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So I've been contemplating a switch to a mechanical flat tappet. I'm planning on pulling the motor to replace a oil pan gasket so I figure it would be as good of time as any do so. Setting the valves every few thousand miles wouldn't bother me so; The two I have in mind are:
Have any of you guys run any of these? I know the Comp Cam is a newer, more aggressive grind, but the car is a DD so I'm thinking maybe the Crane would be easier on the valve train. BTW I already have Isky 235D springs so that is taken care of. Also will these cams run a little "smaller" than my current cam since a mechanical opens & closes the valves quicker than an equivalent hydraulic? Any input is appreciated
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So I've been contemplating a switch to a mechanical flat tappet. I'm planning on pulling the motor to replace a oil pan gasket so I figure it would be as good of time as any do so.
Wow man, that sounds really familiar. I pulled my engine this winter to do an oil pan gasket and figured I might as well do a solid cam. Went from an xe268h to an Isky Z-25.
With your carb you might want to tighten up the LSA. That'll give you more mid range torque. Those high LSA's (112) give a nice tabletop torque curve, smoother idle, better top end, but kinda soft in the middle. Like a 40yr old fat guy.
Those are both BIG cams though. I think you'll notice either one would feel pretty big.
How high do you plan on spinning the engine? I think you may even want to upgrade the springs - again.
Look carefully at straight pattern cams. With your heads you might benefit from them. It would help with mid-range as well, which is nice on a DD car. I'm not trying to push you to my cam, but i'm just saying those are the reasons I picked the cam that I did. The Z-27 might be up your alley, 248/248 @.050.
How do you like your tru-trac? I've also just upgraded to 3.73's and a true-trac, but haven't had a chance to try driving it yet.
I've looked at the the Z-27 too, but an engine builder (my old neighbor) told me to stick to a wider LSA as it plays nicer with a crappy exhaust (Edelbrock TES). When I picked my current Isky on a 108 LSA(he helped me choose it) I was planning on long tubes but with my sportlines I have resigned to keeping the shorties. BTW: I love the true trac it is like an open diff just cruising but will get the car sideways leaving two nice big black stripes when called upon! (No clutches to wear out either!)
AH, I see. Well I should enjoy the true-trac as well then
In light of your mild springs, i'd lean towards the Crane. The slower ramp rates will help your valve train live longer as well.
I wonder why they spec such a huge lash though..?
Either of those will work very well for you.
I don;t think you'll find them "bigger or "smaller" than what you have now.
But you should make more overall power in the rpm range you have and will be using.
If you want a cam that is very simular but just a shade "milder". An excellent "Street cam" that likes a closed exhaust system, consider this popular Lunati made /Ultradyne designed cam.
#401ALUN grind # 01-UF15-UF16-12 A 1.6/1.5 split ratio or 1.6/1.6 rocker set would be assume. kicking the lift up to equal the others yet with shorter adv duration but really, just fine with 1.5 rockers.
here is the cam card http://static.summitracing.com/globa...n-401a3lun.pdf
All these are good cams for you. Just another one to consider.
Do you have any ET/MPH timeslips for your current combo?
The Y pipe scavedging effect ( or lack of) in your exhaust system is very critical to how it works with the cams exhaust valve timing. Check out Flowmasters Y250300 scavenger Y pipe.
Did you degree in your Isky cam. Should work best with a bit of cam advance to maximize the low/mid range torque. (104° intake C/L.) It does favour a open long tube header, free flowing exhaust system.
What are you looking for in a new cam? More torque down low? More top end power? nicer idle?
Have you tried the car with the open Y pipe to see how the motors (cam timing) likes or does not like the closed exhaust system?
Have you maximized/dialed in the ignition advance curve to best suite the motor.??
AH, I see. Well I should enjoy the true-trac as well then
In light of your mild springs, i'd lean towards the Crane. The slower ramp rates will help your valve train live longer as well.
I wonder why they spec such a huge lash though..?
The isky 235D springs are quite aggressive for a stock diameter spring.
The advertized duration and relative running lash needs to be qualified to make a real comparison.
The crane cam is measured @.020" lifter rise with lash clearance ramps designed to work with a wider valve lash. (longer sloping lash ramp on the lobe)
Where the comp cam is measured at .015" lifter rise. and tighter lash with narrower faster ramps. Unless you convert one to the other or actually measure the cams the same and account of the valve lash effect on the real valve timing you will be suprised at which actually has longer or shorter net running duration at the valve in the running motor, which is more or less noisy ( or not) at idle and which makes best power overall. The paper specs can be very decieving. Put both cams on a "cam doctor" and plot the lobe lift curve and net valve lift curve with lash and the truth comes to light. You'll find very similar lobes to the crane lobes used in the F280-2 cam, in the comp cams lobe library ( hi torque series) and near identical off the shelf cams to the crane cam. EG Comp CS 280B-8. #12-221-5.
Hard to tell the horses without a program. If you study the cam lobe designs in each companies published cam lobe libraries you see more similarities than differences. Old school, new school, the line gets blurred when you actually look beyond the surface. take that further and look at few other companies lobe libraries and you really see some common design trends. Whois copying who.
Thanks for all the info guys. After going thru all the cam manufacturer's catalogs I've found it is like trying to compare apples to oranges. To answer the questions so far, my 1st time home porting efforts yielded 250/185cfm at .500 (28") IIRC. I've got my timing locked out at 35 degrees currently, with an additional 14 degrees from ported vacuum.
The current Isky is installed 4 degrees advanced. I'm quite happy with it actually, seems to produce good power and pulls to 6500 easily (it gets a little unhappy below 1500 with the TC locked though.)
Haven't been to the strip yet but plan to rectify that soon. Bristol should be opening anyday.
I just think I'm leaving something left on the table with the current combo. I was hoping for maybe a 15-20hp increase with the faster ramps and wider LSA that better suits the exhaust. Of course the reduced overlap would make it more streetable right? Maybe I'm asking for too much from a cam swap. LOL
