I finally got my 847 motor together with comp 987 springs.

I had a 10.8:1 compression ratio before the cam swap, as well as regular head gaskets. I bumped the head gaskets up to impala head gaskets, which I believe brings me to 11.2:1. I also put on some home-ported heads and true dual exhuast with x-pipe and bullets. My setup now goes as follows...

-forged 355
-eagle 6" I beams
-balanced rotating assembly
-ross 90450 pistons
-impala ss head gaskets
-home ported heads
-comp 987 springs
-crane gm847 cam (234/242)
-csr electric water pump
-coated hooker longtube headers
-custom x-pipe and dynomax bullets
-fuel pressure regulator
-ngk tr55 plugs
-taylor 10mm wires
-walbro 255lph fuel pump
-spec stage III clutch
-10-bolt with 4.10 motives
-summit girdle cover


My idle has gone from 900 with the cc305 to around 1600 with the 847. Is this normal for switching from a small cam like a cc305 (220/230) to a large cam like a gm847 (234/242) and keeping the same tune? And why does it idle at 1600 normally and drop down to 900 only when the SES light comes on?

 

Also, would having the tune for the cc305 still, would that cause the 847 to become less lopey? I'm beginning to think this is not an 847.

 

It wont really lope until the idle is down at 700 to 900. If you could pull the codes its throwing it would be a greater help, but a tune is well in order, you have changed quite alot and it is not suited for it. The 114 lobe sep of the CC305 will hold more cylener pressure down low, the GM 847 will let more blow through making it less volumetric efficient down low, but more up high. The heads and compression also change those figures, and a timing curve suited for a CC305 will not suffice on a motopr with more head flow and a less efficient cam. I would bet that its throwing the light after it warms up and reaches closed loop.

 

you need to get tunercat and a monitoring program and get your IAC readings into the right position. a free, not so right fix would be to adjust the TB blades also if its causing you that much grief right now. but temporary fixes make longterm problems.

and why would you use a cc305 tune on a gm847 built motor...

 

The tune should work fine. You've got other problems.

 

Uhh.. You need to tune for the 847 cam.. Contact Madwolf (Ion) and find out what he thinks about this..

 

Sounds like you have a IAC failure. You won't know for sure until you get the codes pulled.

Once you get it together why don't you bring it by charlotte and get a dyno tune.

 

I bet I have a vaccume leak or something. When I was looking over stuff, I noticed a crack in the hose that goes from the pass. valve cover to the TB or intake. Not sure.

I guess I should check for more vaccume leaks.

I will be moving to Charlotte somewhere around mid to late summer to go to school at NASCAR Technical Institute or UNCC. So, I do plan on getting a tune when I come up there since I'll have some money saved up. How much do you charge for a dyno tune? What would you say your reputability is like?

 

Uhh.. It will run fine. It may not run to its full potential, but it will run fine. I am sure madwolf will disagree because it is in his best interest to do so.

 

My car with a tune for the 224/230 ran a 14.9 :1 a/f ratio at WOT with just a bigger cam added, before with the smaller cam in we dynoed it and it hit in the 12.9 to 11.5 range all the way up. Bryan adjusted for the new cam and it fell right in line.

What was weird is that it would idle like crap (IAC 160) until it reached closed loop, then the IAC counts came down and it had a somewhat smoother idle. Then when it was retuned (through the mail) it settled into the nice rumpidy right off.

The cams are so different not to mention that he added alot more airflow with the ported heads. Youre right it will run , but it will run poorly.

The tube youre talking about from the valvecover to the T/B shouldnt pull out enough vacuume to matter at low speeds, and even at higher speeds it still wouldnt effect driveabilty noticebly.

 

I work for Pcmforless.com, the most experienced longest lasting company in this buisness without incident.

 

I got the idle somewhat under contol. Remember the hose I was talking about that goes from the valve cover to the front of the intake? Well, the fitting below that was open, so I put a plug over it. Now my idle came down to around 900 in closed loop when the SES light comes on and around 1100 in open loop. I'm guessing I've got a few more leaks to take care of, but I'll figure it out when the new pcm gets in.

 

I went from a Comp 305 to a Comp XE 236/248 (all pre-blower) and needed to pull quite a bit of fuel out at some spots. Car ran like crap with the bigger cam and the initial CC305 programming, including bucking and surging at some part throttle conditions during normal cruising - not "fine" at all...

 

Daggum! I was told the biggest I should go with a stock-headed 355 is 234/242! What the hell? How is the cam surge on that cam? Do you have ported heads? Would I be better off sticking with the 234/242 since my heads are basically stock?

 

Yes my heads are ported, but I'm running a 383. After tuning there was no cam surge at all. I just sold the cam to someone with a 355, so we'll see how it does in his car.

If you're already running a 234/242, I doubt you'd see much off a differnce with a 236/248 - might even run worse on your setup. Dunno - I'm far from a cam expert. If you're dead set on a change, I'd talk to Steve at Thunder Racing or one of the other recommended vendors or board sponsors, who've been there, done that, with LT1 cams .