Just when I thought I had accomplished something with the gun-drilled cams...
someone tells me about these. Stock cast iron hollow cams from the Mitsu Evo. Not only are they way way way thinner-walled than mine they are also cross-drilled. I am green with envy!
Now when you consider these are from a car that is easily capable of more than twice the HP I'll likely make and be spinning ay 8k rpms compared to my 6.3k as well as being 33% longer than a 3 cylinder cam how can anyone really believe my meager/conservative and short little gun drilled cams are gonna go flying apart because of a teensie little 9.5mm bore thru them!?!
Hell, I may buy another gun-drill and open mine up to 12 or 14mm now. Would still leave more wall thickness than these have by a LONG shot.
Anal? Moi? You ain't seen nothin' yet...
Got all the data in on the gun-drilled cams and while I'm satisfied with the results I've discovered some things I just can't live with as-is.
Total weight-savings on gun drilled cams ended up at .875lb. Not bad but I'm looking for about 50% additional weight loss on them. Also I want to balance the cams to each other. As they are in stock form the left one is considerably heavier than the right one. I've come up with a plan to net me double the weight savings I just got as well as make each cam weigh the same amount. I should end up at at gross weight savings of 1.58-1.6lbs with the added benefit of blueprinted/balanced cams.
Here's the specs as of today:
Stock cam weights:
Left: 2392g (5.26lbs)
Right: 2097g (4.61lbs)
Combined: 4489g (9.875lbs)
Gun drilled cam weights:
Left: 2181g (4.8lbs)
Right: 1909g (4.2lbs)
Combined: 4090g (9lbs)
Weight removed by gun drilling: 397g (.875lb)
Stock cam weights with mounting hardware, less pulleys
Left side: 2540g (5.59lbs)
Right side: 2198g (4.84lbs)
Total: 4738g (10.42lbs)
Now here's where the anal comes in:
If I drill the left cam again, this time to 12.7mm (.500") I can effectively reduce the weight-savings over original gun drilling by an additional 35%. By doing so that will make it slightly lighter than the right cam with all it's hardware bolted on. Then by going back in and sleeving it's front/rear threaded sections with 7075 aluminum (over 70% lighter than the cam material) I can bring the weight back up to the same weight for each cam. But it doesnt stop there.
The formula I'm using dictates I'll need to make my own mounting hardware for pulley and CPS sensor disc. To that end I've done the math for timing belt pulley and CPS sensing disc mounting bolts out of titanium at 35% less weight than stock. Timing belt pulley washers also out of titanium at 35% less weight. And CPS disc and washer out of 7075 aluminum at a 70% weight savings. This will bring the now-lighter left cam back to a near-identical weight of the right cam with identical lightweight hardware used on both cams.
Lightweight cams should then be:
Left: 1985g (4.37lbs)
Right: 1985g (4.37lbs)
Combined: 3970g (8.75lbs)
Net difference: less 768g (1.69lbs)
Affect: 16% lighter than stock
If my numbers are correct this would accomplish several things:
1. Remove an additional 50% more weight from the original gun drilling which would put my total cam rotational weight loss at 1.58-1.6lbs.
2. Make both cams weigh EXACTLY the same amount.
3. Lower the engine COG slightly (hey every pound helps!)
4. Dramatically enhance the already lightened valve train and reduce additional parasitic and frictional losses.
The pic above is of my original plan earlier today to just open up the front & rear of the left cam and leave the center bore as-is. Unfortunately the math didn't add up to a high enough weight loss to match the right side cam until I rebored the entire length then sleeved with 7075 aluminum for pulley mounting on the left cam.
The mounting hardware in pic with a yellow dot will be made from titanium and the orange dot items will be 7075 aluminum
I'd love to remove more weight from the right side cam and easily could. But I'd rather keep the cams weight-matched, balanced and identical to each other than save an additional 2.5 ounces on the right cam only.
Amazing difference between soaked/scrubbed and ultrasonic
cleaning of cams...
in this pic you can see the stark difference
in length/mass between the left longer, heavier cam (front) and the shorter,
lighter right cam (rear). Also the difference in a 72hour
heated bath in cleaner/degreaser and another hour at the kitchen sink
which was done to both cams after I got them out of the heads.
Not being satisfied with either of them I put the left cam in the ultrasonic cleaner this morning to see if it could help. These are too long to fit in my
I couldn't even begin to approach these results with a brass brush, solvents, soaps (even with pumice), scotchbrite pads et al. Yet an hour in the