https://www.hotrod.com/articles/back-basics-recurve-hei-distributor/
http://www.superchevy.com/how-to/97438/
http://garage.grumpysperformance.com/index.php?threads/finding-top-dead-center.967/
http://garage.grumpysperformance.com/index.php?threads/timing-tabs-and-indicators.1015/
http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/
https://pontiacstreetperformance.com/psp/distcurve.html
http://garage.grumpysperformance.co...stalling-the-intake-manifold-distributor.464/
https://www.onallcylinders.com/2019...-advance-curve-without-a-distributor-machine/
https://www.onallcylinders.com/2016/01/08/tuning-an-hei-distributor/
https://www.speedwaymotors.com/GM-H...ical-Advance-Curve-Weight-Spring-Kit,740.html
https://www.amazon.com/Pirate-Mfg-D...CE1F661RTCP&psc=1&refRID=C0QTGMMWPCE1F661RTCP
http://outintheshop.com/faq/hei.htm
Back To Basics: How To Recurve An HEI Distributor
Rocky RotellaAuthor
Sep 13, 2018
Reliability, a simplistic design with many interchangeable components, and heavy support by OE-replacement and aftermarket manufacturers alike makes GM's HEI among the best executed distributor systems ever produced. It was used exclusively by all GM brands beginning in 1975 and it carried on throughout the '80s.
The HEI was originally developed to generate high spark intensity for igniting the lean mixtures associated with low-compression V8s. Performance took a back seat to emissions and fuel economy and lazy advance curves were the result. Despite its catalytic-converter-era lineage, a conventional HEI with mechanical advance can be an excellent choice for today's modified engines with proper preparation.
Despite rotating at 2,000 rpm, the bright camera flash makes this GM HEI appear as if it's standing still. It gives clear insight on how the centrifugally-activated flyweights press against a specially formed center cam (or center plate) to mechanically advance spark lead. This happens as engine rpm increases while a pair of small springs control the advance rate.
Installing lighter-tension advance springs in an HEI that remains in its original application is oftentimes enough to produce noticeable results. But what happens when installing a used HEI in a non-stock application? One cost-effective solution is salvaging GM advance components from donor HEIs and combining them with the advance springs found in a commercially-available HEI advance curve kit. Here's how!
GM produced dozens of uniquely-shaped center cams and weights for its HEI over the years. Each is stamped with a three-digit identification number. Shown are a handful of those commonly found in popular applications that provide reasonable mechanical advance amounts for modern performance applications.
After decades of pirating advance components from swap-meet and salvage-yard HEIs, our collection includes several dozen individual GM center cams and centrifugal weights. Using our vintage Allen Syncrograph distributor tester (model 22-250), we painstakingly recorded the amount of mechanical advance that each center cam and weight combination yielded with a standard advance spring set and compared them to the many aftermarkets advance curve kits available.
Moroso's number-72300 HEI Advance Curve Kit includes three pairs of color-coded springs that directly correlates to spring tension. While we rarely use the light tension (gold) springs or its center cam and weights, the medium- (silver) and heavy-tension (gray) are excellent and make it worth the $15 purchase.
00:00 / 01:46
None of the aftermarket HEI advance curve kits included center cams and/or weights shaped identically to GM's high-quality originals. Instead, the kits share a common, oddly-shaped set that was little more than a one-size-fits-all assembly. The medium- and heavy-tension advance springs in those kits were of value, however, and those in Moroso's number-72300 HEI Advance Curve Kit, which can be purchased from any number of sources for less than $15, proved the best.
Installing a new GM center cam is straightforward. After removing the advance springs and weights from their posts, remove the E-clips retaining the cam and carefully pry upward until it's completely free. Using some fine sandpaper to polish the posts makes center cam installation easier. Proper orientation is required for optimal results so be sure that center cam numbers face up with clockwise rotating HEIs and down with counterclockwise rotation.
The chart below contains the mechanical advance values (in crankshaft degrees) for several GM center cam and weight combinations commonly found in some of the corporation's most popular '70s and '80s Chevrolet V8-powered passenger cars and light truck applications. They can be used in GM HEIs of any other make and excellent results are generally possible when combining them with Moroso's medium-tension (silver-colored) springs.
Mechanical Advance
Center Cam Number: Advance with 139 Weights: Advance with 053 Weights:
364 22 21
368 21 20
370 24 23
Knowing exactly how much spark advance, in crankshaft degrees, is ideal for maximum performance can vary with static and dynamic compression ratios, combustion chamber shape, fuel octane, piston dwell time as related to crankshaft stroke length, and other factors. We suggest consulting with an engine building and/or tuner professional who specializes in your particular make before swapping mechanical advance components. An excessive amount of spark advance can lead to detonation, which can damage your engine over time. Be sure to listen intently for any signs.
The new advance springs simply slide onto each respective post. Moroso's medium-tension springs tend to provide an advance curve that begins around 1,200 engine rpm and reaches maximum advance by 3,600 rpm. That's ideal for a typical street engine that operates on pump gas. Don't forget to lubricate the weight posts and slide as well as its contact points on the center cam with lightweight oil or grease to ensure smooth operation.
http://www.superchevy.com/how-to/97438/
http://garage.grumpysperformance.com/index.php?threads/finding-top-dead-center.967/
http://garage.grumpysperformance.com/index.php?threads/timing-tabs-and-indicators.1015/
http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/
https://pontiacstreetperformance.com/psp/distcurve.html
http://garage.grumpysperformance.co...stalling-the-intake-manifold-distributor.464/
https://www.onallcylinders.com/2019...-advance-curve-without-a-distributor-machine/
https://www.onallcylinders.com/2016/01/08/tuning-an-hei-distributor/
https://www.speedwaymotors.com/GM-H...ical-Advance-Curve-Weight-Spring-Kit,740.html
https://www.amazon.com/Pirate-Mfg-D...CE1F661RTCP&psc=1&refRID=C0QTGMMWPCE1F661RTCP
http://outintheshop.com/faq/hei.htm
Back To Basics: How To Recurve An HEI Distributor
Rocky RotellaAuthor
Sep 13, 2018
Reliability, a simplistic design with many interchangeable components, and heavy support by OE-replacement and aftermarket manufacturers alike makes GM's HEI among the best executed distributor systems ever produced. It was used exclusively by all GM brands beginning in 1975 and it carried on throughout the '80s.
The HEI was originally developed to generate high spark intensity for igniting the lean mixtures associated with low-compression V8s. Performance took a back seat to emissions and fuel economy and lazy advance curves were the result. Despite its catalytic-converter-era lineage, a conventional HEI with mechanical advance can be an excellent choice for today's modified engines with proper preparation.
Despite rotating at 2,000 rpm, the bright camera flash makes this GM HEI appear as if it's standing still. It gives clear insight on how the centrifugally-activated flyweights press against a specially formed center cam (or center plate) to mechanically advance spark lead. This happens as engine rpm increases while a pair of small springs control the advance rate.
Installing lighter-tension advance springs in an HEI that remains in its original application is oftentimes enough to produce noticeable results. But what happens when installing a used HEI in a non-stock application? One cost-effective solution is salvaging GM advance components from donor HEIs and combining them with the advance springs found in a commercially-available HEI advance curve kit. Here's how!
GM produced dozens of uniquely-shaped center cams and weights for its HEI over the years. Each is stamped with a three-digit identification number. Shown are a handful of those commonly found in popular applications that provide reasonable mechanical advance amounts for modern performance applications.
After decades of pirating advance components from swap-meet and salvage-yard HEIs, our collection includes several dozen individual GM center cams and centrifugal weights. Using our vintage Allen Syncrograph distributor tester (model 22-250), we painstakingly recorded the amount of mechanical advance that each center cam and weight combination yielded with a standard advance spring set and compared them to the many aftermarkets advance curve kits available.
Moroso's number-72300 HEI Advance Curve Kit includes three pairs of color-coded springs that directly correlates to spring tension. While we rarely use the light tension (gold) springs or its center cam and weights, the medium- (silver) and heavy-tension (gray) are excellent and make it worth the $15 purchase.
00:00 / 01:46
None of the aftermarket HEI advance curve kits included center cams and/or weights shaped identically to GM's high-quality originals. Instead, the kits share a common, oddly-shaped set that was little more than a one-size-fits-all assembly. The medium- and heavy-tension advance springs in those kits were of value, however, and those in Moroso's number-72300 HEI Advance Curve Kit, which can be purchased from any number of sources for less than $15, proved the best.
Installing a new GM center cam is straightforward. After removing the advance springs and weights from their posts, remove the E-clips retaining the cam and carefully pry upward until it's completely free. Using some fine sandpaper to polish the posts makes center cam installation easier. Proper orientation is required for optimal results so be sure that center cam numbers face up with clockwise rotating HEIs and down with counterclockwise rotation.
The chart below contains the mechanical advance values (in crankshaft degrees) for several GM center cam and weight combinations commonly found in some of the corporation's most popular '70s and '80s Chevrolet V8-powered passenger cars and light truck applications. They can be used in GM HEIs of any other make and excellent results are generally possible when combining them with Moroso's medium-tension (silver-colored) springs.
Mechanical Advance
Center Cam Number: Advance with 139 Weights: Advance with 053 Weights:
364 22 21
368 21 20
370 24 23
Knowing exactly how much spark advance, in crankshaft degrees, is ideal for maximum performance can vary with static and dynamic compression ratios, combustion chamber shape, fuel octane, piston dwell time as related to crankshaft stroke length, and other factors. We suggest consulting with an engine building and/or tuner professional who specializes in your particular make before swapping mechanical advance components. An excessive amount of spark advance can lead to detonation, which can damage your engine over time. Be sure to listen intently for any signs.
The new advance springs simply slide onto each respective post. Moroso's medium-tension springs tend to provide an advance curve that begins around 1,200 engine rpm and reaches maximum advance by 3,600 rpm. That's ideal for a typical street engine that operates on pump gas. Don't forget to lubricate the weight posts and slide as well as its contact points on the center cam with lightweight oil or grease to ensure smooth operation.
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