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NA build - but odd power/compression currently


RobPhoboS

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This is going to be a bit of a long post, apologies !

 


2004 350z - DE - 135k (burning a bit of oil but no streams of smoke! - full bottom end rebuild this coming winter - funds pending)

 

 

Dyno session 1

 

Over Christmas I did my timing chain (no issues before, just age/mileage) and I decided to do cams (JWT C8), springs, revup oil pump, water pump etc.
On the first dyno session, aside from these things done the car had stock headers, stock intake, straight pipes, cobra sports y-pipe back (2x 2.5" to 3", then 3" back).

 

Intake temp:10 deg (Feb)

310bhp (@fly)
(it's a comparison to my first dyno there back in Nov 2012)

 

48475901801_6f5934ff0f_h.jpg


 

WHP/AFR

 

48476047622_1ed35ea029_h.jpg

 


 

 

Dyno session 2

 

The next dyno session I had added the following by this point:
Kaaz 1.5 diff
Z1 'Race' intake with the large 6" velocity stack and filter
Kinetix Velocity
75mm TB

Note - the very first runs we did had the stock intake connected, we noticed it was down and thought it was odd. So I then installed the Z1 intake but the dyno was the same.
So my initial conclusion was that the Kinetix was causing the loss but clearly started to extend the power curve further to the right. hmmm
I had assumed (with a couple of other folks) that my car could breath in properly but not out, however it doesn't seem that was really the full issue.

 

Intake temp: 24 deg (May)

292bhp (@ fly)

 

48476097892_1c7f9a4fad_h.jpg


 

WHP/AFR

 

48475951961_460b821302_h.jpg

 

 

Dyno session 3

 

PPE long tube headers (JWT advised spec on these).
HP Ignition coilpacks (decided to refresh them as I had original ones on the car).
Fresh plugs.

Motordyne XYZ-pipe with resonator.

 

Intake temp: 25-27 deg (Aug)

300bhp (@fly)

 

48475776811_a015aad22b_h.jpg

 

Pink line is from May, so you can see the PPE's have gained at the lower end at least.

 

 

Knock detection disabled (was troubleshooting idea)

 

48475776936_1055892bb5_h.jpg


Once again comparison to Feb (WHP)

 

48475921677_cf8ffef0aa_h.jpg


Ok, so we made the low end come up nicer now, and the curve itself looks quite nice - however, the numbers aren't, in comparison to my initial run of the year.
Jez also disabled the knock sensor for a couple of runs too, just in case that was causing a problem, it made a few more hp but nothing obviously wrong there.

 

This seems like either the Kinetix is struggling for some reason (but hasn't on other cammed NA cars - it stretches the power curve to the right), or something else has gone wrong (timing?).


Engine parts as of August 2019:
Uprev tune
Kinetix Velocity plenum
JWT C8 Cams & springs
Z1 3" Race intake with 6" velocity stack/large filter
Ferra stem seals
PPE Longtube headers (spec advised by JWT)
RevUp oil pump
Motordyne resonated Y-pipe
3" back Cobra Sports resonated exhaust
New waterpump/timing chain/gallery gaskets/o-rings etc
Stock heads/bottom end (rebuilding in winter)
Stock injectors
HP Ignition coils

 

I did a dry comp test back in Nov, the results were around 185-195psi.

After doing the cams this year my compression was down to around 155psi.

 

JWT said that the pressure would be down perhaps by 15psi but not to this extent.

So maybe I didn't do the November testing correctly (I'm sure I did) but with this current one I know I did it properly for sure.

 

I decided to do a wet compression test, followed a day later by a leak down test, here are my results:

 

Wet Comp was about 7% more than dry (around 165psI).

Leak Down (I'd imagine anything over 8% isn't ideal but I knew the rings are worn):


48570986792_607f623e51_b.jpg
48570839646_772558a19f_b.jpg
48570986607_1174f8991d_b.jpg
48570985962_dbf64d7c4b_b.jpg
48570839911_729909c9bf_b.jpg
48570839206_46315bc204_b.jpg

 

 

So that confirms what I knew anyway, the rings are worn (no problem as bottom end stuff is waiting to go in).

I couldn't hear any obvious air leaking or bubbles in the coolant overflow.


Could that result just be a mix of the C8's/rings and the relatively low HP readings due to rings ?

 

I've messaged back and forth with a few of you on here (plus JWT and the US forum), and your input has been hugely appreciated !

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1 hour ago, davey_83 said:

Are you still using the stock fuel pump? If so fueling at top end may be at its limit. 

Yep still stock fuel pump and injectors (I do plan on changing injectors but wasn't sure about pump). 

 

I was initially thinking that the timing could have been out by 1 tooth as someone on the US forum had the same problem, and almost same parts. They had it on the ex cam chains (no sensor for exhaust unfortunately on DE). 

 

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11 hours ago, G1en@waxandshine said:

Did Jez say how much the intake temp effects power?

worth asking as 10deg to 25deg could be significant. 

 

Yep, he did say that the dyno figures that out, and you can go see the difference it calculates. As to how accurate it is, we're not totally sure. However, yes it's quite a difference in conditions! (more so for humidity iirc) 

 

 

10 hours ago, davey_83 said:

I'd say the cams are bleeding off the compression, so I'm surprised to see the C8's noted as suitable for stock bottom end. Seems higher comp pistons are need to pull back what's been lost. 

 

I guess technically the C8's fit and work but like all aftermarket cams, not optimally out of the box. 

I didn't expect the difference to be quite like this, granted the rings clearly aren't helping eh. 

 

Thank you for taking a look :thumbs:

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I had Tomei Poncams fitted to my Almera GTi SR20DE and these were a plug and play application, with gains throughout the rev range so it is possible to do. For a more track focused application, sacrificing low end for middle and top seems a given. 

 

Re the timing, I don't think you'd be making the power you are being a tooth out. However if you've read similar issue over the pond, it might be work a check.

 

I doubt you'd gain any more knowledge from here than what Jez would have told you at the time sadly. However I'd personally look towards fueling as no doubt the fuel pump and injectors will be working very hard to keep up. 

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your reduced compression is definitely going to loose you quite a bit of power.

If the injectors or pump were an issue I would expect the graph to fall off a cliff when maxed out or show a different Air fuel ratio but all looks normal.

add some 11:1 comp pistons and it should pick up well at the top end.

Very good thread though, nice to see the different effects that each engine change brings.

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