Converter built for my car to stall around 2600. 3500lbs, 3:42 gears, 28" tires, 455. Cruise 60mph@2950 rpm-that's 400+ rpm slip! Nail the gas at 60mph and rpm jumps to 4500!? Shift point is 5500rpm-rpm only drops 1000 on shift at wot!?! So, does this sound right to you? It seems loose to me. This is NOT a complaint!(yet). Converter guy has an excellent reputation for making things right. I have sent an e-mail to him(I'm sure he's very busy). Converter swap on my car isn't easy for me in 90 degree weather even if it's free. So if this is what you all would expect then I guess I'll leave it. Thanks,
Something is wrong. (brilliant statement on my part, eh) This sounds more like the transmission than the converter. My trans did that at the end of last year but we knew it was worn out. Our 455's can be really hard on the clutches.
I agree with your analysis of a loose converter. If it were the transmission slipping constantly it should burn the fluid and probably leave you sitting along the highway somewhere. Bob H.
The convertor is the most important part of the trans. It will make ir break your combo. What does it flash to? Punch it in low gear from a roll and watch the tach and see what the RPM jumps to. What size is it and who built it? I have had 3 convertors in the race car and just got it right.
I was taught the only way to determine true converter flash rpm was to leave the trans in high gear with the kickdown disconnected and floor the throttle. this puts the highest load possible on the converter and gives a true indication of stall speed. your converter sounds way to loose for your combination.
Thanks guys Doug and Bob, the trans did not slip with the stock converter but I did wonder if it's a combination of the two. Maybe the verter is a little loose but the extra torque multiplication in third at wot is slipping the clutches. Any easy test? Chris, it easily brake stalls to 2500 I haven't had the guts to go over that. As far as flashing it I have traction issues so I can't get an accurate figure. GranSportSedan, manual valve body so I can easily test third gear stall. I suppose leaving in third(and second) would answer questions about the trans clutches and true stall but it seems like it would be awfully hard on things. What do you all think...is that the right test at this point? Thanks again,
We need to see where it flashes. With a manual valve body put it in 2nd gear rolling a little and see what it flashes to. It seems to be way loose Im guessing its a 10 inch?
When the car is stopped the trans will return to 1st whether the kick down is hooked up or not. When the car is sitting still and the trans isn't turning it makes no difference what gear it is in the load on the converter will be the same. Bob H.
Everyone wants a high stall converter to get the engine into it's power range as soon as you mash the gas pedal. Getting the right converter is no easy task, and the right converter will make you think you are driving another car. What you want is a converter that is very efficient( built tight) for regular street driving, but it stalls where you need it to when you jump on it. It takes an experienced person to look at a dyno sheet and get it right the first time. Even so, it may take several tries. I can tell you this right now. If you can easily brake stall it to 2500 RPM, the true stall, never mind the flash stall, is much higher. The right (efficient) converter should drive right through the brakes, and turn a street tire well before it's rated stall. If you want to get an estimation of the true stall, do as described earlier. Un hook the kick down wire. Drive the car at the lowest speed possible, and still be in 3rd gear. In 3rd gear, jump on it and watch where the tach needle goes instantaneously. That will be an estimation of true stall. The best way would be if you had a trans brake activated, and you nailed it at the line, and watched where the tach jumped to. Definition of stall speed is the highest impeller RPM attainable, while the turbine is held stationary. Think of the impeller as the front half of the converter and the turbine as the back half. Bottom line, sounds like you are way too loose.
Hold on folks. I missed the return communication from my builder. It came the next day(e-mail). I had no doubts about him! Thanks!
Builder is thinking that the wrong converter got thrown in the box. Waiting on a serial number check. BUT before I drove up the ramps to look for the serial number I got the nerve to brake torque it in THIRD GEAR. Started turning the M/T et street radials(20psi, dry rough concrete)at 3300rpm. I'd guess the 3rd gear clutch pack would have to be fairly healthy to hold under those conditions, right?
Update. Another converter coming. Tested/verified. One step tighter. Return label included. Looking forward to comparing numbers but not to the swap! Could I get some input on the 3rd gear brake torque test?(see above) (manual valve body remember) 1) Is it a good sign of healthy trans clutches? 2) It didn't take a bunch of throttle to do this. Indicative of good old 455 midrange torque? Or can any ole sbc do the same? Thanks as always,
I wouldn't worry about your clutch material. If you had a problem, your fluid would show it. It would look like metal flake paint, and the fluid would be gritty.
Update....swap went fine. My expectations were errant as this is my first loose converter behind a 455. I may go a different rout next year but am thrilled with the performance and ok with the slight cons that are inherent of a loose converter. Evidently, if I would have gone a cheaper rout the cons would have been MUCH more evident so NEVER cheap out on your converter as all the guys in the know will tell you! CHRIS, sorry my skull is so thick....I took my buddy out and we actually flashed the converter from a slow roll. No other test came close to the same results. Even the third gear brake torque showed less rpm then a first gear flash. The momentum of that 70 pound crank hitting that verter really 'flashes' it. (of course you knew that didn't you!) For the record I'm a happy customer, and I thank you all for your help and patience with me!
Glad I could help. That convertor is the most important piece of the puzzle. Now can really try to dial it in with trap speed RPM and tire size to see how much slippage you actually have. 5 -7% is where you like to be at.
