SBC tunnel ram w/2x450 holleys problems - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-22-2004, 02:38 PM
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SBC tunnel ram w/2x450 holleys problems

Engine: Built SBC350 with hyd roller, Mallory comp9000 dist, accel plugs, accel race wires(all new).
Trans: T1-0 4 speed
Rear: 373 posi
OLD INTAKE / CARB: Victor Jr(1 inch taller model) Holley 750 3310-c VAC secondaries.

New Intake(actually old): Weiand Tunnel Ram
New Carbs(actually old): Holley 450cfm mech secondaries(list 9776): rebuilt with Holley parts(not my first carb rebuild) everything was triple checked.
Running 285 Jets(main), 65 Power valve, 31 squirter, 30cc pump and pink pump cam in position 1.
Engine pulls 11-12 vacuum with tunnel ram setup(beleive it or not it surprised even me).
Idle speed @950
Set all floats to just dripping out
Fuel pressure 4-5 psi, any higher was overwhelming needle and seats.
Idle mixture was set using vac gauge, about 1 1/4 turns out is max(@12)
Acc pump set to open with any throlle movement, good fuel coming out squirters
Timing same as old 18 inital with @35 total

Old combo ran like a champ, no bogs or anything

Problem: Anything other than part throttle and it bogs/stumles/backfires through carbs.

I have tried to up the squirters to 37 not much change
I tired putting them down all the way to 25, ran worse(28's were so so)
So I put 31's back in, and tried different pump cams, not much change.
I have tried to fatten the mixture to 2 turns out, no change.
I have disconnected the back carb and had worse results.

Any suggestions???

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Old 11-22-2004, 02:48 PM
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Sounds like you've got it spot on.

Did you change anything in the valvetrain?

Have you tried running an "excessive" amount of timing to see how it responds?
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Old 11-22-2004, 03:11 PM
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Didn't change anything in the valve train. Timing is next on the to try list(got too dark today), the only thing I haven't done is to pull the plugs and check em for fouling.
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Old 11-22-2004, 03:33 PM
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Yes , fresh set of plugs and set the timing @ or around 3000 RPM to 28-34 * And you might try lowering the power valves to 3.5s
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Old 11-24-2004, 04:32 PM
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update

Well 3 of the plugs were fouled, probably from when I was adjusting the floats and all the tuning attempts.
I cleaned all 8 plugs and reinstalled. One wouldn't fire no matter what, 2 others were intermitent.
Sooo I changed 3 plugs with old plugs.
Reset carbs to 31 squirters and it ran well. Upped the timing to 22 initial and ran a little better. Installed 37 squirters and ran even better.
No more backfiring....oh wait...I was messing with pump cam and backfire came back. One cylinder is intermitent again. The plugs are carbon fouling. I have the Plug Gap reduced to .045 from the old plugs that were .060. I am thinking there is less spark and more carb thus the fouling. I am going to try and clean and gap all at .060 and try again.
Idle mixture screws were set at 1 turn also.

As a side note I would never run just one carb of a dual setup. I think it nuked one plug and it runs horrible if I try it now. I found the recommendation of tuning only one at a time on some web sites.
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Old 01-26-2005, 04:22 PM
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Update: Cleaned and gapped plugs to .060 this is keeping the plugs from fouling now.

Since I have @11 vacuum I changed Power Valve to 8.5 from 6.5 that was recommended, this made a huge difference, upped the squirters to 37's and changed the cam to second hole. Has absolute ton of power now about 2500 rpm. Still just a little bog then takes off from idle.

Question, do you think a 9.5(available only in standard flow, 10.5 seems too high) power valve would help or should I try .040 or larger squirters.
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Old 10-12-2010, 10:07 AM
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sounds like your running it down

i have been doing some reading before i get to my tunnel ram project 355 with a cam that barely lets the intake valve close lol not really i dont have specs yet but i believe its a little over .500 lift one of the issues i have seen most in my research anyways is that you need to tune your engine for more air flow maybe a new cam would be my recommendation if you havent already got one for the tunnel ram intake but make sure you let us know how you ended up like i said i still have one to tune when i get home and even worse i have a built 355 aftermarket heads headers and dual 770cfm carbs so hopefully you can help me in the right direction good luck bro

oh yeah heres my setup any pointers?

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Old 10-12-2010, 03:54 PM
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When you replaced the PV and the problem was gone. That PV could have been ruptured from the backfire causing to dump a lot fuel into the motor. Stay with the 6.5
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