Cam Lift question Please - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 08-26-2010, 10:19 AM
Registered User
 
Last photo:
Join Date: Jan 2008
Location: Washington State
Posts: 272
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Cam Lift question Please

I am not up on exactly how designs work on cams.
I understand the duration and lift etc..but when it comes to
picking and or having one cut for you seems like a shot in the dark.
My question is what or why would the cam lift on exhaust be higher
than the cam lift on the intake? I have a cam I am hoping will work good
and the desk top dyno numbers look impressive. Usually the exhaust lift is
the same or less than the intake lift. My cam lift(s)is .578 int .608 exh
Can someone explain to me the benifit of having the exhaust valve stay
open longer? Doesn't that encroach into the lift of the next intake???
Thanks for the advise.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 08-26-2010, 10:47 AM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,654
Wiki Edits: 0

Thanks: 15
Thanked 58 Times in 55 Posts
While there will be different views on this that`s what it`s all about.
Let`s take the first example, the small block chevy, most stock SBC heads have pretty much the same exhaust port which is short and with a good shape, in stock form it`s efficient. The intake side is not so great without work. I only use dual pattern cams in SBC`s when the exhaust system isn`t as good as it could be. If the system is going to be free flowing and opened up I use a single pattern. Next example, Small block Ford, in stock form the exhaust ports are absolutely horrible, kinked and small, so any help the cam can give the exhaust side is of benefit. If you want to get into technical details of it, go to any big cam company`s web site, comp cams, isky, or just do a general web search on dual pattern cams. I`ve seen some say that what I said about sbc heads isn`t true that the exhaust isn`t so good and the intake is great, however, myself or others I`ve raced with never did much work to a exhaust port simply because it wasn`t needed.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 08-26-2010, 10:49 AM
my87Z's Avatar
Veteran/Firefighter-EMT-I CRT
 
Join Date: Mar 2009
Location: maryland
Age: 30
Posts: 1,685
Wiki Edits: 0

Thanks: 6
Thanked 11 Times in 11 Posts
Quote:
Originally Posted by Fastest65
I am not up on exactly how designs work on cams.
I understand the duration and lift etc..but when it comes to
picking and or having one cut for you seems like a shot in the dark.
My question is what or why would the cam lift on exhaust be higher
than the cam lift on the intake? I have a cam I am hoping will work good
and the desk top dyno numbers look impressive. Usually the exhaust lift is
the same or less than the intake lift. My cam lift(s)is .578 int .608 exh
Can someone explain to me the benifit of having the exhaust valve stay
open longer? Doesn't that encroach into the lift of the next intake???
Thanks for the advise.

you have what are called single pattern cams and dual pattern cams. a single pattern cam will have the same duration and lift on both the intake and exhuast lobes ie; 270/270 220/220 .470/.470" a single pattern cam works well with a motor that has a good set of heads on it, ones with good flowing exhuast ports as well as a car that has a free flowing exhaust. then you have the dual pattern cams, ones with a higher duration and or lift on one lobe or the other. typically you will find that most dual pattern cams come with more duration and lift on the exhaust side simply because with the intake valve being larger it will allow more fuel in than the exhuast valve can let out in the same amount of time. dual patterns are a rather old technology and were produced because not that many people were using aftermarket heads on their motors but using production heads such as the double/camel hump heads which have restrictive exhaust ports and therefor need the cam to open the exhaust valve open more and longer. but now-a-days with more and more people using aftermarket heads there really is no benifit to the dual pattern cam ecept for the fact that it may raise your curve up slightly and creat a touch more peak hp/tq.

since most cams out today still use the dual pattern design you could do something like what i did where i offset the dual pattern by using a larger rocker arm (1.6) on the intake and the stock size (1.5) on the exhaust. but when using any production heads i would still use the dual pattern and take advantage of the extra lift and duration on the exhaust but with most aftermarket heads it is obsolite
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 08-26-2010, 10:59 AM
Registered User
 
Last photo:
Join Date: Jan 2008
Location: Washington State
Posts: 272
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Dual Pattern Cam Answers-Thanks

My cam is the Isky 396284/294 hyd roller, 578int lift, 608 exh lift
I have the old 3964291 LS6 rect port heads with 2.19/1.88 valves.
Was wondering how this thing is going to respond and of course how she will sound. My buddy's desk top dyno software says with my setup she'll
be 539hp @ 5500 7 565tq @ 4000
Oh I have a 454 +.060, SRP 141636 w/-14 dome, 108.9cc heads to the best
of my knowledge I will be right on or around 9.7 depending on which head
gasket I go with for thickness.
Commets please?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 08-26-2010, 11:05 AM
my87Z's Avatar
Veteran/Firefighter-EMT-I CRT
 
Join Date: Mar 2009
Location: maryland
Age: 30
Posts: 1,685
Wiki Edits: 0

Thanks: 6
Thanked 11 Times in 11 Posts
Quote:
Originally Posted by Fastest65
My cam is the Isky 396284/294 hyd roller, 578int lift, 608 exh lift
I have the old 3964291 LS6 rect port heads with 2.19/1.88 valves.
Was wondering how this thing is going to respond and of course how she will sound. My buddy's desk top dyno software says with my setup she'll
be 539hp @ 5500 7 565tq @ 4000
Oh I have a 454 +.060, SRP 141636 w/-14 dome, 108.9cc heads to the best
of my knowledge I will be right on or around 9.7 depending on which head
gasket I go with for thickness.
Commets please?

no,no,no the headgasket thicknesses shouldn't vary that much. you want your "in the hole" (piston @TDC to deck) clearance + your deck to head clearnace (called quench) to be at an optimal .039-.045" so if you are in the hole by .015" then you should be looking for a .030" headgasket, dont go messing with the quench as you will be messing with detonation
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 08-26-2010, 11:13 AM
my87Z's Avatar
Veteran/Firefighter-EMT-I CRT
 
Join Date: Mar 2009
Location: maryland
Age: 30
Posts: 1,685
Wiki Edits: 0

Thanks: 6
Thanked 11 Times in 11 Posts
those heads with some minor port, bowl, valve work, 9.7:1 CR, that cam, and a decent dual plane intake and 850cfm DP on a 468cid should produce atleast 550/550 i think the sim may be a bit conservitive. you have to remember that those heads were on a 454 back in 70-71' that "produced" 450hp and most all would say that it was a very conservitive estimation. most belived it to be over 500hp
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 08-26-2010, 11:13 AM
Registered User
 
Last photo:
Join Date: Jan 2008
Location: Washington State
Posts: 272
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
my87Z..thanks more please

The old pistons were .045 in the hole. this was out
of a reman AC Delco 454 +.030 engine. I was told that is
typical for GM's stock pistons to be .045 +/-. These SRP
#141636 forged alum I've been told are like others like KB's
in that they are .020-.025 in the hole. I was going to have the block
decked but chose not to due to wanted to run pump gas..BUT!!
want to be 9.5-9.7. No way of knowing I guess how much in the hole
the new pistons will be until she is together. Unless you know???
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 08-26-2010, 11:16 AM
my87Z's Avatar
Veteran/Firefighter-EMT-I CRT
 
Join Date: Mar 2009
Location: maryland
Age: 30
Posts: 1,685
Wiki Edits: 0

Thanks: 6
Thanked 11 Times in 11 Posts
Quote:
Originally Posted by Fastest65
The old pistons were .045 in the hole. this was out
of a reman AC Delco 454 +.030 engine. I was told that is
typical for GM's stock pistons to be .045 +/-. These SRP
#141636 forged alum I've been told are like others like KB's
in that they are .020-.025 in the hole. I was going to have the block
decked but chose not to due to wanted to run pump gas..BUT!!
want to be 9.5-9.7. No way of knowing I guess how much in the hole
the new pistons will be until she is together. Unless you know???

no, the only true way is to measure when it it all together. in my opinion you shouldn't even buy your head gaskets until you have measured, never by them blindly. and never buy "all inclusive" gasket kit's as they will typically set your quench through the roof.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 08-26-2010, 11:27 AM
Registered User
 
Last photo:
Join Date: Jan 2008
Location: Washington State
Posts: 272
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
my87Z & doublevision THANKS.more please

I have not purchased head gaskt yet and won't till the very end.
After she is together (short block) my only way to get more out of
it if the pistons are more than .015-.020 is to shave the heads or
reduce head gasket thickness. I really do not want to mill the heads
as I am basing my calcs on Mortec and other site for the "cc" measurement
on the 291 which come up as 108.9. Which who knows if that is correct
and/or if they have been mill already in the past.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 08-26-2010, 11:38 AM
my87Z's Avatar
Veteran/Firefighter-EMT-I CRT
 
Join Date: Mar 2009
Location: maryland
Age: 30
Posts: 1,685
Wiki Edits: 0

Thanks: 6
Thanked 11 Times in 11 Posts
Quote:
Originally Posted by Fastest65
I have not purchased head gaskt yet and won't till the very end.
After she is together (short block) my only way to get more out of
it if the pistons are more than .015-.020 is to shave the heads or
reduce head gasket thickness. I really do not want to mill the heads
as I am basing my calcs on Mortec and other site for the "cc" measurement
on the 291 which come up as 108.9. Which who knows if that is correct
and/or if they have been mill already in the past.

do search for cc'ing heads it can be done in your backyard with about 10-15.00 of drugstore supplies and a CD or peice of plexi glass. and you really dont want to reduce the headgasket thinkness more than .005" one way or the other so that you maintain the quench that i mentioned. this is very important. while you are searching this site you should also look up the work quench. it is not something to be minipulated by much and certainly not to gain a quarter point of compression
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 08-26-2010, 11:52 AM
Registered User
 
Last photo:
Join Date: Jan 2008
Location: Washington State
Posts: 272
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
my87Z...again..thanks

I will remember that bit of good info on the quench.
"you want quench to be right on or dam close to .045..!!"
and quench equals "in the hole plus gasket thickness"
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 08-26-2010, 12:40 PM
Registered User
 
Join Date: Nov 2004
Location: California
Age: 67
Posts: 828
Wiki Edits: 0

Thanks: 27
Thanked 21 Times in 19 Posts
Since you have the pistons, and apparently don't want to deck the block, assemble the short block, measure the "in the hole distance", plan a gasket to yield .045 quench, and adjust (mill) the heads to produce your desired CR. Unless you find that you are so far down in that you need to mill the block (or replace pistons) to get to .045. Then, you're looking at a tear down anyway.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 08-26-2010, 01:08 PM
engineczar's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2002
Location: In Flowbench nirvana
Age: 52
Posts: 1,630
Wiki Edits: 0

Thanks: 5
Thanked 43 Times in 40 Posts
Getting back to the original question. Picking whether or not a cam uses a dual pattern or single pattern lobe and or higher lifts on the intake or exhaust side is in many cases a function of the intake/exhaust port flow ratio. While there's no magic ratio number most stock type heads flow somewhere around 65%-70% with the exhaust flowing about 70% of the intake. A lower ratio usually dictates a weaker exhaust port which is helped with more duration/lift/rocker ratio, and consequently a ratio above 70% might require less to prevent over scavenging.
__________________
BSE Racing Engines
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 08-26-2010, 01:51 PM
Registered User
 
Last photo:
Join Date: Jan 2008
Location: Washington State
Posts: 272
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
engineczar..thanks one more ? please

with the 291 rect port heads I have and knowing what the
ports are in them, "in your opinion is the dual pattern cam I have the
optimum choice"? or should I sell it and buy a single pattern
with say .600/.600 with a 246/256 dur on a 110 or 108 LS?
I kind of like the numbers on the one I have..I am more concern with
go power than sound power, but would like her to sound nasty as hell
as a secondary bennie.
Thoughts?
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 08-26-2010, 02:17 PM
engineczar's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2002
Location: In Flowbench nirvana
Age: 52
Posts: 1,630
Wiki Edits: 0

Thanks: 5
Thanked 43 Times in 40 Posts
Those heads in stock form are in the 71% I/E range. If I didn't already have a cam and had to pick one I would probably look at a single pattern cam to start. Those heads are pretty lazy at low RPM's due to how big the ports are. In your case I'm not sure you'd see any big changes going from your current cam to something else until the RPM's get up there. What sort of compression ratio do you have and what's it going in to? and what do you have for an exhaust?
__________________
BSE Racing Engines
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
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:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
327 cam question... Jim Rockford Engine 12 10-26-2009 05:57 PM
Timing chain/ Cam reusing question Biscuit6447 Engine 19 10-23-2009 06:22 AM
Cam Question pena0724 Engine 13 03-07-2009 05:59 AM
Anybody dealt with this guy on ebay? Or through Dirttrackthunder.com? killerformula Hotrodders' Lounge 20 08-31-2008 05:12 PM
A question about dual lift profile engines. dmc12mk3 Engine 8 06-16-2004 10:31 PM


All times are GMT -6. The time now is 12:36 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.