Engine: Tuned with vacuum gauge

[RDWEAVER]

Today I thought I would check my intake manifold vacuum on my V-8 Studebaker. I was in the process of checking the tune on the engine. The 289 was completely rebuilt last year and runs great but it never hurts to check.

I adjusted idle screws on the carb. I checked the timing and it was little beyond (ahead of) the mark on the damper, maybe a half inch so I figure about 8 degrees initial advance. It's a WCFB carb with ported advance unhooked. Motor was warmed and idle was at 675 RPM. The vacuum gauge was steady at 11" Hg. at idle. Normal is supposed to be 17-21"Hg. If I speed up the engine it will go up to 20"Hg. at about 2500 RPM. I have a tune up guide that lists a lot of the readings encountered when tuning with a vacuum gauge and the cause of the abnormal readings. Well, this says that my valve timing is late or late ignition timing. I am sure the timing is correct...... I double checked this. But if I advance the timing more it will move up to about 17"Hg. Problem with this is when the weighted advance and vacuum is all in its too much advance on the ignition. It is a Pertronix conversion in the distributor. I am using a reground R1performance spec. cam from Phil Harris. Do I need to try to change my valve timing?

[StudeRich]

You should not need to change your Valve Timing, Studebaker didn't when using the R2 Cam, however what are the Valve Clearances Set at?

On a Stock Grind R1/R2 Cam, the Intake AND Exhaust should be at .026 to .027 Cold to achieve .024 to .025 Hot, and IF you have an R2+ Harbit/Fairborn Cam, you COULD go a little tighter than the stock setting.

[bensherb]

By 2500 rpm all your advance should be in. What is your total advance? You should get about 30 degrees from the mechanical advance and another 15 degrees from the vacuum advance for a total of about 45 degrees. 675 rpm seems a bit low for an idle, my 289 won't idle that low well,I run it around 800-900, but you should get around 20"hg vacuum at idle.

[RDWEAVER]

I can set the idle up higher and the go up some but not to 20. It might make 14. I am not sure about total advance. I will need to find a tape for the diameter of the balancer.
And then get back to you after checking the advance curve.

[Bud]

Like Rich says, check the valve lash as incorrect clearance will cause a low vacuum reading. A stock non R distributor should have about 24 degrees centrifugal advance at 2400 engine rpm and around 15 degrees vacuum advance at 13 inches vacuum. A low and steady reading does indicate incorrect valve or ignition timing, but a vacuum leak will also give a low reading. Be sure that there no vacuum leaks and adjust the valves before doing anything else. The 289 in my 62 GT has an R3 cam in it and it shows around 16 inches of vacuum at 650 rpm and my Avanti with an Isky ST5 cam shows about the same. It is also possible that the harmonic balancer is assembled incorrectly which is tough to do but not impossible which puts the timing mark in the wrong location. Bud

[RDWEAVER]

Like Rich says, check the valve lash as incorrect clearance will cause a low vacuum reading. A stock non R distributor should have about 24 degrees centrifugal advance at 2400 engine rpm and around 15 degrees vacuum advance at 13 inches vacuum. A low and steady reading does indicate incorrect valve or ignition timing, but a vacuum leak will also give a low reading. Be sure that there no vacuum leaks and adjust the valves before doing anything else. The 289 in my 62 GT has an R3 cam in it and it shows around 16 inches of vacuum at 650 rpm and my Avanti with an Isky ST5 cam shows about the same. It is also possible that the harmonic balancer is assembled incorrectly which is tough to do but not impossible which puts the timing mark in the wrong location. Bud

It runs too good for the balancer to not be assembled correctly. I can check valve clearance again. I can rule out vacuum leaks. I am still looking for a tape to stick on the balancer to determine the advance curve. I hope I didn't get an R3 cam by mistake.

[PackardV8]

Yes, an R1 cam will have lower vacuum, especially if used with the dished 8:1 pistons. Which pistons were used and which head gasket? If you have Phil's R2+ performance cam (similar to the Iskenderian ST5), it will have still lower vacuum than the 17-21", but it still should pull 15-16" minimum.

It's possible to get very close to an exact timing reading without a timing tape. Use a dividing caliper, measure between UDC and the IGN mark. IIRC, that should be four degrees. Then mark out more increments of the same. You'll be able to read it within a degree or two.

As an experiment, advance the idle timing until it reaches the highest vacuum reading and begins to drop. Back off to the highest steady reading and let us know what you find.

Try two or three different timing lights. None but the very simple units can be trusted. The "dial-back" units are especially prone to giving erroneous readings.

Setting up a distributor on the engine is a slow and tedious process. Then, if it needs to be changed, the distributor has to be removed anyway. If you have an R1 cam, you need the R1 advance curve in the distributor. Consider pulling your distributor and having the centrifugal and vacuum advances set on a machine. It goes much quicker and is more accurate.

Finally, don't worry too much about what the timing light says. Each engine, especially one built to a semi-custom spec, will need to be done by ear. Advance the timing until it pings on a hard uphill pull on a hot day, then back off until it doesn't. And don't be a CASO and try to get by with regular grade fuel. As few miles as our Studes get, buy the best name brand fuel, as often as possible from the same pump at the same station. That will narrow the variables of your tune.

jack vines

[RDWEAVER]

Yes, an R1 cam will have lower vacuum, especially if used with the dished 8:1 pistons. Which pistons were used and which head gasket? If you have Phil's R2+ performance cam (similar to the Iskenderian ST5), it will have still lower vacuum than the 17-21", but it still should pull 15-16" minimum.

It's possible to get very close to an exact timing reading without a timing tape. Use a dividing caliper, measure between UDC and the IGN mark. IIRC, that should be four degrees. Then mark out more increments of the same. You'll be able to read it within a degree or two.

As an experiment, advance the idle timing until it reaches the highest vacuum reading and begins to drop. Back off to the highest steady reading and let us know what you find.

Try two or three different timing lights. None but the very simple units can be trusted. The "dial-back" units are especially prone to giving erroneous readings.

Setting up a distributor on the engine is a slow and tedious process. Then, if it needs to be changed, the distributor has to be removed anyway. If you have an R1 cam, you need the R1 advance curve in the distributor. Consider pulling your distributor and having the centrifugal and vacuum advances set on a machine. It goes much quicker and is more accurate.

Finally, don't worry too much about what the timing light says. Each engine, especially one built to a semi-custom spec, will need to be done by ear. Advance the timing until it pings on a hard uphill pull on a hot day, then back off until it doesn't. And don't be a CASO and try to get by with regular grade fuel. As few miles as our Studes get, buy the best name brand fuel, as often as possible from the same pump at the same station. That will narrow the variables of your tune.

jack vines

Jack- Yes this engine has the Hyperutectic dished pistons with the steel (thin) head gaskets.

I don't think I have the R2+ cam.... no noticeable valve overlap lope. I will have to check my paperwork from Phil. Anyways I just checked it again this morning and by adjusting the diz and keeping the idle below 850 the best it does is 14. Rev it up and it jumps up to 19. ????
Thanks.

[tsenecal]

Thanks for some great tips, Jack. My 289 with R1 cam, and flat top pistons, still needs to be "dialed in". Your contribution will help me out immensely. I have the old basic timing light, and had considered buying the dial back style, but with your comment about them, I may reconsider. With enough good marks on the balancer, it may not be necessary.

[Dwain G.]

Where exactly is the vacuum gauge being connected on the engine?

[345 DeSoto]

Shouldn't a "hotter" cam run a bit less vacuum...

[Champ51]

Before spending too much time on the car, check your vacuum gauge for accuracy. I just had to replace one after finding it no longer read correctly.

[RDWEAVER]

Where exactly is the vacuum gauge being connected on the engine?

I am connecting the gauge into the intake manifold on the 3/8" pipe threaded hole on the rear left side of the manifold. I have a fitting installed there just for this test. I think if I had had a brake booster it might hook up there.

[RDWEAVER]

Before spending too much time on the car, check your vacuum gauge for accuracy. I just had to replace one after finding it no longer read correctly.

I did this today, I rigged up some fittings for my refrigeration gauge and compared these two. They were the same reading.

[RDWEAVER]

I found another balancer plate in the shed and measured the diameter. It is 7.93750". Studebaker's 4 degree mark is .2850" from U.D.C. 1.