79. My ZZ1 came with a HEI distributor and has vacuum advance, mine is operational. I would not ever consider not using the vacuum advance. I do plug the vacuum advance line to check/adjust the engine timing and reconnect it. With vacuum advance an engine runs cooler in traffic and get better gas mileage. Learned this 44 years ago.

[Edward J.]

Re: best wa vs gm way ??

Francis, a few pictures might help. Some of the newer GM crate engines have the newer designed heads and intakes, and may vary in height, Air cleaners filters also vary in height. as do the carburetor base gaskets thicknesses. It maybe a possibility that you can fab some plates to lower the engine through the mounts.

[Duke W.]

Re: best wa vs gm way ??

Most crate engines are intended for non-emission controlled applications, so you set the intial advance at an engine speed below where the centrifugal begins with the VAC disconnected and the signal line plugged. Then total idle timing with the VAC connected should be about the sum of initial and full vacuum advance.

32 degrees total intial plus centrifugal is very conservative for Gen I heads... 38 is closer to ideal, but 32 is about ideal with Vortec heads.

What you should do is take the entire centrifugal map from where it starts to where is stops with a dial back timing light, and it can probably be improved with lighter springs.

Be sure to hook up the vacuum advance to a full time, not ported, vacuum source on the carb, and check that it meets the Two-Inch-Rule.

Remember, GM provides a warranty. The spark advance map, compression ratio, and fuel octane recommendation is VERY CONSERVATIVE, so Bubba, who times the engine "by ear" after a few brewskies doesn't overadvance and detonate it to death.

Guys who have dial back timing lights and the pdf of my 2012 San Diego National Convention presentation know better.

Duke

[Joe L.]

Re: best wa vs gm way ??

the new G M crate motor is installed and running,I have two questions for our NCRS engine guy's
1) how to solve the height issue of the carb. air cleaner now being used ? in order to close the hood I need to reduce height by about 1*

2) timing set up....G M spec sheet says run engine @ 650 rpm,set timing to 10*BTDC,with vac.disconnected (as per normal)
they say to leave vac disconnected.This setting will produce 32*degrees total advance at W O T."this engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve..".. notes the Dist .#93440806 came supplied on the engine with a vac. can ....do you suppose GM advises this to cover the emission side of thei after market business ?
I am all ears for the proper /best way to set up the engine. Just for information 350/330HP coupled to an orig.1966 powerglide engine,..,our goal is to have a good running engine and a very family driveable corvette.(not looking to take to the races)

hope you can chime in Duke and Joe Lucia and others,
Francis

Francis------



You present some vexing challenges.

As far as the hood clearance issue goes, there are really only 2 things you can do to reduce the height by 1". The first would be to find an extremely low profile air filter, assuming you aren't already using one. I can't advise as to which one since I've never used one of these and have very little knowledge of what's available.

The second thing you could do is to use a lower profile intake manifold. However, this is not really an option for you since, unfortunately, the 350/330 hp uses Vortec heads. That, in turn, requires the use of a Vortec manifold. The problem is I don't know of a Vortec manifold that has a lower profile than the one you have. There might be one from some truck application but I wouldn't know anything about it.

There is one thing I really don't understand here, though: C2's with L-76 or L-79 used a high rise aluminum manifold with Holley carb. It fit fine under the standard small block C2 hoods. I really didn't think the Vortec manifold on your 350/330 was any higher than those manifolds, so I don't understand why you're having the hood clearance issue. Are you using the stock Corvette "drop down" air cleaner?

A far as the distributor issue goes, I have not the slightest idea why GM says not to use the vacuum advance. Personally, I don't like any street engine with no vacuum advance. To me, vacuum advance is a basic requirement of a street engine. I'd follow Duke's advice on this one.

[Terry D.]

Re: best wa vs gm way ??

Agree with Ed, pictures would help. There are aftermarket intake manifolds that are shorter.

Terry

[Duke W.]

Re: best wa vs gm way ??

I know Scott Marzahl managed to install a Z-28/LT-1 manifold under his '67 small block hood with the OE air cleaner. I recall he did have a clearance issue on the right front, but found a solution. You might want to contact him through the TDB email function.

Duke

[Francis F.]

Re: best wa vs gm way ??

sorry Duke failed to mention the vortec heads and alum intake.I appreciate the info,and will be doing the set up you suggest.I have seen your pdf and I have a dial back timing light.As far as the air filter height,I'm using the air filter supplied it has the typical 3"filter.Before purchasing the engine I was told their could be a height issue.I will try to contact the member you gave me. alsowhen I drove the car with no vac .connection I noticed a higher than normal operating Temperature.Perhaps when connecting the vac. temps will return to normal (155-170).
Thanks to Joe,Jim,and ed also

[Joe L.]

Re: best wa vs gm way ??

sorry Duke failed to mention the vortec heads and alum intake.I appreciate the info,and will be doing the set up you suggest.I have seen your pdf and I have a dial back timing light.As far as the air filter height,I'm using the air filter supplied it has the typical 3"filter.Before purchasing the engine I was told their could be a height issue.I will try to contact the member you gave me. alsowhen I drove the car with no vac .connection I noticed a higher than normal operating Temperature.Perhaps when connecting the vac. temps will return to normal (155-170).
Thanks to Joe,Jim,and ed also

Francis


The air cleaner supplied is almost certainly not a drop down style. It will almost certainly cause height problems. The problem is the drop down style might not fit on your supplied carb----a real conundrum.

The vacuum advance will lower engine temps. That's one of the reasons I consider it essential for street operation.

[Duke W.]

Re: best wa vs gm way ??

You can find the pdf here:

DukeWilliamsEngineTuningPerformance&EconomySeminar .pdf (application/pdf Object)

My understanding is that the optimum WOT spark advance for Vortec heads is 32, but that might be conservative, so you might want to try 34-36 and see if that improves the SOTP feel.

The spring kit mentioned in the pdf is for single point distributors. There is a different kit for HEI, but I have used single point springs in HEIs. The HEI kit number should be easy to find with a Google search.

The reasons to use vacuum advance on a road engine are thoroughly explained in the pdf. In addition to lower low speed driving coolant temperatures, it will reduce fuel consumption.

Duke

[Francis F.]

Re: best wa vs gm way ??

Yes you are correct Joe,my orig. drop down has two 3/8 pipe elbows on the bottom of.It .it was an A I R engine when it left the factory for La.
and it does not sit down properly on the Holley #670 provided.I found an air filter 1"shorter in height,will try soon with the base unit supplied.
I will work on the vacuum set up next.
thank's Francis

[Francis F.]

Re: best wa vs gm way ??

Duke,I don't know what I would do with out you and the members of this orginization..Thanks again.
Francis

[Francis F.]

Re: best wa vs gm way ??

JOE,yes one of the problems to overcome.I got a filter today ,looks similar to the corvette type and is 2* tall as opposed to the orig. 3*filter and looks like problem solved..
I appreciate all your input thank's,Francis