ok the bug to repower is not as strong now as it was several hours ago. It sounds like even after repowering my fuel economy may not improve a great deal. My 454 is a perfectly good engine with less than 50,000 miles. I wonder if the 3 speed transmition is what is killing the mpg. Todd

quote:

I wonder if the 3 speed transmition is what is killing the mpg.

Sometimes its the absence of that raw egg under the right foot.

Todd as I have posted before, the 454 with a carb has fuel consumption only limited by the size of line going to the fuel pump.

I look at my fuel consumption on a yearly basis, as part of our pleasure budget. It doesn't seem so bad that way. Another way to look at it is to take your expenses for one trip and write down the figure. Then calculate the same trip with better mileage. Consider the amount saved, and think of cheaper ways to save that amount instead of trading engines or coaches.

Now, if we were on the road a lot, with 3-400 miles a day, things would look different. For example, Rusty and MWrench have a different set of numbers than we do.

Sometimes, a person just does an engine swap because he can. Or he wants to.

Rusty, I agree that the 6.5 T/D would be a good swap. I know that the 6.2 was an option on my 86 P-30, and the accessorys are basicaly bolt on. I am interested in your gear ratio. I am running a 4.56 with 19.5 wheels and I think with a 4L80E would be close. Think I remember yours as a 4.10, If I made the swap it would be in a 31' Regal. I pull a 3000 lb trailer most the time. My coach GVW is pushing the max 14,500, I like my BBC, but the thought of 10+ mpg sure would be nice. Just asking for thoughtful input.
Doorman

I may be talking out of text here, but without a doubt a four speed automatic trans will definitely make a difference over a three speed automatic in an auto or truck. So, I gotta believe that it would be the same in a RV?

I think my diffy is 4.10:1. And if IIRC, the 4L80E's OD ratio is 1:.75.

My GVW is 16,000 lbs., but I usually run at less than 15K.

With the Sun Coast Converters TC, spline shaft, and HD rebuild, my 4L80E can handle 850 lb.-ft., up from the stock 450. The AMG engine is rated at 230HP/430 lb.-ft. (Up from 190/360. Fuel economy averages around 11.5+ mpg.

If I were doing an engine swap today, I would seriously consider a trans with a locking converter. A powerful engine and a heavy MH with toad makes for a lot of heat in the converter. A lockup converter gets rid of a lot of this. The normal way to get rid of the converter heat is to put in in the engine cooling system, either directly through the heat exchanger in the radiator tank or indirectly into the air that is supposed to cool the radiator.

That's why a 4L80E and not a TH400.

I think the best "bang for the buck" would be an overdrive unit. Gear Vender Overdrive is a solid unit and several members here have them.

quote:

Originally posted by Bill N.Y.:
I think the best "bang for the buck" would be an overdrive unit. Gear Vender Overdrive is a solid unit and several members here have them.

There is no doubt about the durability and repair-ability of a TH400. Same for the GV, as long as you don't do engine braking with it in OD.

The 4L80 or 4L85E is not rated for the torque of an HT502, but it is only 10% under. I mention this in reference to the title of this thread. Perhaps gentle throttle and shifting techniques could let you cheat a little. For example, my kickdown switch is disconnected, so I can avoid full-throttle downshifts if I choose. I also back off a little on the throttle to allow the modulator avoid full-throttle upshifts. I also avoid high rpm downshifts on engine braking, or setting up a powerslide out of a corner. The same techniques can make any automatic trans last longer.

The 4L80E or 4L85E is more difficult and expensive to repair, as well. A TH400 can be rebuilt alongside with no special tools, save a little metal flashing from the hardware store. Not so for the 4L80E.

The 4L80E/85E are electronic trannies and require their own computer to operate them in an engine that does not have the matching inputs. Or, there are some aftermarket manual shift conversions out there. I just can't remember who.

The 4L80E/85E trannies have two strong virtues, that could very strongly influence the selection process:

1. A lockup torque converter. This saves a little gas and avoids a lot of overheating of the fluid seen in hard use of a non-locking converter. Packard did that in the late '40s, but it took GM a little longer.

2. A built in overdrive, effectively making it a 4 speed tranny. With the right computer, it is really nifty. We have a truck with one, and it works well. I am saving up for its eventual rebuild or replacement, as they have a shorter life than a TH400. The built-in overdrive makes the integrated unit shorter than a TH400/GV setup. This makes usage of an H pipe or X pipe a simpler installation, and allows more forward placement of either device.

My suggestion for whichever trans is chosen, is that a performance rebuild be done by a reputable performance tranny builder. There are a lot of improvements that can be done by the right shop. Even though the 4L80 series is not used by as many racers as the TH400, racers have them in their tow trucks, so there is a good knowledge base out there.

My own two cents is to go for the crate 572 from Chevy, use the ZZ502 cam and oval port heads with a Weiand dual plane manifold. Or the Arizona Speed and Marine injection. GM sells this unit, too, but I don't know the number. Behind it an Allison 6 speed. The one they put in garbage trucks. Between the weight and the operators' throttle habits, I believe this is the worst service for an automatic transmission, and Allison built them accordingly.

I haven't seen anything like this before! An LS Chevy engine, put in a 1970s SOB!

The sound of the drive bys is amazing....

I've started the video at the best part...

https://youtu.be/oKj5pAZTuVc?t=284

There is apparently a series on youtube series of videos of the work being done....

Happy Motoring,
Matt

cool huh!!!