I have a holley 780 vac secondary carb. after a few trips to the track I realized that increasing the squirted from a .025 to a .028 resulted in a drop in 60' times. My question is what size have you found to work best. I want to try a couple but dont know where to begin. My combo is: 71 Chevelle 454ci approx 9.5-10.0 comp a mild summit cam approx .483 lift torque topps off at 4000-4500. edelbrock performer RPM intake, 049 heads TCI Breakaway conv. TH400, 373 posi on 295/15 drag Radials. I have done all the Power valve tuning with a vac gauge and jetted per my best track outings of 76 primary and 82 secondary This gor me a best of 13.08 at 108.20 MPH. I really want to get this into the 12s before I store it.
Milan

Then go back to the smaller squirter. You could also try a smaller pump cam and see if the 60' times pick up more. The only thing I can figure is maybe the pump shot is too big and too quick causing the engine to go rich at launch . . .

Its hard to pick a squirter and pump cam based on 60' times though - 60' times IMO are more dependent on traction, how you stage the car, and launch technique. I play with the squirters and pump cams only to eliminate a rich bog or lean stumble.

By drop in 60' times. I meant quicker!!!

ttt

I run .031 size squirters in my 825 mighty demon, which is what it came with. I have tried other sizes but these seem to work best. I also have done quite a bit of tuning with different pump cams to get it running how I want it. If you are not getting a bog off the line and it feels strong I would not mess with it the squirter size personally. Your trap speed indicates that your car has 12 second potential. What are your 60 ft times now? Being a vacuum secondary carb maybe you should look at getting the secondaries to open faster if you haven't already done this. This could also help your 60 ft times.

Jeff

Ah, I see. Maybe you could go smaller on the main jetting then. If less fuel makes it quicker out of the hole maybe a leaner mix will make it quicker the rest of the 1320 . . .

I thought stock jetting on that carb is 72F/76R.

the way I understand it is he lowered his 60 ft times by going to a richer accelerator pump shot, not leaner.

Jeff

My HP950 has 78's square,,,you're running more jet,with less cam and compression than I've got. I'm running the same heads,intake,gears and a th350 too. Try leaning it down some.

For the strip, you should tune the squirters for the quickest 60' and 330' times. Keep increasing the squirter size till performance drops off or your spotter see's a black puff of smoke off the line.

With a vacuum secondary carb, you only have one squirter/pump shot. A double pumper has two. This means you may need a much larger shot with the VC carb to launch strong.

Eventually, you can play with pump cams, but squirter size is my first step in tuning.

With my 850 race DP, I have 40's in the front and 35's out back.

i ran a 780 carb years ago jetted 77 and 79, but i do not remeber if it had powervalve or not,i'll lean towards no because i really did not care for tuning with them. and the squirter was a 37. remember any squirter nozzle over 40 should be used with the jumbo (slotted) squirter screw ;)

Thanks for all the feedback guys. I have been tracking all my runs and any other data on my laptop. I have tried leaner jetting and it did not improve at all. I have gone richer and it slowed as well. I feel I have enough data that I am comfortable with the jetting and PV for now I have done no accell circuit tuning. Hence my question. Please keep in mind that it is a 780 vac secondary. (Only one squirter) I ran over to summit and picked up an .035 squirter and some pump cams. I thought I would try the green and them back off from there. What do you think. I may end up hitting the Nitrous on Wed if I cant get my 12.99 slip!!! I really dont want to but...any how I would appreciate your thoughts on the squirter and cam.
Thanks
Milan


Thanks

Jeff I have a weak secondary spring in there now. Its the second from the weakest. I drove it around with diff springs untill I didnt feel the transition (BOG) into the secondaries.My 60' time are .194-.199 this year but I lost 8 mph on the top end due to some experimintation with leaner jetting and removal of my 4 hole spacer. At least I believe thats why. My 1/8 mile tiomes have also fallen off

Todd (it is Todd right) I have no spotters I usually have to go it alone. I was thinking that I should go richer but I was unsure how much richer and time is precious now that it is late in the year.
Robert I am confused, My data shows me making MPH improvements every time I jetted up to a max of 76-82 I tried 76-84 and lost 4 mph on the same day. I believe double pumpers go a different route as far as tuning. due to the opening rate of the secondaries. What are your thoughts?

For pump cams I use green on the primaries and pink on the secondaries. I really like the green it gives a very strong spray just off idle. Using it in the secondaries made it go then bog so I tried the pink instead, but of course you don't have to worry about the secondary pump. If I went too big on the squirter size it made the car go then bog, which indicates that it is running out of gas and needs a longer pump shot but this can also be changed with different pump cams. Another thing I did is buy a wire drill set. This way instead of buying several different size squirters I can just drill mine out, which saves money and time. If you can get your 60 ft's into the 1.8's you will probably be in the 12's so also give some thought to your launch technique. You are lucky to be by the Summit store. I have been there and it is awesome! Let us know how it goes.

Todd what pump cams are you using with your carb? Does it have 30cc acc pumps on it? I used to use .035 front and .037 rear shooters on my old 850 Holley but my 825 Mighty Demon likes a smaller pump shot.

Jeff

Jeff I have found my best 60' launching from Idle. I have tried it all over the place and logged the data. I would be more than willing to try anyone suggestion!

Thanks Again
Milan

Originally posted by Jsavdog:
Todd what pump cams are you using with your carb? Does it have 30cc acc pumps on it? I used to use .035 front and .037 rear shooters on my old 850 Holley but my 825 Mighty Demon likes a smaller pump shot.Jeff Jeff,

I currently have a pink cam on the front with the 30cc pump. The rear is a brown cam with a 50cc pump. This carb is a race 850 list # 8162 and has the NASCAR style roller secondary linkage...opens real quick at a certain throttle opening position.

I'm guessing the staging rpm uses up a certain amount of the initial shot of the 30cc pump and when I launch and go to immediate WOT, the 50cc pump gives a longer shot for a strong launch.

This street setup uses a PV out front and I had to tune in more front pump shot with the PV over having it blocked...previous track setup was locked out timing, no PV's at all, and 35 quirters front & rear with the same pump setups of 30cc front, 50cc back.

Mine is far from optimized, but works as is, so I've pretty much left it alone...for now. Will tweak as track time allows.

I'm not sure a squirter change will get you .08 of a second. The squirter circuit is only there to cover the transition from idle to open throttle. If you have a bog or hesitation, then a squirter or cam change is in order. If not, changing the accelerator pump system won't help.

It seems you have the jetting sorted out. What about ignition timing? On the dyno a few years ago, we picked up 27 hp by advancing the timing 3º.

Pat Early in the cars track life(several years ago) I made changes to the base timing and checked total with the vac can hooked up. I tried several base settings Looking back my better performances were at 15 base I believe that left my total around 32-36. I tried more timing but it didn't help. I have recurved the mech advance since and I am installing the lightest springs to date for this evening. I get so caught up in improvement and times is so limited I guess I am guilty of too many changes at once! I can't help myself!!!! I think I really need to have someone watch my rear tires for spin also.

Going lighter on the secondary spring is the functional equivalent of going leaner on the rear jets. You open the secondaries quicker with the light spring which adds proportionally more air to the same amount of fuel during the transition. Once the secondaries are mostly open it doesn't make as much difference because there will be enough air flowing to pull proper amount of fuel through the venturi.

I agree with Pat's assesment of squirter changes. Should be used only to fix a stumble and should not result in any ET change unless there was a bog of some type.

I went with a 35 shooter and green cam in #1 slot. I had no improvement at all!!! just as I was going to return to original then I removed the air filter. It left so hard The CD player SHOT out of the dash!!!. Best run of the cars life(in sig). The tires broke loose. I could hear them squeel. My summary is this. I never had a bog because it was tuned out due to the vac secondary nature of the carb( VS the double pumper crowd) you cant tune a vac secondary carb by listening for bog on the line if you hear it it just means that you secondary opening rate needs adjustment. I believe that to tune a V.S. carb the jetting and PV circuit comes first. (tuned with a vac guage for the PV) and (track time for the jetting). then the opening rate on the secondary I tuned mine on the street with light to moderate acceletation and went lighter untill I had a noticeable bog. then back off. I played with this setting for an entire summer before I could leave it alone! (I think that was why I had no bog at the lights) then tune your squirter circuit for 60' times. THEN Go back and retune the secondary opening rate on the street as before and re test at the track. I will now do just that and then see what happens at the track. My guess is that only then will I be able to tune my advance curve properly with the correct mixture in the cylinder. Sorry so long didnt mean to babble. Thanks for all the input!!!!
Milan
Milan