Brought to you in part by:

M&M Restoration & Tool Supply Store

Great deals on auto restoration supplies!

.


NOTICE! The old Mustangsandmore.com is a read-only archive.
Currently the Search function is inoperative, but we are working on the problem.

Please join us at our NEW Mustangsandmore.com forums located at this location.
Please notice this is a brand new message board, and you must re-register to gain access.

  Mustangsandmore Forum Archive
  Ford Racing
  Effect of lobe seperation angle

Post New Topic  Post A Reply
profile | register | preferences | faq | search

next newest topic | next oldest topic
Author Topic:   Effect of lobe seperation angle
Clevo377
Gearhead

Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000

posted 10-29-2001 04:29 AM     Click Here to See the Profile for Clevo377        Reply w/Quote
If everything else stays the same. What effects would changing the LSA of a cam be. Say, if you went from 104 to 106, to 108, to 110, to 112. Is 2 going to make a noticable difference? if so what effect will 8 have?

Paul

kid vishus
Gearhead

Posts: 7251
From: middle of NC
Registered: Oct 2000

posted 10-29-2001 06:04 AM     Click Here to See the Profile for kid vishus        Reply w/Quote
I'm all ears when this one gets answered. That is one of the many things I dont understand real well.

bluestreek
Gearhead

Posts: 1724
From: Athens,GA
Registered: Jul 2001

posted 10-29-2001 12:14 PM     Click Here to See the Profile for bluestreek        Reply w/Quote
The LSA is the mumber of degrees between intake and exhaust lobe centerlines. The LSA can be fine tuned.. By narrowing the LSA, you can increase Cylinder pressure and higher rpm potential by allowing the intake to close earlier and the exhaust to open later. This increases the amount of time that the piston has to travel before exhausting, but may increase the potential for detonation..

Widening the LSA can be tuned to decrease the chance of detonation and improve low end and idle quality..

The duration of the cam must be adjusted for any major rpm range changes..

The lift and size of the valves, will effect the flow potential and velocity of any given head design and cam duration.. Too much flow and duration, without enough compression to keep the velocity up, will cause poor performance and poor intake vacuum.

It goes on and on... .. It's best to tell the cam maker exactly what you are putting it in and what you want out of the combination.. They have computers to take the guess work out of it..

disclaimer: huh??

69maverick
Moderator

Posts: 1539
From: Thomaston,CT.
Registered: Jan 2001

posted 10-29-2001 04:01 PM     Click Here to See the Profile for 69maverick        Reply w/Quote
quote:
Originally posted by Clevo377:
If everything else stays the same. What effects would changing the LSA of a cam be. Say, if you went from 104 to 106, to 108, to 110, to 112. Is 2 going to make a noticable difference? if so what effect will 8 have?

Paul



The effect on a motor with a 104 is it would act like it had more compression becouse the cylinder pressure would be higher than a motor with a 112. You would need higher octane fuel with the 104 than the 112. But I think BS's post pretty much covers it!!

cpmaverick
Gearhead

Posts: 1669
From: Manhattan Beach, CA
Registered: Jan 2000

posted 10-29-2001 11:39 PM     Click Here to See the Profile for cpmaverick        Reply w/Quote
This also affects overlap. If you increase the LSA, you have less overlap. If you decrease it, overlap increases.

You want some overlap because the exiting exhaust gases have a velocity, and the momentum of them leaving draws intake gases in more effectively than if the valve was shut before the intake opened. Of course you do not want intake gases exiting out the exhaust port either.

How much overlap is sort of a black art, I'll leave it to the cam manufacturers. But generally more overlap will bring your power peak to a higher RPM.

------------------
-Charlie Ping
1970 Maverick Grabber
[email protected]
Daily Driver
http://www.maverickgrabber.com

Clevo377
Gearhead

Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000

posted 10-30-2001 05:40 AM     Click Here to See the Profile for Clevo377        Reply w/Quote
Thanks for the replies.

So if I had two cams, one with 250 and 104 LSA, and the other 260 with 108 or 110 LSA. Would they be similar? (given they are installed on the same intake centreline) i.e how much effect does a couple of in the LSA make. Is overlap the main thing that is affected?

I guess an application for this would be if I wanted to obtain higher lift, but given the profiles available I had to go for a longer than optimal duration, I could custom grind the specific cam at a wider LSA to make up for the lost bottom end.

Alternatively, If I wanted more top end but wanted to keep the lift at a reasonable level for reliablility/maintenance reasons, I could grind less LSA into the cam to get where I want to be.

Paul

69maverick
Moderator

Posts: 1539
From: Thomaston,CT.
Registered: Jan 2001

posted 10-30-2001 08:24 AM     Click Here to See the Profile for 69maverick        Reply w/Quote
I'm far from an expert on this but I might try a different ratio rocker to gain more lift. I haven't done the math but if you went from a 1.6 to a 1.7 rocker a cam with .500 lift it would be around .530? with a 1.7 rocker.

bluestreek
Gearhead

Posts: 1724
From: Athens,GA
Registered: Jul 2001

posted 10-30-2001 10:23 AM     Click Here to See the Profile for bluestreek        Reply w/Quote
Clevo377, I found a link you can click on that is pretty good at explaining the basics.. It's a 2 wheeler site, but gives good info that you may be able to use.. I still say that you need to talk to the cam experts to get what you need..

http://www.nightrider.com/biketech/camlsatable.htm

Here's another one:

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

[This message has been edited by bluestreek (edited 10-30-2001).]

Clevo377
Gearhead

Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000

posted 10-30-2001 05:11 PM     Click Here to See the Profile for Clevo377        Reply w/Quote
Thanks Bluestreek. I don't actually have any specific requirements, just curious

Paul
P.S Those links were interesting, thanks.

n2oMike
Gearhead

Posts: 3058
From: Spencer, WV
Registered: Jan 2001

posted 11-03-2001 12:42 PM     Click Here to See the Profile for n2oMike        Reply w/Quote
In a nutshell...

Decreasing lobe seperation:
1. narrows the powerband
2. moves the powerband lower
3. makes the idle choppier
4. makes more power
5. pumps up the midrange

Increasing lobe seperation
1. widens powerband
2. makes the idle smoother
3. takes away from the midrange
4. produces less maximum power

Racers usually use tight lobe seperations. The only exceptions are Pro-Stock, where 500+ ci are revved to the moon with cams so HUGE, tight LSA's produce too much overlap, and nitrous/blower/turbo applications where overlap sends all that extra fuel mixture out the tailpipe!

Tight lobe seperations increase overlap and can help increase velocity in overly huge intake ports (4bbl 351C). This will pump up the midrange, and make the engine feel less "lazy". Some 351C drag race cams have lobe seperations as low as 102-104 degrees. Automatics generally need a tighter lobe seperation for extra midrange.

Small engines with big ports LOVE tight lobe seperations, large engines with small ports work better with wider angles between the lobes.

A tighter lobe seperation also allows you to use a slightly larger cam in a lower rpm range. If you want maximum valve timing without revving the engine to the moon, a tighter lobe seperation can make it happen.

Good Luck!

------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367

All times are ET (US)

next newest topic | next oldest topic

Administrative Options: Close Topic | Archive/Move | Delete Topic
Post New Topic  Post A Reply
Hop to:

Contact Us | Mustangsandmore Front Page

Copyright 2006, Steve LaRiviere. All Rights Reserved.


Ultimate Bulletin Board 5.47d

Amazon Honor System Click Here to Pay Learn More

[Build a free Mustangsandmore.ws Home Page!]

[Posting Pictures]

[About M&M][Members' Pics]

[M&M Conventions] [M&M Mug Shots] [Tech Articles]

[M&M Bookstore] [M&M Restoration & Tool Supply Store]