Cam Specs

[Dan the man]

I was watching Graveyard Cars tonight and Mark gave the specs for the cam and the intake had more lift and duration than the exhaust, the cam was for a hemi. I've noticed this alot on the hemi's and some other engines too, these were naturally aspirated engines as well. I thought that the exhaust was to have more lift and duration unless it was a turbo charged. Please explain this

 

[GTX JOHN]

We like to see the exhaust flow around 75% of the intake port.
If the exhaust is better or worse we try to crutch it with changing around
the camshaft specs to balance it.

Just my opinion = Every engine guy has his own flow theory and strategy!

 

[Bewy]

Some smaller Jap/European engines have cams with less duration. It is called thinking outside the square. As Isky says on his website, is extra exh duration just a 'habit'. [ Because the factories used it with restrictive manifolds, pipes & mufflers ].

 

[Dan the man]

We like to see the exhaust flow around 75% of the intake port.
If the exhaust is better or worse we try to crutch it with changing around
the camshaft specs to balance it.

Just my opinion = Every engine guy has his own flow theory and strategy!

That makes sense

 

[33IMP]

Might have something to do with different rocker ratios on the intake and exhaust on a gen2 hemi.

 

[rumblefish360]

I was watching Graveyard Cars tonight and Mark gave the specs for the cam and the intake had more lift and duration than the exhaust, the cam was for a hemi. I've noticed this alot on the hemi's and some other engines too, these were naturally aspirated engines as well. I thought that the exhaust was to have more lift and duration unless it was a turbo charged. Please explain this

As John said and Bewy pointed out, the HEMI engine acts and reacts a little differently than a wedge head or a cantered valve head. The HEMI head is an excellent breather. There really is no sense of adding more duration, intake or exhaust, to get the job done. Sometimes, adding more because of the thinking more or bigger is better doesn’t always bare fruit and can actually hurt performance.

Might have something to do with different rocker ratios on the intake and exhaust on a gen2 hemi.

That’s is a possibility.

 

[MOPAROFFICIAL]

I was watching Graveyard Cars tonight and Mark gave the specs for the cam and the intake had more lift and duration than the exhaust, the cam was for a hemi. I've noticed this alot on the hemi's and some other engines too, these were naturally aspirated engines as well. I thought that the exhaust was to have more lift and duration unless it was a turbo charged. Please explain this

Port design and other things that can be limitations call for a compensating event...like more int valve lift.
This is where a flowbench can be helpful...with other obvious things