Thank you Joshua. I appreciate your working that out.

Lou, I also value your judgement on this. I think the lockup 904 makes the most sense. I have decided to start collecting the parts for the switch, but am in no hurry to tear into it. It drives too nicely now to mess with much. Refinement is now the name of the game.

Sam

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I think the 904 is a wise choice,but just to be sure why not cruise around for a week or so without using the overdrive in the T5 to get a feel for what it will be like with a 1/1 final drive ratio? I ran a th700 behind a265 Hemi 6 and a 2.92 rear end,it was OK. The 265 would make a ton more torque than a 225 and I found it sufficient.I now run a 318 stroked to 349 and a A518 with a 3.23 rear ratio,it works really nice. What in getting at is it would take a lot of careful decisions to get a 225 auto overdrive working in a relatively heavy car,the lockup feature would be taxed pretty heavily I would have thought. There is also a lot of fabrication to do,the easy part is mating it to the engine!

One thing that makes this decision more difficult is I do not know for sure what the cam is in this engine. It was custom ground for the turbo application, and then the turbo came off. It seems to have a ton of torque, and lives nicely with the current overdrive combination. If I cruise in 4th at 40-45 MPH it pulls 15-18" of vacuum on level ground and seldom slips below 10 on the hills. Of course drifting downhill it pops up to 20 or maybe a tad over. That would be down into the 20% VR row on the computer. This engine will actually accelerate in 4th gear at 1200 rpm without complaining. It does not like to rev over 4500, and lives most happily between 1600 and 2200 rpm.

I am pretty sure the cam is some kind of RV grind. For what it is worth, the cam grinder said he spread the overlap of the centerline a few degrees so as to minimize blowing the incoming charge out the exhaust. This goes beyond my memory a bit, and beyond my expertise for sure. Doc would know what this meant. I will try to dig up the cam card, but have not seen it for awhile.

If I go with a lock-up 904, I have the choice of electronic, or hydro mechanical. If electronic, then I could make the lock up feature manual, on the shifter, and take full control over when it engages, just as I do now with 5th gear. Another choice would be to use the ECU to control map and rpm for lockup. I would have to give up the ECU control of the fan for this, but that would be a minor concession.

How much does the rpm drop when lock up engages on a lock-up torque converter? I want you guys to know how much I value your input on all these ideas. You can read on line all kinds of things, but unless you know the source, the information is of questionable value.

Sam

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Sam my stock truck 85 truck has the lock up convertor and it works fine. It does try and lock up a bit early for me and I have a shift improver kit to install that will take care of the early lock-up issue. I would guess that when it locks up it drops the rpm 2-300 rpm. I don't have a tach. Others have told me that it may be worth 1-2 MPG on the highway.

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I have done research on the 904 lockup, and I can get reman with either hydraulic or electric lock up. The electric is about $200 more. What are the pros and cons of both? I think I could pick a map and rpm to have lock up happen with my ECU. But if hydraulic works fine, I would be happy with that. Rick C has already reported that his hydraulic works fine. Any bad experiences out there with either? Thanks as always.

Sam

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Sam- it is possible to fine tune the lockup point as well as eliminate the lockup altogether by installing a stiffer spring or shimming a spring on the top of a hydraulic valve body. Chrysler even had a factory lockup shudder correction kit for the late 70s lockup 904s that consisted of nothing but a stiffer spring. I have been driving Mopars with lockup 904s for years and never had a problem with them (unless they were worn out and needed to be rebuilt, and even that is a breeze).

I say go with the hydraulic and avoid the headache of the electronically controlled lockup.

Thanks Reed. I am now trying to figure how I can get the cruise RPM quieter with no OD.

I did as Steve suggested and drove the car around in 4th all day, (well, not 5th anyway). I found out one of the major reasons I want the overdrive: I really dislike the drone that gets set up in the exhaust at 2400 rpm. When I do shift to 5th, the rpm drops down to just around 1900, and the exhaust gets quiet. This is huge to me. Admittedly I could put better mufflers on, but I remember quite well how the stock muffler got noisy when I put 2.25" exhaust on this car. If I can cruise at 2K, I am happier. 2500 rpm can be very annoying with that pipe diameter and length. And this is with resonators on the end, which quiet it down some.

Joshua I did some more careful calculations, and it seems you are right about the rear ratio being 2.93. It cruises at 52mph @ 2000 in 5th. When I divide 40 mph by the 5th ratio of .79, it comes up to 52mph. 2.93, is the number the calculator returned when entering 40mph at 2000. I am pretty confident in the correctness of the 52mph at 2k in 5th.

Sam

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I understand completely. I usually drive my van on the highway, and any kind of drone (exhaust, transmission, tires, whatever) gets old really fast. I much prefer a quiet vehicle.

That being said, how much energy have yo put into sound deadening and insulation? I have been researching how to make my van be as quiet as my Lincoln when I drive it. Over the past few years I have found THIS site to be very useful in planning how I am going to soundproof my van when i get around to gutting the interior and redoing it.

Are you running a single muffler or do you also have a resonator (a la the F body system)? You might consider adding a resonator under the trunk.

Maybe go to a 2.76 rear?

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Based on all comments So far, here are my leanings and a possible sequence:
1. Purchase and install 904 with hydraulic lock up.
2. Maybe bigger wheels and tires.
3. Maybe real mufflers.
4. Maybe downsize tail pipe (after mufflers).
5. Better sound proofing.

This is a long term project. I will need to collect all the peripherals such as dip stick, shift levers, neutral lock out switch, shifter, yoke, driveshaft, inspection plate, flex plate, etc. It may be awhile brfore I know how I feel about the gearing and the noise. In the mean time all the comments here have been helpful. Thanks.

Sam

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Sam, I totally agree with your wife on transmission choise! I am currently driving an old Mercedes Wagon with a 4-speed manual gearboc, and I HATE IT! I really like a good manual 5/6-speed in a sports car, but that's it!
Besides, I makes me suddenly feel very old, when I roll up to a red light and stall the engine because I forget to engage the clutch!

I have a '80 904 w/lockup in my '77 Aspen Wagon now, and it broke down recently. There are a couple of things I will modify during the overhaul process, you may want to do the same mods on the lock-up 904.

A 'shift correction' package (not a 'shift' kit) may be a useful thing to apply to the valve body, before you mount the 904 in the car. It just open up some of the holes for improved oil flow in the valve body, and replace some springs. It will improve shift quality and lower the strain on parts. It also gives you the opportunity to adjust the activation rpm for the lock-up function. Raising the speed for the activation of the lock-up function is actually a major issue! You will absolutely hate it when it engages too soon. The '78-79 versions locked up far too soon, the '80->up is a little better, but you should definitely prepare yourself for an adjustment.

Oregon Performance Transmissions-Shift-Correction-Package

My engine speed drops about 250-300 rpm on lock-up, and you should see a ~2-3 mpg improvement on fuel consumption.

I remember postings here from a member with a truck, where he describes using a button to actuate the lock-up on an electronically controlled 904.

Aggressive Ted has a good recipe for cutting exhaust sound, without cutting performance.

Olaf

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Aspenized

That is the kit that I have for my truck too.

Sam, you may talk to Charles Brooks (Bigslant6fan) about the lock up transmission and how they shift. He is pretty knowlegable about them.

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I agree, that seems like some kind of RV grind. And that totally explains why you're happy with a little 225 at 1900-2100 rpm on the highway, which is about where the average stock 5.0 Mustang lives (my '89 was 2000 at 70mph), when both of those examples are roughly 3000 lbs. (Looking at the behavior of a 6000 lb truck is useful for concept... perhaps not for direct comparison.)

All the stories about getting better mileage with 3.23 than 2.76 have merit-- IF you're running a stock cam where the engine can't breathe as well down low. But you've seen that your combo can handle it. (When you find those cam specs, I'd love to know more.)

I also totally agree with the exhaust drone problem. Since you already have your target RPM in mind, I'd highly recommend not losing sight of it. Sitting in a drone machine will make you wish you sold the car instead of doing all that work on it.

To match the .79 overdrive and the current 2.93 gears, you'd need an equivalent of 2.31 behind a non-overdrive transmission. Good luck finding that. And if you did, you'd be so underwhelmed with 1st gear acceleration that.... well, that would be the other reason you'd wish you sold it. For the 8.25 axle I've heard of 2.76 gears, and I think maybe even 2.45 but my memory says there's some kind of special carrier needed to make it feasible in the housing. That was a direction that manufacturers went in the 70s with the first gas crunch, and cars ended up being very non-exciting slugs to drive. Overdrive is probably the major factor to a muscle car revival in the 80s and 90s. Sure does increase the fun factor!

My own experience with many different stick-shift cars is that a total gear ratio for off-the-line (that's 1st x rear gear) that feels good is about 9-10. (IE. 3.09 first x 3.23 rear). Too much more than that presents traction problems on the street, especially without limited-slip. Another issue: with a total 11:1 or 12:1 gear and an engine that runs like you describe, I'm ready to shift out of 1st before I'm even halfway across the intersection. An automatic wouldn't need quite so much, thanks to the slippage of the torque converter.... The typical slant six automatic in the 60s would have been 2.45 first * 3.23 rear = 7.9:1. With the low end torque you describe, you'd need even a little less... might be happy with 7.5, but I don't think I'd attempt below 7.

Drag racers can just ignore the prior paragraph. You guys live in a whole different world.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Just to throw out a suggestion here,have you considered the A500? The 904 is by far an easier swap of course,but it sounds like you have your car so well set up for an overdrive it would be a shame to lose that luxury. You have already modified the rear cross member for the T5, the A500will need more space back there,but all the 904 linkages etc will fit. The critical thing of course is fitting it to the slant ,but I thought I read somewhere there was a smallblock to slant adapter on some slant six powered cars so they ran a 727 with the low mounted starter? These parts may not be around anymore,just thinking out loud!

Didn't Lou run a 500 in his 68 using the A100 slant to 727 adapter? If so, I'm sure he'll chime in this topic. I have one of those adapters and the eventual plan is to go with the 500/518 in my 87 D100.

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65 Dart station wagon slant 6 - now under construction
47 Dodge Custom 4 Door sedan
87 D100 Short Bed slant 6

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