350 TBI tows 5000/6000lbs

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donforeman
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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Sun Jun 03, 2018 3:01 am

Yes, but this is slowly creeping past whats reasonable. The engine has very low miles and is a solid runner that doesn't leak a bit of oil. I never have not got to where I needed to go, it just means dropping down a gear and going slower. Yes a 406/383 with mpfi would be even better. For now I guess I will use it as is and keep scanning the ads in case something not beat shows up.

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Re: 350 TBI tows 5000/6000lbs

Post by travis » Sun Jun 03, 2018 8:33 am

I would do a cam/lifters/springs, adjustable FP regulator, y-pipe, and a chip. Should be relatively inexpensive with a hft cam and could easily add 40-50 more hp with corresponding torque gains. A slightly looser lockup convertor is also an excellent upgrade but pricey for one with enough beef for the gvw’s your looking at. If you need more then I would certainly be looking for a diesel or big block...it is absolutely no fun to change engines in a van.

On my friends ‘93 Chevy 1/2 ton 4x4 with a 5 speed/3.42’s, we added a little Crower 204/208, .414/.417 lift cam on a 112 lsa, stock springs (very mild cam), afp regulator set to 14 psi iirc, a “thermomaster” chip, dual exhaust with no cats (seems like it was 2” pipes...it’s been a few years), a 160* t-stat, a tbi spacer, and a basic cold air kit. It was a pretty dramatic difference over the stock setup and would get 20 mpg on the highway

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Re: 350 TBI tows 5000/6000lbs

Post by cardo0 » Sun Jun 03, 2018 12:14 pm

donforeman wrote:
Sun Jun 03, 2018 3:01 am
Yes, but this is slowly creeping past whats reasonable. The engine has very low miles and is a solid runner that doesn't leak a bit of oil. I never have not got to where I needed to go, it just means dropping down a gear and going slower. Yes a 406/383 with mpfi would be even better. For now I guess I will use it as is and keep scanning the ads in case something not beat shows up.
Yes a loose thumb rule I use is 1ft-lb torque for every cubic inch. And this can vary greatly but works pretty well for stock engines. But often I see engine w/trans on Craigslist that could make sense after selling the 350 and 4L60E. Just how time do you have for a driveline swap when I'm sure you'd rather be wrenching on your race car?

I've seen several BB w/TH400 still a suburban with reasonable miles. If you have the time it could really be fun for not much $$.

Good luck.

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Re: 350 TBI tows 5000/6000lbs

Post by CamKing » Sun Jun 03, 2018 3:56 pm

For what the OP wants out of this, all he needs is a cam, lifters, springs, and a tune.
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donforeman
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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Sun Jun 03, 2018 7:39 pm

Thank you all for the help. I do see where a larger engine, larger vehicle, better transmission, etc would help at times. I also appreciate the feedback that recommends trying the smaller improvements first. I will try the cam and re-tune first. I figure even if the van does end up for sale, who ever buys it next will like a little more than the 140 rwhp. I pulled the distributor out about a year ago and the cam is definitely a flat tappet cam. The tops of the lifter bores in the block are fully machined for rollers though. I heard though in 94-95 some blocks are machined but not drilled and tapped for the roller. So I will have to wait and see if I can use a roller cam or I am stuck with the flat tappet.

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Re: 350 TBI tows 5000/6000lbs

Post by PRH » Mon Jun 04, 2018 7:37 pm

As for the heads not being part of the problem.....I seem to recall reading on a marine forum(I know..... not gospel) that swapping out the non-swirl port marine heads of the same vintage for the swirl heads was about a 30-40hp loss.
The marine heads were similar what would come on the z-28’s and trans-am’s from around 1991 or so.

From the factory, the 95 g30 engine is 200hp, the 97 Vortec 350 is 255hp.
Somewhat handy with a die grinder.

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Re: 350 TBI tows 5000/6000lbs

Post by gmc406 » Mon Jun 04, 2018 8:31 pm

I just thought of something, because it’s a G30 , I wonder if he doesn’t have the HD version 350. It was rated at 180hp@4000 and 295ft/lbs at 2400. The HD version also only had 8.3:1 compression.

If so, no wonder you have power issues.



http://cars.automotive.com/chevrolet/g3 ... t3-12-2-1/

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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Mon Jun 04, 2018 9:07 pm

My G30 is the light duty version. 14 bolt SF diff, 4l60e and the l05. Its what is supposed to be rated a 200. TBI Chips has a chassis dyno graphs in the 140 range too. They say the factory rating is a little optimistic.

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Re: 350 TBI tows 5000/6000lbs

Post by econo racer » Tue Jun 05, 2018 1:14 am

I would try a tbi spacer and a Magnaflow muffler then re dyno.

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Re: 350 TBI tows 5000/6000lbs

Post by MTENGINES » Tue Jun 05, 2018 1:24 am

econo racer wrote:
Tue Jun 05, 2018 1:14 am
I would try a tbi spacer and a Magnaflow muffler then re dyno.
Raising the Injectors helps out a bit, Spectre had a universal carb hat that flowed better than stock. those few mods do help stock. but then again, just stick in a cam like mike suggests, the stock cam is the weak link here. with no overlap and no lift, its amazing a team of engineers was able to detune an engine to 1/2 hp per cube

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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Wed Jun 06, 2018 9:07 am

I did find a fairly clean late 90s 7.4l c2500 with 115k miles for $3400. Its a 9 hour trip but I think I am going to take a peek at it this week. I think the 454 will be a overkill for what I am towing most of the time, but it may work better than the 350 on the steep grades we have here in Oregon.

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Re: 350 TBI tows 5000/6000lbs

Post by cardo0 » Wed Jun 06, 2018 2:05 pm

9 hours? Ooch! Tell him you got cash and meet him halfway. But that BB is what you really need and you won't look back. 4L80E? Those steep grades will burn up any 4L60E towing 6000lbs.

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Re: 350 TBI tows 5000/6000lbs

Post by jeff swisher » Wed Jun 06, 2018 3:05 pm

I built a 350 for my neighbor in his 3/4 ton truck 1991.
I ported his heads and installed the 268H cam and gained ZERO power anywhere.

Waste of time, it was also a TBI.
Maybe the tune is all you need if you can tune them.
His MPG was always in the 10-12 range from new.
My 6000 lb ford E150 with 302 2 barrel would out run it. I had the 260H and flat tops with ported heads that one was 1984.

It would get 17.6 MPG pulling my bayliner to the river. Not using OD and 350 gears OD was too steep for the little 302.
so 2700-3100 rpm with quick timing curve. I did take it to the 1/4 mile track and the 302 van ran 18.0.


If money was tight I would stick an iron q jet intake on it with a q jet carb and then the head work and cam will show it's stuff.
If you go that deep.
I would not add the performer intake with it's flat floor I never cared for that intake.

Going with a generic RV grind on say a 112 LSA will probably kill the low end TQ and only gain 500rpm on the top.Talking the 204-214 generic cam.
I have done those deals 30 years ago and not anymore.. I reach for the 260H on a 110LSA and make more power everywhere and better MPG.
Good cam In a heavy tow rig .

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Re: 350 TBI tows 5000/6000lbs

Post by Brian P » Wed Jun 06, 2018 5:02 pm

Back in the 1970s when this van was designed and the 1980s when it was built ... you slowed down on hills when towing, that's just how it was. The towing torque and horsepower race is much more recent than that.

5000 lbs trailer + 5000 lbs van + 1000 lbs other stuff = 11000 lbs total weight. 40 mph = 58.6 ft/s. If it's a 10% grade then that's 5.86 ft/s upward, lifting 11,000 lbs. That's 117 horsepower right there not counting any losses, and you've only got 140 hp to work with. You've also got a bodyshell that never saw the inside of a wind tunnel. Lousy aero doesn't matter so much when you get bogged down going up a hill, but it doesn't help.

The newer vehicles have more power (my modern van has a Chrysler 3.6 Pentastar with double the power!) and transmissions with more gears so that they can make better use of it.

With 28" tall tires (guess) and 4.11 gears, your engine is doing about 3000 rpm in direct drive (3rd) at 60 mph not counting torque converter slippage. It is probably not able to go down to 2nd at that speed without putting the engine revs above a good operating range for the current torque curve. If the hill is steep enough that it won't pull 3rd, you'll have to slow down enough that it can use 2nd.

I think your gearing is about right for what you're doing with it, but she needs more power if you want it to keep up with modern vehicles. How to do that without killing the gas mileage ... I'll defer to others. I wouldn't use a high-slip torque converter in this application - it will make more heat and won't help mileage. Keep the lock-up. If it doesn't currently lock in 3rd (or 2nd!), get it to. Throwing away precious power in the form of slippage is the last thing you need.

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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Wed Jun 06, 2018 9:37 pm

Thank you for the replies. The truck I was looking at has some overheating issues that were not mentioned in the ad. So I am back to looking at want ads. Yes the van does fine if you slow down, but you cant do that too much or you become a traffic hazard. The 4l60e was rebuilt by me with all the towing upgrades, so who knows how long it will last. Its no 4l80e though. I took down the pan last week and it was spotless inside even after towing pretty often for the last few months.

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