Dissapointing results switching to 7" converter
 

Recently bought a new 7" converter from a reputable converter company.

Had run an old tried and true Munsinger 8" for eternity. That converter flashed to ~6,200 RPM with my combo (255/294 HP 350 SBC, powerglide, 2.08 1st gear)

Was looking to try an additional ~500 RPM stall. Converter company stated they would recommend a 7" converter for this application. Put it in the car. No other changes. They got the converter quite close, as it flashes right around 6,600 RPM. So far so good, right... WRONG... Car lost a FULL TENTH in 60' and is down .2 to .25 in 1/4. Car is confirmed to be hooking up with no spin. Big end speed is only 1/2 MPH off when the ET is .25 down, so Engine HP is still there and slip is same as old 8" Munsinger at big end so this tells me the converter is pretty efficient once it gets to overunning the sprag on the big end.

It seems the 7" converter just physically has much less torque multiplication than the 8" at a given stall speed....

Anyone else have similar experience that can chime in?? Feel free to PM me, if you'd rather not discuss in public...

Kevin Panzino

Re: Dissapointing results switching to 7" converter
 

Kevin,
I've been avoiding this one, hoping someone else would handle it.
You are pretty much correct in your analysis I believe.
The theory behind the 7" is #1, lighter weight, which is always good,
and # 2, to be able to achieve a higher stall without having to bend the pump fins into much of a negative configuration.
Now, seeing the stator is actually physically smaller than the 8" Opel style unit, you are going to have a hard time getting a fabricated 7" stator to be able to multiply the same amount of torque as the 8".
Remember, at the approx. 2 to 1 multiplication ratio , the more torque you start with, the more you'll have after the converter.
If your car is in the middle of the pack now ( not necessarily yours personally), you can see where the problem lies.
There are still plenty of top qualifying SBC cars that are still using 8" converters.
If your car is not there yet, you'd be wise to spend your money elsewhere right now.
The 7" converter is not going to be the magic bullet you're looking for...in my opinion.

Re: Dissapointing results switching to 7" converter
 

We tried a 7 inch convertor in my wife's GT/JA 85 Cutlass 327/250 PG. Back to back with our normal 8in convertor it lost a tenth. Flashed 200 RPM more that the 8 inch. We found the convertor was falling back on the flash point when it shifted. We lost a few hundredths in 60 ft as well.

Re: Dissapointing results switching to 7" converter
 

Kevin,

I just when through the discovery process of 7" vs 8" with the Super 10. My final decision came after talking at length with Gary Hettler and Charlie Plott with ATI.

ATI built me a high stall, mechanical diode 8" converter that is the cat's meow :)

Re: Dissapointing results switching to 7" converter
 

I have two friends that went to 7" converters in their SS/GT carbureted cars. Already fast, sorted out cars. Both picked up everywhere. I decided I had to have one of those!
Two 7" iterations later, my 8" ATI was still quicker and faster. Depends on the combo, like many other things. Or, I'm doing something very wrong. A strong possibility. LOL
LT1 SS car, 3 speed.

Re: Dissapointing results switching to 7" converter
 

Thanks for all the replays guys. We seem to be seeing a pattern here.
Hopefully the converter supplier will work with me on exchanging it for an 8"....I would certainly hope so since he recommended the 7"....

Re: Dissapointing results switching to 7" converter
 

Could race weight and RPM range of the two examples be factors in the 7" converters working? Thanks

Re: Dissapointing results switching to 7" converter
 

7 inch convertor typical stall is in the 6000-9000 RPM range

8 inch convertor typical stall is in the 4000-7000 RPM range


Where is your peak power? If its in the lower end of those ranges a 7 will not help you

Re: Dissapointing results switching to 7" converter
 

Do you have a torque curve you could share?


Or stated another way, do you know your torque at 6,200 rpm and torque at 6,600 rpm?

Re: Dissapointing results switching to 7" converter
 

Would the ones who picked up tell how high they go through the traps RPM wise?
Then the ones where 8 worked better give finish line RPM. The higher usable RPM range motors will probably pick up with the 7" as suggested.