[F-BIRD'88]

14psi boost will require at least 100 R+M/2 octane even with low 7.5:1cr.
max 10psi on pump gas. start power tuning at low boost 5psi until you find the tune.
what is the carb model ##'s

[mustang 671]

Originally Posted by F-BIRD'88

What is the model list number stamped on the carb air horn?
stock metering blocks...or.

Pri and sec idle and high speed air bleed size? Primary and sec idle feed restriction size.?
Primary power valve restriction size.?
Use small precision drills or wire gauges to measure and gauge that with a dial caliper.

Think about getting some blower carbs. 650-750DPers

i have the carbs set up back to back ( as thats how i bought them with the billet linkeages ) i have converted the front one to have 2 x metering blocks and the rear one only has a primary metering block as there isnt room for the secoundary one . so at least i can jet 75% of it . will need to double check on id of air ways etc .

[F-BIRD'88]

If you do not have a boost retard box set the LOCKED timing at 26-28deg to start power tuning.
Max WOT power spark timing will be 26(high boost) to 32deg (low boot) @WOT. on pump gas.
Excessive timing under boost on pump gas will break parts. Sneek up on the tune. Jetting and timing.

For initial start up-warm up idle to get it set up (idle mixture etc) use 36deg BTDC locked timing.
Then reduce for testing under power.

[mustang 671]

i only have the 2x pulleys . so do i restrict the rpm for now or get another pulley ? of just keep a eye on the boost guage as im not too sure if it will produce 14psi ?? with my pulley ratio

thanks on the springs .

the tubes come out of the sides of the vac sec's and join together with a t piece then go into the back of inlet manifold below the charger.

also the ball bearing in the vac sec have been removed to both carbs .

will look for the part number on the carbs.

now i get these numbers confused. i have converted the front one - is it 4150 to 4160 or 4160 to 4150 ? as i have added metering blocks and the rear carb has a metering block to the primary

[F-BIRD'88]

If you have a sec metering pate in one carb (like a 4160carb uses) make sure its stamped 21
and or the main jet hole is .080" or bigger. What number is on teh sec nmeting plate?
Like I said you are going to spend more dialing in these carbs than they are worth.
Get two blower carbs ..

[mustang 671]

Originally Posted by F-BIRD'88

If you do not have a boost retard box set the LOCKED timing at 26-28deg to start power tuning.
Max WOT power spark timing will be 26(high boost) to 32deg (low boot) @WOT. on pump gas.
Excessive timing under boost on pump gas will break parts. Sneek up on the tune. Jetting and timing.

For initial start up-warm up idle to get it set up (idle mixture etc) use 36deg BTDC locked timing.
Then reduce for testing under power.

ok - explain what you been by locked timing ? and 36 d btdc locked timing ? i havent a dizzy and have to do everything by the way of imputting figures on a graph, i can change it exactly so not a problem - but i think you mean locked timing in the way of when i get to say 3000 rpm the timing curve is flat and for eg 36d btdc remains flat along the higher rev range so a flat ign line for that rev range being 3000 and above ?

[cobalt327]

Originally Posted by mustang 671

guys this is great thanks so much . i have this weekend to get all of these tips in place for next wednesday .

ok compression ration is 7.48 to1
i have a 14 psi max ratio on the pulleys . ( so weiand say )

i had to have a new pulley machined to fit over my rattler harmolnic balancer to save space so thats why the top one it larger than normal . bottom pulley is 45 and top is 51 teeth so its 0.88 so its being underdriven.

i can regulary get hold of 98 octane gas .

thanks t bird for the tech stuff . just what i needed. i have 6.5 power valves . so they must be getting pulled open all the time ?

so my .72 in the primary also seem to rich ?

will check my plug gaps . i have just been sold a cooler plug from champion and i havent gapped them . i wonder what they are factory set at ?

i have larger headers and also nice elderbrok victor heads . so feel confident on them . what about my air filters and scoop . i hope i am not restricting air flow ?

i have a ecu so will have to speak with them regarding boost and timing retard box and how that will work with it ?

what about colour for fuel squirt cams ? and colour of spring on sec's ?

also the vac sec's have 2x air tubes coming out of them and are fixed to the manifold "below " the supercharger !! is this where it should be plumbed in to read vacum to open the vac sec's?

thanks guys . good job !!

The carbs are referenced for secondary opening if connected to each other. Could be boost referenced if connected below blower. The vacuum would need to fall below 6.5 in/Hg to have the power valves open, so there's almost no chance they're opening all the time unless there are other problems. Take a vacuum reading below the blower and use that to see what power valve you need. If the vacuum is excessively low, there could be other issues that need attention. If the carbs aren't boost referenced, the power valves will stay shut.

You have secondary metering blocks w/changeable jets, I take it?

If you are .88 underdriven, w/a 355 cid engine, and a blower displacement of 411, I'm getting about 11 psi. Still a good bit of boost for a street vehicle. With the static CR you have, that puts the effective compression ratio at about 13:1 at max boost, so you may well need to blend in race gas. Remember no detonation, else the pistons will fail.

Boost formula I used:
[(25.58) times (Blower Displacement) times (Blower Drive Ratio)] minus 14.7 divided by the engine displacement in cubic inches equals the theoretical boost in psi.

[F-BIRD'88]

Those hoses coming out of the sec diaphram housing lid do not connect to the intake manifold.
They do not work like that. That is not boost referenced power valves.
Do not test like that. ALl the tubes re for is to equalize the sec opening rate between the front and back carb.
Its just a vac balance. They just connect together.

You cannot test at 14psi boost without boost referenced power valves. (unless you remove them and jet the carbs way up to compensate.) ( drag race only)
Consider yourself warned. Stop what you re doing . You car not ready to test #14psi with those jerry rigged carbs.

[mustang 671]

the primarys are .72 and sec's are .78 so do you think they should be changed to .80 ? as i have .80's

will check the number on the metering block

yes i thnk i have converted from 4150 to 4160 with the addito of the metering blocks.

to be honest i am saving up for fuel injection so if i can hold off i will use the current carb bodies and fit injectors into the inlet manifold. but probably a job when i have some money saved up

[F-BIRD'88]

Locked out timing is locked. It is fixed it does not advance with rpm. No ECU control.
You need a electronic boost ignition retard box. Not some ECU from a EFI system. Get a clue or it will be a very short ride.

Locked timing is the same at idle as at max rpm. No mechanical advance ---no ECU timing control.
Blower motors do not use the same timing curve as a N/A car. ECU from a EFI system will not work.
remove or disable.....

[mustang 671]

ok will connect them together so they are balanced. i read somewhere that there is a tube that goes from the carbs into the inlet manifold to measure vacum ?

[F-BIRD'88]

Just buy two 750cfm blower carbs. Holley, barry grant, quck fuel,, AED. Pick one.

[F-BIRD'88]

Originally Posted by mustang 671

ok will connect them together so they are balanced. i read somewhere that there is a tube that goes from the carbs into the inlet manifold to measure vacum ?

Yas you need to modify the carb for a boost referenced power valve
What you got is not that.

[mustang 671]

Originally Posted by F-BIRD'88

Locked out timing is locked. It is fixed it does not advance with rpm. No ECU control.
You need a electronic boost ignition retard box. Not some ECU from a EDI system. Get a clue or it will be a very short ride.

Locked timing is the same at idle as at max rpm. No mechanical advance ---no ECU timing control.
Blower motors do not use the same timing curve as a N/A car. ECU from a EFI system will not work.
remove or disable.....

i have this ecu so i can get spot on figures and not a dizzy set up . so i can put into the ecu what figures i want. i havent pulled this from a car. its a completey open map that i can add figures to . i cannot remove as i no longer have a dizzy , i have a toothed wheel on the crank and a sensor to count the teeth etc for timing. so what figures would you reccomend. i posted a chart on page 1 asking the question ?

[mustang 671]

just looked at weiand boost chart and for my 0.8 underdriven it shows around 12 psi for a 350 but i have a 351 with a 30thou over bore. so i think around 11psi approx