Re: More cam Thoughts
[Re: blownzoom440]
#945972
03/10/11 06:19 PM
03/10/11 06:19 PM
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Joined: Feb 2003
Posts: 4,953 Houston, Texas
TheOtherDodge
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master
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Houston, Texas
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Well selecting a cam should be more than looking at just one attribute. Just like a motor combo, you have to look at everything. I would never just pick a cam because of LSA or because of lift, etc. As a general rule, a wider LSA will lessen the overlap, thus giving a smoother idle and broader powerband. But, with that said, a cam with an LSA of 110 could actually have less over lap than a cam with 112 LSA. You just have to look at the valve timing events.
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Re: More cam Thoughts
[Re: TheOtherDodge]
#945974
03/10/11 08:29 PM
03/10/11 08:29 PM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
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Canton, Ohio
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Quote:
As a general rule, a wider LSA will lessen the overlap, thus giving a smoother idle and broader powerband. But, with that said, a cam with an LSA of 110 could actually have less over lap than a cam with 112 LSA. You just have to look at the valve timing events.
Overlap can only be changed two ways. LSA and Duration/split duration.
For instance if you wanted a 240* duration @.050cam on a 108 LSA Your overlap will be fixed.
You cant move the valve timing events around and change the overlap and have the same 240* @.050 cam on a 108 LSA
Further though Boost is Boost, But, Boost from a Turbo comes with more exhaust back pressure then a blown race motor requireing some different cam considerations.
Like you stated, sometimes not opening the intake valve 20* to 35* after TDC. The reason for this is that even after the exhaust valve closes the pressure in the cly may still be 10#+ So you need to allow the piston to travel lower in the bore to atleast to the equalizing pressure of the Turbos boost before you open the intake valve.
On a blown race motor your not going to have those kind of back pressure problems unless your running a highly restricive exhaust. Witch you wouldnt,unless your a fool
Back pressure can be reduced with turbos too by running a bigger turbo but you wont get the faster spooling you might want. Everythings a comprimise.
With the OP,s theoretical engine and 6# Mild boost Id run the bigger of the two small cams.
As a General rule BDS {Blower Drive Service} recommends when picking a cam for a mild blown motor. Pick it as if you were going going run it NA in the rpm range you want it to run at. They like 110 LSA for gas and 112 for Alchol.
Last edited by Sport440; 03/10/11 08:39 PM.
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Re: More cam Thoughts
[Re: Sport440]
#945977
03/10/11 09:45 PM
03/10/11 09:45 PM
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Joined: Jul 2005
Posts: 8,647 ELYRIA,OH
blownzoom440
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Joined: Jul 2005
Posts: 8,647
ELYRIA,OH
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and the factors to say 20 hp was the later intake opening,longer ex duration. later intake opening=better facuum betterVE% i think. longer exh dur cooler intake charge=more hp
Last edited by METAL STORM; 03/10/11 09:49 PM.
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Re: More cam Thoughts
[Re: blownzoom440]
#945978
03/10/11 09:57 PM
03/10/11 09:57 PM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
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I checked your numbers and your first 254/110LSA cam has 39* overlap. your newer cam 252/113LSA has 30* overlap. The OP,s 240/108LSA cam has 24* overlap{approx} its probably 24.5 based on a MP 484 cam. So thats less overlap then your motor with its 30* so 24* should be better yet. So I think the overlap is acceptible of the 108 cam. The duration of 240* of the 108 vs the 232* .050 of the 114 cam will be the Trump card, for power on this "Theoretical Combo" IMHO between the two cams listed as options. Just bench racing here, dont know for sure. But If i were building the OP,s combo in my garage, deciding on witch cam. Im picking the 108LSA 284/241
Last edited by Sport440; 03/10/11 10:20 PM.
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Re: More cam Thoughts
[Re: Sport440]
#945979
03/10/11 10:22 PM
03/10/11 10:22 PM
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Joined: Jul 2005
Posts: 8,647 ELYRIA,OH
blownzoom440
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Joined: Jul 2005
Posts: 8,647
ELYRIA,OH
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interesting now that all of the figures are out with the op cams.i need to ponder them more. [I checked your numbers and your first 254/110LSA cam has 39* overlap. your new cam 252/113LSA has 30* overlap.] for my cams the 110 cam would not make boost past 8 psi even at 25% OD on the blower it quit at 5%OD.[10.90/? with the 113 cam the carbs held it back at 10 lbs at 10%OD[10.41/129 the cam in mine now is .646/.631 291/306 @ .020 260/269 @ .050 .050 in op 21 cl 59/exh op 69 cl 19 with 40* overlap at .050 without lash on a solid roller[.018 I/E] w 14lbs boost and more.
Last edited by METAL STORM; 03/11/11 10:06 PM.
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Re: More cam Thoughts
[Re: Sport440]
#945980
03/11/11 12:26 AM
03/11/11 12:26 AM
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Joined: Feb 2003
Posts: 4,953 Houston, Texas
TheOtherDodge
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Quote:
Quote:
As a general rule, a wider LSA will lessen the overlap, thus giving a smoother idle and broader powerband. But, with that said, a cam with an LSA of 110 could actually have less over lap than a cam with 112 LSA. You just have to look at the valve timing events.
Overlap can only be changed two ways. LSA and Duration/split duration.
For instance if you wanted a 240* duration @.050cam on a 108 LSA Your overlap will be fixed.
You cant move the valve timing events around and change the overlap and have the same 240* @.050 cam on a 108 LSA
Correct. I hope I did not give the impression that you can change overlap once it is ground in the cam, because as you stated, you can't. I meant that when you have the cam ground, you can change the LSA then to change the over lap.
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Re: More cam Thoughts
[Re: blownzoom440]
#945982
03/11/11 10:00 PM
03/11/11 10:00 PM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
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Quote:
interesting now that all of the figures are out with the op cams.i need to ponder them more. [I checked your numbers and your first 254/110LSA cam has 39* overlap. your new cam 252/113LSA has 30* overlap.]
for my cams the 110 cam would not make boost past 8 psi even at 25% OD on the blower it quit at 5%OD.[10.90/? with the 113 cam the carbs held it back at 10 lbs at 10%OD[10.41/129 the cam in mine now is .646/.631 291/306 @ .020 260/269 @ .050 .050 in op 21 cl 59/exh op 69 cl 19 with 40* overlap at .050 without lash on a solid roller[.018 I/E] w 14lbs boost and more.
First, can you fix my error in your capture of my quote. I stated 242*"incorrect" instead of the 252* for the 113 LSA cam.
Second, Im a NA guy and not a boost guy so Im just bench racing for the OP, because he"s a local guy. So as not to hijack his post, "more cam thoughts" But Im going to include yours.
In requards to your opinion of not using the 108 LSA, Id like to ask your reasons or reasoning in this case.
Also, I cant explain your boost differences. Wheres the boost being lost? Not in the overlap,IMO So where? Let me lay out your 3 cams along with the OP,s 108 LSA cam in a comparative way to see if it helps.
duration .050---LSA--OL--boost---OD%--IO.BTDC
OP,s 240 @.050--108--24-----NA--------12*BTDC
MS,s 254 @.050--110--39----8psi-25%---17*BTDC
MS,s 252 @.050--113--30---10psi-10%---13*BTDC
M,260/268@.050--112--40---14psi-NA/%--21*BTDC
Not being a blower guy, I dont understand the boost problems between the 254 and the 260/268 cam. What are your thoughts.
Last edited by Sport440; 03/11/11 10:03 PM.
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Re: More cam Thoughts
[Re: Sport440]
#945983
03/11/11 10:17 PM
03/11/11 10:17 PM
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Joined: Jul 2005
Posts: 8,647 ELYRIA,OH
blownzoom440
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Joined: Jul 2005
Posts: 8,647
ELYRIA,OH
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i would only embarrass myself by letting you think i could explain it. i thaught it may be a cracked port leaking for all i knew.a cam change made it better and i left it at that going from cam 1to cam 2.
Last edited by METAL STORM; 03/11/11 10:19 PM.
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Re: More cam Thoughts
[Re: blownzoom440]
#945984
03/11/11 10:58 PM
03/11/11 10:58 PM
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Joined: Jul 2005
Posts: 8,647 ELYRIA,OH
blownzoom440
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Joined: Jul 2005
Posts: 8,647
ELYRIA,OH
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from jegs helpfull tips on blower cams. it is to help retain cylinder pressure with 112/114 lsa. edit:i forgot to drag it back. Supercharger Engine Camshafts The choice of camshaft can make or break a blower motor. A legend in the industry, Lunati offers several camshafts specifically designed to work with Weiand blower kits. In addition, the following are a few basic guidelines for selecting the proper cam for your motor. Obviously, the amount of boost your supercharger produces is going to be a factor in choosing a camshaft. Weiand offers three different levels of superchargers, and each requires a different type of cam. The "mildest" of Weiand's blowers are the Pro-Street superchargers, which are set to produce from 5 to 7 pounds of boost. The company recommends a hydraulic cam for these applications - where the engine will not be spun past 6,500 rpm and has several grinds available. All of these cams are ground on a 112 to 114° lobe center line, which helps maintain cylinder pressure to maximize horsepower at these lower boost levels. Keeping the cylinder pressure up also gives you excellent throttle response. The milder cams that Weiand offers are great for street performance enthusiasts who want to gain about 100 to 120 streetable horsepower. The company also offers slightly "bigger" cams for the next performance level up. For 6-71 and 8-71 blowers, Weiand again recommends running a hydraulic cam, as long as you keep the boost level below 10 PSI. Weiand also offers cams for these type of applications. For your higher boost levels (which includes all 10-71, 12-71, and 14-71 applications) in gasoline burning engines, the company recommends running a flat tappet or roller cam with a 110° lobe center line. This cam design provides good overall power on pump gas and also aids in engine cooling. Plus, the 110° center line provides even sharper throttle response and helps lower initial cylinder pressure (you won't miss the cylinder pressure with these blowers, since they make plenty of boost).
Last edited by METAL STORM; 03/11/11 11:05 PM.
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Re: More cam Thoughts
[Re: 6bblFLASH]
#945989
03/14/11 10:57 PM
03/14/11 10:57 PM
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Joined: Dec 2008
Posts: 1,200 UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Quote:
Just benchracing a few thoughts with some freinds: You have a motor with a ROOTS type supercharger making 375hp.on a dyno. Cam is 108C/L and 68* overlap 284* duration. Makes 6-lbs boost. Swap cams to a 114 C/L 56* overlap 278/290 duration cam, same 6-lbs boost,,,,,,, How much power difference would you expect?????????
Just joining you guys on the bench racing here ...........my thoughts would be the less overlap the better with only 6lbs boost as cooling wont be an issue , too much overlap when using boost will have air/fuel wasted out of exhaust port , boosted engines will tolerate a later opening intake valve due to difference in manifold pressure over non boosted...........not sure a split pattern is the best way to go with the boost you're running , the later closing exhaust valve may hinder cylinder fill.
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