308 V12 conversion begins

I fluxed pretty much joint before tacking so the tacks didn't leave anything inside then I purged during the full welds wher I could.

I liked the flux over all. It gives a good result if the joint is a good tight fit, but not so good if if there is much of a gap, say over .04".

 

I don't have the bends I'd like to use for the front 2 into 1 so one to the heads I guess.

 

I just got a cal from Web Cam. The cams are back from copper plating and going on the machine for rough grind. Progress.

 

The cams were made from 8620 steel. This a pretty strong steel that case hardens well. I want the lobes and journals hard, but the shaft part wants to be more tough than hard and it’s the copper that lets this happen. The entire part gets copper plated then the lobes and journals are rough ground which removes the copper from these surfaces only. Next the cams go to the heat treaters and are carburized, the carbon soaks into the bare steel but does not go through the copper plating leaving the shaft part as 8620, but making the wear surfaces more like 8680 to a depth of about .030”. Then the actual hardening is done and the wear surfaces with their now high carbon content get to about 65C Rockwell while the base metal only goes to about 45-50C.

 

I looked and the cam accel/decal ramps today. The 2 lobes I picked have very difference designs. It looks like the intake is about a 30 degree vs 45 on the exhaust and they are not at the same lift points and they have different blend radii. I’m seeing the max allowable lash on the intake as about .012” and the max on the exhaust as .008”. Normally you would expect the intake lash to be less than the exhaust but because the tails are so different a design setting the intake at .006 and exhaust to .008 costs a ton of low end hp…at least it does on the simulator as the sim says the engine is hyper sensitive to intake seat to seat duration. It looks like the correct lash setting are .010-.012 on the intake and .006-.008 on the exhaust with both erring toward the loose side if possible.
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Sorry…….clearly what I was thinking didn’t translate well into a post.

A cam has a few distinct regions to it. At the very bottom where the cam first stars to move the valve are the acceleration/deceleration ramps. These are designed to gentle start the valve moving and gently stop the motion so there is no bouncing or banging to beat up the valve train. thr graphs show the shape of the ramps with zero lash and maximum acceptable lash. Simple enough.

The problem is that these features can add a ton of seat to duration which is a bad thing as it allows all kinds of reversion pulses to form, allows cylinder blow-down which effectively lower compression ratio and other bad things. On the intake cam I selected increasing the lash by .002” decreases the seat to seat duration by 4 degrees but only decreases the .050 lift duration by about 1 degree and that helps make hp down low. If I go too high on the lash though I would hit and exit the cam on the main ramp instead of the accel/decal ramps and beat the snot out of the valve train so you want to be in just the right spot…anyplace else and you are giving up hp or giving up engine life.

 

Here is other cam design. It has no actual accel/decal ramps, just a radius to serve the purpose. These cams would want the lash set in the .002-.005 range to be in the right spot.
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Ok, I'm not done with the headers. I didn't notice before but thefront headers ended up a little crooked some how.....anyway I couldn't bring myself to leave it so I cut #4 apart a little bit and fixed it. I have a little more welding on tube 1 & 3 and I think I'm going to order a new bend for tube 2 to give me a little more clearance to get the nut on the stud. I'll order the bends for the 2 into 1 too I guess.
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Yes and no. Yes lash decreases lift and that is a bad thing but designing the cam to work with more lash means there is more margin for error in valve adjustment and therefore allows longer maintenance intervals. Everything is a compromise.

 

This whole lash thing got me thinking if I would have been better off with a cam that has less lift but wants less lash. I laid the intake )blue line)and exhaust (red line)I ordered set to what I think is the correct lash (.010 Intake, ,008 Ex) over another intake option that has .007 less lift but wants only about .002 lash (green line).

The lower lift cam ends up with .001 more lift than the higher lift cam, the seat to seat and .050 duration of the higher lift higher duration cam ends up less than the lower lift lower duration cam, but the higher lift cam has about 5 degrees more duration from about .200 lift up to .400. This all says the intake cam I ordered will make more hp from idle to redline than the lower lift lower lash option just like the simulator says it should in spite of needing more lash causing it to end up as the lower valve lift option.

It also look like both the exhaust and intake I ordered will do a better job of picking the valve up and setting the valve down gently than the low lash design option and will do so over a .008+ lash setting window vs the low lash design that really wants to be help in a .002- window.

I know….engineer types get excited by boring sh*t and you want pics of something being cut or welded, tonight.
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I hear you, but I’m a big fan of leaving things stock.


I actually prefer the diaper anyway, which goes to show there is just no accounting for taste