We are currently running on the new domain and server: www.Speed-Talk.com

IMPORTANT: Update your bookmarks to https://www.speed-talk.com/forum/
(Right-click the URL and select "Bookmark this link")

cam suggestions for 355

General engine tech -- Drag Racing to Circle Track

Moderator: Team

CGT
Guru
Guru
Posts: 1887
Joined: Sun May 10, 2009 12:29 pm
Location:

Re: cam suggestions for 355

Post by CGT » Mon Jan 20, 2020 9:19 am

jeff swisher wrote:
Mon Jan 20, 2020 8:31 am
1.7 ratio in a sbc is not worth the expense in my book for the small gains.
Read a little here about it.
That's a generic statement if I ever heard one. I guess that thread is somehow proof to never put a 1.7 rocker on a sbc.. :D

I remember one time I lent a friend a set of higher ratio rockers to try on an engine he was dynoing for a customer. The customer was going to make a decision of buying them (his own higher ratio rockers) from the results. The customer decided not to buy them after seeing the results, he thought they weren't worth enough power to justify buying them....they made 8-10 average more hp in the range the engine was to be operated in.

I remember thinking...What did you think they would make 50 horsepower more? :lol:

I've seen ratio changes do nothing on the dyno, I've seen gains like I just mentioned, and I've seen gains of more than that. "Worth the expense" is completely relative to a lot of different things.
There are basically two types of people. People who accomplish things, and people who claim to have accomplished things. The first group is less crowded.
Mark Twain

Golf is a good walk spoiled.
Mark Twain

User avatar
CamKing
Guru
Guru
Posts: 9346
Joined: Wed Aug 08, 2007 4:05 pm
Location: Denver, NC
Contact:

Re: cam suggestions for 355

Post by CamKing » Mon Jan 20, 2020 10:31 am

trmnatr wrote:
Mon Jan 20, 2020 1:52 am
[The 1.7 rocker won’t add any duration at .050” as that’s solely.050” tappet lift which is controlled by the camshaft lobe however the higher rocker ratios will provide more valve lift and make the seat duration at the valve longer with more valve area under the lift curve
Here's how it actually works.
When increasing the ratio, the seat duration stays the same, because the higher ratio requires a higher valve lash(if you were running .015" with 1.5 rockers, you would go to .017" with 1.7 rockers). If it's hydr, the point the lifter goes solid, is the same, so the seat duration is the same.

Since .050" duration is measured at the lifter, rocker ratio doesn't change it. What it does change, is how it acts. Say you have a cam that's 260 @.050" lifter rise. With a 1.5 rocker, that equates to 260 @ .075" Valve Lift. Now if you put a 1.7 on it, it 260 @ .085" valve lift. That would mean it about 264 @ .075" Valve lift, when comparing the 1.7 ratio lift curve to the 1.5 ratio lift curve. This holds true at ever valve lift point. Going up in rocker ratio keeps the seat duration the same, while increasing the velocity, acceleration, lift, and area.
Mike Jones
Jones Cam Designs

Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449

superdirtbag2
New Member
New Member
Posts: 9
Joined: Sat Nov 21, 2015 4:15 pm
Location:

Re: cam suggestions for 355

Post by superdirtbag2 » Mon Jan 20, 2020 5:26 pm

Now things are starting to make sense in terms of rocker ratio and duration. In relation to head flow, an engine with weak heads wouldnt gain as much as one with strong upper lift flowing heads by increasing rocker ratio and may even make less power if heads backup around the rockers created new max lift number...I assume. But since it is increasing valve speed, on a good higher lift flowing head is the valve moving past those lift points too fast to make a difference?
My father, brother, and I all go by the motto "enough is good, more is better, and too much must be just right" at least when it comes to horse power!

Again I thank all who have responded...

trmnatr
HotPass
HotPass
Posts: 16
Joined: Fri Dec 06, 2019 4:01 am
Location: Maryland

Re: cam suggestions for 355

Post by trmnatr » Sun Feb 02, 2020 5:26 pm

CamKing wrote:
Mon Jan 20, 2020 10:31 am
trmnatr wrote:
Mon Jan 20, 2020 1:52 am
[The 1.7 rocker won’t add any duration at .050” as that’s solely.050” tappet lift which is controlled by the camshaft lobe however the higher rocker ratios will provide more valve lift and make the seat duration at the valve longer with more valve area under the lift curve
Here's how it actually works.
When increasing the ratio, the seat duration stays the same, because the higher ratio requires a higher valve lash(if you were running .015" with 1.5 rockers, you would go to .017" with 1.7 rockers). If it's hydr, the point the lifter goes solid, is the same, so the seat duration is the same.

Since .050" duration is measured at the lifter, rocker ratio doesn't change it. What it does change, is how it acts. Say you have a cam that's 260 @.050" lifter rise. With a 1.5 rocker, that equates to 260 @ .075" Valve Lift. Now if you put a 1.7 on it, it 260 @ .085" valve lift. That would mean it about 264 @ .075" Valve lift, when comparing the 1.7 ratio lift curve to the 1.5 ratio lift curve. This holds true at ever valve lift point. Going up in rocker ratio keeps the seat duration the same, while increasing the velocity, acceleration, lift, and area.
I agree, just trying to explain it in typing only is not my strong point lol

Only difference I have seen is the stud rockers with a solid don’t take up the lash until about the same tappet lift such as a .020” lash is not taken to zero until around .020” lifter rise & this was multiple ratios through 1.7 or 1.8 rockers! I found the rocker to not be pivoting until the lash is taken up when the poly lock jams against the fulcrum

Now going from 1.5 stud to 1.5 shaft with stud rocker lash of .016” , at .016” the shaft rockers were a bit more seat duration at the valve, which was because they pivot only always working at their ratio. At .024” lash, the shat rockers were the same at the valve (open and close) and with 1.6 the same open and close (I was going by when it’s .000” lash to .001” lift and was a major pita) while 1.6 rockers had to be .026” lash. I didn’t see much if any change in the stud rockers

I also posted a chart a while back where I measured the valve lift every 2 degrees btdc on both valves and atdc on both and on the intake I went through .300” or .400” lifter rise
www.autotransdesign.com www.gzmotorsports.com
www.cranecams.com www.prosystemsracing.com
www.hardblok.com
Please say a prayer for all that serve and gave all to serve this Holiday and everyday!

trmnatr
HotPass
HotPass
Posts: 16
Joined: Fri Dec 06, 2019 4:01 am
Location: Maryland

Re: cam suggestions for 355

Post by trmnatr » Tue Feb 11, 2020 8:08 pm

superdirtbag2 wrote:
Wed Jan 15, 2020 6:57 pm
Greetings and Thank you in advance to all who read and reply,

Building a bucket list 355 chevy for daily driver crewcab s10. Not a too mild mannered 355 tho...
afr vortec heads
190cc Street Head Flow Chart
.200 .300 .400 .500 .550
Int 135 213 253 276 279
Exh 110 158 190 207 211
edelbrock rpm vortec intake non airgap (gets pretty cold here). 735cfm holley, off of 428 cobrajet, with spacer(s) if/as needed. 1 5/8 long tube headers.
Shortblock= 9.7 :1 comp with 65ccheads...propersized dish and valve reliefs for above mentioned heads with zero deck and felpro head gasket. torqueplate honed line honed square decked etc...windage tray...possible block filler to bottom of freeze plugs, as current setup runs below 190 even in summer. Custom oil pan. Msd e-curve dist.

Have searched a few companies and filled out a couple forms for a solid roller...Comp for example showed a cs xr268 r10...or CS XR274 R-10.
After looking at these and the specs i guess my main question would be would the xr268 be better with a 1.7 rocker setup over the xr274 with a 1.6 rocker? Taking into account the 1.7 rockers effect on duration as well as lift has me stepping into territory I am not totaly understanding of. As well as the 110 lobe separation. I do need power brakes to work reliably.

The truck has a 2500stall converter, th700r4, and 3.73 rearend. It has a basic smallblock in it now, but am looking for more within reason...and yes I do realize thats a subjective statement, but none the less am wondering what the more knowledgable individuals on here have to say.

Again thank you God bless and Semper Fi

p.s. anyone willing to hoot a guess on hp/tq and rpm?
If you consider hydraulic roller i would use a custom Crane hydraulic roller and their good retro lifter or GM lifters if you have a roller block, cam specs below
284/292 @.006" tappet lift
222/230 @.050" tappet lift
141/150 @.200" tappet lift
.509"/.528" lift W/ 1.5 rockers
108° lobe center, 103° intake center line
This is a selection of lobes and lobe center I came up with for 350 with 9.5:1 to 10:1 compression with GM 291, 461 etc with mild work or Dart 180 Iron Eagle heads which is what the motor below has

Here is a video of that camshaft
https://s510.photobucket.com/user/331Tr ... 3.mp4.html
www.autotransdesign.com www.gzmotorsports.com
www.cranecams.com www.prosystemsracing.com
www.hardblok.com
Please say a prayer for all that serve and gave all to serve this Holiday and everyday!

Post Reply