Need to know some cam science.
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From: St Clairsville, Oh
Need to know some cam science. Witch is better for FI lift or deration or just like N/A both. I am torn between the GT2-3, LS6, or my 228/228 .588/588 114. On all of the cams i can go with 1.75 or 1.8 rockers. I have -15cc pistons(4.03) on the way along with my 317 heads. I want to know so i dont have to do a cam swap in the car. I have done so many that i am kinda sick of them on my car. I think i have done 6 cam swaps in a year.
Originally Posted by goober35
Witch is better for FI lift or deration or just like N/A both. I am torn between the GT2-3, LS6, or my 228/228 .588/588 114. On all of the cams i can go with 1.75 or 1.8 rockers. I have -15cc pistons(4.03) on the way along with my 317 heads. I want to know so i dont have to do a cam swap in the car. I have done so many that i am kinda sick of them on my car. I think i have done 6 cam swaps in a year.
That 228/228 cam would be a really bad choice, I don't have specs handy for other two cams.
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From: St Clairsville, Oh
Well my cam comes out to 0.
228/228 lsa114
Add the intake and exhaust durations 456
Divide the results by 4 114
Subtract the LSA 0
Multiply the results by 2 0
Check my math since 0*0=0 I know this is right but i dont know if this a perfect formula. If it is i would say i have a really bad *** turbo cam.
228/228 lsa114
Add the intake and exhaust durations 456
Divide the results by 4 114
Subtract the LSA 0
Multiply the results by 2 0
Check my math since 0*0=0 I know this is right but i dont know if this a perfect formula. If it is i would say i have a really bad *** turbo cam.
Originally Posted by goober35
Well my cam comes out to 0.
228/228 lsa114
Add the intake and exhaust durations 456
Divide the results by 4 114
Subtract the LSA 0
Multiply the results by 2 0
Check my math since 0*0=0 I know this is right but i dont know if this a perfect formula. If it is i would say i have a really bad *** turbo cam.
228/228 lsa114
Add the intake and exhaust durations 456
Divide the results by 4 114
Subtract the LSA 0
Multiply the results by 2 0
Check my math since 0*0=0 I know this is right but i dont know if this a perfect formula. If it is i would say i have a really bad *** turbo cam.
Teching In
Joined: Sep 2004
Posts: 36
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Hi guys. I am new here and found this a very interesting forum.
re your cam overlap calculations - correct me if wrong - but it appears that you are using duration @ 0.050" valve lift - the normal rating of a cam for comparative purposes.
the problem with the duration at that lift is it does not work for overlap calculations. You need the duration from seat to seat (advertised duration - normally measured @ 0.006" on a hydraulic cam)....
The duration on the seat will be more than what they rate the cam at 0.050" and this will alter your calculations.
A SECOND way to calculate overlap is to use the cam timing. You simply add the timing BTDC (sometimes ATDC on some turbo grinds) the intake opens and the same for when the exhaust closes ATDC....
for example if a cam timing spec is:
Intake opens at 30 degrees BTDC
Closes at 70 degrees ABDC
Exhaust Opens at 70 degrees BBDC
Closes at 30 degrees ATDC
then overlap is 30 + 30 = 60 degrees, typical of a street machine making around 1hp per cubic inch with a reasonable combo.
Hope that helps.
I also note on an overlap formula posted on the web that although they use the x 2 multiplier in their formula - they don't do it in their examples - thereby provinding answers that are 50% of actual.
re your cam overlap calculations - correct me if wrong - but it appears that you are using duration @ 0.050" valve lift - the normal rating of a cam for comparative purposes.
the problem with the duration at that lift is it does not work for overlap calculations. You need the duration from seat to seat (advertised duration - normally measured @ 0.006" on a hydraulic cam)....
The duration on the seat will be more than what they rate the cam at 0.050" and this will alter your calculations.
A SECOND way to calculate overlap is to use the cam timing. You simply add the timing BTDC (sometimes ATDC on some turbo grinds) the intake opens and the same for when the exhaust closes ATDC....
for example if a cam timing spec is:
Intake opens at 30 degrees BTDC
Closes at 70 degrees ABDC
Exhaust Opens at 70 degrees BBDC
Closes at 30 degrees ATDC
then overlap is 30 + 30 = 60 degrees, typical of a street machine making around 1hp per cubic inch with a reasonable combo.
Hope that helps.
I also note on an overlap formula posted on the web that although they use the x 2 multiplier in their formula - they don't do it in their examples - thereby provinding answers that are 50% of actual.
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So what is the right answer regarding that formula, what is accurate and what is not?
Justin, your 228/228//114 is a very good starting point. Is it the cam someone would run for 800rwhp? Probably not but at onset of your project (6-8psi) you get the added duration to make power and and it's only in higher boost levels where folks start to get picky.
Justin, your 228/228//114 is a very good starting point. Is it the cam someone would run for 800rwhp? Probably not but at onset of your project (6-8psi) you get the added duration to make power and and it's only in higher boost levels where folks start to get picky.
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From: St Clairsville, Oh
I am going to have to start to get realy picky on cams. I am looking to run 12-15# it all depends on how much power it will make. I am aiming for 700 but will be happey if i get 650. So a cam is going to play a big factor in this aplication. I was going to run 5-7 i would not care. Any sugjestions. If anyone has some good spec they are running let me know. The more i know the faster i can go. I know there are a lot of turbo guys out there with custom ground cams. Any one want to tell me what the specs are or do i have to just start PMing people.
Teching In
Joined: Dec 2003
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From: Waterford MI
Keeping overlap down on a turbo'd engine is important hence the big lsa's but you also need to look at valve events and not just overlap etc. In a turbo or any FI engine for that matter it is important to open the exhaust valve earliar to allow sufficient time for a blown down period of the cylinder otherwise you will suffer from excessive pumping losses.
Josh
Josh
my old cam: 226/224 .523/.510 115* would you consider this to be a good fi cam for 800rwhp? it was 
put a good system around it and let the FI do the work.
if you are interested in really fine tuning the powerband for a specific application (drag racing intensive) then you will want to get picky.
put a good system around it and let the FI do the work.
if you are interested in really fine tuning the powerband for a specific application (drag racing intensive) then you will want to get picky.
David that is by far the weakest cam I have ever seen. You'll never sell that thing.....wait ...the UPS guy just came......the cam I bought from you just came. I hope it will do 650+ for me