Dave
Is that gas mileage towing your Saturn? It seems low for a gasser on its own considering a recent new engine,etc.I would think a 8-12 range would be more in line.

Neil

Not close Coaster. 8-12 is dreamworld for a 454 pulling 13,500# motorhome. 6-7 is reality..period.

Even headers will give you torque but I don't believe the mileage claims.

As a disclaimer I must admit that I have never checked the mileage on this coach. But since it has a pretty new engine and I know the weight is about right. There is no reason to think it isn't the same as the other 100 or so Barth guys who have commented on the subject.

quote:

8-12 is dreamworld for a 454 pulling 13,500# motorhome. 6-7 is reality..period.

Ditto for even a 24 footer at 10,500 lbs running on the flatlands......probably based on the max amount of fuel one can pour through the holes of a Quadrajet........

Must be something about 454s. I get 6 mpg +/- hauling 20,000# with a toad. I had a pickup & a Suburban with 454s. Both got 10-12 mpg @ 30 mph, or 80 mph, towing, or bare. The only difference was in oil consumption in the Suburban. It had a well-worn hot-rodded engine that could pull stumps, but the normal evolution was 1 qt. oil per tank of gas. At 80 mph it burned 2 quarts per tank.

Lee's probably right about the max amount of gas that can be poured through a Quadrajet.

Olroy, I've always joked it was limited by the 3/8" line and condition of the fuel filter. This probably is less than true and the quadrajet is not limiting either. The 327's that were in my boat were fitted with low volume quadrajets rated at 16 gph at 4000rpm. Just think what 750 cfm's could do.

Oh, oh, gotta defend the Qjet here........I have gone back and forth from Holley to Qjet on various big block chevies. The Qjets always gave better mileage, particularly at part throttle.

How about changing the rear end ratio with an overdrive?

Another thought. Has anyone done an engine swap to a diesel? This seems like it would be a good option. Look at the price difference as much as $25,000. Seems like you could put a nice 5.9 diesel Cummins from a Dodge 3/4 ton pickup in there and increase the mileage to 12 to 15. Makes sense both in long lifespan and resale value. With gas prices up so high I am seeing all kinds of class A's at half of what they were selling used a year ago. Thanks to the mighty 454!!!

quote:

Originally posted by Haoleman:

How about changing the rear end ratio with an overdrive?

A gear vendors OD will help mileage a little, but their installed cost is considerable. It would take a lot of gas saving to pay it back. I bought mine for engine longevity and hill climbing.

quote:

Another thought. Has anyone done an engine swap to a diesel? This seems like it would be a good option. Look at the price difference as much as $25,000. Seems like you could put a nice 5.9 diesel Cummins from a Dodge 3/4 ton pickup in there and increase the mileage to 12 to 15. Makes sense both in long lifespan and resale value. With gas prices up so high I am seeing all kinds of class A's at half of what they were selling used a year ago. Thanks to the mighty 454!!!

That would be a good swap to look at. If I needed an engine today, I would look into it. Or a Duramax. The right price on a donor vehicle would be a prime consideration.

The first thing I would look at would be how much weight would be on the front suspension. You could do some moment arm calculations on Dodge trucks to get a good idea, then do the same on the MH.

The second thing would be sump clearance on the big crossmember. Driveshaft angle can enter into things if the engine is raised or tilted.

Doghouse clearance would be another issue, but a distant third.

I think adding a Durmax or any newer diesel to a P30 would require a degree from NASA. With the wireing harness and drive by wire, it would be a challenge. Then again,if there is a will there is way.

An older 12v cummmins or possibly a Izuzu Mechanical Diesel from an old NPR would be interesting.

The pre-'94 28' Breakaways have the Cummins 5.9L (probably the 12V); I replaced the early GM 6.5L TD in mine with an AMG 6.5L TD with a few extras. Both get 10-11mpg at around 16K lbs.

The Duramax is an Isuzu...

I was told, and I don't know this to be accurate, that exchanging a 454 engine and transmission for a duramax lbz with an allison 6peed transmission would add between 3 and 4 hundred pounds.

I considered a Duramax/Allison when StaRV II got its transplant. The additional weight over the AMG 6.5L TD/4L80E was, IIRC, <100 lbs.

What stopped the process was that, in addition to the increased effort in converting the electrics, was that the Duramax/Allison ensemble is something like 2.5" longer than the stock engine. The driveshaft on the coach is already quite short, and I didn't want to deal with the deflection issues.

With AMG's improvements over the original GM 6.5L TD (Block is approx 25% stronger, and uses 18:1 pistons instead of the original 21:1) and the custom features I ordered (Improved IP, Hi-Pop injectors, non-wastegated turbo, and Phazer geared camshaft drive), I figure I have a 250K mile engine, which has already proved itself as economical, if not as powerful as the LBZ. StaRV II already had an HD 4L80E installed when I got it.

Anyway, for anyone considering a conversion, I highly recommend Peninsula Diesel in MI, rwhere I got my engine. With the extras the long short block price was around $10K delivered. Duramax/Allison combos, when available, seem to run $15K for like-new (at least the only ones I found did).

I do have a rebuildable 6.5L with the desireable 599 block (slight scoring in cylinders 5-8) with tested turbo (OEM new w/ 15K miles), levelled heads, 130 gph water pump with dual thermostats, and gasket set, if someone is interested. The engine was placed out of service due to blown head gaskets, and since I had it in the shop, replacement was preferable to rebuild. Main need would be exhaust manifolds and studs, plus accessories. I'd recommend 18:1 Mahrle or equivalent pistons.

This engine got about 9-9.25 mpg for the 12K miles I had it in StaRV II (@16K lbs.); oil consumption was normal (qt/1500 miles) even with the cylinder issues. Being stock, it's rated at 190HP and about 390 lb.-ft. torque.

FWIW, I just ran across these figures for the Allison 1000:

Weight 330 lbs.

Length 27.35 inches. 3.1 longer than the regular truck TH400.