How big of cam with EFI

Discussion in 'High Tech for Old Iron' started by izanurse, Oct 11, 2017 at 12:58 PM.

  1. izanurse

    izanurse Well-Known Member

    Hello all,

    I couldn't seem to find a thread on this, so here goes. I'm curious about cam size and an aftermarket EFI. I have a 455 with aluminum TA Stage 1 heads and a hemi killer cam. My plan is to use the base FAST system. I welcome all input.

    Thanks,
    Allen.
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    I think if you look at a particular EFI, you will find a specific minimum vacuum that the engine must produce at idle. That will dictate how big a cam that you can run with that system. Do some research on the system that you want to run, pretty sure you will find that spec.
     
  3. izanurse

    izanurse Well-Known Member

    Thanks Larry.
     
  4. BillA

    BillA Well-Known Member

    How much vacuum do you currently have at idle? I've seen 8" as the minimum most of the TBI systems need to operate properly.
     
  5. izanurse

    izanurse Well-Known Member

    I'm not sure. I had this engine built then sold it and bought it back. I know it worked fine with power brakes. Then I read somewhere that lobe angles of 106-110 aren't good with self learning EFI. I may run it on a stand just to see.
     
  6. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    If it's multi-port there is no minimum.
     
  7. 300sbb_overkill

    300sbb_overkill Well-Known Member

    A sbc 383 I built for a friend has this cam;

    https://www.summitracing.com/parts/hrs-111153-08s/overview/make/Chevrolet

    The specs in the ad are with 1.5:1 rockers and his is setup with 1.6:1 roller rockers so instead of .585" lift he has .624" of lift with 108 LSA, 247* in. and 249* ex. @ .050". He runs a FAST EZ EFI throttle body fuel injection that runs great with that cam on top of a high rise single plane intake into Dart 215 heads with about 10.9:1 compression!

    How much bigger than that are you planning?

    He can set the idle down to around 500 RPM and make it sound like the beginning of that Van Halen song, "Hot For Teacher" ! That thing makes around 580 HP, has the rev limiter set @ 7,500 after he told me he had it spinning all the way to 8,500! I said "NOOOOOOOO the rods are only rated for 7,500 RPM" but he said it was still pulling @8,500!(he now has the rev limiter set @ 7,500 as mentioned) The Fast EZ EFI never missed a beat, runs great and I would imagine it doesn't have that much vacuum with the above mentioned cam.
     
  8. pbr400

    pbr400 68GS400

    The hemikiller is 241/241 (or similar, I think there’s a couple versions). If an sbc runs well with a 247/249, surely a 455 will work with smaller.
    Patrick
     
  9. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    This is one of my favorite dyno videos. It's so old that the resolution sucks by today's standards, but that car idles at around 1.5inHg vacuum and runs bottom 9's in the 1/4. Runs on an ancient by today's standards EMS-Pro (Megasquirt-1 on batch fire). It's since been updated to a Megasquirt 3, full sequential, etc.

     

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