1973 L48 tuning

[Douglas C.]

Am I correct that 73 stock distributor is limited to 14 degrees at around 4,200 RPM and Q Jet probably lean jetting. I assume a recurve to be around 36 all in (initial plus mechanical) under 3,000 and jetting change would enhance the factory tune. Anyone have a combination that refines overall driveability and performance?

Tks. Doug

[Duke W.]

Re: 1973 L48 tuning

I'm not sure what the centrifugal specs are of the '73 base engine, but they are in the CSM and AMA specs that you can download from the GM Heritage Web site. So what are they? And what are the VAC specs? TH400 or four-speed?

Do a Web search:

"tuning vintage corvette engines for maximum performance and fuel economy"

Use the quotes so the search engine looks for that exact phrase.

Pay particular attention to the chart on emission controlled engines, which includes converting OE ported vacuum advance configurations to full time and selecting the best functional fit VAC using the Two-Inch Rule.

A good starting point for the base engine spark advance map is 30 centrifugal at 3000-3500. That will require 6-10 initial to achieve the optimum WOT advance of 36-40, and a proper 16 degree VAC will place total idle advance at 22-26, which is in the optimum ballpark for base engines. with low the overlap 3896929 camshaft.

Duke

[Douglas C.]

Re: 1973 L48 tuning

I'm not sure what the centrifugal specs are of the '73 base engine, but they are in the CSM and AMA specs that you can download from the GM Heritage Web site. So what are they? And what are the VAC specs? TH400 or four-speed?

Do a Web search:

"tuning vintage corvette engines for maximum performance and fuel economy"

Use the quotes so the search engine looks for that exact phrase.

Pay particular attention to the chart on emission controlled engines, which includes converting OE ported vacuum advance configurations to full time and selecting the best functional fit VAC using the Two-Inch Rule.

A good starting point for the base engine spark advance map is 30 centrifugal at 3000-3500. That will require 6-10 initial to achieve the optimum WOT advance of 36-40, and a proper 16 degree VAC will place total idle advance at 22-26, which is in the optimum ballpark for base engines. with low the overlap 3896929 camshaft.

Duke

Talking 4 speed. I would also go to full manifold vacuum. Looking up the 73 factory specs it shows 12 initial and 14 distributor degrees at 4,200. Vacuum advance pod is probably i
n the 15 degrees range. I would not want to go beyond the factory 12 initial since the say, 15 vacuum pod would create around 27 idle idle. Beyond that may create low end towing the boat feeling. I think setting the distributor stop bushing at around 24 to get total all in of 36 and set springs to have that in around 3,000 rpm. Then cruising down the highway would be around 51 degrees. Maybe at that point best to get a vacuum pod a few degrees less than 15.

Just seeing is someone here has come up with a very nice balanced driving / performance combination.

Tks. Doug

[Duke W.]

Re: 1973 L48 tuning

14 distributor degrees is 28 at the crank and 12 initial would be 40 total WOT advance. 12 initial and 28 centrifugal is very unlikely for an emission controlled engine. What was your source?

The spark advance map I suggested for base small blocks in my previous post is proven.

Duke

[Douglas C.]

Re: 1973 L48 tuning

14 distributor degrees is 28 at the crank and 12 initial would be 40 total WOT advance. 12 initial and 28 centrifugal is very unlikely for an emission controlled engine. What was your source?

The spark advance map I suggested for base small blocks in my previous post is proven.

Duke

The site mobile.corvettestory.com under 1973, Ignition. It refers to distributor # 1112098.
It is not clear on distributor or crank degrees, so your point is well taken. I've looked and found conflicting data.

I know your previous write up and that is well written and on the money. I'm just wondering if by 73 with emissions components not found in 1970 and prior if your specifics would change somewhat.

Your information is always appreciated.

Tks. Doug

[Douglas C.]

Re: 1973 L48 tuning