Recommended stall speed?

[olds307 and 403]

Not a dumb question, I wondered the same thing on slippage. A good lock up converter with a better clutch should not slip, no matter the power. Does that still apply to a decent non lock up converter? I am considering the Hughes 2500 stall BOP non lock TH350/400 converter for my 70S. I do run just an external trans cooler and don't want any higher highway rpm.

 

[Canon_Mutant]

This is why I always hated getting talked into a 3200rpm non-lockable converter [didn't know what lockable was yet] in my old Impala 327 with a T400 behind it and 3.08s. Truthfully, powerband wise, a stall speed that high made sense the way my small block was setup on the track but driving on the highway was a complete PITA [We'll leave why the Impala needed a big block for another time]. Now, if I had REALLY tall gears out back it would have run more respectably on the track [for back then] but then you've got other problems trying to drive 70. Though mostly 55 signs back then it doesn't mean we ever drove it. But, at just 55 with 3.08s was 2200, not 3200. Of course, it was also a 70s tech hi-perf converter [don't know how much it has evolved?] but always seemed like most highway driving had 3rd gear slipping and the extra transmission cooler was a must. Oh, but it was cool because Garth had a transmission cooler on his Chleby!

Anyway, short story long [sorry], that is why I always suggest being conservative on the converter stall speed unless you are living on the track? Street cruiser? If you know your cruise rpm is less than your stall speed, there will be slippage and extra heat. Assuming your "2500rpm" spec'd converter is based "on your" engine setup, you are going to want at least 3.08 gears or higher on 26" tires at 70mph. Put some 3.42s behind it and you really wake the ole girl up in the occasional skirmish, your cruise range will always be above 2500 even at 55, and your gas mileage will $uck. Keep the 2.78s, 2500 will be fine at 70, better mileage, but not as much in a skirmish . . . always a trade off. Lots of 55-65 around you? Taller gears or lower stall speed on a street cruiser, IMO [I vote taller gears]! 70-80 like most places, you're fine.

Place diverging opinions here

 

[olds307 and 403]

My 70 will never be a mileage machine, I want to get the 424ci 403 stroker done by next winter, just need a girdle, studs, cam and main bearings. I plan on adding a Lockright and keeping the 2.78 gears. Right now with about the tallest 14" tires, it revs at 2400 rpm at 60 mph, so 70 mph should be perfect and I only run the external trans cooler.

 

[motorheadmike]

Who builds an old car for mileage? Buy a Honda.

Get a big engine, a loose converter, and some tall gears and have at it. If you need something that drives well on the highway there are plenty of overdrive transmission options - don't self limit, make the compromise and burn the fuel. Especially in the US, your gas is so much cheaper than ours.

 

[olds307 and 403]

Planning on 424ci SBO, 2500 stall and 2.78's with a locker with 26" tall slicks at the track. A 4L80E is a PITA and so is a 5 or 6spd manual to install plus $$$. My 88 Cutlass should get 30 mpg, I don't want single digit mpg or 3500+ highway rpms out of the 70. Premium is $1.25 a liter here in Melville,Sk Canada.

 

[Canon_Mutant]

Who builds an old car for mileage? Buy a Honda.

Get a big engine, a loose converter, and some tall gears and have at it. If you need something that drives well on the highway there are plenty of overdrive transmission options - don't self limit, make the compromise and burn the fuel. Especially in the US, your gas is so much cheaper than ours.

Well, at the bottom of Olds307 and 403's credits, it said 9:1 350 and 2.78 gears so I assumed this was a cruiser.

But, as for "go buy a Honda" . . . it is not a matter of building it for mileage but just efficiency. Maximizing performance AND mileage. Trying to make and older car more efficient like the newer ones is not impossible.

As I've posted elsewhere, I can actually make the next potty stop with mine before I need a refill . . . and it would hit 60 in 5.2 with NO traction on the old setup. Now, yeah, I've got overdrive and a dialed in CCC and may eventually go EFI [all advantages] but that doesn't mean without these things you need to just dump gas out the freakin' tailpipe and have a car nearly impossible to cruise anywhere in?

My current bladder's gas mileage requirement is 18-20mpg which I could do before the current state of scatter. Right now, it doesn't get such great mileage laying all over my garage floor . . . so hopefully that's going to get better eventually.

But, I'm actually anxious to see how all the suspension/wheel/tire changes I'm making and the 3.73 up to 3.42 gears help to improve both? While helping mileage slightly, higher gears with all of that torque isn't necessarily a bad thing for performance either and it should be better on an auto-x or road course cuz I'm more interested in twisties and canyon carving at this point than purely ETs. True, a different power band than the huge bore small block above but I'm running Bowtie's 2200 [spec'd] that feels more like 2400 with the torque I'm making but it works great with my foot in it. Of course, I've got lockup so my 1800-2200 cruise range [soon to be dropping slightly] doesn't roast the torque converter or the transmission. And, I just ran the new PURDY stainless lines right into my 4 row. No cooler required . . . but I've got a temp gauge anyway just in case?

Just wasting gas because you are putting cubes under the hood is [well] just wasting gas but I thought he was asking for a recommendation and it sounds like the mind is already made up . . . put in a 424 and floor it! Nothing wrong with that . . . but I didn't know that!

Just sharing ideas and options here peeps . . . thought that is what this place is for?

 

[olds307 and 403]

I was disappointed with my good running 9 to 1 Olds 350 with the part throttle leaned right out to the point where it actually caused a higher rpm miss. I can adjust the part throttle in 2 minutes on the Qjet. Also a lot of part throttle timing for 9 to 1. I had to switch from a 30 degree can to a 20 degree can, lost some crispness but elimated some bucking under load. With a 2004R and 2.78 gears running around 1700 to 1900 rpm on the highway using non ethanol premium, I got 19 mpg Imperial, not impressive. The 424 will make massive torque compared to the 350, no that launch is bad with it. I would like either 4L80E with a 3.42 posi or a T-56 and a 3.90 posi but you need one with the other and both will set me back at least $1000 dollars and probably more for the trans. I figure 350 hp/450 ft/lbs with iron SB heads or an easy 400 hp/500 ft/lbs with Procomp heads. I just hate cars that rev to the moon on the highway and getting to anywhere is a distant to travel up here plus premium is $5.00 a gallon up here and the price is on the low side right now.

 

[Canon_Mutant]

Sounds like a plan to me . . .