Hey Guys,
I've got my 68 442 out and running around again but there's a fear that is always in the back of my head as I drive her around. When I first had it the 400 threw a rod, shattered a piston head and ruined a couple internals (luckily NOT cracking the matching # block). Well, I know these 400 blocks are NOTORIOUS for doing that so I'm always scared to death of it doing that again.

Now my uncle and I (mostly my uncle) rebuilt the motor really well and I have faith in his build, but should I be worried about having a little fun in this car? I mean when I hammer her she jumps to 5500rpm and though it's awesome, it scares me to death. Is my fear of driving this car with some "fun" rational?

 

Yeah, we've all been there, scared to death to really get on the happy pedal after a catastrophic failure.

 

Those are excellent, dependable street motors. Now the catch is was it rebuilt correctly? I would caution about living in the 5500 rpm range. No reason to really be there, no power to be made in that range.

 

Two solutions...

#1 Get a MSD 6AL box, and set the rev limiter to 5k....

#2 Build a 455 to play with, wrap up the 400 and put it in the corner.

Option #1 is considerably cheaper than #2

 

Here's my problem though, It's an auto trans (working on a manual one for the future) so when I hit it, the kickback cable sends it down and that's when my revs jump to that range.



Hey Rambow, Option #2 is my future goal when I finally re-do this car right, just so when I can have a motor to play with and have the original #'s matching motor on the side.
Do you have a link to option #1?

 

www.summitracing.com

in their search window type "MSD 6AL"

There are other ignition boxes that also include rev limiters.. If you aren't aware how they work, I'd do some research just so you understand whats going on.

The ignition boxes serve several purposes, the rev limiting is only one of them.

 

Thank's so much! I just finished watching some videos on them. Definitely something I wanna look into buying, not just because of the rev limiter now

 

Doesn't the newest Pertronix have a rev limiter as well?

And, does your trans have a shift kit? Because if it's stock, it shouldn't rev past about 4500.

- Eric

 

It's not the original th400, it's a th350 built with a shift kit. But, it only does that when it I hammer it and it down shifts. If I hammer it from a start it won't rev that high, it shifts somewhere between 3500 and 4000.

 

If you're worried about overrevving, and you've got an automatic, I'd change the shift points and not worry about it.

- Eric

 

I'm a newbie at this stuff, and am literally learning as I go with this car. Like I said, my uncle does most of the work and I learn from him. Unfortunately he's in Florida until summer. Is there anyway you could explain to me how to do this or point me in the direction of a tutorial or something that explains how to do it.

 

Well, Ummmm... Actually, No.

I have only the most general knowledge of automatic transmissions, because any car I've ever cared about had a standard.

Basically, though, shift points are determined by the fluid pressures in different circuits, and those pressures are determined by a centrifugal governor (or speed sensor), a vacuum modulator (or engine load sensor), and a way of sensing engine RPMs. When you install a shift kit to improve performance, you alter the settings of a number of valves and orifices, to raise the shift points (to match the power curves of high performance camshafts) and to make shifts "harder" (faster locking), so as to lose less power between shifts.

Just as you can raise shift points, you can lower them as well. If your car is equipped with a camshaft that needs to rev to 5,500 RPM to reach full power, then one would hope that the rest of the engine was built to take those speeds in stride. If it is not equipped with such a cam, then there is no benefit to revving it that high, and, in fact, it might be harmful if the rebuild did not include higher-RPM improvements.
If you have a high-revving cam, as mentioned, then you will lose performance if you lower the shift points, but if you don't have one, then you may actually gain performance, as you will be shifting closer to the actual power peak of the engine.

The bottom line is that you need to know what's inside your engine, how it's set up, and what kind of conditions it was designed to survive under.
I'd get in touch with your uncle and ask him the questions you've been asking us, as he has an intimate knowledge of exactly what went into your engine and why, and can likely answer them better than we can, and we here collectively know absolutely nothing about it at all.

There are a number of sites out there that have good information about the function of automatic transmissions, but I do not know specifically where to direct you. Your Chassis Service Manual has an excellent section on the operation of your automatic transmission, with very nicely produced full color fold-out diagrams of its functions under every condition. I'd recommend starting there, as the CSM is one of the finest, and most often overlooked, sources of information about the way your car works.

- Eric

 

or just buy a rev limiter, set it at 5k or 5500 and don't worry about it.

LOL. Seriously, trying to set the trannys manual shift points via the governors is a PITA, even for people who know how to do it...

On another note- fixing the trannys automatic shift points still won't help you if you accidentlayy shift it into neutral while wide open- or if something in the rear breaks while your wide open and it free revs.... The limiter would save you in those cases.

 

All true, and I would never discourage a rev limiter.

My only question is, If the trans has a shift kit that raises the shift points, and you rev limit the motor, doesn't that mean that in a full-throttle situation, the transmission won't shift up because it will never hit its shift point?

- Eric

 

Check your tach. My 455 pushes to 5000 rpm's and is still pushing plenty of power. I haven't checked it yet but I'm pretty sure the tach is off.

 

That was my concern as well

 

The transmission shifts up on its own under partial throttle, regular drivign right?
The way i read your initial problem, you describe where it won't shift up only happens when you are wide open, correct?

If it doesn't shift until 5k+ under regular cruising conditions, you've got some other issues besides the governor.

But as long as it shifts normally with normal driving, then you are fine.

If the motor winds up and bounces off the rev limiter and it hasn't shifted up to 3rd yet, it will shift then, just as if you let your foot off the gas and coasted.

MOST automatic transmissions have the opposite problem, they shift way too eary for anyone looking for performance... IE: 3500 upshifts to 3rd.

I know some drag racers who have extensively tweaked their governor springs to get their upshifts right at peak RPM in each gear, so they can just leave the car in drive during the race- very consistant times.

on the street though... its easy, if you want it to shift up, just lift your foot off the gas.

 

My problem is down shifting. If i'm in say second, and I hit and the kickback cable goes and it shifts down to first that's when it'll rev high, up to 5500 before shifting, sometimes even jumping down right into the 5000 - 55000 range.

 

i know how you feel i had a '66 ford galaxy that went up in flames and now every time i drive a carbureted car i fear it will burst into flames lol i always keep fire extinguishers in the olds in case something happens i would hate to lose another classic!

 

.... Ok you clarified the problem a bit...
I was thinking that it was simply not shifting after a regular windup TO 5k or 5500...

But if you are kicking it down from 2nd and it instantly jumps to 5k or 5500, you are just going too fast for 1st gear. its outside the operating range, and it takes the transmission a few seconds to upshift.

If you do it from a dead stop, i'll bet it up-shifts around 3500 or so.

is this a Th350 or Th400? If its a Th350, your TV kickdown cable is too tight- and a TH400, you need ot bend the switch away from the pedal... In both cases you just need to make it a little HARDER to kick it down, and need to adjust the cable or switch to activate later.

You should not intentionally be trying to kick it down to 1st gear if going that fast.

 

Yes, at 3500 is about the time my trans shifts from a dead stop, which is great. It's when it kicks down, and it is a th350 so it uses the kick down cable. Thanks for the advice! I'll definitely look at doing that. Maybe I just shouldn't hit the pedal so far at higher speeds lol