Before I installed any mods on my 2005 6MT coupe, I dynoed it to get a baseline of HP and torque. I don't trust "butt dyno." Riding with my windows down and hearing my car at WOT gives me enough butt-dyno that I know not to trust myself. So according to the Dynojet a month ago, my stock coupe had a peak HP of 245.63 and a peak torque of 221.49 ft./lbs. These numbers were SAE corrected for humidity, temp, and elevation. (as they should be.)

This past weekend, I installed a Z-tube, Amsoil air filter, and a 3/8 Motordyne plenum spacer. I took my car into the same shop and ran it on the same dyno. Peak HP = 247.06 and peak torque = 219.74. That's a peak gain of about 1.5 HP and a loss of about 1.75 ft./lbs. of torque.

But what you don't see is that the graphs (which I will post when I get access to a scanner) show a 1-5 HP loss across all of the RPM range until you hit about 6200 RPMs which is where you get a tiny blip of 1.5 HP gain for about 100 RPMs. On the torque side of things, you see a 0-5 ft/lbs loss of torque until you hit about 5800 RPMs where you gain 0-1 until fuel cutoff.

I'm not knocking Tony's product. It looks like it works great for the 03-04s. I'm just reporting what has been measured on my 2005 6MT. The only thing that I can think of is that the new design of the lower plenum and the variable exhaust valve timing do not like the increased air flow or that the new plenum design is causing the spacer to change the air flow in the intake so much that it actually interferes with the over-all flow. I don't know. I'm not an engineer and am mearly speculating.

 

BTW, I did do an ECU reset following the install because I was getting a slight pinging after take off. Once reset, the ping went away. The dyno was done after about 200 miles of driving over 4 days. The first dyno was done under very similar circumstances.

 

Not what I would call a good comparison. Need to do everything on the same day. Run your baseline, then compare each mod individually, followed by the impact of the mods together.

 

Granted that it's not exactly a scientific comparison, but the Z tube alone should have shown higher gains. Has anyone had better or similar results with an '05?

 

I would have done that if I owned my own dyno or had unlimited funds to rent out a shop for hours at a time, but alas I do not. I thought that the SAE corrections in the Dyno would compensate for any changes to the environment. Considering the only difference was 5 degrees F warmer in temp (the humidity was the same, barometer was within .1 of both days, and the elevation does NOT change), the dyno changed the SAE correction factor from a 1.06 to a 1.07 factor. The dyno DID compensate for the the temp obviously. Let's say I should be expecting a conservative 5 HP gain from the spacer, 2 from the Z tube, and 1 from the high flow air filter. That's a total of 8 RWHP gain. According to the dyno, I lost an average of about 3RWHP since the changes. So what you are saying is that I can expect an 11RWHP loss from a variance of 5 degrees in temp? Throw out the fact that the dyno increased the correction factor and the difference would be in the ballpark of 15HP. I don't think so. Yes, I agree that you can expect some changes from day to day on the same dyno, but I have kept the variables controlled enough that the results are valid...at least to me.

It seems to me if someone throws out a positive butt-dyno review of popular mod, everybody is like "Awesome, great, I'm buying one." But if someone puts out a negative review of a popular mod, one even based on real, measured results, everyone suddenly discounts the dyno, track, etc. Isn't there the possibility that the spacer might not help out the '05 considering that they changed the design of the plenum to help the engine breathe better? The extra 18HP from the 04s to the 05s came from some kind of design change.

It's also common knowledge that the combination of certain mods can result in loss of power by removing too much back pressure, etc. This could be the case here. New plenum design (for better air flow) + spacer (for better airflow) = bad airflow? Maybe. Since I'm the only one I know of who has an 05 with the spacer AND "before and after" dyno numbers, I'm going with my results. Spacer is coming out.

 

Do you know what the coolant temps were the start and end of each dyno pull?

The power robbing effects of 200F+ vs. 190F coolant is amazing. The latest example witnessed was a 2005 Enthusiast 350Z -- 235HP vs. 250HP. Same car, same dyno, same day. A similar loss happened to an 03 AT Sedan I know of. Stillen documented 4degrees = 4HP on a 350Z dyno pull. Check out the link. http://stillen.com/news_select.asp?id=60

The AIT Sensor also affects timing, but it's normally not a factor with open hood dyno runs.

 

I'm going to run it at the track next Thursday and see what happens. But considering the temps have risen in the past month, I'm sure the times will prolly be slower.

 

wanna sell your spacers? let me know

 

Interesting. My buttdyno told me different, but hard numbers are hard numbers...

 

I do appreciate you sharing your results, but at the same time, you need to be spot on in your testing. I question the accuracy of dynos when they try to normalize the results between different days... so the concept of hard numbers is a bit soft.

As mentioned though, need to monitor oil and coolant temps too, that can cause the results you're seeing. If you're running a CAI, that could be the culprit.

 

I would say that even if you take into account any negative dyno variances, any gain with the plenum spacer on a 2005 is marginal. The scary thing is what if the dyno was actually reporting yesterday's results HIGHER than they should be? Ouch!

 

if the coolant temp was not controlled, as well things like heat soak considered, trhe numbers aren't 'hard' numbers.

As Dave pointed out - a 10 degree coolant difference is huge to reported HP.
Something as simple as your car being slightly cooler when you did your baseline could destroy you comparison.

 

Like I said, if the variance between dyno runs can nullify the gains shown by the mod, then the mod is not giving much, if any, gains.

It's funny. When I posted that I was dynoing my car stock before any mods, everybody was like "That's great. That's what you need to do before you start modding." So I do it, mod my car, find out that the popular spacer mod did not do much, if not rob power, and no one wants to believe the results. If the results had shown a power GAIN of 10 HP, noone would even think to debate the results.

The VQ engine is tuned very well, even better on the 2005s. There's not much you are going to get by simple bolt on mods. Maybe 20 HP at the most from spacer, cats, cat-back, etc. The only way to get significant gains is to go FI. I'm not even going to waste any money on this stuff anymore. Just save up for a SC.

 

You guys blow this whole temp thing way out of proportion. I've never been around a group that is so focused about this. If the correction factors are basically the same, the engine is at normal operating temp as it was in the prior test, and this was the same dyno machine, his data is legit. I find the Stillen link rather humerous also. They have a 315whp 350Z and they're acting like a 4whp difference between runs is some huge deal. That's mearly 1% of the engine's power and that's well within the differences of making back to back passes on the dyno. I've even seen swings of 5whp with my old Maxima WITH cool downs and this holds true for any other car I've had or seen dynoed. Turbo cars can be really flaky and see swings up to 15whp. In the real world, you're not going to see an engine making the same power, run to run, even if the operating temp is exactly same. An engine is not a precision instrument.

scoobybri-

Concerning backpressure, the word you're looking for is velocity. Add too large of an intake and/or exhaust and you can hamper intake/exhaust velocity by creating volumetic turbulence in the chamber because there is too much space. Add too small of an intake/exhaust and you create a bottleneck (ie backpressure). The goal is to maintain maximum velocity. Backpressure does not create torque or "lowend power". That's a myth that just doesn't seem to die.

I think you're on to something though. The 298hp VQ's intake manifold is designed for highend power hence the reason these cars make more power above 6000rpms. It's also the reason they have less power in the low to midrange. Adding the spacer could have possibly created turbulence in the intake manifold, hampering additional power gains. In the lower rpms, this may be actually hurting power (like you saw) until the intake velocity is equalized and the turbulence is gone.

 

Finally, a voice of reason. Thanks for chiming in. I was feeling the heat from the spacer fanboys.

As for the term back-pressure, I was referring to exhaust mods. What I meant was the pressure created by the constriction of the exhaust from the cats,etc. Without a certain amount of pressure, some engines actually lose power (which I'm sure you know). If that's the wrong term for this phenomenon, I stand corrected.