Hey I took off the Holley 670 and switched to a Holley S/A 770 and Proform Vac Advance HEI. I have lost so much low end torque but other then what I mentioned above noting else has changed. I have the Base timing set at 12* and all the vac. lines are plugged and its not running lean....may be a tad on the rich side.......my sig will tell the rest...........is this normal or is there anything I can check. Other than that the car runs Perfect.


Thanks
Brian Felts

 

since you bought a holley and have lost performance during the swap, i'd say you have a few day's worth of tuning to do it all. carbs aren't meant to be just bolted on and ran without proper tuning. your also going to want to check the advance in the distributor to see how much and how soon it comes in.

 

what kind of tuning are you thinking of? I am also looking for a tech number to find what kind of curve the Dist has. The loss just comes down low.



Thanks guys
Brian Felts

 

firs thing your going to want to do it check the timing advance. disconnect the vacuum advance and slowly rev the engine about 500 rpm at a time and check the timing as it goes up. record how much and how soon your advance comes in. you may need help of someone to do this. the other thing is after that to check the jetting. have someone drive behind you and see if it smokes black. this is a great starting point without having to pull the spark plugs. try and jet it richer to see if you gain anything. if you don't, go leaner. you may want to try different accelerator pump cam's or vacuum springs for your secondaries if you have vacuum secondary carb.

 

THanks Zippy thats what I have been looking for.




Brian

 

Like he said check the ignition curve....

Unless you have a big cam & some more than avg compression, that 770 just killed your torque possibility.

IMO you should have stuck with that 670...

Try jetting it down a tad & see how it reacts. Should reactive posotive with better throttle reponse & more torque. Check it out.

 

Well I am running a LT-4 Cam with 1.6 roller rockers with 2500 stall converter and 3.73 gears and performer RPM


Brian

 

hmmm ok....i have the 770 too....well i took it off & am gonna be using my other 750dbl pump

You have quick change springs for the secondaries. Heavy vehicles over 3300lbs usually like the stiff spring, not medium. And with a smaller type stall (2500) i would be puttin the stiff spring in.

but what i would first do is put in a new set of plugs, take a few safe hard throttle passes....then pull those plugs & see how they look. Then re-jet if necessary

What type of heads?

 

SDPC 350 2 bolt block LT-4
cam..LT-4 Powered rods......Crane Gold 1.6 rockers...Vortec 64cc heads.Holley S/A 770...ALum. Driveshaft...3.73 gears with Eaton Posi...underdrive pullys...Rebuilt 700R4 with Vette Servo and B&M shift Kit...B&M 2500 stall converter...MSD ignition...A/C Delete No SMOG junk....1997 SS leather interior...B&M Shifter... Ultimate TBI mods...14X3 K&N open Element Non-Drop...Hooker headers....3" exhaust with Flowmaster Cross flow 16X8 Wheels from 97 RS Spohn LCA's Spohn Panhard Bar..LETS PLAY FORD!!