kotik

So trying getting top speed again.

Currently have APX two piece rotors, killer bee intake with bee hive and stock size tires. Last time i could only do 192mph, but i didnt have an intake and had oversized tires (295front and 345back), outside temp was around 75.

So today i tried again, temps are 55f, same road, but in the evening. Elevation is 850feet(is that too high?). I was only able to squeeze 195mph, last few mph i was really crawling. Alignment is good, car doesnt have any issues that im aware of. Why cant i get to advertised 198mph?? With my mods i should touch 200...

Speed is based of my kenwood navigation, at 150mph it is exactly on the spot with the heads up display(maaaybe about 1mph off hud), the dash speedo shows about 2-3mph more at 150mph.... Is the advertised speed based on the dash speedo reading(at a glance looked like 200mph).

P.s. I contacted michellin (i have pss), provided them cars axel weight to get the correct tire pressure for high speed runs. They advised 41psi front and 37psi rear for 320km/h run, and for speeds up to 260km/h its 39/35.

teking

I assume those are hot tire pressures?

erichg1000

well I've read you can lose up to 3% of power for every 1000 feet of altitude. So that could be a factor. The unsprung weight reduction should help in acceleration and handling but i don't personally think it will help all that much in top speed as you are overcoming aero drag more than weight at that point although it's still a factor.

At that speed heat soak isn't a factor so I don't think the beehive will help much either. I would say it's altitude/air density and or headwinds

Aero drag increases exponentially to speed so it takes a ton more power to increase top speed.

FNBADAZ06

What are your ECT's when you try this ? I don't have the tuning table in front of me, but memory tells me 205+ ECT starts pulling timing to defeat any KR....hence, you won't have your full rated 505 SAE HP at 6350 RPM. To really know the answer to your top speed quest question(s), you'll need to see what the ECU see's at the time of your top speed runs. It could be anything from high ECT's, catalytic converter overtemp protection (dumps fuel, making you run overly rich), knock retard at full load at terminal speed, etc.

PRE-Z06

I agree with the above, I'd log it to see if you haven't tuned it for CAI and as asked above was there a headwind? Cooler weather should help counter the higher altitude and though it's denser meaning more drag, the gain in power will more than offset it.

kotik

Thanks for all responses. What is ect? How do i measure it? It wasnt a windy day. Car is not tuned for the intake(its advertised that tuning isnt necessary with this product, and gains should be there. Car pulls better in 6th, so i know gains are there).

I can provide one more fact: the clutch pedal. I mentioned before that i was having issues. No problems during 1-4th, then 5th wot, tried the top speed attempt, no go so i went to put it in 6th and clutch stuck halfway and felt very light. After about a minute it went back to feeling normal. I then filled up with gas and went for it again(10-15min later) and this time clutch felt limp after 4th wot, so i threw it in 5th, lifted up the pedal and continue going. There is 0 slip that is observed by me. I have tracked a few times (road course) and never had an issue. Any thoughts?

Rock36

I would imagine if your clutch is slipping some, you could lose a few mph on the very top end eventhough your engine is turning at peak power at 6300 rpm in 5th gear.

kotik

There are no signs of slippage. I never experienced a slip, and rpms are climbing consistent with speed. It just pretty much accelerating at a rate of 1km/h /2sec after 190mph. Perhaps if i find road open enough to keep going, maybe it would have gained an extra 1-2mph, but at my power level shouldnt i get there at a bit more rapid pace?? I know my only power mod is intake, but i figured the light weight rotors would add to my whp...

I ran other cars with a satisfactory results. Ran ls3 c6, h/i tune and i did circles around him, same for a turbo cayman (moded).

FNBADAZ06

ECT...Engine Coolant Temps.

5th gear is long legged, so the acceleration will drop dramatically once you go into 5th in a top speed run. The RPM/MPH climb is pretty slow once you hit 175 or so.

GMuffley

You are within 1.6% of the advertised limit--under ideal circumstances. I don't see a problem.

wolf8218

Make sure your windows are closed.

^_^

Btw you should dyno tune your car. I think I heard from your other threads that you're out of warranty anyways.

PRE-Z06

Is the clutch fluid dark after you make a high speed run? Are you saying it sinks to the floor during a single gear pull?

FNBADAZ06

Another thing.....you mentioned in a prior post that your clutch pedal is half way to the floor when performing these pulls in top gear. That's an indication that the clutch assembly is overheating, much like the issue we have when a drag launch is performed with a stock clutch, where the clutch is slipped for the initial launch.

I was having the same exact issue when doing WOT pulls in top gear......the aerodynamic forces are so big at those speeds, the clutch began to slip as the engine loads increased. End result, 5th gear at 170+ I went for the clutch pedal to coast down and the pedal was on the floor.

Happened on the HPDE's I drive with long straights where I could run 4th up to the limiter.....de-clutch to hit my brake point in the turn, pedal on the floor.

kotik

Ha, sounds about right. Is there an issue with the clutch?? I was told that it is worn and that is why it's doing it. Previous owner swears he never raced the car (doesn't look abused) and I never did either (no standing start launches). Car is at 27k miles, but been doing this since i got it at 18k.

kotik

similar to what FNBADAZ06 is describing.

I go to do some pulls on the autobahn (usually I do it once a week as a stress reliever from work). I will go 2,3,4th redline (on the first run all is great) then into 5th (no issue) and then i'll WOT 5th to about 180-190mph... then i will go to throw it in the 6th for cruising, and the pedal will feel very light and won't come back all the way up (stays about half way to the floor). I will then just lift it up with my foot, cruise at 100 for about a minute, and if I were to switch gear again the pedal will be fine, HOWEVER if i were to immediately redo the same run, it would get smooshy after 4th redline.... It very much seems like a heating issue.

I change cluch fluid at any sign of darkness. I don't see any particular dirt in it, it just gets a little murky, so i change it out via ranger method. I never did a clutch flush, should I? Is it possible something is stuck somewhere that the ranger method is not taking care of?

kotik

I preffer to open the window at about 180mph and stick my tongue out

no, but I do have them all closed.

I didn't tune it because there are not many reputable tuners here (none that i'd trust, or they are ubber expensive). Another reason is that the dealer here said they will do good will if my engine ever goes kaput.

kotik

I'm modified, and should have more power, so should still reach it.

most previous cars that i've owned were able to hit top speed without an issue.

what would be ideal circumstances?

JwT

Well I'm thinking that without a tune you may not get the mph you seek. Here's a silly thought, before you try again detail the car. And I mean a full paint detail, wash, clay bar and a very good wax. Believe it or not that could pull an additional 3 mph. Just my 2 cents

MTIRC6Z

I saw some wind tunnel testing done by, I believe it was Hot Rod Magazine a while ago, proved even the best wax accomplished absolutely nothing...still the car would at least look nicer while at speed

Cheers, Paul.

Z06Ronald

drive downhill.