The interweb is awash with instructions on how to dail in a cam. You need some gear which you might not have though.
Valve lift and cam lift are different because of the rocker arm ratio.
I once read something about turbo cam grinds, although I didn't actually grasp it. It said something about maintaining a greater pressure differential between the intake of exhaust or something

it seems all your measurements are in thousandths of an inch

cam lift:
the amount the cam lobe is pushing the push rods.
321 and 289 divided by 1000 will give you the amount in inches...
ie 0.321" and 0.289" (times this by 25.4 if you want them in mm)

duration adv:
most likely means the duration of the cams lobe (how long each valve stays open for)
measured in degrees relative to the crank shaft.
ie 264 is the valve stays open for 264degrees of the cranks rotation.

duration at 050:
means how long (in degrees relative to crank) the cam holds the valve open above .050 of an inch (or maybe how long the cam holds the push rod above .050 of an inch).

valve clearance:
distance between the valve and the lash pad when the valve is shut and the cam isn't pushing on the push rods.

valve lift.
the distance the valve comes away from the cylinder head (ie how far it opens)

Hi, I assume that this is in an L20b? I have a few ideas concerning your problems.

Sounds like the exhaust lobes are ground to "471c" profile and intakes to "477c" (whatever that means to Wade). Nothing wrong with this, it gives your intake the fast opening (and obviously higher lift) needed to get good initial flow, good for torque throughout the rev range.

I think stock L20b duration at 50thou lift was about 204 degrees, with about 410 thou total valve lift, so your exhaust profile is basically stock with a little more lift, and your intake being 212 would be termed a 'sports' profile, but with extra high lift. Overall I think it would be an excellent street turbo cam (mild), clearances of 12thou is normal and safe, usually you go 2 thou less on the intake but considering the intake profile is rather aggressive in its opening I think their figures are fine. Stock is 8(I) and 10(E) thou cold, I think. If in fact the cam does lift the intake valve that high (specs often vary from the real world) you would basically be binding the inlet springs, the datsun books reckon they bind just over 460thou lift (I've never lifted stock springs that far) - you'd better check that VERY SOON or you'll wipe out your inlet lobes or drop the rockers. Maybe crank it by hand with a 10thou feeler guage between the spring coils to see if it binds on the guage.

***This cam will certainly create more OVERLAP than a stock one (unless the lobe centres are over about 112-114 degrees, you can calculate that from the opening and closing figures), your main problem with an EFI system is upsetting the MAP signal at idle and low speed due to this overlap and the later closing inlet valve. What inlet manifold vacuum does it pull at idle? Any increased overlap creates LESS vacuum in the inlet at idle and low speed, the ECU sees this as more throttle and will select a higher load zone. Do you have a Throttle Position Sensor? If you have a TPS installed you must select it to control the load selection at idle, or until the engine makes boost (ecus differ on how they use the tps signal). This enables correct selection of the load zones in the ecu. You may also find you can advance the ignition timing at idle/low speed with the cam because the low vacuum caused by the overlap actually means there is lower cylinder pressure and additional advance helps smooth things out (I run 38 degrees advance at idle with my L20B turbo and "wildish" cam - more duration than you but moderate lift). Cam selection goes hand in hand with turbo size, you should get very good streetable performance with that cam if your turbo is around the T28 -T3 size, should be very responsive and driveable.

ALL THAT BEING SAID - if you're out a tooth on the chain when you installed it, it'll run like crap regardless.

ndiggles thanks that was a really helpfull post. I am running an l20b yes, with a tdo4 wrx turbo, slightly smaller than a t28 more a t25 id say. The ecu does run a map sensor and i think the cac at idle was around 20 ish maybe a bit less, didnt pay much attention. When the cam lobe is pushing all the way down, the outer spring is not binding but would be getting close maybe 0.5 -1mm clearance so im assuming the inner spring would to be ok. Yea it runs a tps 0-5v and im positive that the cam chain is on the right gear teeth! The problem would be that since i dont have an adjustable cam gear the cam positioning would be as they ground it sinse the cam locks in to the gear pin etc. Do most regrinds grind them so you can just put them in (assuming you set up lash pads, coil binding etc) or is it expected to use adjustable cam gear and cam dial gauge etc? Thanks fellas, its in the w/shop atm for a retune so ill see how it goes and recheck everything when i get it back. So a more wild turbo grind would leave the exhaust and up a few inlet grinds?

no probs sikdatto - if it pulls around 20 inHG on your guage at idle then you SHOULD be right regarding the ecu map selection - I'd still have a look to see if the ecu is using the 0-5v as a reference for selecting load zones, I've seen plenty of tps sensors on engines that are only using the MAP, and I always just ran off MAP till I put the big cam in and had to run a TPS to tune the bloody thing.

I would never put a new cam in without doing the precise and fiddly thing of dial guage/degree wheel checking. You just dont know what you've got otherwise, plus you dont know how moving the cam later on will affect performance/piston-valve clearance etc. Also like I said previously the cam data always seems to differ by some amount when you get the cam into the car. I think you'll find your inlets arent opening the full 485thou (rocker wipe pattern/lash pads and rocker clearance can affect this, and it also affects timing data to a large degree). You'll notice a big difference if you're out by more than about 4 degrees in the timing, generally, I found with the stock L20b cam that RETARD will make the car doughy and slow to boost, too much ADVANCE will feel the SAME BUT you'll find it makes heaps of boost very quickly (on the guage!) but the car doesnt go anywhere (i'd say its due to the exhaust opening earlier which puts a lot of heat to the turbine, spools the turbo well, but the inlet valve is closing too early to allow it all in, combined with a little inlet reversion past the inlet valve because it opens too early while the piston is rising on the exhaust stroke)

You should have some adjustment on your stock cam gear, 1 2 and 3, the other holes that allow you to advance the cam (if its stock nissan), they can get you very close for dialling in a cam (each hole will advance the cam 4 crankshaft degrees) although in order to do this properly you'd need to measure the valve lift off the spring retainer with a solidly mounted dial guage and put a degree wheel on the crank pulley, then turn it over by hand and check the timing figures against the data you have for the cam - they might have "inlet lift at top dead centre 60thou" and if yours is 40thou you know that its retarded - if you keep turning it and find it reaches 60thou at 10 degrees AFTER TDC the cam is 10 degrees retarded, with your stock cam sprocket that'd mean you'd go back 2 holes, or 8 degrees to get it close to 10 and check it again (but if your're already on hole 1, the starting hole, you cant go back, but you can retard the whole sprocket 1 TOOTH on the chain which is 18 CRANK degrees, then ADVANCE the cam the 2 holes to advance it 8 degrees, making 10 degrees total RETARD at the crank so it matches the timing data) Its pretty involved for most people and requires patience and precision.


A more wild turbo grind would require a larger turbo, really, its all about where you want your power band. The close to stock exhaust profile of your cam would be there to provide solid, high velocity flow to the turbo to help it spool at low revs and to reduce the overlap so the exhaust backpressure from your small turbo doesnt come back into the cylinder during overlap and upset the inlet cycle (a typical 'turbo' grind) - basically a cam with lots of lift but short duration and wide lobe centres that will make lots of torque over a wide band, in an L20b wont make much power over 5000rpm, the torque peak will be around 3000, so you match the turbo to come on song before(preferably, if you can) the torque peak so you you put boost into the engine at the RPM it is most able to take in more air (this would be your situation). Then if you want more power you chuck in more boost, which wont be as much as a higher revving engine due to combustion control at the lower engine speeds (higher speed engines inherently have better knock resistance due to faster rate of combustion).

If you want to make more power than that allows you you'll have to make the torque at a faster rate, by making it at a higher rev, which means a cam that can breathe at higher revs, and this starts becoming a large naturally aspirated cam with late closing inlet to cram in boost at high revs and narrower lobe centres for overlap to scavenge the cylinder of exhaust gas and make use of the LARGER turbo you'll use which has less exhaust restriction because of its wheel/housing size. This combo becomes laggy and peaky, but more efficient at high revs.

Cams are pretty cool things, and the one thing us L series boys lack is valve area, so capitalise on knowing about cams so we can beat as many mulitvalvers as we can before they get wise