VTurkey

I've read a lot about the 4.3 on here, so don't flame me for posting this. This is more of a guestimate technical question than about the engine or swap itself.

I have 94 chevy c1500 (2wd) with the chevy 5 speed and super built 4.3. I didn't build it, I didn't actually know it was built until I drove a blazer with the same engine which was had nowhere near the same power, and my mechanic told me it had more power than his v8 in his silverado. He also said it contributed to the mostly rotten frame being basically snapped in half right between the leaf springs. It's a farm truck being held together with 2x4s. The engine though purrs, sounds like a loping race car and it's hard not to burn out. Here is my question about mileage. When I drove to colorado and back 3 years ago with it (4000 mile round trip) it didn't skip a beat, and I consistantly got 23 mpg on the highway going about 70, a few tanks I got 24 in the plains. I usually got between 16 and 18 in the city. Better than my 3.0. The chevy has stock tires, basically the same size as stock toyota tires. In my stock '88 sr5 extd cab with the v6 5 speed, what would cause this mileage to drop? Would it drop? stock tires, stock truck, no lift or anything. They weigh close to the same probably, the Chevy a little heavier, it is just standard cab short bed. I have just seen people on here post even without big tires still getting 15/17 at best with the 4.3 in their yota. I actually really want to put a diesel in, but I am unsatisfied with the lack of power people tend to get without doing a crazy vw tdi or expensive toyota 6 diesel. I just couldn't go with anything even slower than the 3.0. And I have this chevy with a racecar v6. I figure I'll wait until I can just afford a landcruiser, and until then have a muscle car yota. But there isn't much point if it gets worse mileage than my 3.0, this is my daily driver and business truck.

Any thoughts would be great.

cbr600rx7

Your probably going to get flamed for many reasons for things said in that post but I will try to keep it clean.

First off you need to consider the transmission gear ratio's to compare 1st-5th gear if 5th gear (your overdrive gear) being critical for highway MPG. The Yota is a R150 trans the Chevy is probably a NV-3500 but you will need to check the RPO code in the dash to see if it is and if it's a close or wide ratio. All NV-3500s have the same 5th gear at a 0.73 OD where the Toyota R150 has a 5th gear OD of 0.84.

Next big concern is you gear ratios. Once again look to the GM RPO codes in the glove box. It's probably somthing like GT4 or somthing along those lines. Next figure out what gears are in the Toyota (it's on the door sticker but you probably know this) the gears could be very different since the 3.0 yotas tend to come with 4.10-4.56s from the factory where the Chevy 2wd work truck could have 3.08-4.10 gears. That is a huge diffrence.

The 4.3 Chevy and the 3.0 Toyota 3VZ are two different animals and make power in very different areas of the powerband.

Is this truck running the stock TBI injection.

VTurkey

Haha well flame away then. I'm a farmer not a truck nerd...have to learn somehow. I appreciate your response. Yes I wondered about the gear ratios. I will find those codes and find the difference. Yes it is TBI. I did mean to mention, I think for sure the GM is much lower geared...I could step on it on the highway and barely ever get it above 85, but certainly not through lack of power. Not that I wanted to go 90 either. Vs the toyota seems like it would just keep going past 100 if it had enough power. Again not that I want to. But thank you for the code pointers. I will find out each and that should help to let me guestimate. I am aware the 4.3 is a torque monster. Especially this one. Supposedly that should help with mileage.

cbr600rx7

If it's a 4.3 TBI it is definitely not a race car motor and you probably should get a new mechanic if he thinks it's stronger then a SBC V8. The L-35 RPO code or LU2 should tell you what 4.3 you have. Being a 2wd work truck it probably has the 165hp/260tq runoff the mill 4.3 in it.

Why do I say it's not a race engine. The Chevy TBI system is super simple throttle body injection. They require a good bit of vacuum to function properly and do not respond well to large cams, the heads are extremely restrictive as is the manifold, TB, intake system, exhaust, and so on. Even chips can not over come this and you find your self spending $2000 in parts to gain 30hp Now the carb and vortec motors are a different story since they have better tune ability.

I have built a 88 350 SBC that had a bad previous build. Had to go 0.060 over with a 9.2 Compression ratio, slightly work over heads eddy cam/manifold, CFM built Throttle body, chipped PCM, headers, good flowing exhaust, electric fan, and tons of other small stuff and the motor probably Gained 35 horses at best but definitely made tons of low end torque that the long rod stroke really shines. Keep in mind that's on a 360ci V8 vs a 262ci V6 so it's very possible the same mods would generate a significantly small gainin performance. FYI the hole process from oil pan to air cleaner was about $3000 with parts and machining.

Get us those RPO codes and gear ratios and we can help crunch the numbers for you.

Charchee

I have never seen a 3.4 get that kind of mileage especially in a half ton. I had a 91 Blazer 2WD and never got better than 19mpg. Those half tons with the 4.3 usually had a 3.42 ratio to compensate for lower engine power. All things being equal, you will probably have more torque and more fuel consumption after the swap. Weight of the truck will factor in but the real variable is going to be the way you feed it. By that I mean air flow, injection and ignition.

To be honest, fuel burn would be way down on my list of questions I'd want answered before taking on a project like you're talking about.

cbr600rx7

Yeah 23-24 seems extremely high even for a 5 speed truck. That would be good for a 4 cylinder 2wd ranger or S10 but maybe with a extremely light foot and highway gear it might be possible under perfect conditions.

Any way get those gear ratios and get back with us. I am assume your buying an adapter plate and mounting the Chevy to the yota trans.

VTurkey

It is a vortec. My mechanic is a 75 year old been working on mechanical things his whole life. I'm not trying to brag or anything like I said im not a truck nerd nor do I try to show off like some hicks do with trucks, it really was just something he grumbled to me after the first time he checked it out when I first got it. All I meant by "racecar" is that it has extremely sensitive throttle response, can spin the tires very easily on pavement, and it sounds like it lopes even it though its fuel injected. I should try and take a video so you know what I mean. The engine looks stock under the hood but it does have headers, and it came with a stack of work receipts that included said headers, "sound fx" exhaust, a fancy clutch a bunch of other little things. I should revisit them. It certainly feels like it has way more hp than 165, though I guess that could be all that torque. I towed a 3500 pound farmall tractor with it on a 16 foot tandem trailer 160 miles and could stay in 4th easy on the vt highway, which is really hilly. I have driven a beefed up k1500 with a 350 stick shift and it isn't that crazy, but it certainly is no where as lack luster as the 3.slow. Also I blew up the muffler when downshifting down a steep hill, due to fuel getting igniting in the muffler...you think thats from an aftermarket exhaust or modded injection? Or just an old vortec...

I'm not worried about swaps I've been studying many of them since getting my yota, including diesels, i've done a bunch of swaps in cars trucks tractors i've made electric machines i can weld fabricate...besides its just a vehicle. all good fun. I just care a lot about mileage because i want to actually drive the damn thing. I am slightly concerned about using the toyota tranny with all that torque, but other people have been doing it. I'll get those codes tomorrow. Ever any codes on the actual GM block other than it saying Vortec? Don't know what to tell you about mileage. I drove like a grandma and it was mostly flat past Ohio. Also im in a rural area, and so "city driving" is still pretty consistent. Also blazers are almost always auto aren't they? Might even be heavier too, especially if its 4wd. And a work truck probably had different gearing then a blazer

cbr600rx7

If it's a 94 it's not a vortec. 96 was the first year

TBI is also not a vortec.

VTurkey

It says manf. in 4/94 in the door, and also says Vortec on the valve covers, but it does have the TBI under the airintake. So not sure what to make of that. Unfortunately all the codes have been worn away in the glove box. All it says in the engine compartment on the fan shroud is "manual transmission" and "4.3 Liter R3G4.385GAEB and then R3G1085WYM0B.

I haven't looked at the toyota codes yet.

Anywhere else on the chevy that could tell me the gears?

If not, I'll just assume worst case scenerio that the chevy is lowest possible, and i'll get the toyota codes.

VTurkey

I just did some reading; Apparently after 1992 they put CPI heads on TBI engines...distinguished by the "vortec" plastic valve covers. Some are saying the CPI heads allowed for 30+ horse power going from 165 to almost 200....maybe that's why it feels like a juicy engine. I'm not that familiar with these engines.

Charchee

Many of the 4.3L engines produced from 92-94 were known as L35-CPI engines. They had 200hp which is more than any of the other 4.3s of that decade. I think they used a single port injection system and CPI heads. At least the hot ones did and there were some of these in the half ton trucks.

The term Vortec has been around a long time. It is a branded description of the design of the combustion chamber which is said to draw in air and fuel in a vortex pattern suposedly creating a more complete fuel burn. Those type engines were around even in the late 80's. It was only until like 92 that they started throwing those badges on some of them as a marketing device. I have seen plenty of them with TBI along with other fuel injection setups they tried along the way.

The 96 and on Vortecs had what they called Vortec heads and multi port injection. Thats wen you started seeing the big badge on the upper plastic cover. The way to tell the difference is the intake. The newer ones have a two piece intake manifold with the top half being composite and the CPI engines had aluminum intakes on both top and bottom like a Toyota engine.

I hope I got all of that right. Go ahead and get on me if I'm wrong. I haven't wanted anything to do with a GP product in a long time. All that being said. I remember seeing the Vortec badge on brand new early model blazer engines but not on my 91 4.3L. Never saw one on a V8 even though some folks called them Vortecs even back then. My boss actually has a TBI 350 Vortec crate motor in his 87 model C1500.

cbr600rx7

The motor is probably a LB4 and not the L-35 since it's a base work truck from the sounds d it. One way to tell is to look at the TBI unit. Lots of people adapt Late model vortec heads and intake manifolds to the SBC however I don't recall seeing vortec very often on any 88-95 TBI trucks that had not been heavy modified. I could very well possibly be wrong and this is only my opinion. However the OP stated the "vortec" was on the valve cover and if I am not mistaken both TBI and vortec motors can use common 4 hole GM valve covers. Only real way to tell if the RPO codes are gone is run the VIN or run the head and block numbers.

In the end it doesn't really matter because the main question is still gearing.

cbr600rx7

You can determine the gearing by also pulling the rear diff cover on the Chevy and just counting the teeth if the rust lets you pull the diff cover that is.

OR
Try the old school way of marking the drive shaft and tire then rotate the drive shaft counting the turns until the tire makes a full rotation. Note you may need to put one tire on the ground or have both in the air depending on if it's LSD or open diff. I don't recomend this method as its not that accurate and calling GM with the VIN would take less time.

Charchee

That's a lot of neato information but there's no real way to predict the true fuel mileage you are going to get. I'm sure you are going to get fewer mpg unless you already have 4.11 gears in your Chevy which I doubt you do. You are going to have to modify your air plumbing and fuel delivery scheme for sure. All of those variables are going to affect your mpg.

The real issue is going to be how your 20 year old Toyota dirvetrain parts are going to like a sudden 30% torque increase after 200K miles worth of wear. I'm not sure if a clutch kit comes with the adapter kit but you're going to need one. Also, I would take a look your u-joints and the gear lash between your ring and pinion at the rear end. If it is more than spec which I'm sure it is, you're about to loose some teeth. Would be kind of like Ray Lewis riding your kids plastic big wheel.

Why don't you just sell the old Chevy and use the money to buy you a 3.4L Yota engine. There is a guy in my town selling a 98 4Runner Limited with just some body damage for $1000. A wrecked rig like that would have absolutely everything you would need to do a complete fuel injected Toyota upgrade. 190hp with 220 lb./ft which is a whole lot better match for your drivetrain and no adapter needed.

If your are set on doing the 4.3 swap then go for it. It will be a cool project and I'd like to see pics of your build up but if you are actually wanting performance and reliability then do it the right way and hunt you up a 3.4 to swap into your Yota or find you a clean old S10 and build you a hot rod out of it. Just my opinion.

cbr600rx7

Both are good options.

Most adapter kids do not come with a clutch unless you add it to the package. However if he upgrades to a 3.4 he might as well do the clutch at the same time. It would be stupid not to.

The 3.4 is by far less work and has a huge aftermarket. Plus it's been covered in detail of the forums a million times.

Of course the 4.3 has been done many times to and he does have a hole donor vehicle right there.

Both swaps are definitely a upgrade but depending on his gear ratios the 4.3 may be way over geared in the yota. And Charchee is dead on OP I would not expect great fuel economy out of the 4.3. If you want better MPG over the 3VZE and that's your main concern then a 3.4 or diesel swap is the way to go.