picking new cam? read this

[sothpaw]

Thought the readers of this forum who are contemplating a cam change might benefit from some lessons I just learned:

The extra parts required to do a cam change are not necessarily just new lifters and springs. Depending on what springs and how agressive the cam is (read: how much lift) you might need much more.

My cam is 566/563 lift, 214/224 dur, and 112 lobe sep. With this cam, or even the GM Hot cam, you need stronger springs to prevent valve float at high rpm operation. What I just learned is: if you use really stiff springs, the 3/8" roller rockers and accompanying rocker arm studs comprise an arangement which flex noticably. This flex will increase wear and prevent the maximum horsepower gain of the cam from being extracted. I think the flex prevents the valves from following the cam as well as they should.

At any rate, to prevent this you have to go a 7/16" roller rocker/stud arrangement. Also, I had to have new, non-stock size pushrods because the clearances of the ported heads would not permit the rockers from going on in the exactly correct position.

So, when contiplating a cam, consider the implications to your valve train. It was an extra cost
that I was not prepared for with my set up. I think a mild cam would skweak by with
the stock valve train. How mild that is I don't know.

 

[Ken]

Any project will involve more than you initially planned for. That's why they tell you to pad your budget by at least a third of the total estimated cost.

_ken

 

[rrubel]

So does this mean you have your Vette back?

Tell me more about the non-stock pushrods. Did you have to get custom ones, or are there standard ones you could use?

[RICHR]

 

[sothpaw]

Pushrods--

They are custom length pushrods. They were necessary because of the ported cylinder heads, not the cam. Basically, with the machining that was done and the head gasket I need to use (94 impala ss iron-head Lt1 gasket, not vette Lt1 gasket) the length of the stock pushrods was not quite right to get the RR's lined up properly.

Back--

Nope. Schedule and cost on this project are blown. I will get the car back, but I can't use it for what it was intended for, June races. I built one month slack into the schedule and it was still not enough.

 

[rrubel]

But it'll be worth it when you're done...

Why did the porting and polishing change the pushrod length? Is it because the valves sit deeper in the heads, so the stems are higher?

[RICHR]

 

[Vettelt193]

I thought you were running Crane Cams roller rockers before? I haven't heard of them flexing at all with your type of cam (specs wise), or with the HotCam. (which is why GM packages the HotCam kit with the Crane rockers) It isnt' bad you are upgrading, but it seems like a big waste of money to me. What did he do to the heads that required the pushrods? that seems strange as well...

 

[rrubel]

Sothpaw, you have 1.6 RR's now, right? If they'll work in my L98, I'll buy them from you when you get your 7/16" ones.
[RICHR]

 

[sothpaw]

Vettelt193,

He machined down where the head gasket goes, I think. He advises that I must use the impala ss head gaskets, which are thiner than stock (I get a little more hp from higher comp. ratio, perhaps) or else it would not seal right. The stock pushrods should have been on the hairy edge of ok, but I guess it was close enough that for good alignment the mechanic put in the new ones (I had new shipped just in case needed on contigency).

Yes, I had crane RR's from GM (had bowtie insignias). It was not the RR that was flexing, it was the 3/8" stud. Whatever spring he used was very stiff. I know that the Hotcam is hard on springs, maybe they use more flexible one that wear out faster than these.

Yes, seems a waste, that's why I wrote this thread. Maybe if you go with less lift and more duration you don't have to use such stiff springs. I think I will be happy with the performance, but if I had known, I would have been able to order the parts on time and get the car back much sooner.

Rich,
See above about pushrods--it's the head gasket partially. As for the RR's yes, I was planning to sell to re-coupe some of the loss. I have 3 extra sets right now--have 2 sets to return to summit! Those guys shipped me parts I couldn't use, and I had them AIRMAILED in...

 

[rrubel]

Lemme know what you want for them... and what the part number is, if you remember, so I can check if they'll work for me.
[RICHR]

 

[Vettelt193]

I know the stud is the weak link, but it just isn't that weak. The studs are made of a hardened metal that is designed to resist flexing.

enough of my resistance.... what is the timeframe of getting your car back now? That is all that really matters at this point! I guess the question should be "How fast until you go fast?"

 

[sothpaw]

I think he was within 2-3 hours of finish last Thursday. But, unfortunately for me, he has closed the shop this week and last friday, so it will be early next week.

Yes, the 3/8" studs are stiff, the 7/16" stiffer. That is all the mechanic can tell. So, I had to trust the heads/cam supplier that going to 7/16" was the right thing. It also says in a book I borrowed, "whenever you change to a healthy performance cam", 7/16" studs/ rockers are in order. I'm thinking it depends alot on the springs and the lift.

 

[grumpyvette]

read this, it will give you the basics on how and why things work



http://victorylibrary.com/mopar/cam-tech.htm

http://www.mercurycapri.com/technical/engine/cam/lca.html

http://victorylibrary.com/mopar/rod-tech.htm

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html

http://www.chevytalk.org/threads/showflat.php?Cat=&Board=UBB64&Number=397334&Forum=UBB64&Words=LSA&Match=Entire%20Phrase&Searchpage=3&Limit=25&Old=allposts&Main=397176&Search=true# Post397334

if cams are a mystery please take the time to read these, it will get you a good start

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm
(read LESSONs 1-8)

http://www.mercurycapri.com/technical/engine/cam/lca.html

http://www.wighat.com/fcr3/confusion.htm

http://www.cranecams.com/instructions/valvetrain/camfail.htm

http://www.mercurycapri.com/technical/engine/cam/index.html

http://www.idavette.net/hib/camcon.htm

http://www.cranecams.com/master/adjustvt.htm

http://www.centuryperformance.com/valveadjustment.htm

http://www.totalengineairflow.com/tech/valvelashing.htm

http://www.chevytalk.com/tech/engine/Cam_Selection.html

http://www.chevytalk.com/tech/101/Cam_Theory.html

http://www.babcox.com/editorial/ar/ar119736.htm

http://www.mercurycapri.com/technical/engine/cam/vtg.html

http://www.n2performance.com/lecture1.shtml

http://www.symuli.com/vw/camp1.html

http://www.symuli.com/vw/camp2.html

http://home.wxs.nl/~meine119/tech/camqa.html

http://www.chevytalk.org/threads/showflat.php?Cat=&Board=UBB64&Number=200511&Forum=UBB64&Words=your%20kidding&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=200510&S earch=true#Post200511

http://www.crower.com/misc/valve_timing_chart.html

http://www.speedomotive.com/Building Tips.htm

http://www.kb-silvolite.com/page05.htm

http://chevyhiperformance.com/techarticles/94138/

http://www.aera.org/Members/EngineTech/engine.htm

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html]