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LittleWeb · 04-11-2017, 09:36 AM

I have a locked up 454 in a 1987 pace arrow that my wife and I are emotional attached too. So I am planning to raise it and drop the engine and transmission out the bottom. I have a replacement motor being built from a local racing engine shop. I am researching what to do with the transmission? I would love to get the another gear to get the RPM's down at interstate speeds.

Skip426 · 04-11-2017, 10:05 AM

Welcome to iRV2.

Sorry to ask all these questions, but providing more info on your set up could help other members give info on a possible transmission upgrade .

Is the current trans only a three speed ?
Do you know the GM designation for the current trans ?
Is your 454 , a carburetor or TBI engine ? Sorry to ask , but I'm not sure what year GM completed the change from carbs.
Have you made the engine shop aware of your intended use for the motor ?

GlennLever · 04-11-2017, 12:33 PM

These guys make overdrive units and have been in business forever.

Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.

LittleWeb · 04-12-2017, 07:49 AM

Good morning;
I just discovered this forum and I plan to make it a part of my leisure life.
I was hoping to answer alot of questions. The engine shop is aware of what I plan to do with the engine. The tranny is a three speed, and I am not sure of the designation but I have seen a couple similar salvaged trannys that were "short shaft". I did talk with a transmission guys that said if i replace it a with the a 400 i would need to shorten the driveshaft. It has a carb. I believe it is quadrajet.

GlennLever · 04-12-2017, 08:30 AM

I would be surprised if the transmission that is in the motor home isn't already a turbo 400.

It was GM's go to heavy duty transmission and there are a lot of them out there.

They came as both a short and long snout of the back. Trucks generally had the short snout.

Shorting a drive shaft is not a big deal and any drive shaft shop can do it.

You do want to make sure the shop has a "lathe" that they can spin the drive shaft on and balance it after it has been shortened.

Skip426 · 04-12-2017, 06:42 PM

Next thing to find out is if the newer version of the 400 , a unit with O/D can be adapted to a carb equipped 454, then to look at the rear end ratio and the O/D % to make sure that the shift into O/D doesn't drop the engine RPM, at highway speed out, of the engines power band.
No sense having an O/D in the transmission if the trans is constantly downshifting due to lack of power.
I've owned a truck that had this issue , any kind of slope of the road would have the truck downshift at highway speed.

Even running empty.

Nick-B · 04-13-2017, 05:40 PM

An '87 possibly '86 GM chassis would have a TH400 or TH425 (beefed up TH400) and carburetor only. The GM 4L80E is basically a TH400 with a 4th gear. They are electronically controlled but there are solutions. Google is your friend!

Deano56 · 04-16-2017, 05:14 PM

Quote:

Originally Posted by Nick-B

An '87 possibly '86 GM chassis would have a TH400 or TH425 (beefed up TH400) and carburetor only. The GM 4L80E is basically a TH400 with a 4th gear. They are electronically controlled but there are solutions. Google is your friend!

I believe the TH425b was a transaxle setup for large front wheel drive cars such as Cadillac or Eldorado. The 4L80E was rated for vehicles up to 8000 lbs. They did make a 4L85E which was good for 16,500 lb and an engine that would produce 460 ft lbs of torque

Jpony56hd · 05-21-2017, 12:41 PM

Although our 88 Gulfstream is Ford based, having gone the Hot Rod motor route a little over a year ago, I have a couple pointers. I got tired of my 460cu in 160hp slug and decided to do something about it. I built a performance Engine, lots of cooling, remote oil/trans coolers BUT missed a Big One. The Transmission! My C6 had 40k on it and was flawless But Stock. Within the first few hundred miles, it destroyed the torque converter(to much HP), replaced it with a Welded performance unit. A few hundred miles later it took out the clutch pack. I Now have a performance Transmission to go with the Engine.

Bubba1 · 05-22-2017, 12:34 AM

You should be able to use the 700R4 transmission. It's basically a turbo 400 trans with overdrive. It can easily be built up to match whatever HP your new engine makes. Can be used with carbureted engines.

Mike H

LittleWeb · 08-08-2017, 08:43 AM

Good Morning,
The project has been slow but we are making progress, we have removed the
seized stock 454, radiators and transmission. I had the turbo 400 rebuilt with a 6 clutch performance package and new torque converter, it is back in place. The engine has been bored and rebuilt which should put out 475 hp. We are currently replacing the motor back in the RV. We are looking at the cooling system and how we can improve that. We are replacing the four core brass and copper radiator with aluminum core and we are removing the air conditioner from the engine.
The question I have is :
The carburetor was a quadrajet and i am wondering what to do with it. The engine rebuilder said I need at least a 750 cfm. I want to keep the cruise control.

spritz · 08-08-2017, 09:32 AM

Morning,
I'm just adding my 2 cents worth. I have 82 PA with the 454 carbed motor, I too think they should have put another gear in tranny even a 60 it seems like its whining.
I replaced original copper radiator with a aluminum radiator into my 64 caddy with a 429 . She runs almost 40 degrees cooler.

No problems with performance.
I'm having a hard time finding one for the PA though. If you find one let me know. I'd appreciate it.
Tim

Jpony56hd · 08-09-2017, 01:49 PM

As for the radiator I had a Summit account and got a Performance Radiator from them. It was Not a bolt in unit and mounting adaptors had to be fabricated. Several of the companies that make aftermarket units will custom make radiators to your specifications but it costs $$$. I used a large pull thru electric fan and used sheet aluminum from the grille opening to the radiator to aid in cooling air flow. As for the carb, I had to go with a Holley as I needed 850cfm due to my engine specs. I do believe there were 750 Qjets on the 427cu in and 455cu in 70"s muscle cars. Excellent idea to rebuild the transmission. I had a good low mileage C-6 and thought it would be ok. Not So! Within the first 200 miles the Torque converter destroyed it's self and next the clutch pack gave up.