LT1 heads are 56cc.

 

Cool. Suggests I am at least thinking of a cam in the right range. Looking pretty seriously at the 230/236 from Combination Motorsports: 230/236 duration, .622"/.624", 112lsa. I would be running it with 1.5 rockers so the lift would be more reasonable (.583/585). .622/.624 seems like a good way to go through springs in a hurry.

 

Will I need to run higher compression to hit 400rwhp NA? My understanding was that stock LT4 heads had higher compression than LT1 heads (smaller chambers). I believe LT1's stock compression ratio is about 10.5:1. LT4's are supposed to be pushing 11:1, am I wrong?

 

GM 847 awesome HP with awesome torque, even Dyno 2000 likes it more than many others. Without going through every grind in the book it shows up as the cam that hits as high a HP or close to bigger cams but retains a torque curve over 400 lbs from practically 2000 rpms up. All the others may make 10 more HP but don't hit 400 lbs of torque till later and don't carry it as long either. HP and Torque on it just hug each other all the way up. Even when you make small changes to it's specs just to see if there is room for improvement on it you start to lose torque instantly. It's one of the biggest cams with the most torque. Not that DYNO2000 is THE authority but it's numbers support a lot of what ppl on the net post.

 

400ft/lbs from 2000 rpm up sounds a little too good to be true. Vipers don't make 400ft/lbs at 2000. Given the specs of the 847, (234/242) I'm guessing this thing pulls well past 6000rpm. Might even push 7000. Anyone have this cam & care to talk about it? There's no way you're not sacrificing some low end on a cam that big?

 

This dyno graph is from a guy on Camaroz28.com. This is with STOCK heads, not ported. He made really good power, but he's shifting at about 6800 I believe on the unported heads. Expect this cam to peak VERY high, 6500+, with a set of ported heads. Power will be nice though.

 

Correct me if I'm wrong, but won't ported heads shift the power band up even further? I'm ok with running my stock shortblock up to 6500-6700. Much past that, I chicken out. Don't really know what a crank sounds like falling out onto the road, and I don't really want to. If ported heads wouldn't shift the powerband up too much more (or at all), this looks like it could be the perfect cam for me.

 

A set of ported heads done correctly increases performance ALL around. Granted plenty more on the top end more so than the lowend but it doesn't have to hurt the low end. Those are the advantages of sticking with either the LT1 or LT4 heads as they offer good lowend flow numbers as opposed to the bigger aftermarkets heads that give up some on the lowend(not that there's anything wrong with that).

I don't take the software too seriously either but it starts the "400lbs" at around 2200 or 2300. and at 2000 it's at least like "380 lbs." aside from when it starts it also shows it carries it further than a few other profiles. If in the least the blasted thing shows how the various profiles tend to be like or what their torque/HP curves pattern like in theory. Basically it looks like the big cam with the smallest lowend sacrifice. Ballparking HP levels of bigger ones but shakes hands with torque a little stronger. But again it's just a wannabe computer dyno, what's important is the pattern it reflects(a very good1) cuz that can't be too far off. The differences in real life numbers or output like you suspect will vary.

 

I'll be more specific: do ported heads alter the rpm at which I would be shifting for optimum performance, or is that determined entirely by the cam? The GM 847 cam seems to make peak power between 6600-6800rpm. I have ported heads, and I wouldn't want to move that shift-point up any higher than it already is.

 

Yes, the heads will have a definitive effect on the powerband. That stock headed dyno graph showed the 847 peaking at about 6100, but the owner himself stated that he's not shifting until almost 6800 because of the extremely light drop off. With ported heads, I'd be expecting to shift at about 7000, which could put you into trouble given the stock PCM's ability, or inability rather, to function above seven grand.

 

The ported heads should increase the output levels ALL across AND extend perhaps a bit further but you control your shift points. You don't have to shift that high. And the ported heads will give you more power at the same levels other "unported heads" make less. So your not necessarily changing it's powerband your extending it. Just how far into the extension you want to shift is up to you. Expect to make more power with relatively the same torque/hp curves in the graph just maybe extended a bit further. The cam does determine it's range, the ported heads can extend it, you do not lose lower for higher, you gain, gain, and then gain again. You simply won't be able to take full advantage of the last gain, the extension or less drop off like Fastbird wrote unless you shift higher, but your current shiftpoints will see a gain regardless.

 

Question......Where can I get this GM 847 cam?

 

I've actually decided against the GM 847. Shifting that high is a little much for me, I think. But seriously, where the hell do you get this cam? I checked Thunder, LS1speed, Combination Motorsports, etc . . . it's like no one carries it. If it's on GM Parts Direct I can't locate the serial #.

Anyway, after having looked around on CZ28.com I found a guy pushing 400rwhp with the TN-230HL 230/236 duration, .598"/.608", 112lsa (Combination Motorsports). Question: does anyone know if I would have to fly-cut pistons with this cam? If I don't, I think I'm pretty much sold on it. Obviously, CM would probably be able to answer that, I just haven't had time to call them yet.

 

Hey what is a Fly-cut piston? I'm buiding a 383 LT1, Forged rods/pistons, steel crank. I'm thinkin about running the 233/242, .569/.576 LSA 114 from Combination Motersports, figured the 383 will make up for the torque lost with a higher duration. Think it will be streetable, making aroung 400-425rwhp, maybe more depending on how good the guy does my heads. keepin the lsa 114 for the turbo/nitrous a little later. Give me some pointers if you can about my low-mid range with this cam. Thanks

 

Fly cut pistons are basically pistons with angled cuts in them (imagine looking at a stock piston with its valve indentations, then magnify the size of those). It allows the valve to stick out further without contacting the piston. This gets to be vital with high-lift cams, although I don't know what the magic point is on an unmilled head where it begins to require it.

 

I knew what it meant to fly-cut pistons. Is .600 lift pushing the limit? I assume having to fly-cut can be determined as much by on duration as lift?

 

I did 350/350 on my 224/230 112lsa with homeported heads and with 11 degrees of KR as well as an arcing plug wire LOL now that its all fixed and I have swapped out the stock 100000 mile 24lb inj to some 30# svos I would like to see what I hit my car has been a real fluke with just that cam I was trapping higher than most with the same setup and thats before I had my spec clutch

 

Weird. Seems that the 224/230 cam with ported heads setup is snakebit for some reason. I can think of four people that immediately come to mind that have been having trouble with them, yourself included. I had it and made 375/363 on an initial tune, but then dropped major compression on two cylinders.

I'm going with a 355 forged rod and piston, Eagle ESP cast crank, and swapping everything over, and getting a custom cam. Should be nasty, well over 400. I may even go with the 383 if I can find the extra $500 for the crank.

 

Finally decided on a cam: Combination Motorsports 233/239 .569/.577 110lsa. Should have some wicked lope but based on some of the dyno graphs I've seen, I shouldn't have too much trouble hitting 400rwhp with this cam. I have another question, though. Check this link:

http://web.camaross.com/forums/showt...hreadid=233687

 

Oh I wasnt saying it was the cam I actually no of a dozen that love the cam and have had no problems these problems were apparent before the cam install and just not fixed until now the cam actually has not made anything worse just gives me a nice kick in the *** when I get into it