Advice on freshening up a 350 tbi

[Overland Suburban]

I have a spare 350 tbi that has some miles that I have decided to freshen up and switch my burb over to old school setup/ carb. Ive never rebuilt an engine before so I have a few questions. There's not much ring ridge at all so I was going to hone and put in New rings, bearings and gaskets. Also was planning on either porting the TBI heads myself and going with a 450 ish lift cam and 600 ish carberator??? Need advice on that! My other thoughts on heads was to just go with Vortec heads since I will be needing a new intake anyways. My thought was with only 450 ish lift the TBI heads might produce better low end mid range torque?? Which is basically what I'm after. I'm thinking more torque than HP but would like to get a bit more RPM to work with so it doesn't dog out at 3500 rpm. 5000 rpm would be doable.

So in a nutshell

I want to build a 300 hp 370 torque/ or thereabouts 350 with a carb. I want 5000 rpm's and that is plenty. I'm hoping I can use my tbi heads and pistons and basically do a budget freshen up. Port heads, cam swap, Hone, rings, bearings.

I would greatly appreciate info from those who have done this with a tbi 350 and would prefer to stay away from the guessing and gestimating of what may or may not work. There are probably 100 threads on this but my google search function doesn't seem to do **** for me.

Thank you in advance for any help

Tracy

 

[mcarlo86]

I'm curious as to why you want to go away from the TBI fuel injection? Just looking for more power? If you are looking to go with a carb, if you can find a good rebuilt Q-jet, they have small primaries and have nice throttle response on the low end. They are about the best carb for fuel economy and power when they are adjusted properly.

 

[Overland Suburban]

Mcarlo86,

I'm looking for around 100 hp more and I can see TBI would be difficult if not impossible to get a chip for. Plus after learning more about the TBI I think I'd much prefer a system that I can tune not some computer that says what I can and can't do. I am going with a Q-jet for sure.

With 36" tires this TBI engine is about 100 hp underpowered. I thought about a 454 but I've heard they are a gas guzzling pig and I'm planning on traveling a lot so some kind of economy is important to me. My thoughts are that a 300 hp 350 will be about as close to enouph power and probably just as good of economy if I keep my foot light which is how I drive anyways. Thank you for the comment

 

[bucket]

You can achieve your goals with TBI. You can achieve your goals with a carb too. Improving the TBI can cost more, but at the same time, converting to a carb requires some changes that will also add to the cost. Modifications to TBI takes a little more homework than a carb swap, but all-weather driveability will be better.

As far as power and torque production goes, I don't believe there is anywhere in the rpm range that a Vortec head produces less than a swirl port TBI head.

I've had small block trucks, big block trucks, TBI trucks and carbureted trucks. They have all got similar mpg, with the exception of one that was noticeably better. But that was a short 2wd with a 305 and very tall gears. Very different from a 4x4 Suburban.

 

[Catbox]

The TBI Swirl Port heads are all done with flow around 4000 rpm.
I have read they are the worst flowing heads mother GM has ever mass produced.
If I were to rebuild the TBI in my '95 Suburban, those heads would not be included in the revision.
I would look into a set of the Vortec heads and matching manifold.
The Summit branded Vortecs seem to be a pretty decent deal.
They are a bit thicker in the right places and have all the little things done to them that will make them great out of the box.

You would easily achieve your goals with those and a small cam.

 

[Overland Suburban]

You can achieve your goals with TBI. You can achieve your goals with a carb too. Improving the TBI can cost more, but at the same time, converting to a carb requires some changes that will also add to the cost. Modifications to TBI takes a little more homework than a carb swap, but all-weather driveability will be better.

As far as power and torque production goes, I don't believe there is anywhere in the rpm range that a Vortec head produces less than a swirl port TBI head.

I've had small block trucks, big block trucks, TBI trucks and carbureted trucks. They have all got similar mpg, with the exception of one that was noticeably better. But that was a short 2wd with a 305 and very tall gears. Very different from a 4x4 Suburban.

Thanks Bucket thats just what I was looking for! My concern was that the TBI heads might make more in the ranges I was looking for but if not I won't mess with the TBI heads and will go with a set of vortec. The Vortec heads will leave me more options in the future anyways

I figured I may be able to get there with TBI it was the technical aspect that worried me, I'm not that good when it comes to the electronic end of things. Good to know a carb 350 does about the same and I kinda figured it would with the right carb.

Thanks for the reply its much appreciated

Tracy

 

[Overland Suburban]

The TBI Swirl Port heads are all done with flow around 4000 rpm.
I have read they are the worst flowing heads mother GM has ever mass produced.
If I were to rebuild the TBI in my '95 Suburban, those heads would not be included in the revision.
I would look into a set of the Vortec heads and matching manifold.
The Summit branded Vortecs seem to be a pretty decent deal.
They are a bit thicker in the right places and have all the little things done to them that will make them great out of the box.

You would easily achieve your goals with those and a small cam.

 

[Overland Suburban]

Catbox, I had read the summit vortec heads were not prone to cracking like the factory as also. I will definately go with the summit vortec heads

Thanks for the reply

Tracy

 

[skysurfer]

A cam swap and Vortec heads will provide a noticeable increase in power, but not 100 hp. Falling down the rabbit hole in search of performance, the limiting factor will then be the stock tbi's air/fuel flow. The injectors are too small to flow enough fuel for that kind of increase, not to mention the cfm limitations. The stock 42mm throttle body can be bored to 46mm and have bbc injectors installed which will support 300+ hp. Or, installing a complete 50mm bbc throttle body is an option, but I've read that idle and partial throttle performance can be tricky to properly tune. Fuel pump is another issue, it has to be upgraded as the stock unit was designed to handle the factory rated 210 hp and not much more. Air in, air out...stock exhaust also has to be changed if it hasn't already. And then there's the ecm chip, gonna have to get a custom chip to handle all the changes unless you drop big money on one of the fancy self-learning fuel injection systems available in the aftermarket. And after all that I still wouldn't expect an extra 100 hp with the stock displacement.

You can see why guys just swap in an LS engine and call it a day.

 

[Overland Suburban]

A few more questions

1 Since I'm going carberated what route would you guys go for fuel delivery keeping in mind reliability? Mechanical pump or pressure regulator with intank TBI pump. Either way I'm planning a return line to the tank to make sure I keep vapor lock at bay

2. With stock Summit Vortec heads what cam will give the best combo of economy and power?

I know, Suburban and economy don't go in the same sentence! Lol

3. What pistons would you use if I end up needing to bore the block. I haven't checked tolerances yet but may as well be prepared.

4. I was thinking edelbrock dual plane airgap intake manifold am I on the right track?

5. Which brand distributor has been reliable for you guys. I don't care much about cost but do care about reliability

6. I will probably build my own bracket for the TV cable for the 700R4 since I'm switching to a carb. I understand to keep ALL the geometry the same so its pulls properly. If there's a bracket that I can buy I will just go that route and save myself all the math if anyone can steer me in that direction.


Tracy

 

[shiftpro]

Catbox, I had read the summit vortec heads were not prone to cracking like the factory as also. I will definately go with the summit vortec heads

Thanks for the reply

Tracy

My engine builder buddy confirms this. But always inspect the valves, seats and guides with any aftermarket "Ready to Run' heads.

 

[4WDKC]

the problems with vortec heads is they have no exhaust crossover and makes it a pita for cold start in the winter. They also use different bolt patter so any accessory that has a bracket connected to the intake may not work or require fab work. The stock heads, cam and intake are **** for anything other than stock. I did the vortec heads and cam swap, had about a grand in it by the time I was done, then I had to tune the tbi and wished I had either swapped in the 454 I had or done an LS swap.

 

[Overland Suburban]

the problems with vortec heads is they have no exhaust crossover and makes it a pita for cold start in the winter. They also use different bolt patter so any accessory that has a bracket connected to the intake may not work or require fab work. The stock heads, cam and intake are **** for anything other than stock. I did the vortec heads and cam swap, had about a grand in it by the time I was done, then I had to tune the tbi and wished I had either swapped in the 454 I had or done an LS swap.

I would never go vortec heads and stay tbi. The tbi unit is very limiting from what I understand and it's a mismatched setup that seriously limits the vortec head. With a carb and vortec heads I can go 300 hp, 400 hp, 500 hp whatever I want to do.

I plan on spending a bunch of time in the mountains with the suburban sometimes 1000 miles from home. Old school setups can be fixed in the woods if you carry 3 spare parts that fit in the glove box and a small tool kit. I like simplicity and its a system I understand.

The tbi 350 is simple and reliable as well it sure would have been nice is they didn't set it up to be such a detuned dog

 

[bucket]

I would never go vortec heads and stay tbi. The tbi unit is very limiting from what I understand and it's a mismatched setup that seriously limits the vortec head. With a carb and vortec heads I can go 300 hp, 400 hp, 500 hp whatever I want to do.

I plan on spending a bunch of time in the mountains with the suburban sometimes 1000 miles from home. Old school setups can be fixed in the woods if you carry 3 spare parts that fit in the glove box and a small tool kit. I like simplicity and its a system I understand.

The tbi 350 is simple and reliable as well it sure would have been nice is they didn't set it up to be such a detuned dog

You can make a lot of power with TBI, it just takes research, custom tuning and usually some decent money (the cost is usually from the tuning and trying different parts that may or may not work). A 454 tbi and proper sized injectors atop a good 4bbl style intake is a good start. But there are other methods too. One that I would like to try is dual TBI units on a dual quad intake. Sure there are much cheaper ways of making the same power, but it would be reliable power and the parts would always be available across the country. And it's something different that's not often seen.

I'm in no way, shape or form trying to get you to stick with TBI. But you certainly can make substantially more power than stock with it.

 

[Overland Suburban]

You can make a lot of power with TBI, it just takes research, custom tuning and usually some decent money (the cost is usually from the tuning and trying different parts that may or may not work). A 454 tbi and proper sized injectors atop a good 4bbl style intake is a good start. But there are other methods too. One that I would like to try is dual TBI units on a dual quad intake. Sure there are much cheaper ways of making the same power, but it would be reliable power and the parts would always be available across the country. And it's something different that's not often seen.

I'm in no way, shape or form trying to get you to stick with TBI. But you certainly can make substantially more power than stock with it.

That sounds pretty cool a 4 barrel tbi unit. I had read that some people did some serious modifications and got impressive dyno numbers. If there was a mod system that was plug and play available I'd be all over the tbi thing. Or if there was a shop around that did tbi mod work I'd build an engine and go pay them to set up the tbi for me. It seems anyone who used to specialize in this kind of help has gone to the wayside, hense my reasoning on it being limited. Also have read many I did it myself testimonies of it ran good but always had a hiccup that steered me away from trying it myself Lol