I am running a Holley 750 right now. 3310, vaccuum secondary.

Last time I was on the dyno, we had to really lean out the primary side to get the mixture close at WOT b/c the secondary side is a fixed metering plate. (Yeah i know, not the best carb when it comes to tuniability :( )

Well I have a secondary metering block that I am going to put on, then I will be on the dyno again to see what all of my new mods netted me.

Once the metering block is on I will be able to change the secondary jetting. Should I go back to the out of the box primary jets? Or should I leave the smaller jets in the primary side until I can do a few pulls?

And if I should go back to stock jets, what size are they for a 3310 750cfm?


-Matt

Stock jets for a 4150 series Holley 3310 are 72 primary, 76 secondary and has a power valve both primary and secondary. The 4160 series 3310 secondary metering plate is the equivalent of 76 jets per the Holley catalog but has no sec power valve. The 4160 to 4150 conversion kit sec metering block comes with 76 jets but no provision for a power valve. This is interesting, since it's common knowledge to go up 8 to 10 jet sizes when removing a power valve. Also the way the 4160 main body is made, there physically is no way a power valve will fit, so the special conversion metering block must be used. I'm using 70 primary, 76 secondary jets in mine. I'm interested in knowing what your dyno tests call for on jetting with a secondary conversion metering block.

Did you change the vacuum secondary spring? I am also using a box stock 3310 and I am thinking about playing with the springs to see if it makes much of a difference. I would also be interested in your results.
Ron

Von, I give you the award for the most suuccint/informative response. graemlins/thumbsup.gif Thanks a bunch.

Ron, I did not mess with the secondary spring, as I do not have the spring kit.

Here is a copy of that dyno graph. Yeah, the numbers are pretty low. I'm hoping to make significant gains though. Since this dyno, I've ditched the AOD for the Tremec, gone to dual elecric fans, fixed some ignition stuff, and hopefully I will be able to tune it better this time.

http://www.chevelles.com/showroom/Matt_Leuck/mattdyno1.jpg

You can see how the primary side starts around 13.7-13.8, then it looks like the secondaries start opening around 3900rpm. After that the mixture richens up to 12:1, then does a little wave, all the way up to 6400.

Any thoughts on this? Should the secondaries be coming in sooner? What would you guys recommend for a WOT mixture. 12.5 or so?

I will definately keep you updated on the secondary metering block stuff. Hopefully I will have it back on the dyno in about 3 weeks.


-Matt

Another off topic thought. That pull was the best of the day going through the exhaust.
For the last pull, we left the tune the same, but opened up the dumps in the exhaust. They are placed after the 3" in 2.5" out X pipe, but before the 2.5" Spintech muffs and tailpipes.

With them open I picked up 6 hp and 20 ft-lbs.

Could the Spintechs and tailpipes be that much of a hinderance?


-Matt