Junkyard Carb'd 5.3 all stock
#1
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From: Mt. Vernon, WA.
Junkyard Carb'd 5.3 all stock
No high dollar build here! just a $250 junkyard engine stuffed into a '73 Nova on a budget. Local performance shop had a $50 dyno day and I wasn't going to miss it!
Quick review of specs:
-2001 5.3 with 106K, now 109K’ish
-Completely stock internals
-Edelbrock dual intake
-Used/rebuild Speed Demon 750
-Ebay 3rd gen SS headers, 1 ¾” Primary, 3” collectors
-3” straight pipes to Thrust mufflers dumped at the axle
-Rebuilt TH350
-2000RPM converter
-Original 2.73 gears
The torque was what I expected, but about 400RPM lower than I expected to see it. The horsepower however was less than I expected, and 1000RPM lower then where a 5.3 SHOULD reach peak at!? WTF! I know I am leaving some on the table in carb and ignition tuning, but I expected a peak of about 275HP @ 5500RPM.
Now don’t worry, I am no Dyno queen, I know a dyno is a before/after tool and that kicking asphalt is what is REALLY important. As a baseline I am happy with how it performs on the road and on the track. This summer I am hoping to stab in a 224R or 228R cam, LS2 chain, hardened pushrods, beehive springs and maybe a trunion etc etc. Oh and some better rear gears!
Any ideas what might cause the HP to come in nearly 1000RPM earlier than in a stock configuration? Thanks for the input!
Quick review of specs:
-2001 5.3 with 106K, now 109K’ish
-Completely stock internals
-Edelbrock dual intake
-Used/rebuild Speed Demon 750
-Ebay 3rd gen SS headers, 1 ¾” Primary, 3” collectors
-3” straight pipes to Thrust mufflers dumped at the axle
-Rebuilt TH350
-2000RPM converter
-Original 2.73 gears
The torque was what I expected, but about 400RPM lower than I expected to see it. The horsepower however was less than I expected, and 1000RPM lower then where a 5.3 SHOULD reach peak at!? WTF! I know I am leaving some on the table in carb and ignition tuning, but I expected a peak of about 275HP @ 5500RPM.
Now don’t worry, I am no Dyno queen, I know a dyno is a before/after tool and that kicking asphalt is what is REALLY important. As a baseline I am happy with how it performs on the road and on the track. This summer I am hoping to stab in a 224R or 228R cam, LS2 chain, hardened pushrods, beehive springs and maybe a trunion etc etc. Oh and some better rear gears!
Any ideas what might cause the HP to come in nearly 1000RPM earlier than in a stock configuration? Thanks for the input!
#2
Tuning?
Could be running rich?
Needs a cam bad even something like a LS2 cam will wake it up a lot in the top end
Most stock 5.3s dyno around 230~ whp i think
A carbed full exhaust one should do a little better
Have not seen that many stock 5.3 numbers to know but it looks like the torque is falling off pretty rapidly after 4,000 rpm
Could be running rich?
Needs a cam bad even something like a LS2 cam will wake it up a lot in the top end
Most stock 5.3s dyno around 230~ whp i think
A carbed full exhaust one should do a little better
Have not seen that many stock 5.3 numbers to know but it looks like the torque is falling off pretty rapidly after 4,000 rpm
#5
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From: Mt. Vernon, WA.
I would say yes on a stingy dyno, but the torque numbers seem about right, if a little early in the RPM and falls off real quick. I am questioning if the 750DP is to large and and the secondary is not getting enough signal to pull additional fuel. So once the secondary squirters are exhausted there is a lean condition. Hence the 4K drop off and the small unsteady waves that starts at about 3750.
As crazy as it may sound, I am considering upping the secondary jets in a hope that it will increase vacuum signal.
But I am also working on the carb and ign tune and it is making a big difference in engine behavior already.
I am open to any thoughts or theories. Thanks for the input.
As crazy as it may sound, I am considering upping the secondary jets in a hope that it will increase vacuum signal.
But I am also working on the carb and ign tune and it is making a big difference in engine behavior already.
I am open to any thoughts or theories. Thanks for the input.
#6
Have you thought about trying a softer spring for the secondaries? If the carb uses the same springs as a holley, you can by a secondary spring tuning kit. Try a purple or the stiffer of the two yellow springs.
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#9
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TECH Enthusiast
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Joined: Oct 2011
Posts: 539
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From: Mt. Vernon, WA.
Update
Update: Over the summer I swapped cam/pushrods/springs, added an AFR gauge and got the dyno on the rollers again. Check out the results here:
https://ls1tech.com/forums/dynamomet...-cam-swap.html
https://ls1tech.com/forums/dynamomet...-cam-swap.html