# last cam question



## Topkat (Sep 9, 2010)

if i change from:
212/225 @.050 .408/.407 LSA 116

to

211/220 @.050 .465/.488 LSA 112
what will the result be?
(67 GTO 400 HO limited slip diff)


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## BearGFR (Aug 25, 2008)

Topkat said:


> if i change from:
> 212/225 @.050 .408/.407 LSA 116
> 
> to
> ...


Both of those are pretty mild cams to start with. I'm assuming those lift figures are at the valve and with 1.5:1 rocker arms? The first one's got a taste more duration, but less lift and also a wider LSA. The tighter LSA and higher lift on the second cam leads towards more overlap which _MIGHT_ give it a lumpier idle, but the shorter duration will reduce overlap some. Chances are both cams will sound pretty much stock. Tough call - I'd say it's a toss-up with a slight preference towards the second cam. 

Just to see if I guessed right, I put the specs for both those cams into my engine modelling program with them both installed "straight up", and the second one made 17 more HP, 4 more ft. lb of torque _*on my engine*_ (your results will vary). The second cam had a slightly wider power and torque band and continued to be "decent" up to about 5600 rpm. Between 3000 and 4500 rpm, the two cams are nearly identical. The first one was "all done" by 5400. Again, keep in mind this was modeled on my 461 engine with decent heads, headers, 9.46:1 compression, and good (low mass, low friction) internals, but generally, all things being equal, I'd expect the second cam to be slightly better with a wider power/torque band that extends higher into the rpm range. Neither one of them made 1 HP per cubic inch on my motor. Both of them made 20" or more of idle manifold vacuum - your power brakes will be very happy with either one.


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## Eric Animal (Oct 28, 2007)

Bear, he best not pull more than 5400 rpms anyway. How did the cams compare at low RPM say 2500-3500 ? eric


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## BearGFR (Aug 25, 2008)

Eric Animal said:


> Bear, he best not pull more than 5400 rpms anyway. How did the cams compare at low RPM say 2500-3500 ? eric


They were the same down low too. 

That's a good point on RPM. Unless upgrading to a good aftermarket forged rod, I'd keep it below 5500.

Bear


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