tpivette89

alot of people on the Street Racing board are talking about torque converters dropping up to 4 tenths from your quarter mile times. i have heard this elsewhere, and was wondering how this piece actually works. Also, due to the low rpm nature of the TPI manifold, which stall speed would work well in my Vette? any ideas on which brand to buy? Thanks

Ed Maher

If you want to make serious gains, you have to keep in mind that a vigilante, or a high end yank can't be touched. If you look around, anyone who gets one of these says it was their best mod. And we're talking about fast cars.

To start with, a vigilante is a 9.5 converter vs. 12" for a stock and a lot of the cheaper aftermarket ones. First of all it is obviuously MUCH lighter, and you're talking about a constantly accelerating piece so it's in effect in every gear.
But the real advantage to a 9.5" converter is that they are so efficient. The larger the converter diamter, the lower it wants to stall. To make a 12" converter stall to 2800, you basically just bend the impellers to make it less efficient so that it slips a little more for you. So yeah you'll get the stall speed, but it will be very loose at low rpms and light load and also won't have any other advantages over stock because it is simply looser and less efficient to let it slip more. Also, that slip is with you everywhere, even on the top end.
A 9.5" converter on the olther hand is a race converter and wants to stall through the roof behind just about anything. So they then design extra efficiency and fixes into it. To make a (oh lets say 5000 stall) 9.5" converter stall at a street level like 28-3600 rpms They make changes that greatly increase the effieciency and also boost the STR (stall torque ratio). STR is the ratio of the torque on the TC output to the torque input fro mthe engine at full stall speed. A stock torque converter has a STR of well under 2:1. A nice vigilante or yank is going to be well over 2. Thats a much more controllable and ideal way to add off the line punch without having to compromise gearing. For example, LS1 A4 cars run way into the 11s with just basic bolt ons like a lid and cat back with a vigilante with stock 3.23 gears. And the LS1 is known as a high rpm motor. Lower gears let you use first and second gear longer than higher gears which offers an interesting tradeoff that a converter covers the only hole from.
Also they are at least few percent more efficient than any large diamter higher stall stock or otherwise converter. And a few percent will buy you 10hp on a 300hp.
And as i already mentioned, they are much tighter at low RPMs and part throttle than a larger diameter converter with the same stall. Basically they make their stall speed in a very linear fashion w/ torque input, giving a rubbe rband sling shot effect as you squeeze the gas. A large diamter converter simply gives you slip until you hit the stall speed, or at least you come close to it, even at light throttle.

They're pricey at around 800, but to me the science and more importantly RESULTS speak for themself.

For more reading go to:
www.converter.com - vigilante
www.converter.cc - yank

for results, do some searches here and at camaroz28.com and ls1.com , the latter 2 having plenty of fourthgen experience showing universal love.

As for LTR TPI. Traxion went 12.5 @ 108 with semi siamesed AS &Ms. He was stuck in the 13s with some other converter.

Ed Maher

That could easily be 12s at 105 with a vigilante and the traction. Being a vette guy, check the corvetteforum.com too, they must be trying them too.

rhuarc30

There's also a company called ACT that's offering a converter they claim is comparable for around 500.