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Cam-More Intake Duration than Exhaust #3193034
11/24/23 01:55 PM
11/24/23 01:55 PM
Joined: Mar 2008
Posts: 553
Kentucky
clovis Offline OP
mopar
clovis  Offline OP
mopar

Joined: Mar 2008
Posts: 553
Kentucky
What is the situation where you would want a cam with more intake duration than exhaust with a big block? Was cam shopping and ran across a cam with 12 degrees more intake duration at .050? It has 242 degrees of intake and 230 of exhaust.


'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
Re: Cam-More Intake Duration than Exhaust [Re: clovis] #3193054
11/24/23 03:51 PM
11/24/23 03:51 PM
Joined: Aug 2003
Posts: 43,157
Bend,OR USA
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Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
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Joined: Aug 2003
Posts: 43,157
Bend,OR USA
Originally Posted by clovis
What is the situation where you would want a cam with more intake duration than exhaust with a big block? Was cam shopping and ran across a cam with 12 degrees more intake duration at .050? It has 242 degrees of intake and 230 of exhaust.

Changing the amount of lobe lift and duration along with changing the lobe separation angle can help you compensate for a set of bad flowing heads, intake and or exhaust system work twocents


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Cam-More Intake Duration than Exhaust [Re: clovis] #3193070
11/24/23 05:38 PM
11/24/23 05:38 PM
Joined: Oct 2021
Posts: 13
USA
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Underthinker Offline
member
Underthinker  Offline
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USA
I use to race a circletrack class that required a Holley 4412, usually ran cams like this.

Re: Cam-More Intake Duration than Exhaust [Re: clovis] #3193095
11/24/23 07:22 PM
11/24/23 07:22 PM
Joined: Aug 2005
Posts: 760
Southington Ct.
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turbobitt Offline
super stock
turbobitt  Offline
super stock
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Joined: Aug 2005
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Southington Ct.
Originally Posted by clovis
What is the situation where you would want a cam with more intake duration than exhaust with a big block? Was cam shopping and ran across a cam with 12 degrees more intake duration at .050? It has 242 degrees of intake and 230 of exhaust.


In some turbo applications, keeping the exhaust closing to about 0 degrees at .050 is desirable when you are running into drive pressure on the turbine. A lot of exhaust duration starts to really hurt performance because the exhaust will dilute the intake charge. Typically works out around 230 degrees exhaust duration depending on LSA.
AG.


1970 Challenger w/572 Hemi street car and my pride and joy. 1986 T-Type with 272 Stage 2 Buick V6 engine - True 8 second street car. Just updated the engine and put down 928 HP @ 35# boost to the ground on chasis dyno. 1976 Cee Bee Avenger Jet Boat - 460 Ford powered.
Re: Cam-More Intake Duration than Exhaust [Re: turbobitt] #3193098
11/24/23 07:58 PM
11/24/23 07:58 PM
Joined: May 2019
Posts: 712
Lake Villa Il
INTMD8 Offline
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INTMD8  Offline
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Posts: 712
Lake Villa Il
Originally Posted by turbobitt
Originally Posted by clovis
What is the situation where you would want a cam with more intake duration than exhaust with a big block? Was cam shopping and ran across a cam with 12 degrees more intake duration at .050? It has 242 degrees of intake and 230 of exhaust.


In some turbo applications, keeping the exhaust closing to about 0 degrees at .050 is desirable when you are running into drive pressure on the turbine. A lot of exhaust duration starts to really hurt performance because the exhaust will dilute the intake charge. Typically works out around 230 degrees exhaust duration depending on LSA.
AG.


^ I agree if you start getting up there in duration and depending on the combo.

I think however if you have a combination with so much turbine drive pressure you are trying to alter the cam specs because of it, you're better off making changes to reduce the turbine drive pressure and just run a single pattern cam.

I've done a lot of experimenting with turbo cams back in the day and to my surprise, even with turbine drive pressure double boost pressure, single pattern cams with more overlap still outperformed reverse split cams with less overlap with similar duration.


69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700
Re: Cam-More Intake Duration than Exhaust [Re: INTMD8] #3193337
11/26/23 01:37 AM
11/26/23 01:37 AM
Joined: Nov 2006
Posts: 2,255
IL
furious70 Offline
top fuel
furious70  Offline
top fuel

Joined: Nov 2006
Posts: 2,255
IL
Originally Posted by INTMD8
Originally Posted by turbobitt
Originally Posted by clovis
What is the situation where you would want a cam with more intake duration than exhaust with a big block? Was cam shopping and ran across a cam with 12 degrees more intake duration at .050? It has 242 degrees of intake and 230 of exhaust.


In some turbo applications, keeping the exhaust closing to about 0 degrees at .050 is desirable when you are running into drive pressure on the turbine. A lot of exhaust duration starts to really hurt performance because the exhaust will dilute the intake charge. Typically works out around 230 degrees exhaust duration depending on LSA.
AG.


^ I agree if you start getting up there in duration and depending on the combo.

I think however if you have a combination with so much turbine drive pressure you are trying to alter the cam specs because of it, you're better off making changes to reduce the turbine drive pressure and just run a single pattern cam.

I've done a lot of experimenting with turbo cams back in the day and to my surprise, even with turbine drive pressure double boost pressure, single pattern cams with more overlap still outperformed reverse split cams with less overlap with similar duration.





yes, but back pressure at 'only' 2x boost is still pretty 'big' for some street sized turbos. The original setup I did in my Fury had 4x at 5000 rpm! It's 2.5x now. These days a person should be able to size their turbos affordably.


70 Sport Fury
68 Charger
69 Coronet
72 RR
Re: Cam-More Intake Duration than Exhaust [Re: clovis] #3193353
11/26/23 08:18 AM
11/26/23 08:18 AM
Joined: Jan 2003
Posts: 1,335
Oregon
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earlymopar Offline
pro stock
earlymopar  Offline
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Joined: Jan 2003
Posts: 1,335
Oregon
Good post for the "Speed-Talk" website, "engine tech" forum. Amongst others there, the fellow that manages the site is a camshaft designer.







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