i need help!!!!!

Teef racing

Teef racing

Forum Member
with a blower motor do i need a cam that will hold open the exhaust valves longer to bleed the pressure from the cylinders? a couple of people have said that it is not necessary on a supercharged motor, but only on a naturally aspirated motor?
 
This all depends on how the engine breathes. Comp Cams Cam help would be the last place I would call for a camshaft.
 
first u need to get ur heads flowed so u can get an intake to exhaust flow ratio. then yes on blower engines u want a 112-114 separation and u definately want more exhaust duration. if ur heads are in the 60s percent range intake to exhaust flow ratio then get a cam with 10-16 degrees more exhaust duration. if ur in the mid 70's ratio then something like 7-10 more degrees on the exhaust. even if the heads have a i/e ratio in the 80's i would still go with atleast 6-10 degrees more exhaust especially if u plan on runnin a good amount of boost. then if u get a flow curve u will know how much lift u will need on ur camshaft. and personally i would get something with about .020 more lift than what the head peak flows...just my 2 cents. u need to have as much exhaust flow as possible to take pressure off the pistons i would prolly the cam installed at a 110-114 centerline for a blow car....depending on how high u wanna rev it and where u want ur power band to be at!!!!!!!!
 
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I post this all over the place. LSA or lobe seperation angle is Bullshit. Overlap degrees is what matters. there is no 112 or 114. compare sevral cams.

250@ 0.050 and a 112lsa and a 250 @ 0.050 and a 108lsa and a 250 @ 0.050 and a 118 lsa.

now do the same with this combo.

220 @ 0.050 and a 112 220 @ 0.050 and a 108 lsa and 250 @ 0.050 and a 118lsa.

You will notice the the lsa has relatively small impacts on overlap until the lobe durations get up there.

Its bullshit science.

Thsi doesn't even include ovelrap and duration at seat to seat as well as at .100 and .200 lifts and the lobes themselves will influence the camshaft overlap cycles tremendously given the ramp rates and lift curves.

1bad Lad said:
first u need to get ur heads flowed so u can get an intake to exhaust flow ratio. then yes on blower engines u want a 112-114 separation and u definately want more exhaust duration. if ur heads are in the 60s percent range intake to exhaust flow ratio then get a cam with 10-16 degrees more exhaust duration. if ur in the mid 70's ratio then something like 7-10 more degrees on the exhaust. even if the heads have a i/e ratio in the 80's i would still go with atleast 6-10 degrees more exhaust especially if u plan on runnin a good amount of boost. then if u get a flow curve u will know how much lift u will need on ur camshaft. and personally i would get something with about .020 more lift than what the head peak flows...just my 2 cents. u need to have as much exhaust flow as possible to take pressure off the pistons i would prolly the cam installed at a 110-114 centerline for a blow car....depending on how high u wanna rev it and where u want ur power band to be at!!!!!!!!
Click to expand...
 
Sean said:
I post this all over the place. LSA or lobe seperation angle is Bullshit. Overlap degrees is what matters. there is no 112 or 114. compare sevral cams.

250@ 0.050 and a 112lsa and a 250 @ 0.050 and a 108lsa and a 250 @ 0.050 and a 118 lsa.

now do the same with this combo.

220 @ 0.050 and a 112 220 @ 0.050 and a 108 lsa and 250 @ 0.050 and a 118lsa.

You will notice the the lsa has relatively small impacts on overlap until the lobe durations get up there.

Its bullshit science.

Thsi doesn't even include ovelrap and duration at seat to seat as well as at .100 and .200 lifts and the lobes themselves will influence the camshaft overlap cycles tremendously given the ramp rates and lift curves.
Click to expand...

dude ur a dumb ass. i am now dumber reading that. sorry but lobe separation angle is overlap degrees. now a lot of people get the intake centerline and lobe separation confused i could understand getting that confused but man come on. yea just like u said our ls head don't flow 300 with a stock valve and stock vj.
 
1bad Lad said:
dude ur a dumb ass. i am now dumber reading that. sorry but lobe separation angle is overlap degrees. now a lot of people get the intake centerline and lobe separation confused i could understand getting that confused but man come on. yea just like u said our ls head don't flow 300 with a stock valve and stock vj.
Click to expand...

i'll listen to sean way before I listen to your dumbass
 
Ahh ok. runn those cam specs I gave you into this overlap calculator.


http://www.wallaceracing.com/overlap-calc.php



Now overlap is a total of LSA and duration. That was the point of my post and you completely missed it. I spend the bulk of my day designing and scienceing out camshafts.



1bad Lad said:
dude ur a dumb ass. i am now dumber reading that. sorry but lobe separation angle is overlap degrees. now a lot of people get the intake centerline and lobe separation confused i could understand getting that confused but man come on. yea just like u said our ls head don't flow 300 with a stock valve and stock vj.
Click to expand...
 
lobe separation is degrees from the centrline of the intake lobe to the centerline of the exhaust lobe. now i do agree that u can change overlap with duration. but if u take the same lobe and move either centerline then u are ganna change overlap and lobe separation. yea ur right i did miss ur point earlier was a whole lot of numbers and not the best explanation. there is a lot that can be done with camshafts. and unless its a serious race engine some of the small changes we are talkin about sometimes don't make much difference. but again some of us like to squeeze every little bit so the little stuff does help. anyways my bad for bein rude i just had to get ya back a little for bashin my heads........
 
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