Zio

Ok guys I have a holley 750 on my car now and it is too big. I was thinking of going to a 650, but i can't seem to find one at a ood price. I know three people that have 600s they want to get rid of. Will a 600 be enough for my engine? Also i was told that it would increase my throttle response A LOT. is this true?
Here is what I have:
350
750 holley
Edlebrock intake
not sure what kinf od heads (supposed to be decent)
9.5:1 compression
MSD ignition
1.6 rockers
headers
dynomax exhaust
2.73 rear (that will be changed)

82camaro

At what rpm is your peak HP(an estimate is ok) A 600 carb will be great up to around 5000 rpm or so. At 6000 rpm a 750 is needed for maximum power(the 600 carb becomes a restriction. Chances are, with near stock heads and a stock cam(if that is what you have) a 600 carb will be fine.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

Jester

If both are properly tuned, changing from a 750 to a 600 shouldn't change your mileage. A 750 is also about right for a decent 350.

To be pulling only 10mpg with that combo you've gotta be doing somethign pretty wrong tho. Get an A/F gauge, and actually tune it instead of just buying another carb. Changing will probably improve your throttle responsea little bit, but not all THAT much. That also is mostly a function of tuning.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

Zio

Sorry guys I also have a comp 268 cam. i was going to have a guy i know do tune the carb. he is known around my area for his work with holley carbs. He says that for a street car that a 650 would probably be the best, but i can't seem to find one. besides a new one. he said with my gears that a 650 would improve my throttle response and MPG. he said with descent driving, tune correctly and a 650 i should get about 15 MPG. Well keep the suggestions coming guys. I would like more opinions than just his.
thanks
Tom

lukerene

600,s are a top thing,,,good for the street,,good HP too ,,easy for D,I,Y deals easy to set up,,,small cam,, 600 vacume,,headers,,nice unrestrictive exhaust,good air cleaner,,get that cold air in,,should go good,,,and be nice to drive,,good for idle to 5,500rpm a little more,if needed,,what rev range do you use ,,where does the engine produce all its power,,and where does TORQUE drop off,,you will be surprised,,check it out ,,some rochesters off the 69 to 70 350,s were rated at 725cfm,,,there a good thing,,,but suck the gas,good fun the holleys,,easy to jet up,and muck around with,,,go get em!!

Zio

when i race i shift at about 5000RPMs, sometimes a little more. does anyone know what jetting i should use for a 600?
thanks
Tom

El Guapo

Most of them will come with just about right jets.

The ODB

wow do they really compose sentences like that in australia? hmmm interesting mate.

the other day I saw a Holley 750 spreadbore for sale at a swapmeet for about $50. A 750 sb has much much better throttle response than a Holley 600.
I didn't get the Holley sb, but I did grab a 1000cfm thermoquad that has smaller primaries than a Holley 600, & only costs me $10.

The guy above is right that you just need to learn to tune the carb you have. If you are running a dualplane intake manifold then it should be pretty simple tuning it for fuel mileage & power. A dualplane on a chevy will generally want slightly larger secondary jet on the driverside of the carb.

Zio

OK, guys thanks for the help. I forgot to mention that I also want to change carburators because i need better gas mileage. right now 87 octane is $2.08 and it is killing me. will a 600 or 650 give me better gas mileage? The ODB, I am confused now i thought that a 750 gave more top end power then low end? (not arguing, just asking) Also I have a spacer under the carb. would it be better if i took that off? I read somewhere that it would give me better throttle response with out the spacer. is this true?
thanks again
Tom

82camaro

The ODB is talking about a spread-bore carb. Small primary's and big secondaries. Try with and without the spacer, it affects different cars differently and it will affect the optimum jet size as well. 600 is plenty big for your application. It has small enough primaries to give you excellent throttle response--a spread bore q-junk or holley won't give you any better response. The smaller bore=better response idea only works to a point, then the advantage of a smaller primary bore disappears--once you find the optimum primary bore size, smaller won't help. Just get a 600 VS.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

super83Z

Well its not plenty big enough it is just adequate. A 600cfm can actually get worse mileage than a 750cfm it all depends on tuning. As long as the carb is tuned properly it will give the car good mileage and power. In the end it all comes down to tuning the carb. Try "dialing" in your 750 before switching to a 600. As you may be reposting the same prob after swapping the carbs.

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I WOULD RATHER PUSH A CAMARO THAN DRIVE AN IMPORT

1983Z28 350w/ edelbrock performer RPM power package , dynomax shorty headers, 700R-4 with shift kit, 750cfm carb, edelbrock 3" exhaust system, ASCD SS hood, 16" IROC rims.

future mods:
completely done over suspension, black paint with flames, Hurst shifter, dakota digital gauge package, procharger supercharger.

merf23

I changed from a holley 600 VS (#1850) to a qjet and increased my milage from about 16 mpg to about 20, improved part throttle cruising and lost nothing at WOT. The primaries on the qjet are considerably smaller than the primaries on the holley which accounts for the improved milage and part throttle response. ALso the mechanical secondaries on the qjet stay closed until about 3/4 throttle....the holleys open/close in response to load, temp, barometer, condition of the air filter, lunar cycle, etc which also hurts milage. I have always used holleys on racing cars, but ill stick with the qjets for daily driving

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1984 Z28 (L69) monochrome tangerine orange with IROC decals and hood
1987 IROC wheels with Goodyear GSC's
305 from 87 IROC with 1994 LT1 cam (203/208 .450/.460")
performer intake
Qjet from 73 Olds
dynomax cat-back, gutted cat
no emissions controls --> passed emissions testing
non WC T-5 with 0.73 5th
3.27 nine-bolt