2007 350Z VQ35HR 6MT

so april 10, 2011 - temperature in seattle was about 55 degrees. not sure on elevation but:

mods: Stillen intakes, headers, HFCs, Nismo S-Tune Exhaust.

i don't recall the baseline - after tuning i put down 294.7 whp and 254 wtq.

a few months later i raced my buddy's 2010 G37S sedan

his mods: Injen CAI, Invidia Exhaust, Osiris Tune, and 4.08 final drive gears

he pulled on my every single time in 4th gear... easily on 3 runs.

fast forward to sometime this year... i installed a Stillen Cat back exhaust (true dual), installed HPS intake tubes.

raced my same friend who didn't make any additional mods and this time around i beat him on 3 different runs on 4th gear (started pulling away).

so today - i went for a retune/redyno.

today's temperature was about 18 degrees hotter than my last time tuning. and i ended up LOSING 18 whp and 10 lbs of tq.

273 whp 245 wtq

thoughts of why the power loss but the ability to beat my friend this time around?


i'm thinking of the few factors:

- Heat Soak from HPS tubes
- 18 degrees hotter temperature
- no more back pressure from S-Tune exhaust (too much flow)
- possible recalibration of dyno?

i ran on the same dyno - tuned and tested by the same guy.

i'm stumped on the loss.

 

Well I will tell you one thing, it's not from "too much flow" through the S-Tune...

Header design has WAY more to do with exhaust velocity/scavenging than your catback does. Sure, catback diameter can affect things, but when you're talking such similar diameters, it's going to make a small difference, and definitely NOT 18whp.

 

yea - i figured that much. i can see a 5 - maybe even 10 whp fluctuation in either direction but an 18 whp drop is substantial... even the tuner was confused.

 

same day (today) on the same dyno....

2006 350Z base model 6MT (my girlfriend's Z)

MODS: K&N drop in filter, Kinetix test pipes, XO2 Exhaust w/ Magnaflow X-pipe, no tune

put down 265.8 whp

meanwhile

2006 Infiniti G35 touring 6MT (friend's G)

MODS: JWT pop charger, ART test pipes, Motordyne Exhaust, MRev2 w/ 5/16th spacer, AND osiris tune

put down 268 whp.

so either
- all these mods these companies are lying about dyno numbers
- dyno machines are all way to different to really compare
- people are lying about posted numbers
- my girlfriend's Z is just a factory freak

 

so she only gained 3whp with a tune? maybe your tuner blows.

jk, i have no idea though

 

peak numbers don't tell the entire story

 

nope. she didn't tune. she just ran dyno numbers. point being. only test pipes and exhaust netted (basically) same numbers as full bolt ons and a tune.

 

Looking at the "big picture" of this topic,the real issue is not the the whp gained(real
or perceived),its the whp realized from the cost of these bolt on mods?
You have to think,is it a good return on the investment?
Looking at these numbers,they the results DO seem a bit strange.There are tuners and,there are TUNERS.Just because some guy invests in a dyno,does the tweaking of
your car,does not mean he/she knows what they are doing.I have similar mods on my Z.
The results from a tune(by one of the best)were a 15whp increase from baseline.
I added various mods over a period of a year or so.Never took my car in for a tune.
The results were excellent.Furthermore,from what I've experienced,the are many guys adding exhaust,headers,spacers etc and doing nothing to get the car tuned toget their bang for the buck.Bottomline,take your car to a tuner that has a proven reputation
on tuning a Z.

 

Lawerence Ojas is the owner of Intec Racing and is the tuner for most cars in our greater seattle areas. He has one of the best reputations for Nissan/Infiniti tuning in the state of Washington. As well as a proven track record of tuning and builds of one of the finest drift cars on the D1 grand prix.

So to answer your question - tuner/reputation isn't a concern to me.

best bang for my buck for return? i bought the stillen exhaust used for $300 and the HPS tubes for $120. so essentially i paid $420 for a 20 whp loss... so definitely no on return but the prices weren't terrible!

however i can't speak for the Rev-Ups G35 that dropped well over $3000 on mods to have 3 more whp over my girlfriend's Z which i spent $300 on. used XO2 exhaust ($80), magnaflow x-pipe ($180), kinetix test pipe (free - traded for stock cats), k&n drop in filter ($40)

i plan on going back to stock intake tubes and redyno to see if heat soak is the issue. then replace my exhaust with one with more back pressure and test again - pretty much going to spend the next month attempting to isolate each mod and seeing what gains and what loses.

as for my girl's car - i will also add parts and redyno then remove and test on her's as well to document each gain/loss.

i'll keep y'all posted!

 

Tires and tire pressure will make a huge difference on a dyno. So does wheel weight and width.

 

lol.. i shoud read posts before i make my own.. my bad lol.
it was a whiskey night.

 

i thought tire pressure will affect grip not whp and tire size and weight affects rotational mass in acceleration/deceleration (again) not whp.

either or

the Z had the 18" stock 35th anniversary wheels (roughly 25 lbs) running at 38 psi

while the G had stock 19" factory forged rays (roughly 21 lbs) running at 35 psi.


i know DE motors (and HR motors) all have a cap of power when going N/A bolt ons. but i'm still baffled by the minimal gains with full bolt ons.

my only educated guess is that with full breather mods - not enough back pressure on a N/A motor results in power loss. i'll be contacting motordyne as well to see what they think

 

Motordyne did a dyno test with different rims (weight) and going from stock 17's to enkei 17's they gained 6.2whp. I think the weight difference was over 5 Lbs after tires were accounted for.

 

Rolling resistance on the dyno rollers is what tire compound and PSI change. Dyno queers run really high psi with the hardest compound tires to get max HP

Next temp will also kill HP. Let's just use JWT pop charger as an example. Hood closed , car not moving because it's on a dyno will pull about 170 degree air and will dyno less power than having the hood open and a fan blowing on it ( simulating a car that is in motion where the JWT will pull air about 8 degree warmer than outside temp)

Btw , bolt ons without tune do make power. My car put down 239 HP stock and 255 HP with bolt ons and no tune.

 

You should educate yourself a bit more. Backpressure is always the enemy, no matter NA or FI engine .

 

tcode:

upon reading - perhaps back pressure is the wrong term.

http://www.mustangevolution.com/forum/f312/t296628/

in reading this... best explanation is combination of breather mods. one explanation showed it as exhaust being like water flowing thru a hose. a straight thru design will just have water flowing out slowly. contrary to holding ur thumb over the mouth of the hose - thus water flowing out faster.
thus - exhaust not necessarily needing a straight thru design but needs to push out "exhaust faster"

despite my driving Zs for the past 3 years - this past year was the first time i've gone into performance mods and driver mods so its still a learning process for me! i understand basics but have a lot more to learn.


terrasmak:

yea - i understand heat soak. and i know it affects - just didn't think it affects THAT much. still tryin hard documentation of heat effects on power. of course i could be way off and wrong. that was one factor i forgot - last year we had a fan blowing to the front end of my car - this year there was no fan AND it was hotter.

i had another friend of mine with a polished engine and he had major heat soak issues. ended up losing 15 - 20 whp as well. as he was posting 269 whp on a cold run and dropped down to 255 on a hot run.


sdgenuis:

i know peak numbers don't tell the whole story - i figured if i lost power in top end perhaps my power band/curves would gain in the low or more consistent power over all - but my curve dropped consistently overall. i left the dyno sheet at the shop but will be back soon to retest and get my sheet up soon!