I get the same question very frequently..."How much HP will your 4L60E's handle?" To accurately answer that question, we'd have to reach a certain breaking point. At this point, we just haven't got there. We currently have them holding up very well in 10 second/600+ HP cars.
The reason many shops rate their transmissions by HP, is because they've reached a common failure point that they can't manage to overcome.

I still can't believe how many posts I read about repeated burnt 2/4 band and 3/4 clutch failures I see. We solved those issues many many years ago. At one time, we had narrowed down our 4L60E's "weakest link" to the output shaft itself. With the release of the hardened 4L65E output shaft a few years ago, we haven't broke any since then.

Yes, we've had 4L60E's break parts over the years. When you find a weak link, you find/make better parts to fix that weak area. At this point, I feel as though we've solved all the problem/weak areas in the '60E.

Too many people get hung up on HP. What we've seen to be harder on '60E's are sub 1.6X 60 ft. times. A 400 HP car that 60's a 1.50 is much harder on a '60E than a 600 HP car that 60's a 1.70. It all depends on WHERE that power is made. Obviously a turbo/blower car is going to be easier on the launch than a car coming out on a 200 shot.

Unfortunately, 4L60E's still have a bad reputation of being weak. This is in part due to too many builders THINKING they can build them...LOL I see customers that have paid close to $3000 for a '60E. They thought they were getting the best. Judging from alot of what I've seen, too many builders just "miss the boat". When that expensive "Race" transmission bites the dust in a short period of time, the customer tends to blame the transmission. We've proven it's not the transmissions fault.

We still see other "Pro Shops" use antiquated parts and build techniques, such as vacuum modulators, kevlar bands, red 3-4 clutches, Trans Go kits, "Load Release" springs, etc. I love the challenge of a customer saying, "I've had this transmission built 4-5-6-7 times and it won't last!" We like changing those customers opinions...Once they have one built correctly.

If a builder wants to build a transmission with a vacuum modulator, they should stick to transmissions for 1975 Caprices. They simply don't belong/work in a '60E. Any "Old School" racers here? When you built a radical street machine with either a TH350 or a TH400 in it, what was one of the big transmission mods? When you go with a big cam, or forced induction, you usually had to go with a manual valvebody. That's because the vacuum modulators these transmissions came factory equipped with just couldn't accurately control them. So now we have misinformed builders putting something in a 4L60E that didn't work 20 years ago? There's no way a modulator will ever control pressure as precisely or quickly as a computer/electronic solenoid.

I hope this helps clear up the "How much will your transmission take" questions. We'll let you know when we reach a limiting factor that we can't improve on.

Thank You,
Frank
CPT