Which is more important in a Blower cam, lift or duration? I have a good reason for this asking this. Thanks, guys.....
More important for what exactly? Why don't you elaborate more on what you are trying to do with it and what your great reason for asking the question is. Then we can help discuss it.
check the blower cams from comp cams believe it has to do with overlap just changed mine to a blower cam and picked up a wack of hp are you running much boost ...and a auto or a stick
Centerline has the most to do with blower cam,then I would concern myself with duration. Most blower cams are a bit retarded.I believe it has to do with the lag in filling the cylinder. Oldmics
REED ground my blower cam with a 114 degree lobe separation , exhaust lift is higher than a naturally aspirated engine
291 DeSoto Hemi, 6-71 5lb boost, 2X500 CFM Carter Competition, hydraulic roller lifter cam, 200-4R. Valve lift is .375..that's right, .375 valve lift, 236/236 @ .050...can't remember the LSA. The reason I ask is because of the low valve lift...Stock being .250...
lift is 50% higher than stock. Remember that hemis breathe well, you don't need as much lift because there's no valve shrouding...right? just a wild guess. As with any engine, lift is usually a function of both duration and valve train geometry things specific to the engine. And as with any engine, you should pick cam duration on a blower motor based on what rpm you will run it at. With a cam with that much duration at .050, plan on a power band in the 2500-6000 rpm range, plus or minus a bit. Gear accordingly.
More info on the cam...112 lobe center, I.O. 6 BTDC/I.C. 50 ABDC, E.O. 50 BBDC/E.C. 6 ATDC. I guess I'm worried that the roller cam might be a little anemic. This is a Street only engine that's not going to be abused, but I'd like it to at least live up to it's "looks", and be adequete for a more or less Stock engine. BTW, it's a Chet Herbert, #7 DeSoto Roller cam from the 50's...
Based on that, the theory is that lift if not as important because the flow is forced through the head. Depending on the power level, better heads and more lift will make more ulitmate power. Using stock heads a little more lift and the forced induction you'll be impressed. I used 112 lobe seperation because BDS said 112 for gas and 114 for alcohol. I know you don't want 106. I have heard tails of the exhaust coming out of the headers as large flames with a blower and 106 lobe seperation.
if car is running get it over to a chassis dyno and hook it up make sure you air ratio is right and see what the curve is you might just be happy with what you have already Dynos dont lie tunning by ear is like changing channels on your tv without the remote ...lol it works but there is a way better way
Be cautious with putting too many miles on those early roller cams,they were made for racing and the rollers are wore out at 10,000miles. this was explained to me by an old time very experienced cam grinder. Ago <input id="gwProxy" type="hidden"><!--Session data--><input onclick="jsCall();" id="jsProxy" type="hidden">
The lobes on the can shouldnt wear at all. There isnt any friction in them. Specially like a flat tappet cam.
The lobes on the can shouldnt wear at all. There isnt any friction in them They have very slight sliding friction, since they have to "spin up" (start rotating) every time the lobe comes around. The real damage is brinneling, or local surface depression, caused by very high local load: the roller wheel is a much, much smaller surface than any flat tappet, and touching a smaller area of the lobe. The wheel flattens the lobe very slightly like a train wheel flattens the rail as it passes. Eventually, small surface cracks will develop.
If at all possible you should try and run a rev kit. This will keep the roller lifter in contact with the cam lobe at all times. When the lifter stays on the lobe it will be easier on the cam lobe wear. When you let the lifter have the valve lash clearance it seems like the lifter starts to pit the lobe on the camshaft >>>>.
Hey 345 I was always amazed at how mild that cam of yours is. Although its a 291, it still has a nice lung sitting on top of it that tends to tame out wilder cams to a degree. As you know I had a .550" lift hyd roller ground for my 330. Still a ways of from being finished but I wanted it to breathe DEEP.....we'll see how it goes. The thing is the std rocker ratio cant be changed easily on an early Hemi to artifically increase the valve lift. Id say run what you have, dial it all in properly and see how you go. If then you want to make a change, its only a cam and you'll be able to run the same roller lifters. Rat
Talk to the folks at Crower. They set me up with the cam and kit for the blown engine in Pinocchio. They really know their stuff.
345 - You have it in allready so go ahead and run it and see what it does. If you don't like it, you'll have a great base experience to make changes from when you select a new grind. The cam in my little blown 283 was small and that sucker runs GREAT. It happened to be a 112 lobe center duration @50 204 intake an d 214 exh and 420 lift. That little engine revs to 6ooo fast. You have more duration it should be excellent. What were your cam specs Rich? Did you ever dyno that engine?
Well, I'm counting on the fact that Chet knew his stuff. That, and the relatively long duration should help...even with the low lift. I'm hoping that the 6-71, long duration, and 112 LSA will do the trick. Like it's been said, fire it up and see how it runs. If I feel that I DO need a cam change, at least I know that I can have a new roller ground for it...
cams are a lot like women example - big flashy cam with impressive numbers - requires high maintenance, additional money to me spent on other parts to keep it happy stock cam - not so flashy - still does good things for you, has good torque in her bottom end, may not rev as high but runs good with little to no maintenance. No additional money is required to be spent on other things. The farther you go above stock cam the more you'll have to invest in the whole set up and them keep after it to keep the set up happy. Then there is only one way to know how a cam works. Try it out. You can read all you want about them and you'll never know until you stick it in and try her. Then there is a wide variety of cams we all want to try every one we see. Hydraulic, solid flat tappet, solid roller, hydraulic roller. But it is expensive to change cams just like women. You usually have to stick with the one you have. But then you always wonder and dream - what if I had a really hot flashy roller cam with all the goodies. Woo that is really cost you to try it out. But then you would have a trophy cam! Then you have other guys opinions about cams, they are all different. One guy likes them huge, the next guy likes them lumpy, and the next says he needs a lot of vacuum. It just all depends and there is still only one way to find out. Try them out. Some guys even like to try used cams. Now that is a whole nuther story that can be expensive and dangerous. You also don't usually get to try out new cams just for fun. The one you have usually needs to go bad first. <!-- / message --><!-- sig -->
I have Crane 901-16 springs installed for just such a reason Can't find that number - do you have any specs or installation data?
PANIC - That should read COMP cams...my mistake...<TABLE cellPadding=4 align=center><TBODY><TR><TD vAlign=center align=middle colSpan=2></TD></TR><TR><TD vAlign=top colSpan=2> <TABLE borderColor=#000000 height=58 cellSpacing=0 cellPadding=3 width=431 border=1><TBODY><TR><TD vAlign=top width=40 bgColor=#000000>Part #</TD><TD vAlign=top width=36 bgColor=#000000>O.D.</TD><TD vAlign=top width=28 bgColor=#000000>I.D.</TD><TD vAlign=top width=50 bgColor=#000000>Damper</TD><TD vAlign=top width=59 bgColor=#000000>Seat Load</TD><TD vAlign=top width=63 bgColor=#000000>Open Load</TD><TD vAlign=top width=38 bgColor=#000000>Coil Bind</TD><TD vAlign=top width=51 bgColor=#000000>Rate (Lbs./In.)</TD></TR><TR><TD>901</TD><TD>1.494</TD><TD>1.080</TD><TD>Yes</TD><TD>101 @ 1.650</TD><TD>242 @ 1.250</TD><TD>1.100</TD><TD>353</TD></TR></TBODY></TABLE> </TD></TR></TBODY></TABLE>
Sorry, bit of a disconnect. I thought you were responding to the prior "rev kit" remark. Your springs (which look on the mild side for a roller) have no pressure on the tappet when the valve is closed (due to lash), which causes them to lag behind lobe speed when beginning to lift and rotate. A rev kit spring pre-loads the tappet directly, which allows normal lash (between the pushrod and the rocker) but keeps the tappet in place at all times. They're pretty light (Comp recos 30 lbs. closed) but a lot of trouble to install.
Agree'd. When I built my blower motor, I had the heads flowed, then took the following numbers Desired - Blower PSI Motor Compression Ratio Head - CFM Desired - RPM range Called up Crower gave them the specs and they ground me a cam specifically for my setup. Motor put a car in the 8's, and was street able when swapping the pulleys I've found mixed matched setups never really run to there full potential.
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