TBI 383 questions

[n4xplay]

I am currently having a 90s 350 block bored and stroked to 383 for my blazer. But my engine builder while looking in to cams for this engine calls me back and says that he has spoke with 2 race shops and 2 chassis dynos tuner shops and they all say the TBI is a waste and the engine will not run to its optimum performance with it, even if it does run it will be a dog! And none of their customers are ever happy with it and they blame the intake manifold cannot flow good enough even aftermarket ones.

So my question to the forum is what are your thoughts ... should I listen and go aftermarket FI or carb or can the system do it, if so what are your CAM recomendations so she will run good and be easy to tune ... I already have everything for the TBI set up minus a few sensors for the block, it supposedly came off a running truck but I don’t know how to verify the ECM or harness are GTG.
Also know that i do not have any knoledge on tuning the system nore do i have the equipment.



plans where 383 9.1 CR going to run the stock truck heads swirl port 193's for TQ going in a 82 blazer 35-37 tires 4.10 with TH350 auto
all I expect the blazer to do is trail runner, camp truck with light trailer pulling and weekend wheeler

 

[dyeager535]

Are you too far into the parts to not go 383? It doesn't really sound like your application requires a 383. I'm not saying a 350 and 383 are the same, but a well built 350 will do quite well, and I can only assume that sourcing the 383 specific parts (and whatever additional machining is to be done) is adding money to the build, that could be spent elsewhere.

The engine will most definitely not run anywhere near correctly as-is if you modify it from stock, in any manner. You will HAVE to have the system tuned properly to get it to run anywhere near it's potential. IMO tuning for a build like this is just as much a longevity/safety issue as it is performance.

Really need to look at the flow characteristics of the heads, intake, injectors, throttle body, cam and exhaust to see if they will "play well" together, with that displacement. A restriction anywhere means a bottleneck for power, and all of those can be changed/adapted to work well together.

I would *think* that Vortec heads, Vortec TBI intake (or carb intake+ adapter), and 454 throttle body would provide for strong low end torque numbers, yet allow enough overall flow to make decent power higher up.

 

[n4xplay]

the block machining, blue printing, rotating assembly has already been balanced and ready for install, so there's no backing out on that part .

as for heads... all the research and homework i have done over the last 6 months leads me to the fact that the 193 heads i already have will out perform the vortec heads in Tq production. plus flow better up till 4500 rpm and i plan to limit the revs to about 5200 at this point. latter i may pony up the cash for better heads but for now my goal was TQ production and set the bottom end up for future success on a budget.

the 383 may seem like over kill but i wanted the extra for mountain passes with a trailer because my wifes family lives, wheels and camps in Oregon so we make a lot of trips plus the varied terrain i like to play in mud, rocks, snow, and sand good torque would allow me to lug the motor with ease but still enough to light them up when needed for clean out. i am mostly a finesse driver

this truck was a basket case from the start 200k on a 305 smoking and burnt up th350 that was stuttering and sliping in 1st 2nd and 3rd im just going threw it from top to bottom and the engine was the biggest motivater and cost. the doaner 90s 350 had a hard 300k on it so i wanted all the internals replaces and going roller cam.

im looking at where i want the truck to be and building it that way one piece at a time

 

[F-ingrob]

im doing the same thing with my 87 tbi
i was told i could order a hip but im still not sure how or where to get one
and my short block is already built

 

[Big Ray]

consider TPI...?

 

[dyeager535]

I think if already into it this far, I'd just go the route of checking how well those heads will work with the 350 throttle body. If the heads flow enough to support the 383, then the next possible bottleneck is going to be the throttle body. I suspect it *probably* flows enough to support a mild 383, but that's an assumption.

I know the TBI heads in reality are supposed to flow pretty well, particularly for low end, so if they will do what you need them to do, no reason to change. I'm a bit curious though, is anyone else running those heads at 9:1 on 87 octane? The Vortecs I *know* will support that, but the TBI's I'm not sure of. I know the TBI ramp is the same idea as the Vortec chamber, just not sure if it's as efficient.

With proper quench you will minimize the propensity to detonate as well. .040" quench is the magic number...typically an .015" "shim gasket", with stock deck height at ~.025".

This might sound cocky, but I don't think those other shops know what they are talking about. On the TBI setup one of the last places I'd look for power limiting is the intake (that I'm aware of, the runners are no bigger or smaller than prior), except of course the throttle bores. And you can't fix that without a bigger throttle body anyway. My suspicion is that they can't, couldn't, or wouldn't tune the motors properly. Not sure how a TBI unit would have any more limitations than a carb. It is, after all, adding air and fuel in exactly the same location as a carb would.

 

[eagle mark]

I am currently having a 90s 350 block bored and stroked to 383 for my blazer. But my engine builder while looking in to cams for this engine calls me back and says that he has spoke with 2 race shops and 2 chassis dynos tuner shops and they all say the TBI is a waste and the engine will not run to its optimum performance with it, even if it does run it will be a dog! And none of their customers are ever happy with it and they blame the intake manifold cannot flow good enough even aftermarket ones. In bold is your mistake, none of them know what you want to do with the engine. Do race shops and DYno shops deal with near stock engines? Yes the TBI heads are a bottleneck... so build accordingly with a cam, I don't know exact RPMs but forget trying to get Dyno numbers above 4500 RPM with TBI heads, there's nothing about the vehicle build you want that needs it, sounds like a driver, tow rig and off roader? Your reading the internet and building a race motor... As soon as you go to a big cam you loose all your bottom end torque, now you need more then the 4:10 gears you have which are a minimum for 35 tires and a trailer. If the cam does not put out power till 2000 RPM? Well you'll need a high stall converter too! Poof, no more fuel milage and you sir have a race truck! Look at a stock TBI truck and it runs all day long under 2000 RPM... goes higher at highway speed but...

So my question to the forum is what are your thoughts ... should I listen and go aftermarket FI or carb or can the system do it, if so what are your CAM recomendations so she will run good and be easy to tune ... I already have everything for the TBI set up minus a few sensors for the block, it supposedly came off a running truck but I don’t know how to verify the ECM or harness are GTG.
Also know that i do not have any knoledge on tuning the system nore do i have the equipment.
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Listen to dyeager535 and others and finish the 383 build to what you want. The TBI heads and a small cam will keep the off idle torque monster. Or add a dual plane intake and headers, still good to go and is what you have planned for vehicle.

So my question to the forum is what are your thoughts ... should I listen and go aftermarket FI or carb or can the system do it, if so what are your CAM recomendations so she will run good and be easy to tune ... I already have everything for the TBI set up minus a few sensors for the block, it supposedly came off a running truck but I don’t know how to verify the ECM or harness are GTG.
Also know that i do not have any knoledge on tuning the system nore do i have the equipment.

PM Me for tuning, it's the best thing you can do for the motor and probaly the least expensive. But it must be done or the changes to motor are a waste of time and money. It's now a differant animal.

Are you too far into the parts to not go 383? It doesn't really sound like your application requires a 383. I'm not saying a 350 and 383 are the same, but a well built 350 will do quite well, and I can only assume that sourcing the 383 specific parts (and whatever additional machining is to be done) is adding money to the build, that could be spent elsewhere.

The engine will most definitely not run anywhere near correctly as-is if you modify it from stock, in any manner. You will HAVE to have the system tuned properly to get it to run anywhere near it's potential. IMO tuning for a build like this is just as much a longevity/safety issue as it is performance.

Really need to look at the flow characteristics of the heads, intake, injectors, throttle body, cam and exhaust to see if they will "play well" together, with that displacement. A restriction anywhere means a bottleneck for power, and all of those can be changed/adapted to work well together.

I would *think* that Vortec heads, Vortec TBI intake (or carb intake+ adapter), and 454 throttle body would provide for strong low end torque numbers, yet allow enough overall flow to make decent power higher up.

If he wants more power up top and willing to spend that much more money... so far all his plans for truck don't warrent the motor he is building? I haven't seen roller cam in here yet either? Flat tappet cam can be done but must run special/expensive oil forever if you want cam/tappets to last.

the 383 may seem like over kill but i wanted the extra for mountain passes with a trailer because my wifes family lives, wheels and camps in Oregon so we make a lot of trips plus the varied terrain i like to play in mud, rocks, snow, and sand good torque would allow me to lug the motor with ease but still enough to light them up when needed for clean out. i am mostly a finesse driver

this truck was a basket case from the start 200k on a 305 smoking and burnt up th350 that was stuttering and sliping in 1st 2nd and 3rd im just going threw it from top to bottom and the engine was the biggest motivater and cost. the doaner 90s 350 had a hard 300k on it so i wanted all the internals replaces and going roller cam.

im looking at where i want the truck to be and building it that way one piece at a time

Seems like your building a motor you don't need or want?

You may have just bought a Vortec L31 engine and been done... already has roller cam... well intake and adapter for the TBI, adjustable regulator and fuel pressure to 15 PSI with a chip/tune for it. It would meet all your goals at a lower cost.

 

[n4xplay]

the calculators for CFM say i will need 631 CFM max thats if i redline 6000 rpm, with my more conservitive 5k-5.2k redline i will only need 547 cfm for flow. my engine builder knows i am not looking for a lumpy cam and my expected redline is 5k.

my gess is the same as you Dyeager that race shops just run carbs or custom EFI and the dyno tune shops dont care to get in to the old GM TBI stuff. i am drawing a blank with quench so i will have to look in to that.

the block i built was a 90-91 TBI truck block, i got it with the throtel bodie intake, distro with ESP modual and heads, thats why i am runing them and the lack of cash for new ones.

 

[eagle mark]

There's nothing about your want's and needs for the vehicle your building purpose that requires an Engine Builder, Race Shop or Dyno!

OK well the engine builder is needed but more as a machinist for the rebuild!

Take a step back! You've learned a lot of stuff you have no need for... You've already got money into 383, now finish it to what the vehicle calls for. 383 does help for all your doing with vehicle specially the towing. Stop worrying about redline! Your plans will never see it? Why plan the motor build there?

Everyone looks at max HP and RPM. Then they never get there when driving and find the motor sucks under 2000 RPM where it's always driven? How does that help?

Find the limits of TBI heads and choose a cam for it!

You could use a 7.4L Throttle body and have stock intake machined to fit bigger throttle blades. You could also use the bigger injectors at stock 12-13 fuel PSI. There's barely enough fuel from stock 5.7L injectors and pressure for a stock motor. Or cheaper route just keep the 5.7L TBI and intake, but you still need adjustable regulator and more fuel pressure just to feed the added cubic inches, let alone more cam.

 

[80' 427]

I would suggest a very small cam. The heads flow horrible and the injector is limited. I would pick something like a 204 214 duration can or a stock vortec roller. Think idle to 4500.
Better to work with your parts than fight them. That cfm calculator figures 100% ve. Take that times .85 and you will see the cfm you really need. Despite what everyone thinks spinning 500 rpm over peak when you need wheel speed isn't bad as long as you have enough valve spring. It is a truck not a race car. If you need more get a set of vortecs and a good intake with an adapter.

 

[Big Ray]

I think if already into it this far, I'd just go the route of checking how well those heads will work with the 350 throttle body. If the heads flow enough to support the 383, then the next possible bottleneck is going to be the throttle body. I suspect it *probably* flows enough to support a mild 350, but that's an assumption.

I know the TBI heads in reality are supposed to flow pretty well, particularly for low end, so if they will do what you need them to do, no reason to change. I'm a bit curious though, is anyone else running those heads at 9:1 on 87 octane? The Vortecs I *know* will support that, but the TBI's I'm not sure of. I know the TBI ramp is the same idea as the Vortec chamber, just not sure if it's as efficient.

With proper quench you will minimize the propensity to detonate as well. .040" quench is the magic number...typically an .015" "shim gasket", with stock deck height at ~.025".

This might sound cocky, but I don't think those other shops know what they are talking about. On the TBI setup one of the last places I'd look for power limiting is the intake (that I'm aware of, the runners are no bigger or smaller than prior), except of course the throttle bores. And you can't fix that without a bigger throttle body anyway. My suspicion is that they can't, couldn't, or wouldn't tune the motors properly. Not sure how a TBI unit would have any more limitations than a carb. It is, after all, adding air and fuel in exactly the same location as a carb would.

I'm not being a smartass...you are the first person I ever heard of who felt that way about those heads...

TBI CHIPS is a great resource for TBI mods...here's an excerpt:

4. The Heads. The TBI heads are the worst flowing heads GM ever released. So the best bang for the buck is GM Vortec head but does require a special intake and lots of EGR work if you need EGR to remain emission legal. These heads are good for a minimum 50hp gain. Another good reasonably priced set of heads that will work nicely without special intakes on a TBI motor is a set of DART 165 iron heads. They flow well and the price isn't bad. The DART 180's also flow well and have a better exhaust flow than many small block heads and so I would keep the cams intake and exhaust duration tighter together. Now if you don't need EGR for emissions testing then check out these heads Click here for more information about Edelbrock 5089 - Edelbrock E-Street Cylinder Heads Next to the cam this is the most important choice. Compression ratios and pistons and all that stuff are not near as important as the head and cam choice. That decision will make or break your engine project and you wallet if your not careful.
Also, tow beasts and 4x4 guys. This section has changed recently after the dyno results cam in for the plum crazy project. While the hp numbers up to 3000 rpms is pretty close to any other head the torque numbers were not. Plum crazy didn't make near the torque numbers the vortec headed projects did and even after a lot of work it didn't make a lot more torque than stock. . Well most 4x4s and tow beasts are more concerned about low end torque than having 500hp at 6500 rpms where they can't use that power. So you do want to keep the intake runner size on the heads at 180cc or less. The comp cams 12-249-4 cam along with the 1.6 rockers that I mentioned on item 2 will make really good power and torque on a 350 TBI motor up to 4000 rpms.


full article

 

[n4xplay]

first off thank you all for your replies .

Mark you are right the 383 was a WANT not a need but I can’t be faulted for that lol. As for listening I am all ears and eyes, I posted here because you all are the subject mater experts for what can be done with the early GM TBI over my local race and dyno shops.

I have no illusions of racing this engine, my only goal is a solid torque producing power plant that will pull from 1k till 4k and displacement makes torque easier. The only racing this engine and truck will see is a joy ride down the local mud strip with the family loaded up. The 5k redline is only my intended stop point for the motor not where I want to make the biggest numbers

my builder/machinist was only talking to the race shop for a cam shaft recommendation and they came up with nothing, so I’m here.

Dare I pose the question, should I run the TBI and TBI heads with say a comp cams CPU or extreme 4x4 stick X4258HR or X4260HR and a tune.

or sell my TBI setup throw a carb on and keep saving for stand alone FI (fast ez) and replacement heads

I will look in to the estimated quench of my engine and will also look in to some budget heads if I can find them, and report back .

 

[dyeager535]

I base my statement on posts over on Thirdgen, where guys have flowed, and shown, that the TBI heads can make power. For *low end* the TBI heads work. The Vortecs revised ports and chamber undoubtedly contribute to their efficiency over the TBI heads, but as Mark alluded to, flow is nothing if it's outside of where the engine is typically used, or the range it is designed for.

Based on the specs I can come up with quickly, the 1991 K5 engine was 210HP@4000RPM. The L31 (Vortec 5.7)was 255@4600RPM. Based on the data you mention (and I've seen +40HP elsewhere too) that puts the figures almost exactly in line, but at a 600RPM higher peak. And thats with roller cam, and CPFI or whatever it was...not a wet runner setup. Torque specs would be more indicative, which I don't see for the 1991 K5 motor, however the L31 was 330@2800RPM if anyone finds late 80's early 90's torque specs and wants to compare. L98 (TPI) specs I could find are 230hp@4,000RPM with 330 foot-pounds of torque at 3,200 rpm.

As far as I'm concerned, low end grunt is great, but it's like sticking a tiny 2 barrel on a 454. If I was going to limit myself, I'd not have started increasing displacement in the first place. I'd have built a 350 with decent low-end, and an upper end that wasn't way out there. Everything on an engine build is a compromise if it's going to be used on the street, and IMO, to build an engine that is the most fun to drive, it needs to have a good balance of low end, and enough upper end to make you smile.

You could throw a TPI setup on a 383 and I'm sure low end would be quite strong, but the motor would be done due to airflow limits as opposed to the rest of the components potential. I don't think I'd worry too much about using TBI as the basis for the motor. Port injection is cool and all, but I think based on the OP's intended usage, spending the amount of money to properly port inject this motor, would gain far less than would be spent. At this point, the 383 is being built, so all that can be done is get the rest of it working with that fact. A roller cam out of another small block would retrofit quite easily, since the 90's block that the OP has will be set up for the roller, just not have the components. Factory roller parts should be very easy to find, and cost effective.

 

[eagle mark]

You have great advice on cam for TBI head motor right here!

I would suggest a very small cam. The heads flow horrible and the injector is limited. I would pick something like a 204 214 duration can or a stock vortec roller. Think idle to 4500.
Better to work with your parts than fight them.

The 2 cams you linked to are Roller, that is another expense to make your engine a Roller Cam, a good expense if you have the budget, if so choose the smaller of the 2.

Forget a carb, TBI is the best carb you can get!

Forget the FAST EZ unless you want to spend big bucks and fuel a beast motor.

TPI works great on low end torque motors, but that is another whole project you don't have parts for.

As stated above there is some Injector limitations, but as a said these can be overcome with adjustable regulator and correct fuel pump. You'll have plenty of fuel to supply HP needs of this type engine.

 

[n4xplay]

most of the info i have about the TBI heads i have from scrounging around reading old old posting from FAST305 and fast355 on thirdgen and fullsizechevy, this member used to be on the against them as well and finaly bit the bullet to end the debate and found out great info about them

 

[dyeager535]

Agree with Mark. With the TBI heads, any cam made for anything other than "stock" is almost certainly going to be wasted due to the heads. You can get whatever cam you want of course, tuning IS in the cards in any case, there is no way around that with EFI.

Just stick with TBI. Every time I hear someone say they threw a carb on in place of EFI, I scratch my head. I drive a modern car daily because it starts and runs every day, in every condition. I *don't* have a carb on any of my vehicles (anymore) because they are the exact opposite. Yes, they can be tuned to run pretty well, under most conditions. To get them to run under all conditions the same as EFI? I don't think so. The "carbs are simpler" argument is idiotic IMO. I can find plenty of posts just on CK5, where people can't get their carbed rigs to run right.

 

[n4xplay]

so for a shopping list,I need :
- 454 TBI base
-should I go with the 65Lb, cop injectors
-adjustable fuel pressure set up

Mark once I get it installed I will be in touch for the tune

thank you all again

(62 fat guy I'm not being a smartass...you are the first person I ever heard of who felt that way about those heads...)
im not knocking what you posted as i have read it and i dident take you as a smart A$$ but i dont blindly follow with out doing my homework yes its up on a web page but there is no stated reasoning to why the heads are junk , my view is there is always tradoffs its like talking to some one about there AT tires, your told ya there great in the snow but suck in mud.../ the head doesnt flow and makes crap HP ... wheres the traid off... my point is everything is good at somthing or was good at somthing and untill you run the AT tires and find out for yourself what there limits are its just passed on information and can be jaded or biased wich is still good but you get my point.

 

[n4xplay]

agree the carb IF used would only be to to use the blazer till EFI is installed and would not be a perminant install by any means.
but at this point i still have plenty of project left to complet before the ingition key gets turned to fire it up, heads may be in the budget afterall

 

[dyeager535]

The flow limits of the throttle bodies are known. If you go 454TB you will need to have the intake bored, or get another one. If you don't NEED the 454TB, don't get it. I don't have it off the top of my head, but I seem to recall the 350TB comes out somewhere just over 500CFM. Does that fit in with what the engine is going to require?

Personally, if my research indicated the 350TB was enough, I'd just go with larger injectors (although if you get a 454TB, it will have them if used), and see if it could be tuned that way. Going 454TB/injectors/intake now will ensure you don't HAVE to change parts later, but you've already got the TB and intake, the only thing you need is injectors. Outside of those, if it can be tuned as-is, I wouldn't spend the money on additional parts. I don't believe an adjustable fuel pressure regulator (AFPR) is in the cards yet either, IF the stock one gets fueling where it needs to be, and the injectors are larger than the 350. With larger injectors, pressure isn't nearly as critical as it is if you are on the ragged edge with smaller injectors. If you want to save money, you can even shim the regulator instead of getting something adjustable (once set you won't change it anyway), but that will involve (easy) tear downs until you get it where you need/want it.

Mark screws around with these things way more than I do, so I defer to his experience, but for a low RPM motor, I just don't see incurring extra expense if the benefit isn't there.

 

[n4xplay]

That sound like a plan bigger injectors stock 350 body and pod spacer with stock heads and intake... mark do you concur?
It won't be optimum but will get it going