How to choose different intake and exhaust cams? - Alfa Romeo Bulletin Board & Forums
 4Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 161 (permalink) Old 06-27-2012, 03:02 PM Thread Starter
Registered User
 
Join Date: Mar 2007
Location: San Antonio, Texas
Posts: 4,063
How to choose different intake and exhaust cams?

As previously discussed here on the bb, Alfa motors respond very well when different cams are used for the intake and exhaust. Doing this allows you to make good power but also maintain torque. I'm curious about how you should choose the second (exhaust) cam in a performance engine. I often see recommendations for 12mm intake cams paired with 11mm exhaust cams.

But, if you are using a modern cam design like, say, RJR's 136 cam or a JK303cam for the intake how do you choose an exhaust cam that will work best with the 12mm intake cam? For instance, should you use a pretty mild cam, something that is close to stock perhaps, or should you choose a slightly less agressive version of the 12mm intake cam? How should the two different cams interact to get the best results?

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series

Last edited by 180OUT; 06-27-2012 at 03:06 PM.
180OUT is offline  
Sponsored Links
Advertisement
 
post #2 of 161 (permalink) Old 06-27-2012, 06:33 PM
Senior Member
Platinum Subscriber
 
alfaparticle's Avatar
 
Join Date: Oct 2004
Location: Columbia SC
Posts: 12,684
I have an RJ136 intake cam. When I first installed it, it replaced a C&B 10.9 cam and I left the other C&B on the exhaust. It was a big improvement. Later on I replaced the exhaust CB47 with a RJ785 and that was even better with improved mid range torque and low end and idle.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
alfaparticle is offline  
post #3 of 161 (permalink) Old 06-27-2012, 07:53 PM Thread Starter
Registered User
 
Join Date: Mar 2007
Location: San Antonio, Texas
Posts: 4,063
Thanks Ed, but I'm wondering if there's a standard criteria for matching one cam with another.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
180OUT is offline  
Sponsored Links
Advertisement
 
post #4 of 161 (permalink) Old 06-28-2012, 05:46 AM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 6,990
Cam information

Quote:
Thanks Ed, but I'm wondering if there's a standard criteria for matching one cam with another.
Good luck with that.

Even if someone concocted a formula, commercial cam builders don`t give you anywhere near enough information for you to have any idea of their profiles.

Every engine is a different animal internally depending on set-up, even the same engine designs.. As with use, and driver preferences.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"
Alfar7 is online now  
post #5 of 161 (permalink) Old 07-15-2012, 03:10 PM
Registered User
 
ToonRboy's Avatar
 
Join Date: Jan 2007
Location: Illinois
Posts: 2,269
Send a message via Yahoo to ToonRboy Send a message via Skype™ to ToonRboy
Quote:
As previously discussed here on the bb, Alfa motors respond very well when different cams are used for the intake and exhaust. Doing this allows you to make good power but also maintain torque. I'm curious about how you should choose the second (exhaust) cam in a performance engine. I often see recommendations for 12mm intake cams paired with 11mm exhaust cams.

But, if you are using a modern cam design like, say, RJR's 136 cam or a JK303cam for the intake how do you choose an exhaust cam that will work best with the 12mm intake cam?
I think they mean non-symetrical. That is to say, the intake and exhaust LC's are not the same. Unfortunately, with fixed cam timing, you have to choose where you like your power in order to choose the right cams. It's not really 12mm this and 11mm that, that makes them different.
ToonRboy is offline  
post #6 of 161 (permalink) Old 07-15-2012, 03:54 PM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 6,990
Cams

Geez...
In the Alfa world "Asymetrical' cams seems to refer to the intake and exhaust being "not the same" cam lobe design. Not LC position but completely different lobe profiles. Most cam builders are using basically the same "profiles" with different lifts which is very old school...but cheap to build.

In the cam building world "asymetrical" could refer to different I/E cam designs, but more likely they are refering to a cam lobes opening ramp and closing ramp being asymetrical. Even then the intake cam lobe "ain`t" the exhaust cam lobe! Totally different ramp/lobe designs.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"
Alfar7 is online now  
post #7 of 161 (permalink) Old 07-16-2012, 04:05 PM
Registered User
 
ToonRboy's Avatar
 
Join Date: Jan 2007
Location: Illinois
Posts: 2,269
Send a message via Yahoo to ToonRboy Send a message via Skype™ to ToonRboy
Well, in typical fashion two paragraphs from Obi-Wan Kenobi touting lobe design, and denegrating Lobe Centers and their affect on valve timing events.

While i didn't really answer the posters question, the master Obi-Wan didn't offer-up anything more...

Of course lobe design is important, but to "match" the exhaust cam to an intake (for, as Obi-Wan [RJ] says, the driver preferences) , I submit that you need the intake cam's valve timing events.

I mean, what the blazes do you think variable-cam timing does? It certainly doesn't change lobe profile!!
(hint: it changes the cam's Lobe Center) But Obi-Wan already knew that.

Last edited by ToonRboy; 07-16-2012 at 04:40 PM.
ToonRboy is offline  
post #8 of 161 (permalink) Old 07-16-2012, 11:30 PM
Registered User
 
Join Date: Feb 2006
Location: Blaine, WA
Posts: 8,761
Can't we dispense with the personality conflicts and keep this technical.

Red 1991 164S, Black 1991 164S, Red 1987 Milano, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
Richard2 is offline  
post #9 of 161 (permalink) Old 07-17-2012, 09:20 AM Thread Starter
Registered User
 
Join Date: Mar 2007
Location: San Antonio, Texas
Posts: 4,063
[
Quote:
Most cam builders are using basically the same "profiles" with different lifts which is very old school...but cheap to build.
Of course there are exceptions in everything, Richard. A couple of years ago I got a chance to drive what is, hands-down, the best 2.0 Alfa I've ever driven. It was a familiar modified Alfa 2.0 i.e., 10.1 compression, ported head, headers. It used dissimilar off-the-shelf cams from two different manufacturers---11mm ex. and 12mm. The car was fast, idled well, and delivered lots of power in a smooth curve to 7k or so.

Now, obviously, the engine builder had been careful in making his camshaft selection. Equally obvious, some combinations will work better than others and this brings me back to my original question. How do we determine what works and what doesn't?

As in all things there is a canon of knowledge, some of it discrete, but I think it will be useful to know something aboiut its basic outlines. For instance, if we start with a intake cam that is 303 degrees seat to seat w/[email protected] what range of exhaust cams will get you in the ballpark for a useful combination? For obvious reasons, it probably isn't a good idea to use a more radical cam on the exhaust side. But is it better to choose an exhaust cam with 11mm lift but which is otherwise similar to the intake? And when will we run into a point of diminishing returns? What would you run into if you used our intake cam with stock 105.48 exhaust cam? There are some cam dymanics at work here and I'm trying to understand the basics.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
180OUT is offline  
post #10 of 161 (permalink) Old 07-17-2012, 12:39 PM
Registered User
 
ToonRboy's Avatar
 
Join Date: Jan 2007
Location: Illinois
Posts: 2,269
Send a message via Yahoo to ToonRboy Send a message via Skype™ to ToonRboy
Quote:
Can't we dispense with the personality conflicts and keep this technical.
Absolutely. You want technical? try this: Cam Design

Or maybe something less technical, like this: COMP Camsģ - Valve Timing Tutorial...

So you see, it's not "what goes best with this 12mm cam?". There's simply not enough information to answer that. If Alfaparticle's response gives any idea of the difference between the RJ (modern) cams and the C&B cams, what would that be?

Last edited by ToonRboy; 07-17-2012 at 12:50 PM.
ToonRboy is offline  
post #11 of 161 (permalink) Old 07-17-2012, 01:39 PM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 6,990
Information

Did you find those enlightening?

Best part:
Quote:
What we intend to do here is show that camshaft design is not some "black art", but rather a series of decisions and compromises based on the exact application of the cam. Only our many years of experience can say whether a certain combination of lobes will work, so you should trust the judgement of those who have engineered these combinations.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"
Alfar7 is online now  
post #12 of 161 (permalink) Old 07-17-2012, 07:15 PM Thread Starter
Registered User
 
Join Date: Mar 2007
Location: San Antonio, Texas
Posts: 4,063
In other words, sit down, shut up, don't question your betters . . . and buy our cams . . .

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series

Last edited by 180OUT; 07-17-2012 at 07:33 PM.
180OUT is offline  
post #13 of 161 (permalink) Old 07-17-2012, 07:37 PM
Senior Member
Platinum Subscriber
 
alfaparticle's Avatar
 
Join Date: Oct 2004
Location: Columbia SC
Posts: 12,684
After a while you learn who you should trust. You listen to testimonials from trusted users and advice from trusted vendors and then you make your most informed decision.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
alfaparticle is offline  
post #14 of 161 (permalink) Old 07-18-2012, 04:07 PM
Registered User
 
ToonRboy's Avatar
 
Join Date: Jan 2007
Location: Illinois
Posts: 2,269
Send a message via Yahoo to ToonRboy Send a message via Skype™ to ToonRboy
Quote:
180OUT - In other words, sit down, shut up, don't question your betters . . . and buy our cams . . .
That's pretty much what I'm hearing...

Quote:
alfaparticle - After a while you learn who you should trust. You listen to testimonials from trusted users and advice from trusted vendors and then you make your most informed decision.
You could do that. Or you can educate yourself and make a really informed decision...

The answers to your questions are out there free to be had without the disparaging remarks from those who know, and would like you to "trust" them with your money and buying decisions.

...at least we now know what "asymmetrical" means when it comes to cam lobes.
ToonRboy is offline  
post #15 of 161 (permalink) Old 07-18-2012, 04:22 PM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 6,990
Education

I`ve been building these engines, since 1967. I suggest you get started with your education. I`ve got nearly 45 years of effort involved with what I do.. Lots of time and effort.

You seem to think that all my information should be shared. I won`t say you are dumb or naive but you guys seem to have a lot of bad luck thinking....

Get yourself a flowbench and get started learning.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"
Alfar7 is online now  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome