I talked to Atl Jar a while back about cam choice. What I was looking for is something that had the characteristics of Comp Cams XE grinds with the specs of a GM 847. What we were able to find are some lobes from Comp Cams that SBC HIR series.

The GM 847 specs are 234/242 .575/.595 112 LSA

Here are the lobes:

http://www.cranecams.com/?show=hydraulicroll#HIR

HIR-234/3600 290 .0040 157 .095 .059 .540 .576 .612 .634 B

HIR-242/3735 298 .0040 166 .112 .071 .560 .598 .635 .657 B

That should put us at a 234/242 .576/.598



Can anyone foresee a problem or complication for that cam choice?

thoughts?

 

Might want to mention what engine you are putting it in, what heads you are using and the flow #'s, and the intended use of the car.... street, strip, ?????

 

Oh Fred, you are such a stickler for details!

Seriously, I'd like to help. But more detail (a lot) would add focus to my response.

Rich Krause

 

Its a street car. I plan on getting AI ported heads to go with it, but I'm fooling with the idea of a more serious cam. I have supporting mods such as long tube headers and what not. I didnt know if that cam would be able to create enough vacuum for breaks and things of this nature or if it would be so agressive that it would introduce a valve to a piston. If this is too agressive I'll wind up going with a GM847, but I wanted some advice first.

 

Is there any way to tell what the cars behavior would be like with this cam VS the 847?

 

TTT

 

They look very similar. I was haivng trouble deciphering the numbers. But the duration at 0.050" is the same and the lift is essentially the same. If you have the advertised duration for both as well as the duration at 0.200" lift it will allow for a more precise comparison.

What are you hoping to gain, more midlift duration? If that's the case the duration at 0.200" would be the best number to get.

Either cam will be marginal on vacuum for brakes.

Rich Krause

 

Its a more aggressive lobe similar to the XE grinds. I was hoping that it would peak lower in the RPM band and hopefully make more power that way. Thats the idea at any rate.

Can anyone provide me with a complete spec sheet on a GM847? So that I know what ICL and what not to get this cam.

edit: I spelt stuph rong

 

TTT

Does anyone have the complete specs on a GM 847?

 

234/242 Duration at .050

112 LSA +4degs of Advance (108ICL and 116ECL)

Valve Events

Open @ .050 BTDC Intake 9 Exahust 57
Close @ .050 ABDC Intake 45 Exhaust 5

Lift with 1.6 Rockers .574/.595

No .200 duration numbers but I would expect:

150/158

Have those specs on file for comparison purposes.

Just did a camshaft that was for an application where the customer wanted about the same HP as a 847 but with more TQ. Ends up the cam should make 5-10more HP and 10-20ft lbs more TQ ar 4500rpm.

Bret