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Looking for feedback on how I'm degreeing my cams

13K views 38 replies 7 participants last post by  eschaider 
#1 ·
It doesn't hurt to have a second set of eyes going over things. I have comp cams stage 3. I'll post pics of the cam cards below so you can see the specs on them. They recommend degreeing them with an intake center line of 114 degrees and exhaust center line of 118 which gives me a lobe separate angle of 116 degrees.

I've received so many varying opinions on where I should actually degree these cams vs what Comp says it gets a little over whelming and in the end I decided to just follow comps recommendations.

Relevant parts of the motor to this - flat top pistons with .050" intake reliefs and no exhaust reliefs. I should be around 10.5 ~ 10.7 compression ratio. Ported heads, 1 7/8 long tubes and still the same 2.9 whipple crusher that was formally at 27.5 PSI with a 3" upper and stock lower.

I have two goals with the setup. Wicked sounding idle and balls out WOT performance. I'm not overly concerned about low and mid range power as the car already produced so much torque there traction was an issue. So I'm concentrating on WOT upper RPM power (like 3500 ~ 4k plus).

I started on the passenger's side and had to advance the exhaust cam 2 degrees to get 117.5 degrees. Intake came in at 113.75 degrees. About as spot on as I can get to the cam cards specs. Piston to valve clearance at 5 degrees after TDC is 0.048" which I'm told by some is more than plenty and others seem skeptical and say I should have more.

So before I go further and degree the other side of the engine to match I'm looking for feedback and see if we can bounce some thoughts and ideas around. Now is the time to change stuff up if need be :)

Thanks guys
Malcolm

Intake card


Exhaust card
 
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#38 ·
Ed, I have seen that link and those pistons and had I been able to get a refund on my Diamond pistons I would have possibly gone that route. It was one of the alternatives I was considering. I did notice you don't specify a gapless top ring as standard. I know people can change and do what ever but was surprised to see that not as a standard setup.
 
#39 · (Edited)
Keen eyes and a good memory there, Malcolm!

In general for a non race application I prefer not to use a gapless top. TotalSeal will consistently recommend the gapless top. On a n/a race engine it is an absolute power enhancement. On a properly tuned blown engine it is also. On the street over time the combustion byproducts the top ring(s) are exposed to can/will gum up the pairing, loosing both the power advantage and ultimately also the ring(s) if the engine is supercharged.

The TS gapless top ring usage is sort of the same phenomena as the gas ports drilled from the piston crown to the rear of the top ring land. On a fresh set of rings and clean pistons they are genuinely impressive. As combustion byproducts begin to occlude the gas ports the combination falls back to a typical top ring style of performance. Perhaps more importantly unless you are racing in a #/inch of displacement class, the marginal power increase is lost in virtually every other application. On a blown engine it is possible to reduce the top pulley diameter by 1/10 of an inch and gain more power. Bottom line, gapless tops at the race track, a strong maybe. Non racetrack use, a resounding no. TotalSeal complicates this process for guys just discovering their technology by consistently recommending top ring placement for their gapless rings.

This discussion has jogged my memory on another no-no. We use 1.5mm rings as standard operating procedure for our top two rings. Increasingly the ring manufacturers, including TotalSeal, are offering 1.2mm and 1.0mm top rings. These are great rings for a n/a racing engine at the race track. They will absolutely reduce internal friction and increase FWHP. On a blown racing engine you can make a case for them although it is a relatively weaker case. On the street there is no place for them in a blown engine. The problem is that you as an engine builder have no control or knowledge of how good or bad the tune is that is being used. When the rings & engine give up the ghost it will always come back to the engine builder's door step. Rarely will the cause be viewed as the tune.

The rings in general and the top ring in particular are a primary heat path from the combustion process through the piston crown, out the lands to the rings, then the cylinder wall and finally the cooling system. The 1.0 and 1.2 mm rings are great n/a drag racing horsepower "secrets" but for a street driven car they are a formula for an early engine rebuild. Their ability to adequately transfer combustion heat energy to the cooling system is diminished by their dimensions / geometry. The reduction is sufficient enough that the engine will experience piston overheating from a fairly impressive heat dam at the top ring. The piston overheating will cause the piston to swell in the bore and suffer what we call black death - which is just a cylinder scuffing and corresponding blackening of the piston skirt from the swollen piston pinching off the oil film in the cylinder that lubricates it.

Ed
 
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