Tim240z Posted January 31, 2005 Share Posted January 31, 2005 Not for my Z, but I figured the information could be used for the Z guys just as easily. This is for my 71 Chevy truck. I am currently running a Holley 750 Double Pumper, but I know it is wayyy over carbed. So, in an attempt to make it a bit more fuel efficient and the throttle a bit crisper, I am going to replace it with a 600 cfm carby. So here is the question. Which carb is best for these purposes (I have always been a Holley DP user): Option 1: Get a Holley 600 cfm Double Pumper Option 2: Get a Holley Street Avenger 670cfm (I think the 570 cfm will be too small) What are the benefits/cons to this 'new' carb? Option 3: Edelbrock performer 600 cfm carb. Again, benefits/cons to this type of carb? Option 4: Go Fuel injection....not really an option due to cost. (even with MS, I would still need to buy a bunch more stuff). Here are the engine specs: 350ci (not been bored, std bore) Vortec heads L98 Corvette cam grind.(heads have upgraded valve springs) Edelbrock Performer RPM manifold 1" carb spacer 1 3/4 primary full length headers TH350 tranny (soon to be upgraded to TH200 4R) The engine almost never sees any more than 5000rpm, and even then that's rare. Any words of wisdom, experiences etc.... Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 31, 2005 Share Posted January 31, 2005 I have a friend who just loves his 670 Avenger on a ZZ4 350/700r4 combo. Good luck! Mike Quote Link to comment Share on other sites More sharing options...
johnc Posted January 31, 2005 Share Posted January 31, 2005 What about an orignal carb like a Quadrajet? Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted January 31, 2005 Share Posted January 31, 2005 I agree with zfan. Try option 2 and let us know how it works out-- What changes as far as mileage, driveability, power. I face the same dilemma here with a similar engine but for my Z (which causes me to rule out option 3). As I recall, the old Carters didn't like corners very well due to float/ float chamber design. Since this is pretty basic to the carb, I doubt if the Edelbrocks are any better. Option 1??. Double pumpers are jetted for max power (richer) so logically the mileage would still suffer, even with a 600. Quote Link to comment Share on other sites More sharing options...
Guest rick458 Posted January 31, 2005 Share Posted January 31, 2005 Have you looked at a 575 Street Demon? about $400 for Vac sec elec choke $440 for mech sec Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted January 31, 2005 Share Posted January 31, 2005 650 DP, lose the spacer... Quote Link to comment Share on other sites More sharing options...
Tim240z Posted January 31, 2005 Author Share Posted January 31, 2005 John C: That is what the truck had prior to the engine build. Never got that great fuel mileage out of it. I love the 750DP, but I'm sure that it is killing my fuel consumption. The intake I have now doesn't have a spreadbore flange, so I would need an adapter...rather not do that. Jamie, Running through the CFM calculation, even a 600cfm carb is likely too large: 350ci*5000rpm/3456=506cfm*0.85 (optimistic % V.E.)=430cfm The spacer should help with low end torque, but I will try it both ways. I think I will stick with what I know and get a 600DP manual choke. Summit has some reman. units, but the new ones aren't that much more, so I will likely go with that. Quote Link to comment Share on other sites More sharing options...
peej410 Posted January 31, 2005 Share Posted January 31, 2005 ive got a 600cfm edelbrock thats got about 1500 miles on it id sell with the tuning kit if your interested Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted January 31, 2005 Share Posted January 31, 2005 Tim, want to sell the 750 dp? I need a larger carb for my Z. Have a 600 vs now. Doesnt do it for me. Douglas Quote Link to comment Share on other sites More sharing options...
Tim240z Posted January 31, 2005 Author Share Posted January 31, 2005 Doug, The 750 was a gift from my Dad, so it has some sentimental value. Sorry man! Quote Link to comment Share on other sites More sharing options...
flibuoy Posted January 31, 2005 Share Posted January 31, 2005 I had been a Holley person for 20+ years until I put an Eldebrock Performer on a warm 355. Had all the tools ready....prepared for several test blasts....took it out of box...started it up...set idle and drove it 6 years...of course a larger Holley probably would have provided several horsepower over 5K RPM...this one was decent on gas, good response and absolutely troublefree...no power valve blowouts...no nothing. Maybe I was just lucky. John Quote Link to comment Share on other sites More sharing options...
MrBonk Posted January 31, 2005 Share Posted January 31, 2005 I really think a proper tuned 650 DP with 50cc Holley Accelerator Pump Conversion Kits in front and back. I had a worked over 650 DP on my 302 for a very long time and loved that card , But i have a buddy that knows those carbs in/out and he tuned it to my car and its needs. I would stick to a 650 or larger just becuase sure a 600 could feed it but long times of WOT a 600 would starve a 350 with some hop ups done to it and its allways better to run a little on the rich side than lean.. Anyhoot just my 2 cents laterZzz Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted February 1, 2005 Share Posted February 1, 2005 Tim, No worries. My engine builder is sold on demon carbs. He said you bolt them on and there is no fussing around with them. I will probably go that way in the end depending on what they cost here. Local guys are asking $1200 nz for them. Might have to go e-bay. Douglas Quote Link to comment Share on other sites More sharing options...
Guest Zyoul8r Posted February 3, 2005 Share Posted February 3, 2005 I've had a few small block chevy's in my time and there is no doubt in my mind you should use the 600 Double Pumper with Mechanical Secondary's (Although with the auto tranny everyone else will probably recommend the Vacuum Secondary's) I just like the response of mechanical. Go the extra step and adjust it for elevation (depending on where you are).... chances are it will still be a little rich for you out of the box. I'm sure you will get many opinion's on this question.... Good luck with your decission Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted February 3, 2005 Share Posted February 3, 2005 Have you looked at a 575 Street Demon?about $400 for Vac sec elec choke $440 for mech sec You might even go smaller say 550. Quicker response lower max RPM and better fuel economy. Usefull Holley Info http://www.bob2000.com/carb.htm Quote Link to comment Share on other sites More sharing options...
johnc Posted February 3, 2005 Share Posted February 3, 2005 The 750 was a gift from my Dad, so it has some sentimental value. Sorry man! Now that's a Gearhead family! Most of the time its, "Son, now that you're out on your own, its time I gave you my grandfather's watch..." But, in the Hepburn family its, "Son, now that you can build you're own small block, I'm going to give you my Holley 750 DP..." Quote Link to comment Share on other sites More sharing options...
Mike C Posted February 4, 2005 Share Posted February 4, 2005 Tim, Glad you still have your truck! My 70 GMC with the big block got 11 mpg. With a JET Stage II 750 Q-jet it now gets 13. I bought one for my Jimmy as well. Q Jet is best of both worlds, but $360 is a lot more than the Holleys. Drawback on my 70 is having to adapt the TH400 kickdown solenoid and mechanical throttle linkage to the cable type arm. Not a problem in your 71. The electric choke is worlds better than the OEM hot air choke as well. Quote Link to comment Share on other sites More sharing options...
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