Big cams/head questions.

[Terrh]

Who's built motors with big cams in it? I don't mean got them built, I mean actual firsthand knowledge.

Suddenly I feel like there's a million things I've overlooked and I just want to know if anyone has answers before I go doing things the hard way or not ordering parts that I'm going to need.

At what lift does piston to valve clearance start being an issue? I've got wiseco pistons and have probably lopped 20 thou off of the head and block (combined). Using a stock thickness metal head gasket.

Are adjustable cam gears really necessary with aftermarket cams or no? I'm going to about 10mm lift and probably 280* duration. I figure as long a piston to valve clearance isn't an issue I doubt I'll need to do much adjusting, at least not at this point in the game. I don't need to eek every single last horsepower out of the motor.

Those of you that have gone with smaller base circle cams, what did you do for valve clearance? I'm thinking about just getting 2mm and 2.5mm (or whatever I end up needing) thicker shims made. Has anyone else done this? It seems like the easiest solution as I kill two birds with one stone.

Anyone that's running stainless valves and bronze guides, what are you running for stem to guide clearance? Supertech and brian crower are giving me conflicting numbers, if I go by BC's numbers the bronze guides I bought are too big inside and I'll have to get inserts made, which irks me because these parts are all brand new.

Is 2.5 thou too much clearance for a stainless exhaust valve? What about 3? It seems like a ton compared to domestic stuff but not that much more than what the factory manual says. Supertech guy wasn't too sure but felt that 3 thou was fine and any less than two was not.

PS: any useless replies like "ask your builder" don't help me. I'm the builder, and none of the part manufacturers seem to be able to give me answers, or at least answers that make sense.

PPS: Thought it might be useful if I added what parts I'm trying to use.
Brian crower +1mm valves, BC springs, BC titanium retainers, supertech bronze guides (hate stock valve guides!) and reground cams with either a 2mm (intake) or 2.4mm (exhaust) smaller base circle.

[Black BNR32]

280/10.8 here...all work done by z-tune/monkeynuts. hopefully they can give you some answers.

[nismo-152]

I have built a few motors with smaller base circle cams. The reason typically for the smaller base circle is that the cam is re-ground. I found the best way to make up this difference is with tomei plus size buckets. Then do your shims.

It is quite important to degree the cams also. Without doing this the cams potential is wasted. If you have never done this before you may want to hire it out or get help from someone well experienced. Your came timing will make night and day of your power and response especially with a long duration cam. Your lift is'nt huge at 10 and will likely be a non issue but it is always safer to check first.

I have often been able to tip the valves or grind the seats down also to get proper clearance without having to get new shims. Works perfectly also.

[Terrh]

yeah, on my last motor build I just ground the valves to fit the old shims. But having to take up nearly 2mm isn't going to be possible.

I've never degreed cams. Did read up on it a little. A friend of mine has done it before and offered to help me out.

I thought 10mm was pretty close to the biggest lift possible? I'm happy that it's not. I like RPM's and valves not hitting pistons.

[gtrjon]

10 mm is not that much lift. mine at 270s with a 10.8 lift. you dont see much over 11mm of lift tho