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TBI vs Quadrajet


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06-17-02, 08:17 PM   #1  
TBI vs Quadrajet

I have just aquired an '87 full size GM van.
The vehicle is in excellent condition except that the V8 engine has been dynamited from driving with the oil light on.
I have just completed with excellent results, a 6.2 diesel to carburated 350 conversion in an '89 GM fullsize van.
My question is, would I be better off to use the TBI set-up on a replacement engine or change it to a more familiar quadrajet?


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06-17-02, 09:57 PM   #2  
if it already had a gas engine with fuel injection on it i would go back with fuel injection, i dont think there is any thing to be gained by putting a quadrajet on a vehicle that was originaly fuel injected, either way you go you will likley get simuliar gas mileage although injected engines tend to have a little more power and overall run better on higher mileage engines.
and you might also consider any emissions testing if applicable to your area, the fuel injected engine does have lower emissions at idle anyway. and may be hard for it to pass emissions with a carb on it.

 
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06-18-02, 10:08 AM   #3  
Joe_F
Stick with the OEM configuration of the engine for the best results.

If it's a Q-jet, keep it that way. If it's a TBI, keep it that way.

Parts are made to be used with each other

 
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06-18-02, 03:20 PM   #4  
Greg the carb is a much simpler swap when going from diesel to gas.You wont need a computer,sensors and wiring harness,if you get a non feedback carb and 1980 or earlier distributer.I hope you don't have emission testing there, you may be in for a suprise if you do.Good Luck

 
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06-18-02, 03:28 PM   #5  
Joe_F
Greg:

A good starting point is to know what's in there now.

What engine/fuel delivery is in there? If it's a TBI V8 (305 or 350), those are among the most reliable out there, you'll be going very backward by putting a carb on there.

A common fallacy is that "carbed is better". If the engine is originally carbed, then yes, that is correct. On a fuel injected application, that is simply an ignorant statement. It is NOT better. Working with the TBI as is IS a better idea.

Again, tell us what you've got.

 
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06-18-02, 06:19 PM   #6  
The engine is a TBI V8 (havn't got it home yet so not sure which one).
The motivation behind using a Quadrajet is familiarity. I generally understand how they work and have pretty good luck setting them up.
However, I welcome your opinions as to whether or not it would be worth the steep learning curve, as I don't have a clue as to how they work.
If it's worth the effort I would probably stick with TBI.


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06-18-02, 06:32 PM   #7  
Greg if its tbi keep it better cold starts,fuel economy slightly better easier to fix.I'm sorry I thought you converted from diesel to gas.

 
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06-18-02, 06:48 PM   #8  
The diesel to gas thing was last fall.
Going to a carburated engine was a relatively simple operation.
After removing a shopping bag full of wires I only needed a half dozen to run the engine and converter lock-up.


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06-18-02, 09:19 PM   #9  
Stay with the TBI like Davo said, it's a simple unit to work on and "tunes" itself. I'm running 250,000 on mine and have never had to go in to it. I have put a pressure regulator kit in another and it only took 30 minutes hood open to close.

I still love the sound of the 4 barrels when you open-em up!

 
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06-19-02, 03:43 AM   #10  
Joe_F
Ah, now we know more information.

Stick with the TBI. Putting a carb on a TBI application is a backward move that's a waste of time and nets a worse running engine.

 
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06-19-02, 07:28 PM   #11  
TBI-4, Quadrajet-0

It looks like TBI will be it.
You all seem like knowledgeable people and I appreciate your opinions.
I'll begin reading about TBI tonight.
I tried searching for the engine type in the options codes but did not have any luck.
Would anyone know how to read these things?


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06-20-02, 02:04 AM   #12  
Get your VIN and log on to alldata.com and sign up.
There is a cost (I think $30.00) but it will give you more info than you need for a year.
On a rainy day, log back on to it and get your printer going. You can make a great service manual binder for your van.

 
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06-20-02, 03:40 AM   #13  
Joe_F
If you're into the truck for the long haul, go with the factory OEM manual. Far superior to anything out there and you'll always have it. You can find them used, just as good as a new one .

That being said, if the 8th digit is K, you have a 350. If it's an H, you have a 305 in that year.

 
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06-20-02, 04:56 AM   #14  
305 's the one.

Thanks a lot for all your help.
I don't like working with anything I don't understand, so I'll have to hit the books.
Would it work to keep the TBI and replace the 305 with a 350?


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06-20-02, 05:35 AM   #15  
Joe_F
No. You have to upgrade the suspension, the brakes and the cooling system. Pitch the van for one with a 350 already in it in such case.

 
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06-21-02, 07:25 PM   #16  
My apologies.

Joe_F:
I must learn to phrase my questions more clearly as I'm not sure what the suspension, brakes or pitching the van has to do with using a TBI set-up from a 5 litre on a 5.7.
As far as I knew the engines are very similar and would only need a larger rad for the increased output.

If I'm reading into your response correctly, you are suggesting that using a TBI set-up on an engine it wasn't designed for would be too complicated or too much trouble.
You may also be suggesting if I read you correctly, that maybe a quadrajet may be more appropriate for my application.


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06-21-02, 08:24 PM   #17  
they are both small block chevy engines you dont even have to upgrade the cooling system, the only thing that i would suggest is finding out if the injectors are the same part # on the 5.0 and 5.7 engines they may be different, and you will most likely have to change the prom on the ecm to one calibrated for a 5.7 the memcal should be the same for the 5.0 and 5.7.

 
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06-21-02, 08:41 PM   #18  
bejay:
Your info suggests that is no big deal to run a different displacement on the TBI.
My knowledge kinda got stuck in the 70's.
Maybe it's time to break into 80's technology.
With the exception of a dead Dynasty I have to yet to get to, I've never had to touch any of the other computer controlled vehicles I have owned.
Must be a testament to their reliability.

I'm going to get this vehicle home this weekend and will see what this computer stuff looks like.


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06-22-02, 01:00 PM   #19  
Joe_F
A 350 has:

1) Larger springs. A GM parts book will likely show different springs for a 350 G van than a 305 G van of even the same payload.
2) Depending on the payload, it has better brakes than a 305.
3) I would upgrade the cooling system at the same time. The radiator is likely questionable anyhow.

Can you just swap it? Probably. Is it right? No. Engines and suspension/cooling/brakes are MATCHED packages from the OEM.

You'll gain very little in HP by swapping in a 350 for a 305 in such an application. Leave it stock and run it as is. Less trouble that way .

 
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06-24-02, 11:50 AM   #20  
Joe_F:
Completely stock automotive projects are certainly one way of doing things, but most certainly not always the best way.
GM vehicles, especially the older, RWD ones are an automotive enthusiasts dream. Pretty much anything fits on anything.

I think my question has been answered.
My objective is to put together a reliable vehicle with minimum headaches.
The simplest thing for me to do would be to rebuild a good 350 that I already have, stick on a fresh quadrajet and plug it in.
Keeping in mind that emissions are not an issue, this swap would be almost like screwing in a lightbulb.
I only have a few questions, like what to do with the electric fuel pump on a quadrajet, but I'll post a new question later.

Thanks for all your help.


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06-25-02, 07:57 AM   #21  
Joe_F
Greg:

You're asking what's the way to get a reliable vehicle...the answer is stock for what you want. Since none of us are GM engineers, we

Swapping a Q-jet on a TBI equipped vehicle is backward thinking (no offense) and any performance guy will tell you that. TBI is more efficient, reliable and predictable than a carburetor....contrary to what anyone will tell you.

Keep in mind that by sticking a Q-jet on a TBI equipped engine (or bypassing it by installing a different year motor) you will have a

slower
less efficient
more troublesome vehicle.

I've done plenty of 350 conversions and starting out from something not a V8 or the same platform runs you into snags along the way. The trick is to make it look and perform like it came that way. Unless you do that, to me, you've done a disservice to yourself

The 350 conversions done right you see out there are done with a lot of planning, tinkering and thought...and also a lot of research and money (trial and error for DIY person perhaps).

My .02

 
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06-25-02, 06:08 PM   #22  
Thanks Joe, I appreciate your input.
I have a 350 from a mid-seventies truck that is in very good condition. It is what I plan to rebuild and use in this '87 van.

Will this older engine work with the TBI if I make the mods that bejay suggested?

This is a tough one. I could almost jam the carb version in there in my sleep.
Don't have much experience with injection, so I guess I'm a little apprehensive.


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06-25-02, 08:47 PM   #23  
Joe_F
Greg,

Don't fall victim to "it's a 350, it must be better". Fact is a 70's 350 without any work is a dog. Small heads, smogged up, terrible carburetion, etc. Putting that in a modern truck is more of a headache (to do it RIGHT) than it's worth. As a Saturday weekend project...maybe, but not for a work van.

Pound for pound, rebuilding the stock motor nets less headaches and you just get in the thing and go.

Again my .02, but take it from all the customers who have paid 5 times for performance engines.

While you don't have emissions testing today, you might find yourself with your pants down in the future, because you can bet it's probably coming. Lol. Not only that, but an emission controlled engine will deliver better fuel economy..which helps in a pig of a truck like a GM Van

Your van, your choice, my advice .

 
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06-25-02, 09:10 PM   #24  
I kind of have to go with Joe on this one. Mid 70's is OK small block but your intake will not work with the TBI on the newer van. In addition, you may be looking at different set up for the old AIR pump (if used), EGR etc... You'll find out on these computer controlled engines that it seems that every sensor is affecting every other sensor else. I had the experience of putting a slight cam in a late 80's 350. According to Crane Cams, it should have worked with the engine with stock computer with a smooth idle and no problems. The engine ran well except that it would code (knock sensor) every once in a while and let go of the ignition timing. After much work and then talking to GM engineers it turned out that the computer "self tests" the knock sensor and spark timing control when engine first hits 203 degrees. The computer is supposed to create a knock and then correct it. Because of the greater duration of the cam lobes the engine would not knock, the computer thought it had no spark timing control so it let go of the timing. Guess who got to change it back to a stock cam?
If you have to rebuild either engine anyway, I would go ahead and put the original van engine back in. Less bad suprises. Let us know what you do and how it turns out!

 
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06-26-02, 07:17 PM   #25  
I came across an excellent site with good basic info on fuel injection.

http://www.goingfaster.com/spo/praisetbi.html

I know that I could replace the engine and just plug everything back where it goes, but I would not run something I don't know inside and out.

I'll get busy reading and try to figure it all out.


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