A friend of mine has developed an argument with me, I want to see what everyone's opinion is. Here is his opinion:

He has drag raced a Subaru WRX AWD Turbo, and he says that if he drops his clutch from 5500 RPMS, that his engine will bog if the tires don't spin.

I believe that if a car is launched from that RPM level, and the tires don't spin, that the car should launch harder. Is this the right way to think about it?

I believe that the same idea applies to 2 wheel drive cars like ours. If you launch one of our cars from 5000 or so, and drop the clutch, and the tires don't spin....doesn't it just launch harder (provided that the drivetrain can take the shock)???

Sorry for my Noobness,

James

 

Correct. The higher the rpms the harder the launch, that is if traction is not an issue. However, in theory you "can" over rpm the car on the launch.

Example:

Car A: Makes peak hp at 5k, launch rpm 5500 or so

Car B: Makes peak hp at 5k, launch rpm 7000 or so

On the initial dump of the clutch for car A, the rpms will drop but the car will start to accelerate since the car is in its powerband. Car B rpm's will also drop but since its launching at 7k the rpms will be alot higher and most likely will already be at peak or past peak power thus giving a worse 60ft for Car B. Atleast thats how I look at it.
I used to launch my car with the rpms through the roof only to find out it didn't help.

-Mark

 

Thanks for the info, are there any more opinions out there??

(Where are the physics majors? )

 

on an wrx your buddy is correct it has a turbo and is a whole different ballgame than an n/a car.....

 

so is that just another way of explaining 'turbo lag" ??

So what if you applied that same philosophy to our cars...what if you had a turbo LS1, and you dropped the clutch at 5000, would it bog as well??

 

Because the vehicle is starting from zero and the engine can not, something must slip. The issue when drag racing is how to generate maximum thrust while slipping. Tires grip better when not slipping, or slipping slightly, than when spinning wildly. Therefore, when launching a manual transmission car, some clutch slip is necessary. The better the tires grip, the higher the engine speed can be at launch but the clutch must slip more to avoid wheelspin.

The clutch slip does not need to be deliberate or controlled. If your tires hook the engine will bog if the clutch doesn’t slip. Conversely, if the tires hooked and the engine didn’t bog, then the clutch slipped. Typically, the best launches involve a combination of clutch slip and mild wheelspin.

This is all true whether the engine is boosted or naturally aspirated.

 

I usually rev it till the oil pressure starts dropping, and then let out the clutch! HAHAHA

 

AWD turbos have a fine line between spin and bog. auto + brake + 2 step for the win

 

I raced an AWD Talon for many years. It requires a quick "slip" of the clutch for the best launch. The same kind of slip you do at a stoplight under normal driving. Dump it too quick, and it will bog. I used to cut 1.53's.

2-step for the win! This makes the launch RPM consistent, and you fine tune the RPM for track conditions. Or, if you are on a Pro Tree, turn it up 300-400 RPM cause you will have to dump clutch quicker.

Al

 

This is a prime example of the value of this site – someone who clearly knows, sharing his knowledge. Thanks.

 

my brothers WRX STI 5500 launch with a little slippage of cluthc launches hard as hell.just gotta get use to it. feels good. if the tires spin in my opinion your hurting yourself on the 60foot where as you find the certain rpm you can launch at perfectly without spinning. just gotta practice the launch. dont dump the clutch a qucik slip is all it needs

 

i agree 2 step ??? specially on a turbo car