Yea I know, not another 847 thread... Well bear with me. This question has definatly not been answered. I know, I searched.

So I spun a rod bearing after only 60,000 mi. (Over heated engine, Mixed oils, Leaking seals EVERYWHERE, and of course, she's been abused...) Anyways, I decided to just do a basic rebuild on the bottom, I had less than .002" of wear on all the walls. So far I've done new crank, one new rod, new bearings, and new piston rings. Then on the top-end I've ordered a Comp Cam 233/242 .569/.587 on a 115 Lsa, along with all the goodies to go along with it. It's not quite as much lift as a 847 but I figure since I know I will be doing a forged 383 here soon (next year actually), it will be good for the nitrous or turbo set-up I want to do at that time. However, my builder has never done a Lt1 before just Gen 1 Sbc's and he seems to think that I'm going to need to clearance my stock pistons in order to acheive enough piston to valve clearance. What do you guys think? Is it neccesary with these big cams on a Lt1 or is that just a thing that Gen 1 Sbc's have? I know he was telling me that on a Gen 1, they have to clearance them for anything over .500 on the lift. I've read all the posts on the 847 and noone ever mentions this so I really don't know. My cam isn't here yet otherwise I would of just put together one cylinder and find out. But if I do need to get clearancing done, I still have time to change my order and get a smaller one in here, even though I'd hate to do that. I just can't afford to put much more money in this thing, my budget is getting pretty much to it's max... Doesn't it feel so great to drop 3k in one night...

 

Why would you replace only one rod? Have the other's been mag'd?

 

Your dynamic compression with that cam will be almost 10:1 The 847 would drop it closer to 9:1. The part that is hurting you is not the lift and the posted .050 duration numbers, but the closing point of the valves.

With anything much over 9:1 it will need some nice tuning to get it to run without detonation on pump gas. If you use that cam mechanically it will be ok, but tune wise you need to get that nailed.

Do not forget to use the appropriate springs.

 

So is there anyway I can easily drop that dynamic compression? Install thicker head gaskets or something? I don't know anything about dynamic compression. My heads will be polished and gasket matched if that makes any difference (Me and a couple buddies are goning to try our luck with porting heads..) When I was talking to Dave at CMotorsorts, he acted like this cam will be perfect for stock heads and will love nitrous. Who knows. I'll have to give them a call. And all the rods looked brand-new (even the one that spun) so we just replaced that one out of caution. the engine wasn't run very long after I heard it. Thanks everyone.

 

Ok, so CMotorsports called me to confirm my order before they ship it out and I changed a couple things. First off, I chose the 230Xr grind so I wouldn't have to worry about the dynamic compression. Then they recommended I purchase 7/16 Studs and Guideplates, a measly $35 so why not. Hopefully this will all work out now.

 

I think the Xr grind is the high-lift version of the 230/236, right? It's the 31xx series lobes, so you have valves that open even quicker. I run the 230/236-112, but with the 33xx series lobes that aren't quite as hard on parts. I had no problems with clearance on a stock bottom end with 1.6 rockers, the heads shaved 0.030, and the thinner Impala gasket (0.029"). I would have your builder check it to be sure. They should do it anyway, but make sure they do.

 

Actually, I think I asked what heads were going on this and what were the numbers, and you said you could get them for me.
Because of the split I didn't deem it too necessary unless you were going to spray.

The TS-230XR is 230/239 .555/.577 114 LSA.
I had Terry call you, because I was worried about the intended use and the size of the first cam on a 3/8 stud.
I know many will say "I run bigger cams than that on my stud", but once you've seen the carnage, it changes your mindset.
Either way, you're covered.

 

Your engine builder is a dumb@ss. Take your parts somewhere else.

Piston clearancing has almost NOTHING to do with peak lift since peak lift occurs nowhere near TDC.

I've run the 847 cam as well as my current cam with .605" lift without ever having to clearance pistons.

Mike

 

Good Job Mike, I'm glad someone gets that!


Anyways WTF is that cam on a 114LSA for?

Personally Mike has said about the best things from a technical standpoint in this whole thread.

Just a few things.....

#1. Stud Size / Strength has to do fully with spring loads and the rocker arm ratio. More spring, more ratio = more bending loads, add RPM to that and it gets worse.

#2. More lift on a cam lobe does not mean it's a more aggressive lobe than one with less lift. Check out lift rule cams, they are way worse than anything else.

#3. Dynamic Compression will go down with a higher ICL (basically LSA) and higher intake duration. The 230 duration on a 114LSA is most likely going to be a lower DCR than a 847.

Not to be a dick about any of this, just watch who you take your advice from.

Bret

 

I was allways under the impression it was the opposite. Glad you cleared that up.