upgrade L48
Le Mans Master
Joined: Mar 2008
Posts: 5,948
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From: Oxford MA-----You just lost the game!!!!
http://www.popularhotrodding.com/eng...s/viewall.html
http://www.popularhotrodding.com/eng...g/viewall.html
http://www.squidoo.com/How-To-Port-Cylinder-Heads
http://65corvette.nonethewiser.net/t...al/diyport.pdf
Keep the shiny side up!
Scott
http://www.popularhotrodding.com/eng...g/viewall.html
http://www.squidoo.com/How-To-Port-Cylinder-Heads
http://65corvette.nonethewiser.net/t...al/diyport.pdf
Keep the shiny side up!
Scott
Last edited by scottyp99; Apr 1, 2012 at 08:43 PM.
Thread Starter
Intermediate
Joined: Apr 2012
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From: hot springs village ar
As mentioned above. There is a difference between factory gross and net HP numbers.
L48 rated at 185 HP is the probably net mid '70s rating when it was really smogged and choked.
1970 L48 10:1s Gross HP -300
1971 L48 8.5:1 Gross HP -270
1972 L48 8.5:1 Net HP - 200
The 1971 and 1972 L48s are virtually the same engine. Only difference is on how the engines were rated.
There is potential in the L48, don't get put off by the net smogged 185 rating, you can liven it up.
Generally most talk HP in gross numbers. Net or rear wheel much better indicator, but more variables involved.
L48 rated at 185 HP is the probably net mid '70s rating when it was really smogged and choked.
1970 L48 10:1s Gross HP -300
1971 L48 8.5:1 Gross HP -270
1972 L48 8.5:1 Net HP - 200
The 1971 and 1972 L48s are virtually the same engine. Only difference is on how the engines were rated.
There is potential in the L48, don't get put off by the net smogged 185 rating, you can liven it up.
Generally most talk HP in gross numbers. Net or rear wheel much better indicator, but more variables involved.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
There's 3 ways that come to mind that would document the cam installed retarded; either the cam/timing gears were different, or the cam was installed with different-than standard positioning of the cam/crank sprockets. The first two would generate alternate part numbers, the latter would be clearly documented in the factory service manual - fair? I would think anyone making this claim could do a little research and easily and quickly find out how (and if) this was done using standard and readily-available references
Last edited by billla; Apr 1, 2012 at 11:01 PM.
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
http://www.superchevy.com/technical/...g/viewall.html
Last edited by 63mako; Apr 1, 2012 at 11:39 PM.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
A casting number on the heads would help a bunch, along with the valve sizes. The heads may be a wash with what you have; the compression boost (about a point) will help a bit, but not much.
Make sure you measure valve clearances and geometry with the change.
Make sure you measure valve clearances and geometry with the change.
Last edited by billla; Apr 1, 2012 at 11:34 PM.
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Thread Starter
Intermediate
Joined: Apr 2012
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From: hot springs village ar
I have to totally disagree with this post. Your L48 has 8.2 to 1 compression. The L82 had 9 to 1 with horrible quench, about .065. If you add the 64 cc heads and a thin gasket .015 (felpro 1094) you can bump your L48 compression up to about 9.4 to 1 with .040 quench. These are the L82 cam specs. 3896962 Hyd. Advertised Duration 312/312, Duration @ .050 222/222, Lift I/E .450"/.460" LSA 114. This same cam was run in the L46 engine with Iron heads and 11 to 1 compression. The L82 cam will run fine with that much compression especially with tight quench. The slow factory ramps close the intake valve much later than a typical 222 duration @ .050 cam so zero detonation issues even with a performance distributor curve. With the performer intake, true dual exhaust I would guess 325HP. Your 650 is fine. Headers will help a lot. The L82 dynoed in this test @ 313 HP. Add performer intake, headers and an extra 1/2 point of compression your close to 350 HP.
http://www.superchevy.com/technical/...g/viewall.html
http://www.superchevy.com/technical/...g/viewall.html
Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
Thread Starter
Intermediate
Joined: Apr 2012
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From: hot springs village ar
Le Mans Master
Joined: Jun 2004
Posts: 6,231
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From: Seattle WA
St. Jude Donor '14
Kinda surprised at some of the estimates here being given for a completely unknown set of truck heads. Unless they're something special, I'd expect around 275-300 HP - the configuration is basically a GMPP 350/290 crate.
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
Last edited by billla; Apr 2, 2012 at 12:14 PM.
Racer
Joined: Mar 2005
Posts: 288
Likes: 1
From: Maple Ridge British Columbia
I have a 1977 L48 that has the original cam, heads and QJet carb. It has an Edelbrock Performer intake, long tube headers and dual exhaust (no cats). It dynoed at 191 HP and 251 TQ at the wheels. If you assume a 25% drive train loss due to the TH350, that would make it 239 HP and 314 TQ Net numbers. So yes, the L48 can be "livened up" quite easily.
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Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Kinda surprised at some of the estimates here being given for a completely unknown set of truck heads. Unless they're something special, I'd expect around 275-300 HP - the configuration is basically a GMPP 350/290 crate.
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
350 HP is too optimistic.
Last edited by 63mako; Apr 2, 2012 at 01:57 PM.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
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From: Seattle WA
St. Jude Donor '14
How can we figure that with zero information on the heads?
I agree with the apples-and-oranges thing regarding measurements - I just wanted to ensure we were all on the same page regarding what that HP number represented.
I guess I'm just overly careful on these "how much power will it make" threads
I agree with the apples-and-oranges thing regarding measurements - I just wanted to ensure we were all on the same page regarding what that HP number represented.
I guess I'm just overly careful on these "how much power will it make" threads
Last edited by billla; Apr 2, 2012 at 02:19 PM.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
I just want to make sure you know that the heads you have are not the vortec heads that everybody talks about. Until we see a casting number, we can't really be sure what you have there, but there were some heads on TBI motors from that era that had what they called a "swirl port", which I guess worked pretty well at very low rpm, for torque, (valuable in a pickup truck) but which are pretty restrictive at higher rpm. There are several guys on this forum who can give you a lot more, and better, info than I can, but they need a casting number, so dig one up as soon as you can, OK?
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Race Director
Joined: Mar 2008
Posts: 15,161
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From: coffee
I was just searching on the 3896962 cam was in the 290hp crate engine that I have and was going to poke around and see what heads might go better with that than the iron 76cc heads that it came with.
I have many bridges to cross before I get there, but it's interesting to see that folks are getting entirely decent numbers out of what I felt was a compromise engine on my part.
I still have dreams of a 383 (or a big block) down the road. I may save up for that and sell the 290 and not bother with upgrading what I have.
I have many bridges to cross before I get there, but it's interesting to see that folks are getting entirely decent numbers out of what I felt was a compromise engine on my part.
I still have dreams of a 383 (or a big block) down the road. I may save up for that and sell the 290 and not bother with upgrading what I have.
Last edited by nate99; Apr 2, 2012 at 03:34 PM.
Thread Starter
Intermediate
Joined: Apr 2012
Posts: 37
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From: hot springs village ar
Kinda surprised at some of the estimates here being given for a completely unknown set of truck heads. Unless they're something special, I'd expect around 275-300 HP - the configuration is basically a GMPP 350/290 crate.
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
Thread Starter
Intermediate
Joined: Apr 2012
Posts: 37
Likes: 0
From: hot springs village ar
How can we figure that with zero information on the heads?
I agree with the apples-and-oranges thing regarding measurements - I just wanted to ensure we were all on the same page regarding what that HP number represented.
I guess I'm just overly careful on these "how much power will it make" threads
I agree with the apples-and-oranges thing regarding measurements - I just wanted to ensure we were all on the same page regarding what that HP number represented.
I guess I'm just overly careful on these "how much power will it make" threads
Le Mans Master
Joined: Oct 2010
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Likes: 843
From: melbourne florida
2023 C3 of the Year Finalist - Modified
Kinda surprised at some of the estimates here being given for a completely unknown set of truck heads. Unless they're something special, I'd expect around 275-300 HP - the configuration is basically a GMPP 350/290 crate.
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...
Note that the Super Chevy results were with an electric water pump, no alternator, dyno headers and open exhaust...so take that number with a grain of salt...or even a whole salt lick
No mention of the (in) famous 4 degrees of retard with the L-82 in the article...