Is a more aggressive cam needed when switching to better heads?

[Broncobowsher]

The ~2000 RPM OEM convertors also have lockup. That makes a huge difference. You can pull an engine down to 1200 RPM and the are direct connect and running efficient. But will have the higher stall so the engines can get into the torque curve quicker. Modern engines turn 6000 RPM without flinching. Not something the basic engine from the 3-speed non-lockup days could think about.

 

[lars]

The ~2000 RPM OEM convertors also have lockup. That makes a huge difference. You can pull an engine down to 1200 RPM and the are direct connect and running efficient. But will have the higher stall so the engines can get into the torque curve quicker. Modern engines turn 6000 RPM without flinching. Not something the basic engine from the 3-speed non-lockup days could think about.

This. I've noticed that mine will stay locked up down to around 1200 rpm and will stay that way unless I put my foot in it. Oddly satisfying, since my engine has enough torque to manage it.

 

[lars]

Could go deeper into the weeds, while everyone in the aftermarket goes off stall speed, the OEMs go off k-factor. Which puts the torque multiplication into the math. You can have the same basic stall speed, but drasticly different torque multiplication. It's how the OEMs really tune the convertor for the application. I really wish the aftermarket would get with it.

Someone, I think it was @Viperwolf1 posted k-factor values for the Explorer torque converters once upon a time. And possibly the equation that it's used in. I remember using that and concluding that the "2000 rpm stall" torque converter I bought from Hughes made sense. But I have no notes so I'm going from (increasingly dim) memory).

 

[ntsqd]

What are you talking about A High stall converter!!! . I have been off roading 1st gen broncos since 1974, you are welcome to your opinion but you are exaggerating the heat issue. All modifications change stock performance, and addressing related issues is part of the game. I increased the heat generated by 15% and increased the cooling by 50%. When you have 30 years experience with converters like the guys at Hughes then chime in. Frankly your exaggerated heat claims are wrong. My god you think a 1800 - 2200 converter is HIGH stall.

I'm glad that I have your permission to state 40+ years of experience, education, and observation.

No, I'm not talking about a drag race style high stall converter. Quit putting words in my mouth. A non lock-up converter always slips, slip in a converter is heat because the converter literally shears the fluid and that turns power into heat* in the working fluid. Below it's stall speed a converter slips up to 100% (idle), at or above it's stall speed the commonly bandied-about number is 3% slippage for a non lock-up converter. A converter with a higher stall speed operated below it's stall speed will turn more of the available power into heat than a converter with a lower stall speed that is operated above it's stall speed. That's an inescapable physical fact. If we arbitrarily pick 1800 RPM as the engine speed then your 2200 stall converter will be making significantly more heat than the OEM stall converter because the OEM converter has stalled by that RPM. No matter what the high stall converter's slip percentage is, it will be more than than 3% that the stock stall converter is slipping. On the street it would be uncommon for the engine to be at 1800 while at or near WOT for very long. Off-road it could and likely would be at that condition for a lot longer, and that will make a lot more heat. On the street that condition might exist for a few seconds at most. Off-road it can easily be several minutes or more. This is what I've been saying all along.

I've long known that the actual stall speed depends on the specific engine that it's behind. The converter maker might sell it as a "2200 RPM Stall" but the output of the specific engine will skew that up or down depending. I'll need to read up on k-factor.

*Fluid shear is EXACTLY how water brake dynos work. Do the energy conversion calc and the numbers can be frightening really fast. 300 HP can take 250 gallons of water from ambient to boiling in a surprisingly small amount of time. And even though the conversion calc is a iffy (no allowances for conversion loss because no idea what the conversion efficiency is) experience proved the calc to be very close to what actually occurred. Water has a higher Specific Heat then does AFT, so if we were using AFT as the dyno's working fluid it would take even less time to heat the 250 gallons to 212°

 

[Broncobowsher]

The math isn't that bad. 746 watts per horsepower. A watt is a watt, same watt in electricity as it is power.
746 x 300 = 223,800 watts. Nearly a quarter megawatt of power. To put that into scale, there was a coal fired power plant near where I went to school. It was built as a 200 megawatt plant. Once built they found they had enough steam to add another 20 megawatt turbine. 220,000,000 watts. 0.1% of the entire output of a modest sized coal fired power plant all dumped into 250 gallons of water for a dyno. Or a transmission, 3 gallons of ATF.
Another way to look at 223,800 watts, is if the voltage were 223.8V, that would be 1,000 amps. Tankless water heaters will bring cold water to scorching hot as fast as the faucet (or several at once) will flow, drawing in the neighborhood of 100 amps. That's half the rated power of the common new home electrical panel.

 

[DirtDonk]

Too bad that, AFAIK, the "Switch-Pitch" converters were only made for GM transmissions.

Haven’t seen that brought up in a forum for a long time. SwitchPitch is actually my username over on some Buick forums!

 

[ntsqd]

The math isn't bad, but I made no allowance for the conversion inefficiency(ies). As I had no way to estimate those I reasoned that the calc was severely conservative in that it would yield the shortest time to boiling and the goal was to know how long of a run time we could sustain. Real world was that as expected we could run longer than the calc predicted, but not by a huge difference. The upshot of that was that the borrowed ~500 HP Stuska dyno was returned and a ~1500 HP (?) Stuska and a 3500 gallon water tank along with a 20HP pump on a variable speed drive was obtained. Been several decades since then so some details are a bit fuzzy, but as I recall Stuska's aren't rated by HP anyway. I do recall that it was sized such that we could run the Olds BBC drag racing block based twin-turbo alcohol 600+ci tractor puller engine that one of the partners owned.

 

[Grey owl]

I'm glad that I have your permission to state 40+ years of experience, education, and observation.

No, I'm not talking about a drag race style high stall converter. Quit putting words in my mouth. A non lock-up converter always slips, slip in a converter is heat because the converter literally shears the fluid and that turns power into heat* in the working fluid. Below it's stall speed a converter slips up to 100% (idle), at or above it's stall speed the commonly bandied-about number is 3% slippage for a non lock-up converter. A converter with a higher stall speed operated below it's stall speed will turn more of the available power into heat than a converter with a lower stall speed that is operated above it's stall speed. That's an inescapable physical fact. If we arbitrarily pick 1800 RPM as the engine speed then your 2200 stall converter will be making significantly more heat than the OEM stall converter because the OEM converter has stalled by that RPM. No matter what the high stall converter's slip percentage is, it will be more than than 3% that the stock stall converter is slipping. On the street it would be uncommon for the engine to be at 1800 while at or near WOT for very long. Off-road it could and likely would be at that condition for a lot longer, and that will make a lot more heat. On the street that condition might exist for a few seconds at most. Off-road it can easily be several minutes or more. This is what I've been saying all along.

I've long known that the actual stall speed depends on the specific engine that it's behind. The converter maker might sell it as a "2200 RPM Stall" but the output of the specific engine will skew that up or down depending. I'll need to read up on k-factor.

*Fluid shear is EXACTLY how water brake dynos work. Do the energy conversion calc and the numbers can be frightening really fast. 300 HP can take 250 gallons of water from ambient to boiling in a surprisingly small amount of time. And even though the conversion calc is a iffy (no allowances for conversion loss because no idea what the conversion efficiency is) experience proved the calc to be very close to what actually occurred. Water has a higher Specific Heat then does AFT, so if we were using AFT as the dyno's working fluid it would take even less time to heat the 250 gallons to 212°

Hey pal you are the one who kept saying HIGH STALL nobody put words in your mouth. Your problem is you are just wrong about the heat issue and you can't admit it. So now you go off on some pointless rant about dynos. The simple fact is the additional heat added by a 1800.- 2000 stall converter can be easily mitigated with cooling upgrades. Nobody is going to get left on the trail with a converter failure. Your whole argument about the heat is ridiculous and baseless. Just like how you kept referring to the converter as HIGH STALL. Lets just agree to disagree.

 

[Grey owl]

I'm glad that I have your permission to state 40+ years of experience, education, and observation.

No, I'm not talking about a drag race style high stall converter. Quit putting words in my mouth. A non lock-up converter always slips, slip in a converter is heat because the converter literally shears the fluid and that turns power into heat* in the working fluid. Below it's stall speed a converter slips up to 100% (idle), at or above it's stall speed the commonly bandied-about number is 3% slippage for a non lock-up converter. A converter with a higher stall speed operated below it's stall speed will turn more of the available power into heat than a converter with a lower stall speed that is operated above it's stall speed. That's an inescapable physical fact. If we arbitrarily pick 1800 RPM as the engine speed then your 2200 stall converter will be making significantly more heat than the OEM stall converter because the OEM converter has stalled by that RPM. No matter what the high stall converter's slip percentage is, it will be more than than 3% that the stock stall converter is slipping. On the street it would be uncommon for the engine to be at 1800 while at or near WOT for very long. Off-road it could and likely would be at that condition for a lot longer, and that will make a lot more heat. On the street that condition might exist for a few seconds at most. Off-road it can easily be several minutes or more. This is what I've been saying all along.

I've long known that the actual stall speed depends on the specific engine that it's behind. The converter maker might sell it as a "2200 RPM Stall" but the output of the specific engine will skew that up or down depending. I'll need to read up on k-factor.

*Fluid shear is EXACTLY how water brake dynos work. Do the energy conversion calc and the numbers can be frightening really fast. 300 HP can take 250 gallons of water from ambient to boiling in a surprisingly small amount of time. And even though the conversion calc is a iffy (no allowances for conversion loss because no idea what the conversion efficiency is) experience proved the calc to be very close to what actually occurred. Water has a higher Specific Heat then does AFT, so if we were using AFT as the dyno's working fluid it would take even less time to heat the 250 gallons to 212°

 

[ntsqd]

Higher stall does make a LOT more heat no matter where you drive it, it's just less of a problem on the pavement.

No, I said higher stall, not HIGH stall. I was implying something higher than stock, which is what a 2200 RPM stall is. How you read that is beyond my control.

Out.

 

[Soylent]

Haven’t seen that brought up in a forum for a long time. SwitchPitch is actually my username over on some Buick forums!

Did you have a Grand National?

 

[DirtDonk]

Nope. No such luck! Mine was a 67 Buick Wildcat. With the 430 and TH400. Great car!
Not a Grand National, but a great car!

Did the GN have a switch-pitch converter? I thought that was a long lost technology by then.
The 67 had it, but it was gone by 68 if I remember.

 

[DirtDonk]

Test drove a GN at the local dealer once. Had the sales guy down to $13,000, but I just couldn’t justify another loan. Too bad too.
Shoulda woulda coulda.

 

[Grey owl]

No, I said higher stall, not HIGH stall. I was implying something higher than stock, which is what a 2200 RPM stall is. How you read that is beyond my control.

Out.

Lol,