My Firebird has been using a bit of water each time it ran. I traced the problem to a crack starting in the head. A few others were starting also. Most likely a little NOS damage from a past life! Anyway, I just got my double humps back. They are 2.02 heads that have been totally rebuilt. Normally, I would not have spent the coin on old heads, but the machine shop owed my and they were done for less that a new pair of Vortecs. I called Edelbrock to find out about a carb and they told me to run the 600 performace carb (1405). I was thinking I would need the 750? What do you think. With my Vette heads (ported and polished, very sweet and very sad they are now junk!) I had a 10.2:1, 350 with a Performer RPM intake, Performer RPM can and Hooker Super Comp headers. The double humps are 64cc (Vette;s were 58cc) so I know compression will be a bit less. What do you think 600 or 750?



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Mark
1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
http://personal.lig.bellsouth.net/~racer383/

I'm running the 750, well I will be when I put the engine in. Just pulled the old one out last night. I used to run a 625 Carter on a stock 350 in a Blazer I used to own.

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68 RS, Ash Gold,pwr windows,Hounds tooth

I have a fairly stout 355 and run a 700 Holley dp. I think a 750 is a bit large. It's surprising what an engine really needs. There is a formula that I don't readily have access to that allows you to figure what you need. I think it's more common than not to over carburate an engine. Perhaps some more experienced engine builders can help here. Some carb manufacturers can also give you specific advice. I've found, for example, that the Holley tech line is a true help.

750 is too big. Here is reference link to size carb properly. It is directly related to RPM and CI displacement:
http://www.mortec.com/carbtip1.htm

I don't have much faith in those formulas. A buddy haad a 77 Camaro with a mild 350, ported heads, 280 lift solid cam, 4:10 gear. The formula said something less than 500 cfm. He put a 600 on it. Engine quit pulling about 5000 rpm. I talked him into trying a 750 that I had. Bingo engine pulled hard to 6200.
If you are going with the edelbrock I would use the 750. Look at the edelbrock dyno test on the rpm system, they used a 750.
Just my opinion.
Stephen

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67 RS/SS 350 700R4
69 SS clone unfinished
72 454 Weekend Racer

650dp for racing,750vs for street strip.

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My68Camaro (http://hometown.aol.com/Dougs68Camaro/index.html)
Doug G.
68 Camaro
406 ci.

Its a pain in the rear, because Edelbrock said to use the 600. It just don't sound right, but then again, my 383 uses a 750. Go figure...

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Mark
1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
http://personal.lig.bellsouth.net/~racer383/

I feel the formula(C.I. x RPM ÷ by 3456 x V.E.))is a little weak in my book.They must have been created for heavy vehicles with no gearing,or to try and protect you from choosing to big a carb.It does produce a very tractable carb on the street though.I know they say thats all the motor will need,but why does the motor always run harder when a little more cfm is introduced ?Even when it's a single plane manifold.
I prefer to use this formula but I will add another 10-20 percent of cfm.
For instance 355 x 6500 ÷ 3456 x .95 = 634.295 cfm.
I will take the figure of 634.295cfm and multiply it by .10(to find 10 percent),wich comes to 63.429 Now add the two,that gives you 697.724cfm.I will never go smaller than this figure.I will go a little bigger(up to 20%) if the vehicle has a combination of plus factors such as,low weight with low gears,or low gears and a stall.



[This message has been edited by mutant 68 (edited 10-06-2000).]

I would definatley use the 750. I am more of a holley fan when it come to carbs. I run a modified 750dp on the 67 when on the motor, and an 830 annular carb on the bottle and street use. My 79 Z28 runs a Q jet ( an 800cfm from a 79Cad) that I have tailored to the engine on a ZZ4 intake. It's a 9.17:1 383 w/ stock exhaust manifolds & SR Torquer heads. I see that in drag racing, you can go over the recomended size by 100cfm. The RPM manifold will keep the torque up there as long as jetting and power valves are matched. Just my opinion Galen

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S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 Restored stock apearance
13:40's @ 101 stock exh.& intake
smog legal
Camaro Lover

Mark,

Try a 3310-2 750 vacuum secondary holley or a properly setup 750 Q-Jet. That way the vacuum secondaries won't over carb. (cfm wise) your engine.

A smaller carb. can actually enhance torque in the lower rpm ranges, but at the expense of a little top end horsepower. It's like moving the power curves over one way or the other. pdq67