I have decided to give these converters one more chance, before going with a clutch
Since I can t get a clear answer from anyone, I feel we need to discuss converters a little and maybe we can learn something

I have a 7" converter that we modded over here and got the stallspeed to about where it needs to be, around 7800, but it slips badly downtrack
and only drops about 400 rpm on shifts, gets very hot, speeds around 152 -153, et s 8.9-9.0

borrowed an other 7", 7400 stall, rpm drop OK, 152-153, best et 8.81

tried a 8" of unknown origin, 7400 stall,rpm drop OK, 158.5 and 8.74

What do I try next? I need that 8000 rpm launch without slipping down track

This is a good question for NHRA comp racers that run small motors. I,m sure these guys would be able to hook you up with some knowledgeable converter makers to get a good combo. What does your horsepower and torque curves look like?

Why do you think you need an 8000 rpm launch speed? That 8" 7400 seemed to work better than the higher stall 7" units. What exactly do you twist this thing to and what is it? Also what trans, gear ratio, rear gear and race weight would help. Where are you getting these converters from and who was modifying them?

the comp and SS guys are pretty tight lipped

IT is a 391 w8 smallblock,9000 - 9100 rpm shifts, 2.19 first, 5.29 rears, 2850 pounds

Well that's not exactly a small engine. Have you dyno'd this engine? The power and torque curves would be interesting to see.

here is what I have, not exactly this combo but should be pretty close

with only 1 ft torque diffence I think I would run a 6800- 7000 stall as at 7000 it makes 637.5 ft torque and peek is 638.8 at 7100
You have plenty of gear to let it climb into its max torque quik enough .
It is hard to build a loose convertor that does not slip in top gear.

Quote:

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Based on that dyno sheet you would like that 7400 stall...
at 8000 stall you would be a long way past peak torque

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That's exactly my thoughts, too much stall, around 7000 would be better in my opinion. The tighter converter was in the right direction as shown by the time slip. I'm assuming this is a powerglide.

just that I had a 1.29 60ft with 7800 and 1.32 with 7400

trans is a 4 speed liberty with a converter drive

How many passes on each to determine that? You are running on DOT tires the difference could have easily been a little tire spin.

Fall back and recovery after the shift. RPM is your friend. The SS and comp guys that I have been fortunate enough to get a glimpse of their combinations (including national record holders), don't care too much about peak tq numbers with higher rpm deals.

Plus they gear the cross rpm to where their stuff falls off 25 to 50hp on they're dyno sheets. They go quicker as long as the engine doesn't drop like a rock after peak HP.


Get flash stall close to shift fallback so you stay in avg. HP for the longest period of time. We are going to try this with our W8 Dart as soon as we get the car finished. Hopefully, ATCO in late October.

Jim, that makes sense to me and somewhat confirms my findings...

problem is that it seems very hard to make a 8000 stall converter that has a 8 - 900 rpm drop from 9000, the one my converter guy here made did not work and he said it was about as tight you (he) can make a 7", does this mean I should go with a 8" and try to get the stall speed up, or

I was always told you want the converter to flash around 500 over the peak torque.Mine will flash 7900 to 8000,I shift at 9000 and it drops 1000 on shift.Mine makes 685torque at 7300 if I believe..Wish you were closer I would let you borrow mine to see what it would do.

Well Ken sounds like you are dealing with some of the same issues I did with a powerglide. Based on your MPH I would guess the engine dynoed is about 50 HP better than your engine running. Funny thing about these dyno sheets is you never see the air they are in the correction factor. I even have trouble believing the correction factor is accurate on these engines. For example my engine dynoed at 900@8600 RPM that should produce speeds over 155 in the quarter. I have been in 600 ft altitude and only ran 153. Was it the car?

I always thought that if I could turn the engine 10,000 the 8,000 RPM stall would run better as the 7" converters seem to keep tightening up as the RPM climbs. I always noticed in the data that the converter would be in stall for a long time on launch and in the shift. Was constinuously told the 8,000 stall would be best with my combo. But, the best 60 ft and ET was with an 8" 6,400 stall converter that I borrowed. Could not get information on it later to build the same converter.

Typically you want stall on launch and break into stall speed in the shifts for torque multiplication, right. Just seems with these screamer engines you just can't find the fine line. You need wheel speed on launch to get the engine up into power. My issue was getting wheel speed without blowing the tires off. If you hooked it too soon it would bog the engine. Seemed that keeping the wheel speed up long enough to get the engine into it's best RPM and the converter over the stall speed was hard to do. Then on the shift the converter would just stay in stall way too long IMO. After seeing the video of your car I was sure the 4 spd was the answer. The ratios are close enough to get off the stall speed quicker in the shifts. But, you should still be looking for a good wheel speed on launch.

Many racers shift into high early with 2spds and let the converter stall for long periods of time. Deadly consistant. Problem is with a 7", even when running a large cooler, the fluid gets hot. The hotter the fluid the thinner it gets making the converter slip more. Another place I expect you heat the fluid is in the burnout box. It's hard to hear your engine wind in the twilight zone in the burnout, but low RPM burnouts build heat in the converter when you have these high stall speeds. I think heat is a major enemy to these converters. IMO You need to get the engine up to stall speed quickly on launch. The only way I know to do this is with wheelspeed then as the car is hooking up the converter is delivering maximum torque and can accelerate the car.

Some people seem to find how to make these work and always seem to run at least 3 gears. But, when you watch them the engine is always running at high RPM even on the launch. Watching your car run is a lot like mine would run. Wouldn't spill you drink in your lap on launch but like a rocket on top end.

If you find yourself to be fed up like me with these animals you can always go in the direction I know works. Tight converters and lots of NOS.

Leon

I had to read that 3 times...

I have never had much faith in those dyno numbers, but they do show where the power is,
and on the converter stuff I think you have it pretty much figured out, now I just have to find one of those people who know how to make these work

and since NOS is not allowed in my class I have to stick to what I have, I have already gone faster than I could dream about just a few years back so I shouldn't complain, but you now how it is...

I'm thinking a clutch just might be your best bet.