I have an 1982 Camaro Z28 that started its life as a V6 Crossfire but is now has a V8 Carbed 4 Bolt 350. The engine is out of a 74' Chevelle. The engine has a street/strip cam with 268/276 Duration and .486" Lift. The current carb is a Holley 750 CFM Double Pumper, you can see it here: http://www.holley.com/0-4779S.asp .

This Camaro WAS a drag car, but I bought it from the original owner and use it as daily driver (A really, really fast daily driver). For all the performance parts in this camaro, it seems to be very sluggish with its acceleration, maybe the 750 CFM is flooding out the engine a little bit causing the engine to not perform at 100%? The engine itself was rebuilt a few months ago, so it is in good condition, further leading me to believe the carb is to "big" and affecting the engines performance.

Do to the cars new life as a daily driver , I'm not looking for speed I'm just trying to get my Camaro up to 20+ MPG as I am currently getting 16 MPG. I talked briefly with a mechanic and he agree that a 750 double pumper is too much and suggested a carb thats 550 CFM or 600 CFM. Does that sound correct, and if so does anyone have any suggestions on what carb I should buy?

Thanks in advance,
- Shaz

 

Doubt you'll ever see 20mpg with any aftermarket carb - not sure you can get it out of a two barrel even.

Beyond what you've been told (which could verry well be true, I have a 600cfm on my 350), the choice is yours as to brand.

But have you read through Holley website tuning instructions and such? Maybe you just need a better carb tune. Maybe accellerator pump needs linkage changed to a lighter shot or something. I'd talk to Holley tech before I threw another carb at it just to see.

 

AAny more details on the engine? What compression? Cylinder heads? Intake? Transmission and rear gears? Distributor and timing curve? The 750 might be a little big, but it can certainly be made to work. 20MPG might be unrealistic...but it will dpend on how heavy your foot is!

 

Transmission is a 700R4 with 3.42 gears and a Eaton locking rear diff. The intake is a Holley Street Dominator High Rise intake. I don't know anything about the compression, cylinder heads, distributor or timing curve, sorry

 

Is the transmission locking up the converter (or was that disabled when converting to carb)? What stall speed? Try to find out some more about the engine. If it is low compression, it will want a pretty agressive timing curve or you will have no low speed torque. However, with stock iron heads from 1974, you could run into detonation.

 

Maybe it's just your choice of words, but if it is flooding, it isn't the fact that it is a 750 CFM that is causing it.

While a 750 Holley isn't the best choice for fuel economy, it should be fine for performance. Start with the basics - the ignition has to be up to snuff, the timing set properly, float levels set properly, throttle cable set up properly. After that, you get into jetting, accelerator pump cam change (that's assuming the accelerator pumps are properly set), power valve, etc., which are basic Holley tuning.

I suggest you start with the Holley tuning sticky in the top section of this forum.

If your timing isn't set properly, or the vacuum advance isn't working, or the torque converter lock-up isn't functioning, you'd be doing very well to get 16 MPG. I hope you have a TV cable corrector bracket on the carb throttle arm.

Oh, your cam isn't exactly a "mileage master". It's designed more for performance than economy.

(BTW, there never was a V6 "Crossfire" set-up. If it truly is a Z28, then it would have had either the LG4 carbureted 305, or the LU5 Crossfire 305.)

 

My bad, I don't know what I was thinking when I said the original engine was a crossfire V6. In correction, the original engine was a crossfire 305-165 (LU5), verified off the VIN.

I don't know what you are talking about, could you please explain to me?

The stall converter is 2000 RPM. That seems really low to me. I re-read the guys craiglist ad, and he might of meant to type 3000 but his finger slipped and hit the 2 instead of the 3. I'll call him up and double check that its really 2000 RPM.

That could be why when you floor it the car seems sluggish. Over carbed, over cammed, and under stalled = slow off the line. Not that I care because I'm just commuting and not racing, but still I want to be able to pass someone quickly when I have too.

Heres the original ad, all the info I have is from it:
CamaraAd.png?t=1298090719

 

As mentioned, you won't see 20mpg - but there's no reason I can see why that carb can't be tuned correctly to that motor - 750cfm is on the high end, but you should be able to tune it down to not overfeed the 350.

The geomtery corrector is a small elbow looking piece attached to the linkage on tne carb so that the proper geometry of the TV cable from the 700R4 is correct, given that it's not a factory carb and has different linkage. The TV cable determines shifts in the 700R4 - much more complicated than the old "kickdown" cables that just "kicked down" to a lower (passing) gear at a given throttle position. The TV cable must have proper adjustment (there's only one setting where it's "right") and must have proper geometry (since an improper angle of the cable from the bracket to the carb linkage can greatly affect the pressure on the cable at different throttle positions).

 

Ah, thanks for explaining the TV cable. You learn something new every day!

As far as MPG is concerned, I work for a mechanic two days a week doing simple stuff like oil changes, mounting tires, helping him with heavy lifting etc. I do ask him some questions, but I also like to ask here on ThirdGen because a lot of you are very knowledgeable on Camaros. When I did ask my boss about the carb, he said that my 750 is to big. He said its not so big that my car won't run, obviously because I drive it too and from work, but that its overfeeding the engine a tad bit more gas then it needs too. He said I could either tune and re-jet it down to try and even things out, or just sell it and buy a 600 CFM Holley, whichever I felt like doing. He also said with a good tune up and a very good carb tuning he didn't see why I couldn't hit 20 MPG. He said he had a 350 powered Camaro back in the 80's, and was able to squeek 22 MPG out of it and still have power to spare. I'll get him to help me, but I'd still like input from you guys!

 

You have an engine built for speed, not for milage. If you really want 20 MPG, you need to swap out some of your 'go fast' parts for more mild pieces. High rise intakes, double pumpers, and big cams are just not gas milage friendly parts. If milage is important to you, I don't think you made a wise purchase.

If you're unsure of the stall, just see what it flashes to and then you'll know.