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Old 08-12-2017, 06:19 AM   #1
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1991 35' Airstream 350
Georgetown , Kentucky
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Engine in 91 350 LE question

Hello all. I recently got a 91 350 LE CLASSIC that has 46000 miles on it and at about 30000, the engine was changed from the 454 to a large block 502 with a supercharger. My question is what is the performance like of the 454 that required this upgrade? I drove this RV back across the states and even with the 502 and the supercharger, it could only maintain maybe 25 to 34 mph over the mountains and I didn't expect that. Is that better than the 454 performance??!!! If this vehicle is just to heavy, should I consider a diesel conversion and if so any ideas on what such a conversion might run?? Thanks to all in advance. Brad Bentz
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Old 08-12-2017, 06:22 AM   #2
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1966 26' Overlander
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the 454 is a semi reliable gas sucking hog that developed lot of heat. Your motorhome is large and heavy and might benefit from a Cummins diesel conversion. There are other here that have done that and you can read their journeys.
Use the search to find them.
I'm a former owner of a Classic 82 28 footer with A 454, but there are owners of your model who will add to this.
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Old 08-12-2017, 06:49 AM   #3
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As I mentioned in your previous thread, I own the same coach.

Mine is stock, and it's performance is about the same as you describe.

Assuming the rest of your drive train is unmodified, I would say that is about as good as it gets. The P30 chassis these motorhomes are built on was designed in the days of 55 mph speed limits and the 350LE body was pushing the upper limit of the chassis.

To make them travel at 75 mph and climb hills in the fast lane, one would need to replace just about every part of the drive train and steer axle. The stock transmission is just 3 speeds so it is hard to keep the engine speed in the power band in all situations. The front axle was nearly overloaded, so new steering components and heavier springs would be required to keep the thing in your lane at higher speeds.

It is difficult to balance the desire to improve the performance with remembering it is 30 year old machine.

We learned to take our time and enjoy the trip.

If we are traveling a long way or need to make time, we take the trailer.



Regards,

JD
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Old 08-12-2017, 09:56 AM   #4
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well stated Jeff. These are older bread trucks basically. Imagine driving a bread truck over the mountains.
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Old 08-12-2017, 04:21 PM   #5
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Cool 345 performance

I have a 345 which we tookoout west with the 454 engine. Going out of Bullead City Arizona the big hill. I hit 30 mph. with the temp gauge at 400 degrees. The unit is radically underpowered. I don't thhink the P32 front chassis can take the weighht of a heavy diesel engine. I would suggest that you do what I did & park it in the woods. Buy a nice airstream treailer & pull it with a diesel pici up truck Preferrabaly a Cummins engine.
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Old 08-12-2017, 05:41 PM   #6
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come'on chaps!

Let's understand that even at 341/2 feet the 454 was at it's limit. Adding another 6" and a 1000 lb of Corain counter-top and oak cabinetry just to round out the weight to 16,000 lb did not help the situation. As an owner of a 350LE, I've learnt to live with a drastically under-powered leviathan meaning take hills as gently as your first kiss, keep the revs under 3500, sit back and just enjoy the experience of owning the pinnacle of American RV engineering albeit 30 years ago.
I must say reading of a supercharged 502 makes my eyes water as I looked closely at an upgrade to a 502 before sinking $7500 into rebuilding my 454. Of the $7500, around $2000 was labor. I seem to remember that the 502 crate motor was priced at around $6300 ($6500 with shipping) so running the numbers and being a cheap-skate at heart,I stayed with the 454. I would think that a supercharged 502 is producing more horsepower and certainly more torque than a stock 454 so my guess is your gearbox and differential ratios could be upgraded. You could also lash-out on a Gear Vendor's overdrive unit as around $3500 to take advantage of the 502. Maybe other, more erudite Forum Members can comment but stay with the plan and cherish that 35 feet of unsurpassed 1991 luxury, preferably sitting beside it as the sun sets on some idyllic spot that warms the Jack Daniels in your goblet! Cheers!:lol
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Old 08-13-2017, 09:33 AM   #7
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true! I used to enjoy the cruise up mountains, slowly with my 454. And a shorter motorhome. You can actually take in the view and stops at a scenic overlook.
WHat scared me more was when the thing stalled or cut off while on the highway. Had to replace all the wiring in the engine compartment.
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Old 08-13-2017, 10:07 AM   #8
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I have taken my first Classic Motorhome (1979 28' with a 454) on a big trip in the Colorado Mountains and going over 3 10k plus passes. Max speed was about 25-30mph uphill using tremendous amounts of fuel. Downhill was just as exciting, since second gear would redline the rpm.
I never was tempted to take my other classics (a 345 and a 310) on that same trip and frankly don't recommend it. Todays technology has vastly improved and the Classics were not build for this new and "improved" speed and environment. Enjoy them in the flat lands.
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Old 08-13-2017, 08:32 PM   #9
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I look at the speed, power, mountain climbing situation a little differently. I have a 280 with the Isuzu which is no ball of fire by any means. I have driven the old stream from coast to coast and back so I have encountered a few grades. The interstates aren't too bad being basically limited to 6%. The state highways on the other hand can be more interesting. Heading to the Grand Tetons we encountered 10 miles of 10% grade up and another 10 miles of the same down. I don't remember the elevation. We hit a grade in Wyoming that was 7% to 8% for 9 miles. That one got up to 9600'. There was another in Nova Scotia that was 13% but only 3 km long.

We certainly didn't set any records on the grades but we did do 16000 miles in 4 months. The relatively few minutes spent going slow in the hills was nothing compared to the many hours we enjoyed touring the countryside. If you consider the amount of time at stop lights, in construction zones or city traffic, the time on grades means even less. It's what happens when you travel and it's all part of the experience. I just sit back and enjoy the ride and at the end of the day I grab a cold one.
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