350 TBI to 454 swap

[Pano]

I have read a lot of threads and decided to replace my good running 350 with a 454 to better tow my 27 ft camper. I considered the 8.1 but with the additional cost and fuel delivery complications I decided the 454 would be easier and pull the trailer fine. I have an 87 V2500 with a TBI 350, TH400 and 4.10 Rear end. It is a 4x4 with a NP208.

I figure it is best to find a donor vehicle to get the radiator, alternator, PS pump, shroud etc.

if I get a pre 87 non TBI is it an easy to convert the TBI to carb?

If I stay TBI how far forward can I look for a donor vehicle and when will I need to consider a newer computer or other issues?

I have been searching and found 90s RVs and PUs with both options.

Thanks

[craig113]

The 454 intake is the same for carb or TBI. I am currently doing a build and found this out a couple weeks ago. Only the SBC changed the intake bolt pattern.

[mattybilt79]

I'm curious to know how much you tow your trailer to justify the over all loss of mpg by swapping in a big block? Don't get me wrong I'm not saying don't do it. I had an 88 v2500 burb with the tbi 350 and 400 trans that could barely get out of its own way but still could pull a trailer. It got over 13 mpg regularly. I sold it and bought a 95 burb 454 with over drive and 4.10s and it averaged 11.8 mpg! I just got rid of it due to reverse going out. Now driving an 85 crew cab dually with a 454 and just put an 87 TBI motor in it and converted it to carb. No base line on fuel mileage don't expect more than 10 out of it. Bought it to pull 5th wheel. I wanted to get away from fuel injection and electronic transmissions etc so I got an older truck. Making the TBI 454 carb'd was easy. I would rather have a cummins though but I was pinched to have my truck up and running asap. You plan on keeping your truck for awhile or updating to a newer one?

[Pano]

I get 9 mpg towing and 11 when not. I only use the truck for camping or yard work so the mpg isn't an issue. It has a new HD suspension and is in great shape.

http://67-72chevytrucks.com/vboard/s....php?p=6305428

As far as getting a new truck, I have had this one since 97 and it has done all I ever wanted. Since getting the camper 2 years ago I am seeing that it would make more sense to get a 10-15k quad cab truck that is newer and can haul the whole family. The alternative is spending a couple grand to install a 454.

I read up on the 8.1 and newer trans but can't get my arms around the 4-5 grand it would take to do it. The 454 would be cheaper and have similar mpg and the power needed.

[Just call me Sean]

My wiring diagrams don't show any difference between the 350 or 454 TBI systems. The computer would be different though.

[mattybilt79]

That's a good looking truck man. I guess the only big question then is emissions where your at, do you have to smog the truck? You can drop a TBI 454 in and swap the puter and everything else should plug in fairly easy. Will have to do some exhaust work for a bbc. You got everything else mentioned already. Just find a good donor vehicle and get everything you need. I see BBC suburbans dirt cheap everywhere out here but not sure about out east where your at. Hell my engine came out of an 87 burb with 82k original miles! To make a TBI 454 run a carb all you need is an hei distributor carb and fuel pressure regulator to bring elec pump pressure down to 4/5 psi.

[Pano]

Does anybody know what year range I should be looking within if I find a donor newer than 1987?

[Pano]

Ok, it looks like Mark IV until 1990, Gen V 91-96 and Gen VI started in 1996. From reading I am leaning toward the IV. Gen V seems to be the least popular. Gen VI seems to be more complicated and expensive and that's why I am shying away from the newer 8.1. Any more advice?

[Cabnchassis]

Every 454 from these trucks I've spent time in only has one mpg rating and its been 10. I think my 350 is a dog on fuel and gets 9-10mpg city but it will still get 14-15 on the hwy with mud terrains and 4.10s in a k2500. I pull a 10K trailer to shows for a friend of mine with mine and it really isn't that bad even on long grades. My truck has lived under a trailer most of it's life cause the PO had a gooseneck and 5th wheel. I have overdrive to go with my 4.10s too so that does play into the driveability a bit but still a 5 mpg loss is nothing to sneeze at. Not to mention these tbi 350s really last. I've seen several still in good shape with close to or beyond 300k and i'm sitting real pretty at 210K.

Having worked out of both trucks I wouldn't personally do it, but I get irritated at trucks that have little power and use loads of fuel. I used to drive a 94 CC dually with the 454 and as a work truck, it was miserable on fuel and not really that powerful an engine. My 92 came rated 210/300 HP/tq the 454 was only 230 hp and 385 tq those same years and was never far beyond of that in TBI configuration. Your truck would have been like 185/295 so you'd gain 55 and 90 respectively but those ratings don't mean much 20 years later they all age a little different. I especially wouldn't pull out a used tbi 454 to replace a reliable TBI 350. I've seen a lot of high mileage tbi 350s over the years. Don't take my .02 though cause the 454 does sound a lot better and that right there might be worth the whole thing if you like hearing the pipes ring.

[Pano]

Once at speed and on level grade the 350 maintains speed fine. It is slow getting to speed and noticeably slows down on hills. It may be me but it seemed to be a bit more of a dog this year than last. It seems I need to have my foot in it most of the time.

I don't have anything to compare it with but if that is typical for a 350 maybe I could live with it until the engine gives me problems.

The trailer is 5600 unloaded so is more like 6500-7000 loaded. The truck is loaded too so probably close to 8000 lbs which is close to the truck rating.

I will post a pick of the combo later.

[BigBlocksRule]

Don't shy away from the Gen VI, it's a great engine. Priority main oiling, all are 4-bolt mains and use factory roller lifters. Can't use a mechanical fuel pump, but that's a moot point when you'll be running TBI. Look for an aluminum timing cover with only 6 bolts.
There are a couple of connectors that are different on a TBI, but most is the same.

[Cabnchassis]

Originally Posted by Pano

Once at speed and on level grade the 350 maintains speed fine. It is slow getting to speed and noticeably slows down on hills. It may be me but it seemed to be a bit more of a dog this year than last. It seems I need to have my foot in it most of the time.

I don't have anything to compare it with but if that is typical for a 350 maybe I could live with it until the engine gives me problems.

The trailer is 5600 unloaded so is more like 6500-7000 loaded. The truck is loaded too so probably close to 8000 lbs which is close to the truck rating.

I will post a pick of the combo later.

Every motor ages uniquely. Two of the same exact motor won't run exactly alike after 20 years. If I were sitting in your spot right now I'd run a compression test to get an idea where you're at there. I had a mystery stumble that almost drove me to sell my truck but I though well let me just run a compression test and see how she's faring. I've never tested a 20 year old engine that hadn't lost a decent amount of compression but mine came out 2-3lbs under factory. That did a lot to help me realize that I was just expecting too much out of that motor.

I know when I lived in the midwest I got used to people's 350s having some power since they have no smog and trucks and cars with good running gear rust apart by the day out there. A lotta guys with cams with and heads and such so there are a lot of high 200 low 300hp trucks running around out there. Truck variant 350s were never built like that though.

When I got into a TBI 350 first it was a rcsb 2wd my aunt loaned and the disappointment was immediate. It was a 91 so gen V but just a turd. It sounded good and ran well but I have no doubt the same engine in my current truck runs better and makes enough more hp that you notice, even though they are identical in build.

So i guess my point is maybe you have a decent motor that you just expect more from like I was geared to in the past or it is entirely possible it's just aged in a way that sapped more power.

Honestly I prefer detroits to small blocks so I don't take it easy on that 350 pulling with it cause I'm not afraid to blow it up and go diesel. Not suggesting a detroit as a solution to you just sharing my experience and pointing out I may not be as bothered by mine cause i keep it wide open a lot.

Another factor at least for me using them for work is mileage. The 5 mpg you'd lose swapping is about what the difference is in mileage in my two. Basically the only time I pick the 350 truck is when I want power windows and A/C or need 4wd. Basically the difference in power output and mileage in my trucks is what you'd be looking at in a swap. If I could only pick one no way i'd take the 50 more hp gm says that gasser has over 5+ better mpg the detroit gets. And the detriot is in a lot bigger heavier truck.

[Pano]

Here is the truck and camper. I have a compression tester and will try to do it this weekend.

[Pano]

I struggle with how much money to sink into the truck. Ideally I would go with the Gen VI or the 8.1 but I could sell the truck, use the few thousand the engine would cost and get a newer used truck equipped to tow and carry the family.

I figured with a MK IV would be cheaper since it is more plug and play.

Maybe I should push the 350 and see what happens.