Hi Guys.

I have a 305, currently stock.

I was looking to replace the carb intake and cam, and in the process maneged to get a really good deal on an Edelbrock RPM Air Gap intake.

Can you guys recomend a carb/cam combination for me?

The car already has a 3" oval exaust, and headers, and will be used as a daily driver.

Also, I read on the holley site that manual transmission cars should go with mechanical secondaries. Why is this?

Thanks

 

PS. The my current carb (q-jet, non cc) is not rebuildable. Engine is pre 87 non cc

 

I have the ZZ4 intake and an Xe256h cam in my LG4. Very pleased with how it performs. I use the 1406 performer carb. It is rated at 600cfm. Without modifications to the heads, you need to stay small so you don't run into clearance issues.

*EDIT* nevermind about the q-jet part.

 

Do you have a manual transmission?

For carbs other than mechanical secondaries (also known as double pumper), such a the Edelbrock Performer/Carter AFB, vacuum secondary Holley and Demon, or q-jet, the secondaries are effectively or directly opened by engine demand - i.e., air flow. They do it in a couple of different ways, but the idea is the secondaries won't open any more than the engine "needs". That's a great concept, but it has one drawback when coupled with a manual transmission - if you back off the throttle between shifts, the secondaries close or start to close, and there's a little delay before they open or start opening again. With mechanical secondaries, the opening is strickly a function of accelerator pedal position, meaning after the shift the secondaries "recover" more quickly.

If you "speed shift" - keep it floored while you shift - this isn't an issue.

Speed shifting a T5 is an "issue", however.

 

Same answer on the other side of the grass....

If you have an automatic, and you run manual secondaries, you can bog the engine if you give it more air than it can handle.

In an automatic with vacum secondaries, if you floor it, you can only open the primaries, so you wont bog the engine. The secondaries will open when the engine has built up enough speed to require them to open.

Also, be careful with the choices of intake carb and cam with the 305. If you give it more than it can handle, you'll have high RPM horsepower, but the loss in torque will make it not very fun in day to day driving. And gas milage will be horrible.

 

It all comes down to the combination. A properly sized DP won't have any problem with bog, even with an automatic. The Holley website under carb tech info has a link to mechanical secondaries that has a chart showing the max DP CFM size that you can run based on engine displacement and min RPMs at which you go WOT. That size will be larger than the size carb you will need for max power based on CFM = (CID x RPM x VE)/3456.

Vacuum secondaries are a crutch. They're probably fine for a tow vehicle or dump truck, but if a DP doesn't work on a performance vehicle, you don't have it set up right.

The RPM intake powerband is 1500-6500. Get a cam with a powerband within that, and have a torque converter (if automatic) that stalls above the greater of the lower powerband of either the intake or cam. Remember, smaller displacement makes a cam "act" bigger, and for SBC they typically assume a 350 when advertising their powerband; so in a 305 the low-end will be higher (and therefore require more stall).