cam recommendation ?

zzebby · April 05, 2005, 10:53:47 PM

Maybe a bit OT , but .....have a old rumpedy rumpedy 396 BBC that was built up in the 70's with a long duration, high overlap cam. Was fun to drive at first but now it needs to be more of a daily. Stick shift 4 speed, 66 Chevelle with 3.55 gears. Now is stock intake and quadrajet, headers, stock heads with hard seats and a .030 overbore.
I'd like a bit more cam than the stock one, but I've been out of this performance spec area for some time so need to know what is todays "accepted" cam specs or maybe even a recommended grind.
thanks

Pics of the 34 coupe on the next post.......if I can figure out how to reduce size............
zzebby

1FATGMC · April 05, 2005, 11:39:17 PM

Quote from: "zzebby"Maybe a bit OT , but .....have a old rumpedy rumpedy 396 BBC that was built up in the 70's with a long duration, high overlap cam. Was fun to drive at first but now it needs to be more of a daily. Stick shift 4 speed, 66 Chevelle with 3.55 gears. Now is stock intake and quadrajet, headers, stock heads with hard seats and a .030 overbore.
I'd like a bit more cam than the stock one, but I've been out of this performance spec area for some time so need to know what is todays "accepted" cam specs or maybe even a recommended grind.
thanks

Pics of the 34 coupe on the next post.......if I can figure out how to reduce size............
zzebby

Besides here you might want to post this on the Chevy Talk Performance board.

Do you know what compression you are running in the motor. If it is high a milder cam might give you too much compression and present detonation problems.

If it is a stock low compression smog motor a cam with less duration might really wake it up.

c ya, Sum

zzebby · April 06, 2005, 12:30:14 AM

Quote from: "1FATGMC"Besides here you might want to post this on the Chevy Talk Performance board.

Do you know what compression you are running in the motor. If it is high a milder cam might give you too much compression and present detonation problems.

If it is a stock low compression smog motor a cam with less duration might really wake it up.

c ya, Sum

It's a fairly stock motor, but not low compression smog moter. It is the 66 original, so with closed chamber heads and the overbore it's probably 10 :1 even with stock pistons.

Crosley.In.AZ · April 06, 2005, 10:05:37 AM

Perhaps you could call Comp cams and ask them?

It would be a place to start.

Perhaps a near stock profile cam?

As Sum mentioned some of the modern profiles are intended to boost operating compression ratio and this could lead to the engine rattling / pinging a bit

Pope Downunder · April 07, 2005, 07:00:27 AM

Quote from: "zzebby"
Quote from: "1FATGMC"Besides here you might want to post this on the Chevy Talk Performance board.

Do you know what compression you are running in the motor. If it is high a milder cam might give you too much compression and present detonation problems.

If it is a stock low compression smog motor a cam with less duration might really wake it up.

c ya, Sum

It's a fairly stock motor, but not low compression smog moter. It is the 66 original, so with closed chamber heads and the overbore it's probably 10 :1 even with stock pistons.

The compression ratio will be a problem. This site is very useful for understanding Dynamic Compression Ratio (DCR) and has a link to a DCR calculator. http://members.uia.net/pkelley2/DynamicCR.html

I used this calculator when building my latest engine for the pickup, and I am pleased with the results. I ended up using a Crane dual pattern cam. Using the DCR calculator and varying some other critical specs will allow you to select the right cam. With todays fuel you have to get this right.

HOTRODSRJ · April 07, 2005, 02:59:37 PM

Some great suggestions here....my pultry turn.

Yes, do the DCR first, but you may not have all the info to do such. I would say that 10 to 1 SCR is a given anywho and with iron heads and such you cannot go too stockish or pay at the pump and retarding the spark/timing.

But, you could pull the heads to see what gasket thickness they are using. We recently did this on a 69 version and ended up adding a thicker gasket (without sacrificing too much optimum quench/squish) lowering the SCR to around 9.6 to 1, then going back with a CompCams XE 274 ( http://www.compcams.com/Technical/Search/CamDetails.asp?PartNumber=11-246-3 )

The cam grinds today are soooooooooo much better than 20 years ago. Anywho....more power, better fuel milage and still a fun beater to boot.

Just another idea??

rumrumm · April 07, 2005, 05:23:31 PM

One of the regulars on the Chevytalk Performance Forum recommends calling at least five or six cam companies like Crane, Comp, Crower, Lunati, etc. and asking for their recommendations. Then average them together and go with the cam that is the closest. Good advice if you don't understand cam technology real well. There are cams these days that will give you not only driveability but also more power than your original cam produced. Steve is right about checking the DCR with those cam specs. It should not be over 8.0:1 with iron heads.

zzebby · April 08, 2005, 12:09:54 AM

Wow you guys are making me nervous........cause I got impatient today and ordered the cam and other pieces from Summit.
Competition Cams p/n 11-234-3 which is grind CBXE256H-10
256 degrees duration on intake and 268 on exhaust.
.480 lift on intake and .485 on exhaust
110 degrees lobe separation

I foggily recall from "the day" having a built small block with 310 degrees of duration and it was wild but streetable. The one I ordered today seems mild by compairison?

?
Anyway, I'm committed now and if it doesn't work out ......well........ pull the engine and change it again. .........or sell it and finish the coupe.
Will post the results
thanks

1FATGMC · April 08, 2005, 12:56:28 AM

Quote from: "zzebby"Wow you guys are making me nervous........cause I got impatient today and ordered the cam and other pieces from Summit.
Competition Cams p/n 11-234-3 which is grind CBXE256H-10
256 degrees duration on intake and 268 on exhaust.
.480 lift on intake and .485 on exhaust
110 degrees lobe separation

I foggily recall from "the day" having a built small block with 310 degrees of duration and it was wild but streetable. The one I ordered today seems mild by compairison??
Anyway, I'm committed now and if it doesn't work out ......well........ pull the engine and change it again. .........or sell it and finish the coupe.
Will post the results
thanks

The problem might be that this new mild one might be too mild and keep the valves closed too long and build too much compression. With the wilder cam you were bleeding off compression, so you could live with more static compression.

If it was me I would still maybe check with them and see what they say. It would always be easier to send the cam back before it is in the motor. That does look like a nice cam with 212 and 218 duration at .050. A good torque cam. You might just be fine.

c ya, Sum

HOTRODSRJ · April 08, 2005, 06:30:03 AM

Quote from: "zzebby"Wow you guys are making me nervous........cause I got impatient today and ordered the cam and other pieces from Summit.
Competition Cams p/n 11-234-3 which is grind CBXE256H-10
256 degrees duration on intake and 268 on exhaust.
.480 lift on intake and .485 on exhaust
110 degrees lobe separation

Unfortunately, you're in trouble I can tell you with your cam selection! The last poster is correct.... The DCR WILL BE too high for pump gas as is. I would at least do the XE268 or XE274 route and NOT have to tear it out again. You might be able to get by with leaving the compression alone and the XEs are both great sounding, very good street behaving cam grinds. I think you will be impressed. Make sure to set the ignition up correctly and if you are using an HEI use vacuum advance and LIMIT it to only 10 -14 degrees. I would set the static timing at 8 and all (about 34ish) in by 2800 rpms.

Otherwise....you have already bought trouble.

rumrumm · April 08, 2005, 07:43:23 AM

It is better to return the cam than to build an engine that won't work properly or destroy itself. I've returned a cam to Summit before. It's no big deal.

enjenjo · April 08, 2005, 10:57:50 PM

The easies way to do this, is to pick ip a set of 71 or newer heads, the so called open chamber oval port heads. They are 110 CC I believe, and with your 10.5 to one closed chamber pistons will give you just about 9 to one compression.

zzebby · April 09, 2005, 04:09:10 PM

With all these responses, I think I have a problem. If I get this right, I need MORE cam or less compression. More cam would be easy as you say to return and exchange it, option 1.
Or option 2 find some later heads as Enjenjo says. mmmmmmmmmm
I know a guy in west Phoenix who has a few sets of heads, but then I'd need to redo them with hard seats $$$$$$$$$$$$. But I get the feeling that that's maybe the best option. The car has a/c and I will be hooking it up this summer and will be dealing with cooling issues I assume.
SSSSOOOOooooo ya'll agree that open chamber heads and the mild cam option is the best overall way to go??
thanks
zzebby :?:

enjenjo · April 09, 2005, 04:50:30 PM

The 70 and up heads already have hardened valve seats.

kb426 · April 12, 2005, 10:24:50 PM

2 more options. More work, not much money. 1st, solid copper head gaskets. Should be available up to 80 thousandths thick. Do the calculations to see how many ccs you need to gain to drop the comp. 2nd, pull the pistons and machine off some dome. Depending on which piston is in the motor, this may be a good or poor option. IMHO, the best answer is to lower the c.r. to 9 or less. If you do this now, you can pick any cam and have good results. You want more low end, less cam. You want more top end, more cam. No longer worrying about detonation caused by too high of static comp. I ran the copper gaskets on my race cars forever. That would be the simplest fix in my world. If you put on the thick head gaskets, you'll also need thicker intake gaskets. Good luck. I have a similar cam in my 8.5 truck engine and I'm very pleased with the all around performance. No pinging on 87 octane.