Cam and intake affecting tq curve
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Teching In
Joined: Jan 2019
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From: Battle Ground, WA
Cam and intake affecting tq curve So I'm curious, tuners chime in, I have a 5.3 with a fabbed intake with short runners. Now I know those short runners don't do anything benificial below 5k rpm. So would a cam with 112 LSA help offset that lack of torque down low? Any input is appreciated! Still learning here.
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From: Euless, TX
When it comes to the cams and timing events IVC is the single biggest contributor to low-end torque. The earlier the valve closes the more cylinder pressure aka higher dynamic compression ratio and the more low-end torque. Without knowing any other specs 112 LSA means nothing. Overlap also plays a part in low-speed torque because of intake charge contamination. Runner length plays a big part in torque curve but then again so do the cam specs. David Vizard has a bit of an un-orthodox method for coming up with cam specs. He first determines the LSA by a graph that has Intake Valve size and Cylinder displacement graphed out. Once the desired LSA is determined he looks at the desired overlap for the application. Desired overlap depends on the application of the engine. From there duration is back calculated. Cylinder head I/E flow ratio also has to be compensated for. Longer duration for cylinder heads with poor flowing exhaust ports.
Thread Starter
Teching In
Joined: Jan 2019
Posts: 13
Likes: 0
From: Battle Ground, WA
When it comes to the cams and timing events IVC is the single biggest contributor to low-end torque. The earlier the valve closes the more cylinder pressure aka higher dynamic compression ratio and the more low-end torque. Without knowing any other specs 112 LSA means nothing. Overlap also plays a part in low-speed torque because of intake charge contamination. Runner length plays a big part in torque curve but then again so do the cam specs. David Vizard has a bit of an un-orthodox method for coming up with cam specs. He first determines the LSA by a graph that has Intake Valve size and Cylinder displacement graphed out. Once the desired LSA is determined he looks at the desired overlap for the application. Desired overlap depends on the application of the engine. From there duration is back calculated. Cylinder head I/E flow ratio also has to be compensated for. Longer duration for cylinder heads with poor flowing exhaust ports.
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From: Central Cal.
Everything you describe about your engine says "good near-stock engine" with good low and midrange. EXCEPT for one thing- the intake manifold. There is no compensating for short runners. I would sell it if I were you and get an LS6 manifold, either stock or a new Dorman copy.
In general, smaller engines need longer runners to compensate for lack of swept volume and piston speed.
All changing a cam will do is work with or against the short runner dynamics.
Either cam for rpm or intake for torque. Since you seem concerned about torque, likely need to swap intakes. Or bolt on a supercharger and get both torque and HP
All changing a cam will do is work with or against the short runner dynamics.
Either cam for rpm or intake for torque. Since you seem concerned about torque, likely need to swap intakes. Or bolt on a supercharger and get both torque and HP
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Joined: Oct 2006
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From: Euless, TX
In general, smaller engines need longer runners to compensate for lack of swept volume and piston speed.
All changing a cam will do is work with or against the short runner dynamics.
Either cam for rpm or intake for torque. Since you seem concerned about torque, likely need to swap intakes. Or bolt on a supercharger and get both torque and HP
All changing a cam will do is work with or against the short runner dynamics.
Either cam for rpm or intake for torque. Since you seem concerned about torque, likely need to swap intakes. Or bolt on a supercharger and get both torque and HP
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The 112 number doesn't really tell us much without the other numbers. Do you have the specs for the cam that's in it now? As other's have mentioned IVC can be earlier to compensate, but then you are loosing top end. We agree the Dorman RNB-615-901 would be a great choice and you'll likely MAKE money from the sale of your intake.
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