cam choice suggestions...

[Guest B250HO]

350 w/ vortec heads machined for .550 max lift (z28 valvesprings/lt4 retainers) wanting as close to 400 horse as possible. Chevyhiperformance used this combo with a comp cams XE268H and squeezed 408hp out of it. They used 1.6 roller rockers to get close to .500 lift- I'd like to advoid the expense of roller rockers (and used stamped rockers) if possible- what came do you guys suggest for my situation? What cam are ya'll using? Thanks alot.

 

oh and budget is pretty tight.......thats why i want to advoid roller rockers, unless it will make a huge power loss.

[grumpyvette]

whats your rear gear ratio, transmission,gearing, stall speed, intake type,compression ratio, are you useing headers and a low restriction exhaust,and are you willing to use a solid lifter flat tappet cam?

 

BTW read thru ALL of this carefully

 

http://www.rustpuppy.org/chp/Welcome.html

 

http://www.compcams.com/information/Products/RockerArms/MagnumRoller.asp

[Guest B250HO]

gear ratio: 3.90

transmission: muncie 4 speed (close gear ratio- think first gear is 2.46)

performer RPM intake and holley 750 double pumper

approx. 10:1 comp. ratio

1 5/8" primary long tubes - rest low restriction exhaust

 

I don't know much about the advantages of a solid flat tappet setup, I figured on running hyd. flat tappet....but I'm open to whatever it takes.

 

I've read through chevyhiperformance magazine's article using the vortec heads....thats why I chose them. In the article they mention that they could have used a hotter cam to gain more power but chose to stick with the XE-268H for some reason. I want to know what cam would go good with this setup to gain some more power.

 

Thanks for your help grumpy

[grumpyvette]

http://www.crower.com/misc/cam_spec/cam_finder.php?part_num=00271&x=18&y=8

 

normally with a 4 speed, 10:1 cpr and 3.90 gears, Id suggest a solid lifter design as it will pull extra rpms, but the vortec heads pretty much restrict that advantage so to maximize what you do have, (great mid range flow and small ports) Id sellect this cam above, (hydrolic flat tappet) its going to lope noticably at idle, but have very good tq/power, especially if you install 1.6:1 ratio rockers

 

as always call the manufacturer and discuss it, they may suggest a wider LCA but while it will make it more street friendly it will kill off a bit of power and tq, personally ID live with the roughter idle and get the more robust tq curve

 

btw

heres the cam IM running (EFI and auto trans, so its sensors and tunning limits requires the WIDER LCA) notice the similar durration...it makes killer tq and works well with a 250 hp shot of nitrous

 

http://www.cranecams.com/index.php?show=browseParts&action=partSpec&partNumber=119661&lvl=2&prt=5

 

something to read thru, keep in mind you need self aligning rockers as you don,t have factory pushrod guide plates

 

http://www.compcams.com/Community/Articles/Details.asp?ID=2132654598

[Pyro]

10:1, 3.90 gear, and a manual trans. I would recommend an old school 280H compcam.

 

Or a cam with about 228 to 232 degress on the intake and a little more exhaust to help out the weak vortec exhaust port.

 

I don't like comp's XE series cams. Sure they make a little more power, but at the cost of quicker lobe wear and extra valve train noise. Plus there will be much less tolerence to any valve train issues which can lead to instant lobe flattening.

 

Avoid 1.6 rockers, sure they will make more power but again, at the cost of quicker cam wear. Don't get caught up in dyno numbers and tricks to make just a little more power. You should also be concerned about cam life. When a cam goes flat, the cam and lifter metal eats up engine bearings.

 

Use diesel engine oil with the new cam, as compcam recommends.

[Guest B250HO]

thanks for the help fellas

[grumpyvette]

CLEARANCE or VALVE TRAIN GEOMETRY ISSUES or lack of lube is far more likely to be an issue than rocker ratios, Ive only had ONE cam loose a lobe in the last 30 years and that was 30 years ago and MY fault as I didn,t carefully check the rocker to rocker stud clearance at the time on ALL the rockers (we all learn some things the hard way)

 

use E.O.S. a good MOLY CAM LUBE, CHECK ALL CLEARANCES CAREFULLY, and use a high ZINC oil durring the break in procedure

 

http://www.engineparts.com/Motorhead/techstuff/caminstall.html

 

http://www.micapeak.com/info/oiled.html

 

read these

 

http://www.cranecams.com/?show=article&id=2

 

http://www.cranecams.com/?show=faq&id=1

[Pyro]

Cam lift rates are being increased for more power and oil antiwear additives are being reduced for emissions. This has lead to a lot more cam failures when aftermarket, high performance cams are used.

 

You should use diesel engine oil even after break-in with flat tappet cams if an aggressive cam prolife and stronger valve springs are used .

 

Can't rememeber where I read it, maybe hotrod or a chevy high performance magazine. But the article was called, "When good cams go bad".

[grumpyvette]

avoiding some of the modern oils designed for roller engines and catilitic equiped engines , and useing a high zinc content oil for flat tappet applications is a valid idea.

[boodlefoof]

May also want to check out Lunati's "Voodoo" series of cams. I frequent an old Camaro forum and there are a number of people who have been pleased with those. With the vortec heads' relatively "weak" exhaust port, a split-patterned cam (with more exhaust duration) will likely be beneficial. The XE cams are a split-patterned cam as well.

 

I'm running a 10:1 355 with the Comp XE274 and must say that my seat-of-the-pants test has me pleased. It is borderline for vacuum and power accessories, but it really comes on around 2500rpm and keeps pulling up to my self-imposed 6500rpm redline. I'm not using the Vortec heads though, so I can't comment about how well those would support the upper end.