Is a Speed Limit Defencer essential to maximizing a stock RB25 or similar engine?

[Temujin]

A friend just bought a Nissan Sylvia S14 which he upgraded with an RB25DET. He also bought a Speed Limit Defencer from HKS (pictured below) because as he claims, the stock RB25DET motor is limited to 180kph and the said SLD will bypass the limitation and allow for full use of the engine.

 

I also put an an RB25DET in my 240Z (which will hopefully be done in January). I've been an avid fan of Hybridz for quite a while now and have never come across a need for this device. Am I missing something? Do I need this LSD too?

 

[Evan Purple240zt]

I don't have my speed sensor connected to the ECU at all, not totally sure you really need that HKS contraption. If he is trying to sell it separately, I would pass.

 

Evan

[johnc]

I don't think engines are speed limited, I think they vehicle chassis is speed limited. There are wheel speed sensors that tell the ECU how fast the car is going. When the pre-set limit is reached the ECU cuts fuel or ignition to the engine to limit power and thus limit speed.

 

With your RB25 swap are you going to hook up any wheel speed sensors to the ECU?

[Careless]

I don't think that's how it works on these types of cars.

 

I was told that an unmodified z31 ECU will cut out at 187 kmh, and will shut the car down, and it needs to be reset. Most of the earlier nissan cars used a speed sensor, or 5th gear speed sensor that would cut the car out at higher rpm's in 5th gear.

 

240sx guys usually cut the wire to the 5th gear sensor, or they run an automatic ecu in a manual equipped car to circumvent the cut-out while retaining tach and speedo function.

 

for the Z31 and RB25, it could be related to the purple wire in the Z31 that removes the rev limiter, and work on the same principle of ecu-feedback signal wire.

 

The SpeedCut Defender works to circumvent that by providing a stable analog signal that will not trigger the igition or fuel hard-cut.

[Canadianz]

I'm with Evan,

 

On my RB25det swap I used an Autometer speedo so the vehicle speed sensor jsut feeds into that. Works great and Ive hit over 200km/h no problem.

[Evan Purple240zt]

Yeah I never had the VSS wire hooked up, and there really isn't much reason to have it connected honestly.

 

Besides, that thing looks like hell LOL.

 

Evan

[kiwi303]

Besides, that thing looks like hell LOL.

 

Evan

 

yep, looks like it fell out the bottom and got dragged along the road by it's cable at some point!

[Temujin]

Thanks for the replies. We're trying to get the stock speedo/tach to work with the RB25 but even if I end up getting new speedo/tach, i'll tell 'em not to make it make a direct connection from sensor to gauges.

[Racinjitter]

I agree with Evan, I have never hooked up the VSS signal wire to the ECU. I have never had a problem in regards to this either. I have taken the vehicle above 160mph.

 

SLD is a waste of money, IMO. Cut the yellow with a green tracer going to the ecu.

 

Careless, The Z31 ecu is speed limited, but as far as I know it doesn't shut the vehicle down, it pulls spark or fuel (I can't remember which). So you can maintain a maximum threshold speed. And it is the purple wire on the Z31 going to the ecu.