I have a 1986 IROC-Z with a 305 TPI engine. I am lookin to upgrade the cam and am wonderin exactly what the specs mean. The cam i am lookin at is from SLP and has a lift of .502/.510 and a duration of 280/288, and a duration at .05 of 224/230. I am wonderin if this hydraulic roller cam is a good choice with my present setup, and what do the lift and duration mean. Is this too much lift or duration that it means less low-end torque, all responses are greatly appreciated. I have edelbrock headers with flowmasters, SLP runners and edelbrock baseplate, as well as 52mm throttle, and have 305 torquer heads in the making.

 

One important point is that the cam you're looking at is a roller type. The 86 IROC came with a standard hydraulic. If you haven't done so already you will have to get your block machined to accomodate a roller camshaft. I think that cam may be a little much for a 305. I could be wrong though, it all depends on your computer and what kind of streetability you want.
As far as what the #'s mean, I'll try to keep it simple. I don't even know the in depth explanations myself. The lift is how far the cam will open the valves with the use of a 1.5 ratio rocker arm. The duration is how long the valve is held open measured in degrees of crankshaft rotation. I'm not sure if I'm right on this if I'm not would someone please correct me.

 

If your motor has conventional hydraulic lifters, then I'd stick with that. To change over to a retro-fit hydraulic roller cam would cost a lot. Go to the Comp Cams internet site and request a recomendation for a new hydraulic cam and lifters set, for your car. They will need to know your modifications and rear gear ratio. They are very helpful and welcome your inquires. Then, go to the Crane Cams site and do the same thing. With the two recommendations you'll be well informed to choose the best cam for your car. The SLP Hydraulics are basicly repackaged generic designs (speed-pro)(blue racer) and can be purchased elsewhere for a lot less. Look for a cam with an intake duration @ .050" of 204 to 218 for a mild 305. If you have low gears like 2.73 I'd lean to the smaller cams. Hope this helps...

[This message has been edited by F-BIRD'88 (edited November 06, 2001).]

 

Whoa ! 224 degrees on the intake will not work very well for your 305 TPI auto. I had 217 degrees on a 305 5-speed (don't worry about lift other than too much will interfere with your piston) and it was a disaster. I spent the next year paying for chips to be cut to solve the problems from messed up vacuum at idle. I wouldn't even use that cam on a 350. Once bitten twice shy I suppose.

IMHO the best bet is keep intake duration under 210 degrees at .050 on the 305.

RP.

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'91 Formula Firebird G92,WS6,5-speed,3.42 a ton of fun to drive.