RX8-TX

Got a question for you guys:
Why do I hear all the time that cars such as Evo's, WRX's, and for that matter turbocharged cars don't have a good top end acceleration?
Am I missing that they are probably refering to AWD cars only?

Thanks in advance!

Ike

Tell that to a Supra, Porsche Turbo, or GN driver and you'll get smacked! :p


It's not turbo cars, it's AWD cars, simply because of the extra power being lost due to the drivetrain. It also has something to do with gearing on certain cars, 4th and 5th in the WRX when it's in stock form is almost like overdrive, luckily 3rd will take you to about 100 and 4th opens up nicely with basic mods. They're no slouch but if you compare a 300bhp AWD car and a 300bhp front or RWD car of relatively equal weight and drag coefficient the RWD or FWD car will usually pull because it's making more HP to the wheels.


Ike

FamilyGuy

The new Bugatti Veyron supercar uses twin turbos and it has a top speed of around 273 mph.... if that's bad acceleration, I would hate to see a fast car. :D

RobDickinson

Not quite, it was so unstable over 200mph it is now limited to that.

No Veyron will be allowed to go quicker, and they couldnt fix it without a complete re-design, which has been quite an embaresment ...

revhappy

I agree with Ike, but also AWD systems are heavier.

Omicron

Um, there is a difference between acceleration and top speed... ...maybe you should have mentioned how quickly it gets TO that top speed. Kinda referencing apples with an orange explanation here... :D

FamilyGuy

My bad, Mr. Greek Letter :D

I don't know about how long it takes to reach top speed, but it can reach 186 mph in 14 seconds even though it uses turbocharging.

jprempe

For the EVO's the reason why people say that it has no top end is because the gearing is so aggressive. The EVO is a 5 spd and 4th gear tops out at 115 mph....5th tops out at 155 mph. On top of that is the fact that the EVO is not the most aerodynamic with that huge FMIC.

the EVO still pulls pretty hard up top but it's no match for a car that has similar power/weight, with better aerodynamics, and a good 6 spd gear box (ie: S2000 or 350z to name a few).

Also, AWD cars tend to run a 1/4 mile about 0.5 second quicker than a RWD or FWD car with the same power/weight. So for example with the EVO, it generally runs a 1/4 mile in 13.5 @ 100 mph. The 350z runs the 1/4 mile about 14.0 @ 100 mph. So from a stop the EVO has an edge but from a roll the two will be nearly idendical in acceleration. So this also leads to the "EVO has no top end" because it's ET's in the 1/4 mile are lower than a 350z and would thus lead you to beleive that it's faster but actually it's the same speed. the big difference is it's 0-30 mph due to the AWD.

jprempe

off topic but I'm not jprempe...can someone let me know how to log out and log back in. Thanks.

4thGen

Quick question for Ike or anyone else who knows. What's a GN?

Ike

Buick Grand National (Also see Turbo Regal), one of the badest turbo cars ever made, if one ever looks like it wants to race you tell him he has a nice car and that you've always wanted one, he will probably back off and won't embarass the hell out of you then :p Here's a video of a modded GN on a dyno, this guy runs low to mid 8s.

http://fasttrackperformance.com/page.../ChrisTTGN.wmv


More videos if you like that one

http://fasttrackperformance.com

wakeech

yup, Chevy actually built a decent turbo engine, and put it in something that to the uneducated eye looks like any other uglo-master American sedan of the 1980's.

anyways, turbo, supercharged, all-motor... it doesn't matter. engines designed and tuned to behave differently at different rpms will *gasp* have different characteristics at those different engine speeds, and thus vehicle speeds.

North American muscle-heads (the majority of car-buying enthusiasts) just have this problem they can't get over about low-end horsepower, and generally don't like "having" to "rev the sh*t" out of their cars to get it to go quickly. i'm not trying to generalise, but i've known a lot of rednecks and this is a fairly typical response.

for guy-who-isn't-jprempe, it's not just the intercooler that's the source of the Evo's drag, but a great many issues with its shape, and whether it actually had an intercooler or not wouldn't make a difference.

FamilyGuy

Absolutely. Most of my relatives who are performance car enthusiasts idealize the muscle cars of the late 60s. They all want big V8 engines and have a mantra "there's no replacement for displacement". Why they are so dead set against forced induction from supercharging and turbocharging is beyond me.

On the other hand, I appreciate their preference for cars that just take off when they slam the gas pedal down. Cars that are civilized until they hit a certain RPM range can be great fun to drive, don't get me wrong.

RobDickinson

Its not top end acceleration that gives turbo's a bad name IMO, they DO generate a pot of power - but all at a cost.

There often complex, expensive and prone to faliure, put the engine under more pressure and need a stronger engine realy.

Plus, on a driving front you have turbo lag so power is not there instantly, and not there at lower RPM.

But whats worse, from a racing POV is the (usual) mountanous torque /power curve for highly tuned/high boost systems.

Think about the sierra cosworth (origonal) - you didnt have this car in the US I think. but it was THE car in the 80's in the uk, launched in 85, 200+bhp out of a 2 litre turbo car - way ahead of anything else on the roads apart from some very exotic stuff.

Thats what the stats said, and yes , it was a great car, but the stats didnt say it all.

A lot of them were stuffed into hedges, mainly because of the turbo, it DOUBLED the HP of the car over only 300RPM, having the turbo spool up in those RPM on a bend was more than to much for many drivers.

Which is why a flat torque curve is usualy best for racing, very predictable, although most times they'd go for more power and tr drive through it.

FamilyGuy

I guess that's two reasons the old school muscle car aficionados prefer bigger displacement to turbos and superchargers.

On the other hand, lots of companies have turbo'd and supercharged cars today that are just as reliable as naturally aspirated ones.

There's one other reason to prefer big V8s to turbocharged 4s and 6s, though. The engine noise. A Ford Mustang GT isn't particular fast for its 4.6 liters of displacement and doesn't have much else to recommend it but it sounds so nice.

AbusiveWombat

Yeah, you can't beat a V8 for sound but....a nice blow off valve sounds pretty cool too.

Ike

That's why I love my flat 4 turbo, great engine note and I get the benefits of a turbo and that good old wooosh! :D Subaru did a hell of a job making an engine that can do it all and keep begging for more, while sopunding burly doing it.

93rdcurrent

My '91 Toyota MR2 turbo sounded pretty bad *** too... I had a stage II Turbonetics upgrade with a new wheel and ceramic ball bearing, UPRD ECU upgrade, Supra fuel rail, intercooler upgrade, Jacob's Electrinics inginition upgrade, HKS headers & Super Dragger exhaust, etc. Pushing 575 hp. When the turbo spooled up to its' 24 psi people ducked.

Anyway I digress, I don't know for certain what my top speed was but I do know that I had it a couple of times over 180 mph and was pulled over by CHP doing in excess of 120. The officer couldn't judge my speed but knew when he got to the bottom of the on ramp that he was going 120 mph and that the Mustang 5.0 supercharged I was racing (I was already a few car lengths ahead of him) and I were definately still getting ahead of him. By the way I never saw the CHP I just got off the freeway and was stopped at a light when he came flying up behind me. Yes I got the ticket, my car towed, and a ride to work.

scientist

i never knew turboed cars didn't have top end?....or AWD machines didn't have top end power

Mc laren F1....awd car

you can only do soo much naturally aspirated....the engine can only suck soo much air in on its own....when its down thats when u need boost to get more into there


lag....thats kinda an issue of the past
newer turbos have less lag because of better turbo design....using twin scroll, titanum alloy for the compressor wheel to reduce inertia, exhaust recirculation, ALS (used on rally cars and the japanese evo 8) aka the bang bang system all these help reduce turbo lag

lag is only mental...when u lower your compression the lag is just the time u waiting for the car to come on boost to gain back the power u losing off boost

another example of the evo....look at how early in the RPMS the torque comes and how quick its on boost

moogle

I feel torque kicking in @ 3000 on my evo.

Hornet

Actually, that car has "quad" turbos.

FamilyGuy

Oops. My mistake. Thanks.

I think I'll buy two when they become available :D

Hornet

Your doing better than me...I just want to press my face up against the glass and look inside one until the butler comes out and chases me away with a broom...