ziggy89

Hey guys I tore up my distributer gear last night and while it ran with a new one (just to get it home) I have a feeling the cam gear is probably beat up too meaning ill need a new cam. Going to pull the motor and check everything my question is right now im debating on going from a flat tappet to a hydraulic roller retrofit cam. No I love my cam profile it works great in my motor on the street and at the track and want to keep the same profile. ive got two cams picked out that should be relatively close to whats in there now.


my cam is cs xe274h-10
.490/.490 lift 230/236 duration at .050 lift and 274/286 advertised duration.


the first cam im looking at is xr276hr
.502/.510 lift 224/230 duration at .050 and 276/282 advertised duration


cam choice number two is xr282hr
.510/.520 lift 230/236 duration at .050 and 282/288 advertised duration


which one do you guys think would be best? im leaning towards choice number two because it has identical duration at .050 lift but choice one has closer advertised duration what do you guys think?

five7kid

iTrader: (14)

The roller lifter profiles are a little more aggressive than the duration numbers would indicate. #1 would probably produce as much or more power than your previous cam did.

ziggy89

would it do it in the same rpm range? that's more of my concern.

sofakingdom

iTrader: (1)

I had a 400/T-5 that I built with a XE274H in it once; really liked it. Unfortunately 2 lobes wiped out.

Comp allowed me to replace it with a XR282HR, and sold me the lifters at a considerable discount. I really liked it too.

I chose the XR282HR because it had the same .050" duration as the XE274H, and I thought I would end up with a very similar cam.

I was wrong. The roller "felt" like AT LEAST one full step larger than the flat, maybe 2 steps. Everything about it just "seemed" bigger. It idled rougher, idle vacuum went down, the RPM band moved up a good 400 RPM and maybe more, it had a noticeably softer leave and considerably stronger mid- and upper-RPM pull, and so on. I'm quite sure the idle was different enough that I would have had to change the converter substantially, had I had an automatic.

I don't know, even knowing what I do now, that I would do differently if I had it to do all over again; but, I will say that there was ALOT more difference in those 2 cams than I expected. If you physically look at the lobes, it's not hard to guess why; the roller snaps the valves open FAR quicker, holds them near max open FAR longer, and drops them back to the seat quicker as well. Even if the .050" duration is the same, the duration at all higher lifts is MUCH greater. At .200" there's probably AT LEAST a 12° difference for example, and maybe as much as 18°. Has a HHHHUUUUUUUUJJJJJJJJJE effect on upper-RPM cyl fill, especially; but the higher adv duration, which I suspect (don't know enough about the design to know) may be due to asymmetrical ramps that slow the valve motion down near closing to avoid valve float (bouncing the valves off the seat) is what makes it run different at idle and low RPMs.

Since you've got such a little motor (383) comparatively speaking (like the cam thing, you wouldn't think the 20 inches would matter that much, but they probably do, for several reasons), I'd suggest that if you like the XE274 and don't want to "go bigger", switch to the XR276HR. If you want to bite off a little bit more, then you could try the XR282.

danryanm

Either cam you choose, you won't regret going to a hydraulic roller. No worries about break-in procedure (a must if you aren't sure you can fire the engine on the first attempt), you can use modern oil without a ZDDP additive, and as stated before, there is a substantial difference in flow characteristics over an "equal" flat-tappet cam.

ziggy89

I just decided to replace my cam with another one of the same grind flat tappet. I like the can and if its not broke don't fix it right.