Hey guys putting a Holley 4160 series on my ZZ305.. HEHE P&P 113s, powermax 2031 emissions cam, 3:73rear... My current mpg with the tbi is like 10-14... Im getting 160miles per full tank... That cant be right... Im hoping going to carb will give me better mileage. I do not drive the car hard during the week, I drive like a little ol'lady with no more then 1/4 throttle..... Let me know guys thanx

 

You should be able to tune this carb to get reasonable mpgs. I have the 4160 on my stock-ish 350 and I get about 18+(US)mpg while driving a mix of old lady and maniac. This is before I did the tuning... haven't run enough after leaning it out to get get a figure afterwards, but I reckon on 22mpg being feasible.

With the 4160, using mostly 1/4 throttle the main mixture setting is not the primary jet as you'd think but the idle settings. These can be adjusted using the two small screws on each side of primary fuel bowl.

I tuned mine up using a wideband O2 sensor that I pinched of my brother.

Good luck,

Si.

 

thanx bro yea i was hoping for bout 18-22 with the holley

 

Something is seriously amiss if you are only getting 10-14 mpg with TBI. Conversion to carb typically lowers mileage.

I hope you have properly considered all that needs to be changed in order to make the conversion. If buying everything new, it would probably be cheaper to fix whatever is wrong with your TBI, and you'd end up getting better mileage than you could with the carb.

Arguable the carb will make more power. Depending upon what exactly you've done to the engine so far, it is likely there's a lot more power left to be found with TBI, though.

What all was done to those heads intended for a 350? A good bit of the answer might be right there. How much PROM tuning have you attempted? What have you done to the exhaust?

If the problem isn't in the induction, you could be carrying it over to the carb conversion.

 

I have done no prom tuning, dont know how or have the time to do it.... The heads are just ported and polished. The exhaust is just a 2.5dynomax catback,supercat, dynomax headers.... Im sure i could get decent mileage with the tbi if i got a prom burned, but ihave not found anyone to do so... thus i am going to carb for easier tuning...

 

You lowered the effective compression by using 350 heads without shaving them. You completely confused the PROM with the head, cam, and exhaust changes.

Have you looked into PROM burning at all? You might want to get in touch with Shifty over on the TBI forum. Most likely what needs to be done would easily be solved by doing that. Tuning on the keyboard has advantages that cannot be duplicated by the getting your hands dirty and smelly method.

Sorry if this sounds like a wet blanket, but I'm a real advocate for improving what you've got, especially for a daily driver.

(Your headers did retain the O2 sensor, correct?)

 

Yes the headers retain the o2 sensor... but my heads are 55cc... they were 58cc but i got them milled ture so they are the same compression as stockers just flow way more..