Due to my turbo manifolds I have to run short valve covers. My heads flow 317cfm at .700 lift and heads are setup with .650 lift springs. I'd like to run the highest lift I can possibly run with short valve covers. One cam I'm looking at is .630 lift with 1.5 rocker arms. The other is .619 lift with 1.6 rocker arm. I'm thinking if I run a larger cam an shorter ratio rocker arm I can get away with more lift. Is that right?

 

Use clay to take a measurement?

Rich

 

The phyiscal size of rockers have as much to do with it as anything (as far as it clearing the valve covers). So, you are going to have to mock it up, like Rich said. Lift numbers, alone, will not tell the story.

 

I'm not real sure how to mock it up without going ahead and buying a cam.

 

Put clay in the top of the valve covers, and turn your motor over, as it sits now, with your 218/230 blower cam. You know what the lift on this is, say its .580

So now when you measure your clearance between rocker arm and top of valve cover ( By measuring how thick the clay is where the rocker arm smashes it ) you can tell how large of a cam you can run.

Say you measure and have .100 clearance with your cam, and your cam has a lift of .580. If you want to use the cam that is .619 with 1.6's you can figure out if it will clear by: Subtract .580 from .619. You have .0390

.0390 < .100 so you will have .06 clearance with that cam. I would not want to run much, if any, closer than this though because weird things could happen. Not to mention if a lifter bleeds down while trying to measure ...

 

Rich, shoebox, Hardcore,

Thank you for your inputs. I understand what I need to do now. I need to go ahead and buy my T&D shaft mount rocker arms I guess before I mock it up.

 

Now that I think about it I'm not even sure I can run shaft mount rockers with the short valve covers. Hmmm...maybe I can modify a set of tall valve covers to clear the manifold only on the outside of the valve covers. I'm running into one thing after another on this build. From what I read that is pretty typical.

 

Shaft mounts are not needed. Use a good set of head studs and follow the advice below.

I would say that with boost, a high lift cam is less important than with an NA setup. I would lean more toward a steeper, more "square" lobe with lift in the high 0.5xx" range to a max of 0.600". Remember, you are going to have positive manifold pressure and are not depending on ram effect to fill the cylinders. You are going to flow a LOT more at low lift than an NA setup would. You also don't need revs like an NA setup does and could use a HR cam unless this is an all out max hp build. Save yourself a lot of trouble and I have yet to be convinced of a SR setup for lot of street miles as no one seems to have low rpm oiling nailed yet.

Rich

 

You know that going to a higher ratio rocker moves the pushrod point closer to the fulcrum so you actually GAIN a little clearance going to a higher ratio. What heads are you running to get those kind of flow numbers? If those numbers are right then you must have the best set of LT heads on the planet.

 

Yea ... Actually, now that he mentions it, what the hell kinda heads do you have on that? And shaft mounts, you dont need them inless your turning some serious RPM's, like upwards of 7000ish ... Which, with this build, your obviously not going to be doing. Swith to good studs, and call it a day.

 

The heads are a set Canfield 220cc heads that I've had converted to reverse flow and worked over. The reason I was going to run shaft mount rocker arms was because of valve geometry. I have a set of crane offset rocker arms new in the box but I figured that shaft mounts were a lot better.

Actually I am planning on turning the engine to 7000 rpm to give more rpms under boost.

Rich, I am definately looking at HR cams because I can't remove the valve cover with the turbo manifolds in place. I understand what your saying about the lower lift cams and I'm going to take youra advice there. I don't have a problem running stud mount rockers either but I'm a little afraid to run the offset stud mount rocker arm. What duration do I need to run with this engine for the horsepower to peak at 7000 rpm. This car is not a daily driver and with boost I'll probably have plenty of power at 6000 rpm that I'll most often shift it at that point. I just want to set the engine up to peak at 7000 rpm.

 

In all seriousness, it probly will have to be a solid roller cam. And will drive half as well as you expect it too on the street. Im not saying it cant be done, but really, to turn those RPM's, its pushing it for a hydraulic cam/lifter set up on a stroker.

 

Thank you, I think your pobably right. I already have solid roller lifters for the setup I was building. It would be cheaper at this point to get the solid roller. I'm not really concerned about streetability that much. As my honda and mountaineer are my daily drivers.

 

7K? My car doesn't seem to mind. And I can show you several others that dont mind it either.

 

We have an HR cam in my friends SC Mustang that turns 7,5000rpm no problem.

Rich