65 3259 715 Holley Vacuum Secondary Spring

[mygt350]

Can anyone tell me which vacuum secondary pump spring works best with their 65 715 CFM Holley? Heavy, light or middle of road?
Thanks

[shelbydoug]

It's calibrated for a standard (plain) spring. The 715 is a 427 carb and is on the car to make it legal for racing. Just for the heck of it, put an 1850 on it (don't tell anyone) and try it. See what you think.

[mygt350]

Doug
Had thought about something like that. May be stupid question but here goes. Will the Lemans float bowls work with a 1850?

[Dynomax]

I have a set of Le Mans float bowls and an 1850...................... I'm also very interested in the answer!

[1967 eight barrel]

Yes, the float bowls will bolt on.  It's also wise to change the metering plate on the non-metering block side to a metering plate that allows jet changes. It's extremely helpful on non-stock applications or vehicles at altitude. Especially with dual quad applications.

                                                                                                     -Keith

https://www.summitracing.com/tx/parts/qft-34-3qft

[shelbydoug]

Yes, the float bowls will bolt on.  It's also wise to change the metering plate on the non-metering block side to a metering plate that allows jet changes. It's extremely helpful on non-stock applications or vehicles at altitude. Especially with dual quad applications.

                                                                                                     -Keith

https://www.summitracing.com/tx/parts/qft-34-3qft

Not only will you get a lot more bottom end, you will get about 3-4 more miles per gallon. It MIGHT however make you NON COMPETITIVE if you choose to run the car in competition at Lemans and Daytonna? Maybe? 

[mygt350]

Doug, Looks like my calendar for LeMans and Daytona is full for "several" more years.

[mygt350]

Keith
So if vehicle remains relatively close to sea level, really don't need to change the 600 plate to one that accepts jets to assist with higher elevation changes?

[1967 eight barrel]

The plate can't be seen unless you remove the bowl. It just allows you to change jets on the secondary side, just like the primary metering block side instead of having to change the metering plate. I am running a  non-factory cam, better flowing heads and other changes that necessitate the ability to change the secondary jets to keep it from going lean on the higher end of the RPM range.
                                                                                                -Keith

[shelbydoug]

The value of the secondary metering block is that it is easier to change jets then to change the plate. Once you have the secondaries set though, you don't need to change jets.

There is also a greater range available with jets then the metering plate.

I'll point out though that the Trans-Am cars that ran the 2x4 Holleys did't use secondary metering blocks. There was no room. They use plates.

My GT350 is running that set up and it doesn't present any kind of an issue. In fact, there are Holley secondary metering plates that are converted to using removable jets.

[mygt350]

Keith and Doug
Great information. Really appreciate your sharing it and the explanation as to why.
Thanks!!

[shelbydoug]

Keith and Doug
Great information. Really appreciate your sharing it and the explanation as to why.
Thanks!!

Box stock 1850's run a 64 main jet. You probably will need at least a 67 or 68. Depends on if you are running headers and what cam. 70's or 71's aren't out of line either. That's going to be a little trial and error.

[1967 eight barrel]

Yes, you can't use a metering block on a dual quad car. The metering plates are made so they use the standard primary block side type jet.