Vacuum leak? Marc has me confused now!

[scottfab]

Originally Posted by RIP

When you draw a vacuum the small white piston in drawn in, separating the points and shutting the pump off. With a hand operated vacuum pump you should be able to see the points open and close. You could try to use your mouth. Suck, baby, suck.

If the contacts are corroded they can be cleaned up with alcohol and covered with dielectric grease. If the pump runs for
ever it might be that
the diaphragm (in the round section of the pump) has a void in it.
It looks like this and is repairable using a rubber from a kitchen glove.

[weldbead]

seems most of the system is under the plenum..can someone tell me where to get fsm's?i need diagrams etc..thx..

[John Boothby]

ebay. Three manuals.

1. Field Service manual covers both standard and ZR-1.

2. LT-5 Supplement. Covers the LT-5 engine.

3. Electrical manual. Covers electrics.

Expect to pay $100 to $150 for all 3.

[Hib Halverson]

Originally Posted by scottfab

If the contacts are corroded they can be cleaned up with alcohol and covered with dielectric grease. (snip)

Now, Scott...

...don't you know alcohol is for drinking and "contact cleaner" is for cleaning electrical connections.

[Hib Halverson]

Originally Posted by We Gone

Another reason they used a 3.07 rear gear was to keep the RPMs under 6500 as the radiator was designed to bypass at higher RPMs due to higher water pressure. They had to keep it cool!!

Originally Posted by Paul Workman

And, too: does not the coolant pump begin cavitation just north of 5500 rpm?

Also, I read a comment (in Heart Of The Beast(?)) regarding the desire of limiting the rpm to place the LT5 in its peak torque region.

Guys, guys...maybe we're "overthinking this"?

The Record Run took place on 1-2 March 1990. Ever been to central TX in March? At night, it's freakin' cold...in the high-20s. Plus, during the 24-hr period the RR was staged, it snowed and rained. At start time on 1 March it was 35°F. Cooling was not an issue because 1) the low ambient and 2) since the engine was running at only part throttle, cooling load was reduced.

Limiting RPM to place the LT5 at peak torque, regardless of what Heart of the Beast may say, was not an issue, either. Besides, with a throttle stop, the engine was not making peak torque, anyway.

The main reasons for the throttle stop were 1) fuel mileage and range, 2) durability and 3) ensuring drivers would not exceed a TPS value which would compromise 1 and 2.

[Hib Halverson]

Originally Posted by John Boothby

ebay. Three manuals.

1. Field Service manual covers both standard and ZR-1.

2. LT-5 Supplement. Covers the LT-5 engine.

3. Electrical manual. Covers electrics.

Expect to pay $100 to $150 for all 3.

I think the car in question is a 94.
The Factory Service Manual set for a '94 has only two volumes covering both VIN P and VIN J (LT5) engines. I've seen them on eBay but, also, Zip Products stocks Service Manuals, and they're the real thing not reprints or scans. In recent years, I've been getting my manuals from Zip. See this web page

[Paul Workman]

Originally Posted by Hib Halverson

Guys, guys...maybe we're "overthinking this"?

The Record Run took place on 1-2 March 1990. Ever been to central TX in March? At night, it's freakin' cold...in the high-20s. Plus, during the 24-hr period the RR was staged, it snowed and rained. At start time on 1 March it was 35°F. Cooling was not an issue because 1) the low ambient and 2) since the engine was running at only part throttle, cooling load was reduced.

Limiting RPM to place the LT5 at peak torque, regardless of what Heart of the Beast may say, was not an issue, either. Besides, with a throttle stop, the engine was not making peak torque, anyway.

The main reasons for the throttle stop were 1) fuel mileage and range, 2) durability and 3) ensuring drivers would not exceed a TPS value which would compromise 1 and 2.

RE: peak torque at the Record Run (RR):

Well, of course the motor wouldn't be making max torque with the throttle stop, compared to WOT. But, rather I was referring to the shape of the torque curve, i.e., where the torque azimuth occurs, assuming no significant change in the curve, regardless of throttle being at 70% vs. 100%.

I refer to one of many graphs I can produce which share the same general torque curve shape as the one (below). Notice the torque reaches azimuth around 5200 rpm for this particular motor - which forms the basis of my comment. (Note: This happens to be a modded motor, but I can produce several graphs - all having very similar curve characteristics if need be.)





Considering the 3.07 differential affect on speed vs. rpm for a stock diff gear: 3.07/3.45 = rpm factor = 0.8899. By multiplying the rpm for a stock ZR-1 (5th gear) required for speed close to the average of the Record Run (6000 rpm ≈ 177 mph from the chart (c/o Haibeck Automotive)), the result is (6000 x .8899) = 5339 rpm w/ the 3.07 differential gear. That's purdy dang close to the peak torque value. Just a coincidence? If Young didn't quote someone for his "HEART OF THE BEAST", he at least did the math, I recon.

[Hib Halverson]

What's a "torque azimuth"?

In your calcs, did you figure tire size?

The RR speed (175.885) was an average so the speeds on the track were faster. About 190 at corner entries or about 5500RPM in fifth gear. The car had slowed to about 170 at corner exits.

[Paul Workman]

Originally Posted by Hib Halverson

What's a "torque azimuth"?

In your calcs, did you figure tire size?

The RR speed (175.885) was an average so the speeds on the track were faster. About 190 at corner entries or about 5500RPM in fifth gear. The car had slowed to about 170 at corner exits.

Originally Posted by Hib Halverson

Guys, guys...maybe we're "overthinking this"?
...

"Apex" would have been a better choice than azimuth, my bad; peak torque, to be clear...is the point.

With that cleared up, my point is/was choosing a 3.07 differential gear would obviously put the LT5 rpm right in the sweet spot of the torque curve; with the LT5 passing through the peak of the curve on every lap and remaining near the peak most of the time.

As for tire size, if the tires were not the stock 315x35x17 size, then the results would be skewed more or less, depending on the amount of departure the tires used on the Run were from the stock tire size. (What were the tire make/model/size used on the Run?)

So, it strikes me that choosing the 3.07 ratio for the differential, resulting in the motor operating near peak torque the whole time (in 5th gear) was not accidental, but a major consideration - along with limiting motor output for all the reasons you mentioned.

[Hib Halverson]

The tires were not stock.

They were Goodyear Racing Eagles which were made specifically for the Record Run. I can't remember the size. I'll have to do some digging to see if I still have that information.

And yeah, the 3.07 axle was selected so the car could run 190 mph in fifth gear. As for if that was the optimal ratio? Maybe not but the 3.07 was the tallest ratio available for a D44 in a Corvette. The 2.73 and 2.59 ratios for D36 gearsets.