Thread: Thumpy Idle

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Originally Posted by dhemi1

Hi guys/gals!

Camshafts are still a bit of a mystery to me.

About what duration do cams make a engine thumpy at idle/poor vaccum?

Is there a general formula/guide I can follow?
Is camshaft duration porportional to vaccum loss?

In a nutshell, what I am asking is, for a street engine how much duration is too much? Or does it come with years of engine building like you guys have?

lol i'm all questions,
thanks in advance,
-CJP

stay in the high 260's to low 270's duration once you start going into the high 280's and up is when it starts getting hard to street the higher duration you go. i usualy ran cams in 268 272 274 & the highest 278 durations for the street. plus you need to run stall converters with some cams and you want to match up the rpm's like let say for example your cam is 2500-5500rpm well you would want a 2500rpm stall converter. also pay attention to the lobe seperations for example 106 degrees of lobe seperation will be racier and snappier than a cam with 114 degrees of lobe seperation but the 114 would be better for higher rpms rather than the 106 but the 106 will reach its power band at a lower rpm than the 114. but me for example just to give you an idea i set up my engines to run anywhere from 1500 - 6000 rpm and run cams in the 270's with 108-114 lobe seperation and around 440 - 470 lift for a SBC.

Originally Posted by speedy55779

stay in the high 260's to low 270's duration once you start going into the high 280's and up is when it starts getting hard to street the higher duration you go. i usualy ran cams in 268 272 274 & the highest 278 durations for the street. plus you need to run stall converters with some cams and you want to match up the rpm's like let say for example your cam is 2500-5500rpm well you would want a 2500rpm stall converter. also pay attention to the lobe seperations for example 106 degrees of lobe seperation will be racier and snappier than a cam with 114 degrees of lobe seperation but the 114 would be better for higher rpms rather than the 106 but the 106 will reach its power band at a lower rpm than the 114. but me for example just to give you an idea i set up my engines to run anywhere from 1500 - 6000 rpm and run cams in the 270's with 108-114 lobe seperation and around 440 - 470 lift for a SBC.

This is where people will get confused.
Never compare one cams duration to another using advertised duration.
The reason being is they are all different.
Always compare camshafts at .050 when you look at duration.

Thanks everyone for the VERY informative replies!
I am definitely taking notes!
So much information! I feel like if I am in my economics class!

Thanks for the link! I have it book marked

-CJP

Originally Posted by erik erikson

This is where people will get confused.
Never compare one cams duration to another using advertised duration.
The reason being is they are all different.
Always compare camshafts at .050 when you look at duration.

what are you talking about the @.050 has to do with the lift on the cam itself.

Originally Posted by erik erikson

This is where people will get confused.
Never compare one cams duration to another using advertised duration.
The reason being is they are all different.
Always compare camshafts at .050 when you look at duration.

I 100 percent agree on that ..!!!!
Did you see the .0045 compared to the .050 numbers on the cam from The ud harold post...........

and who cares that you ahve to pop the car into neutral at every light because of ridiculous duration its fun that way!!!!!!

Originally Posted by gassersrule_196

and who cares that you ahve to pop the car into neutral at every light because of ridiculous duration its fun that way!!!!!!

Some of us just push in the pedal on the left.....

whatever floats your boat

Originally Posted by speedy55779

what are you talking about the @.050 has to do with the lift on the cam itself.

.050 is one of the industry's standards when you compare cams duration.
Every single cam company has a different advertised duration.

Originally Posted by Yellow72

Some of us just push in the pedal on the left.....

L.M.A.O.