First impressions: GM847, stock bottom end, M6 car
10-09-2006, 10:47 AM
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First impressions: GM847, stock bottom end, M6 car (Cross-posted at CamaroZ28.com)
After about 30 hours of wrenching, I finally have the GM847 in my stock bottom end car. The cam is not a true GM847, but rather Cam Motion's version of it. I'm not sure how the valve opening / closing specs compare to the GM847, but here are the basic specs:
234/241 @.050 .575"/.596" (1.6 rockers) 112 LSA
Here are my powertrain mods (suspension stuff left out to save space):
First impressions, after having a Comp XE 224/230 (CC 503):
Also, for those of you that are worried about spinning bearings after cam swaps, here's how I installed the head bolts:
It took forever and was NOT a fun process... but at least now I know that if the car DOES spin a bearing, it won't be due to improper head bolt installation.
More updates to follow. I think I'll drive the car to the grocery store to put a few more miles on it...
After about 30 hours of wrenching, I finally have the GM847 in my stock bottom end car. The cam is not a true GM847, but rather Cam Motion's version of it. I'm not sure how the valve opening / closing specs compare to the GM847, but here are the basic specs:
234/241 @.050 .575"/.596" (1.6 rockers) 112 LSA
Here are my powertrain mods (suspension stuff left out to save space):
- Combination Motorsports Stage 2 heads, (2.00" intake, 1.6" exhaust valves), ARP 3/8" rocker studs
- CC 977 valve springs
- CC pro magnum SA 1.6 roller rockers
- CC chome moly pushrods
- LT4 Xtreme duty timing kit
- CAI, trick flow elbow, 52mm TB / airfoil (ported by NOMAD)
- 30# injectors
- Kooks emissions LT's, Kooks Y, Hooker catback
- 4.10 gears
First impressions, after having a Comp XE 224/230 (CC 503):
- Exhaust volume is almost 100% identical to the XE 224/230, but there's a bit more chop once it gets up to temp
- The car probably needs new lifters. With almost 64K on them, the stockers bleed down almost immediately when the engine shuts off... especially with .596" exhaust lift.
- The Speed Inc full tune that I had for the old cam seems to hold up OK, but I am sure that a new tune could help. I have no data logging software so I'm not sure how the A/F is doing.
- Throttle response in low RPM's is almost identical to the old cam. But the powerband is way different. For example, the XE 224/230 would start pulling around 3K and keep pulling steadily until redline. The 847 however, feels like the XE cam at 3K, then turns into a ROCKET at 4K. I did one WOT blast in 3rd gear starting at 3K just to make sure the valve lash was set correctly. The tach hit 4K, then JUMPED to 6K -- that's right... it blew the tires off in 3rd gear.
Also, for those of you that are worried about spinning bearings after cam swaps, here's how I installed the head bolts:
- Chased all 34 head bolts holes (a LOT of crap came out, no wonder people have gotten false torque readings!)
- Soaked the ARP bolts in penetrating oil
- Cleaned bolts with a steel-bristle brush
- Placed cylinder heads on block w/o head gasket
- Applied moly lube to each bolt and torque-cycled the new bolts 5 times in 25-45-65 sequence
- Cleaned moly lube off bolt holes and bolts
- Put on head gaskets
- Applied ARP thread sealer to each bolt
- Performed final install by step-torquing bolts 25-45-65
It took forever and was NOT a fun process... but at least now I know that if the car DOES spin a bearing, it won't be due to improper head bolt installation.
More updates to follow. I think I'll drive the car to the grocery store to put a few more miles on it...
10-09-2006, 05:25 PM
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what does proper head bolt torque have to do with spinning bearings?
I understand that it possibly distorts the deck, or even the cylinder bores when torqued (the whole reason for using a "torque plate" for honing). but how does that little bit of load have any effect on bearing life?
anyway. sounds like a real hairy setup you have. I have a CC503, and have considered a larger cam, but was worried about the loss in torque.
I understand that it possibly distorts the deck, or even the cylinder bores when torqued (the whole reason for using a "torque plate" for honing). but how does that little bit of load have any effect on bearing life?
anyway. sounds like a real hairy setup you have. I have a CC503, and have considered a larger cam, but was worried about the loss in torque.
10-09-2006, 07:26 PM
#6
i was wanting do to the 847 cam in my car also. I heard it on a car at pep-boys, lol, and it sounded crazy. Some people say its "old" tech. for a cam, but f-that. Nice to see you did it to a stock bottom-end. Makes us true budget builders (not a $6k "budget build") feel safe about doin it to our motors.
10-09-2006, 07:48 PM
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Cam Motion actually recommended the cam to me based on what I entered in my cam request form (road race setup, not worried about streetability 
). Not sure if they're following the trend, but it will be interesting to see how the car does with more driving and tuning.
Depending on how it drives over the next week or so I might look into getting my intake manifold ported. Jim @ Speed Inc mentioned that they have personally seen gains of 20 RWHP on heads/cam N/A LT1s. If this cam is starving for air, that might be my next mod.
). Not sure if they're following the trend, but it will be interesting to see how the car does with more driving and tuning.Depending on how it drives over the next week or so I might look into getting my intake manifold ported. Jim @ Speed Inc mentioned that they have personally seen gains of 20 RWHP on heads/cam N/A LT1s. If this cam is starving for air, that might be my next mod.
