I remember pointing this out on the spacer plate thread some time back.
After talking to Doug Stewart at Crawfords He is telling me oil temp (hot) seamed to be much more important than water temp. I do know back in my drag racing days the pro stock boys were all running water temps of 210-220 because that is were there engines produced the best power. The Nascar guys all run there temp around 205-215. Doug did point out that after 8 dyno runs there was so much heat build up the numbers just started going down.
I still have not installed the Crawford plenum yet. Been to busy with work and I guess Im waiting for someone to do a dyno on that setup. Its always good to read your replys DaveB

 

Hi Scoobrybri,

I haven't been able to dyno a spacer on the 05 MT lower plenum yet so until then I suppose anything is possible. And I am very curious.

On a fluid dynamics level though its hard to imagine how flow (or HP) could be reduced. There are essentially two factors involved in optimizing flow through the intake manifold.
1) Pressure drop
and
2) Tuning frequency

Of these, the plenum spacer should only affect pressure drop. The goal is to minimize pressure drop as much as reasonably possible. The new 05 lower plenum is different from the 04 lower plenum in that the 1/4 wave tuning frequency was increased to resonate at a higher RPM.

On the pressure drop aspect the plenum spacer can only decrease pressure drop by increasing the total flow area available to the runner inlets. So this suggest what ever it is, a reduction in HP is not a result of increased flow area.

On the 1/4 wave tuning of the runners, the runner length and diameter is unchanged so it is difficult to see how the tuning frequency may have changed. If there was a change in tuning frequency it would most likely result in both a peak and dip in HP curve. (not an across the board drop) The peak and dip would also occur right next to eachother as a result of the misalignment. It would also tend to occur at the runner tuning frequency high up in the RPM.

When you noticed an across the board downward shift of HP my guess is it probably is related to engine coolant temperatures. I've done a lot of dynos and have seen first hand how powerful an effect engine coolant temperatures have. And its not the coolant temperature itself per say, its what the ECU does as a result of the measured engine coolant temp. There is a direct relation (a controlling coefficient) between the engine coolant temperature, as measured by the ECU, and how much spark timing advance the ECU will allow. And spark timing has a powerful effect on both HP and TQ.
If the engine is cool, the ECU will advance the timing to produce more HP. If the engine is hot the ECU will try to protect the engine by pulling back timing to reduce the possibility of detonation or ping.

So the ECU is constantly monitoring and adjusting parameters to maintain a balance between maximum performance and engine safety.

If there really is a decrease in HP, this is something I really want to see and understand. On a technical level it would be a real curiosity to see how HP could be decreased by increased flow area above the runner inlets.

Some have mentioned turbulence being a possible cause but I know this is not a factor. It all comes down to mass flow. Also, in my testing I was never able to detect the effect of oil temperature. I'm sure extremes of oil temperatures will make a difference but they will generally parallel engine coolant temperature if you allow 30 minutes cool down between each set of pulls. One day, I did a series of tests on various different mods and did a total of 21 dyno pulls. Same car, same day, same everything... Did a baseline at the beginning of the day and redid that same baseline at the end of the day and got the exact same results. (+/-2HP)
The important point was that the ECU was reset with each set of 3 pulls and the coolant temperature was maintained at 192 degrees F (+/-2'F). The pulls were also done on a dyna pack so that helped to eliminate the variable effect of hot tires on rollers. And the oil was relatively hot at the beginning and end of the test.

You will see on my webpage "techinfo" link a description of how I do comparative dynos. For the greatest possible accuracy, it really is best to control all the variables as much as possible. In your case, my guess is it's most likely not possible to see a decrease in performance as a result of a spacer. Its probably related to coolant temperature more than any other variable.

What would have been really good to see is you were able to remove the plenum spacer while it was still strapped down on the dyno, then immediately do a re-dyno at the same coolant temperatures. Weather the spacer is dynoed before or after baseline shouldn't make a difference if all the variables are truly controlled.

I will try to do this test myself if I can get my hands on an 05 MT.

Tony Colette

 

I wouldn't say that it has anything to do with fanboyism. It's more an issue of properly testing things so your results are valid. Bottom line, you can't draw a direct comparison with your dynos.

However, as Dave and Tony mentioned, there might be something else out there causing the results you're seeing that is specific to the '05s.

 

I agree with this. In a nutshell, an engine will be a peak effiency when the block and cylinder heads are at operating temp (normal operating temp coolant and oil temp) and the intake manifold and intake are cool. This is the very reason you see many gearheads at the track and dyno icing the intake manifold between runs. What effects the numbers of the VQ30/35/40 the most is heat soak of the intake components. Once these components become heat soaked, the power numbers start dropping. The VQ motors are relatively high compression motors with very touchy knock sensors. When everything becomes heatsoaked, the motor will start detonating (you can't really hear it) and the knock sensor instantly starts retarding timing and richening the A/F ratio. It wasn't uncommon for my Maxima to run .2 and 1.5mph slower with a baking engine vs letting it sit cool off slightly for 30-45 minutes between runs.

 

Maybe it's because the 05s are tuned so well that additional intake mods doesn't make that much of a difference. Other factors contributed to the apparent power loss. For example, it was easier to achieve better power gain in the G35 sedan vs the G35 coupe. The better tuned the vehicle, the less likely you would be able to gain more hp.

 

On both of the "before" and "after" runs, my car was driven to the dyno shop (about 12 miles) where it sat about 1.5 hour before dynoing. I then started the car, let it idle for about 1 minute and then drove it onto the dyno, which is about another minute or so. The car was then run twice. I did this to have the fluids warm but not hot when the car was dynoed.

I really did try to keep the variables controlled the best that I could.

As for the fanboy comment, I said this because if I had posted a big gain, no one would have ever thought to argue against the numbers.

 

I agree with you Scoobybri, everyone always say you have to get a before and after dyno to really know the difference....you do it, the numbers come out lower and now they cry something else..

The bad part of this story is that I just ordred the 1/2" spacers last thursday and expect them any day now. Saturday I went to the dyno, baseline run, and made 241rwhp and 223lb/ft torque and I will be going back soon to do a run with just the spacers installed. If I pull the same or lower #'s then I think its safe to say the spacers/plenum are a bad buy for the '05's

 

Remember the spacer and plenum are two different items.
Crawford fixed the problem with the front ports. The spacer has also helped in the early
Plenums. Doug at Crawfords told me I would be surprised with His new plenum.
Time will tell.

 

Chaz, I'm anxious to work with the runs and see how your stock 05 6MT compares with the stock 04 6MT. At peak hp you car appears to be a flippin' beast! I also wonder if Nissan realized what companies like Crawfordzcar were doing about 1+ years ago. They probably found the hp/tq numbers due to their products were real and found another way to get the same results (in the same areas) without incorporating their products, i.e. raised plenum or longer headers. My best guess is that they changed the lower manifold to result in similar gains (as far as hp) but they lost out on the tq and just wrote it off. Give me a week to go through the data and I'll see what we come up with.

BTW, Adam's plenum spacer really helped his sedan along. It's fair to say that the spacers make hp on the 2003 and 2004 models. You can be the CFL baseline on the 05's and hopefully you won't have to be one of the first to see how the motordyne return policy works.

 

I wouldn't try to return it, I would just try to get what I paid for it, heck I got in on the GB so someone will be saving money anyways.

 

I just wanted to highlight this so that DIZZ would see that pressure drop is what it's all about! Straight from "the man" himself... Mr. Motordyne.

 

I'm not trying to return mine either. Tony had not tested it on the 2005s yet and I knew I would be a guinea pig. I'm really curious to see your "after-spacer" numbers, Chaz. Your base dyno numbers are similar to mine. Post 'em when you get 'em! I'd love to take a day where I take the G in, run it sans spacer, cool down, install spacer, rerun dyno but that gets a little bit expensive, polly like $150 or so. We should see if we can get anyone to sponsor something like this. I'll do it again if someone sends me $150! Haha!

 

Todd, do you know what the cost is from Next Level Performance to do a dyno by myself?

 

It costs me $125 an hour to rent the dyno at the shop I go to so I figured about 1-1.5 hours for a dyno, cooldown, install, and redyno.

 

Scoobybri it sounds to me like you did a good honest review of your dyno and a took a reasonable approach to have all things equal in the tests. I suppose it's possible Tony is right about temp variables etc. but only more people testing can help determine the veracity of those suggestions.
For now it seems the spacer is not a positive move for the '05 cars. We'll have to see more results for everyone to be comfortable with that I suppose.