Converter stall speed vs spool up
09-22-2009, 09:25 PM
#1
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Converter stall speed vs spool up I have used the search feature and have found members with many different thoughts in rule or theory on stall speed vs spool up. None decisive as to rule of thumb! OH! By the way, sorry this is a long post but I did not know how to get answers otherwise. I am no expert by any imagination. Just trying to learn!
First, I would like to assume the subject vehicle will be 650 -750 hp & 95% street driven low compression turbo 408. The goal is to maximize performance via Torque Converter (spool up).
I am naturally interested in optimizing my own vehicle (setup as in sig below) but also in others opinion from real world experience with their own setups. I will post this in Performance Truck forum also.
Further let’s assume all things being equal as far as set up, exhaust, fairly aggressive cam, 4l80e, turbo, triple disk same manufacturer converter where lock up will not be a problem, weight, etc. Also assume flash and brake stall to be equal in rpm.
And most importantly, NO TRACTION ISSUES to deal with.
To over exaggerate the scenario assume stock 4l80e converter @1800 VS quality aftermarket 4000 rpm stall converter.
I have always believed as rpm increases so does torque output to a point of max. ie. Lower RPM less HP, higher RPM more HP as a generalization.
Even though you may be able to get 3-5 lbs boost on the stock unit @ 1800 RPMs heck even double the engines output with 15 lbs. My thinking is the overall power output at this relatively low RPM should be MUCH less than that obtained from the same engine at 4000 RPMs at the same boost level. Is this correct or is there a bust in my thinking?
Also assume the time it takes to reach each stall RPM is equal, (1,800 vs. 4,000)
Some members of the Truck Performance forum indicate success with the low stall stock 4l80e converter and their theory of LOADING the turbo sooner to expedite boost as opposed to a converter with a higher RPM flash or stall level.
I am probably wrong but the time in mil seconds to reach the 1,800 rpm lockup VS time it takes to reach 4,000 rpm lockup of the higher stall converter would not be measurable. Please guide me in the right direction or share your knowledge.
First, I would like to assume the subject vehicle will be 650 -750 hp & 95% street driven low compression turbo 408. The goal is to maximize performance via Torque Converter (spool up).
I am naturally interested in optimizing my own vehicle (setup as in sig below) but also in others opinion from real world experience with their own setups. I will post this in Performance Truck forum also.
Further let’s assume all things being equal as far as set up, exhaust, fairly aggressive cam, 4l80e, turbo, triple disk same manufacturer converter where lock up will not be a problem, weight, etc. Also assume flash and brake stall to be equal in rpm.
And most importantly, NO TRACTION ISSUES to deal with.
To over exaggerate the scenario assume stock 4l80e converter @1800 VS quality aftermarket 4000 rpm stall converter.
I have always believed as rpm increases so does torque output to a point of max. ie. Lower RPM less HP, higher RPM more HP as a generalization.
Even though you may be able to get 3-5 lbs boost on the stock unit @ 1800 RPMs heck even double the engines output with 15 lbs. My thinking is the overall power output at this relatively low RPM should be MUCH less than that obtained from the same engine at 4000 RPMs at the same boost level. Is this correct or is there a bust in my thinking?
Also assume the time it takes to reach each stall RPM is equal, (1,800 vs. 4,000)
Some members of the Truck Performance forum indicate success with the low stall stock 4l80e converter and their theory of LOADING the turbo sooner to expedite boost as opposed to a converter with a higher RPM flash or stall level.
I am probably wrong but the time in mil seconds to reach the 1,800 rpm lockup VS time it takes to reach 4,000 rpm lockup of the higher stall converter would not be measurable. Please guide me in the right direction or share your knowledge.
09-22-2009, 09:40 PM
#2
Hmm ...you sure get theoretical about this stuff.
Its not that complicated I don't think. You are talking ability to build boost off the line.
Well depends on where your turbo spool up. If it spools up at 3000 rpm than a factory stall that is like 1800 is not going to give you much boost off the line. If your turbo spools up at 5000rpm and you have a 3500 stall they again you aren't going to get much boost off the line.
I don't have my auto and stall swapped into my 99TT yet in next few weeks but from my experience in my talon race car its pretty much as said above. I have stock stall in talon which is like think 2500. I have stock little turbo that spools up at like 2500.
If I set my two step to 2000 then don't get any launch boost. If set it to 2750 where it is now I can get like 15psi and get a great launch.
If set it to 3000 not going to help much and car will push thru the brakes.
Have to find the sweet spot and a two step is great for that.
When I swap in my big turbo next spring which is llikely going to spool up by 4500 or so then obviously will change out stall to like a 5000 stall. Or would have to use a small shot of spray to get the turbo spooling.
So everthing will depend on your turbo choice pretty much . Once you have the turbo figured out then you can figure out your stall required but keep in mind a big torque motor like a 408 or bigger can pull the rated stall up quite a bit . So a 3400 stall might act more like a 4000 stall.
I am expecting to build pretty great boost with my py3400 and current turbos or upgraded ones that do have about 300 or so higher spool up think I read. But i also have nitrous if do have to hit it with a small shot 75 to 125 say.
Its not that complicated I don't think. You are talking ability to build boost off the line.
Well depends on where your turbo spool up. If it spools up at 3000 rpm than a factory stall that is like 1800 is not going to give you much boost off the line. If your turbo spools up at 5000rpm and you have a 3500 stall they again you aren't going to get much boost off the line.
I don't have my auto and stall swapped into my 99TT yet in next few weeks but from my experience in my talon race car its pretty much as said above. I have stock stall in talon which is like think 2500. I have stock little turbo that spools up at like 2500.
If I set my two step to 2000 then don't get any launch boost. If set it to 2750 where it is now I can get like 15psi and get a great launch.
If set it to 3000 not going to help much and car will push thru the brakes.
Have to find the sweet spot and a two step is great for that.
When I swap in my big turbo next spring which is llikely going to spool up by 4500 or so then obviously will change out stall to like a 5000 stall. Or would have to use a small shot of spray to get the turbo spooling.
So everthing will depend on your turbo choice pretty much . Once you have the turbo figured out then you can figure out your stall required but keep in mind a big torque motor like a 408 or bigger can pull the rated stall up quite a bit . So a 3400 stall might act more like a 4000 stall.
I am expecting to build pretty great boost with my py3400 and current turbos or upgraded ones that do have about 300 or so higher spool up think I read. But i also have nitrous if do have to hit it with a small shot 75 to 125 say.
