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  1. #1
    Member 92BlackVette's Avatar
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    Default Tuned Port Fuel Injection LT1?

    Please explain to me why people buy Tuned Port Fuel Injection stickers for their LT1 (1992 and 1996) Corvettes?

    Maybe I am not understanding something?

  2. #2
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    Because TPI is better than a LT1.

    L-98 has:
    no optispark
    makes more torque
    easy to mod
    looks better under the hood


    Just a better engine in my opinion. A classic 350 small block. If the LT-1 was better they would still be making them and sticking them in other models.

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    Quote Originally Posted by nelson84 View Post
    If the LT-1 was better they would still be making them and sticking them in other models.
    Another of your uninformed comments
    The LT1 was the ultimate development of the conventional SBC format built since 1955 before GM went to the much superior LSX engine.
    Change of head design on LSX has resulted in a much more powerfull engine in stock form.
    Times change things move on ; otherwise we would still be driving flathead V8.

  4. #4
    Member Schrade's Avatar
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    LT1 IS a tuned port injected motor, same as L98..

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    Quote Originally Posted by vetteoz View Post
    Another of your uninformed comments
    The LT1 was the ultimate development of the conventional SBC format built since 1955 before GM went to the much superior LSX engine.
    Change of head design on LSX has resulted in a much more powerfull engine in stock form.
    Times change things move on ; otherwise we would still be driving flathead V8.
    No you are wrong. The LT1 is not the same engine that was built from 1955. They moved the distributer to the front(optispark). They call the LT1 the Gen II engine and the LS1 is the Gen III and you guessed it the 1955 to 1991 is the Gen I engine.

    Hope this helps.

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    Quote Originally Posted by nelson84 View Post
    The LT1 is not the same engine that was built from 1955. They moved the distributer to the front.
    1955 to 1991 is the Gen I engine.
    So what "Gen" is the L31 Vortec 350 engine ;
    built '96 - "00?

    The LT1 has the same basic dimensions as the Gen I engines.Same bore spacing , same external dimensions , same head bolt pattern so it is a development of the original SBC.Many of the Gen I and II parts interchange.
    You can even run a Gen I distributer on a Gen II with the right carb intake.
    http://paceperformance.com/index.asp...D&ProdID=22961
    Gen III is a completely different engine having no common parts with either Gen I or II

    They moved the PCV valve and changed the oil filter type in 1967;they went to a roller cam and 1 pce seal RMS in 1987; didn't make it a new type of engine.

  7. #7
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    Wow...really cool info. What amazed me so much about the LT1 was the "Reverse Flow Cooling". Why would they not do that on all engines? Seems like a good idea and makes a lot of sense. Would this be one of the reasons the LT1 holds up so well?

  8. #8
    Member Schrade's Avatar
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    They're not even arguing about 'tuned port injection', which is what OP was askin' about.

    'Tuned port injection' means one injector (or more, like LT5) per cylinder. L98, LT1, LT5, are tuned port motors.

    edit:
    The injector IN EACH PORT has it's own pulsewidth. The pulsewidth duration is TUNED for that cylinder. Tuned port injection.

  9. #9
    Member 92BlackVette's Avatar
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    Alright I understand the LT1 could be converted to a L98, TPI but from the factory my 1992 is referred to as: Multi-port injection (MPI) system --> notice "tune," isn't used.

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    There are a number of interesting assumptions in this thread...

    An LT1 cannot be converted to an L98.

    "Tuned Port Injection" like "Generation 2 Small Block V8" were marketing terms. "Tuned Port" was a name coined by Chevrolet marketing weenies back in the early 80s for the port fuel injection system used from 85-91 on the Corvette and until 92 on the Camaro and the Pontiac Firebird. It gets its name from its long intake runners, the lengths of which were selected or "tuned" to cause an increase in low-speed torque.

    The "Tuned" name was dropped in 92 in favor of another, even less descriptive moniker "Multi", but the 92 LT1 (along with the later L99 and LT4), also, used intake port length tuning to affect torque...but the port length was much shorter, which raised the rpm for which the runner length was "tuned". This also allowed the LT1 its higher rpm range and greater power.

    The Generation 2 (or "Gen 2") Small-Block V8 arrived in 1992 in Corvette and in 1993 in Camaro, Firebird and the GM B-car. While its block architecture was very much the same as the traditional small block (the so-called Gen 1 of 55-91), there was a big change in the cylinder head and cooling system to acomplish the "reverse flow" cooling discussed above.

    "Nelson84" is incorrect in saying the L98 (350 cuin version) of the Tuned Port engines are "easier to mod". Reality is each engine has good points and bad points as far as their potential for modification, but, if "modification" means significant increases in horsepower and an extension of the engine's rpm range, the L98s big problem is the tuned port system itself. The intake manifold, the runners and the plenum are highly restrictive and a big problem when modification for high horsepower and high rpm are the goal.

    "Nelson84" makes the misleading statment that the L98 makes "more torque". It is true that, in stock trim, the L98 engine has slightly more torque output between off-idle and the mid-range rpms but, if you consider the entire useable torque curve of the engine and the torque peak, the LT1 makes "more torque".

    As for "no Optispark" well....yeah, the L98 had the rear-mounted distributor, but that "no Optispark" is an advantage, I think, is debateable to a certain extent. I'll admit that the early ABITS distributors where flawed by poor moisture sealing but that flaw was eventually eliminated. The later ABITS distributors were not the reliability/durability problems the first ones were and were a much more accurate way to control ignition.

    No doubt, TPI systems look better under the hood. The long runners are pretty darn sexy.

    Another comment above that Tuned Port means one injector per cylinder is not correct. The LT5 has two injectors per cyinder. "Tuned Port" refers to the length of the intake runner not the number of injectors per port.

    Yet another comment above, the one about being able to backdate a Gen II with a Gen I distributor by changing the intake manifold, is not correct.

    Someone asked about the Vortec 350 truck engine. GM called that "Gen IE" and they were basically the Gen I engine with the best of the Gen II cylinder head, but no reverse flow cooling.

    Lastly, the final interation of the Gen II, the 330hp SAE net, LT4 was the most powerful production Small-Block V8 which used the traditional block design. If the old gross power rating system used in the muscle car era had still been valid, that engine would have been rated at about 410-430 hp. Such a power level would have been impossible using the L98 style induction and 2-bolt main cylinder block.

  11. #11
    Member Schrade's Avatar
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    Quote Originally Posted by Hib Halverson View Post

    Another comment above that Tuned Port means one injector per cylinder is not correct. The LT5 has two injectors per cyinder. "Tuned Port" refers to the length of the intake runner not the number of injectors per port.
    Who said that? I see that nowhere in this thread, except in my post, where I noted the exception for LT5...

    Quote Originally Posted by Schrade View Post
    They're not even arguing about 'tuned port injection', which is what OP was askin' about.

    'Tuned port injection' means one injector (or more, like LT5) per cylinder. L98, LT1, LT5, are tuned port motors.

    edit:
    The injector IN EACH PORT has it's own pulsewidth. The pulsewidth duration is TUNED for that cylinder. Tuned port injection.
    Seems you're also saying that injector pulsewidth variation is not 'tuning'??? The air volume is not variable, whereas the fuel is variable (tuned). Clarify please...

  12. #12
    Member Schrade's Avatar
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    Seems to me also that since the LT5 says 'Tuned Port Injection' on the side of the car, that the LT5 is 'tuned' in the intake ports, and pulsewidth of the injector(S) is what is 'tune-able'. At least that's how Ray C. Bohacz looks at it, as a professional wrencher and writer (page 20, column 1). He makes more that me, and puts it into writing, so I have to agree with him, unless someone informs him that he's wrong, and he changes it.

    I gotta' believe that LT1 and LT4 are also considered tuned in the ports, like L98 and LT5.

    (the rest of the article is VERY informative, if anyone wants to read it)

  13. #13
    Member 92BlackVette's Avatar
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    I like this thread! My problem, and reason for starting this thread is derived from the following product (you can see why by reading the bottom):



    Source:92 LT-1 CONSOLE SPEC PLATE Corvette Parts and Accessories - Zip Corvette

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    That console plate is not correct. It should not say "Tuned Port Injection" but my guess is all the plates sold for 85-96 say that. It's cheaper to make them that way. Also, some people feel "tuned port injection" is a cool name so there's the feel good aspect, but "tuned port injection it is not. If the plates were accurate, the 92-96 items would say "multi-port injection".
    Quote Originally Posted by Schrade View Post
    Who said that? I see that nowhere in this thread, except in my post, where I noted the exception for LT5...
    Oops. I misread that part of your post. I apologize for misquoting it.
    Seems you're also saying that injector pulsewidth variation is not 'tuning'??? The air volume is not variable, whereas the fuel is variable (tuned). Clarify please...
    I am not saying that. The injector pulsewidth variation which takes place when the engine controls are in closed loop is not from where the "tuned port" injection name comes.

    It comes from the fact that the intake port runner length is "tuned" to increase torque in a specific rpm range...hence the terms "tuned port". If Mr. Bohacz said otherwise, he's got it wrong.

    Indeed, the LT1 and LT4 used intake port tuning to enhance performance but not in the same way as did the L98 and other TPI engines and the "tuned port injection" moniker was never applied to them by GM.

  15. #15
    Member Schrade's Avatar
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    Well, I'm not agreeing here at all...

    In my opinion, it's injection, that occurs in the intake port, and it's 'tune-able'. Yes the airflow design is 'tuned', but that is a fixed, UNtune-able function. The injection is tune-able. It HAS TO be, since the intake design was based on flow characteristics for a 305 TPI.

    (that's according to Bohacz also, but, maybe he's wrong there too?)

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