My Gs400 Is Slow! Why?

[BlexusGS]

I have a 2000 GS400 with 79,000 mi. It has a K & N intake (modified downward by the wheelwell) and a Borla Exhaust. I realize that the 19" wheels and the 75lbs. subwoofer setup in the trunk has an effect on the performance but the car does NOT feel like a 300+ HP car! I got a throttle body cleaning from the dealer as well as a transmission flush, however it still has original spark plugs.

When I modified the K & N intake as a "cold air" setup by the wheelwell - the first time I took it for a ride (right after I cleaned the filter again) it seemed a little slower off the line but it boosted so hard at around 3000 RPM that it was unbelievable; it felt like the car had a little turbo very fast and happy with results. I don't know why or how I lost this performance feeling? Now it's slow off the line and when I mash the gas to the passing gear it just feels like it picks up a little NOT like how it used to. I want to do a PI torque converter but before I do that I have to find out what is wrong with my car; it's not right. The car does NOT have a rough idle or anything like that, it seems to be riding fine, just SLOW! :( :( . BTW my car idles at 400 RPM while in drive w/ the brake on.

Please someone help me, shed some light on this subject. Any suggestions or advise would be extremely helpful.

Nick

[Shoemaker]

you might be losing compression do to a seal leak ... also like you said ... try changing sparks ... it might help ... you should start thinking about your timing belt soon ...

Shoe

[BlexusGS]

Shoe,

Thanks for the reply, I do plan on changing the spark plugs soon; any recommendations. Aslo, I had my timing belt serviced about 5 mos. ago.

One other thing I forgot to mention in my initial post, when I hit the gas (WOT) I hear a kind of "tin" noise at higher RPM's almost like air but I don't think it is. It is too loud and too noticeable to be my intake sucking in the air. The sound of the engine noise at high RPM's I would think would drown out the sucking sound of the intake. What could this be - something having to do with a seal or valve leak like you suggested??? Thanks.

Nick

[dbgs400]

I might like to add that part of your problem is your 19" wheels. I too have a gs400 a 98 with the K&N and a few other mods but when I went from the stock 17"s to 18"s I noticed a big difference in off line accel and braking, it's because of the larger diameter of the wheels and the added unsprung weight, try putting your stockers back on the rear and see how much of a difference it makes as the smaller diameter will lower the final drive ratio a bit. I know on my car quite a bit of the snap came back with the smaller t/w combo..Give it a try it's cheap..

[BlexusGS]

I appreciate the reply but the overall diameter is the same as my stock 16" wheels. The only difference is that I have morre wheel and less tire. The weight difference is only about 4lbs. more at each corner. This is why I'm not too sure about your particular theory. Thanks for the suggestion though.

Nick

[SKperformance]

LMAO

4 pounds ???????

Who told you your upgrade in wheel size is only 4 pounds more?

My 20 inch tires weigh 28 and 29 lbs each. The stock ones are much less, closer to 30 lbs rim/tire total.

[BlexusGS]

I'm almost positive I weighed my stock wheel w/tire and then the new wheel w/tire and there wasn't a tremendous difference. Check this out, I just looked around on the internet and found that...

Weight of my 225/55/16 Pirelli PZero tires are 26Lbs. each(Edgeracing.com)

Weight of 1999 LS400 stock 16" wheels are 25 Lbs. each (Lextreme)

These have to be similar to my 2000 GS400 stock 16" wheels.

Weight of my new 245/35/19 Toyo Proxes P4 tires are 23.8Lbs. each (Edgeracing.com)

Weight of my new 19" Ace Trend (NOT CHROME) are ???

Now... the stock setup is running at 51Lbs. each corner. If you subtract the weight of my Toyo's you will have about 27Lbs. left over for my new 19" wheels. Add on 4 more Lbs. like I thought... now your at 31Lbs. Your telling me that my super light racing alloys are a lot heavier than 31Lbs. NO WAY! Go to Edgeracing.com and look at all the styles... you will find TONS of 19" wheels around the 26 - 30Lbs. range. I love that website because it posts weights of wheels and tires - very helpful. Thanks,

Nick

[BlexusGS]

Back to the drawing board! :-)

[JDM Aristo]

LMAO

4 pounds ???????

Who told you your upgrade in wheel size is only 4 pounds more?

My 20 inch tires weigh 28 and 29 lbs each. The stock ones are much less, closer to 30 lbs rim/tire total.

Hey, even if its true that ur new wheels only weigh 4 more pounds, the physics behind it is quite simple... torque, and acceleration are related by the amount of rotating mass....wider wheels wider mass....lower acceleration.... haha guess payin attention in hs and college does pay off :-)

[stroked4.6]

Beyond the rim factor which will make the car seem slower the K&N might be the problem. Yes it felt good at first but the oil on the filter can sometimes go into the intake tube due to the induction. I would remove the MAF and clean that. I bet your MAF has some of that K&N oil on it and is messing up with the reading therefore *BLEEP*ting on your performance. And yes I would change your plugs. Im not sure what yours are rated at but I always try and change the plugs on my cars at around 60K miles. Im changing the plugs on mine this weekend with NGK plugs.

[92Lex]

Put the stock filter back on and see if it makes your car feel any faster. But really, maybe it feels slower cuz it's not boosted yet.... :whistles:

[BlexusGS]

JDM...I agree with your rotating mass example but my rim might be wider than the stock rim BUT if you put my new wheels w/tires next to my stock wheels with tires it's only 1/2" difference in width. The stock rim width is 1.5" smaller (7.0" vs. 8.5") but the stock tires kind of "balloon" around the rim whereas my aftermarket tires are flush almost inward as compared to its rim. I don't think 1/2" more patch contact will make my car feel that much slower. Oh...BTW my car was running lean for almost 1 year!!!! There was always a CEL appearing then re-appearing. I thought it was because of my intake when it actually was a faulty o2 sensor all along. Now fixed, the car runs MUCH better!

[deejay35]

did you do the ecu to go with the intake?

[Jwagonmd]

I had 19's on my car and it was moving really slow, went back down to 17's and I feel a big difference in performance.....depends what you want. Show or go........

[BlexusGS]

BOTH! AND I WILL HAVE IT... eventually. Need more $$$ though. LOL! I am having the S-AFC installed and tuned by a dyno shop. Then we'll see if that helps.

[Jwagonmd]

Good luck, its going to be tough. Thats why its always go have mutiple cars....

[Steele006]

Yo Nick...changing your plugs would not do any justice...those Iridium plugs are good for 120k miles.

I also noticed you put a Supra LSD with 3.76 gears in it. Was this before or after you had acceleration problems? With those low gears, LSD or not, you should be burning the tires through 1st and 2nd gear!!! My stock GS400 can do that depending on pavement, but it's a 1 wheel wonder :(

ECU upgrade is probably whats holding your car back at this point, because the computer doesn't do a very good job at re-mapping once mods have been done....you're getting WAY more air but the factory mapping is starving it for fuel.

Give us an update on how things are coming along.

Steele

[dssnosher]

little off topic question that was mentioned in this thread: timing belt. Which models have timing belts and which ones have chains?

[BlexusGS]

Steele...I have a brand new Supra (torsen) 3.76 LSD, PI TC and B & M tranny cooler all just sitting in my garage waiting to be installed. My acceleration still sucks but it's weird, when I re-set the ECU AND clean (re-charge) my K & N filter the car is very much faster but only for a few hours??? It literally feels like I did nothing a day later. Could I have a faulty MAF? There aren't any codes (CELs) thrown on the dash but all I hear is people with GS4XX's that can spin a little from a stand still. I have 19" wheels on in the summer and I use the OEM 16" 5-stars for the winter; I can't even spin those (unless I break torque)!!! One other thing I DO have a custom box w/2 12" subs that must weight around 80lbs. could that be my ONLY problem? I'd like to get my car straight before I install these "goodies."

Thanks,

-Nick

[Steele006]

Hey Nick,

I have stock 17's and with 4 people in the car I have spun out from a light trying to accelerate. The sub-box isn't going to make THAT much of a difference, but take it out and see what happens.

The ECU upgrade I am talking about though is one you can get from SRT. I don't know if they sell just the piggy-back ECU by itself or only with the Intake upgrade. Apparently, from the research I have done, without the piggy-back ECU an intake upgrade is like throwing money out the window.

Give SRT a call and see what they can do for you.

SRT - Swift Racing Technologies

[BlexusGS]

Thanks for your responses. I am actually looking to buy an Apexi SAFC II very soon. It will so the same as the SRT piggyback and then some. There is a guy on Club Lexus that has only an intake and exhaust who gained around 25 hp and 48 Ft/lbs of torque all at the wheels!!! I am looking forward to doing this but I will pay extra $$$ and have a dyno shop install and tune it for maximum performance. First and foremost is my transmission mods...I'll keep you posted. ^_^