750 Holley carb.

[JimNolan]

Guys,
   Can anyone tell me if there's something wrong with a Holley 80508S 750 cfm Carburetor. It's about $100 cheaper than the one I was considering buying. I get sceptical when the prices don't relate comparatively. The 770 Avenger Carb is $400 and the 750 is $300 with the same electric choke and vacuum secondary. Help. Thanks, Jim

[fe66comet]

The avenger has more adjustments and adjustable secondary mixture screws along with four idle jets.

[My427stang]

I havent liked the Avenger series in any size.  In both the 670 and 770 version I have found that low rpm transition can be lean, and it generally takes work on the main well, specifically blocking the lower feeds, to get the booster to come in when it should.  Some can get away with an aggressive pump cam to mask it, but it is a tuning flaw IMO

I have not used the 80508, but if it matches a 3310, I think it would be fine.  Do you need electric choke?  If not, its hard to beat a classic 3310, if cheap enough you could even buy and add the electric choke yourself.

Another comment, although typically most of us dont use Edelbrock carbs, in your low RPM use, they can work pretty well and are very tunable. An electric choke 750 Edelbrock is a nice driving carb

[fe66comet]

I have always been an AFB fan so i might be a little bias LOL

[JimNolan]

427stang,
    The 80508S is the same as the 3310 except it has an electric choke for 20 more bucks. Now, the secondary's are a plate, so changing jets isn't an option after I get it. The Primary is jet. With what you know about my engine,  does 75 secondaries sound about right. Jim

[bartlett]

thats the carb I run ... I like it    I had to change the primary jets and the secondary spring.   works real good ....

[JimNolan]

Bartlett,
   My 390/406 is running a 600cfm with 65 primary jets. It can't run any lower jet, I tried. Do you remember what you came down to for your application. The 80508 comes with 70 primaries. I figured I'd end up going with a silver spring for the secondary's, that's what the 390/406 runs. It gets decent gas mileage and run's pretty good, I know I'm loosing on top end, but it rarely gets there. I could use more cfm though. Jim

[My427stang]

Jim,
The secondary plate generally doesnt need changing, I say generally because I have tuned with one, but its usually because I am trying to keep the primaries overly lean for some oddball experiment

I'll look in my books tonight to see if the 80508 is really an electric choke 3310, there may be different internals.  However, if it is close, I'd bolt it on out of the box, don't try to extroplate what the 600 likes to what the 750 will want.

[JimNolan]

Well I'll wait until tomorrow before I order it. I figured because my VE was around 94% @ 4500 rpm, the engine would take it and if I run rich at cruise I could just come down in jet size. I'll wait for your opinion though.  Everything else is already on the engine or sitting here beside me except the carburetor and rocker stands from Precision Oil. I hope the stands get here soon because I'd like to get the lifter tray and lifters set and buttoned up. Jim

[My427stang]

Jim, the 3310 and 80508 use the same metering blocks, same secondary plate, and have the same plate and venturi dimensions.  It is indeed almost the same carb

The only difference is the 80508 has a .025 pump shooter and the 3310 comes with a .031, not a difference worth noting.

I'd say if the price of an 80508 is good, go for it. 

[JimNolan]

DONE!!!!   I don't know if I calculated the cfm correctly or not. But, in my engine analyzer I kept bringing the cfm up until the VE and BMEP started going down at 4500 rpm without affecting the VE and BMEP at 2000 rpm. Using the Wallace and Holley carb recommendations just recommended 660 - 835 cfm. I needed a little closer estimate. The VE and BMEP calculations doesn't leave nothing to guesswork. "If it's correct". Thanks again, Jim

[bartlett]

My dyno paper work does not say the primary number.. It does say went down 4 jet sizes.   It also says they changed the spring to a light purple spring.

hope that helps ya

[JimNolan]

Bartlett,
   Yes that does help me. I figured I'd be climbing back down on the primarys. It has the .031 pump discharge nozzle not the .028. I really liked the Avenger Carb. But, the one I've got has a special made accelerator pump cam that I made to keep it from stubbling off line. Just like 427stang said he'd heard about other people doing. After thinking about it and running numbers I figure I can't be far off with the 750.   

[My427stang]

You are making a good choice with a 750.

An aluminum headed 410 with a mild cam, stick car, should be happy as can be with a 750, no need to go smaller.

If the new carb fights you a little, like the SA, before you go inside, try a pump cam change.  I have had good luck with the blue pump cam on 3310s.

[JimNolan]

You are making a good choice with a 750.

An aluminum headed 410 with a mild cam, stick car, should be happy as can be with a 750, no need to go smaller.

If the new carb fights you a little, like the SA, before you go inside, try a pump cam change.  I have had good luck with the blue pump cam on 3310s.

    Ross,
        I'll remember that. I did order the SA, mainly because I've never had an aluminum carb before. The SA had the glass float level also. I've got a quick change secondary vacuum cover plate I was going to install on the carb before I put it on the engine. I'll just change the cam from the get go and see what happens. Thanks, Jim  PS  I'm sending you a e-mail, you decide it's worth on posting for information. And, going in and changing jet sizes on the primarys will totally depend on plug color. I'd bet Bartlett would be right about jet sizes for cruise configuration.