Well i put on a dyno day for a local website over this last weekend...put something like 30 cars on the rollers....one of which was my 98 GS400

mods are pretty simple.
K&N drop in filter (stock airbox)
HKS axle back exhaust
Apex-i SAFC II (ashtray mounted)
and wideband tuned on the street by yours truly.

also some things of relevance
20x10.5 Maya DTV's with big 285/30's
stock tq converter
stock rear end
dyno was a dynojet 2wd

pulls were done in manual mode, 3rd gear, rolling into the throttle just after 3k.....full throttle by 3500 (only way to keep it in gear)

results were
239.2 whp
236.5 wtq



also you will see 2 runs on this chart....for my own curiosities...i did the first run with the ETC button in its middle setting (econo?) thats the red line....2nd run (blue line) was done with the trans in "pwr mode" as you can see there is a .5whp difference and a 2ft lbs of tq difference. its safe to say the electronic transmission controller (ETC) has no affect on horsepower (as people have mentioned in threads about the ETC)

just sayin'

lol


let me know what you guys think

 

...not bad but IMHO I think it should be higher. I have basically the same "power" mods as you except I have the S&S headers (well, and a K&N intake wheras you have the K&N drop in filter) and I pulled almost 282whp and 306wtq. I know your huge wheels/tires definitely lowered your power numbers but by more than 40whp?

My headers I feel attributed 15-18whp and my intake probably attributed +4whp over your drop-in setup...so roughly a total of 20whp more. 239whp + 20whp = ~260whp. I dyno'd my car on an AWD dynojet on stock 16" wheels. Still, can the difference of wheel sizes make up that 22whp (282whp -260whp) difference? That's almost 30hp (crank) lost!

Check out the maintenance on your car and make sure that all o2 sensors and MAF sensor is working properly and efficiently. Otherwise, you could be tuning your Apexi SAFC II over poorly operating sensors and not getting the results that you would have.

Thanks for sharing your info though...!

 

im confident in my numbers and the state of my car. TRUST me when i say the wheels made a 20-30whp difference. i was actually thinking it would make around 220 to the wheels (based on previous actual trap speeds vs actual weight) i was pleasently suprised with 240. ive dyno'd a looooot of cars over the years and big wheels and tires makes a ton of difference (not to mention the gear ratio difference) i watched a camaro put down 44whp more when he ditched his 20" craiger wheels (with 305 tires) for stock 16" wheels/tires. the power is there.

i on the other hand think 240whp is a dang good number. ill go back when i can find some stock wheels/tires to dyno on...just to prove a point...kinda like i did with the ETC thing lol

 

...not bashing at all. Just making sure that you have your car in tip-top condition before you tuned it and dyno'd it. Which you just indicated that everything is fine. I will also get my car dyno'd again soon...this time with my 19's. This new dyno shop that I am going to HAS dyno'd GS4's before unlike the dyno shop that I went for the first 2 times...I was the first GS4 that they ever dyno'd. I can't wait to try this new shop, maybe they can squeeze out more power.

The funny thing is my 16" wheels/tires are only maybe 4-5lbs less (at each corner)overall than my 19" setup. With 245/35's up front and 275/30's in the rear. I'm sure it will make a difference but in my case I don't think it would be 25+ whp...especially on a dyno where your only moving the rear wheels. So the weight difference in the fronts are a moot point...

 

still some good pulls. I'd still like to see how a lightweight 16 or 17 wheel does

 

your wheels must be really light. mine are pretty heavy. i weighed my rear wheels and they were 38lbs. tire rack says my tires weigh 31lbs. thats 69lbs of wheel/tire per corner. tire rack says the stock 225/55/16 tire is 26lbs i cant imagine the wheel weighing more than 25lbs. (stock rx8 17x8 wheel weighs 28, a friend of mine just weighed his) so about 50-55lbs for stock...20-25lbs of rotational weight will kill a bunch of hp. you may not see a 20-30whp gain if your wheel/tires are as light as you say....but i most deffinetely will with my setup.

there is also a 1 inch difference in tire heights, thus affecting my final drive ratio's and reducing my total tq output...and we all know hp is tq over time (5252) so looking at my chart, more tq will = more hp.

march 7th is the next dyno day....i might have to find some wheels/tires lol

 

...gotcha. Wow, those are heavy! My 19X9.5 rears are 29lbs...fronts are 27.5lbs. Still, not as light as I wanted them. Those Forgestars are like 24lbs for a 19X9.5!!! I was very close to getting a set last year but was really looking for a lip design...which I think they have now.

I think the 16" oem wheel/tire combo is around 54-55lbs...my 19" setup is 58lbs for the fronts and 60lbs for the rears.

 

there is a 11lb difference between my 20x9.5's with 245/30/20 and my 20x10.5's with 285/30/20 i forget the exact numbers (i have them written down at home, when i weighed them all with tires, but only the rears without tires) but i remember there was an 11lb difference between fronts and rears.

what kind of wheels do you have? still seems pretty lightweight considering your 19x9.5 wheel weighs 1lb more than a stock 17x8 rx8 wheel.

ive looked up wheel weights on 20's before, and mine were most deffinetely on the lighter side. (these are Altstadt type II's, 3 piece, just rebadged as maya)

 

wouldnt different dyno machines produce different numbers? not everything is created equal right?

at leats its good to know GS4's are ALMOST 1:1... rwhp:rwtq.

 

I have these...

http://superbuytires.com/Ace%20Forge...?finish=Chrome

They say chrome but the centers are a high satin powder coat and the barrels/lips are chrome I believe. 2 piece forged.

I remember when I was looking into the Vossen's (1pc wheels) and the same size wheels were 34 and 36lbs; front and rear respectively.

 

yes different dyno's most deffinetely put out different numbers. there is a lot of factors involved with dyno numbers. im pretty happy with the results so thats all i can ask for

some pics from the dyno courtesy of Josh Wolfe of JWolfeProductions.com

 

Cool to see your numbers.. thanks!
I want to get a baseline as soon as this weather gets into the 70's..

 

i feel really stupid......





hahaha!




after i looked at the pics for a minute....i noticed in one of them, my rear brakes are glowing red......when i put the car on the rollers and strapped it down (thats me in the pic strapping it down) i had the ebrake on so the car wouldnt roll on the drum..........


my dumbass forgot to take the ebrake off during the runs!!!!!11 omg i feel like an idiot! haha!

so my car makes 240whp with the ebrake on lololololololololol :facepalm: lol

 

Wow! I wonder how much your car will make without it. You should get it re dynoed!!

 

lol im going to

there is another dyno day march 7th...ill re-dyno then and talk to the owner about doing a wheel swap on the dyno....pending i find a set of stock wheels and tires lol