He's got stock heads on it, that means he's likely got pressed in rocker studs, Comp does not recommend the XE line with pressed in studs as they tend to pull the studs loose.
Good point and I just assumed it wasn't as critical with their smaller grinds. I'd surely fix that weakness to be able to run a better matched cam. Or at least pin them. I've pushed far more spring pressure than these little cams require and I'd travel cross country running any of these little cams up past peak all the way there and back without wincing one little bit about pins letting loose. Remember that these are just glorified short duration higher lift RV style grinds running faster ramps here. And why on earth wouldn't this same setup not need screw in's for the 268 grind? Isn't its rec'd spring pressure and extended rpm range not going to warrant a similar setup anyways? All I can say say for sure is that it seems you guys are overcamming this gentlemans motor with his current hard parts setup. Look at historys faults and do some quick math. 1st gear is a measily 7.38 multiple and 2nd isn't much better on the upshift for tall gears at 4.38 ratio. You can calculate the engines low speed torque multiplication numbers and do the rest of the math yourself. It's not pretty at all and I can guarantee you that it's a turd off the line while you're waiting for the gears to get you up on the cam. IMO, it's downright silly to think that you can just slip in any old midrange cam grind and be happy on a low compression/low torque/poorly quenched/short stroke small block. Been there.. done that.. and you might want to ask for more opinions before throwing your cash and time away. Now swap those gears to 3.50's?.. then it changes everything. 268H with mild gear and stall will transform that car. Oh well.. in this combo.. at least it'll sound cool and you can race from rolling starts and do burnouts while you wear the rear brakes out since you'll need to power brake its tires loose. Skinny snow tires out back will make it seem more powerful down low and the yellow smoke is awesome too.
It didn't sound right to imply that the XE line needs screw in's.. but the 268 High Energy line wouldn't.. so I checked Comp's rec'd spring #'s. Same exact springs/load requirements and the OP will be converting to studs either way he goes. So, by the logic being used around here.. then he may as well step up to an even larger grind. The stroker McGurk syndrome says it'll pull like hell after about 2- 3 seconds of waiting for the cam to come in.. then tthe heads will go away and it'll shift and start the countdown all over again. Probably be doing about 80+ before the cam really comes in during 3rd gear. Yee haa.. better get the suspension and brakes in good working order. I've seen these kinds of mistakes dozens of times.. made more than a few myself.. and most stock sporty 4 and 6 cylinder cars will make him think he wasted some cash somewhere along his buildup. Wrong cam choice for the engine torque and gear multiplication is usually a biggie. But then again.. everybody's got to learn these lessons and it's always easier to avoid lumps on someone else's dime.
I'm going off Comp's recommendations in their catalog. The more aggressive ramps are why they don't recommend the XE cams with pressed in studs. As for spring pressures, the 268H will work fine with stock springs.
The 268H has a .456" lift, which is about the most you can safely go without screw-in studs. The 268XE definitely needs the screw-in studs. I agree that these engines benefit from a dual-pattern cam. I like the idea of the more gentle closing rates of the Lunati Voodo cams. That should help with longevity. I've heard that the Comp XE series is pretty brutal on valvetrain components -- especially valve seats.
wow. I have to say that I'm surprised at this type of advice from you. It's usually much more prudent, fact filled and correct. From a timing spec standpoint.. the High Energy series is not drastically different than the Extreme Energy lineup. The lifter rise is more aggressive?.. yes.. but we're not talking racy solid roller profiles by any stretch. They're all just low-midrange street cams. Which explains why they'd rec' the same exact spring for both. I'm not sure what catalog you're looking at.. but the one <Here> lists a spring #942-16 with 115 @ 1.7 and 284 @ 1.2. And moves from there to part #972-16 with 124 lb @ 1.8/293 @ 1.250. And.. the product discription says "HYDRAULIC: Good for daily driven performance vehicles. Mid-range power. Slightly lower gears. Mild rough idle. And to finish off the reality check.. I've tested many springs and the OP will be lucky if those old stockers even hit 80 lbs of seat pressure. Many older springs are even in the low 70's. Sure it'll still run. but that's WAAAYYY too little spring if you want to be revving past 6,000 rpm. This is NOT a little cam for this paticular motor. It'll want to rev and the spring won't let it. But at least you won't have to worry about the head flow stalling the power band up top. It'll just get bled off by the intake valve bouncing around. Have a look at this slo-mo video to get an idea what can happen when he overrevs it on a stock spring. This is a 4 valver.. but the principle is just the same. http://s163.photobucket.com/user/GrocMax/media/valvetrain%20videos/almost_tossing_rocker_zpse955b687.mp4.html?sort=3&o=2#/user/GrocMax/media/valvetrain%20videos/almost_tossing_rocker_zpse955b687.mp4.html?sort=3&o=2&_suid=139190884131607910335946721299 Might want to also check guide to retainer clearance too. Anything over .450 valve lift is pushing it close without guide and seal modification. And even moreso with crappy underspec'd stock springs. As anyone who's ever mushroomed lifters and/or pounded out cheap factory valve locks/retainers will tell you(installed height changes for the worse and causes even more loss of control).. over-revving of stock parts could cuase a real mess.
Anytime you change cams to a more aggressive grind,not matching components will usually always lead to disaster,heed these guys advice!
My answer was based on a combination that would work and make good streetable power. Yes, newer cams with better technology may make a few more ponies but were not talking super stock here. If he wanted the most power he probably wouldn't be changing the cam. Just my opinion.
So, what's not "fact filled" about Comp's recommendations ?:16suspect The question about needing to change springs with the High Energy line is quite clear in it's answer in Comp's catalog. Maybe you should take the time to READ the catalog before making erroneous assumptions. When I said "will work with stock springs" I did not mean that it was OK to use old worn out springs. Quite the contrary, you should always use fresh springs, not those that are old in both years and mileage
After the reread of my post, I have to apologize for the calling out type of attitude. I write faster than I should sometimes and it comes out more serious sounding than it's intended to be. The things that really threw me was the reply that seemingly downgraded the XE cam while throwing another vote into the HE cams hat. One of those cams will most definately help crutch that stock head more than the other and if you care to.. I'll leave you to figure out why. It's obviously not because of any LSA variance. And I don't care if they just got made yesterday or 2 decades ago.. stock springs would void what little of your cam warranty actually exists. Stock springs are absolutely horrid for seat/open pressures on any performance cam beyond a tiny RV grind. That's also a major part of the reason that stock sbf stuff falls over a very steep cliff after about 5,500 rpm. OEM's build them for low rpm torque where spring surge is not a major concern and they were never intended to make power when revved. Trying to prove otherwise ends up being futile in the long run. As I think more about it.. I don't beleive I've ever seen or measured a stock sbf spring beyond about 87 lbs @ 1.7 installed height. Have you or anyone else? Any part numbers by chance? Just keep in mind that any disagreement with yourself or others viewpoints is never intended to be a personal atack. Some guys know lots of specific stuff.. and I want to know some of what they know too. :Handshake
One of the things I enjoy here is learning from other people & sharing what I know.I`ve been doing a lot of study lately on static & dynamic compression ratios.It gets pretty complicated,but the most important thing in choosing the correct cam for your application,is matching your intake valve closing at .050 lift to your dynamic comp. ratio.I`ve degreed many cams & basically paid no attention to this,only concerning myself w/ either advancing or retarding the cam to change the rpm where you want it to pull at.The way I look at it is that I`m never to old to learn.So I don`t let myself get upset about what anyone else says,I just research what they say & try to learn more about it.We all want the same thing,cars that run & perform like they should,& not end up w/ a pile of junk.
i had a edelbrock rpm cam in my impala, just enough to make the car more zippy, without going over the top. last thing you want to do is overcam the motor.
Motor got new pistons to make it a 305, ported and polished stock heads, screw in studs, holley 650, edlebrock performer intake, headers, flame thrower coil with plutronics in the distributor and still running the c4 tranny. My best friends dad has been a Ford Guru and picked this cam out for me saying it would be the best street/strip set up for me.
