holley help

[68dustin]

ok i have:
302
9:5:1 compression
forged pistons
trick flow 202 heads
Weiand X intake
Mild cam (cant really remember specs.. 513 lift.. with ??? duration
4:11 gears
t-5z tranny
msd 6a ignition box
msd boost timming master
running base timming 14
distributor locked at 32 max timming
boost timming box retarded down to 23 degrees max timming
Holley blow thru carb (750 by carb shop)
paxton boost ref fuel pump (for now going electrical in a few months)
Paxton novi 1200 with 7-8 pounds of boost (for now 14 when new fuel pump gets on)
shorty headers with 2-1/2" exhaust dumped at axle



carb shop blow thur carb....
750 double pumper
31 squirters 31 squirter in rear 30cc accl
72 front jets
78 rear
4.5 power valv

now for my problem area:

from a dead stop i really dont have any sputter in the carb, but when im crusing and stab the gas it falls on its face and then takes off. I have been playing with the acclerator pump & nozzles. Now my question is i have 31 squirters in the front and rear should i up grade to the next size in the rear or front? My pump cams are set in the first hole and are pink.
thanks

 

[brianj5600]

A wideband would be a good investment. They tell why it stumbles. If it is a rich stumble you might try disabling the secondary squirter just to test. There have been a few turbo guys run w/o secondary squrters. The reason is that if the PVCRs are drilled bigger and the PV opens before there is positive pressure it will go very rich. Once there is boost and the air density increases the the A/F ratio will be where it needs to be. I tried running mine w/o a spring on the PV, but it still opened too soon. Usually blowers don't have that problem.

 

[68dustin]

my wideband goes lean when it happens.

 

[brianj5600]

It gets tricky when it misfires. A cylinder not firing releases a lot of oxygen into the exhaust and the wideband thinks it is a lean mixture. Does it start off getting richer and and then shoot lean?

Usually you need more pump shot off idle than cruise. That is what makes me think it is going rich. The pink cam is a very agressive cam. You should be able to see the pump shot in the datalog. Try stabbing it a little slower and see what the A/F ratio looks like. Rolling into as quickly as you can w/o making it misfire should give you some good data. Can you data log manifold pressure too?

 

[68dustin]

thanks.. will give it a try tomorrw... i have a smaller nozzle "28" that i can throw on there. I will try that just to see what happens. Should the primary shooter be bigger than secondary?? I belive the stumble happens before the secondary's even open. I can get it to stumble by just tapping the pedal. I also dont have a lap top to data log..

 

[zookeeper]

Could it be timing? I've tuned blown motors before, and used similar timing methods and specs as naturally aspirated motors. I suspect it just needs more timing than what you're allowing. Also, blow motors seem to need more carb. My brother built a 350 Chevy with a 6-71 and a pair of 600 Holleys running 1:1 linkage and it was barely enough at high rpms. My boss had a 289 with a centrifugal blowr and ran an 850 to get good power. From your description, I'd say it's either lean or has too little timing, but it's tough to tell without seeing it.

 

[zookeeper]

As for going to a smaller accel nozzle, I wouldn't. My mild 302 runs a pair of Holleys, 1:1 carb linkage and a pair of 25 nozzles and it has NO hesitation at all. So if anything, I'd suggest going with a bigger squirter. In fact go up a few sizes from what you have and see what the difference is, one size is not enough to know if you've made a difference at all. Go up like 3 sizes and test drive it again.

 

[10secgoal]

Change out that pink cam. that's sometime not enough fuel for a engine close to stock. The cam dictates the amount of fuel that is released from the squirter. You can put a 42 squirter on a pink cam and it won't seem any more fuel, only change the timing of it. There is less resistance with a bigger squirter so it seem for of the fuel up front form the same cam.

 

[brianj5600]

It is dangerous to compare cfm requirements of a draw through on a roots to a blow through with a centrifugal. A blow through does not have to flow more cfm when measured at the carb. It flows air that is compressed. The volume is the same at the carb. A draw through has to flow enough atmospheric pressure air so that when it comes out of the blower it stays compressed. I also find it hard to believe that a 289 needed an 850cfm carb to make good power unless it was turning more than 8500rpm. CFM needed for blow through is pretty much what ever the same motor needs normally aspirated. If anything smaller.

 

[68dustin]

Im running 32 total timming by 2800 rpms and them pulling 1-1/2 degrees out per pounds of boost, total in boost is 22. I really didnt get much of a chance to play with it this weekend, but i did drive it. I noticed before the bogg the car goes lean on the wideband. Its hard to explain when the bogg is: say ur crusing at like 2500 rpms and just tap the gas to the floor. "thats the only bogg" it chokes then takes off. In full throttle banging gears there isnt anything. Which color cam should i swap it out for??? I will be ordering bigger nozzles in a few days. Im not ready to commit to a 50 cc pump yet. Also what is the max nozzle you can run before you have to upgrade pumps?

 

[brianj5600]

One thing to try that might help is checking the float level. If they are too low it takes longer to get the main system flowing. I drilled my squirters out. If you have or have access to numbered bits it is pretty simple with a pin vise. I got my bits from a local hobby shop. Squirters are stamped with the diameter of restriction in thousandths. It gets expensive buying squirters until you get the right ones.

 

[68dustin]

i have my float level just under the opening.... it barley trickles out when the car is running... that is a easy adjustment and will give that a try tonight. I really want to thanks u guys for giving me pointers... sooner or later i will get it fixed..

 

[brianj5600]

Being a manual makes it tougher. My converter flashes 3200 and it gets the mains flowing pretty easy.