perma tune vs Bosch heat observations

[konish]

All,
Just replaced my Perma Tune with a good, used box and it seems to work great. One observation I made was that my Perma Tune box exterior never really got hot. The Bosch box gets very warm (borderline hot). I'm wondering if this has anything to do with the fact that the Perma Tune seems to be filled with some kind of potting compound, which would also explain its weight (almost 2X that of the Bosch unit)? At any rate, its the first time I've been able to hear the Bosch box "whine" that folks refer to all the time about these boxes...the P-tune was quiet. Just thought I'd share and see if I couldn't get educated about these things in the process...

R/
Dustin

[Early_S_Man]

Dustin,

One reason the Bosch unit may be warmer to the touch is the difference between oxidized bare magnesium and clean, anodized aluminum in the ability to dissipate heat. Another very significant difference is that the heat-generating semiconductors are mounted on the bottom plate and mounting bracket of the Permatune ... whereas the Bosch semiconductors are mounted just below the fin area of the top side of the case.

The epoxy potting compound probably has no real bearing on this matter ... because there is so little contact area with the heat-generating pair of transistors and SCR that are mounted to the bottom plate.

[konish]

Warren,
Thanks for the info. Seems like the Bosch design is perhaps superior in dissipating heat due to the semicondictors near the fin area as opposed to the mounting plate and bracket. I was a little concerned at first, but when I took a step back and noticed how big the cooling fins are in realtion to the size of the box, it started addding up...the box is going to get hot which is presumably why the Bosch engineers designed all that surface area to get rid of it. Thanks again....you are a true resource for someone learning the ins and outs of the 911.

R/
Dustin

[A Quiet Boom]

Dustin,

Glad to hear it's working! Did the box solve the other problems you were having? I think you metioned in one thread that you were concerned about the coil.

[konish]

Chris,
I meant to e-mail you to tell you I received the box..thanks so much. Also, so far, so good, but I have yet to really take it out for an extended cruise. The coil tested fine so I'm ruling that out for now...along with Loren and Warren's advice on the Bosch black coil being a solid piece. I have along road trip coming up and I just want to make sure evrything is 4.0 before proceding.

R/
Dustin

[A Quiet Boom]

That's great. That particular box cam with the motor that's in my car now so I was certain it was in working order (I got to hear the car run). As for your heat question MSD boxes run a little hot as well especially the 7AL3 I had in my old drag car, I swear I could have welded with the spark it put out! but all that power made a lot of heat. I'd definately agree with Warren on the corrosion vs. anodized issue why not polish the box? Might look really cool

[Lorenfb]

The extra heat in the Bosch unit results from its' design. The unit uses a
oscillating inverter which basically dissipates the same power no matter
what the RPM is. The Perma-Tune's power consumption is basically a function
of RPM. This is because it only dissipates power when a spark is required.
They both at high RPMs will have about the same power/heat dissipation.