Increased power for Chevy 3500 Class C

[Moving_on_Down]

We recently bought a 1999 20' Chateau on a Chevy 3500 cutaway chassis. We love everything about this RV. Just took it on a month-long trip out west and everything works as it should. The engine is a 350 and runs perfectly. Only problem: after moving down from a 35' so we wouldn't have to tow a toad, I would still like to tow or 1989 Wrangler on occasion. The 350 just doesn't have enough power for this. We towed a 22' pontoon boat (just under 3000# w/ trailer) from the factory to home and the RV struggled on the upgrades. I don't want to strain it with the Jeep. I noticed in the owner's manual for the chassis that the Chevy 3500 came with an optional 454. How hard would the swap be? I would want a rebuilt engine and transmission, but should I also find a donor vehicle for all the peripherals? Would the donor have to be a 3500 van? Any recommendations on a shop to do the swap (preferably on the East Coast)?

[Cobra21]

We bought a 21' motorhome with the 350 and am quite satisfied. With the shortness of the rig we didn't feel the need to have a toad. It has very easy maneuverability being that short. That said it is also great for putting in and taking out boats at the ramp. But yes... it is no race horse!!

Brian

[srd357]

Install a Gear Venders underdrive. Or lower your axle ratio. Both will be a lot cheaper.

[klutchdust]

With the cost of rebuilding engines today and if it were my vehicle I would look into Gm crate motors. You can upgrade to newer fuel injection systems AND they come with a 3 year

warranty. Check first at having an engine rebuilt, it's not cheap. Also go to a transmission shop, not the chains, and speak to someone that knows transmissions to see what your best

options are. Pairing that motor and tranny together will give you the best towing package. A 350 is only going to produce a certain amount of horsepower.

[Moving_on_Down]

Some sage advice here! I'll forget about swapping for the big block. As some of you have suggested, what I find annoying is having to run at high revs to climb steep grades. I suppose building up the 350 won't really let me climb grades at significantly lower rpms - that would require more low end power, which one generally gets from greater displacement. That's what I hoped to get with the 454. Stroking from 350 to 383 or so might help some, but I'm not sure it would be worth the cost. Maybe I'll just look up the power curve for my engine and get a tach to ensure that I'm running at the best rpms on the climbs (shifting manually, of course, which I already do). Oh, and I'll feed the squirrels that run alongside, as suggested.

[carringb]

Keep in mind it probably has the 4L60E transmission, vs the 4L80E that came mated to the big block. You might not want to increase power too much without addressing the transmission too.

There's lots of stuff available to make that motor more powerful, however none of it is van-specific, so it could involve some trial-and-error on your part.

I think a big-block swap could be really difficult to make work considering GM no longer manufacturers wiring harnesses for that generation van. Painless Performance might be able to build one, but I found that they don't like building full OBDII-compliant harnesses for some vehicles (in my case, I needed one for a '96 Chevy Impala-SS build, and ended up rebuilding a fire-damaged harness on my own). IF you found a donor van, if would make things much easier, except big-black vans were very rare.

[Hank85713]

Instead of swapping, check with a performance shop and ask them about building your 350 into a 383 with a stroker kit. would be much cheaper I would think and you would pretty much be able to keep what components you have in service. Oncew again find a reputable shop, you may have to call around to find someone. Get a truck magazine for gassers and see if there are any ads for nearby shops.

Just an idea. Also look at some of the chebby websites for trucks/vans. There should be people there that can help ya a lot better.

[j-d]

That 496/8.1 isn't that rough on gas when running with a light load. Don't hold me to this, but I honestly believe the Class C chassis with 8.1 did not also get the Allison transmission like the Pickup chassis did. At least Ford provided TorqShift in both of the product lines. Not to say the GM HydraMatic is a bad unit. Just not competitive with Allison and TorqShift on a features basis. More like Ford's 4R100. Never heard of somebody with 454 GM or 460 Ford in a Class C complaining about lack of power. Ford's V10 is supposed to perform better than the two old V8's, then the 8.1 beyond that.
Gene, I continue to rejoice that you're pleased with your 5.7's performance. I continue to express caution that, in general, the 5.7 in a Class C is at the upper limits of its capabilities. We have a 1996 5.7 EFI in our boat. One person on board, it's HOT. Two it's Great. Three it's OK. Four it's a Dog.

[Gene_in_NE]

Moving on Down wrote:
We recently bought a 1999 20' Chateau on a Chevy 3500 cutaway chassis. We love everything about this RV. Just took it on a month-long trip out west and everything works as it should. The engine is a 350 and runs perfectly. Only problem: after moving down from a 35' so we wouldn't have to tow a toad, I would still like to tow or 1989 Wrangler on occasion. The 350 just doesn't have enough power for this. We towed a 22' pontoon boat (just under 3000# w/ trailer) from the factory to home and the RV struggled on the upgrades. I don't want to strain it with the Jeep. I noticed in the owner's manual for the chassis that the Chevy 3500 came with an optional 454. How hard would the swap be? I would want a rebuilt engine and transmission, but should I also find a donor vehicle for all the peripherals? Would the donor have to be a 3500 van? Any recommendations on a shop to do the swap (preferably on the East Coast)?

I will have to take your word for it that the 1999 Chevy 3500 had the 5.7 liter 350 Cu Inch motor and also the 7.4 liter 454 Cu Inch motor.

I do know that my 5.7 liter 350 Cu Inch in my 2002 Chevy 3500 could have been ordered with the 8.1 liter 497 Cu Inch motor. I have the 350 CI and it feels like it has enough power to pull 3,500 lbs. I consistently pull about 2,000 lbs without any problems and get an accurae 12.1 miles per gallon. Here B+ motorhomes is a long running thread of a gentlemen that purchased the same model of RV as mine with the 497 CI that loved the power.

[RV_daytrader]

how about changing the rear??...my small class C has a 4.10 rear, and a couple guys who have put in a 4.56 rear say it made a BIG difference in hill climbing!

[tenbear]

I have the 2004 Chevy Express, 3500 HD chassis with the 6.0L. We have gone coast to coast and found it to be fine. Our friend has the 5.7L engine and says he wishes he had the 6.0L. Seems there is a greater difference than suggested by the displacement numbers.

[tatest]

The 350 of that vintage is a L31, Vortec 5700. It came in power ratings 255-350 HP.

The contemporary 454 was a L29, Vortec 7400, rated at 290 HP, with about 20% more torque at low RPM, thus it makes more power at the running speeds you probably find more comfortable. But it doesn't make that much more power than the 350 at peak output, because the truck build of the 454 doesn't run as high an RPM as the small block can.

You can get a fairly decent gain with the 350, maybe 60-90 HP, by replacing the intake manifold and injectors with those pulled off a L31 built for marine applications. Those engines were designed for continuous high output at high rpm, rather than flexibility over a wide range of RPM.

There are more ways to build it. The truck motor you have is a popular starting point for performance builds of Chevy small blocks, because those Vortec heads are great. Earlier truck engines needed expensive aftermarket heads for significant power gains, with the Vortec good heads came free from the factory. At the 350 displacement, it is not hard to build to 350 HP, and stroking to 383 still gets you a reliable engine for truck service.

You have to understand what you are doing. To get more power, you improve air flow through the engine so that it gets more air (and fuel) at high RPM, raising the torque peak to a higher RPM. The tradeoff is that the larger flow passages reduce velocities at lower speeds and power settings, costing low end torque. Which is why for a truck you build maybe for 300-350 HP, rather than 400+ (certainly possible, Cup cars get 700 HP out of a 350 by running 7000 rpm).

A lot depends on what you mean by "struggling." If you don't like that the transmission is downshifting, and the engine running 4000-5000 rpm to get up the hill, these upgrades of the 350 don't work for you, because they are about improving the performance at higher RPM.

Chevrolet Performance sells a number of different truck small blocks as replacements for the pre-Vortec 350, which was only 160 HP, not the 255 you have now. Most bring performance up to the level of the Vortec, options that go beyond are sometimes not street-legal, particularly going back to carb motors on vehicles that were multi-point fuel injected and computer controlled to meet emissions standards and still have high levels of performance.

[the_bear_II]

After pulling my 5th wheel for the first time I realized I needed more power. I had a 350 swapped for a 454 and after spending $2500 to make the swap and get out all of the bugs (bad vibration damper, fan clutch and new 4 row radiator, burnt spark plug wires) It really didn't make that much of a difference...sure I was able to go up hills about 15MPH faster while towing.

On a 6% grade that meant I was doing 43 instead of 30.... whoopee.

After awhile, to save wear and tear on the drivetrain, I learned to just keep it in first gear and cruise up 6% to 10% grades at 22MPH and enjoy the scenery. Often I'll feed the squirrels as they run along side. A real bonding with nature experience.

Now I've gone to a Duramax Diesel and Allison trans equipped truck....made all of the difference in towing up 6 and 10% grades....This truck more than meets my needs.

Moral of my post.... Get a more powerful MH.

[donn0128]

IMHO you would be wiser to yank the 350 and install a 4 bolt 350 truck motor built up. If you already have the 4 bolt truck motor, pull it havd have it built. 3 to 4K to get it built vs 8 to 10K to find suitable motor and trans and then trying to shoe horn it into the chassis seems a no brainer to me.

[j-d]

Engine Swap Cautions:

1. Be sure the 350 and 454 use the same CHASSIS. That's right, Chassis. I do NOT know about GM, but when we had a Dodge, I went to replace the anemic 318 engine. What I wanted was a 383 big block but wound up with a 360 small block. A man who had worked for Dodge told me "Good Thing - They used different crossmembers for the Slant Six, the Small V8, and the Big V8.

2. Particularly if you have to emissions test, you're on track about Donor Vehicle. It is VERY possible that not only is the Engine Control Module different, the wiring harness might also be different. This may go deeper than you want to cut.

Counterintuitive that the 350/5.7L will fall short and the new 6.0L does a decent job, but true. It's a different engine, not just 0.3L displacement.

If you want to get radical, you can Stroke your 350 to 6.2L (377, 383, something like that. Also years ago there was a 400-CID small block. I think it was a special block, though, not something you can create from a 350.

Any case, you'd have to allow for, or be sure the ECM allowed for, greater fuel demand from the larger engine.