Goal Of 1hp per CI Accomplished
01-21-2019, 10:55 AM
#41
Pro
Thread Starter
The AFB is rated at 550 CFM, and the later Holley at 585, both at 1.5" Hg depression, which is the defacto industry standard depression for rating 4-bbl. carbs. Two-barrel flow ratings are at 3".
The LT-1 manifold is good for 5-10 HP and a larger carb no more than a handful.
I question the peak torque rating of over 380 lb-ft. Typical small blocks with a CR close to ten produce about one lb-ft per cubic inch of displacement on a lab dyno. Peak torque is primarily a function of displacement and CR. Within the 327 family peak torque ratings ranged from 344 to 360 lb-ft, a range of less than five percent, but the highest power rating, 375 is 50 percent more than the lowest, 250. Of course, both torque and power ratings were overstated by at least ten percent, but relative comparisons washout the nonsense.
Headers and a high overlap cam will improve peak torque and power, but in the car with manifolds and mufflers most of whatever they contributed on the lab dyno will disappear.
That's why I recommend chassis dyno tests. It's the as-installed in the chassis available rear wheel HP that counts, not what a lab dyno shows, and as is typical the test started in the mid 3000 range, so you don't know what it does below that range, which is where you spend most of your driving time around town.
The "327 LT-1" configuration I referenced earlier makes, with OE exhaust manifolds and STP correction on a lab dyno, low 330s lb-ft peak torque at 4500 with 80 percent available at 2000 and about 360 HP at 6500. On a chassis dyno with SAE correction peak torque is in the 270-280 range and about 280 RWHP.
Duke
The LT-1 manifold is good for 5-10 HP and a larger carb no more than a handful.
I question the peak torque rating of over 380 lb-ft. Typical small blocks with a CR close to ten produce about one lb-ft per cubic inch of displacement on a lab dyno. Peak torque is primarily a function of displacement and CR. Within the 327 family peak torque ratings ranged from 344 to 360 lb-ft, a range of less than five percent, but the highest power rating, 375 is 50 percent more than the lowest, 250. Of course, both torque and power ratings were overstated by at least ten percent, but relative comparisons washout the nonsense.
Headers and a high overlap cam will improve peak torque and power, but in the car with manifolds and mufflers most of whatever they contributed on the lab dyno will disappear.
That's why I recommend chassis dyno tests. It's the as-installed in the chassis available rear wheel HP that counts, not what a lab dyno shows, and as is typical the test started in the mid 3000 range, so you don't know what it does below that range, which is where you spend most of your driving time around town.
The "327 LT-1" configuration I referenced earlier makes, with OE exhaust manifolds and STP correction on a lab dyno, low 330s lb-ft peak torque at 4500 with 80 percent available at 2000 and about 360 HP at 6500. On a chassis dyno with SAE correction peak torque is in the 270-280 range and about 280 RWHP.
Duke
I wanted the lab dyno test as a reference for the work that was put into it and not to satisfy my ego. No more, no less. I don't need a dyno test once the engine is in the car. I figure once I get it on the road and go through the gears, the smile or the frown on my face will be the ultimate test result.
I have read the Carter AFB had a 600 CFM rating. Summit racing recommends 1.5 CFM per cubic inch.
Last edited by 6T2Vette; 01-21-2019 at 10:56 AM.
01-21-2019, 11:48 AM
#42
Race Director
Member Since: May 2000
Location: Redondo Beach USA
Posts: 12,487
Received 1,974 Likes
on
1,188 Posts
Most lab dynos need to be periodically calibrated, and I've definitely run across a few that appear to read high. I know a lot about the physics going on inside an IC engine, but you've provided very little detail on your configuration. Roller cams and headers usually yield greater peak torque on a lab dyno than flat tappet cams and cast iron exhaust manifolds, but based on the dyno data I've collected for many years on 327-based engines your peak torque figure is an outlier, which is why I question it.
A well system engineered road engine with a moderate to high overlap cam will achieve about 90 percent peak VE with the production exhaust system. If replaced with a properly configured racing exhaust system, VE should reach 100 percent, and the approximate ten percent increase in VE will improve peak torque by about the same amount, and both occur at approximately the same engine speed.
You should get a chassis dyno test once you get the car broken in and optimally tuned. It only costs about a hundred bucks and will likely be very illuminating. Do it on an Dynojet inertia dyno, start the pulls at 1000, and use SAE air density correction.
The AFB rating I quoted is based on a copy of a decades old letter from Carter that was sent to me by the original recipient. It specified the flow rate at 2" Hg depression, but this was before 1.5" Hg became the defecto standard. Since flow varies with the square root of depression, it was a simple matter to convert the 2" rating to 1.5".
Since engines of a given displacement can have widely varying power ratings based on how they are configured, displacement is a poor way to select carburetor size. I use two rules of thumb - provide at no more than 1.5" depression flow about equal to 85 percent VE at the redline or provide maximum flow demand at no more about 1.5" Hg depression, which can be derived from simulation programs. For racing engines no more than 1". Oversizing a carb can cause poor fuel metering at light loads and poor throttle response, which is important on road engines.
For a stock or mildly modified engine, most OE four-barrel carbs meet the above requirements.
Duke
A well system engineered road engine with a moderate to high overlap cam will achieve about 90 percent peak VE with the production exhaust system. If replaced with a properly configured racing exhaust system, VE should reach 100 percent, and the approximate ten percent increase in VE will improve peak torque by about the same amount, and both occur at approximately the same engine speed.
You should get a chassis dyno test once you get the car broken in and optimally tuned. It only costs about a hundred bucks and will likely be very illuminating. Do it on an Dynojet inertia dyno, start the pulls at 1000, and use SAE air density correction.
The AFB rating I quoted is based on a copy of a decades old letter from Carter that was sent to me by the original recipient. It specified the flow rate at 2" Hg depression, but this was before 1.5" Hg became the defecto standard. Since flow varies with the square root of depression, it was a simple matter to convert the 2" rating to 1.5".
Since engines of a given displacement can have widely varying power ratings based on how they are configured, displacement is a poor way to select carburetor size. I use two rules of thumb - provide at no more than 1.5" depression flow about equal to 85 percent VE at the redline or provide maximum flow demand at no more about 1.5" Hg depression, which can be derived from simulation programs. For racing engines no more than 1". Oversizing a carb can cause poor fuel metering at light loads and poor throttle response, which is important on road engines.
For a stock or mildly modified engine, most OE four-barrel carbs meet the above requirements.
Duke
Last edited by SWCDuke; 01-21-2019 at 11:57 AM.
01-21-2019, 01:56 PM
#43
Pro
Thread Starter
Most lab dynos need to be periodically calibrated, and I've definitely run across a few that appear to read high. I know a lot about the physics going on inside an IC engine, but you've provided very little detail on your configuration. Roller cams and headers usually yield greater peak torque on a lab dyno than flat tappet cams and cast iron exhaust manifolds, but based on the dyno data I've collected for many years on 327-based engines your peak torque figure is an outlier, which is why I question it.
A well system engineered road engine with a moderate to high overlap cam will achieve about 90 percent peak VE with the production exhaust system. If replaced with a properly configured racing exhaust system, VE should reach 100 percent, and the approximate ten percent increase in VE will improve peak torque by about the same amount, and both occur at approximately the same engine speed.
You should get a chassis dyno test once you get the car broken in and optimally tuned. It only costs about a hundred bucks and will likely be very illuminating. Do it on an Dynojet inertia dyno, start the pulls at 1000, and use SAE air density correction.
The AFB rating I quoted is based on a copy of a decades old letter from Carter that was sent to me by the original recipient. It specified the flow rate at 2" Hg depression, but this was before 1.5" Hg became the defecto standard. Since flow varies with the square root of depression, it was a simple matter to convert the 2" rating to 1.5".
Since engines of a given displacement can have widely varying power ratings based on how they are configured, displacement is a poor way to select carburetor size. I use two rules of thumb - provide at no more than 1.5" depression flow about equal to 85 percent VE at the redline or provide maximum flow demand at no more about 1.5" Hg depression, which can be derived from simulation programs. For racing engines no more than 1". Oversizing a carb can cause poor fuel metering at light loads and poor throttle response, which is important on road engines.
For a stock or mildly modified engine, most OE four-barrel carbs meet the above requirements.
Duke
A well system engineered road engine with a moderate to high overlap cam will achieve about 90 percent peak VE with the production exhaust system. If replaced with a properly configured racing exhaust system, VE should reach 100 percent, and the approximate ten percent increase in VE will improve peak torque by about the same amount, and both occur at approximately the same engine speed.
You should get a chassis dyno test once you get the car broken in and optimally tuned. It only costs about a hundred bucks and will likely be very illuminating. Do it on an Dynojet inertia dyno, start the pulls at 1000, and use SAE air density correction.
The AFB rating I quoted is based on a copy of a decades old letter from Carter that was sent to me by the original recipient. It specified the flow rate at 2" Hg depression, but this was before 1.5" Hg became the defecto standard. Since flow varies with the square root of depression, it was a simple matter to convert the 2" rating to 1.5".
Since engines of a given displacement can have widely varying power ratings based on how they are configured, displacement is a poor way to select carburetor size. I use two rules of thumb - provide at no more than 1.5" depression flow about equal to 85 percent VE at the redline or provide maximum flow demand at no more about 1.5" Hg depression, which can be derived from simulation programs. For racing engines no more than 1". Oversizing a carb can cause poor fuel metering at light loads and poor throttle response, which is important on road engines.
For a stock or mildly modified engine, most OE four-barrel carbs meet the above requirements.
Duke
True I didn't include the specifics for this engine in this thread as this is an update for the benefit of those that remember my previous thread on the build of this engine. Perhaps I can condense it. I started with a 1962 327ci 340HP. I replaced the domed pistons with flat tops reducing my compression to 9.6 or 9.8. I replaced the cam with a hydraulic roller Voodoo cam #2012017-10 (operating range 1600-5600). I kept the original camel back heads, but I had them massaged and added hardened valve seats. I used roller tipped rockers. I converted the original distributer to Electronic ignition, replaced the original coil with a Pertronix Flamethrower. The dyno shop used their own headers. I plan on using the original Rams horn exhaust which has 2.5" exhaust. I hope this info helps justify or explain the readings given a reasonable margin for error.
I don't feel a need for a chassis dyno as the engines are put to the extreme, something I never plan to do. I already got the numbers I expected and got. I don't need to spank this baby to clear it's lungs. :-)
Bob
Last edited by 6T2Vette; 01-21-2019 at 01:59 PM.
01-21-2019, 02:06 PM
#44
Racer
Thanks for that Duke. I now understand a little bit better where you're coming from. Do the poorly calibrated lab dynos always read higher?
True I didn't include the specifics for this engine in this thread as this is an update for the benefit of those that remember my previous thread on the build of this engine. Perhaps I can condense it. I started with a 1962 327ci 340HP. I replaced the domed pistons with flat tops reducing my compression to 9.6 or 9.8. I replaced the cam with a Voodoo cam #2012017-10 (operating range 1600-5600). I kept the original camel back heads, but I had them massaged and added hardened valve seats. I used roller tipped rockers. I converted the original distributer to Electronic ignition, replaced the original coil with a Pertronix Flamethrower. The dyno shop used their own headers. I plan on using the original Rams horn exhaust which has 2.5" exhaust. I hope this info helps justify or explain the readings given a reasonable margin for error.
I don't feel a need for a chassis dyno as the engines are put to the extreme, something I never plan to do. I already got the numbers I expected and got. I don't need to spank this baby to clear it's lungs. :-)
Bob
True I didn't include the specifics for this engine in this thread as this is an update for the benefit of those that remember my previous thread on the build of this engine. Perhaps I can condense it. I started with a 1962 327ci 340HP. I replaced the domed pistons with flat tops reducing my compression to 9.6 or 9.8. I replaced the cam with a Voodoo cam #2012017-10 (operating range 1600-5600). I kept the original camel back heads, but I had them massaged and added hardened valve seats. I used roller tipped rockers. I converted the original distributer to Electronic ignition, replaced the original coil with a Pertronix Flamethrower. The dyno shop used their own headers. I plan on using the original Rams horn exhaust which has 2.5" exhaust. I hope this info helps justify or explain the readings given a reasonable margin for error.
I don't feel a need for a chassis dyno as the engines are put to the extreme, something I never plan to do. I already got the numbers I expected and got. I don't need to spank this baby to clear it's lungs. :-)
Bob
The following users liked this post:
6T2Vette (01-21-2019)
01-21-2019, 02:47 PM
#45
Pro
Thread Starter
I just wanted to point out that the cam you used has a pretty early closing intake valve, and even though you dropped the static compression by more than a point, you are still running a fairly high dynamic compression ratio for cast iron heads (probably 8.2:1 or so). It’s partly responsible for your good torque number.
Bob
01-21-2019, 05:03 PM
#47
Pro
Thread Starter
Bob
01-21-2019, 09:32 PM
#48
Pro
The Lanati Cam Card for the 20120710 / 60110 shows I/C at 31.5 ABDC. And the card shows to install 6 degree advanced. So the part I'm not sure is what will be the I/C position when installed advanced to card specs? Or is that 31.5 at .050" lift?
The following users liked this post:
jet-tech (01-21-2019)
01-21-2019, 10:10 PM
#50
Pro
Bob, in an earlier post you noted that you used roller tip rocker arms. Do you mean a stamp steal rocker arm with roller tips and a long slot or full roller with roller bearings in the trunions and the tips?
01-21-2019, 11:08 PM
#51
Pro
Thread Starter
Bob