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Thread: Tunnel Ram Tuning Tips

  1. #1
    EASYSTROKE
    Could anyone give me some tuning tips for my setup. I have a 10.1 454 with a mild hyd cam runnning ported oval port heads,bassett ot headers, and a weiand tunnel ram with two holley 600 vac secondaries. Anyone have any jet size suggestions. I have already been told to install lighter springs for the secondaries. Any other info would be appreciated. I also read an aticle that said the tunnel ram likes more timing advance at low RPMS to help drivability.
    Thanks,
    easystroke

  2. #2
    XClutchboy725
    I've got Dual Holley 6109's (750 Double Pumpers) with mechanical secondaries.
    My jets are around 70 Primary and secondary
    My cam is pretty mild also (.542 lift 306 duration)
    and YES! Tunnel Rams do like lots of Advance to idle right.
    I'm going to have 5 degrees advance taken out of my distributor soon. That way I can still idle at about 12 or 13 and rev up to 38 degrees total.
    Hope that helps...

  3. #3
    nastyhabit
    if your running a small cam why run a tunnel ram it will run better with an 850 dubble pumper unless your going for the looks leave the carbs stock dont change the springs it should be fat the way it is run it hard check to see the color of the plugs if there black and the boat runs good great if you dont know how to tune dont f-it up and go lean if you have an msd or like distrib and has 20 digrees built in ad 15 go to35 see what happens if you go to high its going to sling out oil through breathers or what ever it can and not run as good-I run low to mid 30,s and run two 1050 dominators the story is you loose hp true but b.s. its not a car and it runs above 4gggs all day but any way good luck---nasty

  4. #4
    LakesOnly
    Stand by Easystroke,
    Hotcrusader76 will be here soon with a more proper and more detailed answer than I could ever give.
    Based on the very limited motor details you have given, I'd recommend:
    76 primary jets and 80 secondary jets.
    Check float level with the boat in the water.
    Lock down distributor advance at 36* at 3000rpm
    Plug reading after good hard runs.
    Don't hold me to it...this should get you in the water; the fine tuning comes later.
    LO
    p.s. In the meanwhile, get back with those cam specs and any other pertinent info...

  5. #5
    Blown 472
    You should tie the vac secondaires together or just shit can them as they might go closed on the top end, keep an eye on them. you can put a small nipple in the top of the secondary diaphram and put a hose between them. Just make sure they dont open then go shut on wot, been there done that. otherwise rock on and read an eye on them plugs.
    ****in whiskey

  6. #6
    LakesOnly
    Originally posted by Blown 472
    ...you can put a small nipple in the top of the secondary diaphram and put a hose between them....
    yeah...I like putting a hose between the nipples too.....:devil:
    LO

  7. #7
    Blown 472
    Originally posted by LakesOnly
    yeah...I like putting a hose between the nipples too.....:devil:
    LO
    um ah he like said nipple or something.

  8. #8
    Hotcrusader76
    Originally posted by EASYSTROKE
    Could anyone give me some tuning tips for my setup. I have a 10.1 454 with a mild hyd cam runnning ported oval port heads,bassett ot headers, and a weiand tunnel ram with two holley 600 vac secondaries. Anyone have any jet size suggestions. I have already been told to install lighter springs for the secondaries. Any other info would be appreciated. I also read an aticle that said the tunnel ram likes more timing advance at low RPMS to help drivability.
    Thanks,
    easystroke
    Easystroke...
    Those 600VS carbs will not jet the same as a typical 650/750 mechanical set-ups because they have smaller venturies and throttlebores as well as different internally sized boosters (straight legs 0.124"-139" and droplegs 0.142"-0.165"). On the same engine with four different venturi sized carburetors the jetting will be different on every one.
    You need to remember that the vacuum signal relys on a port within the primary side of the carburetor and when there is any variance in tolerance between the two, the secondaries will open at different rates and or times. That's bad!!!
    What you can do to prevent this variable opening between both carburetors is to siamese the vacuum cansisters together via a port drilled through the top of each canister and connected via a hose. It's not as hard a mod as it sounds but is absolutely critical to a motor's "successful" performance results.
    Now assuming your fuel pressure is between 6-8psi and the float levels are at factory level just below the sight hole, while shaking the boat side to side, not spilling out and also ensureing that your timing is around 12-14 Initial and that it comes in fast to 32-33 full advance for these small carbs, you will be armed with the basic baseline to nail down your jetting for a "dual carb" set-up.
    Set your idle mixture screws all the way in "closed". Then back each one out (2 per carb) one complete turn. This will zero your idle calibration.
    Next you need to set your transition circuit via the idle speed screw. In order to do this you need to visually see the bottom of each carburetor and ensure the transfer slot is "barely" exposed. This is a good starting point for the process of increasing your idle so your motor will stay running without getting too close to having the transistion slot over exposed. Once the motor is running at 800-900RPM (based on your mild BBC application listed above minus the LSA on the cam) you can now look into proper jetting...
    As far as jetting goes I assume you're running stock rear metering plates, meaning they have no adjustability? If so then you might want to consider adding secondary blocks to enchance your tuning capabilities. It's not a hard modification and if you're real savy you can add the four corner idle while you're there. Four corner idleing capabilities on a tunnel ram will help tune each cylinder and it will offer a better temp.balance on the motor @idle and off-idle.
    Primary jetting should be somewhere around 71-73 (powervalve at 6.5 or less only), where as the rear is normally factory set at 75 (but sometimes varies based on the application list number). Anything more on this jetting will bend the A/F ratio well below 12:1 and you'll begin to run overly rich. Remember...it's AIR>>>>>TO>>>>>FUEL>>>>RATIO...not.... I'm running a BBC with a tunnel ram so I should jet it like my buddy does
    Important safety note- Running rich at the start is always better than lean...so jetting higher and coming down off the jet will save you time and money on pistons.
    The squirters should be around 25 stock but often can be found to be 28. 28 is good for double pumpers and often can be set to 31 but with a vacuum secondary a 31 in tandem isn't too high for such a small carburetor. If you have an immediate bog after launching then increase your squirters to 31 from 28 and consider jetting up only one on the primary from your initial setting.
    Make sure your eyes don't bleed at idle... if they do you can perform something more technical and check the boosters on the carburetor which are the "finger" like projections coming into each bore on the carburetor.
    Ensure that all boosters are not dripping at idle (800-900RPM)...If so then you need to lower the respective float on that side or check to ensure the main air-bleed (the little brass hole like thing next to the booster) isn't clogged with crud. Sometimes these get dirty and block the air-flow which instantly richens the main circuit. The outside little brass holes are for the idle and when those clogg you'll become overly rich at idle....Dripping boosters are very common on boats with high float settings...often misleading them into lowering the jet sizes.
    Best thing to do is just squirt some brake-cleaner inside the holes to clean them out. WARNING...DO NOT START YOUR MOTOR FOR AT LEAST AN HOUR AFTER DOING THIS OTHERWISE YOU'LL HAVE MORE THAN CARBURETOR PROBLEMS.....you're best bet is clean them when they're off the motor.
    Of course I could go on and on aboat checking the jets underway...I mean when you're on the water...but I'll let some of you other gurus expand on that...I'm tired of typing right now.
    Hey even better.....give me a call at work...and I can walk you through the check just the same.
    LAST BUT NOT LEAST.....LISTEN UP HERE!!!!!!!!!!! I know alot of you so call carburetor killers have removed those factory chokes and all....well make sure you plug the hole that the choke recieved it's heat signal from...otherwise you'll be chasing a vacuum issue and you'll have no idea where it came from...an even better sign is the tell tale sign of a freight train whistle while accelerating.....ask aka"Hallet19"....it really sounds cool but does nothing but crap out your idle causing you to blame the carb builder or set your idle mixture higher....but it does help your CFM ask my oval track racers:wink: ....
    Goodnight and sleep tite....
    ~Ty

  9. #9
    Blown 472
    Dude, you been hanging out with Jer too much.

  10. #10
    Hotcrusader76
    Originally posted by XClutchboy725
    I've got Dual Holley 6109's (750 Double Pumpers) with mechanical secondaries.
    My jets are around 70 Primary and secondary
    My cam is pretty mild also (.542 lift 306 duration)
    and YES! Tunnel Rams do like lots of Advance to idle right.
    I'm going to have 5 degrees advance taken out of my distributor soon. That way I can still idle at about 12 or 13 and rev up to 38 degrees total.
    Hope that helps...
    Jeff if I remember correctly your set-up involves Holley tunnel ram part numbers on those carburetors right? I believe they are and running lower jets like that actually compliments the boosters Holley installed under that part number. If you were to separate those carbs and run them as single applications on any motor they would run really really lean.
    What is your LSA on that cam? 110-108 I imagine. Anything less than 110 on a tunnel ram needs a four corner idle circuit to feed the beast with it's nasty overlap.
    Ok...now I'm going to bed....

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