63 FI Timing Question/Vacuum Advance

[John F.]

Does 8 deg initial timing sound right at 750-800 RPM?

With Vacuum Advance disconnected and hose plugged i'm getting 25deg advanced at 2500RPM
With Vacuum Advance connected i'm getting 42deg advance at 2500 RPM

thanks

[Don H.]

Re: 63 FI Timing Question/Vacuum Advance

John, I assume you are running a "022" distributor. I just installed one and that is about what I was getting BUT I am not an expert so hopefully others will respond. Don H.

[John F.]

Re: 63 FI Timing Question/Vacuum Advance

Correct Don. All stock. Distributor is 1115091. Vacuum advance I believe is 022 but possibly an 028. Hopefully I'll get more responses.

[Duke W.]

Re: 63 FI Timing Question/Vacuum Advance

Does 8 deg initial timing sound right at 750-800 RPM?

With Vacuum Advance disconnected and hose plugged i'm getting 25deg advanced at 2500RPM
With Vacuum Advance connected i'm getting 42deg advance at 2500 RPM

thanks

Probably not, but you haven't provided enough data. The '63 FI engine OE VAC was the 15.5" 201 15, but it was ported vacuum advance. OE centrifugal is start @ 700, 24 @ 4600, so you should be running 14-16 initial and no vacuum advance is added at idle.

Ideally you should convert to full time vacuum advance with a 8" B28 (OE 236 16) as used on '64-'65 SH/ FI engines along with as close as you can get to the companion centrifugal curve, start @ 700, 24 @ 2350.

1963 was the first year that Chevrolet equipped Duntov cam engines with vacuum advance and they clearly screwed the pooch. God only knows why they chose ported vacuum advance for the FI engine. The 340 HP engine used the same VAC with full time advance, but the VAC didn't pass the Two-Inch Rule. I struggled with idle instability and stalling until I figure out the Two-Inch Rule and converted my 340 HP SWC to the '64 map circa 1965. It was sweet running after than and more low end torque.

They got it right in '64 including full time vacuum advance for the FI engine, and I recommend that '64-'65 SHP/FI spark advance map for all mechanical lifter small blocks including LT-1, which has an emission control oriented spark advance map.

Google my name San Diego Corvette and study my tuning seminar.

Duke

[John D.]

Re: 63 FI Timing Question/Vacuum Advance

Correct Don. All stock. Distributor is 1115091. Vacuum advance I believe is 022 but possibly an 028. Hopefully I'll get more responses.

John, The Distributor COIL is an '091. The '63 FI distributor itself is an '022. The service replacement/aftermarket vacuum advance is a B28.

If the vacuum advance was original it would be a 201. The'63 vacuum advance is a rare two piece front vacuum advance.

It's late and I have been working unloading the vendor trailer from Corvette Carlisle. Now my shop/garage is totalled. Whew!!!!

Hope I figured out your post correctly. 750 RPM on a '63 with an 097 cam is really a low idle.You must have a very good engine. John D.

[John F.]

Re: 63 FI Timing Question/Vacuum Advance

Thanks Duke. As John D corrected me, I do have the 022 distributor and the B28 VA. I'm a bit confused by what the book says with the centrifugal advance Start at 0 deg @ 700 RPM, intermediate at 11 deg @ 700 RPM and end at 24 deg @ 4600 RPM. Start and intermediate are both at 700 rpm with 0 and 11 deg are confusing to me.

[Duke W.]

Re: 63 FI Timing Question/Vacuum Advance

That's an obvious error in the shop manual. The '63 FI centrifugal is the same as all other '63 Corvette engines, so the intermediate is 11 @ 1600. The intermediate is right in the AMA specs, but the maximum is wrong, which is correct in the shop manual.

Duke

[John F.]

Re: 63 FI Timing Question/Vacuum Advance

Ok thanks. Thought that was strange. So if the centrifugal advance is working properly and I set the initial timing to 14-16 deg advanced like you suggested, I should be around ~25-27 deg at 1600RPM and ~35-37 deg at 4600RPM or am I off? appreciate the help and advice, as I'm not knowledgable at this.

[Duke W.]

Re: 63 FI Timing Question/Vacuum Advance

The problem with trying to set initial timing, assuming your centrifugal is OE, you have to bring engine speed down below 700, which is where the centrifugal starts. Good luck getting it to run long enough to do the job before it stalls.

A better way is to rev the engine a few hundred RPM above the point of maximum centrifugal and set what's called total WOT advance in the 36-40 range lwith a dial back timing light, as high as possible in that range as long as it doesn't detonate. Make sure the VAC is disconnected and the signal line plugged with a golf tee.

Even though the centrifugal starts below reasonable idle speed on your engine, it's lazy - doesn't all come in until 4600.

The first thing you should do is use a dial back light to determine what the centrifugal specs are... OE or something different. If OE get a Mr. Gasket 928G spring kit and install the lightest springs which are either silver or gold. That should get total centrifugal in by no more than 3500, but about 2500 is ideal for your engine.

If you want to understand all this better, google my name san diego corvette and download and study my tuning seminar.

If you want to optimize the "tune" of your engine, convert it to full time vacuum advance, and the B28 will pass the Two-Inch Rule assuming it has a OE equivalent Duntov cam or something close.

Duke

[John F.]

Re: 63 FI Timing Question/Vacuum Advance

Hi Duke,

Here is some more info. Running 110 Cam2 Racing Gas with 097 Duntov cam. Not sure what the HG measures yet but will work on figuring that out. Running a new CC B28 canister.

With VAC disconnected
4800 RPM - 30deg
1600 RPM - 15 deg
650/700 RPM - 7 deg

With VAC connected
4800 RPM - 48deg
1600 RPM - 33deg
650/700 RPM - 8deg

thoughts? i'm thinking I need lightest springs like you suggested? probably too advanced on the high end?

[Duke W.]

Re: 63 FI Timing Question/Vacuum Advance

I guess you didn't read my tuning seminar that I recommended earlier in the thread. If you did you would know that optimum total WOT advance is in the range of 36-40 and brought in as quickly as possible with detonation being the limiting factor. Rather than being too advanced, the engine is considerably under-advanced, which is leaving power and fuel economy on the table. At that value initial will be in the range of 12-16.

It looks like the VAC is adding 18 rather than the 16 degree spec. max, but that shouldn't be a problem. With a quicker curve total maximum cruise advance - if you're cruising at above the rev level where centrifugal is all in, will be in the low to mid fifties.

I've set up many mechanical lifter cam small blocks with this map including my own '63 340 HP engine back circa '65 when I figured out that Chevrolet basically screwed it up, and all owners were very happy with the new found low end torque (and sometimes top end power) and lower fuel consumption.

I doubt if your engine needs Cam 2 race gas - at least for detonation control the way your spark advance map is currently set up and even with the aggressive map I recommend - but it will help ward off the percolation demons.

Measure the thickness of the head gaskets at the corners of the head-block interface. All '63 SHP/FI engines were assembled with two .018" head gaskets at Flint, and rebuilt engines usually have thick composition gaskets, so the actual CR with OE equivalent pistons, the OE 461X heads (60-61 cc chambers) and nominal deck height is about 10.8, and if the decks are high, which is common, it could be as low as 10.5, which is a far cry from the advertised 11.25:1.

When you report idle vacuum be sure to also report the actual idle speed, and I recommend about 900.

Duke

[John F.]

Re: 63 FI Timing Question/Vacuum Advance

Sorry Duke. I'm trying. I read a few things you wrote but it's a little over my head. Just trying to tweak this FI motor to run smoothly and there are too many variables for this young guy. I run the Cam2 because that is what was recommended by Jerry B and it's a top flight car that doesn't get driven too much. Gail P built the unit for me. I'll have to check the head gaskets.

Here is the latest after I bumped up the initial timing from 8 to 15.

No VAC connected and vacuum gauge connected where canister would normally plug in.
800-900RPM 15deg with 7in hg
1000 RPM 17deg with 11in hg
2500 RPM 34deg with 20in hg
4500-4600 RPM 36deg with 20in hg

With VAC connected
800-900 RPM 17deg
1000 RPM 19deg
1400 RPM 39deg
2500 RPM 50deg
4500-4600 RPM 55deg

It has rough idle if below 1000 rpm but that may be my spider which I'm going to replace or could be that it's running 210-230deg here in the driveway.

[Duke W.]

Re: 63 FI Timing Question/Vacuum Advance

Your idle vacuum reading is not valid. The '63 FI system is set up with ported vacuum advance, so unless it's been modified, teeing into the VAC signal line won't give a valid manifold vacuum reading at idle speed, but since the B28 VAC is fully deployed at only 8" it's seeing some vacuum advance at idle, but it doesn't pass the Two-Inch Rule, so the total idle advance is dithering around, which can lead to poor idle quality and stability. Total idle advance should be constant.

Try teeing into the ratio lever signal line.

Your total WOT advance is now at the bottom of the 36-40 range, and it should feel stronger, SOTP, and lighter springs will make it stronger down low.

Full time vacuum advance is a very good idea, but off the top of my head I'm not sure how to implement it on the '63 FI system. The air meter could probably be modified to move the VAC signal port to below the throttle plate as can be done with carburetors.

Maybe John D. has an idea.

When the tank is nearly dry, put in about 3 gallons of pump premium, and test for detonation and percolation. If if runs okay run the test again until you feel comfortable that it will run okay on pump premium. If the first test fails, just add some race gas. Usually detonation can be controlled with as little as a 25 percent blend of race gas or avgas, and about 50 percent will usually significantly mitigate percolation to the point where it's not a big issue other than under extreme conditions were you wouldn't want to be driving a car without AC, anyway.

Duke

[John F.]

Re: 63 FI Timing Question/Vacuum Advance

I'm not sure I completely understand the 2 inch rule or why it doesn't pass or what I should do to get it to pass. I did put about 40 miles on the car this afternoon and it ran much better and had a good idle at 700-800 RPM . The only issue was getting out of first gear. it seamed like it needed too many RPMs to getup and go and wanted to hesitate at 1500-2000 RPM. It did have much more power at the low end but I think it should still be more. I'll try getting some lighter springs and see what that does but what do you suggest on how to fix the total idle advance? I'm not really looking to modify the air meter. As far as the vacuum reading I took, it was unhooked from the VAC and plugged directly into the gauge. No Tee. wouldn't this be where I want to measure it since it's going directly into the B28?

[Kent S.]

Re: 63 FI Timing Question/Vacuum Advance

Regarding a source for full time vacuum, I think I remember a fitting on the back of the plenum for a Power Brake vacuum source. I used this on an FI unit I had in a '57, but it was made of mix and match parts so maybe the plenum was not a '63.