cam timing - Page 2 - 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
  #16 (permalink)  
Old 09-08-2010, 11:33 AM
Registered User
 
Join Date: Feb 2010
Location: Ohio
Posts: 112
Wiki Edits: 0

Thanks: 0
Thanked 5 Times in 4 Posts
Straight up timing is defined as when the lobe separation angle and the intake centerline angle are the same. Most racing cams are ground with no advance in them, so if they are installed "dot to dot", that is straight up: a 110 lobe separation cam will be installed at 110 intake centerline. Most aftermarket street cams are ground with 4 degrees advance. If you have a aftermarket street cam with 110 degrees lobe separation angle and put it in dot to dot, your intake centerline will be 106 degrees. You would have to put in a 4 degree bushing and retard it back to 110 degrees intake centerline to be straight up, even though dot to dot is what everyone thinks is automatically straight up timing. It is dependant on how the cam is ground.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #17 (permalink)  
Old 09-08-2010, 12:10 PM
randolphi's Avatar
Registered User
 
Join Date: Aug 2010
Location: South Central Texas
Posts: 46
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Flow rate of reed valves,----

I like the reed valve idea, but feel that locating them between manifold&head port would be more effectual, however, I do not know of any " reeds" that could control up to a 4in pistons airflow or pressure "needs"
Reply With Quote Quick reply to this message
  #18 (permalink)  
Old 09-08-2010, 12:43 PM
Dirty Biker's Avatar
Bold As Love
 
Last photo:
Join Date: Aug 2010
Location: In my van, down by the river.
Age: 38
Posts: 378
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Well we were talking about putting the reeds in the head next to each intake port on the head I think, thats the only way it would work I reckon. As far as them being an obstruction in the air flow, (compared to no reeds at all) that may be true, but at higher rpms when they are no longer needed, they would simply be open all the time so it would be a matter of having a big enough reed cage to flow the cfms needed for the hp desired. My 38 mm carb on my husky for example could theoretically flow a whole bunch, not sure exactly sure how much and at what vacuum but if each cylinder had a reed cage like a rm250 suzuki that could make 57 horsepower, that would be about 456 horses right? To flow more you could have a reed cage with 6 reeds in it per cylinder (my husky reed cage only has four reeds) and get more flow that way. There may be bigger reeds that would be better I dunno. Its all just kinda a new idea I guess! Anyways for sure at least it would let you run that long duration cam without the reversion at low rpms and still have the high rpm magic once the intake runner inertia kicked in at higher rpm. Kinda the best of both worlds I guess.

As far as handling a four inch piston, I am pretty sure the positive(reverse) intake pressure on a bigger piston is not that much more than the two stroke motor with no camshaft at all. If it is any credit to this, my husky motor has nearly a 3.5 inch piston. The reed valves they make for these motors are made out of some crazy amazing stuff, they can go for lots and lots of miles "flapping in the breeze" or whatever you wanna call it. The ones I took out of it when I upgraded to boysen dual stage reeds looked like the original ones from 1981 according to Andy at the husky shop I go to.

Between this reed stuff and the spanny chambers we are talking one crazy motor here... Crazy!!!!!
Reply With Quote Quick reply to this message
  #19 (permalink)  
Old 09-08-2010, 01:08 PM
benwantland's Avatar
Member
 
Last photo:
Join Date: Oct 2004
Location: Iowa
Posts: 199
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
All the theoretical discussion going on here is fun, but I think this gets to the meat of the original question:

Quote:
Originally Posted by Adam65
Straight up timing is defined as when the lobe separation angle and the intake centerline angle are the same. Most racing cams are ground with no advance in them, so if they are installed "dot to dot", that is straight up: a 110 lobe separation cam will be installed at 110 intake centerline. Most aftermarket street cams are ground with 4 degrees advance. If you have a aftermarket street cam with 110 degrees lobe separation angle and put it in dot to dot, your intake centerline will be 106 degrees. You would have to put in a 4 degree bushing and retard it back to 110 degrees intake centerline to be straight up, even though dot to dot is what everyone thinks is automatically straight up timing. It is dependant on how the cam is ground.
They're just words, and a lot of this phraseology isn't exactly textbook, but the widely-accepted meaning of installing a cam "straight up" is that the Lobe seperation and Intake centerline are the same, or, in other words, at TDC at the end of the exhaust stroke, the cam is perfectly centered between its intake and exhaust events.

The general consensus among folks who seem to know is that installing the cam 4 degrees advanced from straight up is usually optimal for street applications, and - as mentioned - most street performance cams are ground this way. Most. And most timing sets are made so that installing dot-to-dot doesn't give any additional advance/retard. Most.

But then, the cam grind could be off a bit, or the timing set could have an advance or retard built in that you're unaware of. Or you could have an adjustable timing set and not be sure how to set it. This is why we "degree" cams when installing them. To make sure they're installed in the intended phase relative to the crankshaft.

FWIW - I've always heard that some of the blame for low-compression emissions engines being dogs in the 70's and 80's was because of retarded (at least relative to what we consider normal, i.e. 4 degrees advanced) cam timing.

In general - if all other aspects of the engine are supportive of the change - retarding the cam pushes the power curve farther up the rpm range (moving valuable power out of the lower rpms), while advancing the cam slides the power closer to the bottom end (due to closing the intake valve sooner, letting the engine build more cylinder pressure, i.e. torque).
Reply With Quote Quick reply to this message
  #20 (permalink)  
Old 09-08-2010, 01:11 PM
topwrench's Avatar
Registered User
 

Last journal entry: fish carb
Last photo:
Join Date: Jul 2010
Location: lillian al.
Age: 67
Posts: 290
Wiki Edits: 0

Thanks: 1
Thanked 2 Times in 1 Post
Quote:
Originally Posted by benwantland
All the theoretical discussion going on here is fun, but I think this gets to the meat of the original question:



They're just words, and a lot of this phraseology isn't exactly textbook, but the widely-accepted meaning of installing a cam "straight up" is that the Lobe seperation and Intake centerline are the same, or, in other words, at TDC at the end of the exhaust stroke, the cam is perfectly centered between its intake and exhaust events.

The general consensus among folks who seem to know is that installing the cam 4 degrees advanced from straight up is usually optimal for street applications, and - as mentioned - most street performance cams are ground this way. Most. And most timing sets are made so that installing dot-to-dot doesn't give any additional advance/retard. Most.

But then, the cam grind could be off a bit, or the timing set could have an advance or retard built in that you're unaware of. Or you could have an adjustable timing set and not be sure how to set it. This is why we "degree" cams when installing them. To make sure they're installed in the intended phase relative to the crankshaft.

FWIW - I've always heard that some of the blame for low-compression emissions engines being dogs in the 70's and 80's was because of retarded (at least relative to what we consider normal, i.e. 4 degrees advanced) cam timing.

In general - if all other aspects of the engine are supportive of the change - retarding the cam pushes the power curve farther up the rpm range (moving valuable power out of the lower rpms), while advancing the cam slides the power closer to the bottom end (due to closing the intake valve sooner, letting the engine build more cylinder pressure, i.e. torque).
BOTH ARE CORRECT!!!
Reply With Quote Quick reply to this message
  #21 (permalink)  
Old 09-08-2010, 02:08 PM
Duntov's Avatar
Visit the NASCAR Hall of Fame
 
Join Date: Jun 2010
Location: Near Charlotte
Posts: 411
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Crazy!!!!!

Quote:
Originally Posted by Dirty Biker
Between this reed stuff and the spanny chambers we are talking one crazy motor here... Crazy!!!!!
You're right Biker, it sounds a bit crazy, but with both you and Tech in on it I'm going to follow to see what it comes to. Makes a pretty good thread.
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
installing distributor/timing on sbc 350 075turbo Hotrodding Basics 38 05-19-2010 07:33 AM
Cam Timing PLEASE HELP!! maxpower_454 Engine 4 04-11-2009 07:02 AM
Cam Timing reflog Engine 13 07-08-2008 10:00 AM
cam advance/retard & dizzy timing wayneair Engine 5 12-14-2005 07:50 AM
Cam Help black66 Engine 3 05-12-2003 06:15 PM


All times are GMT -6. The time now is 09:27 AM.


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.