Rev Limiter Help Please (1 Viewer)

[The Counterfeiter]

Since I can't get any fuel crew chiefs to respond to my emails, I was trying to back into what revs DSR dragsters are turning at 330+ mph. 332 mph = 487 ft/sec divided by slick rollout (using static number of 110" - 115") times 3.2 rear end ratio gives me well over 9000 rpm. Assuming zero clutch or tire slip, tires would have to grow to about 134" rollout for revs to be below 8250 limit. Am I on the right track here or has DSR found a way to circumvent the rev limiter?

 

[e]

Well, not going to be any real help here, but you're sure going after this deal the same way I was thinking.....I too was wondering about the rpm's turned on that run.....Guess I'll just wait like you and see if an answer comes along.................................e

 

[Nitrohelper]

.....found a way to circumvent the rev limiter.....

yes , since shortly after they were allowed the electronic timing control....

 

[none]

For starters it's not a rev-limiter. It is a timing retard. When you hear a Pro Stock car on the line waiting for the tree he (or she) is on the limiter which will not allow the engine to rev any higher than a certain RPM. In the nitro ramks, the retarder comes in and backs timing out of the engine effectively reducing power, but it does not limit the RPM.

Also if I remember correctly the retard doesn't come in until 3.8 seconds, therefore in this case it would have no effect at all. Now that may have been adjusted and I'm not aware of it, but I believe that was the setting.

Alan

 

[****er]

It's pretty simple as long as it all works in order, one unit pulls timing out--- you setup the other unit to bring it back in-----------

 

[twostep]

They can effectively 'slingshot' past the limiter, up to a point. Schu had one in place when he ran 337. I never hear them mentioned any more; are they still even required?

 

[Nick Name]

An actual rev limiter which disrupts ignition firing would be a disaster in a nitro motor.

 

[flapjack]

I never hear them mentioned any more; are they still even required?

I didn't see anything in the rule book regarding a timing retard or rev limiter device. What's up with that?

 

[john]

well over 9000 rpm.

That's it.

 

[Bross Hawg]

They are still required and Alan is correct. It retards ignition timing. If you used an actual rev limiter, which basically shuts off spark to random cylinders, it would be an impressive engine explosion...aka similar to Matt Hagans. There is an interesting article out about new large valve cylinder heads being used. Not sure of the validity, but supposedly they are in use on DSR and JFR cars currently.
::rag Racing Online::: 332 MPH = Money + New Cylinder Heads - 04/20/12

 

[Bullet]

An actual rev limiter which disrupts ignition firing would be a disaster in a nitro motor.

I might be missing something, but how would taking spark away be any different than a cylinder going out (except that it would be all 8 cylinders out)?

I guess that in itself would cause the catastrophic failure?

 

[none]

Paul,

The problem would occur when it comes back on.

Alan

 

[Nick Name]

Alan, you treed me.

 

[Nitrohelper]

..... any different than a cylinder going out .....

Because Nitromethane carries it's own oxygen, there is a condition that occurs known by the slang term of "hydraulic" ...
That is actually incorrect in the true sense of a "hydraulic" in a non Nitro burning engine...
The term Chemical Engineers use is "to compression fire" - that is what pushes head gaskets out, and sometimes the connecting rods... And blew-up the railroad cars in the '50s...
When the liquid of a dropped cylinder is exposed to the rising pressure of the cylinder trying to re-light, an uncontrolled explosion can take place...
The same condition is sometimes created when a driver pedals the car down track, and it knocks the blower off...

 

[twostep]

Not sure of the validity, but supposedly they are in use on DSR and JFR cars currently.
::rag Racing Online::: 332 MPH = Money + New Cylinder Heads - 04/20/12

The writer acts as if a team that develops an improved cylinder head is doing a deed akin to whizzing in someone's Full Throttle. Good Lord...if they figured out how to run a larger valve, good for them. The whole idea is to outperform you opponent, correct?

In R1 at Charlotte, only Tony Schumacher was significantly quicker than 3 small-valve cars, 2 of which would be labeled 'little teams'...and Brandon was low in R2...so as of right now, other than dazzling top speeds, there's no clear-cut advantage.

 

[Bullet]

Paul,

The problem would occur when it comes back on.

Alan

Because Nitromethane carries it's own oxygen, there is a condition that occurs known by the slang term of "hydraulic" ...
That is actually incorrect in the true sense of a "hydraulic" in a non Nitro burning engine...
The term Chemical Engineers use is "to compression fire" - that is what pushes head gaskets out, and sometimes the connecting rods... And blew-up the railroad cars in the '50s...
When the liquid of a dropped cylinder is exposed to the rising pressure of the cylinder trying to re-light, an uncontrolled explosion can take place...
The same condition is sometimes created when a driver pedals the car down track, and it knocks the blower off...

How come we don't see explosions when a car drops a cylinder then picks it back up? Or more often than not does it push out a head gasket or break a rod?

 

[twostep]

How come we don't see explosions when a car drops a cylinder then picks it back up? Or more often than not does it push out a head gasket or break a rod?

No expert here, just a guess, but I would imagine it's because a dropped cylinder/picked up cylinder is a one-hole, one-time event....it goes dead, it comes back, that's it. Not that upsetting in the overall scheme of things. With an actual rev limiter, you've got rapid-fire, continuous off-on events occurring in all 8 holes - something a blown nitro engine would never tolerate.

 

[Nitrohelper]

..... a car drops a cylinder then picks it back up.....

First it's Nitromethane - liquid dynamite, that's what separates the boys from other racers...
Second it depends on cylinder pressure and temperature rise as the cylinder is relighting - also sometimes the rods are in the diaper and you don't see a big ball of fire...
Anybody that has tuned Nitro cars for any length of time ,will occasionally say after a mess comes back to the pits-
"I wonder why it did that?"

 

[JON]

If that fuel cut and parachute thingamyjig was set to go off at (say) 330mph, I guess teams would go to 330 mph.

 

[Bullet]

First it's Nitromethane - liquid dynamite, that's what separates the boys from other racers...
Second it depends on cylinder pressure and temperature rise as the cylinder is relighting - also sometimes the rods are in the diaper and you don't see a big ball of fire...
Anybody that has tuned Nitro cars for any length of time ,will occasionally say after a mess comes back to the pits-
"I wonder why it did that?"

I can see cylinder temperature being a big factor.

No expert here, just a guess, but I would imagine it's because a dropped cylinder/picked up cylinder is a one-hole, one-time event....it goes dead, it comes back, that's it. Not that upsetting in the overall scheme of things. With an actual rev limiter, you've got rapid-fire, continuous off-on events occurring in all 8 holes - something a blown nitro engine would never tolerate.

I can see the frequency and magnitude being a problem.