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:

1. Chased all 34 head bolts holes (a LOT of crap came out, no wonder people have gotten false torque readings!)
2. Soaked the ARP bolts in penetrating oil
3. Cleaned bolts with a steel-bristle brush
4. Placed cylinder heads on block w/o head gasket
5. Applied moly lube to each bolt and torque-cycled the new bolts 5 times in 25-45-65 sequence
6. Cleaned moly lube off bolt holes and bolts
7. Put on head gaskets
8. Applied ARP thread sealer to each bolt
9. 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...

 

That sounds awesome....Especially the part about it turning into a rocket at 4k and blowing off the tires in 3rd I can't wait until I have the extra cash to do some serious power mods to my car.

 

That cam is a wicked one! I remember the days when I had my CC306 cam with the similar power band. It was a lot of fun, and man did it pull like a MF up top!

Enjoy your car man!

 

There are many people that spun bearings after a cam swap and never touched the heads. I did not think that was part of the "spun bearing" equation.

 

it's not.....

 

December update...

I took the car to the dyno just over a month ago to get a baseline and make sure that things were runnning right. I had Louis from LG Motorsports datalog the car with HPTuners.

When I saw the numbers I was pretty disappointed: 371RWHP / 345RWTQ SAE (DynoJet).

...Then I looked at the datalog...

3" of vacuum at WOT
11:1 AF/R above 5500 RPM

It turned out that the airfilters were absolutely filthy. My dumb@$$ forgot to clean them when I tore the motor apart. The car is up on jackstands due to an unrelated issue but once some replacement parts come in I should be able to drive it a bit before it snows like crazy.

Any guesses what power it'll put down once I iron out the kinks? I think 380+ is pretty reasonable.

 

Can you post up the dyno chart?

 

I did not know HPT would datalog the LT1 PCM. I need to do some more checking in on that.

 

It does, but only to a limited extent. For example, it couldn't get injector duty cycle.

I'll get the datalog from Louis later this week and let you guys know what its capabilities are.

Dyno scan is coming tomorrow once I get a free minute in a computer lab.

 

Like Shon said, it's not. I'm pretty sure it's mostly due to the motor seeing higher rpms.
Some aspects of the LS1 stuff will work with the OBDII LT1's. It will work, just not all of the functions can be displayed.

 

Did you try another dyno run without the dirty air filter????

 

Not yet. It was part of a club function and there were ten guys in line after me. We didn't discover the air filter problem until later when we had a chance to go over the data logs.