In addition, center mass reduction will increase the lobe's forward momentum to overall mass ratio, but is it doubtfull the mitsu engineers employed this fact in why they used them?

 

Best I could do..... the cams are cast hollow. You can look in through the relief holes and see the rough casting of the internals. Also, the cam gear bolt and cam position sensor bolt have a smaller ID than the cam casting. In other words, you couldn't get a drill bit in there to do the job, unless you drill the larger ID first, and then weld on the "end caps" for a lack of better word.

The crank and flywheel spin at twice the rate of the camshaft. Wouldn't it be easier to cut rotational mass there, instead of the cam? Bigger bang for the buck IMO. And easier to!

 

big thanks to Mike for talking to Tomei - they confirmed their cams are NOT hollow - they use their own billet "slugs"

In doing some research today, I could not find anyone to even sell me Evo blanks

 

Eye, they be cast, they be....

I don't really know what the other bits (cam positon bolt and cam gear bolt) look like or how they fit so I can't really comment on how I would drill it.

However, there is a possibility of some good news. If the OEM's are cast, you can be pretty sure that you wouldn't need to gundrill the thing from a surface finish and run out point of view. It would be possible to just drill it if the material is soft enough and again if all the parts above allow.

 

Pluses with hollow cams shafts:

1.) Reduce engine weight - overall this probably has the same effect as strapping balloons to your engine. i.e. not much

2.) Reduce rotational inertia - reduces the load required to speed it up and slow it down. This won't have anywhere near the effect of the flywheel, but it _will_ have an effect on your cam sprocket and timing belt, however little.

3.) Thermal capacity - The hollow camshaft will heat up and cool down much faster. How this might effect the performance/clearance etc I don't really know.

4.) Torsional rigidity and torque capacity - we've been talking about the same camshaft size with/without a hole down its length. But if you look at it another way, for the same weight, a slid camshaft would be a lot thinner and therefore a lot weaker and more flexible which probably won't allow for the cam profile mitsu wantes to use.

In the end, I think any shortcomings that a solid camshaft might have can be compensated by better profiles on the cams. Having said that, having a hollow one I think is better, if only by a very slight margin.

If anyone has an unhardened blank what wants drilling (God knows where you might get it from), I might give it a go. For free of course, but I can't guarantee much except for that I won't go through the side!

 

putting some numbers to it, the difference in torque is around 0.1Nm if you accelrate from 3000-7000rpm in 2 secs. This is for all 4 cams.

p.s. this is a v.rough calculation, I'm taking the hole as 20mm in diameter.

 

Or simply drill it one size smaller than the threads all the way through. Perhaps not quite as light but still hollow and pleanty lighter than solid billet.

Adam can you check out the viability of getting the tomei's or hks gundrilled??

P.S. doubleugly what is the weight of the stock cam, lets get down and dirty here..

 

the best my bathroom scale will read is +/- .5#'s. I measured 5 different times weight of the camshafts, and every time each camshaft came up at 3#'s. Remember that's +/- .5#'s. I stepped on the scale, got my weight five different times (and it was the same always), and then held the exhaust cam 5 times, and the intake cam 5 times. Each reading said the cams weight 3#'s each.

Sorry, I'm not one of those culinary experts that have a +/- 1 oz. scale hanging in my kitchen. I do have sharp knives though

 

i don't think a bathroom scale is accurate to +/- .5 pounds... especially not the spring loaded ones, maybe the digital ones. the thing is repeatability has nothing to do with accuracy in this instance. repeatability just means it's consistently off.

 

Don't know what Adam's going to say. But I rekon it won't be easy if the whole shaft is hardened (not just the faces). If you get a hard bit inside the shaft you stand a good chance of losing your drill bit. Which is probably more expensive than the camshaft.

 

I can tell you right off the bat that none of these firms are going to do any sort of "special" batch for us

 

What do the solid cams weigh?

 

it's a digital scale. I weigh about 185#''s, the cam weighs about 3#'s. Do the math, even if it's consitantly off, it doesn't have to be accurate for the full weight, jsut the difference between me and me+cam. 3/185 = 1.6%. If it cosistantly picks up a weight change of 1.6%, well there you go. Whether the final weight is 182 or or 189 or (insert your number here), the scale is measuring a 1.6% weight change in the 185# range. It means the cams weigh 3#'s each +/- .5#'s.