Cam timing question...

[Stage5]

Let me start off with introducing myself. My name is Elijah and i got my start with American muscle. I learned quite a bit about the ls series motors and their performance characteristics. But I have always been a fan of high revving motors, so i started looking for alternatives and stumbled upon a youtube video of a vh45 at 9k and i have been a Nissan/ Infiniti fan ever since. So i decided to do a 300zx build (vg33 bored to 3.5, GT675rs turbo kit, 4.9 final drive, nistune, the works) and im stuck on the cam gears.

Now to my question.

I have always understood that cams with low overlap/ tight LSA's where best for low to mid range torque and vice versa. And that advancing the intake cam or retarding the exhaust increases overlap and moves the torque peak and powerband around in the rpm range and vice versa.

When it comes to VTC it functions by advancing the intake 20* (increasing overlap) from off idle to about 5800 RPM to increase torque within that range. But during periods of idling and RPM's over roughly 5800 RPM the intake cams are in the zero advance position (reducing overlap), smoothing the idle, and increasing high rpm torque.

This seems to contradict what i have been taught. It would seem that its operation would cause a lost in low and mid range power below 5800 (due to the advance) RPM's, and a lost of top end above it. Now is what i have been taught wrong? Or is that while the cam is in the zero advance position it is actually retarded, moving the power higher in the RPM range. And the advance moves the power lower in the RPM range and builds more torque.

I know there is a lot more to all this cam timing/ science stuff that i haven't even touched yet. So im hoping to get some clarification from someone who knows it all.

Thanks in advance. Any help is greatly appreciated.

[evildky]

first of all your intended build hase some serious flaws
the vg33 is a single cam motor (one in each head) which does not have vvt so you might want to re evaluate your plan

and while you didn't specify your intended axle, the R200 case found in the z's I don't think will fit a 4.9 which is insanely high anyhow and you'll be left wiht a car that is misirible on the road, there might be a truck high pinion case than can fit such a gearset but who wants to spin 5000 rpm in overdrive to do 60 mph

onto the cam discussion, when talking about single cam pushrod engines (1 cam in the valley) vs single cam (one in each head) and a twin cam (2 in each head) they all will respond differently, the single cam and pushrod engines of course have the intake and exhaust lobes on a single cam so when you advance or retard the car you move both the intake and exhaust timing, and keep in mind when dealign with a turbo motor you want less overlap and more duration

[Stage5]

Yeah the SOHC thing was pointed out to me by a fellow on TT.net. I misread a post on another forum that lead me to believe that there was a dohc variant, but i digress.

And the r200 will fit a 4.9, they make the r&p for them in that ratio. I should have mentioned that this is not intended as a DD. It may be taken on the streets sometimes to commute to the local car meet, or just because i feel like it. This thing will be semi stripped and im looking to shave a hefty 500lbs off it. But it might not matter now as the tt z32 comes with a R230, and i have experienced the difference a qualife diff makes. So im growing rather fond of the idea of using one.

I know you want more duration and less overlap which is why its not making sense to me that overlap is being increased during low rpm.... Does anyone have anymore clarification for me in accordance with VTC???

[evildky]

the TT came with the R230, the n/a came wiht the short snout R200, you can swap over the irs cradle or simply adapt to the R200, thsi changes the pinion flange so the driveshaft will need to be swapped ro modified as well, I suspect they make the quaiffe for R230 I knwo they make tifor the R200, and I suspect the R200 version will be cheaper or at least easier to find as it's used in so many cars over so many years, the R230 has a reletively short production life

[BigTDogg (MA)]

the TT came with the R230, the n/a came wiht the short snout R200, you can swap over the irs cradle or simply adapt to the R200, thsi changes the pinion flange so the driveshaft will need to be swapped ro modified as well, I suspect they make the quaiffe for R230 I knwo they make tifor the R200, and I suspect the R200 version will be cheaper or at least easier to find as it's used in so many cars over so many years, the R230 has a reletively short production life

Pretty sure the 200 won't fit in the TT (230) subframe. You need to swap the entire rear subframe to swap diffs, in addition to the driveshaft. The mounting points are different IIRC.

4.10 Leader Gears in the R230 with a an upgraded LSD is the ultimate rear end for the Z32, IMO. You get the strength of the R230 (R200s have broke with a hair over 500RWHP, halfshafts snap), with a final drive higher than the R200. SPL used to sell the Quiafe, but now they sell the Kaaz LSD (link).

[Stage5]

Yeah, If i went the route of R200 it would be a complete swap. Ill try to find the article but there is a way to build up the R200 to be just as strong. And i have found the Quiafe for $1500. But i have never fully understood diffs (I kinda know a little bit of everything, im trying to fill in the blanks....) So if i was to get the Quiafe could you use 4.10 leader gears??

[BigTDogg (MA)]

So if i was to get the Quiafe could you use 4.10 leader gears??

Yes.

The only way to beef up the R200 is to replace the half shafts ends going into the diff. That's what snaps, IIRC.

[evildky]

I didn't say that the R200 was a direct fit I said it could be adapted, as in cut and weld, sorry I guess my version of adapting parts is a little different than yours

and there are plenty of R200's seeing well north of 500 whp (mostly long snout) in heavy track use and they are dang near bulletproof, taking punnishment from VG's L6, 2JZ, Rb SBC, etc, there is a reason this diff is still being used in production cars more than 30 years after it's first

and the halfshafts are nto apart of the diff, they are a part of the shaft or in some cases are independant pieces, the Z32 unequal lenght halfshafts for use in the vsld version might be weak bit the Z31 cv shafts hold up great under abuse

[Stage5]

Hmm.... That gives me something to think about. I just ran the numbers and i like the speeds that rear end set up would give me. I wasnt sure how the Quiafe worked and whether you could change the ratio, Its good to know that you can. If my budget warrants it, and a set of the gears show up for sale then ill grab them. Back to the drawing board for a little R&R....

[BigTDogg (MA)]

I didn't say that the R200 was a direct fit I said it could be adapted, as in cut and weld, sorry I guess my version of adapting parts is a little different than yours

Point taken, lol. I don't mind fabbing, but if there's a plug and play solution, I'm all over it.

and there are plenty of R200's seeing well north of 500 whp (mostly long snout) in heavy track use and they are dang near bulletproof, taking punnishment from VG's L6, 2JZ, Rb SBC, etc, there is a reason this diff is still being used in production cars more than 30 years after it's first

Also good to know. Not that I expect to hit 500RWHP anytime soon, but in the future it might be nice

and the halfshafts are nto apart of the diff, they are a part of the shaft or in some cases are independant pieces, the Z32 unequal lenght halfshafts for use in the vsld version might be weak bit the Z31 cv shafts hold up great under abuse

Right, however the half-shaft splines are different for NA and TT. I hadn't thought or heard about swapping Z31 halfshafts, which might also be a good idea.

I wasnt sure how the Quiafe worked and whether you could change the ratio, Its good to know that you can.

The differential is it's own unit and adapts to the ring gear. If you use an OEM TT ring gear, your ratio is 3.69 to 1. If you use the leader gears (need both ring and drive, they come as a set), your ratio is now 4.10:1. I wouldn't go any higher than 4.10:1. The NA is 4.08:1, and at 70mph I hover around 3k RPM, IIRC. Maybe 3200 and 65 is 3K, not 100% sure. Any higher, like a 4.9:1 is crazy, IMO

[evildky]

The differential is it's own unit and adapts to the ring gear. If you use an OEM TT ring gear, your ratio is 3.69 to 1. If you use the leader gears (need both ring and PINION, they come as a set), your ratio is now 4.10:1. I wouldn't go any higher than 4.10:1. The NA is 4.08:1, and at 70mph I hover around 3k RPM, IIRC. Maybe 3200 and 65 is 3K, not 100% sure. Any higher, like a 4.9:1 is crazy, IMO

fixed

[BigTDogg (MA)]

If you use the leader gears (need both ring and PINION, they come as a set), your ratio is now 4.10:1.

fixed

Semantics, but yes, that is correct.

[evildky]

looks funny when spelled with all caps for some reason?

[Stage5]

Lol. It does. Ok, so im def going for the diff. I may swap the gears if i have the money when i stumble upon them.