P90A Head to Solid lifter

[Ben's Z]

I am taking my hydraulic motor to a friend for rebuild. My hydraulic cam has some lobe pitting. If that came is shot, I think I will convert to a solid lifter set up, using the Time Sert deal. However seeing as I only want 250-270 horse at the wheels for now (and thus going to use the factory T3 turbo), would buying a performance N/A cam be a waste? I plan on using all mechanical methods for my horsepower goals, no ECU change. Using the factory T3 and hydraulic cam if it turns out to be ok will probably be fine I am guessing. Putting on a cam good for 6500-7000 would be pointless with the T3 turbo correct? If I do need a new cam, would would you recommend? A performance hydraulic cam or a solid cam for potential future power increases? How about the cam specs or a part number for either?

Edited March 1, 2012 by Ben's Z

[78zstyle]

With your HP goals, a stock cam would be best.

[Gollum]

If you're not changing the EFI, do NOT change the cam profile, period. The more you move from the factory profile the more you'll be un-optimizing timing and fuel somewhere on the map.

[Ben's Z]

Ok, so if this cam is shot because the lobes are too corroded, should I still switch to a solid lifter cam of stock specs. Like one off of a standard solid cam P90 head?

[HowlerMonkey]

The P79 "a" cam might be interesting in a p90 head.

[Ben's Z]

With a stock ecu?

 

The P79 "a" cam might be interesting in a p90 head.

[Gollum]

The P79 A cam is definitely a sweet cam for a street driven turbo motor, but you have to remember, it has almost 10 degrees more duration, about a quarter tenth of an inch more lift (with might not sound like much, but consider how that affects time at low lift when combined with the duration), and the BIG difference imo, it has 8 degrees more overlap compared to the P90A M cam.

 

It would run fine, but you just have to be willing to deal with the fact it won't be as good of a tune as the stock cam, and that tune isn't spectacular to begin with. You'll have to adjust either the AFM or fuel pressure because the fuel curve requirements will change, and that will leave the rest of the curve you can't optimize for as much percentage off as the difference between cam. So if the A cam makes 2% more/less volumetric efficiency at a given rpm, say 2,000 then your tune will be roughly that 2% off + variances in the stock tune. The stock tune will tend to be a bit on the safe side, so as long as the A cam doesn't make TOO much extra power anywhere below peak then you should be okay.

 

The real issue arises though when you start raising boost. Say stock for stock the new A cam makes 4% less power at 1,500, which might be possible considering the differences. This might be acceptable at stock levels, as the only difference is that you'll be quite a bit rich when you punch the gas when cruising down the city streets in 4th gear (trust me, I used to use 4th gear for almost all my driving, I found myself that low quite often without ever having issues getting up to speed). But now let's factor in extra boost. Say you're running 14psi (about what you'll need to reach the 250+whp mark). Let's assume you tuned for the extra boost with a rising rate fuel pressure regulator, and let's assume you bought what 90% of people buy, which is the fixed rate type which are either a static 1:1 or 2:1 (meaning for every pound of PSI they add 1 or 2 PSI of fuel, respectively). Odds are that's NOT enough extra fuel for the extra boost, so you'll end up turning up the RRFPR to "work best for full power" which leads you to let's assume a static fuel pressure of 55lbs.

 

Now when you're at 1500-2000rpm in 4th gear and you give it a little bit of juice you end up with BLACK SMOKE and fouled plugs.... No fun. It might just be a 3-5% difference in the state of mixture, but that can make just enough of a difference when you have zero control over the ECU map...

 

Keeping the cam and head as close as stock as possible, will give you a better chance at getting the thing to run nicely at the power levels you're looking for. Remember, most that get to 300whp end up with aftermarket ECU systems for a reason. It's not that the stock ECU can't do it at all! In fact I encourage you on your endeavor. I like seeing people make the stock system work. I can just take some serious trial and error. Learn from the example I just shared, and get a RRFPR with an adjustable ratio (usually comes with disks you insert inside under the spring). And for what it's worth, I've seen ratios like 5-8:1 extra fuel per psi of boost be much closer to accurate in practical use. The lower ratio ones that are common seem to be more geared towards people that are only raising boost a few psi and need the extra safety net, and are usually installed on cars that are still mapping to where the boost is at.

 

And on that note, the ECU takes an average of information cells, not just stuck right in it. It averages out from adjacent cells in the direction it came from and logically heading to, in order to give you a smooth fuel curve, not a jagged one. In an ECU like the turbo MR2, the stock map goes up a good 4 PSI higher than the stock regulator goes. This has the benefit of preventing failure in an over boost situation, but also helps the ECU average out the fuel when you're bouncing in and around peak PSI, because it's rarely a perfectly flat line of PSI information that the ECU is reading.

 

My theory personally is that the stock tune on the L28ET is just fine to 10psi as long as everything is in good working order, but you probably won't want to live there for very long without an intercooler because the stock ECU doesn't compensate for hot intake temps very well.

[HowlerMonkey]

"A" cam will have zero negative effect on the stock ecu because the stock ecu is unbelievably non-exact.

[Ben's Z]

What about if I later upgrade to the 300zx ecu? What about it working with the stock T3?

 

"A" cam will have zero negative effect on the stock ecu because the stock ecu is unbelievably non-exact.

[Gollum]

"A" cam will have zero negative effect on the stock ecu because the stock ecu is unbelievably non-exact.

 

Yes and no. The stock ECU is DEFINTELY "non-exact" but that doesn't mean it's "not consistent". From what I've seen the ECU tends to be a bit overly cautious, but I don't have enough seat time at the dyno to tell exactly how closely it mirrors the profile of the stock cam. Obviously the more modern the ECU the tighter it tends to be, and straying as far as an aftermarket intake on most OBD-II+ cars will require a retune to reoptimize the curves.

 

I just don't like giving out suggestions to members that could, in the end, be more headache than it's worth.

 

What about if I later upgrade to the 300zx ecu? What about it working with the stock T3?

 

Be warned of overthinking your goals. The Z31 ECU upgrade is a great idea, but it opens up a whole different realm of modifications you're performing. Now you need to find an ECU and do wire splicing, install the corresponding MAF, convery the dizzy with the right CAS sensor from said Z31, etc. For the time, cost, and energy you're not too far from being able to do a super cheap MS conversion, unless you can find a scorching deal from someone parting out their turbo Z31.

 

That said it'd work with the stock T3 just fine. The ECU doesn't really care about the specs of the turbo, just how much air it's putting into the engine, and at what temp. You can usually get an OEM ecu to handle a much larger turbo with very little adjustment, while changing things like head flow will require immediate attention to the tune.

[HowlerMonkey]

I'm speaking from experience even though it was 24 years ago at the Z shop of miami.

[Ben's Z]

Ok found out my hydraulic P90A cam is shot. Should I go to a used or new cam, or should I just switch to adjustable lifters or stock with the hydraulic set up??? I think the consensus for my power goal of 250-270 at the wheels deems the stock profile proficient. Chime in.

Edited March 23, 2012 by Ben's Z