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Author Topic:   Lobe centers with an A/T on a small block
Nos351C
Gearhead

Posts: 3000
From: Rohnert Park, CA USA M&M member#591
Registered: Jul 2000

posted 02-26-2001 02:20 AM     Click Here to See the Profile for Nos351C   Click Here to Email Nos351C     Edit/Delete Message   Reply w/Quote
Quick refresher course please guys
with an A/T its not recommended to run a 108 right? Does that stay true assuming the A/T has a convertor stall set up to match the cam?
I know the downsides to the 108 Vs. 110 or 112, like less low RPM power, rougher idle, somewhat "peakier" powerband etc. etc.
FYI this is for a 9.5:1 302, mostly street, some "other"...

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Marcus
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69maverick
Gearhead

Posts: 897
From: Thomaston,CT.
Registered: Jan 2001

posted 02-26-2001 10:32 AM     Click Here to See the Profile for 69maverick   Click Here to Email 69maverick     Edit/Delete Message   Reply w/Quote
From what I know on the street you want to stay more near the 110 side but no more than
112. With the auto.You would really want a stall converter. I'm not sure but I think you would want atleast 10.5:1 if you were to go with the 108 lobe sep.

[This message has been edited by 69maverick (edited 02-26-2001).]

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Dave_C
Gearhead

Posts: 744
From: Gadsden, Al
Registered: Aug 99

posted 02-26-2001 11:06 AM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
For that compression ratio the 110 is good. for a lower number you need more.

I run a 104 in my 383W, but it has almost 13:1 compression and a 5000+ stall converter.

I ran a 106 for a while with the same compression and a 4200 converter and it worked well.

Don't really know what efffect it has on idle. Mine will idel in gear at 900 rpm when warmed up. Powerband is pretty wide. comes in around 2500 and pulls very hard all the way to 65-6600. It will rev all the way to 7200 easily, but is shifted at 6800 for consistency.

Later,

David Cole

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Nos351C
Gearhead

Posts: 3000
From: Rohnert Park, CA USA M&M member#591
Registered: Jul 2000

posted 02-26-2001 12:00 PM     Click Here to See the Profile for Nos351C   Click Here to Email Nos351C     Edit/Delete Message   Reply w/Quote
The way I learned it, was that the narrower lobe center would have more valve overlap and as a result have a rougher idle...
all the cams I have played with have been 110's...
guess I'll stick with what works...

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Marcus
What are we closer to?
The moon? Or Europe?
My site

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n2oMike
Gearhead

Posts: 1547
From: Spencer, WV
Registered: Jan 2001

posted 02-26-2001 01:17 PM     Click Here to See the Profile for n2oMike   Click Here to Email n2oMike     Edit/Delete Message   Reply w/Quote
For otherwise IDENTICAL camshafts in a typical naturally aspirated engine....

Within reasonable limits, a tighter lobe seperation angle makes the power range narrower, but larger. Tighter lobe seperation angles generally produce more peak power. Narrowing the lobe seperation angle also moves the power band LOWER in the rpm range.

A 244/254 cam with a 106 LSA will make more power, and make it earlier than an otherwise identical cam with a 114 LSA. However, the 114 cam will idle cleaner and pull more smoothly off idle than the more punchy 106. It will also RPM higher than the 106.

Tighter lobe seperaton angles also produce really choppy idles that most of us like.

Most drag race cams are around 104-108, while street cars generally use 110-114 lobe seperation angles. For hot street cars, I generally like somewhere between 106-110, unless they rely on nitrous or a blower, then wider can be better.

As far as advancing or retarding a cam that's already been ground... Advancing it generally moves the power lower in the rpm range, while retarding the cam (within limits) moves it higher up the scale.

This is really just the basics... but enough to get you in trouble.

Good Luck!

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

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Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 02-26-2001 03:27 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Always 108 or less on a modified SBF with an automatic and low compression.

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Alex Denysenko Co-Administrator and Moderator NHRA/IHRA/SRA member
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link

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