Dumb question re 70 LT-1

[Ed H.]

Re: Dumb question re 70 LT-1

E10 has three percent less energy than straight gasoline, so the lmileage drop would be tough to measure.

The 3310 is a generic carburetor and is likely very rich.

LOL, my nose says it's rich, but curiously the plugs don't look 'bad'.

If the compression ratio was lowered at some point that could increase fuel consumption by 5-10 percent.

Pistons are stock, but I am uncertain as to gasket thickness. When I rebuilt it in '78 I also used thicker gaskets and saw numbers ave 15 mpg.

The ported vacuum advance and lazy spark advance map probably costs at least 5 percent relative to the optimum map, which would be the same as OE on the 365/375 HP 327s.

I need to check 'ported'. Now running 11 degrees advance @ 1700, 19 @ 3200, 28 @ 4400. Reading your San Diego Paper, I think that's 'lazy' :-)

A change in axle ratio without installing the proper speedo gears or a non-OE revs per mile tire could cause either an indicated increase or decrease in fuel consumption.

Speedo currently not working but, from memory, was accurate. Tire dia approx the same as before.

The driving environment is a big factor. As the ratio of highway/freeway driving to around town driving goes down, fuel consumption will increase as it will when average trips length is reduced.

So there are a lot of variables, but the first things I recommend you work on (oops, erased it...) carb and advance.

I'm still waiting on Holley to confirm jets and power valves. I'll check vac levels this week. It will likely be later July/Aug before we do dyno time.

Duke

Thank you, again, for your assistance. I very much appreciate it.

[Ed H.]

Re: Dumb question re 70 LT-1

I really wonder why anyone with a HP Corvette gives a rats ass about the gas mileage. Just asking?

Well for one thing I'm curious. Since once it was 15 or better, and now it's 11, I'd like to know why. If you wouldn't, that's quite OK, too.

[Edward J.]

Re: Dumb question re 70 LT-1

Ed, I always take the easiest stuff first, timing, mixture, tire pressure, auto choke setting ( make sure not staying on to long), do not let the car idle when started for to long after start). when looking for the best fuel economy it has a lot to do with driving habits, so keep in mind easy take offs and shift points. I also note that here in the northeast winter and summer fuel blends effect mileage (winter blends drop mileage) Hope this helps.Ed

[Ed H.]

• Normally plugged into carb port under front float bowl, which I believe to be the correct location.

[Tom D.]

Re: Dumb question re 70 LT-1

Love the mention of Monfort. My Dad talked about that company a lot. He raised cattle.

[Duke W.]

Re: Dumb question re 70 LT-1

• Normally plugged into carb port under front float bowl, which I believe to be the correct location.

.

That's high for a LT-1... 12" in that idle speed range would be what I expect.

Is the VAC port on the car set up for full time or ported vacuum advance? I believe the OE VAC was stamped 201 15. What's the data stamped on the installed VAC. You may have to loosen the dist. cap to see the stamped data.

Duke

[Terry M.]

Re: Dumb question re 70 LT-1

Love the mention of Monfort. My Dad talked about that company a lot. He raised cattle.

Monfort had huge feed lots in Greeley Colorado. You could smell them before you could see them. The truckers hauled "swinging beef" from Colorado all over the country. Their tractors were very powerful and the consistently ran 90+ mph. I had to stop for fuel before they did, even with my modified a 32 gallon gas tank. Those were fun times. I hauled Strohs west and Coors east. That paid for the trip.

[Joe L.]

Re: Dumb question re 70 LT-1

That's high for a LT-1... 12" in that idle speed range would be what I expect.

Is the VAC port on the car set up for full time or ported vacuum advance? I believe the OE VAC was stamped 201 15. What's the data stamped on the installed VAC. You may have to loosen the dist. cap to see the stamped data.

Duke

Duke------


The LT-1 distributor used vacuum control GM #1115360.

[Ed H.]

Re: Dumb question re 70 LT-1

That's high for a LT-1... 12" in that idle speed range would be what I expect.

Is the VAC port on the car set up for full time or ported vacuum advance? I believe the OE VAC was stamped 201 15. What's the data stamped on the installed VAC. You may have to loosen the dist. cap to see the stamped data.

Duke

OK, I cheated. Paper work from Dave Fiedler indicates "201 15 vacuum control".

When Comcast decides I'm worthy of receiving email I'll augment with a photo of vac line to carb connection. Taking photos with phone and emailing to myself works great, sometimes...

OK, I figured out another way...

[Duke W.]

Re: Dumb question re 70 LT-1

The carb can be internally configured for either ported or full time vacuum advance. Easy way to tell is remove the line from the VAC and feel whether it has vacuum or tee a vacuum gage into the signal line and see if it shows the same vacuum as teeing into the choke vacuum break hose.

I believe the VAC varied over the three years that the LT-1 was in production. Answers are in the AMA specs...not the part numbers, but the specs.

Duke

[Joe L.]

Re: Dumb question re 70 LT-1

The carb can be internally configured for either ported or full time vacuum advance. Easy way to tell is remove the line from the VAC and feel whether it has vacuum or tee a vacuum gage into the signal line and see if it shows the same vacuum as teeing into the choke vacuum break hose.

I believe the VAC varied over the three years that the LT-1 was in production. Answers are in the AMA specs...not the part numbers, but the specs.

Duke

Duke------


Upon doing some further checking, I find some variance as to what vacuum control was used for 1970 LT-1. Some sources say it was the GM #1116201. Some say it was the GM #1115360. And, some say it was the GM #1116163.

The GM #1116201 was discontinued from SERVICE in January, 1965 and replaced by the 1116163. However, it's possible the 1116201 was used in PRODUCTION after that time. The 1116201 and 1116163 have similar specifications. The 1115360 has considerably different specs.

[Duke W.]

Re: Dumb question re 70 LT-1

Joe - are you sure it's 1116201 and not 1115201?

It's very odd that GM replaced the "201" with the ...163 in '65 as the 201 was used in several later production engines including the '67 L-71 and maybe in the '68/9 versions, and I think it's first use was '62, but may go back farther. Typical published specs are start @ 8", 15@15.5"

I have always described the ...163 as a "boat anchor" because it may take as much at 18" to fully deploy, so it doesn't even meet the Two-Inch Rule for a base pre-exhaust emission control engine. The aftermarket picked up on the parts books applications for the 163, and it's still available in most brands and stamped B1 for the same applications that GM calls out the 163. Base engines with full time vacuum advance should use the 15" B22. which is within production tolerance of the 201.

The only application I know of for the ...360 is L-72. Specs are start @ 6", 12 @ 12" and it's okay to use when converting L-72s to full time vacuum advance.

Duke

[Joe L.]

Re: Dumb question re 70 LT-1

Joe - are you sure it's 1116201 and not 1115201?

It's very odd that GM replaced the "201" with the ...163 in '65 as the 201 was used in several later production engines including the '67 L-71 and maybe in the '68/9 versions, and I think it's first use was '62, but may go back farther. Typical published specs are start @ 8", 15@15.5"

I have always described the ...163 as a "boat anchor" because it may take as much at 18" to fully deploy, so it doesn't even meet the Two-Inch Rule for a base pre-exhaust emission control engine. The aftermarket picked up on the parts books applications for the 163, and it's still available in most brands and stamped B1 for the same applications that GM calls out the 163. Base engines with full time vacuum advance should use the 15" B22. which is within production tolerance of the 201.

The only application I know of for the ...360 is L-72. Specs are start @ 6", 12 @ 12" and it's okay to use when converting L-72s to full time vacuum advance.

Duke

Duke-----


GM #1116201 is the only part number I have. I can find no reference, at all, going back to at least 1959 of any part of GM #1115201. If it ever existed, it was either a PRODUCTION-only part number, a part only used on non-Chevrolet GM models prior to 1973, or a Delco parts system-only part number. I kind of doubt any of these possibilities, though, since 1115201 would have been a part number in a series that Delco-Remy generally used for ignition coils (e.g. 1115202 and 115207 are coils)

[Ed H.]

Re: Dumb question re 70 LT-1

The carb can be internally configured for either ported or full time vacuum advance. Easy way to tell is remove the line from the VAC and feel whether it has vacuum or tee a vacuum gage into the signal line and see if it shows the same vacuum as teeing into the choke vacuum break hose.

I believe the VAC varied over the three years that the LT-1 was in production. Answers are in the AMA specs...not the part numbers, but the specs.

Duke

OMG, the more one thinks one knows, the more stuff one knows one doesn't know... I need to parapharse my Mother, who had her Masters in Shakespeare, "Duke, it's Greek to me!" 'choke vacuum break hose'. Heck, I just discovered the choke isn't working. This car never had an automatic choke in my tenure, so it's all new to me. Car starts fine, but has a bit of a time deciding whether to keep running for a bit, LOL. I thought perhaps the fast idle needed an adjustment and discovered the required infrastructure is elsewhere.

The VAC line has an indicated ~ 16" at idle. You mentioned that you thought that was high. I'll see if I can get my hands on second to compare readings.

It will all work out, but in the mean time I'm losing my self reading things by John Hinckley, your San Diego presentation (I tried to print it, but white text on a black background doesn't work so well for printing purposes.) But it's all good, and we're having fun. If I've not mentioned it, Holley has responded and been quite helpful. In addition I've had some most instructive and helpful PMs, too.

Thank you, all! Ed

[Duke W.]

Re: Dumb question re 70 LT-1

Most Holleys have a small plastic vacuum pot that's connected to the choke linkage. Its purpose is to crack open the choke valve when the engine fires. It sees manifold vacuum full time, which is why it's a good place to tee into when converting from ported to full time vacuum advance. I'm not sure of the 3310 configuration, but since it was a widely used replacement carb, I expect it has a conventional Holley choke system. Your CSM should explain it for the OE Holley and I expect the 3310 is very similar.

Duke