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Switching TBI over to Carb, performance gains?

Discussion in 'The Garage' started by MudFrog, Aug 26, 2005.

  1. MudFrog

    MudFrog 1/2 ton status

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    I've been looking at going with a completely different engine with carb as I've been doing a lot more mud and my stock 350 w/ tbi just does not have the power to turn the tires in this Virginia Red Clay. I would build up the FI but do to the cost and everyone I know of that has tried it has had issues so I'm gonna go carb.

    So the question. Should I see a decent power increase just by going to a carb and putting in a beefier cam? Most of the guys in my club seem to think just ditching the FI and putting in a larger cam will gain me decent power for not as much money as going with a completely different engine. Are all of the other parts on the TBI model 350's carb compatible (minus the intake manifold)? I also know a new fuel pump will need to be used. Can I use a Cam from an older model 350 or do I still need one specified for TBI? I'm assuming the specify TBI just for the mildness of the Cam since it is computer controlled.

    Any thoughts?
     
  2. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    I dont know about the power difference... however I put a tbi 1991 chevy caprice police 350 in my truck...
    took the intake off.. put a 1989 z-28 aluminum intake on and a holley truck avenger. You have to realize that if I kept the tbi.. I could have gotten the chip from the cop car.. but I wanna change my cam/heads out and not have to worry about something telling me NO.... fark that... I just do it and no brain to over ride it..... :haha:
     
  3. 6.2Blazer

    6.2Blazer 1/2 ton status

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    If simply comparing replacing the stock TBI with a carb and nothing else you would probably see no power difference.......if anything it would lower the power. Keep in mind that GM went from a power rating of about 160 hp on a stock carbed 350 to 210 hp on the TBI version, along with better economy and driveability.

    Overall it depends on exactly all you want out of the engine. A guy I work with recently installed a GM Vortec crate engine along with a few other mods into his TBI truck (kept all of the stock TBI and computer stuff) and it runs really strong.
     
  4. MudFrog

    MudFrog 1/2 ton status

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    The main reason is because you can build a higher HP engine that is carb'd for a lot less then TBI.

    I would plan on doing a decent size cam and maintaining the current heads, although eventually changing the heads.

    I have been told (which I'm in no way an engine expert so I tend to beleive what I hear), that just changing the intake manifold, a bigger cam and changing to a carb will yield a bit more power then it is in it's current configuration.

    Stupid question but would it not gain at least a little more power just from going to a 670 cfm carb as opposed to the 450cfm tbi?
     
  5. 6.2Blazer

    6.2Blazer 1/2 ton status

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    You won't gain any power going to a bigger carb unless the cfm rating of the current setup is limiting the engine........and any gains will typically be on the top end of the powerband. Low end power can be the same or even less with a bigger carb (there are a lot of variables besides just cfm rating of a carb).

    A good example is a friend of mine who's running a big block Ford. He's played around with different carb setups including a small 2-barrel version up to a Quadrajet. Even though the 2-barrell has a significantly lower cfm rating it has a stronger seat-of-the-pants pull off the line, but the top end does suffer some.

    Again, it just depends on what you want. If it's going to stay a flat land mud bogger and you want a really radical motor, than carb may be the way to go. However if you ever do any trailriding I would personally hate to lose the driveability and angle ability of the TBI just to get a little more power.
     
  6. MudFrog

    MudFrog 1/2 ton status

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    I'm not totally giving up trail for mud, but I will be doing 80% mud. As far as the driveability on angle's and so forth, I plan on running a truck avenger, I have seen several guys follow me with those and they did not sputter on any hill climbs.

    As for the power I'm trying to get more upper end power. My truck does not currently have enough power to spin the meats very fast in the mud to keep me going. The engine ends up bogging down and I lose all propelltion.
     
  7. MudFrog

    MudFrog 1/2 ton status

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    I might just hold off and buy a new engine that has both the HP and TQ that I'm looking for, instead of building up mine.
     
  8. Thunder

    Thunder 3/4 ton status

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    You have one big problem with carbing a TBI motor to get more top end power.. The Heads. They dont flow. They are pretty much done for at 4500 RPM. Its a waste of money to put a Carb, Cam, and intake on without getting better heads Unless you want a low rpm torque motor.
     
  9. big_truxx

    big_truxx 1/2 ton status

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    but also keep in mind that the mr goodwrench 350 is rated at a lot more than 160.... more like 225... so it depends on what you have. had a mr goodwrench 350 with headers which a dd told me it was right around a stock 454 power... 265/350 hp/tq...

    id say imho depends on what you want. i think i am gonna go back to a carb on my 89 scotsdale 454 tbi crew dually... just for simplicity and power. and not wanting to guess that a summit cam will be compatable with the tbi and be wrong...
     
  10. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Putting a carb on a TBI engine doesn't help you out a whole lot. Like mentioned above, the engines are designed to have made all their power by 4500 - 5000 rpm. So putting a carb on it would allow it to flow better through the carb for sure, but your engine won't be making any more power as it will not be utilizing the extra flow. Basically, you'd be taking away the economy, and low end torque to make up power in the high range that doesn't exist :)

    However, if you are planning on building a big high performance engine with a big lumpy cam, etc, then yeah, go for a carb, becuase most of those engines are built with all their power being built in an RPM range that the TBI cannot support.
     
  11. dirtwarrior17

    dirtwarrior17 Banned

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    A performance efi system will cost you around 1k... I could have a edelbrock efi system for 400 bucks more than i paid for my tbi but now i can modify the fuel curve however i want to cope with mods.

    670 cfm tbi and a 2" efi manifold will run you 600 bucks new but can be had for 300 bucks on ebay.

    I'd look for some deals before you go carb... you will lose, low end tq, throttle response, gas mileage, and a little driveability if you go carb.

    I paid about 3200 all together(10:1 compression longblock with l-79 cam and camel hump heads, projection efi manifold, 670 cfm tbi, headers, k and n, fuel pump, prominator, and labtop all bought NEW) and ended up with a 330 hp 390 ft lb TBI 355...

    That is more than enough power to satisfy me for now... but when i get back from iraq the first thing im gonna do is put some darts or afrs on there.
     
  12. MudFrog

    MudFrog 1/2 ton status

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    Here is the problem I have with that. I have several friends who have tried to build up their TBI engines and nobody could ever get the computer to handle the mods correctly. The engines ended up running like crap. Not to mention it will be so much cheaper to build a carb'd engine.
     
  13. Thunder

    Thunder 3/4 ton status

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    Its not hard to build a TBI engine to make good power. The mistake most people make is buying a bunch of mis matched non computer frendly performance parts and trying to get a stock or aftermarket generic chip work with them. Usually takes time on a dyno and someone who knows how to burn chips and some $$$ to get things right.
    But........
    If you build your engine around the chip which is the brain of your engine things go much better. The best thing is to get a hold of a good chip burner Like:
    http://www.fastchip.com
    http://www.affordable-fuel-injection.com/ CK5 vendor with 10% discount for members.
    http://www.cfm-tech.com/gm_tbi_camshaft_heads.htm
    http://www.turbocity.com
    and talk to them. They have programs for many performance combos that work. And will recomend heads, Cam, intake, exhaust, mods that are known to work well with their programed chips. With the right chip and proper mods done right you can get around 280 Hp from a stock TB, More Hp can be made with a bigger modified TB Good heads cam intake ECT.
    You dont have go back to the stone age to make power. The GM TBI is a very good reliable unit if you want to work with it.
     
  14. dirtwarrior17

    dirtwarrior17 Banned

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    Nice sig thunder... :D

    what he said...

    You simply can't modify your motor buy and chip from jegs and expect it to run titty. If you want to make up and over 300 you need to burn a new fuel map.

    If you don't want tbi that bad then go for the carb... but if your willing to spend a little more time and money on it you won't regret keeping the tbi.

    I had a carb and manifold ready to slap on her when i found out about this thing...

    http://misterbill.homeip.net/aboutprominator.asp

    basically with a labtop YOU make the changes to the fuel map wherever you see fit. You can modify and change fuel maps while your driving down the road and it will save 6 seperate fuel maps which can be changed with the turn of a nob once you burn them. Its looks complicated at first but once you do a little research it starts to look more and more like english.
     
  15. MudFrog

    MudFrog 1/2 ton status

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    My buddies used custom burned chips from some of the more reputable places online, not a basic performance chip.

    I would be willing to keep the TBI as I really do enjoy the easy starts, no stalling, etc.. but I'm also wanting a motor up around 400 HP and I don't want to spend $4000.

    How do the FI models handle Nitrous? Anyone know. I sell NOS and I saw they make a 100-150 shot for a stock TBI 350. I would never throw 150 at a stock motor, but I would throw 100-125 at a mildly built 350.

    The way I figure it is if I can get my motor (whether it be a FI or Carb'd engine) up to around 330 HP plus a 100 shot of Nitrous then I would be more then happy with the performance.

    Anyone stroke their TBI 350 to a 383?
     
  16. Mad-Dog

    Mad-Dog 1/2 ton status

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    Amen brother.... :bow:
     
  17. dirtwarrior17

    dirtwarrior17 Banned

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    Straight up all the performance tbi stuff will cost you about 1k including the labtop and prominator. Probably less if you hit up ebay.

    330 hp is very reasonable with the right tbi setup... there are guys over at thirdgen.org pushing 400 ponies with holley's tbi and manifold. But they burn their own chips and have figured out which cams tbi likes.

    Don't know about the NOS...

    Theres plenty of guys with tbi 383's on here...

    Speak up brothers...
     
  18. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    well it seems that when I floor it... I get to about 3k rpm's then she launches into action...
    I definitely need a cam... however I may be able to get a fuel injected 454 with all wiring... may just go that route.... stocker shouldnt do bad...

    my current motor is
    1991 caprice police 350 9c1 (L05), cast heads, truck avenger, z-28 intake, full length headers and true duals..
    I dunno my new hp ratings but seems bad and sluggish....

    but stock engine with tbi, manifolds, single exhaust is
    195hp @ 4400rpm
    295 torque @ 2400rpm
    I would love to dyno it right now to see if my mods did better or worse...

    I have been debating a cam/head/intake change...

    vortec heads = need new intake.. so no reason for me to just change the intake right now and not the heads...but for $300 used heads and $150 intake I could just go 454 injected.. I just dont really know if I want a brain in my truck. I like it stupid.... :haha:
     
  19. dyeager535

    dyeager535 1 ton status Premium Member

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    As dirtwarrior is alluding to, people can't burn a chip "remotely" and have it work on your system. Even someone that has tons of experience in tuning via the chips is going to take 25+ attempts to get it really dialed in well.

    If you don't have to send a company datalogs, and keep going back and forth trying new chips from them, with a datalog each time, they can't even begin to get close. Just as GM did, they design in a margin of error to keep things safe.

    Just as an example, on my MAF TPI setup I started with a 1987 305 PROM, with the 350 specific hardware. It ran ok, I drove it over 1000 miles, and economy was decent. (13MPG out of about 30 gallons, about 2 hours at 60 MPH up and down a mountain pass, the rest up and downhill on logging roads) But it had some problems with jerkiness, throttle following, and hesitation on acceleration. And that's with a really mild motor that should be pretty happy with stock TPI. BUT, with new heads, base, cam, and exhaust combined, it was apparently just too much for the setup to compensate for. I burned a stock 1989 Corvette .bin (PROM) and installed it, and the truck is 10 times better in all conditions now, but still not perfect.

    I don't think I'll ever be happy with a carb again. If I was solely racing, or doing something like mud 100% of the time where it's pedal to the metal always, then a carb might still work for me. In those situations, the difference between EFI and carb is blurry. But when you start talking about starting in any condition, idle quality, and general driveability, a carb will NEVER match injection, no matter how much you play with it. Those alone are the reasons I can't see myself going back to a carb.

    It's like starting out with a 454 and then having a 6 cylinder installed. You've been spoiled and know what things are SUPPOSED to be like. :)

    I think that's really what you have to ask yourself: are you willing to trade driveability by giving up the injection? If you can stand to deal with the quirks that invariably come with carbs (hot or cold start issues, flooding, stalling, etc) then no reason not to switch. It is certainly easier to make any motor (especially when talking a decent amount of power) run decent with a carb than with stock fuel injection.
     
  20. MudFrog

    MudFrog 1/2 ton status

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    That is exactly where I'm at. Right now I think the trade off would be worth it as I cannot even compete in the local bogg's as my engine just does not have the required power to spin the meats fast enough in the mud / clay. I think what I will do is find an engine (454 or 383) and run a carb for at least a year. This will also allow me to decide if the trade off is worth it.

    If it is not I will sink some money into a good MPFI. I think I read somewhere that the Edelbrock version was rated up to like 500 hp. I know it's pricey but hey.. what are tax returns for?
     

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