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I had my engine checked over and the valves touched up. Part of the deal was to dyno it. Just to set the table properly, the dyno sheets below are without any accessories and with headers (had thermocouples in them to track exhaust temps). I also had the runs limited to 6000 rpm----------too expensive of an engine to risk a small chance of blowing it up.
Short story, it made 461 hp @ 5900 rpm with the complete air cleaner in place and 477 hp @ 6000 rpm with only the base in place.
If that's a stock motor that's exceptionally strong. Very nice.
Maybe I should not say exceptionally strong - headers can really wake up rectangular port heads so that probably accounts for a little of that horsepower.
Last edited by DansYellow66; 11-12-2015 at 06:24 PM.
If that's a stock motor that's exceptionally strong. Very nice.
Maybe I should not say exceptionally strong - headers can really wake up rectangular port heads so that probably accounts for a little of that horsepower.
The published GROSS HP for this engine is 435 @5800 RPM. This was measured (or was most likely measured) with headers, and without alternator and water pump, and other accessories at the GM testing labs.
Of course they also played with RPM to get whatever HP Marketing and Sales wanted to show on the order forms. As shown by "427/435" this SHP engine continued to make horsepower as the RPMs increased past 5800.
The numbers shown by the dyno sheets indicate a healthy engine.
Larry
Last edited by Powershift; 11-12-2015 at 07:11 PM.
I've been thinking on the "stock" status. 15+ years ago, the aluminum cam pulley wore down and the chain jumped a bunch------------result 16 bent valves and 8 dented pistons. Every thing was replaced with stock parts including the piston compression. I can't remember if it got an over bored. Could be a 0.010 or 0.030 over bore. I'm going to call the guy that checked the engine and dynoed it to see if he measured the bore. There could be an extra 6 cubic inches.
I've been thinking on the "stock" status. 15+ years ago, the aluminum cam pulley wore down and the chain jumped a bunch------------result 16 bent valves and 8 dented pistons. Every thing was replaced with stock parts including the piston compression. I can't remember if it got an over bored. Could be a 0.010 or 0.030 over bore. I'm going to call the guy that checked the engine and dynoed it to see if he measured the bore. There could be an extra 6 cubic inches.
An NHRA tech inspector might quibble over a few cu in but if they went back with stock replacement pistons for the cleanup bore I think most everyone else would still consider it a stock engine.
The published GROSS HP for this engine is 435 @5800 RPM. This was measured (or was most likely measured) with headers, and without alternator and water pump, and other accessories at the GM testing labs.
Of course they also played with RPM to get whatever HP Marketing and Sales wanted to show on the order forms. As shown by "427/435" this SHP engine continued to make horsepower as the RPMs increased past 5800.
The numbers shown by the dyno sheets indicate a healthy engine.
Larry
GM used production exhaust manifolds (and open exhaust) to rate engines (SAE gross), even L88, and ZL-1. The did do development work with headers on the latter two since they were designed for racing, but those numbers were not reported in the official factory literature or AMA specs - only press articles.
The L-71 cam has sufficient overlap to harness wave dynamics with a well designed set of headers, and the headers using in this test qualify as such since they have smooth bends and large primary tubes that appear to be about 2" OD.
Based on back to back test data I have on SHP small blocks with both manifolds and headers, I would estimate that headers add about 10 percent peak torque and about 5 percent peak power compared to the OE manifolds (with open exhaust), but in the car with a suitable street exhaust system the difference will be approximately cut in half due to exhaust back pressure.
Add in the lower SAE net air density, production exhaust manifolds, exhaust back pressure, and driveline loss the SAE corrected RWHP will likely be on the order of 70 percent of the measured lab dyno numbers - something in the range of 325-350 SAE corrected RWHP, which would be somewhere around 400 SAE net at the flywheel using a 0.85 driveline efficiency factor.
Guys that test on a chassis dyno with the OE manifolds after having the engine tested on a lab dyno with headers and data corrected to STP conditions are usually disappointed with the SAE corrected RWHP numbers and estimated SAE net at the flywheel, but that's how the real world works, and with the restrictive OE sidepipe system rather than the under-the-car system, the numbers are even more disappointing.
As a general rule, small blocks of the era had more inflated gross torque and HP numbers than big blocks, which were actually fairly honest as insurance companies were becoming increasing concerned with big power numbers.
GM used production exhaust manifolds (and open exhaust) to rate engines (SAE gross), even L88, and ZL-1. The did do development work with headers on the latter two since they were designed for racing, but those numbers were not reported in the official factory literature or AMA specs - only press articles.
The L-71 cam has sufficient overlap to harness wave dynamics with a well designed set of headers, and the headers using in this test qualify as such since they have smooth bends and large primary tubes that appear to be about 2" OD.
Based on back to back test data I have on SHP small blocks with both manifolds and headers, I would estimate that headers add about 10 percent peak torque and about 5 percent peak power compared to the OE manifolds (with open exhaust), but in the car with a suitable street exhaust system the difference will be approximately cut in half due to exhaust back pressure.
Add in the lower SAE net air density, production exhaust manifolds, exhaust back pressure, and driveline loss the SAE corrected RWHP will likely be on the order of 70 percent of the measured lab dyno numbers - something in the range of 325-350 SAE corrected RWHP, which would be somewhere around 400 SAE net at the flywheel using a 0.85 driveline efficiency factor.
Guys that test on a chassis dyno with the OE manifolds after having the engine tested on a lab dyno with headers and data corrected to STP conditions are usually disappointed with the SAE corrected RWHP numbers and estimated SAE net at the flywheel, but that's how the real world works, and with the restrictive OE sidepipe system rather than the under-the-car system, the numbers are even more disappointing.
As a general rule, small blocks of the era had more inflated gross torque and HP numbers than big blocks, which were actually fairly honest as insurance companies were becoming increasing concerned with big power numbers.
Duke
What would be an approximate RWHP and torque be on a chassis dyno???
GM used production exhaust manifolds (and open exhaust) to rate engines (SAE gross), even L88, and ZL-1. The did do development work with headers on the latter two since they were designed for racing, but those numbers were not reported in the official factory literature or AMA specs - only press articles.
The L-71 cam has sufficient overlap to harness wave dynamics with a well designed set of headers, and the headers using in this test qualify as such since they have smooth bends and large primary tubes that appear to be about 2" OD.
Based on back to back test data I have on SHP small blocks with both manifolds and headers, I would estimate that headers add about 10 percent peak torque and about 5 percent peak power compared to the OE manifolds (with open exhaust), but in the car with a suitable street exhaust system the difference will be approximately cut in half due to exhaust back pressure.
Add in the lower SAE net air density, production exhaust manifolds, exhaust back pressure, and driveline loss the SAE corrected RWHP will likely be on the order of 70 percent of the measured lab dyno numbers - something in the range of 325-350 SAE corrected RWHP, which would be somewhere around 400 SAE net at the flywheel using a 0.85 driveline efficiency factor.
Guys that test on a chassis dyno with the OE manifolds after having the engine tested on a lab dyno with headers and data corrected to STP conditions are usually disappointed with the SAE corrected RWHP numbers and estimated SAE net at the flywheel, but that's how the real world works, and with the restrictive OE sidepipe system rather than the under-the-car system, the numbers are even more disappointing.
As a general rule, small blocks of the era had more inflated gross torque and HP numbers than big blocks, which were actually fairly honest as insurance companies were becoming increasing concerned with big power numbers.
Duke
So, according to this explanation 462 gross horsepower and 615 gross ft. lbs. torque would net 323 RWHP and 430 ft. lbs. torque? Am I doing this correctly, or am I still missing something???
I don't know where you came up with 615 lb-ft, but if you want to estimate a ballpark range of what an absolutely stock - everything set to OE spec just like it left St. Louis- L-71 will do on a Dynojet with SAE air density correction, multiply the advertised peak torque and power numbers by 0.70-0.75.
I don't know where you came up with 615 lb-ft, but if you want to estimate a ballpark range of what an absolutely stock - everything set to OE spec just like it left St. Louis- L-71 will do on a Dynojet with SAE air density correction, multiply the advertised peak torque and power numbers by 0.70-0.75.
Duke
Duke,
From laboratory engine stand test with no exhaust system except manifolds, and no accessories, it would take 615 gross ft lbs torque to realize 430 at the rear wheel at 70% loss. It would take 462 gross horsepower to realize 323 RWHP at 70% loss. That's what I took from what you said in post #13. I'm either a slow learner or a blockhead. Please help me understand! I am trying to estimate a ballpark range of what a lab dyno might look like if I have a peak 323 RWHP and peak 430 RWT.
I called the engine builder and asked if he had miked the bore. He didn't remember doing that, but he remembered how good the bores looked and they had no ridges. As it had around a 100,000 miles on it (odometer quit long ago), it must have had an overbore when I had it overhauled 15 years and about a 1000 miles ago.
Duke,
From laboratory engine stand test with no exhaust system except manifolds, and no accessories, it would take 615 gross ft lbs torque to realize 430 at the rear wheel at 70% loss. It would take 462 gross horsepower to realize 323 RWHP at 70% loss. That's what I took from what you said in post #13. I'm either a slow learner or a blockhead. Please help me understand! I am trying to estimate a ballpark range of what a lab dyno might look like if I have a peak 323 RWHP and peak 430 RWT.
I would question the 430 TQ number. Is it an auto car? They often flash high TQ numbers due to converter flash.
But 323 RWHP would end up in the 410-425 or so HP range probably. With real headers and open exhaust it could gain another 30-40 probably.
11-12-2015, 05:34 PM
L71 Dyno Run
As shown by "427/435" this SHP engine continued to make horsepower as the RPMs increased past 5800.
