After a recent complete rebuild, a local Z expert has run a diagnostic on the car and informed me that the exhaust cams are retarded. When building the engine I did go to a lot of trouble making sure the marks were all where they were supposed to be but he assured me it was really easy to get wrong. Being an old engine builder and an engineer, I have a lot of good tools available (degree wheels and dial indicators) and was wondering if anyone had some ideal degree settings for the cams that I could now dial the cams in at for optimum performance?
So you do in fact have adjustable cam gears? Or is the mechanic guy saying you have put the belt on incorrectly?
They are retarded compared to what? Factory settings or just what he thinks? The marks on the rear timing belt covers aren't always exact, much better off counting the teeth on the belt. There are some gains to be had with changing the exhaust cam timing, you will need to make or buy some adjustable cam sprockets though.
If you did it ghetto style and just adjusted it by moving the cam over 1 tooth on the belt would this have the same effect or is it too great a jump??
Truly Ghetto. One tooth is 7.5deg advance, you generally want some finer adjustment than that usually 4-5deg is where the sweet spot it.
Haha, is there benefits of using adjustable gears on only the intake or only the exhaust side? If so which would be the best side to play with... I'm guessing intake side first.
exhaust actually is the one that sees the most benefit. Intake is already advanced with VTC. With the VG (from memory, haven't done it, but read it) an advance of about 4-5deg can show some good gains in the midrange.
Exhaust advance Yep Andy is spot on in that most twiddling is done with the exhaust cams - In fact the JWT R5 #500 cams have a 4 degree advance built in to the exhaust cams to improve the mid range.
JWT cams come with a +4 advance in their cams . Reason being in the ninetys there werent the breather mods available today so the advance helped spool the bigger turbos and give a little more midrange . But with todays supporting mods available you will find that taking the advance out with adj cam gears may work better .
Is it easy enough to adjust the adjustable cam gears once the timing covers are off, or will the cams find their resting point and throw your timing out?
Resting point I've had a cam spring to its resting point while doing a belt - not such a big deal - just had to use my extreme he-man strength to move it back to its original position.
Your adjustable gears should have degrees of advance marked along the adjustment "slots" and the timing belt mark doesn't change on the teeth, your just rotating the sprocket on the cam itself so it won't matter if it's at rest or on the belt, you dial in 4 degrees, it's at 4 degrees assuming you've put the belt on correctly.
Thats a good point. It appears that the exhaust cams are not the only thing that's retarded. I can't brain. I have the dumb
Yes though while you are adjusting and have loosed off the 4 bolts which are used to do the adjustment can the inner part of the gear where the cam is attached to go to its resting point, while the outter part of the gear stays in place held by the belt? Or do you rotate the whole crankshaft/cams to a resting point for each one to do the adjustments where the cams are not under pressure from holding and valves open e.g your working on the drivers side head, rotate both intake and exhaust to all valves closed make adjustments there with no pressure from the vavle springs.
That 7.5 degrees at the camshaft is 15 degrees at the crank, the 4-5 degree sweet spot is also crankshaft advance. All cam timing references are relative to crankshaft position not camshaft, so you can see how 1 tooth out on the cams is really a big difference in base engine timing and is definately not the way to do it.
The PITA about adjusting zed cam gears is the best way to do it is to grab the cam shaft on the hex behind the shaft covers with a shifter. Bad part is to do this properly you have to pull the plenum and remove cam covers. Someone enlighten me about how to adjust them without the cam covers off and the ability to hold the cam shafts still while you move the gears?
