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Thread: Spacing question

  1. #1
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    Spacing question

    I'm looking for specs on stock injector spacing/fuel rail spacing for my project. Does anyone have specs for tpi, lt1, stock configuration?

    Would like to see if I can make it work for my application.

    What I need is simply measurements for spacing of injectors on each side-to see if a stock tpi or lt1 rail may fit so I can source one. Specs could be either the Rail itself or the manifold itself.

    Searched around here and the net, no answers...


    ...Fwiw, I decided to go mpfi using gm system pieced together and use a dual plane street intake. CHALLENGE! May use GM style rail or fab myself, but hoping some oe rail will work. Can't wait to see how much fun getting the bungs to correct depth with the dual plane will be-as the sbc looks like a finger crossed in that area! Worst case, probably make extentions off the rail to get it right. May retardistically work itself out.....
    THANKS!

  2. #2
    Fuel Injected! TINBENDER59's Avatar
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    Quote Originally Posted by 405cubes View Post
    I'm looking for specs on stock injector spacing/fuel rail spacing for my project. Does anyone have specs for tpi, lt1, stock configuration?

    Would like to see if I can make it work for my application.

    What I need is simply measurements for spacing of injectors on each side-to see if a stock tpi or lt1 rail may fit so I can source one. Specs could be either the Rail itself or the manifold itself.

    Searched around here and the net, no answers...


    ...Fwiw, I decided to go mpfi using gm system pieced together and use a dual plane street intake. CHALLENGE! May use GM style rail or fab myself, but hoping some oe rail will work. Can't wait to see how much fun getting the bungs to correct depth with the dual plane will be-as the sbc looks like a finger crossed in that area! Worst case, probably make extentions off the rail to get it right. May retardistically work itself out.....
    THANKS!

    I'll check it out tomorrow for ya, "I have 3 LT1 rail sets, Ill sell ya one cheap. look at this http://www.ebay.com/itm/CHEVY-Small-...#ht_1018wt_867

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    Wicked intake and a good price. Any good leads on something for more low end response?

  4. #4
    LT1 specialist steveo's Avatar
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    rails are one of the easiest things to make, you should just diy.

    lt1 stock rails are really shitty slip fit oring things. they aren't stable at all unless bolted solid to an lt1 intake.

    also it's more optimal to feed both rails in parallel, lt1 has series feed rails.

  5. #5
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    Quote Originally Posted by steveo View Post
    rails are one of the easiest things to make, you should just diy.

    lt1 stock rails are really shitty slip fit oring things. they aren't stable at all unless bolted solid to an lt1 intake.

    also it's more optimal to feed both rails in parallel, lt1 has series feed rails.
    Lol nice to know. Tpi rails any good? Supposedly same spacing as lt....
    Idk if either will pan out on a performer rpm anyway, may use square or even rectangle stock in the event the injectors end up offset to keep things as they should be.

    I just cant accept the belief that some huge 7000 rpm intake is the right thing for my application....
    with rev limited to 5800+/- etc and my purpose for a semi-daily driver.
    Understanding dry vs wet flow and all, i just dont see cruise rpm generating enough heat to cause major power loss.
    What little i do know, generate torque and you get driveability and better economy-hence the PITA i face. I do plan to take notes as I go, maybe I can help someone else later on.

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    down here we use dual plane highrise manifolds with 4 bbl TB's on 355 strokers but a lot of people end up rebuying manifolds to go with the single plane just for more extreme WOT power.if you wanted low rpm torque for pure street/tow duties long runner tpi manifolds would be the go.cam selection is a major to get right theres no point having a cam that starts working at 2500 with a manifold that runs out at puff at 4500 etc.
    having full control over spark helps with big manifolds you can run more advance down low where the manifold is soggy then lower timing as rpm rises and it comes on song and then begin advancing again and you dont have to worry about airspeed through the carb to get atomisation so the manifold will work better at lower rpm compared to being topped with a carb.i have 1 6L stroker here thats carbed with big single plane and a pretty good cam its strong right off idle and fully on song by 2000 and pulls till the cows come home.before tuning the carb with a wideband it was soggy till 3600 rpm then it would take off.the same goes with twin tunnelrams people say they are bad for low rpm power we have a worked 454 with twin 660 dp's it drives like its injected but with no vacuam advance it sucks the gas but it has unbeleivable grunt from idle to 6500.its all in the tuning

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    Fuel Injected! TINBENDER59's Avatar
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    Quote Originally Posted by delcowizzid View Post
    down here we use dual plane highrise manifolds with 4 bbl TB's on 355 strokers but a lot of people end up rebuying manifolds to go with the single plane just for more extreme WOT power.if you wanted low rpm torque for pure street/tow duties long runner tpi manifolds would be the go.cam selection is a major to get right theres no point having a cam that starts working at 2500 with a manifold that runs out at puff at 4500 etc.
    having full control over spark helps with big manifolds you can run more advance down low where the manifold is soggy then lower timing as rpm rises and it comes on song and then begin advancing again and you dont have to worry about airspeed through the carb to get atomisation so the manifold will work better at lower rpm compared to being topped with a carb.i have 1 6L stroker here thats carbed with big single plane and a pretty good cam its strong right off idle and fully on song by 2000 and pulls till the cows come home.before tuning the carb with a wideband it was soggy till 3600 rpm then it would take off.the same goes with twin tunnelrams people say they are bad for low rpm power we have a worked 454 with twin 660 dp's it drives like its injected but with no vacuam advance it sucks the gas but it has unbeleivable grunt from idle to 6500.its all in the tuning


    this is what I have, and it is a beast, the motor in the build went south due to a bad machine shop measurment--long story!! anyway it is now an LT1 with TPI intake, the rest is the same, soon to get a new cam (boost low and mid torque, current cam is stock LT1) and 30lb injectors, then back to the dyno for a final tune. it is a little lean right now with the TPI vs the LT1 intake

    http://www.gmtruckcentral.com/articles/lt1swap.html

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    Fuel Injected! TINBENDER59's Avatar
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    I'll still get those measurments, I over slept today, and was almost late for work. LOL sorry

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    Fuel Injected! TINBENDER59's Avatar
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    Quote Originally Posted by steveo View Post
    rails are one of the easiest things to make, you should just diy.

    lt1 stock rails are really shitty slip fit oring things. they aren't stable at all unless bolted solid to an lt1 intake.

    also it's more optimal to feed both rails in parallel, lt1 has series feed rails.
    I wouldnt run a fuel rail that wasnt bolted down???? so I don't understand that statement?? and at 45psi, Parallel, or series aint gonna make diddly difference. Unless, of corse, you are unleashing 1000hp at 9K+ at which point it would be a little bit different fuel delivery process IMO??? But you can rework the LT1 and TPI rails to be parallel fuel delivery with rubber fuel lines with AN fittings, My next project will be thus,

  10. #10
    RIP EagleMark's Avatar
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    For a cheap MPFI the LT1 intake can be converted to a distributor? And if you PM Lextech he has one for sale with all the work done. IIRC it does not have injectors but the intake work needed was done...
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    Cheap and easy to convert LT1 to distributor??? Having looked at this project years ago, I never thought a "good" conversion was cheap or easy.

    Why would high rpm and high horsepower make a difference in series vs parallel plumbing? It's about line size, rail size, pump flow, injector flow volumes, etc. Running in parallel reduces number of restrictions and reduces pressure waves transmitted through system. Crossfire injection system was an extreme example. OE manifolds used larger injector on when TB's plumbed in series. Changing to parallel allows equal size injectors without mismatched fueling. That engine produced what... 205 hp at maybe 4500?

    TINBENDER59, along with injector spacing, be sure to measure the angle of the holes in the fuel rail (if any). The Gods of Fire and Destruction love it when injectors are installed in fuel rails at an angle that prevents best O ring sealing.

    Steveo, any advice on how to DIY a set of rails with relatively basic tool for non-machinists? Seems like consistently measuring compound angles would be a bit tricky when setting up a rail in a drill press. Same for boring the manifold. Not sure I agree with "really shitty fit" O'ring comment. 'I've been doing this since the days when GM trainers freaked out if you didn't treat every O ring with kit gloves. I can count on one hand, maybe, the number of problems I've seen with properly installed rings in properly machined holes.

    405 cubes, sometimes the best intake available to us as street guys is the one that does the least damage. Putting a GM TPI intake on a large cube engine would make stupid huge amounts of torque... until 3500 rpm or so. An old F.I.R.S.T. TPI would do much better but most people don't want to spend the money to buy one. So you have to pick from what's left over. Intake manufacturers will list an intake's operating range based on a range of engine displacements and list those numbers as a guide. Because an intake is listed from 2500-7000 rpm does not mean it will make best power on your engine at 7000. It only implies the intake will not be happiest with a low end cam, tall rear gears, and a tight converter.

    For viewing pleasure, the F.I.R.S.T. system installed:

  12. #12
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    Good points, and agreed.
    -even a stock rail has 400hp capability. Why waste budget on high$$$ kits....
    Think tpi &lt1 share spacing, but different angle.

    -re the intake-used 7101's are 50-100$ and with 1500-6500 rpm range on a 350, with my increased displacement it brings it to around 1300-5400 rpm. Seems very ideal :)

    Re:tpi- seems it would choke me out sooner, and given the 400's cooling system requirements ...the whole distributor hole deal...When an off the shelf edelbrock has it dead located...currently im a little uneasy with that route.


    Fwiw factory flex fuel injectors offer good lb/hr numbers-probably what i will use.
    Quote Originally Posted by 1project2many View Post
    Cheap and easy to convert LT1 to distributor??? Having looked at this project years ago, I never thought a "good" conversion was cheap or easy.

    Why would high rpm and high horsepower make a difference in series vs parallel plumbing? It's about line size, rail size, pump flow, injector flow volumes, etc. Running in parallel reduces number of restrictions and reduces pressure waves transmitted through system. Crossfire injection system was an extreme example. OE manifolds used larger injector on when TB's plumbed in series. Changing to parallel allows equal size injectors without mismatched fueling. That engine produced what... 205 hp at maybe 4500?

    TINBENDER59, along with injector spacing, be sure to measure the angle of the holes in the fuel rail (if any). The Gods of Fire and Destruction love it when injectors are installed in fuel rails at an angle that prevents best O ring sealing.

    Steveo, any advice on how to DIY a set of rails with relatively basic tool for non-machinists? Seems like consistently measuring compound angles would be a bit tricky when setting up a rail in a drill press. Same for boring the manifold. Not sure I agree with "really shitty fit" O'ring comment. 'I've been doing this since the days when GM trainers freaked out if you didn't treat every O ring with kit gloves. I can count on one hand, maybe, the number of problems I've seen with properly installed rings in properly machined holes.

    405 cubes, sometimes the best intake available to us as street guys is the one that does the least damage. Putting a GM TPI intake on a large cube engine would make stupid huge amounts of torque... until 3500 rpm or so. An old F.I.R.S.T. TPI would do much better but most people don't want to spend the money to buy one. So you have to pick from what's left over. Intake manufacturers will list an intake's operating range based on a range of engine displacements and list those numbers as a guide. Because an intake is listed from 2500-7000 rpm does not mean it will make best power on your engine at 7000. It only implies the intake will not be happiest with a low end cam, tall rear gears, and a tight converter.

    For viewing pleasure, the F.I.R.S.T. system installed:

  13. #13
    RIP EagleMark's Avatar
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    Steveo, any advice on how to DIY a set of rails with relatively basic tool for non-machinists?
    There is a guy who did a write up for everyone to follow on how to drill an intake with a hand drill the injector holes that had a bubble site on it? No I won't link it!

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    Haha...

    The tech is so much better in that site.
    Last edited by 1project2many; 11-26-2013 at 09:18 PM.

  15. #15
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    As far as simple tools-only rails, id go square tube mild steel.
    If round had to be used you can clamp or temporarily tack weld the ends TO a square piece, so that you facilitate consistency of angle from piece to piece.

    Drilling can be fun on round-use a high speed and very little force, until hole is to drill diameter. Then push.
    Die grinding little flat spots can help.

    I did see a blasphemy of machining rails elsewhere.. And to clear up some myths-dont pre drill with smaller sizes and step through several sizes to get there. The POINT of the drill guides it, not the sides. You might run a 1/8 bit on your punch mark, but dont drill through!
    Rule of thumb. Punch, pilot, drill. Rant over.

    Not that ive done it before on fuel rails, just done a bazillion things similar. Lol just had a guy with an artificial hand come in and we revised some stuff on his hand. I love my job!

    Huge question-referring to rust inhibitor. Nickel or tin plating? Immunol? Seems fuel wouldnt erode either one.
    Lol, i have several home-made tools i coated with dykem and its still on after years of use, submerging in thinner, and all other kinds of misuse and abuse. Is it worth nickel plating them?

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