How much should a converter slip at higher rpm's for a street/strip application behind a 455 engine? I am using a TCI Breakaway rated at ~2600 stall. Here's an example of the amount of slip I'm talking about: If I'm cruising at 3000rpm's in high gear my speed is about 70 mph, if I push the throttle down the tach. will jump to 3900 rpm's immediately, while staying in the same gear. This is close to 30% slippage, does this seem high to anyone else?
I think you are talking about converter efficiency, which differs from converter stall. The optimum converter for a given combination will be relatively tight for good street operation, yet stall higher when you really romp on it. When I was looking for a replacement SP converter for my stock 13" unit, I e-mailed JW, and asked for his recommendation. The problem I had, was the stock 13" converter was giving a low stall of around 1100-1200 RPM, which I found unusable on the street. The high stall wasn't really that high either, maybe 2000 RPM. I ended up with a TSP 12" converter rated at 3200/1800. JW told me that I would never see that 3200 RPM stall unless I locked it up solid with slicks at the track. He told me street tires would break loose long before I reached the actual stall speed of the converter. He was right. If I power brake my car in high stall, it will turn the tires at about 2600 RPM. In low stall, about 1500. In other words, the converter will stall higher when needed, but not slip excessively on the street. This is why, when it comes to converters, you often get what you pay for. There is no such thing as a 2600 RPM stall converter, or any other number stall. Stall speed is determined by engine torque, car weight, car gearing, and other things. This is why a good converter manufacturer, like Coan, will want to know everything about your combination, so that they can build the correct converter for you. It sounds like your converter is slipping excessively to me. That justs wastes gas and creates heat. Hope you have a good cooler.
Larry Good info! You said your car will footbrake 2600. What kind of flash stall do you see??? Is it close to 3200??
I never really looked. It's hard to on the street. Take your eyes off the road for an instant, you could be in trouble, and at the track once a year, there are other things to worry about. I'll see if I can enlist one of my friends to watch the tach while I drive. I'm sure it does flash to at least 3200, especially if I punch it from a dead stop, or just off idle. Even in low stall, it turns the tires without even getting into the secondarys.
Thanks Larry, I understand everything you're are saying. My question has to do with the amount of slip at higher rpm's, at the end of the track. The amount of slip is relatively consistant, about 900 rpms at any rpm above 3000 rpms. This 900 rpm change is the difference between cursing rpm and floored rpm's at the same speed same gear. I was under the impression that the slip would be anywhere from 3% to 10% at the upper rpm range (past flash). Is there anything wrong with the converter I have? With street tires the tires will break traction at ~2600 rpms. I'm not sure what the flash would be but the information I've given indicates something like 3500 rpms. My spare converter: I have a Torco converter that has been upgraded from it's original "high performance" standard. I had this converter installed back a year or more ago. It began to slip more and more as time went by. Initially it would foot brake to ~2800 rpms, about 6 months later it would foot brake to ~3300. Torco stood behind their product and paid for me to ship it back and strenthened it. Not sure what they did exactly ("stronger springs" was their quote)? I have it on the shelf as a back-up, but I don't have strong confidence in it. I'm not looking for a lock-up converter, just one that slips less at the upper rpms. Can I have my cake and eat it to INEXPENSIVELY. My trap speed ranges from 107 to 109 I know the Buick torque is a tough test for the $200 torque converter.
Craig, It's kind of hard to judge the amount of slip looking at your tach. Try this, RPM =MPH X Axle ratio X 336/Tire diameter. Put your numbers into that formula using your trap speed. Then see what RPM you are turning through the traps, and compare the 2. See how much slip you have that way.
Nothing wrong.... 3000-3900 isn't bad at all. You mainly check converter slip by rpm vs mph going thru the lights at a race track. Yes loose converters do tighten up with rpm, you went from 2600 rpm slip to 900. At 4000-4500 is will be half that. You are right, you are working off a $200 converter. It is probably fine. :TU:
You know last time I went to the strip my intension was to reset my tack after my 2-3 shift so I could recall (from the tach) what max. rpm I reached at the traps. Of course I never remembered to do it while I was there. I do have a spreadsheet with gear vs rpm, but I can't post it because it's a .xls file. Thanks for the comments! Yo, Rick when will you be visiting Fayetteville track again? I don't like being the only non-black Buick.
Just came back from dyno. My BM Holeshot 3000 converter slips 2500rpm@7000rpm only making 400rwhp and 400rwftlb hitting the rev limiter. Car runs 12 flat on the 1/4, 3800lbs, which to me indicates more hp than the dyno says. Need another converter for sure to break 11, just don't know which brand to get.
That's a lot of rpm's. I would run out of gear with that much slip and I've go 3.42:1 with 27.25" diameter tires. Of course I never go past 6000rpm's.
Wow, you sure got some slip. You are going to have to spend a little to get a good enough of a converter. Call ATI or Coan, PTC, Pro Edge. Make sue you let them know what you are stalling at with what you have. It will give them a better idea of what converter you need. :TU:
B&M Holeshot 3000 converter I had one in my 69 olds cutlass s built 455 th 350 trans with 373 gears. And it ran 12.20s/12 teens and seemed to have too much slip and would run out of gear in the 1/4. So i took it out and swap to a holeshot 2400 and the car went 11.80s and still had some gear at the end of the 1/4. Billy.
Holeshot 2400, sounds interesting... What rpm can you power brake to (just before the tires break loose while on the brake)? I combined actual rpm readings with some calculations and found out my slip percentage is 22% at 3800 rpm's and 9% at 5600 rpm's. I'm not sure where where my peak torque is but for my application I don't need this much slip in the upper rpm range.
Rpm Almost 2000 rpm and then the tires would brake loose. Would flash at 2500 and my 60 ft time was not as good as the holeshot 3000 but my top end speed was more. Holeshot 3000 had a 1.63 60 ft. and went 110 mph at 5500 rpm in the 1/4. Holeshot 2400 had a 1.78 60 ft and went 116 mph at 5500 rpm in the 1/4. Billy.
Converters. With the holeshot 3000 best was 12.18 at 110 mph. Holeshot 2400 best was 11.82 at 116 mph. This was in a 3900lb 69 cutlass s olds with a semi built 455 with a 850 holley-dp and torker intake and a th-350 trans and 373 gear 12 bolt rear. The motor run on pump gas and was a torque monster and did not need a whole lot of converter behind it. That was six years ago and the car to this day is still running strong on the street and strip and has never been gone into yet. I made the big mistake of selling it. :ball: Billy.
