#1  
Old 09-09-2019, 12:31 PM
Johnny406's Avatar
Johnny406 Johnny406 is offline
Ultimate Warrior
 
Join Date: Jan 2006
Location: Colorado Springs, CO
Posts: 2,874
Default Split vs. Straight Duration Camshafts in a Race Car?

I know that a split duration camshaft is the better choice for our Pontiacs, especially stock and mild performance street applications that are running a full exhaust/cat converters etc. No doubt the Pontiac engineers knew what they were doing and restricted dog leg exhaust motors like ours certainly benefit more from the split duration than other class of motors do.

My question is: For a aftermarket head open exhaust racecar, is that still the case?

For example, I'm about to start building a new 428 to replace my long in use 463. I will transfer over my 74cc 292cfm KRE heads and will be running around 11.0:1 compression with my Hooker Super Comp headers.

I have a 290B6 on the shelf (.540 lift .255/.266 @ .050 duration) but would that cam be any better or worse than say a Comp 306S solid cam that is a straight profile (.555 lift .260 @ .050 duration)?

Again, open headers with 18" 3" extensions for the crankcase exac.

__________________
Johnny US Army Retired
1978 T/A 463 Pontiac, KRE 74cc 292CFM D-ports, Lunati VooDoo, V-max lifters, TKII, ATM 850 E85 carb, TCI TH-350 race tranny, 3600 converter 3.73 12 bolt 11.63@116.68mph
1981 T/A 4-speed 406 Pontiac, Merrick ported 6X heads, Comp 270S cam, Crosswind intake 750 Street Demon, 3.42 30 spline Eaton posi street car.
1980 Formula 350 Pontiac back burner project
1972 LeMans 350 Pontiac
  #2  
Old 09-09-2019, 02:16 PM
Jack Ferris's Avatar
Jack Ferris Jack Ferris is offline
Ultimate Warrior
 
Join Date: Dec 1999
Location: West Jordan UT
Posts: 2,861
Default

Cant beat the 290B

__________________
Jack Ferris
RestoRacing LLC
www.restoracing.com
Sandy, UT
---------------------------------------------------
  #3  
Old 09-09-2019, 02:38 PM
Mike Davis's Avatar
Mike Davis Mike Davis is offline
Ultimate Warrior
 
Join Date: Jun 2000
Location: Athens Ga, or at a NMCA race
Posts: 1,994
Default

290B,
then swap rocker ratios around to see what it likes.
1.5 Int/1.5 Exh
1.65 Int/ 1.5 Exh
1.65 Int/1.65 Exh
1.5 Int/1.65 Exh

That will tell you if the engine wants more on intake or exhaust side.
Changes can also be made in the valve lash as well.
Better the exhaust port flows less cam in needs.
I just swapped from a 1.65 rocker to a 1.6 on the exhaust side only on a Comp .440 lobe cam and the car picked up a tenth in the 1/4.

__________________
66 GTO Nostalgia Super Stock/Street Legal Car
421 CID, stock block, Wenzler Intake, 2- Carter 750 AFB's, 3.90 Gears, Full Factory Interior, Full Exhaust, Stock Suspension 3750LBS 9.77@136.99
Multiple NSCA/NMCA World Champion

66 GTO 389 3x2, 4 speed, 4.33 gear, Montero Red 33K original Miles
67 GTO 2dr Post, 428, Tri Power, 3.55 Gears
80 Trans Am Black SE Y84 W72 WS6
  #4  
Old 09-09-2019, 03:47 PM
Skip Fix's Avatar
Skip Fix Skip Fix is offline
Ultimate Warrior
 
Join Date: Dec 1999
Location: Katy,TX USA
Posts: 20,541
Default

Some theory depends on airflow exhaust/intake ratio on what split to use.

__________________
Skip Fix
1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs
  #5  
Old 09-09-2019, 04:43 PM
pastry_chef's Avatar
pastry_chef pastry_chef is offline
Suspended
 
Join Date: May 2003
Location: Ottawa
Posts: 2,300
Default

Quote:
Originally Posted by Johnny406 View Post
74cc 292cfm KRE heads and will be running around 11.0:1 compression with my Hooker Super Comp headers.
Any flow numbers available?

What intake will you run?

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -4. The time now is 09:29 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017