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TBI 350........beef it or swap it

G-Force8

G-Force8

1/2 ton status
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May 15, 2005
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Whuz up gang

I have a '91 1500 Burb with the TBI 350, and basically, I want power and I need it reliable and legal ( for this regularly driven truck ). I've been looking for '91 3/4 ton 2wd Burbs with the TBI454 basically for a straight motor swap, the 2wd steering box for crossover steering and to pirate the rearend.

My question is, has anyone modified the TBI 350 in a lifted,daily driven and wheeled '87-'91 Suburban and experienced satisfactory power numbers ? I read an article in an older Offroad mag on a TBI 383 that put out 360HP and over 410 ft-lbs under 3k rpm. Will the stock computer handle more with a little tweakin'?

I plan to drive this truck regularly on the street and frequently offroad in mud,on trails and on rocky/twisty terrain and I need low-end grunt as well as decent high-end horsepower.

I'd like to keep the factory-type TBI setup for its simplicity if at all possible for easy servicing and part-finding. I'm not opposed to Nitrous,a turbo or a proven Supercharger either.

Any suggestions on building the bottom end? computer friendly roller cams? aluminum heads? Any haters wanna rag on the 350?


I'm basically trying to see if this motor can make decent reliable power spinning 36-38" tires under a Suburban.


Any and all experiences with these motors,swaps like the one I'm considering or any other interesting ideas welcome......


open the gates:D
 
yes they do test smog

there is no budget, but like I said, I'd like to keep the TBI setup for its simplicity and lack of clutter. I don't want to go into aftermarket injection systems and computers on this truck, at least not for a while , if ever.
 
Only thing I'd suggest if you decide on the small block route, is to go with a 383, and use a newer block that already has the roller stuff in it, and one piece rear main seal.

There are a few benefits to re-using the stock roller stuff (if not the cam) but the main one is cost. The cost vs. benefit of a roller cam IMO is not worth it unless you are racing.

If you can use a two bolt block, it will be no problem to find a good roller candidate for buildup, if you must use a 4 bolt block, a bit tougher to find.

Aluminum heads are overrated any more, same (but iron) heads make more power, just with a weight penalty. However, as you inch up in price, Aluminum heads become more and more viable. The new Vortec Bow Tie heads might be a good setup, depending on how much they cost new, complete. But always keep an eye on the aftermarket heads...the GM stuff gets quite close price-wise to aftermarket on the "good" stuff.

I'd say 360HP would require more than a "little" tweaking of the whole setup. Article posted up on thirdgen.org (currently down) was about a TBI 305 that a magazine had done a bunch of work to, and the whole thread plus the article was indicative of what needs to be done to make more power than the systems were originally designed for.
 
Aluminum heads dissipate heat more quickly and will tolerate higher compression ratios with lesser octane fuel. For the most part with trail trucks you won't be able to use this to your advantage with low rpms and crawl speeds. Its something more beneficial to drag racing, or other high rpm situations.
 
Yes, the problem with dissipating heat better is that it costs power, (heat=power) and the increases in compression ratio are necessary to reclaim the heat energy lost due to the head material. Thus, net gain for AL heads vs. Iron is pretty much nothing, except the advantage of weight, and welding is somewhat more of an option too I guess.

Either way, best to go with whatever heads do what you need them to do, in whichever material.
 
I have been considering either a set of World Iron heads or GM vortec iron heads with a little port work.

Thanks for the feedback guys
 
Vortecs do great, but the article you are referencing, what did they do about the valve springs? Was the cam that small?

If you keep the cam lift low (right around .450 @ 50), non-roller, and lower RPM, the vortecs will work real well. However, even on my VERY mild roller cam from crane, the stock Vortec springs weren't enough, so that was additional expense.

As long as whatever heads you decide on (if not Vortecs) has the proven fast burn chamber and the flow numbers to work where you want them to, you should be good.
 
i have tbi 350 in my lifted k5. decent power considering its stock. lookin to do exhaust soon tho. gearing is also important
 
I have been doing a bunch of research on swaping in a GM 330hp 350 crate motor with my TBI setup. CFM-tech and Turbo City both make kits to make it work with the TBI. I dont have to pass smog but I think it would. You can email Turbo City to find out, they have been really helpful to me. Also they make a kit to work with the GM HT383 motor but thats out of my price range.
 
I have actually been looking at Turbo City for their H.O. throttle bodies

Didn't see anything yet on making the 330HP GM vortec motor work with TBI

I'll have to look again

mucho appreciado
 
For the Turbo City kit just go to their web page and type in under FIND 970-505 that will give you the kit. CFM-tech has changed their site and I cant find the kit but I know they have one, you will just have to call them.
 
Just get one of these along with the TBI kit:xtremefimotor] This is a very good TBI motor. I have bought a few parts from this guy and have been nothing but pleased.

There is really no reason to buy a GMPP 350 HO motor. You can build your 91 TBI motor to equal a 350 HO specs. With the right chip programing, Bored to 600 cfm (46mm) TB, 65 lb hr injectors, cam, intake, flat top pistons, and some porting work on your 193 heads.
Some people think TBI heads are junk. But that is really not true. Is not hard to get them to build just as much power as Vortecs with a little porting. TBI heads are not a high RPM head but they can build a lot of power up to 5500 RPM which is ideal for a truck.
BUT FYI here is the link to CFM-Techs 350HO kithttp://www.cfm-tech.com/gm_tbi_camshaft_heads.htm But i dont think you will see 330 HP out of it using TBI without some work. I think with their chip and TB you will see around 310 Hp
To really tune a TBI engine for max power you need a flash programmer and burn your own chips.
 
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The big block would give you the grunt you're looking for and should be a fairly simple swap. If you can get the eprom from the donor vehicle you would be good to go. If you can't I could burn you one using the stock 7.4 binary. You probably would need a bigger radiator but you would need that with a 383 or even a hot rodded 350.

If you stick with a small block, I would definitely go with a 383 for the added torque with all other things being equal. You could go on up to a 415 or 427 but the cost climbs pretty steeply then. The stock 5.7 throttle body, 1 11/16" bores, flows enough air to make around 330 to 340 hp and 400 to 410 lbs-ft of torque on a 90% VE 383. This requires non-stock intake, heads, cam and exhaust.

PM me if you would like a build sheet for the 383 TBI motor I put together for my 90 Blazer. 370 hp at 5200 and 420 lbs-ft at 3500.

David
 
Thunder said:
Some people think TBI heads are junk. But that is really not true. Is not hard to get them to build just as much power as Vortecs with a little porting.
Click to expand...

I've gotta take exception to this. :)

Vortecs have entirely redesigned ports, which you simply can't do by porting TBI heads, and airflow alone doesn't=power. You simply can't make a TBI combustion chamber perform like a Vortec/Fast Burn chamber, which means combustion efficiency is never going to be as good based on the heads. If TBI heads are good for their original purpose because of the swirl ramp (low end torque, perfect for a truck) why bother porting them which, unless they are restricting power at low RPM's, will only increase the RPM at which major gains are noticed, and interfere with the combustion chamber mixing?

Port TBI heads as much as possible and the best you will end up with is heads that are similar to some good flowing "camel humps", which are still left in the dust by Vortecs.

Last I had some heads rebuilt (COMPLETE rebuild: surfaced, new matched springs, new valves/valve job, cleaned) they came out to right around $300. I could port till the cows come home, the time spent would never be worth the $200 extra you could spend to get some Vortecs. Or some of the pro-toplines or whatever they are called this week.

The beauty, if there is any, of the TBI heads is that you simply slap them on and use everything as the engine was assembled...no goofy intake problems, no EGR problems, no timing or fueling differences, etc. But even iron L98 heads are a jump up from the TBI stuff, and they'd be a bolt on too.

All we're doing is bench racing heads here, :) I've never seen back to back motor testing where a TBI head has been run against a Vortec head, with both tuned as well as they could be. There is a reason that no head currently in use by GM on production vehicles, (ever since the V8 Vortec debuted and as a matter of fact, even the TBI setup that DID make it into the Vortec V8 era used Vortec heads) has an intake port or combustion chamber that even remotely resembles the TBI heads.
 
I will agree that vortecs are a better performance head. They flow better and build more power on the top end.
But there is no way stock Vortecs will make the kind of torque in low and mid range that a ported 193 TBI head will.
TBI heads have the same size intake runners as Vortecs. They also suffer from the same thing other SBC heads. Small Exhaust ports. Port match, Open up the exhaust. Smooth the casting flash in the intakes, Smooth out and shape the swirl ramp for better flow (do not remove it). Un shroud the valves and they start to perform very nicely.
As I said in my other post they are an excelent head for a TBI truck. They build all their power under 5000 RPM.
Rember we are talking TBI and 2.5 ton trucks here. Not TPI or MPFI. Nor building a drag racer.
193 heads can be rebuilt and ported for around $600.
Same price as Vortecs. then there is a matter of $400 for a manifold and EGR plumbing needed for Vortecs.
Aftermarket heads like WORLD, Dart, ECT run $800+ But you will loose some low end with them But gain a lot on the top.
G-Force was asking about all his options with TBI and reliable power and still meet smog. I was just trying to pont out that if you are on a budget. TBI heads are a viable option for making power for a truck
I do all my own port work and dont mind spending 8 hours behind a die grinder.So doing a set of heads doesn't cost me much
 
Thunder said:
But there is no way stock Vortecs will make the kind of torque in low and mid range that a ported 193 TBI head will.
TBI heads have the same size intake runners as Vortecs. Rember we are talking TBI and 2.5 ton trucks here. Not TPI or MPFI. Nor building a drag racer.
Click to expand...

So why did GM use Vortec heads on their *trucks*? They are CPI, I give you that, but if TBI heads were better or even close to being equal than Vortecs, GM would have kept the TBI casting and simply improved flow. Again, GM used true Vortec heads with TBI in limited applications, so injection has little to nothing to do with the advantage.

Instead, they completely redesigned intake runners, completely re-vamped the combustion chamber, and threw the TBI head design in the trash, along with all the other dated heads.

The volume of the runners might be the same, but flow is nowhere close. It can't be, TBI heads have a gigantic ramp right at the valve, instead of a good combustion chamber and inlet path that do the same thing without hurting flow.

If the Vortecs move more air (flow) at the same port volume, which is proven, velocity increases, and velocity is where power is at, ESPECIALLY when combined with sufficient volume. I could show flow bench results, but even ported TBI heads don't match stock Vortecs on the intake side. Don't neglect the fact of more quench with the Vortec chambers, and with the improved combustion, you need less timing and can run higher compression on the same gas.

But you are right: Poster wants options, porting the existing heads will save you money, all things considered. Emissions requirements and EFI will add to a Vortec build a fair amount of money. If you have no visual emissions, then they start to make more sense.
 
Heres a few numbers to digest:
Ported 193 TBI heads:
Valve Lift------Intake Flow---------Exhaust Flow
.050--------------35.6----------------------31.0
.100--------------72.4----------------------60.5
.150-------------105.8---------------------87.3
.200-------------133.4--------------------124.2
.250-------------154.1--------------------147.3
.300-------------180.6--------------------171.5
.350-------------195.5--------------------184.7
.400-------------209.3--------------------196.3
.450-------------217.4--------------------203.7
.500-------------224.3--------------------215.6

Ported L98s:
Intake CFM

.100- 65.9
.200- 128.2
.300- 185.7
.400- 228.9
.500- 251.3 (max flow is at .525 lift)
.600- 239.2

Exhaust CFM

.100- 55
.200- 108.9
.300- 155
.400- 180
.500- 186
.600- 190.4

350 Cast Iron # 083
Lift/Intake/Exhaust
.100 44 41
.200 101 82
.300 155 125
.400 182 137
.500 196 140

Stock Vortecs
PORT SIZE: 170
CHAMBER: 64cc
VALVE SIZE: 1.94 / 1.50
FLOW @ .100: 70 / 48
FLOW @ .200: 139 / 101
FLOW @ .300: 190 / 129
FLOW @ .400: 227 / 140
FLOW @. 500: 239 / 147

I realise flow numbers dont mean a whole lot. But I really get sick and tired of people saying TBI heads are bad heads. Yes the intake is a little restricted but the exhaust will out flow most all other sbc heads even in stock form.
with the right cam they can be made to work very well.
 
Thunder said:
Heres a few numbers to digest: (ba-leeted for space)


I realise flow numbers dont mean a whole lot. But I really get sick and tired of people saying TBI heads are bad heads. Yes the intake is a little restricted but the exhaust will out flow most all other sbc heads even in stock form.
with the right cam they can be made to work very well.
Click to expand...

Where are the numbers from? Valve sizes?

Lots of reading on the swirl ports here:

http://www.thirdgen.org/techboard/tbi/336750-tbi-tpi-heads-headflow.html?highlight=tbi+porting+heads

http://www.thirdgen.org/techboard/tech-general-engine/192114-another-l05-crate-motor.html

Questioning the numbers because the numbers he got aren't even close to the above, if I read the posts right.

You are right, flow numbers aren't everything. Check out the exhaust to intake ratio of the "best" aftermarket heads out there that compare in volume, I think you'll find that the ratio is quite near the Vortecs.

However, even those TBI head numbers above on the intake side, if believable, are similar to the Vortecs, *untouched*. If the intake side is limited, so is the exhaust, no matter how well it flows. (not to mention velocity)
 
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